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The purpose of this study was to compare dose and image quality of wireless detectors for digital chest radiography. Entrance dose at both the detector (EDD) and phantom (EPD) and image quality were measured for wireless detectors of seven different vendors. Both the local clinical protocols and a reference protocol were evaluated. In addition, effective dose was calculated. Main differences in clinical protocols involved tube voltage, tube current, the use of a small or large focus and the use of additional filtration. For the clinical protocols, large differences in EDD (1.4-11.8 μGy), EPD (13.9-80.2 μGy) and image quality (IQFinv: 1.4-4.1) were observed. Effective dose was <0.04 mSv for all protocols. Large differences in performance were observed between the seven different systems. Although effective dose is low, further improvement of imaging technology and acquisition protocols is warranted for optimisation of digital chest radiography. [ABSTRACT FROM AUTHOR]

The treatment of brain arteriovenous malformations (AVMs) can be performed as a minimally invasive X-ray-guided procedure using a microcatheter for navigation to reach the target site. The performance of the interventional vascular surgery devices used for AVM was compared in four hospitals. The relation between image quality and the entrance surface air kerma (ESAK) was assessed for the default protocols for digital subtraction angiography (DSA) and fluoroscopy. A custom phantom, built with PMMAand aluminium plates was used to mimic the attenuation properties of the patient head. Image quality was assessed using low-contrast objects and catheters embedded in two phantoms. Differences were found in the ESAK values, especially for the fluoroscopy, whereas for DSA, the ESAKvalues were similar. The differences in image quality can be related to acquisition parameters, such as kVand filtration, and post-processing. The proposed method can be used to optimise the existing AVM protocols. [ABSTRACT FROM AUTHOR]

Novel iterative image reconstruction methods can help reduce the required radiation dose in x-ray diagnostics such as computed tomography (CT), while maintaining sufficient image quality. Since some of the established image quality measures are not appropriate for reliably judging the quality of images derived by iterative methods, alternative approaches such as task-specific quality assessment would be highly desirable for acceptance or constancy testing. Task-based image quality methods are also closer to tasks performed by the radiologists, such as lesion detection. However, this approach is usually hampered by a huge workload, since hundreds of images are usually required for its application. It is demonstrated that the proposed approach works reliably on the basis of significantly fewer images, and that it correlates well with results obtained from human observers.

Purpose: In mammography, images are processed prior to display. Model observers (MO) are candidates to objectively evaluate processed images if they can predict human observer performance for detail detection. The aim of this study was to investigate if the channelized Hotelling observer (CHO) can be configured to predict human observer performance in mammography like images., Methods: The performance correlation between human observers and CHO has been evaluated using different channel-sets and by including aspects of the human visual system (HVS). The correlation was investigated for the detection of disk-shaped details in simulated white noise (WN) and clustered lumpy backgrounds (CLB) images, representing respectively quantum noise limited and mammography like images. The images were scored by the MO and five human observers in 2-alternative forced choice experiments., Results: For WN images the most useful formulation of the CHO to predict human observer performance was obtained using three difference of Gaussian channels without adding HVS aspects (R LR 2 =0.62). For CLB images the most useful formulation was the partial least square channel-set without adding HVS aspects (R LR 2 =0.71). The correlation was affected by detail size and background., Conclusions: This study has shown that the CHO can predict human observer performance. Due to object size and background dependency it is important that the range of object sizes and allowed variability in background are specified and validated carefully before the CHO can be implemented for objective image quality assessment., (Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Purpose: In mammography, images are processed prior to display. Current methodologies based on physical image quality measurements are however not designed for the evaluation of processed images. Model observers (MO) might be suitable for this evaluation. The aim of this study was to investigate whether the non-pre-whitening (NPW) MO can be used to predict human observer performance in mammography-like images by including different aspects of the human visual system (HVS)., Methods: The correlation between human and NPW MO performance has been investigated for the detection of disk shaped objects in simulated white noise (WN) and clustered lumpy backgrounds (CLB), representing quantum noise limited and mammography-like images respectively. The images were scored by the MO and five human observers in a 2-alternative forced choice experiment., Results: For WN images it was found that the log likelihood ratio (R LR 2 ), which expresses the goodness of fit, was highest (0.44) for the NPW MO without addition of HVS aspects. For CLB the R LR 2 improved from 0.46 to 0.65 with addition of HVS aspects. The correlation was affected by object size and background., Conclusions: This study shows that by including aspects of the HVS, the performance of the NPW MO can be improved to better predict human observer performance. This demonstrates that the NPW MO has potential for image quality assessment. However, due to the dependencies found in the correlation, the NPW MO can only be used for image quality assessment for a limited range of object sizes and background variability., (Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

