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BACKGROUND: In order to reduce the impact of CT radiation, low-dose CT is often used, but low-dose CT will bring more noise, affecting image quality and subsequent 3D reconstruction results. OBJECTIVE: The study presents a reconstruction method based on wavelet transform-total variation (WT-TV) for low-dose CT. METHODS: First, the low-dose CT images were denoised using WT and TV denoising methods. The WT method could preserve the features, and the TV method could preserve the edges and structures. Second, the two sets of denoised images were fused so that the features, edges, and structures could be preserved at the same time. Finally, FBP reconstruction was performed to obtain the final 3D reconstruction result. RESULTS: The results show that The WT-TV method can effectively denoise low-dose CT and improve the clarity and accuracy of 3D reconstruction models. CONCLUSION: Compared with other reconstruction methods, the proposed reconstruction method successfully addressed the issue of low-dose CT noising by further denoising the CT images before reconstruction. The denoising effect of low-dose CT images and the 3D reconstruction model were compared via experiments. [ABSTRACT FROM AUTHOR]

Delamination in carbon fiber reinforced polymer (CFRP) composite structures plays a significant role in reducing the stiffness and strength of the structure, thus downgrading the integrity and reliability of the system. Aiming at the problem that traditional linear Lamb wave technology is not sensitive to the layered defects of composite materials and the existing nonlinear Lamb wave method is difficult to locate and detect damage, this paper proposes an ultrasonic tomography method based on Lamb waves to detect and reconstruct the delamination defects in CFRP plate. The dynamic finite element analysis method is used to simulate the propagation process of A0 mode Lamb waves in the 14-layer cross-layer CFRP defect plate. Sixty-four sensors perform fan-beam scanning on the composite plate in an equal-angle arrangement to obtain time-of-flight data corresponding to the sensing path. The layered defects of the composite material are imaged and evaluated by the filtered back-projection method. The experimental results show that this method can obtain high-quality reconstructed images of layered defects. [ABSTRACT FROM AUTHOR]

Multi-organ segmentation from whole-body computed tomography (CT) scans has gained increasing research interest over recent years. While the learning-based segmentation algorithm has lately achieved tremendous success, the need for detailed annotation of multiple organs further increases the manual burden. With a limited number of annotated volumetric datasets, it would be beneficial to apply the trained model from such a set to CT images acquired from other sites with different scanners. Nevertheless, the discrepancy among training and testing images significantly deteriorates segmentation performance. While there are many domain adaptation efforts, in this work we proposed a filtered back-projection based algorithm for performing domain adaptation for CT imagery. An optimal CT reconstruction kernel was obtained by minimizing the disparity between two images. Furthermore, since the Gaussian kernel is an eigen-function of the Fourier transformation, the adaptation computation was proven to be simple linear filtering. The proposed method was tested and compared with multiple methods to demonstrate improvement by employing such a model/theory-based adaptation approach. The proposed method, used in conjunction with a common convolutional neural network, such as the U-Net or V-Net, with or without the domain adaptation, achieves high accuracy in a multiple-organ segmentation task. Approximately 30% of data was used for training, 70% was used for testing, and an average dice of 0.88 was achieved in 8 organs.

• The reduction of CIT approach to FBP algorithm. • The rapid 2-D CIT algorithm of electron density profile. • The possibility of detection small ionospheric irregularities. The usage of a satellite cluster of satellite-to-satellite sounding of the ionosphere makes it possible to obtain the global height distribution of an electron density between 200 and 500 km height range in the orbital plane of the cluster. This paper introduces a novel rapid two-dimensional ionospheric radio tomography algorithm that uses total electron content (TEC) data measured between low Earth orbit (LEO) satellites. This algorithm reduces the problem of the ionospheric radio tomography to the rapid filtered back-projection (FBP) algorithm, which was not previously used in the computerized tomography of the ionosphere, and which allows to obtain a high resolution nowcast. Data sets of TEC measurements were simulated via IRI-2016 model and used as an input for the developed algorithm. The reconstructed profiles of the electron density were compared with those profiles from IRI-2016 model to calculate the difference between them. The obtained accuracy is comparable to the accuracy of algebraic reconstruction algorithms (ART), which are classical in the ionospheric radio tomography, and makes it possible to use the developed method to detect local disturbances in the ionosphere that is demonstrated on a test case in this paper. [ABSTRACT FROM AUTHOR]

Introduction: Quantitative evaluation is recommended to improve diagnostic ability and serial assessment of dopamine transporter (DAT) density scans. We decided to compare the ordered subsets expectation-maximization (OSEM) with filtered back-projection (FBP), and to investigate the impact of different iteration and cut-off frequencies on SBR values. Methods: We retrospectively examined 27 consecutive patients. SPECT reconstruction was performed using OSEM and FBP with Chang's attenuation correction (AC). Iterative reconstruction parameters were used with different iterations ranging from 2, 4, 6, 8, and 10 with fixed 10 subsets and different subsets including 5, 10 and 15 with fixed 6 iterations. Reconstruction with FBP were performed with different critical cut-off frequencies of 0.3, 0.4 and 0.5. Results: Comparing SBR derived by OSEM reconstruction with 10 subsets but different iterations revealed statistically significant intraclass correlation (ICC) in both right and left side. There is also no significant difference between different OSEM reconstruction with different subsets and ICC was excellent in all patients. ICC for FBP reconstruction with different cut-off frequency revealed good ICC in all patients. However, lower degree of SBR showed higher decrease in ICC with insignificant and poor correlation in patients with SBR<0.2. While comparing OSEM and FBP, good correlation was observed in total patients, there was poor correlation between these reconstruction methods in lower SBR values. Conclusion: Our study showed that change in FBP reconstruction parameters can greatly impact the SBR value of 99mTc- TRODAT-1, especially in patients with more severe disease. However, OSEM reconstruction revealed better reproducibility for SBR using different iterations. [ABSTRACT FROM AUTHOR]

