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• Dose reduction attributable only to a tin filter was evaluated with FBP CT images. • The estimated dose reduction rate for low-dose chest CT was 22–25%. • This reduction rate was markedly lower than those (about 80%) previously reported. To reevaluate a tin filter's (TF) dose reduction effect in computed tomography (CT) using a combination of an anthropomorphic chest phantom and a rod-shaped phantom. A third-generation dual-source CT system equipped with a built-in TF was employed. A chest phantom was scanned under low-dose conditions of 0.2 to 1.0 mGy with the TF at 100 kV (TF100kV) and without it at 100 kV and 120 kV (NF100kV and NF120kV). To eliminate effects other than that of the TF, only filtered back projection (FBP) was used for image reconstruction. On the images of the rod phantom placed inside the lung field, the CT number and the spatial resolution using the modulation transfer function (MTF) were measured. Using these indices plus the noise power spectrum (NPS) that was also measured, the detectability index based on the non-prewhitening model observer (d ' NPW) was calculated. The CT numbers and MTFs were almost identical across the three conditions. The area under the NPS curve was decreased by 13–17% with the TF compared with non-TF conditions. NPS increases at low frequencies of < 0.06 mm−1 observed in NF120kV and NF100kV were eliminated by TF100kV. The potential dose reduction by the TF, estimated using the d ' NPW values, turned out to be 22 to 25%. Based on the analysis of the FBP images of a chest phantom, the dose reduction attributable only to the TF was estimated at 22–25%, notably lower than those reported in previous studies. [ABSTRACT FROM AUTHOR]

• DRLs can help the imaging related to treatment planning in radiation oncology. • The intention is to propose RPRLs and compare these values with published data. • Results show variations in CT planning which call for optimization of procedures. To present results of the first national survey on reference levels of CT imaging performed for the treatment planning purposes in radiation oncology in Croatia. Data for CT protocols of five anatomical regions including head, head and neck, pelvis, breast, and thorax were collected at eight radiation oncology departments in Croatia. Data included volume CT dose index (CTDI vol), dose-length product (DLP), scan length and set of acquisition and reconstruction parameters. Data on a total of 600 patients were collected. Median values of scan length, DLP and CTDI vol were calculated for each acquisition protocol. Third quartiles of the median CTDI vol and DLP values were proposed as the national radiotherapy planning reference levels (RPRL). The largest CoV were assessed for RT Breast (63.8% for CTDI vol), RT Thorax (79.7% for DLP) and RT H&N (21.2% for scan length). RT Head had the lowest CoV for CTDI vol (1,9%) and DLP (17,2%), while RT Breast had the lowest coefficient of variation for scan length (12.8%). Proposed national RPRLs are: for RT Head CTDI vol16cm = 62 mGy and DLP 16cm = 1738 mGy.cm ; for RT H&N CTDI vol16cm = 35 mGy and DLP 16cm = 1444 mGy.cm ; for RT Breast CTDI vol32cm = 16 mGy and DLP 32cm = 731 mGy.cm ; for RT Thorax CTDI vol32cm = 17 mGy and DLP 32cm = 865 mGy.cm ; for RT Pelvis CTDI vol32cm = 20 mGy and DLP 32cm = 1133 mGy.cm. Results of this study show variations in CT imaging for treatment planning practice at the national level which call for optimization of procedures. [ABSTRACT FROM AUTHOR]

• Mis-centering and over-scanning on chest CT are frequent in patients with COVID-19. • Patients with arms by side are more likely to be mis-centered and over-scanned. • Mis-centering and over-scanning are associated with higher radiation doses. Optimization of CT scan practices can help achieve and maintain optimal radiation protection. The aim was to assess centering, scan length, and positioning of patients undergoing chest CT for suspected or known COVID-19 pneumonia and to investigate their effect on associated radiation doses. With respective approvals from institutional review boards, we compiled CT imaging and radiation dose data from four hospitals belonging to four countries (Brazil, Iran, Italy, and USA) on 400 adult patients who underwent chest CT for suspected or known COVID-19 pneumonia between April 2020 and August 2020. We recorded patient demographics and volume CT dose index (CTDI vol) and dose length product (DLP). From thin-section CT images of each patient, we estimated the scan length and recorded the first and last vertebral bodies at the scan start and end locations. Patient mis-centering and arm position were recorded. Data were analyzed with analysis of variance (ANOVA). The extent and frequency of patient mis-centering did not differ across the four CT facilities (>0.09). The frequency of patients scanned with arms by their side (11–40% relative to those with arms up) had greater mis-centering and higher CTDI vol and DLP at 2/4 facilities (p = 0.027–0.05). Despite lack of variations in effective diameters (p = 0.14), there were significantly variations in scan lengths, CTDI vol and DLP across the four facilities (p < 0.001). Mis-centering, over-scanning, and arms by the side are frequent issues with use of chest CT in COVID-19 pneumonia and are associated with higher radiation doses. [ABSTRACT FROM AUTHOR]