The treatment of brain arteriovenous malformations (AVMs) can be performed as a minimally invasive X-ray-guided procedure using a microcatheter for navigation to reach the target site. The performance of the interventional vascular surgery devices used for AVM was compared in four hospitals. The relation between image quality and the entrance surface air kerma (ESAK) was assessed for the default protocols for digital subtraction angiography (DSA) and fluoroscopy. A custom phantom, built with PMMA and aluminium plates was used to mimic the attenuation properties of the patient head. Image quality was assessed using low-contrast objects and catheters embedded in two phantoms. Differences were found in the ESAK values, especially for the fluoroscopy, whereas for DSA, the ESAK values were similar. The differences in image quality can be related to acquisition parameters, such as kV and filtration, and post-processing. The proposed method can be used to optimise the existing AVM protocols., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Evaluation of image quality (IQ) in Computed Tomography (CT) is important to ensure that diagnostic questions are correctly answered, whilst keeping radiation dose to the patient as low as is reasonably possible. The assessment of individual aspects of IQ is already a key component of routine quality control of medical x-ray devices. These values together with standard dose indicators can be used to give rise to 'figures of merit' (FOM) to characterise the dose efficiency of the CT scanners operating in certain modes. The demand for clinically relevant IQ characterisation has naturally increased with the development of CT technology (detectors efficiency, image reconstruction and processing), resulting in the adaptation and evolution of assessment methods. The purpose of this review is to present the spectrum of various methods that have been used to characterise image quality in CT: from objective measurements of physical parameters to clinically task-based approaches (i.e. model observer (MO) approach) including pure human observer approach. When combined together with a dose indicator, a generalised dose efficiency index can be explored in a framework of system and patient dose optimisation. We will focus on the IQ methodologies that are required for dealing with standard reconstruction, but also for iterative reconstruction algorithms. With this concept the previously used FOM will be presented with a proposal to update them in order to make them relevant and up to date with technological progress. The MO that objectively assesses IQ for clinically relevant tasks represents the most promising method in terms of radiologist sensitivity performance and therefore of most relevance in the clinical environment., (Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

This paper studies low contrast detectability (LCD) performance of two model observers in CT phantom images acquired at different kVp levels and compares the results with humans in a 2-alternative forced choice experiment (2-AFC). Images of the Catphan phantom with objects of different contrasts (0.5 and 1%) and diameters (2-15 mm) were acquired in an Aquilion ONE 320-detector row CT (Toshiba Medical Systems, Tokyo, Japan), in two experiments, selecting (80-100-120-135 kV) with fixed mAs and varying the mAs to keep the dose constant, respectively. Four human observers evaluated the objects visibility obtaining a proportion correct (PC) for each case. LCD was also analyzed with two model observers (non-prewhitening matched filter with an eye filter, NPWE, and channelized Hotelling observer with Gabor channels, CHO). Object contrast was affected by kV, with differences up to 17% between the lowest and highest kV. Both models overestimated human performance and were corrected by efficiency and internal noise factors. The NPWE model reproduced better the human PC values trends showing Pearson's correlation coefficients ≥0.976 (0.954-0.987, 95% CI) for both experiments, whereas for CHO they were ≥0.706 (0.493-0.839). Bland-Altman plots showed better agreement between NPWE and humans being the average difference Δ and the range of the differences Δ±2σ (σ, standard deviation) of Δ=-0.3%, Δ±2σ = [-4.0%,4.5%]. For CHO, Δ=-1.2%, Δ± 2σ= [-10.7%,8.3%]. The NPWE model can be a useful tool to predict human performance in CT low contrast detection tasks in a standard phantom and be potentially used in protocol optimization based on kV selection., (Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Slabs of polymethyl methacrylate (PMMA) or a combination of PMMA and polyethylene (PE) slabs are used to simulate standard model breasts for the evaluation of the average glandular dose (AGD) in digital mammography (DM) and digital breast tomosynthesis (DBT). These phantoms are optimized for the energy spectra used in DM and DBT, which normally have a lower average energy than used in contrast enhanced digital mammography (CEDM). In this study we have investigated whether these phantoms can be used for the evaluation of AGD with the high energy x-ray spectra used in CEDM. For this purpose the calculated values of the incident air kerma for dosimetry phantoms and standard model breasts were compared in a zero degree projection with the use of an anti scatter grid. It was found that the difference in incident air kerma compared to standard model breasts ranges between -10% to +4% for PMMA slabs and between 6% and 15% for PMMA-PE slabs. The estimated systematic error in the measured AGD for both sets of phantoms were considered to be sufficiently small for the evaluation of AGD in quality control procedures for CEDM. However, the systematic error can be substantial if AGD values from different phantoms are compared.

Background and Purpose: Postoperative imaging of cochlear implants (CIs) needs to provide detailed information on localization of the electrode array. We evaluated visualization of a HiFocus1J array and accuracy of measurements of electrode positions for acquisitions with 64-section CT scanners of 4 major CT systems (Toshiba Aquilion-64, Philips Brilliance-64, GE LightSpeed-64, and Siemens Sensation-64)., Materials and Methods: An implanted human cadaver temporal bone, a polymethylmethacrylate (PMMA) phantom containing a CI, and a point spread function (PSF) phantom were scanned. In the human cadaver temporal bone, the visibility of cochlear structures and electrode array were assessed by using a visual analog scale (VAS). Statistical analysis was performed with a paired 2-tailed Student t test with significant level set to .008 after Bonferroni correction. Distinction of individual electrode contacts was quantitatively evaluated. Quantitative assessment of electrode contact positions was achieved with the PMMA phantom by measurement of the displacement. In addition, PSF was measured to evaluate spatial resolution performance of the CT scanners., Results: VAS scores were significantly lower for Brilliance-64 and LightSpeed-64 compared with Aquilion-64 and Sensation-64. Displacement of electrode contacts ranged from 0.05 to 0.14 mm on Aquilion-64, 0.07 to 0.16 mm on Brilliance-64, 0.07 to 0.61 mm on LightSpeed-64, and 0.03 to 0.13 mm on Sensation-64. PSF measurements show an in-plane and longitudinal resolution varying from 0.48 to 0.68 mm and 0.70 to 0.98 mm, respectively, over the 4 scanners., Conclusion: According to PSF results, electrode contacts of the studied CI can be visualized separately on all of the studied scanners unless curvature causes intercontact spacing narrowing. Assessment of visibility of CI and electrode contact positions, however, varies between scanners.