Ultra-low-dose vs. standard-of-care-dose CT of the chest in patients with post-COVID-19 conditions-a prospective intra-patient multi-reader study.

OBJECTIVES: To conduct an intrapatient comparison of ultra-low-dose computed tomography (ULDCT) and standard-of-care-dose CT (SDCT) of the chest in terms of the diagnostic accuracy of ULDCT and intrareader agreement in patients with post-COVID conditions. METHODS: We prospectively included 153 consecutive patients with post-COVID-19 conditions. All participants received an SDCT and an additional ULDCT scan of the chest. SDCTs were performed with standard imaging parameters and ULDCTs at a fixed tube voltage of 100 kVp (with tin filtration), 50 ref. mAs (dose modulation active), and iterative reconstruction algorithm level 5 of 5. All CT scans were separately evaluated by four radiologists for the presence of lung changes and their consistency with post-COVID lung abnormalities. Radiation dose parameters and the sensitivity, specificity, and accuracy of ULDCT were calculated. RESULTS: Of the 153 included patients (mean age 47.4 ± 15.3 years; 48.4% women), 45 (29.4%) showed post-COVID lung abnormalities. In those 45 patients, the most frequently detected CT patterns were ground-glass opacities (100.0%), reticulations (43.5%), and parenchymal bands (37.0%). The accuracy, sensitivity, and specificity of ULDCT compared to SDCT for the detection of post-COVID lung abnormalities were 92.6, 87.2, and 94.9%, respectively. The median total dose length product (DLP) of ULDCTs was less than one-tenth of the radiation dose of our SDCTs (12.6 mGy*cm [9.9; 15.5] vs. 132.1 mGy*cm [103.9; 160.2]; p < 0.001). CONCLUSION: ULDCT of the chest offers high accuracy in the detection of post-COVID lung abnormalities compared to an SDCT scan at less than one-tenth the radiation dose, corresponding to only twice the dose of a standard chest radiograph in two views. CLINICAL RELEVANCE STATEMENT: Ultra-low-dose CT of the chest may provide a favorable, radiation-saving alternative to standard-dose CT in the long-term follow-up of the large patient cohort of post-COVID-19 patients.

Equivalent thicknesses of beam hardening filters consisting of aluminium, copper, Al/Cu and Al/Gold combinations and plumbiferous acrylic for 40 to 150 kVp diagnostic spectra.

PURPOSE: Beam hardening filters used to reduce patient doses typically consist of aluminium, copper, or a combination of both. Optically transparent filters containing lead in plumbiferous acrylic became available. One vendor also uses a combination of aluminium and gold. Data is provided to compare filter thicknesses in terms of half-value layer (HVL) for clinically relevant kVp. METHODS: Equivalent filter thicknesses were defined by identical kVp and 1st HVL. Equivalent copper filter thicknesses were calculated for aluminium and typical filters found in radiographic and interventional systems. A verified semi-empirical spectrum calculation programme and National Institute of Standards and Technology (NIST) mass attenuation coefficients were applied. Lead acrylic filters were simulated by a two-component model of acrylic plus lead with mass thicknesses determined by matching 1 HVLs in Al at RQR5 using filter specifications. RESULTS: Coefficients are provided to convert mm Cu to mm Al and vice versa for tube potentials from 40 to 150 kVp. 1 mm Al corresponds to 27.8 ± 1 µm Cu over the entire energy range simulated. Using this simple model as opposed to simulations of all individual filters made from Al/Cu combinations (1 and 2 mm Al, 1 Al + 0.1 and 0.2 Cu, 1.5 Al plus 0.3 and 0.6 Cu, 2 Al plus 0.1 Cu) for the entire energy range results in differences in equivalent Cu thicknesses below 4 µm Cu (3 µm for 50-150 kVp). kVp dependence is larger for filters containing larger Z elements. 1 mm Al plus 10 µm gold used by Shimadzu corresponds to 75-80 µm Cu, depending on kVp; plumbiferous acrylic with nominal filtrations of 1 Al plus 0.1 Cu, and 1 Al plus 0.2 Cu corresponded to 124-132 µm, and 206-232 µm Cu, respectively. CONCLUSIONS: Experimental verification of the equivalence of aluminium and combined aluminium plus copper filters showed excellent agreement between calculated copper equivalent thickness and measurements with copper filters for clinical beams from 40 to 150 kVp.

Contrast-enhanced dual energy mammography with a novel anode/filter combination and artifact reduction: a feasibility study.

