92 results on '"Dikaios N"'
Search Results
2. Multiparametric MRI for detection of radiorecurrent prostate cancer: added value of apparent diffusion coefficient maps and dynamic contrast-enhanced images
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Abd-Alazeez, M, Ramachandran, N, Dikaios, N, Ahmed, H U, Emberton, M, Kirkham, A, Arya, M, Taylor, S, Halligan, S, and Punwani, S
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- 2015
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3. MO-0218 A likelihood-based particle imaging filter using prior information
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Fullarton, R., primary, Volz, L., additional, Dikaios, N., additional, Schulte, R., additional, Royle, G., additional, Evans, P., additional, Seco, J., additional, and Collins Fekete, C., additional
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- 2022
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4. Discrete Shearlets as a Sparsifying Transform in Low-Rank Plus Sparse Decomposition for Undersampled (k, t)-Space MR Data
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Protonotarios, N.E. Tzampazidou, E. Kastis, G.A. Dikaios, N.
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The discrete shearlet transformation accurately represents the discontinuities and edges occurring in magnetic resonance imaging, providing an excellent option of a sparsifying transform. In the present paper, we examine the use of discrete shearlets over other sparsifying transforms in a low-rank plus sparse decomposition problem, denoted by L + S. The proposed algorithm is evaluated on simulated dynamic contrast enhanced (DCE) and small bowel data. For the small bowel, eight subjects were scanned; the sequence was run first on breath-holding and subsequently on free-breathing, without changing the anatomical position of the subject. The reconstruction performance of the proposed algorithm was evaluated against k-t FOCUSS. L + S decomposition, using discrete shearlets as sparsifying transforms, successfully separated the low-rank (background and periodic motion) from the sparse component (enhancement or bowel motility) for both DCE and small bowel data. Motion estimated from low-rank of DCE data is closer to ground truth deformations than motion estimated from L and S. Motility metrics derived from the S component of free-breathing data were not significantly different from the ones from breath-holding data up to four-fold undersampling, indicating that bowel (rapid/random) motility is isolated in S. Our work strongly supports the use of discrete shearlets as a sparsifying transform in a L + S decomposition for undersampled MR data. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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- 2022
5. Evolution of multi-parametric MRI quantitative parameters following transrectal ultrasound-guided biopsy of the prostate
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Latifoltojar, A, Dikaios, N, Ridout, A, Moore, C, Illing, R, Kirkham, A, Taylor, S, Halligan, S, Atkinson, D, Allen, C, Emberton, M, and Punwani, S
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- 2015
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6. PO-1667 Statistical limitations in particle imaging tomography
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Fekete, C., primary, Dikaios, N., additional, Baer, E., additional, and Evans, P.M., additional
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- 2021
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7. An end-to-end assessment on the accuracy of adaptive radiotherapy in an MR-linac
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Axford, A, primary, Dikaios, N, additional, Roberts, D A, additional, Clark, C H, additional, and Evans, P M, additional
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- 2021
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8. Processing of transmission data from an uncollimated single photon source
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Dikaios, N., Dinelle, K., Spinks, T., Nikita, K., and Thielemans, K.
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- 2006
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9. Comparative evaluation of two commercial PET scanners, ECAT EXACT HR+ and Biograph 2, using GATE
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Karakatsanis, N., Sakellios, N., Tsantilas, N.X., Dikaios, N., Tsoumpas, C., Lazaro, D., Loudos, G., Schmidtlein, C.R., Louizi, K., Valais, J., Nikolopoulos, D., Malamitsi, J., Kandarakis, J., and Nikita, K.
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- 2006
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10. Mathematical models and deep learning for predicting the number of individuals reported to be infected with SARS-CoV-2
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Fokas, A. S., primary, Dikaios, N., additional, and Kastis, G. A., additional
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- 2020
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11. Predictive mathematical models for the number of individuals infected with COVID-19
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Fokas, A.S., primary, Dikaios, N., additional, and Kastis, G.A., additional
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- 2020
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12. Proton Computed Tomography: A Case Study for Optimal Data Acquisition
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Panagiotidou, M, primary, Collins-Fekete, CA, additional, Evans, P, additional, and Dikaios, N, additional
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- 2019
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13. Comparative evaluation of two commercial PET scanners, ECAT EXACT HR+ and Biograph 2, using GATE
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Karakatsanis, N. Sakellios, N. Tsantilas, N. X. Dikaios, N. and Tsoumpas, C. Lazaro, D. Loudos, G. Schmidtlein, C. R. and Louizi, K. Valais, J. Nikolopoulos, D. Malamitsi, J. and Kandarakis, J. Nikita, K.
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Physics::Medical Physics - Abstract
Geant4 application for tomographic emission (GATE) is a generic Monte Carlo simulation platform based on a general-purpose code GEANT4 and designed to simulate positron emission tomography (PET) and single photon emission tomography systems. Monte Carlo simulations are used in nuclear medicine to model imaging systems and develop and assess tomographic reconstruction algorithms and correction methods for improved image quantification. The purpose of this study is to validate two GATE models of the commercial available PET scanner HR+ and the PET/CT Biograph 2. The geometry of the system components has been described in GATE, including detector ring, crystal blocks, PMTS etc. The energy and spatial resolution of the scanners as given by the manufacturers have been taken into account. The GATE simulated results are compared directly to experimental data obtained using a number of NEMA NU-2-2001 performance protocols, including spatial resolution, sensitivity and scatter fraction. All the respective phantoms are precisely modeled. Furthermore, an approximate dead-time model both at the level of single and coincidence events was developed so that the simulated count rate curve can satisfactorily match the experimental count rate performance curve for each scanner In addition a software tool was developed to build the sinograms from the simulated data and import them into the software for tomographic image reconstruction where the reconstruction algorithm of FBP3DRP was applied. An agreement of less than 0.8 mm was obtained between the spatial resolution of the simulated system and the experimental results. Also the simulated scatter fraction for the NEMA NU 2-2001 scatter phantom matched the experimental results to within 3% of measured values. Finally the ratio of the simulated sensitivities with sources radially offset 0 and 10 cm from the central axis of each of the two scanners reaches an agreement of less than 1 % between the simulated and experimental values. This simulation code will be used in a second phase in order to study scatter phenomena and motion artifacts. The simulation results will be used to optimize image reconstruction algorithms, with emphasis on dynamic PET studies. (c) 2006 Published by Elsevier B.V.
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- 2006
14. Acceleration of motion-compensated PET reconstruction: ordered subsets-gates EM algorithms anda priorireference gate information
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Dikaios, N, primary and Fryer, T D, additional
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- 2011
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15. Respiratory motion correction of PET using motion parameters from MR
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Dikaios, N., primary and Fryer, T.D., additional
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- 2009
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16. Double Scatter Simulation using the Polarized Klein-Nishina formula
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Dikaios, N., primary, Spinks, T. J., additional, Nikita, K., additional, and Thielemans, K., additional
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- 2006
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17. Scatter Simulation Including Double Scatter
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Tsoumpas, C., primary, Aguiar, P., additional, Ros, D., additional, Dikaios, N., additional, and Thielemans, K., additional
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18. Scatter simulation including double scatter.
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Tsoumpas, C., Aguiar, P., Ros, D., Dikaios, N., and Thielemans, K.
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- 2005
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19. Noise estimation from averaged diffusion weighted images: Can unbiased quantitative decay parameters assist cancer evaluation?