Background: Low peak kilovoltage (kVp) computed tomography (CT) may be used to reduce contrast medium doses in patients at risk of contrast medium-induced acute kidney injury if image noise can be controlled by increasing X-ray tube loading (mAs). Purpose: To evaluate objective and subjective image quality in 80-kVp CT with reduced contrast medium dose and compensated mAs for unchanged image noise in patients with estimated glomerular filtration rate <45 mL/min compared with the standard 120-kVp protocol. Material and Methods: 80-kVp CT with 300 mg I/kg in 40 patients (body mass index 18–32 kg/m2, glomerular filtration rate <45 mL/min) and 120-kVp CT with 500 mg I/kg in 40 patients (body mass index = 17–30 kg/m2, glomerular filtration rate ≥45 mL/min) was compared on mean hepatic attenuation, image noise, contrast medium enhancement, signal-to-noise ratio, contrast-to-noise ratio, effective radiation dose, and subjective image quality. Results: There were no significant differences regarding median hepatic post-contrast attenuation, image noise, contrast medium enhancement, signal-to-noise ratio, contrast-to-noise ratio, or effective dose between the 80-kVp and 120-kVp cohorts: 114/110 HU; 14/14 HU; 57/53 HU; 8.0/7.4; 3.8/3.5; and 5.3/5.9 mSv, respectively. However, subjective image visual grading showed statistically significantly inferior scores for 80 kVp for six of eight items. After exclusion of seven inferior examinations not caused by the chosen kVp technique, only three items showed inferior scores for 80 kVp. Only 5% of gradings regarding overall image quality were <3 of 5 points. Conclusion: Despite lower subjective image quality, objective data indicate that 80-kVp CT with reduced contrast medium doses and compensated mAs may have the potential to provide satisfactory diagnostic quality in patients with body mass index <30 kg/m2, which could benefit patients at risk of contrast medium-induced acute kidney injury. [ABSTRACT FROM AUTHOR]

Background: Hepatic computed tomography (CT) with decreased peak kilovoltage (kVp) may be used to reduce contrast medium doses in patients at risk of contrast-induced acute kidney injury (CI-AKI); however, it increases image noise. To preserve image quality, noise has been controlled by X-ray tube loading (mAs) compensation (TLC), i.e. increased mAs. Another option to control image noise would be to use iterative reconstructions (IR) algorithms without TLC (No-TLC). It is unclear whether this may preserve image quality or only reduce image noise. Purpose: To evaluate image quality of 80 kVp hepatic CT with TLC and filtered back projection (FBP) compared with 80 kVp with No-TLC and IR algorithms (SAFIRE 3 and 5) in patients with eGFR <45 mL/min. Material and Methods: Forty patients (BMI 18–32 kg/m2) were examined with both protocols following injection of 300 mg I/kg. Hepatic attenuation, image noise, enhancement, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and subjective image quality were evaluated for each patient. Results: Comparing TLC/FBP with No-TLC/IR-S5, there were no significant differences regarding hepatic attenuation, image noise, enhancement, SNR and CNR: 114 vs. 115 HU, 14 vs. 14 HU, 55 vs. 57 HU, 8.0 vs. 8.4, and 3.8 vs. 4.0 in median, respectively. No-TLC/IR-S3 resulted in higher image noise and lower SNR and CNR than TLC/FBP. Subjective image quality scoring with visual grading showed statistically significantly inferior scores for IR-S5 images. Conclusion: CT of 80 kVp to reduce contrast medium dose in patients at risk of CI-AKI combined with IR algorithms with unchanged tube loading to control image noise does not provide sufficient diagnostic quality. [ABSTRACT FROM AUTHOR]

The influence of computed tomography (CT) reconstruction algorithms on the performance of machine-learning-based CT-derived fractional flow reserve (CT-FFR ML) has not been investigated. CT-FFR ML values and processing time of two reconstruction algorithms were compared using an on-site workstation. CT-FFR ML was computed on 40 coronary CT angiography (CCTA) datasets that were reconstructed with both iterative reconstruction in image space (IRIS) and filtered back-projection (FBP) algorithms. CT-FFR ML was computed on a per-vessel and per-segment basis as well as distal to lesions with ≥50% stenosis on CCTA. Processing times were recorded. Significant flow-limiting stenosis was defined as invasive FFR and CT-FFR ML values ≤ 0.80. Pearson's correlation, Wilcoxon, and McNemar statistical testing were used for data analysis. Per-vessel analysis of IRIS and FBP reconstructions demonstrated significantly different CT-FFR ML values (p ≤ 0.05). Correlation of CT-FFR ML values between algorithms was high for the left main (r = 0.74), left anterior descending (r = 0.76), and right coronary (r = 0.70) arteries. Proximal and middle segments showed a high correlation of CT-FFR ML values (r = 0.73 and r = 0.67, p ≤ 0.001, respectively), despite having significantly different averages (p ≤ 0.05). No difference in diagnostic accuracy was observed (both 81.8%, p = 1.000). Of the 40 patients, 10 had invasive FFR results. Per-lesion correlation with invasive FFR values was moderate for IRIS (r = 0.53, p = 0.117) and FBP (r = 0.49, p = 0.142). Processing time was significantly shorter using IRIS (15.9 vs. 19.8 min, p ≤ 0.05). CT reconstruction algorithms influence CT-FFR ML analysis, potentially affecting patient management. Additionally, iterative reconstruction improves CT-FFR ML post-processing speed. [ABSTRACT FROM AUTHOR]