To investigate within phantoms the minimum CT dose allowed for accurate attenuation correction of PET data and to quantify the effective dose reduction when a CT for this purpose is incorporated in the clinical setting. The NEMA image quality phantom was scanned within a large parallelepiped container. Twenty-one different CT images were acquired to correct attenuation of PET raw data. Radiation dose and image quality were evaluated. Thirty-one patients with proven multiple myeloma who underwent a dual tracer PET/CT scan were retrospectively reviewed. 18F-fluorodeoxyglucose PET/CT included a diagnostic whole-body low dose CT (WBLDCT: 120 kV-80mAs) and 11C-Methionine PET/CT included a whole-body ultra-low dose CT (WBULDCT) for attenuation correction (100 kV-40mAs). Effective dose and image quality were analysed. Only the two lowest radiation dose conditions (80 kV-20mAs and 80 kV-10mAs) produced artifacts in CT images that degraded corrected PET images. For all the other conditions (CTDI vol ≥ 0.43 mGy), PET contrast recovery coefficients varied less than ± 1.2%. Patients received a median dose of 6.4 mSv from diagnostic CT and 2.1 mSv from the attenuation correction CT. Despite the worse image quality of this CT, 94.8% of bone lesions were identifiable. Phantom experiments showed that an ultra-low dose CT can be implemented in PET/CT procedures without any noticeable degradation in the attenuation corrected PET scan. The replacement of the standard CT for this ultra-low dose CT in clinical PET/CT scans involves a significant radiation dose reduction. [ABSTRACT FROM AUTHOR]

• Spatial resolution in VMI images is not affected by iterative reconstruction. • Image contrast in VMI images is improved with radiation dose. • Frequency distribution of noise is not affected by iterative reconstruction. • Contrast to noise ratio is improved with iterative reconstruction. • Appropriate leverage of exposure factors aid to optimize VMI image quality. To assess the quality of images obtained on a dual energy computed tomography (CT) scanner. Image quality was assessed on a 64 detector-row fast kVp-switching dual energy CT scanner (Revolution GSI, GE Medical Systems). The Catphan phantom and a low contrast resolution phantom were employed. Acquisitions were performed at eight different radiation dose levels that ranged from 9 mGy to 32 mGy. Virtual monochromatic spectral images (VMI) were reconstructed in the 40–140 keV range using all available kernels and iterative reconstruction (IR) at four different blending levels. Modulation Transfer Function (MTF) curves, image noise, image contrast, noise power spectrum and contrast to noise ratio were assessed. In-plane spatial resolution at the 10% of the MTF curve was 0.60 mm−1. In-plane spatial resolution was not modified with VMI energy and IR blending level. Image noise was reduced from 16.6 at 9 mGy to 6.7 at 32 mGy, while peak frequency remained within 0.14 ± 0.01 mm−1. Image noise was reduced from 14.3 at IR 10% to 11.5 at IR 50% at a constant peak frequency. The lowest image noise and maximum peak frequency were recorded at 70 keV. Our results have shown how objective image quality is varied when different levels of radiation dose and different settings in IR are applied. These results provide CT operators an in depth understanding of the imaging performance characteristics in dual energy CT. [ABSTRACT FROM AUTHOR]

• Deep learning-based reconstruction (DLR) allows noise reduction. • DLR is an effective technique for the ultra-high-resolution computed tomography. • DLR could improve the image noise caused by high definition detector. This study aimed to assess the noise characteristics of ultra-high-resolution computed tomography (UHRCT) with deep learning-based reconstruction (DLR). Two different diameters of water phantom were scanned with three different resolution acquisition modes. Images were reconstructed by filtered back projection (FBP), hybrid iterative reconstruction (hybrid-IR), and DLR. Image noise analysis was performed with noise magnitude, peak frequency (f p) of the noise power spectrum (NPS), and the square root of the area under the curve (√AUC NPS) for the NPS curve. The noise magnitude was up to 3.30 times higher for the FBP acquired in SHR mode than that for the NR mode. The f p values of the FBP were 0.20–0.21, 0.34–0.36, and 0.34–0.37 cycles/mm for normal resolution (NR), high resolution (HR), and super high resolution (SHR) mode, respectively. The f p of hybrid-IR was 0.16–0.19, 0.21–0.26, and 0.23–0.26 cycles/mm for NR, HR, and SHR mode, respectively. The f p of DLR was 0.21–0.32 and 0.22–0.33 cycles/mm for HR and SHR mode, respectively. √AUC NPS showed that the highest value in FBP images of the SHR mode was up to 1.89 times that of the NR mode. DLR in the HR and SHR modes showed high noise reduction while suppressing f p shift with respect to FBP. The new DLR algorithm could be a solution to the noise increase due to the high-definition detector elements and the small reconstruction matrix element size. [ABSTRACT FROM AUTHOR]

