Lead aprons and thyroid collars: to be, or not to be?

Wearing lead aprons and thyroid collars for long periods of time has a subjective component: to balance the effective dose reduction with the effort of carrying a heavy load. Occupational radiation exposure has decreased dramatically in the last century within the health care system. During the same period the use of lead aprons and thyroid collars has also gone up. Therefore, a question that may be raised is: how safe is safe enough? In order to promote stakeholder involvement, the aim of the present study was to investigate staff's experience of discomforts associated with wearing lead aprons and thyroid collars for long periods of time, and also to investigate staff's willingness to tolerate personal dose equivalent (expressed as radiation dose) and the corresponding increase in future cancer risk to avoid wearing these protective tools. A questionnaire was developed and given to staff working in operating or angiography rooms at Skaraborg Hospital in Sweden. The results from the 245 respondents showed that 51% experienced bothersome warmth, 36% experienced fatigue and 26% experienced ache or pain that they believed was associated with wearing lead aprons. One third of the respondents would tolerate a personal dose equivalent of 1 mSv per year to avoid wearing lead aprons, but only a fifth would tolerate the corresponding increase in future cancer risk (from 43% to 43.2%). In conclusion, discomforts associated with wearing lead aprons and thyroid collars for long periods of time are common for the staff using them. At the same time, only a minority of the staff would tolerate a small increase in future cancer risk to avoid wearing them. The present study gives an example of stakeholder involvement and points at the difficulties in making reasonable decisions about the use of these protective tools.

Predictors of radiation dose for uterine artery embolisation are angiography system-dependent.

This study sought to achieve radiation dose reductions for patients receiving uterine artery embolisation (UAE) by evaluating radiation dose measurements for the preceding generation (Allura) and upgraded (Azurion) angiography system. Previous UAE regression models in the literature could not be applied to this centre's practice due to being based on different angiography systems and radiation dose predictor variables. The aims of this study were to establish whether radiation dose is reduced with the upgraded angiography system and to develop a regression model to determine predictors of radiation dose specific to the upgraded angiography system. A comparison between Group I (Allura,n= 95) and Group II (Azurion,n= 95) demonstrated a significant reduction in kerma-area product (KAP) and Ka, r (reference air kerma) by 63% (143.2 Gy cm2vs 52.9 Gy cm2;P< 0.001,d= 0.8) and 67% (0.6 Gy vs 0.2 Gy;P< 0.001,d= 0.8), respectively. The multivariable linear regression (MLR) model identified the UAE radiation dose predictors for KAP on the upgraded angiography system as total fluoroscopy dose, Ka, r, and total uterus volume. The predictive accuracy of the MLR model was assessed using a Bland-Altman plot. The mean difference was 0.39 Gy cm2and the limits of agreement were +28.49 and -27.71 Gy cm2, and thus illustrated no proportional bias. The resultant MLR model was considered system-dependent and validated the upgraded angiography system and its advance capabilities to significantly reduce radiation dose. Interventional radiologist and interventional radiographer familiarisation of the system's features and the implementation of the newly established MLR model would further facilitate dose optimisation for all centres performing UAE procedures using the upgraded angiography system.

Surveillance of small, solid pulmonary nodules at digital chest tomosynthesis: data from a cohort of the pilot Swedish CArdioPulmonary bioImage Study (SCAPIS).

