Strategies for Reducing Radiation Exposure From Multidetector Computed Tomography in the Acute Care Setting

Many tools and strategies exist to enable reduction of radiation exposure from computed tomography (CT). The common CT metrics of x-ray output, the volume CT dose index and the dose-length product, are explained and serve as the basis for monitoring radiation exposure from CT. Many strategies to dose-optimize CT protocols are explored that, in combination with available hardware and software tools, allow robust diagnostic quality CT to be performed with a radiation exposure appropriate for the clinical scenario and the size of the patient. Specific emergency department example protocols are used to demonstrate these techniques.     

Radiation Dose from Diagnostic Computed Tomography in Saskatchewan

Objective

To calculate the effective dose from diagnostic computed tomography (CT) scans in Saskatchewan, Canada, and compare with other reported dose levels.

Methods

Data from CT scans were collected from 12 scanners in 7 cities across Saskatchewan. The patient age, scan type, and selected technique parameters including the dose length product and the volume computed tomography dose index were collected for a 2-week period. This information then was used to calculate effective doses patients are exposed to during CT examinations. Data from 2,061 clinically indicated CT examinations were collected, and of them 1,690 were eligible for analysis. Every examination during a 2-week period was recorded without selection.

Results

The average provincial estimated patient dose was as follows: head, 2.7 mSv (638 scans; standard deviation [SD], ±1.6); chest, 11.3 mSv (376 scans; SD, ±8.9); abdomen-pelvis, 15.5 mSv (578 scans; SD, ±10.0); abdomen, 11.7 mSv (80 scans; SD, ±11.48), and pelvis, 8.6 mSv (18 scans; SD, ±6.04). Significant variation in dose between the CT scanners was observed (P = .049 for head, P = .001 for chest, and P = .034 for abdomen-pelvis).

Conclusions

Overall, the estimated dose from diagnostic CT examinations was similar to other previously published Canadian data from British Columbia. This dose varied slightly from some other published standards, including being higher than those found in a review conducted in the United Kingdom in 2003.     

Image Quality in Low-dose Multidetector Computed Tomography: A Pilot Study to Assess Feasibility and Dose Optimization in Whole-body Bone Imaging

Objective

To study the impact of dose parameters on image quality at whole-body low-dose multidetector computed tomography (CT) in an attempt to derive parameters that allow diagnostic quality images of the skeletal system without incurring significant radiation dose in patients referred for investigation of plasma cell dyscrasias.

Methods

By using a single cadaver, 14 different whole-body low-dose CT protocols were individually assessed by 2 radiologists, blinded to acquisition parameters (kVp and mAs, reconstruction algorithm, dose reduction software). Combinations of kVps that range from 80-140 kVp, and tube current time product from 14–125 mAs were individually scored by using a Likert scale from 1–5 in 4 separate anatomical areas (skull base, thoracic spine, pelvis, and distal femora). Correlation between readers scores and effective doses were obtained by using correlation coefficient statistical analysis, statistical significance was considered P < .01. Interobserver agreement was assessed by using a Bland and Altman plot. Interobserver agreement in each of the 4 anatomical areas was assessed by using kappa statistics. A single set of parameters was then selected for use in future clinical trials in a cohort of patients referred for investigation of monoclonal gammopathy, including multiple myeloma.

Results

Several sets of exposure parameters allowed low-dose whole-body CT to be performed with effective doses similar to skeletal survey while preserving diagnostic image quality. Individual reader's and average combined scores showed a strong inverse correlation with effective dose (reader 1, r = –0.78, P = .0001; reader 2, r = –0.75, P = .0003); average combined scores r = –0.81, P < .0001). Bland and Altman plot of overall scores shows reasonable interobserver agreement, with a mean difference of 1.055.

Conclusion

Whole-body low-dose CT can be used to obtain adequate CT image quality to assess normal osseous detail while delivering effective doses similar to those associated with conventional radiographic skeletal survey.     

Referral Patterns for Dual-Energy Computed Tomography in Diagnosis and Management of Gout: Ten-Year Experience at a Canadian Institution

Purpose

To analyze the utilization, indications, and outcomes of dual-energy computed tomography (DECT) gout imaging in clinical practice.