• Overview about recent advances in X-ray breast imaging in two- and three-dimensions. • Multimodal grating-based phase-contrast mammography improves soft-tissue contrast. • Absorption-contrast breast computed tomography towards clinical implementation. • Developing propagation- and grating-based phase-contrast breast computed tomography. Breast cancer is a globally widespread disease whose detection has already been significantly improved by the introduction of screening programs. Nevertheless, mammography suffers from low soft tissue contrast and the superposition of diagnostically relevant anatomical structures as well as from low values for sensitivity and specificity especially for dense breast tissue. In recent years, two techniques for X-ray breast imaging have been developed that bring advances for the early detection of breast cancer. Grating-based phase-contrast mammography is a new imaging technique that is able to provide three image modalities simultaneously (absorption-contrast, phase-contrast and dark-field signal). Thus, an enhanced detection and delineation of cancerous structures in the phase-contrast image and an improved visualization and characterization of microcalcifications in the dark-field image is possible. Furthermore, latest studies about this approach show that dose-compatible imaging with polychromatic X-ray sources is feasible. In order to additionally overcome the limitations of projection-based imaging, efforts were also made towards the development of breast computed tomography (BCT), which recently led to the first clinical installation of an absorption-based BCT system. Further research combining the benefits of both imaging technologies is currently in progress. This review article summarizes the latest advances in phase-contrast imaging for the female breast (projection-based and three-dimensional view) with special focus on possible clinical implementations in the future. [ABSTRACT FROM AUTHOR]

• CT contributes to the majority of radiation dose associated with diagnostic imaging procedures. • Substantial variations in scan protocols and radiation doses necessitate monitoring of CT doses. • Commercial radiation dose monitoring software capture information on scan factors and dose indices. • Users must understand the strengths, applications and limitations of dose monitoring software. In the last few years there has been an increasing interest on radiation dose to patients undergoing various diagnostic or therapeutic procedures with the use of ionizing radiation. Especially for CT examinations and interventional procedures, where it is known that patient doses are much higher than conventional radiography, new norms have been published that require to have appropriate radiation dose indices registered in the patient medical record. Because of these demands, dose monitoring has been recommended and adopted into many clinical practices as a routine procedure for every patient and every examination. Dedicated dose monitoring systems (DMS) that facilitate data collection and processing, statistical comparisons, reporting and management of radiation dose related information have been devised and are being used worldwide. In this review paper, a brief flashback to the reasons that necessitated dose monitoring in radiology will be first presented. Furthermore, since the focus of this manuscript is on CT, the CT dosimetry principles and metrics will be summarized. The limitations of these metrics will be also discussed, so that DMS users are aware of the semantics of the parameters shown in the DMS reports. The operation of DMS systems will be outlined to make users aware of functions, limitations, and available options of DMS systems. Furthermore, the usefulness of DMS systems as an optimization tool will be presented and discussed. Finally, information about the DMS solutions available in the market and relevant links will be presented. [ABSTRACT FROM AUTHOR]

• CT PNS has become a well-established preoperative diagnostic tool providing a mandatory 'roadmap' for FESS. • The phantom study was performed first, in order to determine protocols to be investigated in the patient study. • A standard CT PNS protocol can be replaced with ultra-low dose protocol. To assess image quality and radiation dose associated with ultra-low dose CT protocol for patients with benign paranasal sinus diseases undergoing functional endoscopic surgery (FESS). We scanned the head portion of Alderson RANDO phantom on a second generation, dual-source, multidetector-row CT scanner (Siemens Definition Flash) using standard-dose and five low-dose protocols. Two radiologists assessed the image quality for each protocol to determine best ultra-low-dose protocols for imaging patients with benign paranasal sinus diseases undergoing FESS. The ultra-low-dose CT protocols were then used for scanning. Thereafter, 40 adult patients (age range 18–54 years, M:F 23:17) were scanned with the four low dose scanning protocols (10 patients per protocol). On both transverse and coronal reformatted CT images, two radiologists assessed visibility of key anatomic landmarks for FESS on a 2-point scale (1 = clear and complete visualization; 2 = suboptimal visualization). Data were analyzed with descriptive statistics and Cohen's kappa coefficient for interobserver agreement. In phantom study, the lowest dose scan protocol (CTDI vol 2.1 mGy, 70 kV, 75 mAs) was unacceptable due to poor image quality. For patient studies, both radiologists gave acceptable image quality scores for ultra-low-dose scan protocol with axial scan mode, automatic tube potential selection and tube current modulation (CTDI vol 2.2 mGy; DLP 22.9 mGy.cm) with up to 60% lower dose compared to prior standard-dose CT (CTDI vol 5.3 mGy; DLP 73.5 mGy.cm). Ultra-low-dose CT protocol provides sufficient image quality for scanning patients undergoing functional endoscopic surgery for benign paranasal sinus diseases. [ABSTRACT FROM AUTHOR]