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Nikolaos, Dikaios, Shonit, Punwani, Valentin, Hamy, Pierpaolo, Purpura, Scott, Rice, Martin, Forster, Ruheena, Mendes, Stuart, Taylor, David, Atkinson, Dikaios, N, Punwani, S, Hamy, V, Purpura, P, Rice, S, Forster, M, Mendes, R, Taylor, S, and Atkinson, D
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Adult ,Keywords: diffusion weighted magnetic resonance imaging ,diffusion weighted magnetic resonance imaging ,Middle Aged ,Models, Theoretical ,Signal-To-Noise Ratio ,Image Enhancement ,IVIM ,Diffusion Magnetic Resonance Imaging ,Head and Neck Neoplasms ,Lymphatic Metastasis ,Image Interpretation, Computer-Assisted ,Carcinoma, Squamous Cell ,Humans ,noise estimation ,Imaging Methodology—Full Papers ,Algorithms ,Aged - Abstract
Purpose Multiexponential decay parameters are estimated from diffusion-weighted-imaging that generally have inherently low signal-to-noise ratio and non-normal noise distributions, especially at high b-values. Conventional nonlinear regression algorithms assume normally distributed noise, introducing bias into the calculated decay parameters and potentially affecting their ability to classify tumors. This study aims to accurately estimate noise of averaged diffusion-weighted-imaging, to correct the noise induced bias, and to assess the effect upon cancer classification. Methods A new adaptation of the median-absolute-deviation technique in the wavelet-domain, using a closed form approximation of convolved probability-distribution-functions, is proposed to estimate noise. Nonlinear regression algorithms that account for the underlying noise (maximum probability) fit the biexponential/stretched exponential decay models to the diffusion-weighted signal. A logistic-regression model was built from the decay parameters to discriminate benign from metastatic neck lymph nodes in 40 patients. Results The adapted median-absolute-deviation method accurately predicted the noise of simulated (R2 = 0.96) and neck diffusion-weighted-imaging (averaged once or four times). Maximum probability recovers the true apparent-diffusion-coefficient of the simulated data better than nonlinear regression (up to 40%), whereas no apparent differences were found for the other decay parameters. Conclusions Perfusion-related parameters were best at cancer classification. Noise-corrected decay parameters did not significantly improve classification for the clinical data set though simulations show benefit for lower signal-to-noise ratio acquisitions. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
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- 2013
20. Multi-scale analysis of apparent diffusion coefficient (ADC) predicts cervical nodal status in patients with head and neck squamous cell carcinoma
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Shonit, P., Purpura, P., Nikolaos Dikaios, Fitzke, H., Bainbridge, A., Price, D., Rice, S., Morley, S., Beale, T., Mendes, R., Forster, M., Carnell, D., Vaitilingam, T., Newton, N., Atkinson, D., Halligan, S., Taylor, S., Shonit, P, Purpura, P, Dikaios, N, Fitzke, H, Bainbridge, A, Price, D, Rice, S, Morley, S, Beale, T, Mendes, R, Forster, M, Carnell, D, Vaitilingam, T, Newton, N, Atkinson, D, Halligan, S, and Taylor, S.
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Head and Neck, Sqaumocellular carcinoma, Diffusion Weighted Imaging, Musltiscale analisys of ADC - Abstract
The study assess multi-scale diffusion parameters (median volumetric nodal region of interest values, inter-voxel histogram distributions, and intra-voxel diffusion heterogeneity as assessed by the stretched exponential model) as classifiers of nodal status in patients with head and neck squamous cell carcinoma (SCC). Low b value (0, 50, 100) derived nodal ADC (perfusion sensitive) was the key parameter facilitating discrimination of metastatic from benign nodes in patients with head and neck SCC. The stretched exponential derived α value together with histogram features of ADC provide an accurate decision tree model for classification of nodal disease.
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- 2013
21. Maximum likelihood ADC parameter estimates improve selection of metastatic cervical nodes for patients with head and neck squamous cell cancer
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Nikolaos Dikaios, Punwani, S., Hamy, V., Purpura, P., Fitzke, H., Rice, S., Taylor, S., Atkinson, D., Dikaios, N, Punwani, S, Hamy, V, Purpura, P, Fitzke, H, Rice, S, Taylor, S, and Atkinson, D
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Head and Neck, Squamous Cell Cancer, DWI, multiparametric ADC - Abstract
The aim of this work was to determine whether classification of benign and metastatic cervical nodes based on diffusion weighted imaging (DWI) could be improved by use of a maximum likelihood algorithm for derivation of ADC parameters. A non linear least squares (LSQ) algorithm is usually used to fit parameters to the measured MR signal intensities as a function of b-value. LSQ assumes that the noise in high b-values is normally distributed whereas in reality it follows a Rice distribution. To account for the Rician noise, maximum likelihood (ML) algorithms have been proposed that provide unbiased ADC estimates. In this work the monoexponential, stretched exponential and biexponential models were examined, with their involved parameters calculated using the LSQ and the ML algorithms.
- Published
- 2012
22. Is Attention all You Need in Medical Image Analysis? A Review.
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Papanastasiou G, Dikaios N, Huang J, Wang C, and Yang G
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- Computer Simulation, Artificial Intelligence, Image Processing, Computer-Assisted
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Medical imaging is a key component in clinical diagnosis, treatment planning and clinical trial design, accounting for almost 90% of all healthcare data. CNNs achieved performance gains in medical image analysis (MIA) over the last years. CNNs can efficiently model local pixel interactions and be trained on small-scale MI data. Despite their important advances, typical CNN have relatively limited capabilities in modelling "global" pixel interactions, which restricts their generalisation ability to understand out-of-distribution data with different "global" information. The recent progress of Artificial Intelligence gave rise to Transformers, which can learn global relationships from data. However, full Transformer models need to be trained on large-scale data and involve tremendous computational complexity. Attention and Transformer compartments ("Transf/Attention") which can well maintain properties for modelling global relationships, have been proposed as lighter alternatives of full Transformers. Recently, there is an increasing trend to co-pollinate complementary local-global properties from CNN and Transf/Attention architectures, which led to a new era of hybrid models. The past years have witnessed substantial growth in hybrid CNN-Transf/Attention models across diverse MIA problems. In this systematic review, we survey existing hybrid CNN-Transf/Attention models, review and unravel key architectural designs, analyse breakthroughs, and evaluate current and future opportunities as well as challenges. We also introduced an analysis framework on generalisation opportunities of scientific and clinical impact, based on which new data-driven domain generalisation and adaptation methods can be stimulated.
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- 2024
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23. Large-scale deep learning analysis to identify adult patients at risk for combined and common variable immunodeficiencies.
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Papanastasiou G, Yang G, Fotiadis DI, Dikaios N, Wang C, Huda A, Sobolevsky L, Raasch J, Perez E, Sidhu G, and Palumbo D
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Background: Primary immunodeficiency (PI) is a group of heterogeneous disorders resulting from immune system defects. Over 70% of PI is undiagnosed, leading to increased mortality, co-morbidity and healthcare costs. Among PI disorders, combined immunodeficiencies (CID) are characterized by complex immune defects. Common variable immunodeficiency (CVID) is among the most common types of PI. In light of available treatments, it is critical to identify adult patients at risk for CID and CVID, before the development of serious morbidity and mortality., Methods: We developed a deep learning-based method (named "TabMLPNet") to analyze clinical history from nationally representative medical claims from electronic health records (Optum® data, covering all US), evaluated in the setting of identifying CID/CVID in adults. Further, we revealed the most important CID/CVID-associated antecedent phenotype combinations. Four large cohorts were generated: a total of 47,660 PI cases and (1:1 matched) controls., Results: The sensitivity/specificity of TabMLPNet modeling ranges from 0.82-0.88/0.82-0.85 across cohorts. Distinctive combinations of antecedent phenotypes associated with CID/CVID are identified, consisting of respiratory infections/conditions, genetic anomalies, cardiac defects, autoimmune diseases, blood disorders and malignancies, which can possibly be useful to systematize the identification of CID and CVID., Conclusions: We demonstrated an accurate method in terms of CID and CVID detection evaluated on large-scale medical claims data. Our predictive scheme can potentially lead to the development of new clinical insights and expanded guidelines for identification of adult patients at risk for CID and CVID as well as be used to improve patient outcomes on population level., (© 2023. The Author(s).)
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- 2023
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24. An Automated Deep Learning Approach for Spine Segmentation and Vertebrae Recognition Using Computed Tomography Images.
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Saeed MU, Dikaios N, Dastgir A, Ali G, Hamid M, and Hajjej F
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Spine image analysis is based on the accurate segmentation and vertebrae recognition of the spine. Several deep learning models have been proposed for spine segmentation and vertebrae recognition, but they are very computationally demanding. In this research, a novel deep learning model is introduced for spine segmentation and vertebrae recognition using CT images. The proposed model works in two steps: (1) A cascaded hierarchical atrous spatial pyramid pooling residual attention U-Net (CHASPPRAU-Net), which is a modified version of U-Net, is used for the segmentation of the spine. Cascaded spatial pyramid pooling layers, along with residual blocks, are used for feature extraction, while the attention module is used for focusing on regions of interest. (2) A 3D mobile residual U-Net (MRU-Net) is used for vertebrae recognition. MobileNetv2 includes residual and attention modules to accurately extract features from the axial, sagittal, and coronal views of 3D spine images. The features from these three views are concatenated to form a 3D feature map. After that, a 3D deep learning model is used for vertebrae recognition. The VerSe 20 and VerSe 19 datasets were used to validate the proposed model. The model achieved more accurate results in spine segmentation and vertebrae recognition than the state-of-the-art methods.
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- 2023
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25. Digital Transformation of Cancer Care in the Era of Big Data, Artificial Intelligence and Data-Driven Interventions: Navigating the Field.