Establishment of Local Diagnostic Reference Levels of Pediatric Abdominopelvic and Chest CT Examinations Based on the Body Weight and Size in Korea

ObjectiveThe purposes of this study were to analyze the radiation doses for pediatric abdominopelvic and chest CT examinations from university hospitals in Korea and to establish the local diagnostic reference levels (DRLs) based on the body weight and size.Materials and MethodsAt seven university hospitals in Korea, 2494 CT examinations of patients aged 15 years or younger (1625 abdominopelvic and 869 chest CT examinations) between January and December 2017 were analyzed in this study. CT scans were transferred to commercial automated dose management software for the analysis after being de-identified. DRLs were calculated after grouping the patients according to the body weight and effective diameter. DRLs were set at the 75th percentile of the distribution of each institution''s typical values.ResultsFor body weights of 5, 15, 30, 50, and 80 kg, DRLs (volume CT dose index [CTDI_vol]) were 1.4, 2.2, 2.7, 4.0, and 4.7 mGy, respectively, for abdominopelvic CT and 1.2, 1.5, 2.3, 3.7, and 5.8 mGy, respectively, for chest CT. For effective diameters of < 13 cm, 14–16 cm, 17–20 cm, 21–24 cm, and > 24 cm, DRLs (size-specific dose estimates [SSDE]) were 4.1, 5.0, 5.7, 7.1, and 7.2 mGy, respectively, for abdominopelvic CT and 2.8, 4.6, 4.3, 5.3, and 7.5 mGy, respectively, for chest CT. SSDE was greater than CTDI_vol in all age groups. Overall, the local DRL was lower than DRLs in previously conducted dose surveys and other countries.ConclusionOur study set local DRLs in pediatric abdominopelvic and chest CT examinations for the body weight and size. Further research involving more facilities and CT examinations is required to develop national DRLs and update the current DRLs.     

Dose quantities for characterization of patients' exposure to radiation in computed tomography and their significance for risk estimation

Summary In order to evaluate patients' exposure to radiation in computed tomography, dose quantities such as the computed tomography dose index (CTDI), multiple scan average dose (MSAD) and dose free in air on the axis of rotation are used. The CTDI and the MSAD, derivable from the CTDI, are a good measure for the absorbed doses in the examined volume, but they do not take the biological sensitivity of the organs into account and do not describe the radiogenic risk that is actually relevant for patients and doctors. The dose on the axis of rotation is not an accurate measure of the effective dose and the radiogenic risk. The declaration of a limit for the dose on the axis of rotation should take the different regions into account, in order to guarantee acceptable image quality on one hand and to avoid an unnecessarily high risk on the other side. As physical dose quantities, the CTDI, MSAD and dose on the axis of rotation are useful to characterize and differentiate between programs and systems concerning radiation exposure. Eingegangen am 16. Dezember 1996 Nach überarbeitung angenommen am 14. M?rz 1997     

Performance of Prediction Models for Diagnosing Severe Aortic Stenosis Based on Aortic Valve Calcium on Cardiac Computed Tomography: Incorporation of Radiomics and Machine Learning

ObjectiveWe aimed to develop a prediction model for diagnosing severe aortic stenosis (AS) using computed tomography (CT) radiomics features of aortic valve calcium (AVC) and machine learning (ML) algorithms.Materials and MethodsWe retrospectively enrolled 408 patients who underwent cardiac CT between March 2010 and August 2017 and had echocardiographic examinations (240 patients with severe AS on echocardiography [the severe AS group] and 168 patients without severe AS [the non-severe AS group]). Data were divided into a training set (312 patients) and a validation set (96 patients). Using non-contrast-enhanced cardiac CT scans, AVC was segmented, and 128 radiomics features for AVC were extracted. After feature selection was performed with three ML algorithms (least absolute shrinkage and selection operator [LASSO], random forests [RFs], and eXtreme Gradient Boosting [XGBoost]), model classifiers for diagnosing severe AS on echocardiography were developed in combination with three different model classifier methods (logistic regression, RF, and XGBoost). The performance (c-index) of each radiomics prediction model was compared with predictions based on AVC volume and score.ResultsThe radiomics scores derived from LASSO were significantly different between the severe AS and non-severe AS groups in the validation set (median, 1.563 vs. 0.197, respectively, p < 0.001). A radiomics prediction model based on feature selection by LASSO + model classifier by XGBoost showed the highest c-index of 0.921 (95% confidence interval [CI], 0.869–0.973) in the validation set. Compared to prediction models based on AVC volume and score (c-indexes of 0.894 [95% CI, 0.815–0.948] and 0.899 [95% CI, 0.820–0.951], respectively), eight and three of the nine radiomics prediction models showed higher discrimination abilities for severe AS. However, the differences were not statistically significant (p > 0.05 for all).ConclusionModels based on the radiomics features of AVC and ML algorithms may perform well for diagnosing severe AS, but the added value compared to AVC volume and score should be investigated further.     

