儿童胸部CT中病人的特定放射剂量与癌症风险

目的评估儿童胸部CT中病人的特定放射剂量与癌症风险,评价影响剂量与风险的因素,包括病人体型、年龄和扫描参数。材料与方法经伦理委员会批准,无需病人知情同意。本研究符合HIPAA。30例病人(0～16岁),根据临床CT数据新近为他们制作了全身计算机模型。代表临床的8个胸部扫描方案,相关参数组合包括领结过滤、准直、     

Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT

PURPOSE: To calculate mean fetal radiation dose from helical chest computed tomography (CT) by using maternal-fetal geometries obtained from healthy pregnant women and to compare the calculated CT doses with the fetal doses reported with scintigraphy. MATERIALS AND METHODS: Maternal-fetal geometries were determined in 23 pregnant women with varying body mass index and fetal gestational age. Monte Carlo techniques were used to estimate the dose that would be received by each fetus from CT scanning performed with the following parameters: 120 kVp; 100 mA; scanning time, 1 second per section; collimation, 2.5 mm; pitch of 1. Craniocaudal extent of the scan was 11 cm, with the most caudal section edge being 5 mm inferior to the xiphoid process. RESULTS: For helical CT, estimated mean fetal doses in micrograys at varying gestational ages were as follows: 3.3-20.2 microGy, first trimester; 7.9-76.7 microGy, second trimester; and 51.3-130.8 microGy, third trimester. These values were all less than mean fetal doses reported with scintigraphy, with 37-74 MBq of macroaggregates of human serum albumin labeled with technetium 99m. If 200 mAs (pitch of 1.8) was used, the mean fetal doses were still less than those with scintigraphy. CONCLUSION: The average fetal radiation dose with helical CT is less than that with ventilation-perfusion lung scanning during all trimesters.     

Computer-simulated radiation dose reduction for abdominal multidetector CT of pediatric patients

OBJECTIVE. Limiting CT radiation dose is especially critical when imaging children. The purpose of our study was to modify and test an accurate and safe tool for evaluating systematic dose reduction for abdominal multidetector CT (MDCT) in pediatric patients. MATERIALS AND METHODS: After validating the computer-simulation technique with a water phantom, we subjected the original digital scanning data for 26 contrast-enhanced abdominal MDCT scans (120 mA) obtained in infants and children (age range, 1 month-9 years; mean age, 3.1 years) to simulated tube current reduction (100, 80, 60, and 40 mA) by adding noise. this procedure created four additional examinations per child that were identical to the originals except for image noise. The 130 examinations were scored randomly, independently, and without prior knowledge of the children's diagnoses by three radiologists for depiction of high-visibility structures, such as adrenal glands and fat in the intrahepatic falciform ligament, and low-visibility structures, such as the extrahepatic hepatic artery, small intrahepatic vessels, and common bile duct. Aligned rank and Wilcoxon's signed rank tests were used for statistical analyses. RESULTS. Simulated tube current reduction significantly affected the detection of low-visibility structures (p < 0.001). Reduced detection in low-visibility structures was evident at a level less than or equal to 80 mA. No loss of detection in high-visibility structures was found at any tube current level (p > 0.5). CONCLUSION. The results of this computer simulation suggest that accurate abdominal MDCT can be performed in pediatric patients using substantially reduced radiation, depending on the indication for imaging. (In our case, the reduction was between 33% and 67%, depending on whether a high-visibility or low-visibility structure was being assessed.) This simulation technology can be applied to MDCT of other organ systems for systematic evaluation of radiation dose reduction.     

CT colonography at different radiation dose levels: feasibility of dose reduction

PURPOSE: To investigate the sensitivity and specificity of polyp detection and the image quality of computed tomographic (CT) colonography at different radiation dose levels and to study effective doses reported in literature on CT colonography. MATERIALS AND METHODS: CT colonography and colonoscopy were performed with 100 mAs in 50 consecutive patients at high risk for colorectal cancer; 50- and 30-mAs CT colonographic examinations were simulated with controlled addition of noise to raw transmission measurements. One radiologist randomly evaluated all original and simulated images for the presence of polyps and scored image quality. Differences in image quality were assessed with the Wilcoxon rank test. Scan protocols from the literature and recent (unpublished) updates were collected. RESULTS: In nine of 10 patients with polyps 5 mm in diameter or larger (sensitivity, 90%) and in seven of 17 patients with polyps smaller than 5 mm, polyps were correctly identified with CT colonography at all dose levels. Specificity for patients without polyps 5 mm or larger was 53%-60% at all dose levels and for patients without any polyps was 26% (at 100 and 50 mAs) and 48% (at 30 mAs). Image quality decreased significantly as the dose level decreased. The median effective doses (supine and prone positions) calculated from protocols reported in the literature and updates were 7.8 and 8.8 mSv, respectively. CONCLUSION: Although image quality decreases significantly at 30 mAs (3.6 mSv), polyp detection remains unimpaired. The median dose for CT colonography at institutions that perform CT colonographic research is currently 8.8 mSv.     