OBJECTIVES: To demonstrate the feasibility of contrast-enhanced dual-energy mammography (CEDEM) using titanium (Ti) filtering at 49 kVp for high-energy images and a novel artefact reducing image-subtraction post-processing algorithm. METHODS: Fifteen patients with suspicious findings (ACR BI-RADS 4 and 5) detected with digital mammography (MG) that required biopsy were included. CEDEM examinations were performed on a modified prototype machine. Acquired HE and low-energy raw data images were registered non-rigidly to compensate for possible subtle tissue motion. Subtracted CEDEM images were generated via weighted subtraction, using a fully automatic, locally adjusted tissue thickness-dependent subtraction factor to avoid over-subtraction at the breast border. Two observers evaluated the MG and CEDEM images according to ACR BI-RADS in two reading sessions. Results were correlated with histopathology. RESULTS: Seven patients with benign and eight with malignant findings were included. All malignant lesions showed a strong contrast enhancement. BI-RADS assessment was altered in 66.6 % through the addition of CEDEM, resulting in increased overall accuracy. With CEDEM, additional lesions were depicted and false-positive rate was reduced compared to MG. CONCLUSIONS: CEDEM using Ti filtering with 49 kVp for HE exposures is feasible in a clinical setting. The proposed image-processing algorithm has the potential to reduce artefacts and improve CEDEM images. KEY POINTS: • CEDEM with a titanium filter is feasible in a clinical setting. • Breast thickness-dependent image subtraction has the potential to improve CEDEM images. • The proposed image-processing algorithm reduces artefacts.

Tailoring the Mass Density of 3D Printing Materials for Accurate X-ray Imaging Simulation by Controlled Underfilling for Radiographic Phantoms.

Additive manufacturing and 3D printing allow for the design and rapid production of radiographic phantoms for X-ray imaging, including CT. These are used for numerous purposes, such as patient simulation, optimization of imaging procedures and dose levels, system evaluation and quality assurance. However, standard 3D printing polymers do not mimic X-ray attenuation properties of tissues like soft, adipose, lung or bone tissue, and standard materials like liquid water. The mass density of printing polymers-especially important in CT-is often inappropriate, i.e., mostly too high. Different methods can be applied to reduce mass density. This work examines reducing density by controlled underfilling either realized by using 3D printing materials expanded through foaming during heating in the printing process, or reducing polymer flow to introduce microscopic air-filled voids. The achievable density reduction depends on the base polymer used. When using foaming materials, density is controlled by the extrusion temperature, and ranges from 33 to 47% of the base polymer used, corresponding to a range of -650 to -394 HU in CT with 120 kV. Standard filaments (Nylon, modified PLA and modified ABS) allowed density reductions by 20 to 25%, covering HU values in CT from -260 to 77 (Nylon), -230 to -20 (ABS) and -81 to 143 (PLA). A standard chalk-filled PLA filament allowed reproduction of bone tissue in a wide range of bone mineral content resulting in CT numbers from 57 to 460 HU. Controlled underfilling allowed the production of radiographic phantom materials with continuously adjustable attenuation in a limited but appropriate range, allowing for the reproduction of X-ray attenuation properties of water, adipose, soft, lung, and bone tissue in an accurate, predictable and reproducible manner.

A spiculated mass target model for clinical image quality control in digital mammography.

OBJECTIVES: Quality assurance of breast imaging has a long history of using test objects to optimize and follow up imaging devices. In particular, the evaluation of new techniques benefits from suitable test objects. The applicability of a phantom consisting of spiculated masses to assess image quality and its dependence on dose in flat field digital mammography (FFDM) and digital breast tomosynthesis systems (DBT) is investigated. METHODS: Two spiculated masses in five different sizes each were created from a database of clinical tumour models. The masses were produced using 3D printing and embedded into a cuboid phantom. Image quality is determined by the number of spicules identified by human observers. RESULTS: The results suggest that the effect of dose on spicule detection is limited especially in cases with smaller objects and probably hidden by the inter-reader variability. Here, an average relative inter-reader variation of the counted number of 31% was found (maximum 83%). The mean relative intra-reader variability was found to be 17%. In DBT, sufficiently good results were obtained only for the largest masses. CONCLUSIONS: It is possible to integrate spiculated masses into a cuboid phantom. It is easy to print and should allow a direct and prompt evaluation of the quality status of the device by counting visible spicules. Human readout presented the major uncertainty in this study, indicating that automated readout may improve the reproducibility and consistency of the results considerably. ADVANCES IN KNOWLEDGE: A cuboid phantom including clinical objects as spiculated lesion models for visual assessing the image quality in FFDM and DBT was developed and is introduced in this work. The evaluation of image quality works best with the two larger masses with 21 spicules.