Cycle-Consistent Generative Adversarial Network: Effect on Radiation Dose Reduction and Image Quality Improvement in Ultralow-Dose CT for Evaluation of Pulmonary Tuberculosis

ObjectiveTo investigate the image quality of ultralow-dose CT (ULDCT) of the chest reconstructed using a cycle-consistent generative adversarial network (CycleGAN)-based deep learning method in the evaluation of pulmonary tuberculosis.Materials and MethodsBetween June 2019 and November 2019, 103 patients (mean age, 40.8 ± 13.6 years; 61 men and 42 women) with pulmonary tuberculosis were prospectively enrolled to undergo standard-dose CT (120 kVp with automated exposure control), followed immediately by ULDCT (80 kVp and 10 mAs). The images of the two successive scans were used to train the CycleGAN framework for image-to-image translation. The denoising efficacy of the CycleGAN algorithm was compared with that of hybrid and model-based iterative reconstruction. Repeated-measures analysis of variance and Wilcoxon signed-rank test were performed to compare the objective measurements and the subjective image quality scores, respectively.ResultsWith the optimized CycleGAN denoising model, using the ULDCT images as input, the peak signal-to-noise ratio and structural similarity index improved by 2.0 dB and 0.21, respectively. The CycleGAN-generated denoised ULDCT images typically provided satisfactory image quality for optimal visibility of anatomic structures and pathological findings, with a lower level of image noise (mean ± standard deviation [SD], 19.5 ± 3.0 Hounsfield unit [HU]) than that of the hybrid (66.3 ± 10.5 HU, p < 0.001) and a similar noise level to model-based iterative reconstruction (19.6 ± 2.6 HU, p > 0.908). The CycleGAN-generated images showed the highest contrast-to-noise ratios for the pulmonary lesions, followed by the model-based and hybrid iterative reconstruction. The mean effective radiation dose of ULDCT was 0.12 mSv with a mean 93.9% reduction compared to standard-dose CT.ConclusionThe optimized CycleGAN technique may allow the synthesis of diagnostically acceptable images from ULDCT of the chest for the evaluation of pulmonary tuberculosis.     

2019—2020年某院眼科住院患者X射线检查模式的变化及其对辐射剂量水平的影响

目的通过分析比较眼科病房住院患者X射线检查部位及辐射剂量构成, 探讨近年X射线检查模式的变化与推行的技术优化对患者辐射剂量水平的影响。方法采用简单随机抽样法回顾性调取浙江大学医学院附属第二医院2019年7月1日至2019年11月31日及2020年7月1日至2020年11月31日眼科病房住院患者的影像学资料, 共516例, 根据检查时间选取2019年258例、2020年258例。依据前期研究成果并结合低剂量CT筛查的相关文献, 项目组在2020年对CT扫描参数与流程进行了一系列优化, 统计优化前后单次检查剂量, 统计两年数字X射线摄影(Digital Radiography, DR)和CT检查的人次、人均检查次数、CT与DR的构成比、人均X射线受检剂量。结果 2020年眼科住院患者胸部CT、眼眶CT的平均有效剂量分别为2.587±1.586 mSv和0.877±0.733 mSv, 明显低于2019年(F=0.52、0.72, P<0.05), 分别降低34.82%、37.13%;胸部DR与头颅CT的平均有效剂量2020年与2019年比较差异无统计学意义(F=6.01、1.81, ...     

An Environmental Scan of the National and Provincial Diagnostic Reference Levels in Canada for Common Adult Computed Tomography Scans

Several regulatory bodies have agreed that low-dose radiation used in medical imaging is a weak carcinogen that follows a linear, non-threshold model of cancer risk. While avoiding radiation is the best course of action to mitigate risk, computed tomography (CT) scans are often critical for diagnosis. In addition to the as low as reasonably achievable principle, a more concrete method of dose reduction for common CT imaging exams is the use of a diagnostic reference level (DRL). This paper examines Canada's national DRL values from the recent CT survey and compares it to published provincial DRLs as well as the DRLs in the United Kingdom and the United States of America for the 3 most common CT exams: head, chest, and abdomen/pelvis. Canada compares well on the international scale, but it should consider using more electronic dose monitoring solutions to create a culture of dose optimization.     