Filtered Back-Projection (FBP) has become an outdated image reconstruction technique in new-generation positron emission tomography (PET)/computed tomography (CT) scanners. Iterative reconstruction used in all new-generation PET scanners is a much improved reconstruction technique. Though a well-calibrated PET system can only be used for clinical imaging in few situations like ours, when compromised PET scanner with one PET module bypassed was used for PET acquisition, FBP with sinogram correction proved to be a better reconstruction technique to minimize streak artifact present in the image reconstructed by the iterative technique.

Background: Model-based iterative reconstruction (MBIR) is a promising reconstruction method which could improve CT image quality with low radiation dose. The purpose of this study was to demonstrate the advantage of using MBIR for noise reduction and image quality improvement in low dose chest CT for children with necrotizing pneumonia, over the adaptive statistical iterative reconstruction (ASIR) and conventional filtered back-projection (FBP) technique. Methods: Twenty-six children with necrotizing pneumonia (aged 2 months to 11 years) who underwent standard of care low dose CT scans were included. Thinner-slice (0.625 mm) images were retrospectively reconstructed using MBIR, ASIR and conventional FBP techniques. Image noise and signal-to-noise ratio (SNR) for these thin-slice images were measured and statistically analyzed using ANOVA. Two radiologists independently analyzed the image quality for detecting necrotic lesions, and results were compared using a Friedman's test. Results: Radiation dose for the overall patient population was 0.59 mSv. There was a significant improvement in the high-density and low-contrast resolution of the MBIR reconstruction resulting in more detection and better identification of necrotic lesions (38 lesions in 0.625 mm MBIR images vs. 29 lesions in 0.625 mm FBP images). The subjective display scores (mean ± standard deviation) for the detection of necrotic lesions were 5.0 ± 0.0, 2.8 ± 0.4 and 2.5 ± 0.5 with MBIR, ASIR and FBP reconstruction, respectively, and the respective objective image noise was 13. 9 ± 4.0HU, 24.9 ± 6.6HU and 33.8 ± 8.7HU. The image noise decreased by 58.9 and 26.3% in MBIR images as compared to FBP and ASIR images. Additionally, the SNR of MBIR images was significantly higher than FBP images and ASIR images. Conclusions: The quality of chest CT images obtained by MBIR in children with necrotizing pneumonia was significantly improved by the MBIR technique as compared to the ASIR and FBP reconstruction, to provide a more confident and accurate diagnosis for necrotizing pneumonia. [ABSTRACT FROM AUTHOR]

In Compton imaging, iterative methods provide good performance but are usually computationally intensive. Thus, direct inverse algorithms such as filtered back-projection (FBP) are preferable when computation time is limited. The conventional FBP method assumes that the point spread function of a back-projection image is isotropic and invariant to incident direction, as required by frequency spectrum analysis. However, most of the time this assumption is not true because the detector geometry is rarely uniform. Therefore the conventional FBP reconstructed image is biased. To solve the geometry non-uniformity problem, this paper proposes an unbiased FBP algorithm that groups Compton events having the same Compton rings using a system matrix decomposition strategy. The proposed method produces more isotropic resolution, and preserves the capability to use frequency spectrum analysis. The algorithm has been applied to data from a 3D position-sensitive detector array with 4 crystals and a digital readout system. The resulting images had more isotropic resolution than standard FBP. [ABSTRACT FROM AUTHOR]

Background: Low kilovoltage (kVp) computed tomography (CT) may be used to reduce contrast medium dose in patients at risk of contrast nephropathy, at the cost of increased image noise.Purpose: To evaluate: (i) the impact of iterative reconstructions (Siemens SAFIRE) on low-contrast object detection to compensate for increased noise instead of increased tube loading when decreasing tube potential; and (ii) the change in iodine attenuation in simulated abdominal CT.Material and Methods: A phantom was scanned at 70, 80, 100, and 120 kVp at fixed effective tube loading (170 mAsEFF) and fixed radiation dose (CTDIVOL 10 mGy). Images were reconstructed with filtered back-projection (FBP) and SAFIRE strengths S1-S5. Iodine attenuation, objective image noise, contrast-to-noise ratio (CNR), noise power spectrum (NPS), spatial resolution, and subjective detectability of low-contrast objects were evaluated.Results: Compared with 120 kVp iodine attenuation increased by a factor 1.6 and 2.0, and image noise increased by a factor 1.9 and 2.5 at 80 and 70 kVp, respectively. Compared with FBP, SAFIRE showed objective reduction in image noise and increased CNR without loss of spatial resolution or any significant NPS alteration, with general tendency to improve subjective detectability of low-contrast objects. At 170 mAsEFF the number of discernible 1.0% contrast objects at 70 kVp/S5 and 80 kVp/S5 was similar to that at 120 kVp/FBP.Conclusion: With the SAFIRE algorithm image noise, CNR and detectability of low-contrast objects may be kept unchanged without increased tube loading when using low kVp settings to reduce contrast medium dose in azotemic patients. [ABSTRACT FROM AUTHOR]