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Papachristou N, Kotronoulas G, Dikaios N, Allison SJ, Eleftherochorinou H, Rai T, Kunz H, Barnaghi P, Miaskowski C, and Bamidis PD
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- Humans, Big Data, Medical Oncology, Digital Technology, Artificial Intelligence, Neoplasms therapy
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Objectives: To navigate the field of digital cancer care and define and discuss key aspects and applications of big data analytics, artificial intelligence (AI), and data-driven interventions., Data Sources: Peer-reviewed scientific publications and expert opinion., Conclusion: The digital transformation of cancer care, enabled by big data analytics, AI, and data-driven interventions, presents a significant opportunity to revolutionize the field. An increased understanding of the lifecycle and ethics of data-driven interventions will enhance development of innovative and applicable products to advance digital cancer care services., Implications for Nursing Practice: As digital technologies become integrated into cancer care, nurse practitioners and scientists will be required to increase their knowledge and skills to effectively use these tools to the patient's benefit. An enhanced understanding of the core concepts of AI and big data, confident use of digital health platforms, and ability to interpret the outputs of data-driven interventions are key competencies. Nurses in oncology will play a crucial role in patient education around big data and AI, with a focus on addressing any arising questions, concerns, or misconceptions to foster trust in these technologies. Successful integration of data-driven innovations into oncology nursing practice will empower practitioners to deliver more personalized, effective, and evidence-based care., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier Inc. All rights reserved.)
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- 2023
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26. A likelihood-based particle imaging filter using prior information.
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Fullarton R, Volz L, Dikaios N, Schulte R, Royle G, Evans PM, Seco J, and Collins-Fekete CA
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- Likelihood Functions, Ions, Image Processing, Computer-Assisted methods, Phantoms, Imaging, Water, Protons, Helium
- Abstract
Background: Particle imaging can increase precision in proton and ion therapy. Interactions with nuclei in the imaged object increase image noise and reduce image quality, especially for multinucleon ions that can fragment, such as helium., Purpose: This work proposes a particle imaging filter, referred to as the Prior Filter, based on using prior information in the form of an estimated relative stopping power (RSP) map and the principles of electromagnetic interaction, to identify particles that have undergone nuclear interaction. The particles identified as having undergone nuclear interactions are then excluded from the image reconstruction, reducing the image noise., Methods: The Prior Filter uses Fermi-Eyges scattering and Tschalär straggling theories to determine the likelihood that a particle only interacts electromagnetically. A threshold is then set to reject those particles with a low likelihood. The filter was evaluated and compared with a filter that estimates this likelihood based on the measured distribution of energy and scattering angle within pixels, commonly implemented as the 3σ filter. Reconstructed radiographs from simulated data of a 20-cm water cylinder and an anthropomorphic chest phantom were generated with both protons and helium ions to assess the effect of the filters on noise reduction. The simulation also allowed assessment of secondary particle removal through the particle histories. Experimental data were acquired of the Catphan CTP 404 Sensitometry phantom using the U.S. proton CT (pCT) collaboration prototype scanner. The proton and helium images were filtered with both the prior filtering method and a state-of-the-art method including an implementation of the 3σ filter. For both cases, a dE-E telescope filter, designed for this type of detector, was also applied., Results: The proton radiographs showed a small reduction in noise (1 mm of water-equivalent thickness [WET]) but a larger reduction in helium radiographs (up to 5-6 mm of WET) due to better secondary filtering. The proton and helium CT images reflected this, with similar noise at the center of the phantom (0.02 RSP) for the proton images and an RSP noise of 0.03 for the proposed filter and 0.06 for the 3σ filter in the helium images. Images reconstructed from data with a dose reduction, up to a factor of 9, maintained a lower noise level using the Prior Filter over the state-of-the-art filtering method., Conclusions: The proposed filter results in images with equal or reduced noise compared to those that have undergone a filtering method typical of current particle imaging studies. This work also demonstrates that the proposed filter maintains better performance against the state of the art with up to a nine-fold dose reduction., (© 2023 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)
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- 2023
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27. Pilot study of optical coherence tomography angiography-derived microvascular metrics in hands and feet of healthy and diabetic people.
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Untracht GR, Dikaios N, Durrani AK, Bapir M, Sarunic MV, Sampson DD, Heiss C, and Sampson DM
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- Humans, Pilot Projects, Tomography, Optical Coherence methods, Angiography, Risk Factors, Fluorescein Angiography methods, Retinal Vessels, Diabetes Mellitus, Type 2 diagnostic imaging, Diabetic Retinopathy
- Abstract
Optical coherence tomography angiography (OCTA) is a non-invasive, high-resolution imaging modality with growing application in dermatology and microvascular assessment. Accepted reference values for OCTA-derived microvascular parameters in skin do not yet exist but need to be established to drive OCTA into the clinic. In this pilot study, we assess a range of OCTA microvascular metrics at rest and after post-occlusive reactive hyperaemia (PORH) in the hands and feet of 52 healthy people and 11 people with well-controlled type 2 diabetes mellitus (T2DM). We calculate each metric, measure test-retest repeatability, and evaluate correlation with demographic risk factors. Our study delivers extremity-specific, age-dependent reference values and coefficients of repeatability of nine microvascular metrics at baseline and at the maximum of PORH. Significant differences are not seen for age-dependent microvascular metrics in hand, but they are present for several metrics in the foot. Significant differences are observed between hand and foot, both at baseline and maximum PORH, for most of the microvascular metrics with generally higher values in the hand. Despite a large variability over a range of individuals, as is expected based on heterogeneous ageing phenotypes of the population, the test-retest repeatability is 3.5% to 18% of the mean value for all metrics, which highlights the opportunities for OCTA-based studies in larger cohorts, for longitudinal monitoring, and for assessing the efficacy of interventions. Additionally, branchpoint density in the hand and foot and changes in vessel diameter in response to PORH stood out as good discriminators between healthy and T2DM groups, which indicates their potential value as biomarkers. This study, building on our previous work, represents a further step towards standardised OCTA in clinical practice and research., (© 2023. The Author(s).)
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- 2023
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28. Age-Dependent Decline in Common Femoral Artery Flow-Mediated Dilation and Wall Shear Stress in Healthy Subjects.
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Bapir M, Untracht GR, Hunt JEA, McVey JH, Harris J, Skene SS, Campagnolo P, Dikaios N, Rodriguez-Mateos A, Sampson DD, Sampson DM, and Heiss C
- Abstract
Femoral artery (FA) endothelial function is a promising biomarker of lower extremity vascular health for peripheral artery disease (PAD) prevention and treatment; however, the impact of age on FA endothelial function has not been reported in healthy adults. Therefore, we evaluated the reproducibility and acceptability of flow-mediated dilation (FMD) in the FA and brachial artery (BA) (n = 20) and performed cross-sectional FA- and BA-FMD measurements in healthy non-smokers aged 22−76 years (n = 50). FMD protocols demonstrated similar good reproducibility. Leg occlusion was deemed more uncomfortable than arm occlusion; thigh occlusion was less tolerated than forearm and calf occlusion. FA-FMD with calf occlusion was lower than BA-FMD (6.0 ± 1.1% vs 6.4 ± 1.3%, p = 0.030). Multivariate linear regression analysis indicated that age (−0.4%/decade) was a significant independent predictor of FA-FMD (R2 = 0.35, p = 0.002). The age-dependent decline in FMD did not significantly differ between FA and BA (pinteraction agexlocation = 0.388). In older participants, 40% of baseline FA wall shear stress (WSS) values were <5 dyne/cm2, which is regarded as pro-atherogenic. In conclusion, endothelial function declines similarly with age in the FA and the BA in healthy adults. The age-dependent FA enlargement results in a critical decrease in WSS that may explain part of the age-dependent predisposition for PAD.
- Published
- 2022
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29. Cocoa flavanol consumption improves lower extremity endothelial function in healthy individuals and people with type 2 diabetes.