Radiation Dose Reduction With a Low-Tube Voltage Technique for Pediatric Chest Computed Tomographic Angiography Based on the Contrast-to-Noise Ratio Index

Introduction

The aim of this study was to evaluate the radiation dose and image quality at low tube-voltage pediatric chest computed tomographic angiography (CTA) that applies the same contrast-to-noise ratio (CNR) index as the standard tube voltage technique.

New Method for Combined Quantitative Assessment of Air-Trapping and Emphysema on Chest Computed Tomography in Chronic Obstructive Pulmonary Disease: Comparison with Parametric Response Mapping

ObjectiveEmphysema and small-airway disease are the two major components of chronic obstructive pulmonary disease (COPD). We propose a novel method of quantitative computed tomography (CT) emphysema air-trapping composite (EAtC) mapping to assess each COPD component. We analyzed the potential use of this method for assessing lung function in patients with COPD.Materials and MethodsA total of 584 patients with COPD underwent inspiration and expiration CTs. Using pairwise analysis of inspiration and expiration CTs with non-rigid registration, EAtC mapping classified lung parenchyma into three areas: Normal, functional air trapping (fAT), and emphysema (Emph). We defined fAT as the area with a density change of less than 60 Hounsfield units (HU) between inspiration and expiration CTs among areas with a density less than −856 HU on inspiration CT. The volume fraction of each area was compared with clinical parameters and pulmonary function tests (PFTs). The results were compared with those of parametric response mapping (PRM) analysis.ResultsThe relative volumes of the EAtC classes differed according to the Global Initiative for Chronic Obstructive Lung Disease stages (p < 0.001). Each class showed moderate correlations with forced expiratory volume in 1 second (FEV₁) and FEV₁/forced vital capacity (FVC) (r = −0.659–0.674, p < 0.001). Both fAT and Emph were significant predictors of FEV₁ and FEV₁/FVC (R² = 0.352 and 0.488, respectively; p < 0.001). fAT was a significant predictor of mean forced expiratory flow between 25% and 75% and residual volume/total vital capacity (R² = 0.264 and 0.233, respectively; p < 0.001), while Emph and age were significant predictors of carbon monoxide diffusing capacity (R² = 0.303; p < 0.001). fAT showed better correlations with PFTs than with small-airway disease on PRM.ConclusionThe proposed quantitative CT EAtC mapping provides comprehensive lung functional information on each disease component of COPD, which may serve as an imaging biomarker of lung function.     

Computed Tomography Fluoroscopy–Guided Percutaneous Transhepatic Bleomycin/Ethiodized Oil Sclerotherapy for Symptomatic Giant Hepatic Hemangioma

PurposeTo determine the safety and efficacy of computed tomography (CT) fluoroscopy–guided percutaneous transhepatic sclerotherapy with a bleomycin/ethiodized oil emulsion for symptomatic giant hepatic hemangiomas.Materials and MethodsThe procedure was performed on 22 patients with symptomatic giant hepatic hemangiomas in an outpatient setting between 2018 and 2020. All patients were followed clinically and underwent contrast-enhanced magnetic resonance imaging after 1 month and again at a mean time of 15 months ± 2. Adverse events were classified according to the Common Terminology Criteria for Adverse Events (CTCAE, v5.0), in which a severe adverse event was defined as an adverse event with a grade of ≥3. The desired radiologic response (volume and index size) and improvement of pain intensity (visual analog scale [VAS]) and other symptoms were recorded as outcomes.ResultsOverall, patients showed a 36.4% ± 8.6 reduction in volume and a 14% ± 1.6 reduction in index size after 1 month, with P values of .002 and .001, respectively. The final follow-up volume and index size were 194.7 cm³ ± 25.8 and 77 mm ± 36, respectively. Moreover, a 53.0% ± 7 reduction in volume and 22% ± 3.7 reduction in index size during the final imaging were reported, with the P values of .001 and .001, respectively. Significant reductions in the mean pain intensity (90% of patients with lower VAS scores after intervention) and symptoms were reported. Four patients were classified as clinically unsuccessful, and were recommended further procedures for residual pain.ConclusionsCT fluoroscopy–guided transhepatic sclerotherapy is an effective, safe, and minimally invasive method to manage giant hepatic hemangiomas in an outpatient setting.