Technical note: Realization and uncertainty analysis for an adjustable 3D structured breast phantom in digital breast tomosynthesis.

BACKGROUND: Projection imaging phantoms are often optimized for 2-dimensional image characteristics in homogeneous backgrounds. Therefore, evaluation of image quality in tomosynthesis (DBT) lacks accepted and established phantoms. PURPOSE: We describe a 3D breast phantom with a structured, variable background. The phantom is an adaptable and advanced version of the L1 phantom by Cockmartin et al. Phantom design and its use for quality assurance measurements for DBT devices are described. Four phantoms were compared to assess the objectivity. METHODS: The container size was increased to a diameter of 24 cm and a total height of 53.5 mm. Spiculated masses were replaced by five additional non-spiculated masses for higher granularity in threshold diameter resolution. These patterns are adjustable to the imaging device. The masses were printed in one session with a base layer using two-component 3D printing. New materials compared to the L1 phantom improved the attenuation difference between the lesion models and the background. Four phantoms were built and intra-human observer, inter-human observer and inter-phantom variations were determined. The latter assess the reproducibility of the phantom production. Coefficients of variance (V) were calculated for all three variations. RESULTS: The difference of the attenuation coefficients between the lesion models and the background was 0.20 cm-1 (with W/Al at 32 kV, equivalent to 19-20 keV effective energy) compared to 0.21 cm-1 for 50/50 glandular/adipose breast tissue and cancerous lesions. PMMA equivalent thickness of the phantom was 47.0 mm for the Siemens Mammomat Revelation. For the masses, the V i n t r a $V_{intra}$ for the intra-observer variation was 0.248, the averaged inter-observer variation, V ¯ i n t e r $\overline{V}_{inter}$ was 0.383. V p h a n t o m $V_{phantom}$ for phantom variance was 0.321. For the micro-calcifications, V i n t r a $V_{intra}$ was 0.0429, V ¯ i n t e r = $\overline{V}_{inter}=$ 0.0731 and V p h a n t o m = $V_{phantom}=$ 0.0759. CONCLUSIONS: Position, orientation and shape of the masses are reproducible and attenuation differences appropriate. The phantom presented proved to be a candidate test object for quality control.

Ultra-low-dose CT vs. chest X-ray in non-traumatic emergency department patients - a prospective randomised crossover cohort trial.

Background: Ultra-low-dose CT (ULDCT) examinations of the chest at only twice the radiation dose of a chest X-ray (CXR) now offer a valuable imaging alternative to CXR. This trial prospectively compares ULDCT and CXR for the detection rate of diagnoses and their clinical relevance in a low-prevalence cohort of non-traumatic emergency department patients. Methods: In this prospective crossover cohort trial, 294 non-traumatic emergency department patients with a clinically indicated CXR were included between May 2nd and November 26th of 2019 (www.clinicaltrials.gov: NCT03922516). All participants received both CXR and ULDCT, and were randomized into two arms with inverse reporting order. The detection rate of CXR was calculated from 'arm CXR' (n = 147; CXR first), and of ULDCT from 'arm ULDCT' (n = 147; ULDCT first). Additional information reported by the second exam in each arm was documented. From all available clinical and imaging data, expert radiologists and emergency physicians built a compound reference standard, including radiologically undetectable diagnoses, and assigned each finding to one of five clinical relevance categories for the respective patient. Findings: Detection rates for main diagnoses by CXR and ULDCT (mean effective dose: 0.22 mSv) were 9.1% (CI [5.2, 15.5]; 11/121) and 20.1% (CI [14.2, 27.7]; 27/134; P = 0.016), respectively. As an additional imaging modality, ULDCT added 9.1% (CI [5.2, 15.5]; 11/121) of main diagnoses to prior CXRs, whereas CXRs did not add a single main diagnosis (0/134; P < 0.001). Notably, ULDCT also offered higher detection rates than CXR for all other clinical relevance categories, including findings clinically irrelevant for the respective emergency department visit with 78.5% (CI [74.0, 82.5]; 278/354) vs. 16.2% (CI [12.7, 20.3]; 58/359) as a primary modality and 68.2% (CI [63.3, 72.8]; 245/359) vs. 2.5% (CI [1.3, 4.7]; 9/354) as an additional imaging modality. Interpretation: In non-traumatic emergency department patients, ULDCT of the chest offered more than twice the detection rate for main diagnoses compared to CXR. Funding: The Department of Biomedical Imaging and Image-guided Therapy of Medical University of Vienna received funding from Siemens Healthineers (Erlangen, Germany) to employ two research assistants for one year.