Delamination is the main type of defect that reduces the performance of carbon fiber-reinforced polymer (CFRP) composite materials and can be detected by traditional linear ultrasonic methods. However, the traditional ultrasonic inspection method only analyzes its position through the waveform change, and it is difficult to intuitively and accurately study the specific shape and position of the defect in the form of images. This study obtains delamination defect images of CFRP composite plates through fan-beam ultrasonic computed tomography (UCT) and finite element simulation. The Filtered back-projection method based on UCT is used as the basic algorithm for reconstructing layered defect images of CFRP plates. To obtain accurate defect size and location, a novel dual-scale morphological filtering (DSMF) method combined with Canny operator is proposed for edge detection of delamination defects. The DSMF method alternately filters by combining two structuring elements of different sizes while suppressing noise as much as possible and preserving the edge details of the image. As the results verify, the use of the DSMF method combined with Canny edge-detection for edge detection significantly reduces the average recognition error from 16.83% to 4.37% compared to existing methods. The results show that the DSMF method can effectively reduce the influence of artifact interference and non-edge pixels on defect-recognition; thus, the size and contour information of the obtained defects are more accurate than existing methods. Experimental studies using realistic composite plates further validated the proposed method. The method of ultrasonic tomography combined with Canny edge detection based on a DSMF method can be well applied to edge detection and contour recognition of layered defects in CFRP materials. [ABSTRACT FROM AUTHOR]

Digital breast tomosynthesis (DBT) is a recently developed system for three-dimensional imaging that offers the potential to reduce the false positives of mammography by preventing tissue overlap. Many qualitative evaluations of digital breast tomosynthesis were previously performed by using a phantom with an unrealistic model and with heterogeneous background and noise, which is not representative of real breasts. The purpose of the present work was to compare reconstruction algorithms for DBT by using various breast phantoms; validation was also performed by using patient images. DBT was performed by using a prototype unit that was optimized for very low exposures and rapid readout. Three algorithms were compared: a back-projection (BP) algorithm, a filtered BP (FBP) algorithm, and an iterative expectation maximization (EM) algorithm. To compare the algorithms, three types of breast phantoms (homogeneous background phantom, heterogeneous background phantom, and anthropomorphic breast phantom) were evaluated, and clinical images were also reconstructed by using the different reconstruction algorithms. The in-plane image quality was evaluated based on the line profile and the contrast-to-noise ratio (CNR), and out-of-plane artifacts were evaluated by means of the artifact spread function (ASF). Parenchymal texture features of contrast and homogeneity were computed based on reconstructed images of an anthropomorphic breast phantom. The clinical images were studied to validate the effect of reconstruction algorithms. The results showed that the CNRs of masses reconstructed by using the EM algorithm were slightly higher than those obtained by using the BP algorithm, whereas the FBP algorithm yielded much lower CNR due to its high fluctuations of background noise. The FBP algorithm provides the best conspicuity for larger calcifications by enhancing their contrast and sharpness more than the other algorithms; however, in the case of small-size and low-contrast microcalcifications, the FBP reduced detectability due to its increased noise. The EM algorithm yielded high conspicuity for both microcalcifications and masses and yielded better ASFs in terms of the full width at half maximum. The higher contrast and lower homogeneity in terms of texture analysis were shown in FBP algorithm than in other algorithms. The patient images using the EM algorithm resulted in high visibility of low-contrast mass with clear border. In this study, we compared three reconstruction algorithms by using various kinds of breast phantoms and patient cases. Future work using these algorithms and considering the type of the breast and the acquisition techniques used (e.g., angular range, dose distribution) should include the use of actual patients or patient-like phantoms to increase the potential for practical applications. [ABSTRACT FROM AUTHOR]

Practical simulations of low-dose CT images have a possibility of being helpful means for optimization of the CT exposure dose. Because current methods reported by several researchers are limited to specific vendor platforms and generally rely on raw sinogram data that are difficult to access, we have developed a new computerized scheme for producing simulated low-dose CT images from real high-dose images without use of raw sinogram data or of a particular phantom. Our computerized scheme for low-dose CT simulation was based on the addition of a simulated noise image to a real high-dose CT image reconstructed by the filtered back-projection algorithm. First, a sinogram was generated from the forward projection of a high-dose CT image. Then, an additional noise sinogram resulting from use of a reduced exposure dose was estimated from a predetermined noise model. Finally, a noise CT image was reconstructed with a predetermined filter and was added to the real high-dose CT image to create a simulated low-dose CT image. The noise power spectrum and modulation transfer function of the simulated low-dose images were very close to those of the real low-dose images. In order to confirm the feasibility of our method, we applied this method to clinical cases which were examined with the high dose initially and then followed with a low-dose CT. In conclusion, our proposed method could simulate the low-dose CT images from their real high-dose images with sufficient accuracy and could be used for determining the optimal dose setting for various clinical CT examinations. [ABSTRACT FROM AUTHOR]

Compton imaging is a gamma-ray imaging technique useful for photons with energies in the range of a hundred keV to several MeV. Measuring gamma rays with a Compton camera results in cone data that needs to be mathematically inverted to determine the incident flux distribution. In the past, filtered back-projection solutions for Compton telescope data required sums of spherical harmonics or stereographically mapping the back-projection, which can result in imaging artifacts. We present a solution to this inversion problem that removes these complexities by embedding the 2-D directional image on the surface of a sphere S^2 into R^3 where it is easily solvable. In this manner we relate 2-D Compton 4\pi imaging to the 3-D Radon transform, which has known solutions. To accomplish this, the cone data is converted to planar data. Additionally we show how the planar geometry can be used to produce a computationally efficient implementation. This reconstruction is demonstrated with a two-plane, double-sided strip, HPGe Compton camera. [ABSTRACT FROM AUTHOR]