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Bapir M, Untracht GR, Cooke D, McVey JH, Skene SS, Campagnolo P, Whyte MB, Dikaios N, Rodriguez-Mateos A, Sampson DD, Sampson DM, and Heiss C
- Subjects
- Brachial Artery physiology, Cross-Over Studies, Endothelium, Vascular, Humans, Lower Extremity blood supply, Polyphenols pharmacology, Pulse Wave Analysis, Vasodilation, Cacao, Diabetes Mellitus, Type 2 drug therapy
- Abstract
Background : diabetes and age are major risk factors for the development of lower extremity peripheral artery disease (PAD). Cocoa flavanol (CF) consumption is associated with lower risk for PAD and improves brachial artery (BA) endothelial function. Objectives : to assess if femoral artery (FA) endothelial function and dermal microcirculation are impaired in individuals with type 2 diabetes mellitus (T2DM) and evaluate the acute effect of CF consumption on FA endothelial function. Methods : in a randomised, controlled, double-blind, cross-over study, 22 individuals ( n = 11 healthy, n = 11 T2DM) without cardiovascular disease were recruited. Participants received either 1350 mg CF or placebo capsules on 2 separate days in random order. Endothelial function was measured as flow-mediated dilation (FMD) using ultrasound of the common FA and the BA before and 2 hours after interventions. The cutaneous microvasculature was assessed using optical coherence tomography angiography. Results : baseline FA-FMD and BA-FMD were significantly lower in T2DM (FA: 3.2 ± 1.1% [SD], BA: 4.8 ± 0.8%) compared to healthy (FA: 5.5 ± 0.7%, BA: 6.0 ± 0.8%); each p < 0.001. Whereas in healthy individuals FA-FMD did not significantly differ from BA-FMD ( p = 0.144), FA-FMD was significantly lower than BA-FMD in T2DM ( p = 0.003) indicating pronounced and additional endothelial dysfunction of lower limb arteries (FA-FMD/BA-FMD: 94 ± 14% [healthy] vs. 68 ± 22% [T2DM], p = 0.007). The baseline FA blood flow rate (0.42 ± 0.23 vs. 0.73 ± 0.35 l min
-1 , p = 0.037) and microvascular dilation in response to occlusion in hands and feet were significantly lower in T2DM subjects than in healthy ones. CF increased both FA- and BA-FMD at 2 hours, compared to placebo, in both healthy and T2DM subgroups (FA-FMD effect: 2.9 ± 1.4%, BA-FMD effect 3.0 ± 3.5%, each pintervention < 0.001). In parallel, baseline FA blood flow and microvascular diameter significantly increased in feet (3.5 ± 3.5 μm, pintervention < 0.001) but not hands. Systolic blood pressure and pulse wave velocity significantly decreased after CF in both subgroups (-7.2 ± 9.6 mmHg, pintervention = 0.004; -1.3 ± 1.3 m s-1 , pintervention = 0.002). Conclusions : individuals with T2DM exhibit decreased endothelial function that is more pronounced in the femoral than in the brachial artery. CFs increase endothelial function not only in the BA but also the FA both in healthy individuals and in those with T2DM who are at increased risk of developing lower extremity PAD and foot ulcers.- Published
- 2022
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30. A few-shot U-Net deep learning model for lung cancer lesion segmentation via PET/CT imaging.
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Protonotarios NE, Katsamenis I, Sykiotis S, Dikaios N, Kastis GA, Chatziioannou SN, Metaxas M, Doulamis N, and Doulamis A
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- Fluorodeoxyglucose F18, Humans, Positron Emission Tomography Computed Tomography, Tomography, X-Ray Computed, Deep Learning, Lung Neoplasms diagnostic imaging
- Abstract
Over the past few years, positron emission tomography/computed tomography (PET/CT) imaging for computer-aided diagnosis has received increasing attention. Supervised deep learning architectures are usually employed for the detection of abnormalities, with anatomical localization, especially in the case of CT scans. However, the main limitations of the supervised learning paradigm include (i) large amounts of data required for model training, and (ii) the assumption of fixed network weights upon training completion, implying that the performance of the model cannot be further improved after training. In order to overcome these limitations, we apply a few-shot learning (FSL) scheme. Contrary to traditional deep learning practices, in FSL the model is provided with less data during training. The model then utilizes end-user feedback after training to constantly improve its performance. We integrate FSL in a U-Net architecture for lung cancer lesion segmentation on PET/CT scans, allowing for dynamic model weight fine-tuning and resulting in an online supervised learning scheme. Constant online readjustments of the model weights according to the users' feedback, increase the detection and classification accuracy, especially in cases where low detection performance is encountered. Our proposed method is validated on the Lung-PET-CT-DX TCIA database. PET/CT scans from 87 patients were included in the dataset and were acquired 60 minutes after intravenous
18 F-FDG injection. Experimental results indicate the superiority of our approach compared to other state-of-the-art methods., (© 2022 IOP Publishing Ltd.)- Published
- 2022
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31. Discrete Shearlets as a Sparsifying Transform in Low-Rank Plus Sparse Decomposition for Undersampled ( k , t )-Space MR Data.
- Author
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Protonotarios NE, Tzampazidou E, Kastis GA, and Dikaios N
- Abstract
The discrete shearlet transformation accurately represents the discontinuities and edges occurring in magnetic resonance imaging, providing an excellent option of a sparsifying transform. In the present paper, we examine the use of discrete shearlets over other sparsifying transforms in a low-rank plus sparse decomposition problem, denoted by L+S. The proposed algorithm is evaluated on simulated dynamic contrast enhanced (DCE) and small bowel data. For the small bowel, eight subjects were scanned; the sequence was run first on breath-holding and subsequently on free-breathing, without changing the anatomical position of the subject. The reconstruction performance of the proposed algorithm was evaluated against k - t FOCUSS. L+S decomposition, using discrete shearlets as sparsifying transforms, successfully separated the low-rank (background and periodic motion) from the sparse component (enhancement or bowel motility) for both DCE and small bowel data. Motion estimated from low-rank of DCE data is closer to ground truth deformations than motion estimated from L and S . Motility metrics derived from the S component of free-breathing data were not significantly different from the ones from breath-holding data up to four-fold undersampling, indicating that bowel (rapid/random) motility is isolated in S . Our work strongly supports the use of discrete shearlets as a sparsifying transform in a L+S decomposition for undersampled MR data.
- Published
- 2022
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32. OCTAVA: An open-source toolbox for quantitative analysis of optical coherence tomography angiography images.
- Author
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Untracht GR, Matos RS, Dikaios N, Bapir M, Durrani AK, Butsabong T, Campagnolo P, Sampson DD, Heiss C, and Sampson DM
- Subjects
- Adult, Forearm blood supply, Hand blood supply, Healthy Volunteers, Humans, Middle Aged, Signal-To-Noise Ratio, Algorithms, Forearm diagnostic imaging, Hand diagnostic imaging, Image Processing, Computer-Assisted methods, Microvessels diagnostic imaging, Tomography, Optical Coherence methods
- Abstract
Optical coherence tomography angiography (OCTA) performs non-invasive visualization and characterization of microvasculature in research and clinical applications mainly in ophthalmology and dermatology. A wide variety of instruments, imaging protocols, processing methods and metrics have been used to describe the microvasculature, such that comparing different study outcomes is currently not feasible. With the goal of contributing to standardization of OCTA data analysis, we report a user-friendly, open-source toolbox, OCTAVA (OCTA Vascular Analyzer), to automate the pre-processing, segmentation, and quantitative analysis of en face OCTA maximum intensity projection images in a standardized workflow. We present each analysis step, including optimization of filtering and choice of segmentation algorithm, and definition of metrics. We perform quantitative analysis of OCTA images from different commercial and non-commercial instruments and samples and show OCTAVA can accurately and reproducibly determine metrics for characterization of microvasculature. Wide adoption could enable studies and aggregation of data on a scale sufficient to develop reliable microvascular biomarkers for early detection, and to guide treatment, of microvascular disease., Competing Interests: The authors have declared that no competing interests exist.
- Published
- 2021
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33. Utility of diffusion MRI characteristics of cervical lymph nodes as disease classifier between patients with head and neck squamous cell carcinoma and healthy volunteers.