BACKGROUND: Digital tomosynthesis (DTS) might be a low-dose/low-cost alternative to computed tomography (CT). PURPOSE: To investigate DTS relative to CT for surveillance of incidental, solid pulmonary nodules. MATERIAL AND METHODS: Recruited from a population study, 106 participants with indeterminate solid pulmonary nodules on CT underwent surveillance with concurrently performed CT and DTS. Nodule size on DTS was assessed by manual diameter measurements and semi-automatic nodule segmentations were independently performed on CT. Measurement agreement was analyzed according to Bland-Altman with 95% limits of agreement (LoA). Detection of nodule volume change > 25% by DTS in comparison to CT was evaluated with receiver operating characteristics (ROC). RESULTS: A total of 81 nodules (76%) were assessed as measurable on DTS by two independent observers. Inter- and intra-observer LoA regarding change in average diameter were ± 2 mm. Calculation of relative volume change on DTS resulted in wide inter- and intra-observer LoA in the order of ± 100% and ± 50%. Comparing relative volume change between DTS and CT resulted in LoA of -58% to 67%. The area under the ROC curve regarding the ability of DTS to detect volumetric changes > 25% on CT was 0.58 (95% confidence interval [CI] = 0.40-0.76) and 0.50 (95% CI = 0.35-0.66) for the two observers. CONCLUSION: The results of the present study show that measurement variability limits the agreement between DTS and CT regarding nodule size change for small solid nodules.

Radiographic and fluoroscopic X-ray systems: Quality control of the X-ray tube and automatic exposure control using theoretical spectra to determine air kerma and dose to a homogenous phantom.

PURPOSE: To develop a method to perform quality control (QC) of X-ray tubes and automatic exposure control (AEC) as a part of the QC of the radiographic and fluoroscopic X-ray system. Our aim is to verify the output from the X-ray tube by comparing the measured radiation output, or air kerma, to the theoretical output given the applied exposure settings and geometry, in addition to comparing the measured kV to the nominal kV. The AEC system for fluoroscopic and conventional X-ray systems is assessed by determining the absorbed dose to a homogenous phantom with different thicknesses. METHOD: This study presents a model to verify the X-ray tube measurement results and a method to determine the dose to a homogenous phantom (Dphantom ). The following input is needed: a parameterized model of the X-ray spectrum, the X-ray tube measurements using a multifunctional X-ray meter, the exposure parameters recorded via imaging of polymethyl methacrylate (PMMA) slabs of different thickness that simulate the patient using AEC, and a parameterized model for calculating the dose to water from Monte Carlo simulations. The output is the entrance surface dose (ESD) and absorbed dose in the phantom, Dphantom (µGy). In addition, the parameterized X-ray spectrum is used to compare theoretical and measured air kerma as a part of the QC of the X-ray tube. To verify the proposed method, the X-ray spectrum provided in this study, SPECTRUM, was compared to two commercially available spectra, SpekCalc and Institute of Physics and Engineering in Medicine (IPEM) 78. The fraction of energy imparted to the homogenous phantom was compared to the imparted fraction calculated by PCXMC. RESULTS: The spectrum provided in this study was in good agreement with two previously published X-ray spectra. The absolute percentage differences of the spectra varied from 0.05% to 3.9%, with an average of 1.4%, compared to SpekCalc. Similarly, the deviation from IPEM report 78 varied from 0.02% to 2.3%, with an average of 0.74%. The SPECTRUM was parameterized for calculation of the imparted fraction for target angles of 10°, 12°, and 15°, kV (50-150 kV) with the materials Al (2.2-8 mm), Cu (0-1 mm), and any combination of the filters, PMMA and water. The deviation of energy imparted from the results by PCXMC was less than 8% for all measurements across different kV, filtration, and vendors, obtained by using PMMA to record the exposure parameters, while the dose was calculated based on water with same thicknesses as the PMMA. CONCLUSION: This study presents an accurate and suitable method to perform a part of the QC of fluoroscopic and conventional X-ray systems with respect to the X-ray tube and the associated AEC system. The method is suitable for comparing protocols within and between systems via the absorbed dose.

Novel method to determine recursive filtration and noise reduction in fluoroscopic imaging - a comparison of four different vendors.