• Estimates were made of number of patients likely receiving cumulative effective dose ≥100 mSv in 5-years from CT exams. • It results in about 2.5 million patients in 35 OECD countries. • Countries were classified into Low: 0 to <1, Medium: 1 to <2 and High: ≥2 patients with CED ≥ 100 mSv/1000 population. • There are 2 countries in Low, 24 in medium and 9 in high number group. • Stake holders in patient radiation safety should attend to the issue of high doses to such large number of patients. To estimate the number of patients in OECD (Organization for Economic Co-operation and Development) countries who receive a cumulative effective dose (CED) ≥ 100 mSv from recurrent computed tomography (CT) exams. Taking into account recently published data on the number of CTs per patient and the fraction of patients with CED ≥ 100 mSv as well as country-specific data for the number of CT exams/1,000 population from OECD publication, this paper makes estimations for 35 OECD countries. The estimated total number of patients with CED ≥ 100 mSv for all 35 OECD countries combined in a 5-year period is around 2.5 million (2,493,685) in a population of 1.2 billion (1,176,641,900), i.e., 0.21% of the population. Expressed per 1,000 population, the range is from 0.51 for Finland to 2.94 for the US, a nearly six-fold difference. Countries with more than 2 patients with CED ≥ 100 mSv in a 5-yr period per 1,000 population are: Belgium, France, Iceland, Japan, Korea, Luxembourg, Portugal, Turkey, and US. The first estimates of the number of patients likely receiving CED ≥ 100 mSv through recurrent CT exams in 35 OECD countries indicate that 2.5 million patients reach this level in a 5-year period. There is an urgent need for various stakeholders including medical physicists, referring physicians, health policy makers, manufacturers of CT equipment and epidemiologists to attend to the issue in the interest of patient radiation safety. [ABSTRACT FROM AUTHOR]

• Deep learning image reconstruction enhances CT image quality and saves radiation dose. • Deep learning image reconstruction reduces noise while maintaining noise texture. • Deep learning image reconstruction maintains low- and high-contrast spatial resolution. • Deep learning image reconstruction improves low- and high-contrast detectability. • Deep learning image reconstruction outperforms partial model-based iterative reconstruction. We aimed to thoroughly characterize image quality of a novel deep learning image reconstruction (DLIR), and investigate its potential for dose reduction in abdominal CT in comparison with filtered back-projection (FBP) and a partial model-based iterative reconstruction (ASiR-V). We scanned a phantom at three dose levels: regular (7 mGy), low (3 mGy) and ultra-low (1 mGy). Images were reconstructed using DLIR (low, medium and high levels) and ASiR-V (0% = FBP, 50% and 100%). Noise and contrast-dependent spatial resolution were characterized by computing noise power spectra and target transfer functions, respectively. Detectability indexes of simulated acute appendicitis or colonic diverticulitis (low contrast), and calcium-containing urinary stones (high contrast) (|ΔHU| = 50 and 500, respectively) were calculated using the nonprewhitening with eye filter model observer. At all dose levels, increasing DLIR and ASiR-V levels both markedly decreased noise magnitude compared with FBP, with DLIR low and medium maintaining noise texture overall. For both low- and high-contrast spatial resolution, DLIR not only maintained, but even slightly enhanced spatial resolution in comparison with FBP across all dose levels. Conversely, increasing ASiR-V impaired low-contrast spatial resolution compared with FBP. Overall, DLIR outperformed ASiR-V in all simulated clinical scenarios. For both low- and high-contrast diagnostic tasks, increasing DLIR substantially enhanced detectability at any dose and contrast levels for any simulated lesion size. Unlike ASiR-V, DLIR substantially reduces noise while maintaining noise texture and slightly enhancing spatial resolution overall. DLIR outperforms ASiR-V by enabling higher detectability of both low- and high-contrast simulated abdominal lesions across all investigated dose levels. [ABSTRACT FROM AUTHOR]

• Measurement of %Stenosis in single energy cardiac CT is considerably overestimated. • Dual energy cardiac CT provides images that are less affected by cardiac motion. • The detail reconstruction kernel provides a more accurate assessment of %Stenosis. • Effective dose in dual energy cardiac CT is lower than in routine gated acquisition. To investigate the effects of heart beat rate (bpm), vessel angulation and acquisition protocol on the estimation accuracy of calcified stenosis using a dual-energy CT scanner. A thorax semi-anthropomorphic phantom coupled with a motion simulator and a vessel phantom representing a 50% coronary artery calcified stenosis, were used. Electrocardiograph (ECG)-synchronized acquisitions were performed at different bpms. Acquisitions were performed using A, B, and C single-energy and D dual-energy protocols. Protocol A was prospective ECG-triggered axial and protocols B and C were retrospective single- and two-segment reconstruction ECG-gated helical acquisitions. Protocol D was prospective ECG-triggered axial acquisition. The vessel phantom was placed at two angulations relative to z-axis. Images were reconstructed using all available kernels with iterative reconstruction. Stenosis-percentage was estimated using the CT vendor's vessel analysis tool. Effective dose (ED) was estimated using the dose-length product method. In protocols A, B, and C, measured Stenosis-percentage increased with bpm. Stenosis-percentage estimate ranged from 56.8% at 40 bpm to 62.6% at 100 bpm. In protocol D, Stenosis-percentage ranged from 59.3% at 40 bpm to 54.8% at 80 bpm. Stenosis-percentage was overestimated on respect to the nominal value in most kernels. The detail kernel exhibited the highest accuracy. Stenosis-percentage was not affected by the vessel angulation. ED for protocols A, B, C, and D was 2.4 mSv, 5.1 mSv, 5.5 mSv, and 2.8 mSv, respectively. Use of the dual-energy cardiac CT examination protocol along with the detail kernel is recommended for a more accurate assessment of Stenosis-percentage. [ABSTRACT FROM AUTHOR]