80kV64排多层螺旋CT低辐射肺动脉成像

目的 研究80 kV 管电压64排多层螺旋CT低辐射肺动脉成像的可行性。方法 64名志愿者随机分为2组。观察组35例采用80kV管电压CT结合右头臂静脉作为团注追踪(bolus tracking) 监测点进行肺动脉成像,对照组29例采用120kV管电压,延迟时间采用团注测试峰值时间+0.7 s,进行肺动脉成像。测量容积CT剂量指数(CTDI_vol)、剂量长度乘积(DLP),计算加权CT剂量指数(CTDI_w)和有效剂量(E),测量肺动脉强化后CT值和背景噪声,计算信噪比(SNR)和对比噪声比(CNR)。5分法对两组图像质量进行目测评分。对DLP、E、SNR、CNR进行t检验;采用Mann-Whitney U检验比较两组图像目测评分结果。结果 观察组DLP和E分别为(146.5±7.6)mGy·cm和(2.5±0.1)mSv,对照组DLP和E分别为(313.4±13.5) mGy·cm和(5.3±0.2) mSv,两者差异有统计学意义(P＜0.001),观察组的辐射剂量低于对照组。图像质量量化评价:观察组和对照组的SNR分别为32.6±3.6和31.35±2.0,差异无统计学意义(P=0.089)。观察组和对照组CNR分别为28.5±3.4和27.6±1.1,差异无统计学意义(P=0.18)。目测评分结果:观察组为5分8例,4分26例,3分1例;对照组为5分5例,4分24例,差异无统计学意义(P=0.76)。结论 80 kV 64排多层螺旋CT结合右头臂静脉作为bolus tracking 监测点可以减少辐射剂量,同时不降低图像质量,是肺动脉造影的首选检查方法。     

80 kV 64排多层螺旋CT低辐射肺动脉成像

Objective To assess the feasibility of minimizing radiation doses using 80 kV 64-row muhidetector computed tomography on pulmonary angiography.Methods 64 volunteers were derided into 2 groups to undergo MDCT pulmonary angiography(collimation,64×0.625 mm;pitch,1.204).The observed group consisting of 35 patients were for pulmonary angiography with 80 kV voltage,300 mAs,0.75 s/roation.The control group consisting of 29 patients were for pulmonary angiography with the standard tube voltage (120 kV),200 mAs,0.5 s/roation and time delay using the peak time on bolus test added 0.7 s.Volume computed tomography dose index (CTDIvol),dose length product (DLP),pulmonary vessel enhancement and back noise were quantified.Signal-noise-ratio (SNR),contrast-to-noise-ratio (CNR),weighted computed tomography dose index (CTDIw) and effective dose (E) were calculated.Results of the two protocols were compared by using t test.Two radiologists used five-point scale to subjectively score arterial enhancement and depiction of small arterial detail.The scores were compared with Mann-Whitney U test.Results The 80 kV protocol had a significantly lower DLP and E than the 120 kV protocol[(146.5±7.6)mGy·cm vs(313.4±13.5)mGy·cm,P<0.001]and [(2.5m±0.1)mGy vs (5.3±0.2)mGy,P<0.001],respectively.The 80 kV protocol and the 120 kV protocol had identical SNR(32.6±3.6 vs 31.3±2.3;P=0.089) and CNR (28.5±3.4 vs 27.6±1.1;P=0.18).No significant difference was found between the two protocols on scores for arterial enhancement and depiction of small arterial detail ( P=0.76).Conclusions 80 kV 64 slices MDCT combined with right brachiocephalic vein as the monitoring site for bolus tracking could be the first choice of pulmonary angingraphy.It can reduce the radiation dose without sacrificing the image quality.     