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Papoutsaki MV, Sidhu HS, Dikaios N, Singh S, Atkinson D, Kanber B, Beale T, Morley S, Forster M, Carnell D, Mendes R, and Punwani S
- Subjects
- Adult, Aged, Female, Humans, Logistic Models, Male, Middle Aged, Observer Variation, ROC Curve, Diffusion Magnetic Resonance Imaging, Head and Neck Neoplasms diagnostic imaging, Healthy Volunteers, Lymph Nodes diagnostic imaging, Neck diagnostic imaging, Squamous Cell Carcinoma of Head and Neck diagnostic imaging
- Abstract
Diffusion MRI characteristics assessed by apparent diffusion coefficient (ADC) histogram analysis in head and neck squamous cell carcinoma (HNSCC) have been reported as helpful in classifying tumours based on diffusion characteristics. There is little reported on HNSCC lymph nodes classification by diffusion characteristics. The aim of this study was to determine whether pretreatment nodal microstructural diffusion MRI characteristics can classify diseased nodes of patients with HNSCC from normal nodes of healthy volunteers. Seventy-nine patients with histologically confirmed HNSCC prior to chemoradiotherapy, and eight healthy volunteers, underwent diffusion-weighted (DW) MRI at a 1.5-T MR scanner. Two radiologists contoured lymph nodes on DW (b = 300 s/m
2 ) images. ADC, distributed diffusion coefficient (DDC) and alpha (α) values were calculated by monoexponential and stretched exponential models. Histogram analysis metrics of drawn volume were compared between patients and volunteers using a Mann-Whitney test. The classification performance of each metric between the normal and diseased nodes was determined by receiver operating characteristic (ROC) analysis. Intraclass correlation coefficients determined interobserver reproducibility of each metric based on differently drawn ROIs by two radiologists. Sixty cancerous and 40 normal nodes were analysed. ADC histogram analysis revealed significant differences between patients and volunteers (p ≤0.0001 to 0.0046), presenting ADC distributions that were more skewed (1.49 for patients, 1.03 for volunteers; p = 0.0114) and 'peaked' (6.82 for patients, 4.20 for volunteers; p = 0.0021) in patients. Maximum ADC values exhibited the highest area under the curve ([AUC] 0.892). Significant differences were revealed between patients and volunteers for DDC and α value histogram metrics (p ≤0.0001 to 0.0044); the highest AUC were exhibited by maximum DDC (0.772) and the 25th percentile α value (0.761). Interobserver repeatability was excellent for mean ADC (ICC = 0.88) and the 25th percentile α value (ICC = 0.78), but poor for all other metrics. These results suggest that pretreatment microstructural diffusion MRI characteristics in lymph nodes, assessed by ADC and α value histogram analysis, can identify nodal disease., (© 2021 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)- Published
- 2021
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34. Quantification of T1, T2 relaxation times from Magnetic Resonance Fingerprinting radially undersampled data using analytical transformations.
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Dikaios N, Protonotarios NE, Fokas AS, and Kastis GA
- Subjects
- Algorithms, Brain diagnostic imaging, Humans, Magnetic Resonance Spectroscopy, Phantoms, Imaging, Image Processing, Computer-Assisted, Magnetic Resonance Imaging
- Abstract
Quantitative magnetic resonance imaging (MRI) estimates magnetic parameters related to tissue, such as T1, T2 relaxation times and proton density. MR fingerprinting (MRF) is a new concept that uses pseudo-random, incoherent measurements to create a unique fingerprint for each tissue type to quantify magnet parameters. This paper aims to enhance MRF performance by investigating (i) the most suitable acquisition trajectory, and (ii) analytical transformations, suitable for radial acquisitions. Highly undersampled MRF brain (k, t)-space data have been simulated and non-linearly reconstructed to exploit the low-rank property of dynamic imaging. Based on our findings, the radial trajectory is the most suitable for MRF compared to Cartesian and spiral acquisitions. Perhaps this is due to the fact that its aliasing artifacts are more noise-like, and that unlike spiral trajectories, it can use analytical transformations that do not require re-gridding. One such analytical algorithm is the spline reconstruction technique (SRT) that is based on a novel numerical implementation of an analytic representation of the inverse Radon transform. Here, for the first time, this algorithm is applied to MR radial data. Reconstructions using SRT were compared to the ones using filtered back-projection. SRT provided images of higher contrast, lower bias, which resulted in more accurate T1, T2 values., (Copyright © 2021 Elsevier Inc. All rights reserved.)
- Published
- 2021
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35. Machine learning for proton path tracking in proton computed tomography.
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Lazos D, Collins-Fekete CA, Bober M, Evans P, and Dikaios N
- Subjects
- Machine Learning, Monte Carlo Method, Phantoms, Imaging, Tomography, X-Ray Computed, Algorithms, Protons
- Abstract
A Machine Learning approach to the problem of calculating the proton paths inside a scanned object in proton Computed Tomography is presented. The method is developed in order to mitigate the loss in both spatial resolution and quantitative integrity of the reconstructed images caused by multiple Coulomb scattering of protons traversing the matter. Two Machine Learning models were used: a forward neural network (NN) and the XGBoost method. A heuristic approach, based on track averaging was also implemented in order to evaluate the accuracy limits on track calculation, imposed by the statistical nature of the scattering. Synthetic data from anthropomorphic voxelized phantoms, generated by the Monte Carlo (MC) Geant4 code, were utilized to train the models and evaluate their accuracy, in comparison to a widely used analytical method that is based on likelihood maximization and Fermi-Eyges scattering model. Both NN and XGBoost model were found to perform very close or at the accuracy limit, further improving the accuracy of the analytical method (by 12% in the typical case of 200 MeV protons on 20 cm of water object), especially for protons scattered at large angles. Inclusion of the material information along the path in terms of radiation length did not show improvement in accuracy for the phantoms simulated in the study. A NN was also constructed to predict the error in path calculation, thus enabling a criterion to filter out proton events that may have a negative effect on the quality of the reconstructed image. By parametrizing a large set of synthetic data, the Machine Learning models were proved capable to bring-in an indirect and time efficient way-the accuracy of the MC method into the problem of proton tracking., (© 2021 Institute of Physics and Engineering in Medicine.)
- Published
- 2021
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36. Statistical limitations in ion imaging.
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Collins-Fekete CA, Dikaios N, Bär E, and Evans PM
- Subjects
- Ions, Monte Carlo Method, Phantoms, Imaging, Signal-To-Noise Ratio, Heavy Ion Radiotherapy, Protons
- Abstract
In this study, we investigated the capacity of various ion beams available for radiotherapy to produce high quality relative stopping power map acquired from energy-loss measurements. The image quality metrics chosen to compare the different ions were signal-to-noise ratio (SNR) as a function of dose and spatial resolution. Geant4 Monte Carlo simulations were performed for: hydrogen, helium, lithium, boron and carbon ion beams crossing a 20 cm diameter water phantom to determine SNR and spatial resolution. It has been found that protons possess a significantly larger SNR when compared with other ions at a fixed range (up to 36% higher than helium) due to the proton nuclear stability and low dose per primary. However, it also yields the lowest spatial resolution against all other ions, with a resolution lowered by a factor 4 compared to that of carbon imaging, for a beam with the same initial range. When comparing for a fixed spatial resolution of 10 lp cm
-1 , carbon ions produce the highest image quality metrics with proton ions producing the lowest. In conclusion, it has been found that no ion can maximize all image quality metrics simultaneously and that a choice must be made between spatial resolution, SNR, and dose., (Creative Commons Attribution license.)- Published
- 2021
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37. Covid-19: predictive mathematical formulae for the number of deaths during lockdown and possible scenarios for the post-lockdown period.
- Author
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Fokas AS, Dikaios N, and Kastis GA
- Abstract
In a recent article, we introduced two novel mathematical expressions and a deep learning algorithm for characterizing the dynamics of the number of reported infected cases with SARS-CoV-2. Here, we show that such formulae can also be used for determining the time evolution of the associated number of deaths: for the epidemics in Spain, Germany, Italy and the UK, the parameters defining these formulae were computed using data up to 1 May 2020, a period of lockdown for these countries; then, the predictions of the formulae were compared with the data for the following 122 days, namely until 1 September. These comparisons, in addition to demonstrating the remarkable predictive capacity of our simple formulae, also show that for a rather long time the easing of the lockdown measures did not affect the number of deaths. The importance of these results regarding predictions of the number of Covid-19 deaths during the post-lockdown period is discussed., (© 2021 The Authors.)
- Published
- 2021
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38. Deep learning magnetic resonance spectroscopy fingerprints of brain tumours using quantum mechanically synthesised data.
- Author
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Dikaios N
- Subjects
- Humans, Brain Neoplasms metabolism, Deep Learning, Magnetic Resonance Spectroscopy methods
- Abstract
Metabolic fingerprints are valuable biomarkers for diseases that are associated with metabolic disorders. 1H magnetic resonance spectroscopy (MRS) is a unique noninvasive diagnostic tool that can depict the metabolic fingerprint based solely on the proton signal of different molecules present in the tissue. However, its performance is severely hindered by low SNR, field inhomogeneities and overlapping spectra of metabolites, which affect the quantification of metabolites. Consequently, MRS is rarely included in routine clinical protocols and has not been proven in multi-institutional trials. This work proposes an alternative approach, where instead of quantifying metabolites' concentration, deep learning (DL) is used to model the complex nonlinear relationship between diseases and their spectroscopic metabolic fingerprint (pattern). DL requires large training datasets, acquired (ideally) with the same protocol/scanner, which are very rarely available. To overcome this limitation, a novel method is proposed that can quantum mechanically synthesise MRS data for any scanner/acquisition protocol. The proposed methodology is applied to the challenging clinical problem of differentiating metastasis from glioblastoma brain tumours on data acquired across multiple institutions. DL algorithms were trained on the augmented synthetic spectra and tested on two independent datasets acquired by different scanners, achieving a receiver operating characteristic area under the curve of up to 0.96 and 0.97, respectively., (© 2021 John Wiley & Sons, Ltd.)