• Digital cholangioscopy (DA) with ERCP is associated with much shorter fluoro time. • DA with ERCP is associated with substantially lower radiation dose. • DA with ERCP is a radiation-sparing alternative to ERCP for complex choledocolithiasis. Endoscopic Retrograde Cholangio-Pancreatography (ERCP) is an well-established endoscopic procedure for the management of biliary diseases. The use of fluoroscopy during ERCP has often raised concerns regarding potential risks from radiation exposure, particularly in complex cases. We investigated whether a new digital single-operator cholangioscopy (D-SOC) system, used adjunctively to ERCP, actually reduces patient radiation exposure. We retrospectively analyzed a prospective database (April 2016 to October 2018) including consecutive patients who underwent successful management of difficult-to-treat biliary stones or indeterminate biliary strictures by using either conventional ERCP (ERCP cohort) or ERCP in conjunction with D-SOC (ERCP/D-SOC cohort). The overall patient radiation exposure outcomes were compared in terms of Kerma Area Product (KAP), Fluoroscopy time (T) and the total number of films (F). Overall, 47 patients (mean 71.8 years, 59.6% males) were included (ERCP cohort = 29, ERCP/D-SOC cohort = 18), referred either for difficult bile duct stones (n = 36) or indeterminate biliary strictures (n = 11). The median KAP, T and F in the ERCP/D-SOC cohort were 12.3 Gycm2, 3.7 min and 4 films respectively, compared with 52.1 Gycm2, 8.4 min, and 5 films respectively in the ERCP cohort. Statistically significant differences (P = 0.0001) were found for KAP and T. Adjunct use of a digital cholangioscopy platform appears to significantly reduce radiation exposure in patients undergoing ERCP for the management of difficult bile stones or indeterminate biliary strictures. [ABSTRACT FROM AUTHOR]

Highlights • CXR for larger sized patients has lower IQ and higher dose than standard size patients. • Similar imaging protocols are typically used for standard and larger size patients. • Routine CXR protocols may require further optimisation for larger size patients. Abstract Purpose To evaluate the influence of being overweight on image quality (IQ), radiation dose and acquisition parameters when undertaking adult chest X-ray (CXR) examinations using routine acquisition protocols. Methods The Lungman chest phantom, with and without chest plates, was used to simulate the chest region for larger size and average adult patients, respectively. Radiographic acquisitions were conducted using 17 X-ray machines located in eight hospitals using their routine clinical protocols. IQ was assessed using relative visual grading analysis (VGA) and 2 alternative forced choice (2AFC) by six observers. Incident air kerma (IAK) was measured using a solid-state dosimeter. Results IQ mean (range) scores between the hospitals were 16.2 (12.0–21.3) with a 56.0% difference and 20.9 (14.1–23.6) with a 50.2% difference for the standard and larger size phantoms, respectively. IAK mean (range) scores 63 µGy (19–136 µGy) with a 150% difference and 159 µGy (27–384 µGy) with a 173% difference for the standard and larger size phantoms, respectively. The chest plates had a significant negative impact on IQ (P = 0.001) and lead to an increased in IAK by approximately 50%. Conclusion Visual measures of IQ and IAK showed large differences between hospitals for standard and larger phantom sizes; differences within the hospitals was lower. Overall, Lungman with chest plates was found to degrade IQ and increase radiation dose by a factor of two. Further optimisation is required especially for the larger sized patient's imaging protocols for all eight hospitals. [ABSTRACT FROM AUTHOR]

Purpose To assess the underestimation of radiation dose to the thyroid of children undergoing contrast enhanced CT if contrast medium uptake is not taken into account. Methods 161 pediatric head, head & neck and chest CT examinations were retrospectively studied to identify those involving pre- and post-contrast imaging and thyroid inclusion in imaged volume. CT density of thyroid tissue in HU was measured in non-enhanced (NECT) and corresponding contrast-enhanced CT (CECT) images. Resulting CT number increase (ΔHU) was recorded for each patient and corresponded to a % w/w iodine concentration. The relation of %w/w iodine concentration to %dose increase induced by iodinated contrast uptake was derived by Monte Carlo simulation experiments. Results The thyroid gland was visible in 11 chest and 3 neck CT examinations involving both pre- and post-contrast imaging. The %w/w concentration of iodine in the thyroid tissue at the time of CECT acquisition was found to be 0.13%–0.58% w/w (mean = 0.26%). The %increase of dose to thyroid tissue was found to be linearly correlated to%w/w iodine uptake. The increase in radiation dose to thyroid due to contrast uptake ranged from 12% to 44%, with a mean value of 23%. Conclusions The radiation dose to the pediatric thyroid from CECT exposure may be underestimated by up to 44% if contrast medium uptake is not taken into account. Meticulous demarcation of imaged volume in pediatric chest CT examinations is imperative to avoid unnecessary direct exposure of thyroid, especially in CT examinations following intravenous administration of contrast medium. [ABSTRACT FROM AUTHOR]