X-ray attenuation of bone, soft and adipose tissue in CT from 70 to 140 kV and comparison with 3D printable additive manufacturing materials.

Additive manufacturing and 3D printing are widely used in medical imaging to produce phantoms for image quality optimization, imaging protocol definition, comparison of image quality between different imaging systems, dosimetry, and quality control. Anthropomorphic phantoms mimic tissues and contrasts in real patients with regard to X-ray attenuation, as well as dependence on X-ray spectra. If used with different X-ray energies, or to optimize the spectrum for a certain procedure, the energy dependence of the attenuation must replicate the corresponding energy dependence of the tissues mimicked, or at least be similar. In the latter case the materials' Hounsfield values need to be known exactly to allow to correct contrast and contrast to noise ratios accordingly for different beam energies. Fresh bovine and porcine tissues including soft and adipose tissues, and hard tissues from soft spongious bone to cortical bone were scanned at different energies, and reference values of attenuation in Hounsfield units (HU) determined. Mathematical model equations describing CT number dependence on kV for bones of arbitrary density, and for adipose tissues are derived. These data can be used to select appropriate phantom constituents, compare CT values with arbitrary phantom materials, and calculate correction factors for phantoms consisting of materials with an energy dependence different to the tissues. Using data on a wide number of additive manufacturing and 3D printing materials, CT numbers and their energy dependence were compared to those of the tissues. Two commercially available printing filaments containing calcium carbonate powder imitate bone tissues with high accuracy at all kV values. Average adipose tissue can be duplicated by several off-the-shelf printing polymers. Since suitable printing materials typically exhibit a too high density for the desired attenuation of especially soft tissues, controlled density reduction by underfilling might improve tissue equivalence.

Factors for conversion between human and automatic read-outs of CDMAM images.

PURPOSE: According to the European protocol for the quality control of the physical and technical aspects of mammography screening (EPQCM) image quality of digital mammography devices has to be assessed using human evaluation of the CDMAM contrast-detail phantom. This is accomplished by the determination of threshold thicknesses of gold disks with different diameters (0.08-2 mm) and revealed to be very time consuming. Therefore a software solution based on a nonprewhitening matched filter (NPW) model was developed at the University of Nijmegen. Factors for the conversion from automatic to human readouts have been determined by Young et al. [Proc. SPIE 614206, 1-13 (2006) and Proc. SPIE 6913, 69131C1 (2008)] using a huge amount of data of both human and automatic readouts. These factors depend on the observer groups and are purely phenomenological. The authors present an alternative approach to determine the factors by using the Rose observer model. METHODS: Their method uses the Rose theory which gives a relationship between threshold contrast, diameter of the object and number of incident photons. To estimate the conversion factors for the five diameters from 0.2 to 0.5 mm they exposed with five different current-time products which resulted in 25 equations with five unknowns. RESULTS: The theoretical conversion factors (in dependence of the diameters) amounted to be 1.61 ± 0.02 (0.2 mm diameter), 1.67 ± 0.02 (0.25 mm), 1.85 ± 0.02 (0.31 mm), 2.09 ± 0.02 (0.4 mm), and 2.28 ± 0.02 (0.5 mm). The corresponding phenomenological factors found in literature are 1.74 (0.2 mm), 1.78 (0.25 mm), 1.83 (0.31 mm), 1.88 (0.4 mm), and 1.93 (0.5 mm). CONCLUSIONS: They transferred the problem of determining the factors to a well known observer model which has been examined for many years and is also well established. This method reveals to be reproduceable and produces factors comparable to the phenomenological ones.

Feasibility of dose reduction using needle-structured image plates versus powder-structured plates for computed radiography of the knee.