PURPOSE: This study attempted to develop a method to measure the applied recursive filtration and to determine the noise reduction of four different fluoroscopic systems. The study also attempted to elucidate the importance of considering the recursive filter for quality control tests concerning signal-to-noise ratio (SNR) or image quality. The vendor's settings for recursive filtration factor (ß) are, unfortunately, often not available. Hence, a method to determine the recursive filtration and associated noise reduction would be useful. METHOD: The recursive filter was determined by using a single fluoroscopic series and the method presented in this study. The theoretical noise reduction based on the choice of ß was presented. In addition, the corresponding noise reduction, evaluated as the ratio of the standard deviation of the pixel value between a series with ß equal to zero (recursive filtration off) and ß > 0, was determined for different pulse rates given by pulses per second (pps), doses (mAs) and recursive filter. The images were acquired using clinically relevant radiation quality and quantity. RESULTS: The presented method to measure the recursive filter exhibited high accuracy (1.08%) and precision (1.48%). The recursive filtration and noise reduction were measured for several settings for each vendor. The recursive filtration settings and associated recursive filtration factors for four different vendors were presented. CONCLUSIONS: This study presented an accurate method to determine applied recursive filtration, which was easy to determine. Hence, for all quality control purposes, including noise evaluation, it was possible to consider the essential noise reduction given by the settings for recursive filtration. It was also possible to compare the recursive filtration settings and associated recursive filtration within and between vendors.

A case study of cost-benefit analysis in occupational radiological protection within the healthcare system of Sweden.

The aim of the present study was to demonstrate cases of cost-benefit analysis within healthcare, of how economic factors can be considered in occupational radiological protection, in agreement with the as low as reasonably achievable principle and present Swedish legislations. In the first part of the present study, a comparison of examples within health economics used by authorities and institutes in Sweden was made. The comparison focused on value of a statistical life, quality-adjusted life year, and monetary cost assigned to a unit of collective dose for radiation protection purposes (α-value). By this comparison, an α-value was determined as an interval between $45 and $450 per man-mSv, for the Swedish society in 2021. The α-value interval can be interpreted as following: Less than $45 per man-mSv is a good investment. From $45 to $450 per man-mSv, other factors than costs and collective dose are important to consider. More than $450 per man-mSv is too expensive. In the second part of the present study, seven cases of cost-benefit analyses in occupational radiological protection were provided. The present study focused specifically on cases where the relevant factors were costs and collective dose. The present case study shows a large variation in costs per collective dose from different types of occupational radiological protection, used at Skaraborg Hospital in Sweden.

Image quality and radiation dose in planar imaging - Image quality figure of merits from the CDRAD phantom.

PURPOSE: A contrast-detail phantom such as CDRAD is frequently used for quality assurance, optimization of image quality, and several other purposes. However, it is often used without considering the uncertainty of the results. The aim of this study was to assess two figure of merits (FOM) originating from CDRAD regarding the variations of the FOMs by dose utilized to create the x-ray image. The probability of overlapping (assessing an image acquired at a lower dose as better than an image acquired at a higher dose) was determined. METHODS: The CDRAD phantom located underneath 12, 20, and 26 cm PMMA was imaged 16 times at five dose levels using an x-ray system with a flat-panel detector. All images were analyzed by CDRAD Analyser, version 1.1, which calculated the FOM inverse image quality figure (IQFinv ) and gave contrast detail curves for each image. Inherent properties of the CDRAD phantom were used to derive a new FOM h, which describes the size of the hole with the same diameter and depth that is just visible. Data were analyzed using heteroscedastic regression of mean and variance by dose. To ease interpretation, probabilities for overlaps were calculated assuming normal distribution, with associated bootstrap confidence intervals. RESULTS: The proportion of total variability in IQFinv , explained by the dose (R2 ), was 91%, 85%, and 93% for 12, 20, and 26 cm PMMA. Corresponding results for h were 91%, 89%, and 95%. The overlap probability for different mAs levels was 1% for 0.8 vs 1.2 mAs, 5% for 1.2 vs 1.6 mAs, 10% for 1.6 vs 2.0 mAs, and 10% for 2.0 mAs vs 2.5 mAs for 12 cm PMMA. For 20 cm PMMA, it was 0.5% for 10 vs 16 mAs, 13% for 16 vs 20 mAs, 14% for 20 vs 25 mAs, and 14% for 25 vs 32 mAs. For 26 cm PMMA, the probability varied from 0% to 6% for various mAs levels. Even though the estimated probability for overlap was small, the 95% confidence interval (CI) showed relatively large uncertainties. For 12 cm PMMA, the associated CI for 0.8 vs 1.2 mAs was 0.1-3.2%, and the CI for 1.2 vs 1.6 mAs was 2.1-7.8%. CONCLUSIONS: Inverse image quality figure and h are about equally related to dose level. The FOM h, which describes the size of a hole that should be seen in the image, may be a more intuitive FOM than IQFinv . However, considering the probabilities for overlap and their confidence intervals, the FOMs deduced from the CDRAD phantom are not sensitive to dose. Hence, CDRAD may not be an optimal phantom to differentiate between images acquired at different dose levels.