This study compared the detectability of simulated tumors using a high-energy X-ray inline phase sensitive digital breast tomosynthesis (DBT) prototype and a commercial attenuation-based DBT system. Each system imaged a 5-cm thick modular breast phantom with 50–50 adipose-glandular percentage density containing contrast-detail (CD) test objects to simulate different tumor sizes. A commercial DBT system acquired 15 projection views over 15 degrees (15d-15p) was used to acquire the attenuation-based projection views and to reconstruct the conventional DBT slices. Attenuation-based projection views were acquired at 32 kV, 46 mAs with a mean glandular dose (D g ) of 1.6 mGy. For acquiring phase sensitive projection views, the prototype utilized two acquisition geometries: 11 projection views were acquired over 15 degrees (15d-11p), and 17 projection views were acquired over 16 degrees (16d-17p) at 120 kV, 5.27 mAs with 1.51 mGy under the magnification (M) of 2. A phase retrieval algorithm based on the phase-attenuation duality (PAD) was applied to each projection view, and a modified Feldkamp-Davis-Kress (FDK) algorithm was used to reconstruct the phase sensitive DBT slices. Simulated tumor margins were rated as more conspicuous and better visualized for both phase sensitive acquisition geometries versus conventional DBT imaging. The CD curves confirmed the improvement in both contrast and spatial resolutions with the phase sensitive DBT imaging. The superiority of the phase sensitive DBT imaging was further endorsed by higher contrast to noise ratio (CNR) and figure-of-merit (FOM) values. The CNR improvements provided by the phase sensitive DBT prototype were sufficient to offset the noise reduction provided by the attenuation-based DBT imaging. [ABSTRACT FROM AUTHOR]

Rapid progress in the field of Cardiac CT is fostered by the advances in CT scanner technology as well as multiple clinical trials demonstrating its role in coronary artery disease and other indications like congenital heart disease, pulmonary vein assessment and pre transcatheter aortic valve replacement. The cardiovascular imager today is responsible for delivering diagnostic image quality while striking a balance with optimized radiation dose. Radiation dose is the result of multiple scanner and patient related factors. Achieving a justifiable radiation dose according to the ALARA principle requires an adept understanding of the factors affecting radiation dose. We review different scan factors and their effect on radiation dose and present strategies for radiation dose optimization in cardiac CT. [ABSTRACT FROM AUTHOR]

• New Icelandic national diagnostic reference levels. • Data collected from all computed tomography scanners in Iceland. • National diagnostic reference levels, based on clinical indications, were established. • Computed tomography examinations have been linked to clinical indications. A diagnostic reference level (DRL) is an investigation level to use in the optimization of a medical exposure using ionizing radiation. The aim of this project was to gather dose data from computed tomography (CT) studies in Iceland with the purpose of updating existing national DRL and proposing DRLs based on clinical indications. Dose data (total dose length product (DLP) and CT dose index) were retrospectively collected from all CT scanners in Iceland for 50 patients for all common CT studies. After cleaning the data, the data set contained total DLP for 8129 patients. Considering dose-relevant parameters such as the number of phases and scan length, each CT study was assigned to one of 42 study types and (at least) one clinical indication. Data were received from seven or more scanners for 13 clinical indications and from all scanners providing coronary angiography. There was considerable variation in the median total DLP from different scanners, e.g., from 13 to 139 mGycm for Sinusitis , and, the range of individual total DLPs varied between scanners. This underscores the importance of monitoring patients' exposure. The study shows that there is room for optimization. New Icelandic NDRLs were proposed for the total DLP of CT examinations based on ten different indications, including: Brain ischemia (1060 mGycm), Interstitial lung disease (310 mGycm) and Appendicitis (690 mGycm). The proposed NDRLs were the first clinical indication based NDRLs in Iceland. The Icelandic Radiation Safety Authority has decided to update the NDRLs based on the results of this study. [ABSTRACT FROM AUTHOR]

There is currently no effective real-time patient dosimeter available for use in interventional radiology (IR). We conducted a feasibility study in a clinical setting to investigate the use of the new dosimeter using photoluminescence sensors during procedures. Reference dosimeters were set at almost the same position of the prototype dosimeter sensors. We found excellent correlations between the reference measurements and those of the prototype dosimeter (r 2 = 0.950). The sensor of the new dosimeter does not interfere with the IR procedure. The new dosimeter will be an effective tool for the real-time measurement of patient skin doses during IR. [ABSTRACT FROM AUTHOR]

Purpose To evaluate the impact of Automatic Exposure Control (AEC) on radiation dose and image quality in paediatric chest scans (MDCT), with or without iterative reconstruction (IR). Methods Three anthropomorphic phantoms representing children aged one, five and 10-year-old were explored using AEC system (CARE Dose 4D) with five modulation strength options. For each phantom, six acquisitions were carried out: one with fixed mAs (without AEC) and five each with different modulation strength. Raw data were reconstructed with Filtered Back Projection (FBP) and with two distinct levels of IR using soft and strong kernels. Dose reduction and image quality indices (Noise, SNR, CNR) were measured in lung and soft tissues. Noise Power Spectrum (NPS) was evaluated with a Catphan 600 phantom. Results The use of AEC produced a significant dose reduction ( p < 0.01) for all anthropomorphic sizes employed. According to the modulation strength applied, dose delivered was reduced from 43% to 91%. This pattern led to significantly increased noise ( p < 0.01) and reduced SNR and CNR ( p < 0.01). However, IR was able to improve these indices. The use of AEC/IR preserved image quality indices with a lower dose delivered. Doses were reduced from 39% to 58% for the one-year-old phantom, from 46% to 63% for the five-year-old phantom, and from 58% to 74% for the 10-year-old phantom. In addition, AEC/IR changed the patterns of NPS curves in amplitude and in spatial frequency. Conclusions In chest paediatric MDCT, the use of AEC with IR allows one to obtain a significant dose reduction while maintaining constant image quality indices. [ABSTRACT FROM AUTHOR]