We report an alternative reconstruction technique for x-ray differential phase-contrast computed tomography (DPC-CT). This approach is based on a new phase line integral projection retrieval filter, which is rooted in the derivative property of the Fourier transform and counteracts the differential nature of the DPC-CT projections. It first retrieves the phase line integral from the DPC-CT projections. Then the standard filtered back-projection (FBP) algorithms popular in x-ray absorption-contrast CT are directly applied to the retrieved phase line integrals to reconstruct the DPC-CT images. Compared with the conventional DPC-CT reconstruction algorithms, the proposed method removes the Hilbert imaginary filter and allows for the direct use of absorption-contrast FBP algorithms. Consequently, FBP-oriented image processing techniques and reconstruction acceleration softwares that have already been successfully used in absorption-contrast CT can be directly adopted to improve the DPC-CT image quality and speed up the reconstruction. [ABSTRACT FROM AUTHOR]

Filtered Back‑Projection (FBP) has become an outdated image reconstruction technique in new‑generation positron emission tomography (PET)/computed tomography (CT) scanners. Iterative reconstruction used in all new‑generation PET scanners is a much improved reconstruction technique. Though a well‑calibrated PET system can only be used for clinical imaging in few situations like ours, when compromised PET scanner with one PET module bypassed was used for PET acquisition, FBP with sinogram correction proved to be a better reconstruction technique to minimize streak artifact present in the image reconstructed by the iterative technique. [ABSTRACT FROM AUTHOR]

Abstract: We present the PyHST2 code which is in service at ESRF for phase-contrast and absorption tomography. This code has been engineered to sustain the high data flow typical of the 3rd generation synchrotron facilities (10 terabytes per experiment) by adopting a distributed and pipelined architecture. The code implements, beside a default filtered backprojection reconstruction, iterative reconstruction techniques with a priori knowledge. These latter are used to improve the reconstruction quality or in order to reduce the required data volume or the deposited dose to the sample and reach a given quality goal. The implemented a priori knowledge techniques are based on the total variation penalization and a new recently found convex functional which is based on overlapping patches. We give details of the different methods and discuss how they are implemented in the PyHST2 code, which is distributed under free license. We provide methods for estimating, in the absence of ground-truth data, the optimal parameters values for a priori techniques. [Copyright &y& Elsevier]

When using cardiac nuclear medicine images for diagnosis, the filtered back-projection (FBP) algorithm can reconstruct positron emission tomography (PET) images under low count rates. However, background strike artifacts in PET images are affected by diagnostic judgment. Hence, this study developed a robust method of removing background strike artifacts from FBP images without reducing image quality. A Jaszczak anthropomorphic torso phantom and a laboratory rabbit were used for performance tests of the proposed method. Parallel computing was applied to optimize the mask size of morphological structure operator (MSO) by minimizing the background standard deviation (Std). The optimal MSO mask size for the evaluated Jaszczak phantom was 3×3. The FBP images processed by MSO had significantly reduced strike artifacts measured by background Std (P=1E-5). After MSO processing, the time activity curve (TAC) of FBP images was stable and resembled the original FBP images (P=0.5). The proposed approach is highly stable and reduces noise by 13.08±2.32 in FBP images after MSO processing with 3×3 mask. [ABSTRACT FROM AUTHOR]

• 3D Tomographic reconstruction of irregular rough particles from their interferometric images. • The error-reduction algorithm and the filtered back-projection are used. • Centrosymmetric and non-centrosymmetric particles are tested. Using a Digital Micromirror Device (DMD), the 3D-reconstruction of programmable rough particles (centrosymmetric or non-centrosymmetric) are done from a set of 120 interferometric images. This can be done using the error-reduction (ER) algorithm for the 2D shape reconstructions and the filtered back-projection for the 3D tomographic reconstruction. [ABSTRACT FROM AUTHOR]

Metal artefacts arising from high-density objects, which appear typically in industrial X-ray computed tomography (CT), significantly influence the quality of the reconstructed image. The detection of defects and the measurement of the internal structures of the tested object, which are important for non-destructive testing (NDT) and non-destructive evaluation (NDE) applications, can be heavily affected by metal artefacts. In practical X-ray systems, limited by the energy of the radiation, the maximum possible penetration for the given radiation source may be smaller than the size of the object. In these cases, the images reconstructed by the filtered back-projection algorithm (FBP) suffer severe metal artefacts. To reduce this kind of metal artefact, we introduce an iterative algorithm based on total variation minimisation (TVM) and an improved analytical algorithm based on FBP for image reconstruction. In our work, a long object, whose size is larger than the maximum possible penetration for the given radiation source, is tested. Then, the validity of the algorithm presented for metal artefact reduction is verified. Firstly, to evaluate the effectiveness of the iterative algorithm based on TVM, several iterative reconstruction strategies are investigated and compared. Secondly, we present an improved FBP algorithm by correcting the filtered projection data, but not traditionally correcting the raw projection data. According to the experimental results for metal artefact reduction, the algorithm based on TVM and the improved FBP algorithm are both considered to have better performance than the original FBP algorithm and the simultaneous algebraic reconstruction technique (SART) algorithm. [ABSTRACT FROM AUTHOR]