Can adaptive post-processing of storage phosphor plate panoramic radiographs provide better image quality? A comparison of anatomical image quality of panoramic radiographs before and after adaptive processing.

OBJECTIVE: The objective of the present study was to study the effect of adaptive image processing on the visibility of anatomical structures in storage phosphor plate (SPP) panoramic images. MATERIALS AND METHODS: Three hundred SPP panoramic X-ray radiographs of children and adolescents were used. The radiographs were post-processed using general operator processor (GOP) technology, resulting in both a standard-processed and a GOP-processed radiograph. Four specialists in dental radiology compared the structural image quality of all standard-processed and GOP-processed panorama images for six anatomical structures, using a six-point scale for visual grading characteristics (VGC) analysis. RESULTS: For three of the anatomic structures - the root canal space of the mandibular left first premolar, mandibular canal left side and periodontal ligament space of the mandibular right first molar - there was a statistically significant difference to the GOP's advantage. For the three remaining structures - dentino-enamel junction of the maxillary right first molar, crista alveolaris of the mandibular left molar area and floor of maxillary sinus right side - no significant difference between standard processing and GOP processing was obtained. CONCLUSIONS: The study demonstrates that it is possible to improve the quality of SPP radiographs and the visibility of anatomical structures by using the GOP technique. Manufacturers' image-processing programs can be further developed, as there is a possibility of improving the diagnostic content of an image with external processing.

A comparison of perceived diagnostic image quality in direct digital panoramic images between standard and advanced external GOP image processing.

Objective: The objective of the present study was to study the effect of adaptive image processing (GOP processing) on the visibility of anatomical structures in direct digital panoramic images. Material and methods: The study comprised panoramic images of 50 consecutive adult individuals aged 18-60 years. Nine dentists working with dental radiology compared the structural image quality of all standard-processed and GOP-processed panoramic images for six anatomical structures, using a six-point scale for visual grading characteristics analysis. Results: For all anatomic structures a statistically significant difference in favour of the GOP was found. Conclusions: The present study shows that it is possible to improve perceived diagnostic image quality of direct digital panoramic radiography using GOP technology compared to the manufacturers' standard processing. Manufacturers' image-processing programs can be further developed, as there is a possibility of improving the perceived diagnostic content of an image with external processing.

Detection and Characterization of Solid Pulmonary Nodules at Digital Chest Tomosynthesis: Data from a Cohort of the Pilot Swedish Cardiopulmonary Bioimage Study.