Purpose Demonstrate an objective procedure to quantify image quality in digital subtraction angiography (DSA) and suggest thresholds for acceptability and constancy tests. Methods Series of images were obtained in a DSA system simulating a small (paediatric) and a large patient using the dynamic phantom described in the IEC and DIN standards for acceptance tests of DSA equipment. Image quality was quantified using measurements of contrast-to-noise ratio (CNR). Overall scores combining the CNR of 10–100 mg/ml Iodine at a vascular diameter of 1–4 mm in a homogeneous background were defined. Phantom entrance surface air kerma (K a,e ) was measured with an ionisation chamber. Results The visibility of a low-contrast vessel in DSA images has been identified with a CNR value of 0.50 ± 0.03. Despite using 14 times more K a,e (8.85 vs 0.63 mGy/image), the protocol for large patients showed a decrease in the overall score CNR sum of 67% (4.21 ± 0.06 vs 2.10 ± 0.05). The uncertainty in the results of the objective method was below 5%. Conclusion Objective evaluation of DSA images using CNR is feasible with dedicated phantom measurements. An objective methodology has been suggested for acceptance tests compliant with the IEC/DIN standards. The defined overall scores can serve to fix a reproducible baseline for constancy tests, as well as to study the device stability within one acquisition series and compare different imaging protocols. This work provides aspects that have not been included in the recent European guidelines on Criteria for Acceptability of Medical Radiological Equipment. [ABSTRACT FROM AUTHOR]

Purpose We used pediatric and adult anthropomorphic phantoms to compare the radiation dose of low- and standard tube voltage chest and abdominal non-contrast-enhanced computed tomography (CT) scans. We also discuss the optimal low tube voltage for non-contrast-enhanced CT. Methods Using a female adult- and three differently-sized pediatric anthropomorphic phantoms we acquired chest and abdominal non-contrast-enhanced scans on a 320-multidetector CT volume scanner. The tube voltage was set at 80-, 100-, and 120 kVp. The tube current was automatically assigned on the CT scanner in response to the set image noise level. On each phantom and at each tube voltage we measured the surface and center dose using high-sensitivity metal-oxide-semiconductor field-effect transistor detectors. Results The mean surface dose of chest and abdominal CT scans in 5-year olds was 4.4 and 5.3 mGy at 80 kVp, 4.5 and 5.4 mGy at 100 kV, and 4.0 and 5.0 mGy at 120 kVp, respectively. These values were similar in our 3-pediatric phantoms (p > 0.05). The mean surface dose in the adult phantom increased from 14.7 to 19.4 mGy for chest- and from 18.7 to 24.8 mGy for abdominal CT as the tube voltage decreased from 120 to 80 kVp (p < 0.01). Conclusion Compared to adults, the surface and center dose for pediatric patients is almost the same despite a decrease in the tube voltage and the low tube voltage technique can be used for non-contrast-enhanced chest- and abdominal scanning. [ABSTRACT FROM AUTHOR]

The aim of this work was to create a model of a wide-bore Siemens Somatom Sensation Open CT scanner for use with GMCTdospp, which is an EGSnrc-based software tool dedicated for Monte Carlo calculations of dose in CT examinations. The method was based on matching spectrum and filtration to half value layer and dose profile, and thus was similar to the method of Turner et al. (Med. Phys. 36, pp. 2154–2164). Input data on unfiltered beam spectra were taken from two sources: the TASMIP model and IPEM Report 78. Two sources of HVL data were also used, namely measurements and documentation. Dose profile along the fan-beam was measured with Gafchromic RTQA-1010 (QA+) film. Two-component model of filtration was assumed: bow-tie filter made of aluminum with 0.5 mm thickness on central axis, and flat filter made of one of four materials: aluminum, graphite, lead, or titanium. Good agreement between calculations and measurements was obtained for models based on the measured values of HVL. Doses calculated with GMCTdospp differed from the doses measured with pencil ion chamber placed in PMMA phantom by less than 5%, and root mean square difference for four tube potentials and three positions in the phantom did not exceed 2.5%. The differences for models based on HVL values from documentation exceeded 10%. Models based on TASMIP spectra and IPEM78 spectra performed equally well. [ABSTRACT FROM AUTHOR]