Purpose: Reducing the patient dose while maintaining the diagnostic image quality during CT exams is the subject of a growing number of studies, in which simulations of reduced-dose CT with patient data have been used as an effective technique when exploring the potential of various dose reduction techniques. Difficulties in accessing raw sinogram data, however, have restricted the use of this technique to a limited number of institutions. Here, we present a novel reduced-dose CT simulation technique which provides realistic low-dose images without the requirement of raw sinogram data. Methods: Two key characteristics of CT systems, the noise equivalent quanta (NEQ) and the algorithmic modulation transfer function (MTF), were measured for various combinations of object attenuation and tube currents by analyzing the noise power spectrum (NPS) of CT images obtained with a set of phantoms. Those measurements were used to develop a comprehensive CT noise model covering the reduced x-ray photon flux, object attenuation, system noise, and bow-tie filter, which was then employed to generate a simulated noise sinogram for the reduced-dose condition with the use of a synthetic sinogram generated from a reference CT image. The simulated noise sinogram was filtered with the algorithmic MTF and back-projected to create a noise CT image, which was then added to the reference CT image, finally providing a simulated reduced-dose CT image. The simulation performance was evaluated in terms of the degree of NPS similarity, the noise magnitude, the bow-tie filter effect, and the streak noise pattern at photon starvation sites with the set of phantom images. Results: The simulation results showed good agreement with actual low-dose CT images in terms of their visual appearance and in a quantitative evaluation test. The magnitude and shape of the NPS curves of the simulated low-dose images agreed well with those of real low-dose images, showing discrepancies of less than +/−3.2% in terms of the noise power at the peak height and +/−1.2% in terms of the spatial frequency at the peak height. The magnitudes of the noise measured for 12 different combinations the phantom size, tube current, and reconstruction kernel for the simulated and real low-dose images were very similar, with differences of 0.1 to 4.7%. The p value for a statistical testing of the difference in the noise magnitude ranged from 0.99 to 0.11, showing that there was no difference statistically between the noise magnitudes of the real and simulated low-dose images using our method. The strength and pattern of the streak noise in an anthropomorphic phantom was also consistent with expectations. Conclusions: A novel reduced-dose CT simulation technique was developed which uses only CT images while not requiring raw sinogram data. Our method can provide realistic simulation results under reduced-dose conditions both in terms of the noise magnitude and the textual appearance. This technique has the potential to promote clinical research for patient dose reductions. [ABSTRACT FROM AUTHOR]

Objective: To compare image quality of a standard-dose (SD) and a low-dose (LD) cervical spine CT protocol using filtered back-projection (FBP) and iterative reconstruction (IR). Materials and methods: Forty patients investigated by cervical spine CT were prospectively randomised into two groups: SD (120 kVp, 275 mAs) and LD (120 kVp, 150 mAs), both applying automatic tube current modulation. Data were reconstructed using both FBP and sinogram-affirmed IR. Image noise, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were measured. Two radiologists independently and blindly assessed the following anatomical structures at C3-C4 and C6-C7 levels, using a four-point scale: intervertebral disc, content of neural foramina and dural sac, ligaments, soft tissues and vertebrae. They subsequently rated overall image quality using a ten-point scale. Results: For both protocols and at each disc level, IR significantly decreased image noise and increased SNR and CNR, compared with FBP. SNR and CNR were statistically equivalent in LD-IR and SD-FBP protocols. Regardless of the dose and disc level, the qualitative scores with IR compared with FBP, and with LD-IR compared with SD-FBP, were significantly higher or not statistically different for intervertebral discs, neural foramina and ligaments, while significantly lower or not statistically different for soft tissues and vertebrae. The overall image quality scores were significantly higher with IR compared with FBP, and with LD-IR compared with SD-FBP. Conclusion: LD-IR cervical spine CT provides better image quality for intervertebral discs, neural foramina and ligaments, and worse image quality for soft tissues and vertebrae, compared with SD-FBP, while reducing radiation dose by approximately 40 %. [ABSTRACT FROM AUTHOR]

Objectives: To present the results of a systematic literature search aimed at determining to what extent the radiation dose can be reduced with iterative reconstruction (IR) for cardiopulmonary and body imaging with computed tomography (CT) in the clinical setting and what the effects on image quality are with IR versus filtered back-projection (FBP) and to provide recommendations for future research on IR. Methods: We searched Medline and Embase from January 2006 to January 2012 and included original research papers concerning IR for CT. Results: The systematic search yielded 380 articles. Forty-nine relevant studies were included. These studies concerned: the chest( n = 26), abdomen( n = 16), both chest and abdomen( n = 1), head( n = 4), spine( n = 1), and no specific area ( n = 1). IR reduced noise and artefacts, and it improved subjective and objective image quality compared to FBP at the same dose. Conversely, low-dose IR and normal-dose FBP showed similar noise, artefacts, and subjective and objective image quality. Reported dose reductions ranged from 23 to 76 % compared to locally used default FBP settings. However, IR has not yet been investigated for ultra-low-dose acquisitions with clinical diagnosis and accuracy as endpoints. Conclusion: Benefits of IR include improved subjective and objective image quality as well as radiation dose reduction while preserving image quality. Future studies need to address the value of IR in ultra-low-dose CT with clinically relevant endpoints. Key Points: • Iterative reconstruction improves image quality of CT images at equal acquisition parameters. • IR preserves image quality compared to normal-dose filtered back-projection. • The reduced radiation dose made possible by IR is advantageous for patients. • IR has not yet been investigated with clinical diagnosis and accuracy as endpoints. [ABSTRACT FROM AUTHOR]