OBJECTIVE: A newly developed computed radiography (CR) detector that uses a storage phosphor plate made of needle-shaped crystals provides improved dose efficiency. The aim of our study was to compare the image quality of standard-dose CR and dose-reduced CR achieved using needle technology for knee imaging in a clinical setting. MATERIALS AND METHODS: We compared standard CR images obtained using a powder-structured image plate (PIP) (ADC Compact Plus) with images obtained using the new needle-structured image plate (NIP) (DX-S). In 30 consecutive patients with knee pain willing to participate in this study, anteroposterior knee radiographs were acquired with both systems at a standard dose. In addition, NIP images were obtained with approximately 75% and 50% of the standard dose (corresponding incident doses: 300, 235, and 154 µGy, respectively). Images were evaluated in a blinded, side-by-side comparison. Six radiologists determined whether there was an appreciable difference in image quality at five anatomic landmarks in regions with high and low differences of attenuation. They also assessed the delineation of selected abnormalities and ranked them using a 10-point scale. The rating scores were tested for statistical differences using an analysis of variance with repeated measures. RESULTS: The mean overall rating scores for the evaluation of anatomic landmarks were 6.97 for NIP images obtained at full dose, 6.48 for NIP images obtained at about 75% dose, 5.47 for NIP images obtained at half dose, and 6.01 for PIP images. There was a significant difference in favor of the CR system with an NIP at the same dose level (p < 0.05). The NIP images obtained at a dose of about 75% were also ranked significantly better than the PIP images with regard to the depiction of both anatomic landmarks and abnormalities. The readers ranked half-dose NIP images inferior to the PIP images with regard to abnormalities and anatomic landmarks in areas with high attenuation, whereas in areas with low attenuation, the image quality was regarded as equivalent to the standard technique. CONCLUSION: NIP technology allows a dose reduction of approximately 25% compared with PIP while still providing higher image quality. Even at the half-dose level, there was no relevant loss of image quality with regard to the delineation of anatomic landmarks in areas with low attenuation in anteroposterior knee images. The higher dose efficiency of the needle-detector CR technology compared with conventional CR can be used either for dose reduction or for improved image quality.

Classification of X-Ray Attenuation Properties of Additive Manufacturing and 3D Printing Materials Using Computed Tomography From 70 to 140 kVp.

Additive manufacturing and 3D printing is particularly useful in the production of phantoms for medical imaging applications including determination and optimization of (diagnostic) image quality and dosimetry. Additive manufacturing allows the leap from simple slab and stylized to (pseudo)-anthropomorphic phantoms. This necessitates the use of materials with x-ray attenuation as close as possible to that of the tissues or organs mimicked. X-ray attenuation properties including their energy dependence were determined for 35 printing materials comprising photocured resins and thermoplastic polymers. Prior to measuring x-ray attenuation in CT from 70 to 140 kVp, printing parameters were thoroughly optimized to ensure maximum density avoiding too low attenuation due to microscopic or macroscopic voids. These optimized parameters are made available. CT scanning was performed in a water filled phantom to guarantee defined scan conditions and accurate HU value determination. The spectrum of HU values covered by polymers printed using fused deposition modeling reached from -258 to +1,063 at 120 kVp (-197 to +1,804 at 70 kVp, to -266 to +985 at 140 kVp, respectively). Photocured resins covered 43 to 175 HU at 120 kVp (16-156 at 70, and 57-178 at 140 kVp). At 120 kVp, ASA mimics water almost perfectly (+2 HU). HIPS (-40 HU) is found close to adipose tissue. In all photocurable resins, and 17 printing filaments HU values decreased with increasing beam hardness contrary to soft tissues except adipose tissue making it difficult to mimic water or average soft tissue in phantoms correctly over a range of energies with one single printing material. Filled filaments provided both, the HU range, and an appropriate energy dependence mimicking bone tissues. A filled material with almost constant HU values was identified potentially allowing mimicking soft tissues by reducing density using controlled under-filling. The measurements performed in this study can be used to design phantoms with a wide range of x-ray contrasts, and energy dependence of these contrasts by combining appropriate materials. Data provided on the energy dependence can also be used to correct contrast or contrast to noise ratios from phantom measurements to real tissue contrasts or CNRs.

Developing and Implementing an Imaging Optimization Study in Pediatric Nuclear Medicine: Experience and Recommendations from an IAEA-Coordinated Research Project.