Abstract: Benford's law is an empirical observation which predicts the expected frequency of digits in naturally occurring datasets spanning multiple orders of magnitude, with the law having been most successfully applied as an audit tool in accountancy. This study investigated the sensitivity of the technique in identifying system output changes using simulated changes in interventional radiology Dose-Area-Product (DAP) data, with any deviations from Benford's distribution identified using z-statistics. The radiation output for interventional radiology X-ray equipment is monitored annually during quality control testing; however, for a considerable portion of the year an increased output of the system, potentially caused by engineering adjustments or spontaneous system faults may go unnoticed, leading to a potential increase in the radiation dose to patients. In normal operation recorded examination radiation outputs vary over multiple orders of magnitude rendering the application of normal statistics ineffective for detecting systematic changes in the output. In this work, the annual DAP datasets complied with Benford's first order law for first, second and combinations of the first and second digits. Further, a continuous ‘rolling’ second order technique was devised for trending simulated changes over shorter timescales. This distribution analysis, the first employment of the method for radiation output trending, detected significant changes simulated on the original data, proving the technique useful in this case. The potential is demonstrated for implementation of this novel analysis for monitoring and identifying change in suitable datasets for the purpose of system process control. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to compare effective and ovarian doses (E and OD, respectively) in hysterosalpingography (HSG) examinations performed with conventional posterioanterior (PA) projections and rotational 3D (3D) techniques. 29 HSG examinations (11 conventional and 18 3D), were performed using a digital C-arm angiographic system. In the conventional technique, we used posterioanterior (PA) instead of an anterioposterior (AP) projection normally used according to the international literature. All information concerning exposure conditions for each patient, were recorded. Thermoluminescent dosimeters (TLDs) were attached on the skin of each patient over the ovaries. In conventional HSGs, average values were for Dose Area Product (DAP) 0.41 Gycm2, for Effective Dose (E) 0.15 mSv and for Ovarian Dose (OD) 0.24 mGy. In 3D-HSGs, they were 14.4 Gycm2, 2.29 mSv and 3.96 mGy correspondingly. Patient doses in 3D-HSGs are of the same order of magnitude with those reported in the literature for conventional technique. However, they are larger compared to the conventional HSG performed with the technique we use in this specific X-ray system. E and OD are much lower with our technique where PA projection and the specific C-arm system are used in comparison with the corresponding values published in the literature for the conventional technique where the AP projection is used. [Copyright &y& Elsevier]

Abstract: Purpose: To develop a new automatic exposure control (AEC) technique based on the contrast-to-noise ratio (CNR) and provide constant lesion detectability. Methods: Lesion detectability is affected by factors such as image noise, lesion contrast, and lesion size. We performed ROC analysis to assess the relationship between the optimum CNR and the lesion diameter at various levels of lesion contrast. We then developed a CNR-based AEC algorithm based on lesion detectability. Using CNR- based AEC algorithm, we performed visual evaluation of low-contrast detectability by 5 radiologists on a low-contrast module of the Catphan phantom, a contrast-difference level of 1.0% (difference in the CT number = 10 HU), and objects 3.0–9.0 mm in diameter. Results: On step-and-shoot scans the mean detection fraction with CNR-based AEC remained almost constant from 88 to 99 % regardless of the lesion size. We observed the same trend on helical scans, the mean detection fraction with CNR-based AEC exhibited a high score from 91 to 100%. Although CNR-based AEC maintains higher CNR for smaller size or lower contrast lesion, radiation dose on 3 mm lesion resulted in about 13 times larger than that of 9 mm lesion size. CTDIvol for the CNR-based AEC technique changed dramatically with the SDZ from 7.5 to 100.0 mGy for step-and-shoot scans and from 9.1 to 121.5 mGy for helical scans. Conclusions: From the viewpoint of ROC analysis-based CNR for lesion detection, CNR-based AEC potentially provide image quality advantages for clinical implementation. [Copyright &y& Elsevier]

Abstract: Diagnostic reference levels provide framework to reduce variability. The aim of this study is to establish, for the first time, a baseline for national diagnostic reference levels in Serbia and Montenegro for the most common X-ray examination types. Measurements of patient dose using kerma-area product meter and entrance surface air kerma assessment were performed on at least ten patients for each examination type, in each of 16 randomly selected hospitals in Serbia and Montenegro, so that a total of 3,026 procedures for nine different examination categories were included in the survey. Exposure settings and individual data were recorded for each patient. Mean, median and third quartile values of patient doses are reported. Results have shown wide variation of mean hospital doses, with factor of four for barium enema to 23 for thoracic spine radiography. Entrance surface air kerma were compared with previously published diagnostic reference levels (DRL) proposed by Commission of European Communities (CEC). Doses for all studied examination types except chest radiography were within European DRL. The reasons for dose variation are discussed. Survey data are aimed to help in development of an on-going national quality assurance and quality control programme in diagnostic radiology. The findings emphasize the importance of regular patient dose measurement to ensure that patient doses are kept as low as reasonable achievable. [ABSTRACT FROM AUTHOR]

Abstract: Dose-area product (DAP) measurements were conducted for 168 coronary angiography (CA) and 89 single vessel percutaneous transluminal coronary angioplasty (PTCA) to examine the factors influencing patient dose beyond the X-ray exposure parameters. It was found that for CA, the DAP increases with the number of catheters used and with the number of vessels with stenosis. DAP values for patients with a prior bypass surgery, were higher compared to those without such a medical record to surgery. In PTCA, the use of coronary stents did not enhance the patient radiation dose significantly. Noticeable differences were found in the percentage contribution of each projection to the total DAP between the three types of single vessel PTCA. Finally low variations in DAP were found among the cardiologists performing both procedures. [ABSTRACT FROM AUTHOR]