Prospective ECG-triggered axial CT at 140-kV tube voltage improves coronary in-stent restenosis visibility at a lower radiation dose compared with conventional retrospective ECG-gated helical CT

The purpose of this study was to compare coronary 64-slice CT angiography (CTA) protocols, specifically prospective electrocardiograph (ECG)-triggered and retrospective ECG-gated CT acquisition performed using a tube voltage of 140 kV and 120 kV, regarding intracoronary stent imaging. Coronary artery stents (n?=?12) with artificial in-stent restenosis (50% luminal reduction, 40 HU) on a cardiac phantom were examined by CT at heart rates of 50–75 beats per minute (bpm). The subjective visibility of in-stent restenosis was evaluated with a three-point scale (1 clearly visible, 2 visible, and 3 not visible), and artificial lumen narrowing [(inner stent diameter???measured lumen diameter)/inner stent diameter], lumen attenuation increase ratio [(in-stent attenuation???coronary lumen attenuation)/coronary lumen attenuation], and signal-to-noise ratio of in-stent lumen were determined. The effective dose was estimated. The artificial lumen narrowing (mean 43%), the increase of lumen attenuation (mean 46%), and signal-to-noise ratio (mean 7.8) were not different between CT acquisitions (p?=?0.12–0.91). However, the visibility scores of in-stent restenosis were different (p?<?0.05) between ECG-gated CTA techniques: (a) 140-kV prospective (effective dose 4.6 mSv), 1.6; (b) 120-kV prospective (3.3 mSv), 1.8; (c) 140-kV retrospective (16.4–18.8 mSv), 1.9; and (d) 120-kV retrospective (11.0–13.4 mSv), 1.9. Thus, 140-kV prospective ECG-triggered CTA improves coronary in-stent restenosis visibility at a lower radiation dose compared with retrospective ECG-gated CTA.     

Low-dose, volumetric helical CT: image quality, radiation dose, and usefulness for evaluation of bronchiectasis

RATIONALE AND OBJECTIVES: The aim of our study was to assess the image quality, radiation dose, and clinical applicability of low-dose, volumetric helical CT in the evaluation of bronchiectasis. METHODS: Volumetric helical CT scans (120 kVp, 3-mm collimation, pitch of 2, and reconstruction interval of 2 mm) were obtained through the thorax at four levels of tube current: 150, 100, 70, and 40 mA. There were a total of 12 patients who underwent CT scan either for suspected bronchiectasis or for lung cancer screening, with three patients allocated to each current level. Five radiologists assessed and compared image quality of the helical CT scans obtained at the various exposure levels. Radiation doses of helical CT performed with four different current settings and of high-resolution CT (120 kVp, 170 mA, 1-mm collimation, and 10-mm intervals) were measured. The diagnostic usefulness of the 40-mA helical CT images was compared with that of high-resolution CT by two observers in 52 patients with known or suspected airway diseases. RESULTS: With helical CT, there was no significant difference in image quality among the four different levels of current (P > 0.05). Radiation doses associated with the 40-, 70-, 100-, and 150-mA helical techniques were 3.21 mGy (range, 3.02-3.57), 4.81 mGy (range, 3.89-5.93), 6.46 mGy (range, 6.01-7.31), and 10.4 mGy (range, 8.93-12.1), respectively, whereas that of high-resolution CT was 2.17 mGy (range, 1.90-2.67). Of 52 patients, 44.5 and 47 patients (the mean of positive interpretations by the five observers) were diagnosed with bronchiectasis at high-resolution and low-dose helical CT, respectively. Of 928 segments, bronchiectasis was seen in 152.5 segments on high-resolution CT and in 193.5 segments on helical CT. The interobserver agreement (k-values) was acceptable for both techniques. CONCLUSIONS: With acceptable images and similar radiation dose, low-dose volumetric helical CT at 40 mA may offer more information than does high-resolution CT in the evaluation of bronchiectasis.     

Low-dose CT in body-packers: delineation of body packs and radiation dose in a porcine model

Purpose

To compare low-dose computed tomography (CT) with standard CT and conventional radiography (CR) regarding delineation of body packs and radiation dose.

Methods

Nine samples of illicit drugs including cocaine, heroin, and hashish were positioned in the rectum of a 121.5 kg pig cadaver. Each sample was scanned on a 64-row MDCT with 120 kV: one standard modulated pelvic protocol (STD), and without modulation at 80 mA (LD80), 30 mA (LD30), and 10 mA (LD10). Additionally, conventional abdominal anterior–posterior radiographs (77 kV and 106 ± 13 mA) were taken. Body pack characteristics (wrapping, content, shape) were rated independently by two radiologists and summarized to a delineation score from 0 to 9 with scores ≥6 representing sufficient delineation. Mean delineation scores were calculated for CR and CT protocols. These were additionally differentiated for readings in soft tissue (S), lung (L), user defined, variable window settings (V), and in cumulative window evaluation including all the other window settings (SLV). Effective doses were calculated (mSv).