The International Atomic Energy Agency instituted a coordinated research project on the evaluation and optimization of pediatric imaging, addressing the lack of consistency in this field. The purpose was to develop and test an optimization schema for the practices of pediatric radiology and nuclear medicine. Methods: A 5-step optimization schema was developed. Once a protocol optimization is identified, the steps are as follows: identification of the imaging situation; collection of administered-activity data and evaluation of the diagnostic image quality at baseline; comparison of baseline administered activity data with published standards or other benchmarks; identification of intervention, if necessary; and implementation of intervention and evaluation. Results: Within the coordinated research project, two sites considered optimization projects regarding nuclear medicine. In this work, renal imaging using 99mTc-dimercaptosuccinic acid (DMSA) projects are presented as examples. Site 1 acquired its standard 300-s static 99mTc-DMSA studies as 5-frame dynamic studies in 29 children. Frames were added to simulate different levels of administered activity. Image quality was subjectively judged on a 3-point Likert scale. A 30% reduction in administered activity with increased imaging duration (350 s) across all age groups was shown to be acceptable. This reduction was implemented and evaluated in 31 subsequent children, yielding administered activities significantly lower than baseline (mean relative differences of 30%, 37%, and 38% for children aged 0-5, 5-10, and 10-15 y, respectively). Site 2 performed a phantom study to determine the impact of lowering administered activity on image noise, finding that administered activities could be significantly lowered if longer imaging times were used. This led to a 50%-70% reduction from baseline with no loss in image quality. Conclusion: A dose optimization approach was applied successfully for several procedures commonly performed in pediatric nuclear medicine. Results are reported for renal cortical imaging using 99mTc-DMSA, leading to significant reductions in administered activity (and thus radiation dose). This optimization schema can be successfully implemented by nuclear medicine clinics seeking to improve their approach to imaging children.

Diagnostic reference levels in pediatric radiology in Austria.

BACKGROUND: Because of the higher sensitivity to radiation in children, optimization plays an essential role in pediatric radiology. Diagnostic reference levels are a helpful tool to optimize patient dose for standard radiographic procedures. METHODS: A nationwide survey was conducted to determine doses and variation in average dose applied to children for standard X-ray examinations. Dose values for chest, skull and abdomen X-ray procedures were determined for newborns, 1, 5, 10 and 15 year olds. RESULTS: Third quartiles of patient doses are provided and compared to European, British and German reference values. Variation in average doses between hospitals (i.e., ratio of maximal to minimal applied average dose) for the same age and examination was found to be typically a factor of eight. Ratios of maximal to minimal applied doses to individual patients were found to be approximately a factor of six higher than variations of average doses between clinics. CONCLUSIONS: While average patient doses indicate the use of good radiological practice in general, variance in average doses applied by different hospitals indicate that audit of dose with respect to reference values will provide guidance for optimization. Such practice should result in lowering doses for pediatric examinations.

Coronary artery stent imaging with 128-slice dual-source CT using high-pitch spiral acquisition in a cardiac phantom: comparison with the sequential and low-pitch spiral mode.

OBJECTIVE: To evaluate coronary stents in vitro using 128-slice-dual-source computed tomography (CT). METHODS: Twelve different coronary stents placed in a non-moving cardiac/chest phantom were examined by 128-slice dual-source CT using three CT protocols [high-pitch spiral (HPS), sequential (SEQ) and conventional spiral (SPIR)]. Artificial in-stent lumen narrowing (ALN), visible inner stent area (VIA), artificial in-stent lumen attenuation (ALA) in percent, image noise inside/outside the stent and CTDIvol were measured. RESULTS: Mean ALN was 46% for HPS, 44% for SEQ and 47% for SPIR without significant difference. Mean VIA was similar with 31% for HPS, 30% for SEQ and 33% for SPIR. Mean ALA was, at 5% for HPS, significantly lower compared with -11% for SPIR (p = 0.024), but not different from SEQ with -1%. Mean image noise was significantly higher for HPS compared with SEQ and SPIR inside and outside the stent (p < 0.001). CTDIvol was lower for HPS (5.17 mGy), compared with SEQ (9.02 mGy) and SPIR (55.97 mGy), respectively. CONCLUSION: The HPS mode of 128-slice dual-source CT yields fewer artefacts inside the stent lumen compared with SPIR and SEQ, but image noise is higher. ALN is still too high for routine stent evaluation in clinical practice. Radiation dose of the HPS mode is markedly (less than about tenfold) reduced.

Performance of semiconductor dosimeters with a range of radiation qualities used for mammography: A calibration laboratory study.