Purpose To investigate the performance of digital tomosynthesis (DTS) for detection and characterization of incidental solid lung nodules. Materials and Methods This prospective study was based on a population study with 1111 randomly selected participants (age range, 50-64 years) who underwent a medical evaluation that included chest computed tomography (CT). Among these, 125 participants with incidental nodules 5 mm or larger were included in this study, which added DTS in conjunction with the follow-up CT and was performed between March 2012 and October 2014. DTS images were assessed by four thoracic radiologists blinded to the true number of nodules in two separate sessions according to the 5-mm (125 participants) and 6-mm (55 participants) cut-off for follow-up of incidental nodules. Pulmonary nodules were directly marked on the images by the readers and graded regarding confidence of presence and recommendation for follow-up. Statistical analyses included jackknife free-response receiver operating characteristic, receiver operating characteristic, and Cohen κ coefficient. Results Overall detection rate ranges of CT-proven nodules 5 mm or larger and 6 mm or larger were, respectively, 49%-58% and 48%-62%. Jackknife free-response receiver operating characteristics figure of merit for detection of CT-proven nodules 5 mm or larger and 6 mm or larger was 0.47 and 0.51, respectively, and area under the receiver operating characteristic curve regarding recommendation for follow-up was 0.62 and 0.65, respectively. Conclusion Routine use of DTS would result in lower detection rates and reduced number of small nodules recommended for follow-up. © RSNA, 2018.

Method for automatic detection of defective ultrasound linear array transducers based on uniformity assessment of clinical images - A case study.

The purpose of the present study was to test an idea of and describe a concept of a novel method of detecting defects related to horizontal nonuniformities in ultrasound equipment. The method is based on the analysis of ultrasound images collected directly from the clinical workflow. In total over 31000 images from three ultrasound scanners from two vendors were collected retrospectively from a database. An algorithm was developed and applied to the images, 150 at a time, for detection of systematic dark regions in the superficial part of the images. The result was compared with electrical measurements (FirstCall) of the transducers, performed at times when the transducers were known to be defective. The algorithm made similar detection of horizontal nonuniformities for images acquired at different time points over long periods of time. The results showed good subjective visual agreement with the available electrical measurements of the defective transducers, indicating a potential use of clinical images for early and automatic detection of defective transducers, as a complement to quality control.

Multi-Institutional Evaluation of Digital Tomosynthesis, Dual-Energy Radiography, and Conventional Chest Radiography for the Detection and Management of Pulmonary Nodules.

Purpose To conduct a multi-institutional, multireader study to compare the performance of digital tomosynthesis, dual-energy (DE) imaging, and conventional chest radiography for pulmonary nodule detection and management. Materials and Methods In this binational, institutional review board-approved, HIPAA-compliant prospective study, 158 subjects (43 subjects with normal findings) were enrolled at four institutions. Informed consent was obtained prior to enrollment. Subjects underwent chest computed tomography (CT) and imaging with conventional chest radiography (posteroanterior and lateral), DE imaging, and tomosynthesis with a flat-panel imaging device. Three experienced thoracic radiologists identified true locations of nodules (n = 516, 3-20-mm diameters) with CT and recommended case management by using Fleischner Society guidelines. Five other radiologists marked nodules and indicated case management by using images from conventional chest radiography, conventional chest radiography plus DE imaging, tomosynthesis, and tomosynthesis plus DE imaging. Sensitivity, specificity, and overall accuracy were measured by using the free-response receiver operating characteristic method and the receiver operating characteristic method for nodule detection and case management, respectively. Results were further analyzed according to nodule diameter categories (3-4 mm, >4 mm to 6 mm, >6 mm to 8 mm, and >8 mm to 20 mm). Results Maximum lesion localization fraction was higher for tomosynthesis than for conventional chest radiography in all nodule size categories (3.55-fold for all nodules, P < .001; 95% confidence interval [CI]: 2.96, 4.15). Case-level sensitivity was higher with tomosynthesis than with conventional chest radiography for all nodules (1.49-fold, P < .001; 95% CI: 1.25, 1.73). Case management decisions showed better overall accuracy with tomosynthesis than with conventional chest radiography, as given by the area under the receiver operating characteristic curve (1.23-fold, P < .001; 95% CI: 1.15, 1.32). There were no differences in any specificity measures. DE imaging did not significantly affect nodule detection when paired with either conventional chest radiography or tomosynthesis. Conclusion Tomosynthesis outperformed conventional chest radiography for lung nodule detection and determination of case management; DE imaging did not show significant differences over conventional chest radiography or tomosynthesis alone. These findings indicate performance likely achievable with a range of reader expertise. © RSNA, 2016 Online supplemental material is available for this article.