- Published
- 2021
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39. Molière maximum likelihood proton path estimation approximated by cubic Bézier curve for scatter corrected proton CT reconstruction.
- Author
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Lazos D, Collins-Fekete CA, Evans P, and Dikaios N
- Subjects
- Algorithms, Likelihood Functions, Models, Theoretical, Monte Carlo Method, Normal Distribution, Phantoms, Imaging, Image Processing, Computer-Assisted methods, Protons, Scattering, Radiation, Tomography, X-Ray Computed
- Abstract
A maximum likelihood approach to the problem of calculating the proton paths inside the scanned object in proton computed tomography is presented. Molière theory is used for the first time to derive a physical model that describes proton multiple Coulomb scattering, avoiding the need for the Gaussian approximation currently used. To enable this, the proposed method approximates proton paths with cubic Bézier curves and subsequently maximizes the path likelihood through parametric optimization, based on the Molière model. Results from the Highland formula-based Gaussian approximation are also presented for comparison. The simplex method is utilized for optimisation. The scattering properties of the material(s) of the scanned object are taken into account by appropriately calculating the scattering parameters from the stopping power map that is calculated/updated at every iteration of the algebraic reconstruction process. Proton track length constraint imposed by the proton energy loss is accounted for. The method is also applied in the case that no exit angle data are measured. Geant4 Monte Carlo simulations were performed for model validation. Our results show that use of Molière probability density function for modelling the multiple Coulomb scattering presents a modest 2% accuracy improvement over the Gaussian approximation and most-likely-path method. Simulations of voxelized phantom showed no essential benefit from the inclusion of the material information into the optimization, while path optimization with energy constraint slightly increased path resolution in a bone/water interface phantom. Method error was found to depend on energy, proton track-length within the medium, and proportion of data filtering.
- Published
- 2020
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40. Stochastic Gradient Langevin dynamics for joint parameterization of tracer kinetic models, input functions, and T1 relaxation-times from undersampled k-space DCE-MRI.
- Author
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Dikaios N
- Subjects
- Algorithms, Humans, Kinetics, Monte Carlo Method, Contrast Media, Magnetic Resonance Imaging
- Abstract
Dynamic Contrast Enhanced (DCE) Magnetic Resonance Imaging (MRI) is an important diagnostic technique that can quantify the structure and function of microvasculature processes, using T1 relaxation times and tracer kinetic maps. However, a series of methodological limitations affect both the accuracy and standardisation of the quantified maps, and consequently their diagnostic ability. The main methodological challenge in the quantification of tracer kinetics is a multi-parameter optimization, with correlated parameters that have different scales, which results in local minima particularly when measurements are highly undersampled. This work suggests a novel data driven optimization scheme, based on a variation of the Stochastic Gradient Langevin dynamics (SGLD) Markov chain Monte Carlo algorithm, which combines stochastic gradient descent and Langevin dynamics. The proposed SGDL algorithm avoided local minima and accurately quantified proton density, T1 relaxation times and tracer kinetics. Joint direct parameterization significantly benefited the quantification of proton density, T1 relaxation times, and the selection of a suitable tracer kinetic model per tissue type. Model based arterial and portal vein input functions were automatically determined during the joint direct parameterization. Observations made on simulated fully and highly undersampled liver DCE MRI data were confirmed on acquired clinical data., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)
- Published
- 2020
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41. Statistical limitations in proton imaging.
- Author
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Collins-Fekete CA, Dikaios N, Royle G, and Evans PM
- Subjects
- Calibration, Electrons, Humans, Uncertainty, Phantoms, Imaging, Protons, Signal-To-Noise Ratio, Tomography, X-Ray Computed methods
- Abstract
Proton imaging is a promising technology for proton radiotherapy as it can be used for: (1) direct sampling of the tissue stopping power, (2) input information for multi-modality RSP reconstruction, (3) gold-standard calibration against concurrent techniques, (4) tracking motion and (5) pre-treatment positioning. However, no end-to-end characterization of the image quality (signal-to-noise ratio and spatial resolution, blurring uncertainty) against the dose has been done. This work aims to establish a model relating these characteristics and to describe their relationship with proton energy and object size. The imaging noise originates from two processes: the Coulomb scattering with the nucleus, producing a path deviation, and the energy loss straggling with electrons. The noise is found to increases with thickness crossed and, independently, decreases with decreasing energy. The scattering noise is dominant around high-gradient edge whereas the straggling noise is maximal in homogeneous regions. Image quality metrics are found to behave oppositely against energy: lower energy minimizes both the noise and the spatial resolution, with the optimal energy choice depending on the application and location in the imaged object. In conclusion, the model presented will help define an optimal usage of proton imaging to reach the promised application of this technology and establish a fair comparison with other imaging techniques.
- Published
- 2020
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42. Correction to: Machine learning classifiers can predict Gleason pattern 4 prostate cancer with greater accuracy than experienced radiologists.
- Author
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Antonelli M, Johnston EW, Dikaios N, Cheung KK, Sidhu HS, Appayya MB, Giganti F, Simmons LAM, Freeman A, Allen C, Ahmed HU, Atkinson D, Ourselin S, and Punwani S
- Abstract
The original version of this article, published on 11 June 2019, unfortunately contained a mistake. The following correction has therefore been made in the original: In section "Multiparametric MRI review," the readers mentioned in the first sentence were partly incorrect.
- Published
- 2020
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43. Machine learning classifiers can predict Gleason pattern 4 prostate cancer with greater accuracy than experienced radiologists.
- Author
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Antonelli M, Johnston EW, Dikaios N, Cheung KK, Sidhu HS, Appayya MB, Giganti F, Simmons LAM, Freeman A, Allen C, Ahmed HU, Atkinson D, Ourselin S, and Punwani S
- Subjects
- Area Under Curve, Biopsy, Clinical Competence, Humans, Image Interpretation, Computer-Assisted methods, Male, Middle Aged, Neoplasm Grading, Prostatic Neoplasms diagnostic imaging, Radiologists, Retrospective Studies, Sensitivity and Specificity, Diffusion Magnetic Resonance Imaging methods, Machine Learning, Prostatic Neoplasms classification, Prostatic Neoplasms pathology
- Abstract
Objective: The purpose of this study was: To test whether machine learning classifiers for transition zone (TZ) and peripheral zone (PZ) can correctly classify prostate tumors into those with/without a Gleason 4 component, and to compare the performance of the best performing classifiers against the opinion of three board-certified radiologists., Methods: A retrospective analysis of prospectively acquired data was performed at a single center between 2012 and 2015. Inclusion criteria were (i) 3-T mp-MRI compliant with international guidelines, (ii) Likert ≥ 3/5 lesion, (iii) transperineal template ± targeted index lesion biopsy confirming cancer ≥ Gleason 3 + 3. Index lesions from 164 men were analyzed (119 PZ, 45 TZ). Quantitative MRI and clinical features were used and zone-specific machine learning classifiers were constructed. Models were validated using a fivefold cross-validation and a temporally separated patient cohort. Classifier performance was compared against the opinion of three board-certified radiologists., Results: The best PZ classifier trained with prostate-specific antigen density, apparent diffusion coefficient (ADC), and maximum enhancement (ME) on DCE-MRI obtained a ROC area under the curve (AUC) of 0.83 following fivefold cross-validation. Diagnostic sensitivity at 50% threshold of specificity was higher for the best PZ model (0.93) when compared with the mean sensitivity of the three radiologists (0.72). The best TZ model used ADC and ME to obtain an AUC of 0.75 following fivefold cross-validation. This achieved higher diagnostic sensitivity at 50% threshold of specificity (0.88) than the mean sensitivity of the three radiologists (0.82)., Conclusions: Machine learning classifiers predict Gleason pattern 4 in prostate tumors better than radiologists., Key Points: • Predictive models developed from quantitative multiparametric magnetic resonance imaging regarding the characterization of prostate cancer grade should be zone-specific. • Classifiers trained differently for peripheral and transition zone can predict a Gleason 4 component with a higher performance than the subjective opinion of experienced radiologists. • Classifiers would be particularly useful in the context of active surveillance, whereby decisions regarding whether to biopsy are necessitated.
- Published
- 2019
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44. Multi-parametric MRI zone-specific diagnostic model performance compared with experienced radiologists for detection of prostate cancer.