Objectives: To explain the technical principles of and differences between commercially available iterative reconstruction (IR) algorithms for computed tomography (CT) in non-mathematical terms for radiologists and clinicians. Methods: Technical details of the different proprietary IR techniques were distilled from available scientific articles and manufacturers' white papers and were verified by the manufacturers. Clinical results were obtained from a literature search spanning January 2006 to January 2012, including only original research papers concerning IR for CT. Results: IR for CT iteratively reduces noise and artefacts in either image space or raw data, or both. Reported dose reductions ranged from 23 % to 76 % compared to locally used default filtered back-projection (FBP) settings, with similar noise, artefacts, subjective, and objective image quality. Conclusion: IR has the potential to allow reducing the radiation dose while preserving image quality. Disadvantages of IR include blotchy image appearance and longer computational time. Future studies need to address differences between IR algorithms for clinical low-dose CT. Key Points: • Iterative reconstruction technology for CT is presented in non-mathematical terms. • IR reduces noise and artefacts compared to filtered back-projection. • IR can improve image quality in routine-dose CT and lower the radiation dose. • IR's disadvantages include longer computation and blotchy appearance of some images. [ABSTRACT FROM AUTHOR]

We report the experimental results of geometric parameter measurement of the single-mode fiber by use of digital holographic micro-tomography technology. Tomography of the single-mode fiber is performed by a filtered back-projection algorithm and a Fourier diffraction algorithm, respectively, to reconstruct the three-dimensional (3-D) map of refractive index. According to this map, we can further get the dimensions of the single-mode fiber by the relate edge detection algorithm of image processing. Experimental results show that compared to the filtered back-projection reconstruction, diffraction tomography based on the Rytov approximation resembles the dimensions of the single-mode fiber. It provides a new way for the nondestructive and on-site measurement of tiny weakly diffracting objects with a cylindrically symmetric structure, such as the single-mode fiber. [ABSTRACT FROM AUTHOR]

Abstract: A novel time-domain spectroscopic EPR imaging approach, that is a unique combination of already known techniques, is described. The first one is multi-gradient Single Point Imaging involving pure phase-encoding where the oximetry is based on . Line width derived from is subject to susceptibility effects and therefore needs system-dependent line width calibrations. The second approach utilizes the conventional 90°–τ–180° Spin-Echo pulse sequence where the images are obtained by the filtered back-projection after FT of the echoes collected under frequency-encoding gradients. The spatially resolved oximetry information is derived from a set of T 2-weighted images. The back-projection images suffer susceptibility artifacts with resolution determined by , but the oximetry based on T 2 is quite reliable. The current approach combines Single Point Imaging and the Spin-Echo procedure to take advantage the enhanced spatial resolution associated with the former and the T 2 dependent contrast of the latter. Pairs of images are derived choosing two time points located at identical time intervals on either side of the 180° pulse. The refocusing pulse being exactly in the middle of the two points ensures that artifacts associated with susceptibility and field inhomogeneities are eliminated. In addition, the net phase accumulated by the two time points being identical results in identical field of views, thus avoiding the zoom-in effect as a function delay in regular SPI and the associated interpolation requirements employed in -weighted oximetry. The end result is superior image resolution and reliable oximetry. In spite of the fact that projection–reconstruction methods require less number of measurements compared to SPI, the enormous advantage in SNR of the SPI procedure makes the echo-based SPI equally efficient in terms of measurement time. The Fourier reconstruction, line width independent resolution and the true T 2-weighting make this novel procedure very attractive for in vivo EPR imaging of tissue oxygen quantitatively. [Copyright &y& Elsevier]

Microfluidic devices aim at miniaturizing, automating, and lowering the cost of chemical and biological sample manipulation and detection, hence creating new opportunities for lab-on-a-chip platforms. Recently, optofluidic devices have also emerged where optics is used to enhance the functionality and the performance of microfluidic components in general. Lensfree imaging within microfluidic channels is one such optofluidic platform, and in this article, we focus on the holographic implementation of lensfree optofluidic microscopy and tomography, which might provide a simpler and more powerful solution for three-dimensional (3D) on-chip imaging. This lensfree optofluidic imaging platform utilizes partially coherent digital in-line holography to allow phase and amplitude imaging of specimens flowing through micro-channels, and takes advantage of the fluidic flow to achieve higher spatial resolution imaging compared to a stationary specimen on the same chip. In addition to this, 3D tomographic images of the same samples can also be reconstructed by capturing lensfree projection images of the samples at various illumination angles as a function of the fluidic flow. Based on lensfree digital holographic imaging, this optofluidic microscopy and tomography concept could be valuable especially for providing a compact, yet powerful toolset for lab-on-a-chip devices. [ABSTRACT FROM AUTHOR]

Abstract: The Filtered Back-projection Algorithm is a relatively perfect algorithm in turntable imaging, it is widely used in CT and signal processing. It is found though analyzing that the time frequency coupling is neglected and the imaging quality descends. A new Filtered Back - projection Algorithm is proposed. The new method is tested using of practice measure data and numerical simulations, which shows that the new algorithm is effective. [Copyright &y& Elsevier]