PURPOSE: To investigate the radiation quality dependence of the response of commercial semiconductor-based dosimeters, and to estimate potential errors and uncertainties related to different measurement and calibration scenarios. METHODS: All measurement results were compared to reference values measured at the IAEA dosimetry laboratory which is traceable to the international system of units (SI). Energy dependence of the response of eight semiconductor dosimeters were determined for five different anode-filter combinations and tube voltages from 25 to 35 kV. For systems capable of deriving half value layer (HVL) and tube voltage from measurements, calibration coefficients for these measurements were calculated. RESULTS: For six dosimeters, the maximum deviations from the reference value of the air kerma measurement were within ±5% as required by IEC 61674. Calibration coefficients for radiation qualities (anode-filter and tube voltage combinations) relative to reference radiation quality Mo-Mo 28 kV deviate up to 12%. HVL and tube voltage measurements exhibited deviations up to 11% and 10%, respectively. CONCLUSIONS: The air kerma responses of modern semiconductor dosimeters have a small energy dependence. However, no dosimeter tested complied with the accuracy limits stated by the manufacturer for tube voltage measurements, and only two dosimeters complied with the limits for HVL measurements. Absolute measurement of HVL and tube voltage with semiconductor dosimeters have to be verified for actual clinical radiation conditions on clinical mammography systems. Semiconductor dosimeters can be used for quality control measurements if individual calibration coefficients are available for the radiation condition applied. If other conditions are applied, additional uncertainty needs to be considered, particularly in the case of HVL and tube voltage measurements.

Diagnostic Reference Levels for computed tomography in Austria: A 2018 nationwide survey on adult patients.

PURPOSE: To define National Diagnostic Reference Levels (NDRLs) for computed tomography (CT) for Austria on adult patients. METHOD: In the course of a nationwide survey on common CT-examinations between June 2018 and November 2018, datasets were requested from all Austrian hospitals and radiology centers with CT-scanners. All facilities were asked to report a minimum sample of 10 representative dose length product (DLP) values per examination type and CT-scanner, including information about scan sequences, iterative reconstruction (IR) algorithms and, if available, patient data. Examination types included into the survey were the most common CT-indications for the anatomic regions head, facial bones, thorax, abdomen and pelvis. 3rd quartiles of CT-scanner median DLPs were calculated and compared to Austrian and international NDRLs. RESULTS: For 76 % of all operating CT-scanners, DLP data was submitted varying from 13 to 172 scanners per examination type. Mean year of manufacture of the CT-scanners was 2011, ranging from 2003 to 2018. In 66 % of the examinations, IR was used. 3rd quartile is on average 21 % lower for scanners using IR algorithms as opposed to scanners or protocols not using IR. In the case of gender differences, the DLP for females is on average 17 % lower than for males. CONCLUSIONS: The new recommendations for CT NDRLs for Austria based on a nationwide survey are on average 13 % lower than the current Austrian NDRLs and correspond well to recent German and Swiss NDRLs. 3rd quartiles for DLP are dependent on gender, the use of IR and year of manufacture of the CT-scanners.

Diagnostic Reference Levels for conventional radiography and fluoroscopy in Austria: Results and updated National Diagnostic Reference Levels derived from a nationwide survey.

OBJECTIVE: Evaluation and updating of Austrian National Diagnostic Reference Levels (NDRLs). METHODS: A nationwide survey on common conventional radiography and fluoroscopy examinations was conducted. In line with Austrian radiation protection standards, all relevant Austrian hospitals and radiology offices/centers were asked to report a minimum sample of 10 representative dose-area product (DAP) values together with patient weight and fluoroscopy time, if applicable. Examinations included for conventional radiography were skull, chest, abdomen, pelvis, lumbar spine and bedside chest x-ray, for fluoroscopy barium enema (single and double contrast) and swallowing (video). Participants were invited via e-mail, followed up by reminders to increase participation rates. Plausibility checks were performed to increase data quality. 3rd quartiles of facility median and mean DAP were calculated and compared to Austrian and international NDRLs. RESULTS: 59% of invited facilities submitted DAP data, 43% submitted additional data on patient weight and 41% on fluoroscopy time. DAP case numbers varied from 1005 to 2121 for conventional radiography and from 182 to 1380 for fluoroscopy. Average patient weight was 75 kg for conventional radiography and 77 kg for fluoroscopy. CONCLUSION: 3rd quartiles derived from the survey are substantially lower than the old Austrian NDRLs (valid till early 2018). Since 3rd quartiles correspond well to European NDRLs, the update would be in accordance with European DRL harmonisation efforts.