- Author
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Dikaios N, Giganti F, Sidhu HS, Johnston EW, Appayya MB, Simmons L, Freeman A, Ahmed HU, Atkinson D, and Punwani S
- Subjects
- Aged, Aged, 80 and over, Biopsy methods, Clinical Competence standards, Humans, Liver pathology, Magnetic Resonance Imaging methods, Male, Middle Aged, Prospective Studies, ROC Curve, Radiologists standards, Sensitivity and Specificity, Magnetic Resonance Imaging standards, Prostatic Neoplasms pathology
- Abstract
Objectives: Compare the performance of zone-specific multi-parametric-MRI (mp-MRI) diagnostic models in prostate cancer detection with experienced radiologists., Methods: A single-centre, IRB approved, prospective STARD compliant 3 T MRI test dataset of 203 patients was generated to test validity and generalisability of previously reported 1.5 T mp-MRI diagnostic models. All patients included within the test dataset underwent 3 T mp-MRI, comprising T2, diffusion-weighted and dynamic contrast-enhanced imaging followed by transperineal template ± targeted index lesion biopsy. Separate diagnostic models (transition zone (TZ) and peripheral zone (PZ)) were applied to respective zones. Sensitivity/specificity and the area under the receiver operating characteristic curve (ROC-AUC) were calculated for the two zone-specific models. Two radiologists (A and B) independently Likert scored test 3 T mp-MRI dataset, allowing ROC analysis for each radiologist for each prostate zone., Results: Diagnostic models applied to the test dataset demonstrated a ROC-AUC = 0.74 (95% CI 0.67-0.81) in the PZ and 0.68 (95% CI 0.61-0.75) in the TZ. Radiologist A/B had a ROC-AUC = 0.78/0.74 in the PZ and 0.69/0.69 in the TZ. Radiologists A and B each scored 51 patients in the PZ and 41 and 45 patients respectively in the TZ as Likert 3. The PZ model demonstrated a ROC-AUC = 0.65/0.67 for the patients Likert scored as indeterminate by radiologist A/B respectively, whereas the TZ model demonstrated a ROC-AUC = 0.74/0.69., Conclusion: Zone-specific mp-MRI diagnostic models demonstrate generalisability between 1.5 and 3 T mp-MRI protocols and show similar classification performance to experienced radiologists for prostate cancer detection. Results also indicate the ability of diagnostic models to classify cases with an indeterminate radiologist score., Key Points: • MRI diagnostic models had similar performance to experienced radiologists for classification of prostate cancer. • MRI diagnostic models may help radiologists classify tumour in patients with indeterminate Likert 3 scores.
- Published
- 2019
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45. Characterizing indeterminate (Likert-score 3/5) peripheral zone prostate lesions with PSA density, PI-RADS scoring and qualitative descriptors on multiparametric MRI.
- Author
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Brizmohun Appayya M, Sidhu HS, Dikaios N, Johnston EW, Simmons LA, Freeman A, Kirkham AP, Ahmed HU, and Punwani S
- Subjects
- Adult, Aged, Aged, 80 and over, Biomarkers, Tumor blood, Humans, Image-Guided Biopsy, Male, Middle Aged, Retrospective Studies, Magnetic Resonance Imaging methods, Prostate-Specific Antigen blood, Prostatic Neoplasms blood, Prostatic Neoplasms diagnostic imaging
- Abstract
Objective: To determine whether indeterminate (Likert-score 3/5) peripheral zone (PZ) multiparametric MRI (mpMRI) studies are classifiable by prostate-specific antigen (PSA), PSA density (PSAD), Prostate Imaging Reporting And Data System version 2 (PI-RADS_v2) rescoring and morphological MRI features., Methods: Men with maximum Likert-score 3/5 within their PZ were retrospectively selected from 330 patients who prospectively underwent prostate mpMRI (3 T) without an endorectal coil, followed by 20-zone transperineal template prostate mapping biopsies +/- focal lesion-targeted biopsy. PSAD was calculated using pre-biopsy PSA and MRI-derived volume. Two readers A and B independently assessed included men with both Likert-assessment and PI-RADS_v2. Both readers then classified mpMRI morphological features in consensus. Men were divided into two groups: significant cancer (≥ Gleason 3 + 4) or insignificant cancer (≤ Gleason 3 + 3)/no cancer. Comparisons between groups were made separately for PSA & PSAD using Mann-Whitney test and morphological descriptors with Fisher's exact test. PI-RADS_v2 and Likert-assessment were descriptively compared and percentage inter-reader agreement calculated., Results: 76 males were eligible for PSA & PSAD analyses, 71 for PI-RADS scoring, and 67 for morphological assessment (excluding significant image artefacts). Unlike PSA (p = 0.915), PSAD was statistically different (p = 0.004) between the significant [median: 0.19 ng ml
- 2 (interquartile range: 0.13-0.29)] and non-significant/no cancer [median: 0.13 ng ml- 2 (interquartile range: 0.10-0.17)] groups. Presence of mpMRI morphological features was not significantly different between groups. Subjective Likert-assessment discriminated patients with significant cancer better than PI-RADS_v2. Inter-reader percentage agreement was 83% for subjective Likert-assessment and 56% for PI-RADS_v2., Conclusion: PSAD may categorize presence of significant cancer in patients with Likert-scored 3/5 PZ mpMRI findings. Advances in knowledge: PSAD may be used in indeterminate PZ mpMRI to guide decisions between biopsy vs monitoring.- Published
- 2018
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46. Whole-body MRI quantitative biomarkers are associated significantly with treatment response in patients with newly diagnosed symptomatic multiple myeloma following bortezomib induction.
- Author
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Latifoltojar A, Hall-Craggs M, Bainbridge A, Rabin N, Popat R, Rismani A, D'Sa S, Dikaios N, Sokolska M, Antonelli M, Ourselin S, Yong K, Taylor SA, Halligan S, and Punwani S
- Subjects
- Adult, Aged, Aged, 80 and over, Antineoplastic Agents therapeutic use, Female, Humans, Male, Middle Aged, Multiple Myeloma diet therapy, Prospective Studies, Treatment Outcome, Bortezomib therapeutic use, Diffusion Magnetic Resonance Imaging methods, Multiple Myeloma diagnosis, Whole Body Imaging methods
- Abstract
Objectives: To evaluate whole-body MRI (WB-MRI) parameters significantly associated with treatment response in multiple myeloma (MM)., Methods: Twenty-one MM patients underwent WB-MRI at diagnosis and after two cycles of chemotherapy. Scans acquired at 3.0 T included T2, diffusion-weighted-imaging (DWI) and mDixon pre- and post-contrast. Twenty focal lesions (FLs) matched on DWI and post-contrast mDixon were selected for each time point. Estimated tumour volume (eTV), apparent diffusion coefficient (ADC), enhancement ratio (ER) and signal fat fraction (sFF) were derived. Clinical treatment response to chemotherapy was assessed using conventional criteria. Significance of temporal parameter change was assessed by the paired t test and receiver operating characteristics/area under the curve (AUC) analysis was performed. Parameter repeatability was assessed by interclass correlation (ICC) and Bland-Altman analysis of 10 healthy volunteers scanned at two time points., Results: Fifteen of 21 patients responded to treatment. Of 254 FLs analysed, sFF (p < 0.0001) and ADC (p = 0.001) significantly increased in responders but not non-responders. eTV significantly decreased in 19/21 cases. Focal lesion sFF was the best discriminator of treatment response (AUC 1.0). Bone sFF repeatability was excellent (ICC 0.98) and better than bone ADC (ICC 0.47)., Conclusion: WB-MRI derived focal lesion sFF shows promise as an imaging biomarker of treatment response in newly diagnosed MM., Key Points: • Bone signal fat fraction using mDixon is a robust quantifiable parameter • Fat fraction and ADC significantly increase in myeloma lesions responding to treatment • Bone lesion fat fraction is the best discriminator of myeloma treatment response.
- Published
- 2017
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47. Prediction of Pediatric Percutaneous Nephrolithotomy Outcomes Using Contemporary Scoring Systems.