Background: Traditional limitations of cardiac CT are related to image noise, blooming artifacts from calcifications and stents, and radiation exposure. We evaluated whether these limitations can be ameliorated by the use of iterative reconstruction in image space (IRIS) instead of traditional filtered back projection (FBP) image reconstruction techniques. Methods: We compared image reconstruction with the use of IRIS with traditional FBP for their effect on image quality, noise, volume of heavy coronary artery calcifications, and stents as a measure of “blooming” artifacts, and radiation dose at cardiac CT. The radiation dose comparison was performed as a matched pair analysis, whereas all other comparisons were performed within the same group of patients. Results: The subjective image quality of IRIS reconstructions was rated higher than FBP reconstructions. Image noise was lower with IRIS than with FBP. The volume of stents and heavy coronary artery calcifications measured lower in IRIS reconstructed series compared with FBP. Similar levels of image noise were achieved with 80/100 kVp of tube voltage with IRIS compared with 120 kVp and FBP, resulting in a 62% reduction in effective dose. Conclusion: Our preliminary experiences suggest that IRIS incrementally improves the CT evaluation of coronary arteries, especially in challenging scenarios. Substantial radiation reduction seems feasible without associated increases in image noise. [ABSTRACT FROM AUTHOR]

The article focuses on the development of new method which suppresses ring artefacts during anistropic computerized X-ray tomography. It discusses the application of an analytical formula involving matrix-vector multiplication under regularization parameter. It also highlights the method efficacy through the experiment using calcified shark cartilage and metal matrix composite samples.

Abstract: A Radon transform algorithm which incorporates the correlated X-ray images (some stock chest radiographs) into the processing of back-projection with the fan-beam geometry reconstruction with the aim of improving image quality was developed and explored. These reconstruction images were evaluated and compared with the original image. Meanwhile, we also made the comparisons with the filtered back-projection method and the Radon transform method without fan-beam geometry; the results also reveal that the proposed method has the best image reconstruction capability than other two methods. The results show that the proposed method produces reconstructed images with quiet high peak-signal-to-noise ratio. [Copyright &y& Elsevier]

We present motivation for performing the filtering step of the widely used filtered back-projection algorithm in a non-Radon domain. For square-error optimal penalized-likelihood regularization, filtering in a domain for which the true projection data is sparse in the angle dimension yields coefficients that are more faithful to the ideal filtered data than directly filtering the observed Radon-domain data. In contrast to traditional regularization techniques that filter each projection independently, the proposed filtering technique delivers improved reconstructions by exploiting the correlation of the data in the angle dimension. This enables meaningful reconstructions to be created even from very noisy projection data. In addition, this approach allows for simple penalty matrices to be constructed, enables penalty coefficient to be calculated in a straightforward manner, and results in an easily computed, closed-form solution for the regularizing filters. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 350–364, 2008 [ABSTRACT FROM AUTHOR]

In this work, a hybrid continuous genetic algorithm (HCGA) based methodology has been developed for optimization of number of projections for parallel-ray transmission tomography. The HCGA calculations with filtered back-projection (FBP) utilize 8 bits for both head and lung phantoms. The effect of selection operator through proportionate, truncation, and tournament schemes has been analyzed along with the introduction of a mixed-selection scheme. Image quality has been measured using root-mean-squared error, Euclidean error and peak signal-to-noise ratios. The sensitivity of reconstructed image quality on various mutation operators, namely standard, gradient-, and offset-based schemes, has been analyzed along with the effect of number of projections. The number of projections has resulted in maximization of image quality while minimizing the radiation hazard involved. The results of HCGA have been compared with FBP as a deterministic technique and simulated annealing (SA) as a stochastic technique for IRT approximation. For the 8 × 8 head and lung phantoms, HCGA, SA, FBP, have resulted PSNR values correspondingly as 40.47, 33.92, 8.28 and 26.38, 20.36, 12.98 dB. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 10–21, 2007 [ABSTRACT FROM AUTHOR]

Abstract: Reconstruction of two-dimensional images by filtered back-projection (FBP) and by the maximum entropy method (MEM) was compared for spectral-spatial EPR images with differing signal-to-noise ratios. Experimental projections were recorded using direct-detected rapid scans in the presence of a series of magnetic field gradients. The slow-scan absorption lineshapes were calculated by Fourier deconvolution. A Hamming filter was used in conjunction with FBP, but not for MEM. Imperfections in real experimental data, as well as random noise, contribute to discrepancies between the reconstructed image and experimental projections, which may make it impossible to achieve the customary MEM criterion for convergence. The Cambridge MEM algorithm, with allowance for imperfections in experimental data, produced images with more linear intensity scales and more accurate linewidths for weak signals than was obtained with another MEM method. The more effective elimination of noise in baseline regions by MEM made it possible to detect weak trityl 13C trityl hyperfine lines that could not be distinguished from noise in images reconstructed by FBP. Another advantage of MEM is that projections do not need to be equally spaced. FBP has the advantages that computational time is less, the amplitude scale is linear, and there is less noise superimposed on peaks in images. It is useful to reconstruct images by both methods and compare results. Our observations indicate that FBP works well when the number of projections is large enough that the star effect is negligible. When there is a smaller number of projections, projections are unequally spaced, and/or signal-to-noise is lower MEM is advantageous. [Copyright &y& Elsevier]

The Compton scattering camera can provide higher detection efficiency since the use of a mechanical collimator is not required. Several image reconstruction algorithms for Compton scattering cameras, such as maximum likelihood method and ART, can provide good imaging performance but are indirect and computational intensive. A direct reconstruction algorithm, such as filtered back-projection, is preferable if computational time is critical. Parra proposed an analytical inversion algorithm from cone-beam projections for Compton scattering cameras with a complete data set. In reality, a Compton camera is always limited by its configuration and can only provide an incomplete data set with a finite range of scattering angles. In this paper, we investigate a filtered back-projection algorithm applied to single 3-dimensional position sensitive CdZnTe detectors. [ABSTRACT FROM AUTHOR]