Evaluation of a corrected implementation of a method of simulating pulmonary nodules in chest tomosynthesis.

Background A method of simulating pulmonary nodules in tomosynthesis images has previously been developed and evaluated. An unknown feature of a rounding function included in the computer code was later found to introduce an artifact, affecting simulated nodules in low-signal regions of the images. The computer code has now been corrected. Purpose To perform a thorough evaluation of the corrected nodule-simulation method, comparing the detection rate and visual appearance of artificial nodules with those of real nodules in an observer performance experiment. Material and Methods A cohort of 64 patients with a total of 129 pulmonary nodules was used in the study. Artificial nodules, each matching a corresponding real nodule by size, attenuation, and anatomical location, were generated and simulated into the tomosynthesis images of the different patients. The detection rate and visual appearance of artificial nodules generated using both the corrected and uncorrected computer code were compared to those of real nodules. The results were evaluated using modified receiver operating characteristic (ROC) analyses. Results The difference in detection rate between artificial and real nodules slightly increased using the corrected computer code (uncorrected code: area under the curve [AUC], 0.47; 95% CI, 0.43-0.51; corrected code: AUC, 0.42; 95% CI, 0.38-0.46). The visual appearance was however substantially improved using the corrected computer code (uncorrected code: AUC, 0.70; 95% CI, 0.63-0.76; corrected code: AUC, 0.49; 95% CI, 0.29-0.65). Conclusion The computer code including a correct rounding function generates simulated nodules that are more visually realistic than simulated nodules generated using the uncorrected computer code, but have a slightly different detection rate compared to real nodules.

Estimating effective dose from 3D imaging with interventional fluoroscopy systems using limited exposure data.

BACKGROUND: Estimations of the effective dose from three-dimensional (3D) rotational imaging with interventional fluoroscopy systems are hampered by the fact that not all systems provide individual exposure values for each projection image included in the examination. PURPOSE: To investigate the error in resulting effective dose introduced by not using individual exposure values for each projection image in the dose calculations for 3D rotational imaging with interventional fluoroscopy systems. MATERIAL AND METHODS: An interventional fluoroscopy system was used to acquire images of two anthropomorphic phantoms. Calculations of the effective dose were performed using two different methods: 1, using individual exposure values for each projection image; and 2, using the mean tube voltage and the total dose-area product (DAP), evenly distributed over a selection of projection images. The second method was also tested in hypothetical examinations to investigate the effects of worst-case scenarios regarding the effect of exposure asymmetry on the error. RESULTS: The error in resulting effective dose obtained when simplifying the dose calculations by using Method 2 instead of Method 1 was within ±14%. The error increased slightly for the worst-case scenarios but was still smaller than ±20%, regardless of anatomical region, tube voltage variation, and patient size. CONCLUSION: Given the uncertainties associated with the effective dose concept as well as of reported DAP values, the present study indicates that dose calculations based on average exposure values distributed over a smaller selection of projection angles can provide reasonably accurate estimations of the radiation doses from 3D imaging using interventional fluoroscopy systems.

Comparison of the low-contrast detectability of two ultrasound systems using a grayscale phantom.

The purpose of the present study was to evaluate the relevance of using a phantom to simulate a clinical situation where small low contrast objects are embedded in relatively homogeneous organs in order to discriminate between different ultrasound machines, taking into account human observer variability. One high-end and one general ultrasound machine using the same probe were included. Images containing 4 and 6.4-mm objects of four different contrasts were collected from a greyscale phantom at different depths. Six observers participated in a 4-alternative forced choice study based on 960 images. Variability was determined using bootstrapping. At four of sixteen depth/size/contrast combinations, the visual performance of the high-end machine was significantly higher. The results indicate that it is possible to use a greyscale phantom to discriminate between ultrasound machines in terms of their ability to reproduce clinically relevant low-contrast objects. However, the number of images and number of observers needed are larger than those usually used for constancy control, if the large uncertainties caused by human observer variability is to be taken correctly into account.