- Author
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Aldaqadossi HA, Khairy Salem H, Kotb Y, Hussein HA, Shaker H, and Dikaios N
- Subjects
- Child, Egypt epidemiology, Female, Follow-Up Studies, Humans, Kidney Calculi diagnosis, Length of Stay trends, Male, Nomograms, Operative Time, Postoperative Complications epidemiology, Postoperative Period, Prognosis, ROC Curve, Radiography, Retrospective Studies, Treatment Outcome, Ultrasonography, Kidney Calculi surgery, Nephrolithotomy, Percutaneous methods, Postoperative Complications diagnosis
- Abstract
Purpose: We evaluate the applicability of contemporary percutaneous nephrolithotomy scoring systems in pediatric patients and compare their predictive power regarding postoperative outcomes., Materials and Methods: We retrospectively analyzed the records of 125 children who were diagnosed with renal calculi and underwent percutaneous nephrolithotomy between March 2011 and April 2016. Predictive scores, which consisted of Guy's Stone Score, S.T.O.N.E. (stone size, tract length, obstruction, number of involved calyces and essence/stone density) nephrolithometry and CROES (Clinical Research Office of the Endourological Society) nomogram, were calculated for all patients included in the study. Patient demographics, stone-free rate and complications were all analyzed and are reported., Results: Median Guy's Stone Score was 2 (IQR 2 to 3) in patients with residual stones (group 1) and 2 (1 to 2) in those who were stone-free (group 2). Median respective CROES nomogram scores were 215 (IQR 210 to 235) and 257 (240 to 264), and S.T.O.N.E. nephrolithometry scores were 8 (7 to 9) and 5 (5 to 6, all p <0.0001). S.T.O.N.E. score demonstrated the greatest accuracy in predicting stone-free rate. Guy's Stone Score was significantly correlated with complications but the CROES and S.T.O.N.E. scores were not significantly correlated with complications., Conclusions: The scoring systems analyzed could be used to predict success of percutaneous nephrolithotomy in the pediatric setting. However, further studies are needed to formulate modifications for use in children. The main variables in the scoring systems, ie stone burden, tract length and case volume, were measured using records from adult patients. Besides these variables, the relatively small pelvicalyceal system and higher incidence of anatomical malformations in children could potentially affect percutaneous nephrolithotomy outcomes., (Copyright © 2017 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)
- Published
- 2017
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48. "Textural analysis of multiparametric MRI detects transition zone prostate cancer".
- Author
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Sidhu HS, Benigno S, Ganeshan B, Dikaios N, Johnston EW, Allen C, Kirkham A, Groves AM, Ahmed HU, Emberton M, Taylor SA, Halligan S, and Punwani S
- Subjects
- Aged, Area Under Curve, Biopsy methods, Consensus, Diffusion Magnetic Resonance Imaging, Entropy, Humans, Male, Middle Aged, ROC Curve, Retrospective Studies, Prostate pathology, Prostatic Neoplasms pathology
- Abstract
Objectives: To evaluate multiparametric-MRI (mpMRI) derived histogram textural-analysis parameters for detection of transition zone (TZ) prostatic tumour., Methods: Sixty-seven consecutive men with suspected prostate cancer underwent 1.5T mpMRI prior to template-mapping-biopsy (TPM). Twenty-six men had 'significant' TZ tumour. Two radiologists in consensus matched TPM to the single axial slice best depicting tumour, or largest TZ diameter for those with benign histology, to define single-slice whole TZ-regions-of-interest (ROIs). Textural-parameter differences between single-slice whole TZ-ROI containing significant tumour versus benign/insignificant tumour were analysed using Mann Whitney U test. Diagnostic accuracy was assessed by receiver operating characteristic area under curve (ROC-AUC) analysis cross-validated with leave-one-out (LOO) analysis., Results: ADC kurtosis was significantly lower (p < 0.001) in TZ containing significant tumour with ROC-AUC 0.80 (LOO-AUC 0.78); the difference became non-significant following exclusion of significant tumour from single-slice whole TZ-ROI (p = 0.23). T1-entropy was significantly lower (p = 0.004) in TZ containing significant tumour with ROC-AUC 0.70 (LOO-AUC 0.66) and was unaffected by excluding significant tumour from TZ-ROI (p = 0.004). Combining these parameters yielded ROC-AUC 0.86 (LOO-AUC 0.83)., Conclusion: Textural features of the whole prostate TZ can discriminate significant prostatic cancer through reduced kurtosis of the ADC-histogram where significant tumour is included in TZ-ROI and reduced T1 entropy independent of tumour inclusion., Key Points: • MR textural features of prostate transition zone may discriminate significant prostatic cancer. • Transition zone (TZ) containing significant tumour demonstrates a less peaked ADC histogram. • TZ containing significant tumour reveals higher post-contrast T1-weighted homogeneity. • The utility of MR texture analysis in prostate cancer merits further investigation.
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- 2017
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49. A comparison of Bayesian and non-linear regression methods for robust estimation of pharmacokinetics in DCE-MRI and how it affects cancer diagnosis.
- Author
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Dikaios N, Atkinson D, Tudisca C, Purpura P, Forster M, Ahmed H, Beale T, Emberton M, and Punwani S
- Subjects
- Algorithms, Area Under Curve, Carcinoma, Squamous Cell diagnosis, Carcinoma, Squamous Cell metabolism, Female, Head and Neck Neoplasms diagnosis, Head and Neck Neoplasms metabolism, Humans, Male, Prostatic Neoplasms diagnosis, Prostatic Neoplasms metabolism, ROC Curve, Reproducibility of Results, Antineoplastic Agents pharmacokinetics, Bayes Theorem, Contrast Media, Magnetic Resonance Imaging methods, Neoplasms diagnosis, Neoplasms metabolism
- Abstract
The aim of this work is to compare Bayesian Inference for nonlinear models with commonly used traditional non-linear regression (NR) algorithms for estimating tracer kinetics in Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI). The algorithms are compared in terms of accuracy, and reproducibility under different initialization settings. Further it is investigated how a more robust estimation of tracer kinetics affects cancer diagnosis. The derived tracer kinetics from the Bayesian algorithm were validated against traditional NR algorithms (i.e. Levenberg-Marquardt, simplex) in terms of accuracy on a digital DCE phantom and in terms of goodness-of-fit (Kolmogorov-Smirnov test) on ROI-based concentration time courses from two different patient cohorts. The first cohort consisted of 76 men, 20 of whom had significant peripheral zone prostate cancer (any cancer-core-length (CCL) with Gleason>3+3 or any-grade with CCL>=4mm) following transperineal template prostate mapping biopsy. The second cohort consisted of 9 healthy volunteers and 24 patients with head and neck squamous cell carcinoma. The diagnostic ability of the derived tracer kinetics was assessed with receiver operating characteristic area under curve (ROC AUC) analysis. The Bayesian algorithm accurately recovered the ground-truth tracer kinetics for the digital DCE phantom consistently improving the Structural Similarity Index (SSIM) across the 50 different initializations compared to NR. For optimized initialization, Bayesian did not improve significantly the fitting accuracy on both patient cohorts, and it only significantly improved the v
e ROC AUC on the HN population from ROC AUC=0.56 for the simplex to ROC AUC=0.76. For both cohorts, the values and the diagnostic ability of tracer kinetic parameters estimated with the Bayesian algorithm weren't affected by their initialization. To conclude, the Bayesian algorithm led to a more accurate and reproducible quantification of tracer kinetic parameters in DCE-MRI, improving their ROC-AUC and decreasing their dependence on initialization settings., (Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.)- Published
- 2017
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50. Whole body magnetic resonance imaging in newly diagnosed multiple myeloma: early changes in lesional signal fat fraction predict disease response.
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Latifoltojar A, Hall-Craggs M, Rabin N, Popat R, Bainbridge A, Dikaios N, Sokolska M, Rismani A, D'Sa S, Punwani S, and Yong K
- Subjects
- Adipose Tissue diagnostic imaging, Adipose Tissue pathology, Adult, Aged, Biomarkers analysis, Female, Humans, Male, Middle Aged, Multiple Myeloma pathology, Remission Induction, Time Factors, Treatment Outcome, Tumor Burden, Magnetic Resonance Imaging methods, Multiple Myeloma diagnostic imaging, Predictive Value of Tests, Whole Body Imaging methods
- Abstract
Cross-sectional imaging techniques are being increasingly used for disease evaluation in patients with multiple myeloma. Whole body magnetic resonance imaging (WB-MRI) scanning is superior to plain radiography in baseline assessment of patients but changes following treatment have not been systematically explored. We carried out paired WB-MRI scans in 21 newly diagnosed patients prior to, and 8-weeks after, starting chemotherapy, and analysed stringently selected focal lesions (FLs) for parametric changes. A total of 323 FLs were evaluated, median 20 per patient. At 8 weeks, there was a reduction in estimated tumour volume (eTV), and an increase in signal fat fraction (sFF) and apparent diffusion coefficient (ADC) in the group as a whole (P < 0·001). Patients who achieved complete/very good partial response (CR/VGPR) to induction had a significantly greater increase in sFF compared to those achieving ≤ partial response (PR; P = 0·001). When analysed on a per-patient basis, all patients achieving CR/VGPR had a significant sFF increase in their FL's, in contrast to patients achieving ≤PR. sFF changes in patients reaching maximal response within 100 days (fast responders) were greater compared to slow responders (P = 0·001). Receiver Operator Characteristic analysis indicated that sFF changes at 8 weeks were the best biomarker (area under the Curve 0·95) for an inferior response (≤PR). We conclude that early lesional sFF changes may provide important information on depth of response, and are worthy of further prospective study., (© 2016 The Authors. British Journal of Haematology published by John Wiley & Sons Ltd.)
- Published
- 2017
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