An anthropomorphic phantom representing a prematurely born neonate for digital x-ray imaging using 3D printing: Proof of concept and comparison of image quality from different systems.

An anthropomorphic phantom for image optimization in neonatal radiography was developed, and its usability in optimizing image acquisition and processing demonstrated. The phantom was designed to mimic a patient image of a prematurely born neonate. A clinical x-ray (neonate <1 kg) taken with an effective dose of 11 µSv on a needle-crystal storage phosphor system was retrospectively selected from anonymized images as an appropriate template representing a standard case in neonatology imaging. The low dose level used in clinical imaging results in high image noise content. Therefore, the image had to be processed using structure preserving noise reduction. Pixel values were related to printing material thickness to result in a similar attenuation pattern as the original patient including support mattress. A 3D model generating a similar x-ray attenuation pattern on an image detector as a patient was derived accounting for beam hardening and perspective, and printed using different printing technologies. Best printing quality was achieved using a laser stereolithography printer. Phantom images from different digital radiography systems used in neonatal imaging were compared. Effects of technology, image processing, and radiation dose on diagnostic image quality can be assessed for otherwise identical anthropomorphic neonatal images not possible with patient images, facilitating optimization and standardization of imaging parameters and image appearance.

Comparison of a personalized breast dosimetry method with standard dosimetry protocols.

Average glandular dose (AGD) in digital mammography crucially depends on the estimation of breast glandularity. In this study we compared three different methods of estimating glandularities according to Wu, Dance and Volpara with respect to resulting AGDs. Exposure data from 3050 patient images, acquired with a GE Senographe Essential constituted the study population of this work. We compared AGD (1) according to Dance et al. applying custom g, c, and s factors using HVL, breast thickness, patient age and incident air kerma (IAK) from the DICOM headers; (2) according to Wu et al. as determined by the GE system; and (3) AGD derived with the Dance model with personalized c factors using glandularity determined with the Volpara (Volpara Solutions, Wellington, New Zealand) software (Volpare AGD). The ratios of the resulting AGDs were analysed versus parameters influencing dose. The highest deviation between the resulting AGDs was found in the ratio of GE AGD to Volpara AGD for breast thicknesses between 20 and 40 mm (ratio: 0.80). For thicker breasts this ratio is close to one (1 ± 0.02 for breast thicknesses >60 mm). The Dance to Volpara ratio was between 0.86 (breast thickness 20-40 mm) and 0.99 (>80 mm), and Dance/GE AGD was between 1.07 (breast thickness 20-40 mm) and 0.98 (41-60, and >80 mm). Glandularities by Volpara were generally smaller than the one calculated with the Dance method. This effect is most pronounced for small breast thickness and older ages. Taking the considerable divergences between the AGDs from different methods into account, the selection of the method should by done carefully. As the Volpara method provides an analysis of the individual breast tissue, while the Wu and the Dance methods use look up tables and custom parameter sets, the Volpara method might be more appropriate if individual ADG values are sought. For regulatory purposes and comparison with diagnostic reference values, the method to be used needs to be defined exactly and clearly be stated. However, it should be accepted that dose values calculated with standardized models, like AGD and also effective dose, are afflicted with a considerable uncertainty budgets that need to be accounted for in the interpretation of these values.

High-resolution CT of transplanted teeth: imaging technique and measurement accuracy.

The aim of this study was to determine the accuracy of crown diameter measurements by dental CT as a tool for preoperative diagnosis before tooth transplantations. Fifty-eight patients underwent clinically indicated dental CT. The diameter of the crowns were measured by CT using a standard protocol (1.5-mm slice thickness, 1-mm table feed, 120 kV, 25-75 mA/s, 2-s scan time/slice, 512 matrix) and a standard dental software package. Postoperatively, the same distances were clinically measured using a sliding gauge. The degree of the deviation between CT measurements and clinical measurements was in the sub-millimeter range. According to the regression analysis, the correlation coefficient equals 0.98 and 0.97, indicating a strong relationship between the CT and the manual measurement of the crown diameter in the bucco-lingual and the mesio-distal direction. The mean deviation of CT measurements with regard to the bucco-lingual diameter of the crown was +0.08 mm (SD: +/-0.38 mm). For the mesio-distal diameter, the mean deviation of CT measurements was -0.24 mm (SD: +/-0.53 mm). These results demonstrate that dental CT promises to be a valuable tool for the evaluation of the potential and optimal size and site for tooth transplantations.