Optimization of exposure in panoramic radiography while maintaining image quality using adaptive filtering.

Objective The purpose of the present study was to investigate the potential of using advanced external adaptive image processing for maintaining image quality while reducing exposure in dental panoramic storage phosphor plate (SPP) radiography. Materials and methods Thirty-seven SPP radiographs of a skull phantom were acquired using a Scanora panoramic X-ray machine with various tube load, tube voltage, SPP sensitivity and filtration settings. The radiographs were processed using General Operator Processor (GOP) technology. Fifteen dentists, all within the dental radiology field, compared the structural image quality of each radiograph with a reference image on a 5-point rating scale in a visual grading characteristics (VGC) study. The reference image was acquired with the acquisition parameters commonly used in daily operation (70 kVp, 150 mAs and sensitivity class 200) and processed using the standard process parameters supplied by the modality vendor. Results All GOP-processed images with similar (or higher) dose as the reference image resulted in higher image quality than the reference. All GOP-processed images with similar image quality as the reference image were acquired at a lower dose than the reference. This indicates that the external image processing improved the image quality compared with the standard processing. Regarding acquisition parameters, no strong dependency of the image quality on the radiation quality was seen and the image quality was mainly affected by the dose. Conclusions The present study indicates that advanced external adaptive image processing may be beneficial in panoramic radiography for increasing the image quality of SPP radiographs or for reducing the exposure while maintaining image quality.

Effect of radiation dose level on the detectability of pulmonary nodules in chest tomosynthesis.

OBJECTIVE: To investigate the detectability of pulmonary nodules in chest tomosynthesis at reduced radiation dose levels. METHODS: Eighty-six patients were included in the study and were examined with tomosynthesis and computed tomography (CT). Artificial noise was added to simulate that the tomosynthesis images were acquired at dose levels corresponding to 12, 32, and 70% of the default setting effective dose (0.12 mSv). Three observers (with >20, >20 and three years of experience) read the tomosynthesis cases for presence of nodules in a free-response receiver operating characteristics (FROC) study. CT served as reference. Differences between dose levels were calculated using the jack-knife alternative FROC (JAFROC) figure of merit (FOM). RESULTS: The JAFROC FOM was 0.45, 0.54, 0.55, and 0.54 for the 12, 32, 70, and 100% dose levels, respectively. The differences in FOM between the 12% dose level and the 32, 70, and 100% dose levels were 0.087 (p = 0.006), 0.099 (p = 0.003), and 0.093 (p = 0.004), respectively. Between higher dose levels, no significant differences were found. CONCLUSIONS: A substantial reduction from the default setting dose in chest tomosynthesis may be possible. In the present study, no statistically significant difference in detectability of pulmonary nodules was found when reducing the radiation dose to 32%. KEY POINTS: • A substantial radiation dose reduction in chest tomosynthesis may be possible. • Pulmonary nodule detectability remained unchanged at 32% of the effective dose. • Tomosynthesis might be performed at the dose of a lateral chest radiograph.

Chest tomosynthesis: technical and clinical perspectives.