Results

The CR delineation score was insufficient (3.1 ± 2.5; 2.4 ± 0.3 mSv). For CT, the SLV window setting performed best (p < 0.01). Its score significantly (p < 0.01) declined with decreasing effective radiation doses: STD (8.8 ± 0.5; 10.6 mSv), LD80 (8.2 ± 0.7; 2.6 mSv), LD30 (6.8 ± 1.3; 1.0 mSv), and LD10 (4.6 ± 1.9; 0.3 mSv). Thus, LD30 was the protocol using the lowest but sufficient dose. Moreover, for LD30 further differentiation between the particular window settings resulted in scores of 6.4 ± 1.3 (L), 6.3 ± 1.2 (V), and 3.1 ± 1.0 (S).

Conclusions

With appropriate window settings, low-dose CT at 30 mA allowed for sufficient body-pack delineation below the dose of CR, which itself performed insufficient.     

迭代重建对于大体型成人的多层螺旋CT中影像质量和辐射剂量的影响

摘要目的比较自适应统计迭代重建(ASiR)和滤波反射重建技术(FBP)用于体质量≥91kg病人时的影像质量和辐射剂量。方法在这项机构审查委员会批准的回顾性研究中,对100例体质量≥91kg[91～181.9kg,平均(107.6±17.4)kg]的成人行单期对比增强腹部盆腔CT检查,由2名阅片者双盲进行ASiR和FBP影像质量的主观测量值和辐射剂量分析,影像质量使用主观标准化数值模拟和客观噪声来评估。     

Impact of iterative reconstruction on image quality and radiation dose in multidetector CT of large body size adults

Objective

To compare image quality and radiation dose using Adaptive Statistical Iterative Reconstruction (ASiR) and Filtered Back Projection (FBP) in patients weighing ≥91?kg.

Methods

In this Institution Review Board-approved retrospective study, single-phase contrast-enhanced abdominopelvic CT examinations of 100 adults weighing ≥91?kg (mean body weight: 107.6?±?17.4?kg range: 91–181.9?kg) with (1) ASiR and (2) FBP were reviewed by two readers in a blinded fashion for subjective measures of image quality (using a subjective standardized numerical scale and objective noise) and for radiation exposure. Imaging parameters and radiation dose results of the two techniques were compared within weight and BMI sub-categories.

Results

All examinations were found to be of adequate quality. Both subjective (mean?=?1.4?±?0.5 vs. 1.6?±?0.6, P?P?P?Conclusion In obese individuals, abdominal CT images reconstructed using ASiR provide diagnostic images with reduced image noise at lower radiation dose.

Key Points

? CT images in obese adults are noisy, even with high radiation dose. ? Newer iterative reconstruction techniques have theoretical advantages in obese patients. ? Adaptive statistical iterative reconstruction should reduce image noise and radiation dose. ? This has been proven in abdominopelvic CT images of obese patients.     

Feasibility of using post-contrast dual-energy CT for pediatric radiation treatment planning and dose calculation

Objectives:When iodinated contrast is administered during CT simulation, standard practice requires a separate non-contrast CT for dose calculation. The objective of this study is to validate our hypothesis that since iodine affects Hounsfield units (HUs) more than electron density (ED), the information from post-contrast dual-layer CT (DLCT) would be sufficient for accurate dose calculation for both photon and proton therapy.Methods and materials:10 pediatric patients with abdominal tumors underwent DLCT scans before and after iodinated contrast administration for radiotherapy planning. Dose distributions with these DLCT-based methods were compared to those with conventional calibration-curve methods that map HU images to ED and stopping-power ratio (SPR) images.Results:For photon plans, conventional and DLCT approaches based on post-contrast scans underestimated the PTV D99 by 0.87 ± 0.70% (p = 0.18) and 0.36 ± 0.31% (p = 0.34), respectively, comparing to their non-contrast optimization plans. Renal iodine concentration was weakly associated with D99 deviation for both conventional (R² = 0.10) and DLCT (R² = 0.02) approaches. For proton plans, the clinical target volume D99 errors were 3.67 ± 2.43% (p = 0.0001) and 0.30 ± 0.25% (p = 0.40) for conventional and DLCT approaches, respectively. The proton beam range changed noticeably with the conventional approach. Renal iodine concentration was highly associated with D99 deviation for the conventional approach (R² = 0.83) but not for DLCT (R² = 0.007).Conclusion:Conventional CT with iodine contrast resulted in a large dosimetric error for proton therapy, compared to true non-contrast plans, but the error was less for photon therapy. These errors can be greatly reduced in the case of the proton plans if DLCT is used, raising the possibility of using only a single post-contrast CT for radiotherapy dose calculation, thus reducing the time and imaging dose required.Advances in knowledge:This study is the first to compare directly the differences in the calculated dose distributions between pre- and post-contrast CT images generated by single-energy CT and dual-energy CT methods for photon and proton therapy.     