The recent implementation of chest tomosynthesis is built on the availability of large, dose-efficient, high-resolution flat panel detectors, which enable the acquisition of the necessary number of projection radiographs to allow reconstruction of section images of the chest within one breath hold. A chest tomosynthesis examination obtains the increased diagnostic information provided by volumetric imaging at a radiation dose comparable to that of conventional chest radiography. There is evidence that the sensitivity of chest tomosynthesis may be at least three times higher than for conventional chest radiography for detection of pulmonary nodules. The sensitivity increases with increasing nodule size and attenuation and decreases for nodules with subpleural location. Differentiation between pleural and subpleural lesions is a known pitfall due to the limited depth resolution in chest tomosynthesis. Studies on different types of pathology report increased detectability in favor of chest tomosynthesis in comparison to chest radiography. The technique provides improved diagnostic accuracy and confidence in the diagnosis of suspected pulmonary lesions on chest radiography and facilitates the exclusion of pulmonary lesions in a majority of patients, avoiding the need for computed tomography (CT). However, motion artifacts can be a cumbersome limitation and breathing during the tomosynthesis image acquisition may result in severe artifacts significantly affecting the detectability of pathology. In summary, chest tomosynthesis has been shown to be superior to chest conventional radiography for many tasks and to be able to replace CT in selected cases. In our experience chest tomosynthesis is an efficient problem solver in daily clinical work.

An Estimation of the Monetary Value of the Person-Sievert Useful for Occupational Radiological Protection within the Healthcare System of Sweden.

ABSTRACT: The As Low As Reasonably Achievable (ALARA) principle includes taking into account economic and societal factors. To consider these factors, decision-aiding techniques such as cost-benefit analysis were introduced by the International Commission on Radiological Protection (ICRP) 50 y ago. Over the years, developments in health economics have led to new ways of deriving the concept of a value of a statistical life (VSL), which now is influencing the monetary value assigned to a unit of collective dose for radiological protection purposes (the α value) used in cost-benefit analyses. The aim of the present study was to estimate an α value useful for occupational radiological protection within the healthcare system of Sweden. A survey based on the stated preference approach was developed and sent to staff who are exposed to ionizing radiation at their work in Region Västra Götaland (Sweden). The survey essentially contained two scenarios: the respondents' willingness to pay for measures against radon exposure at home and their willingness to accept compensation for x-ray exposure at work. Answers from 718 respondents were collected. In the sensitivity analysis of the survey, the overall median VSL based on the two scenarios was calculated to be $50 million (IQR $10 to 363 million). The corresponding α value was established to $1,600 person-mSv -1 ($2,100 person-mSv -1 if excess burden of taxes is excluded). The recommended α value is in the high end compared to other studies but within the interval of values being used by nuclear utilities today. The α value should be seen in the light of ICRP's recommendation about stakeholder involvement as an important part of the optimization process.

Visualization of the distortion induced by nonlinear noise reduction in computed tomography.

Purpose: We developed a method to visualize the image distortion induced by nonlinear noise reduction algorithms in computed tomography (CT) systems. Approach: Nonlinear distortion was defined as the induced residual when testing a reconstruction algorithm by the criteria for a linear system. Two types of images were developed: a nonlinear distortion of an object (NLDobject) image and a nonlinear distortion of noise (NLDnoise) image to visualize the nonlinear distortion induced by an algorithm. Calculation of the images requires access to the sinogram data, which is seldomly fully provided. Hence, an approximation of the NLDobject image was estimated. Using simulated CT acquisitions, four noise levels were added onto forward projected sinograms of a typical CT image; these were noise reduced using a median filter with the simultaneous iterative reconstruction technique or a total variation filter with the conjugate gradient least-squares algorithm. The linear reconstruction technique filtered back-projection was also analyzed for comparison. Results: Structures in the NLDobject image indicated contrast and resolution reduction of the nonlinear denoising. Although the approximated NLDobject image represented the original NLDobject image well, it had a higher random uncertainty. The NLDnoise image for the median filter indicated both stochastic variations and structures reminding of the object while for the total variation filter only stochastic variations were indicated. Conclusions: The developed images visualize nonlinear distortions of denoising algorithms. The object may be distorted by the noise and vice versa. Analyzing the distortion correlated to the object is more critical than analyzing a distortion of stochastic variations. The absence of nonlinear distortion may measure the robustness of the denoising algorithm.