Multiplanar and 3D imaging of the central airways: comparison of image quality and radiation dose of single-detector row CT and multi-detector row CT at differing tube currents in dogs

PURPOSE: To compare in an animal model the image quality of multiplanar reformation and three-dimensional (3D) reconstruction images of the central airways by using single-detector row computed tomography (CT) and multi-detector row CT at varied tube currents and to compare radiation dose. MATERIALS AND METHODS: Five dogs each underwent five consecutive helical CT examinations (one single-detector row CT examination at 240 mA and four multi-detector row CT examinations at 240, 120, 40, and 20 mA), with 0.8-second gantry rotation time. Multiplanar reformation and 3D reconstruction images were created from each of the 25 CT acquisitions. The images were randomized and blindly reviewed with consensus agreement by three radiologists who graded image quality by using a five-point scale. In a separate review, the three radiologists independently used a four-point scale to rank the comparative image quality of the multi-detector row CT 3D images, while blinded to specific tube currents. The radiation doses were measured for each type of scan, and the relative radiation dose length products that were normalized to single-detector row CT values were used to compare radiation doses of the various CT techniques. Statistical analysis was performed with the Wilcoxon signed-rank test and the Friedman analysis of variance test. RESULTS: Image quality was consistently ranked higher for multi-detector row CT images than for single-detector row CT images (P =.03). Although there were no distinguishable differences between images obtained with multi-detector row CT at 240, 120, or 40 mA, images obtained with 20 mA were given a significantly (P =.04) lower relative rank (mean, 2.4) than those obtained with higher tube currents (mean, 1.4-1.7). Multi-detector row CT radiation doses were 1.64, 0.82, 0.27, and 0.14 (for 240-, 120-, 40-, and 20-mA multi-detector row CT, respectively) relative to the dose for 240-mA single-detector row CT. CONCLUSION: Multi-detector row CT is superior to single-detector row CT for multiplanar and 3D imaging of the central airways. Substantial dose reductions can be made, while maintaining high image quality.     

Reduced radiation dose helical chest CT: effect on reader evaluation of structures and lung findings

PURPOSE: To assess, by using computer simulation, the effect of the use of reduced computed tomographic (CT) tube current on reader evaluation of structures and lung findings on images obtained at clinically indicated chest CT examinations. MATERIALS AND METHODS: The noise level in the raw scan data of 150 clinically indicated conventional tube current (200-320-mA) chest CT examinations was modified to simulate tube current reduction to 100 and to 40 mA. A total of 450 image sets were thus available. Four radiologists blinded to the tube current used assessed the image sets in random order for 14 structures and lung findings and ranked subjective image quality by using a five-point scale (1 = nondiagnostic, 2 = inferior, 3 = adequate, 4 = good, 5 = excellent). After a 3-week interval, the 150 conventional tube current image sets were rescored so that intraobserver agreement could be assessed. The McNemar statistic was used to determine whether there were more scoring disagreements between interpretations of the conventional and those of the reduced tube current scans or between the two interpretations of the conventional tube current scans. RESULTS: When overall agreement for 14 structures and lung findings was pooled over four observers, significantly more disagreements (P <.05) were seen when scores were compared between conventional and reduced tube current scans than when scores were compared between repeated interpretations of the conventional tube current scans. There was a significant decrease (P <.05) in the subjective image quality of reduced tube current scans compared with the subjective image quality of conventional tube current scans. CONCLUSION: These data indicate that reduced tube current does affect reader evaluation of structures and lung findings and reduces a reader's subjective assessment of image quality.