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.     

Material density iodine images in dual-energy CT: Detection and characterization of hypervascular liver lesions compared to magnetic resonance imaging

PurposeTo determine the diagnostic potential of Material Density (MD) iodine images in dual-energy CT (DECT) for the detection and characterization of hypervascular liver lesions compared to monenergetic 65 keV images, using MRI as the standard.Materials and methodsThe study complied with HIPAA guidelines and was approved by the institutional review board. Fifty-two patients (36 men, 16 women; age range, 29–87 years) with 236 hypervascular liver lesions (benign, n = 31; malignant, n = 205; mean diameter, 29.4 mm; range: 6–90.6 mm) were included. All of them underwent both contrast-enhanced single-source DECT and contrast-enhanced abdominal MRI within three months. Late arterial phase CT imaging was performed with dual energies of 140 and 80 kVp. Protocol A showed monoenergetic 65 keV images, and protocol B presented MD-iodine images. Three radiologists qualitatively evaluated randomized images, and lesion detection, characterization, and reader confidence were recorded. Liver-to-lesion ratio (LLR) and contrast-to-noise ratio (CNR) were assessed on protocol A, protocol B, and MRI. Paired t-tests were used to compare LLR, CNR, and the number of detected lesions.ResultsLLR was significantly increased in protocol B (2.8 ± 2.33) compared to protocol A (0.77 ± 0.55) and MRI (0.61 ± 0.66). CNR was significantly higher in protocol B (0.08 ± 0.04) compared to protocol A (0.01 ± 0.01) and MRI (0.01 ± 0.01). All three observers correctly identified more liver lesions using protocol B vs protocol A: 83.13% vs 63.64%, 84.57% vs 68.09%, and 79.37% vs 65.52%. There was no significant difference between the three observers in classification of a lesion as benign or malignant. However, higher diagnostic confidence was reported more frequently by the experienced radiologist when using protocol B vs protocol A (84.6% vs 75%).ConclusionMD-iodine images in DECT help to increase the conspicuity and detection of hypervascular liver lesions.     

Spectral CT: Preliminary Studies in the Liver Cirrhosis

Objective

To investigate the value of spectral CT imaging in the diagnosis and classification of liver cirrhosis during the arterial phase (AP) and portal venous phase (PVP).

Materials and Methods

Thirty-eight patients with liver cirrhosis (Child-Pugh class A/B/C: n = 10/14/14), and 43 patients with healthy livers, participated in this study. The researchers used abdominal spectral CT imaging during AP and PVP. Iodine concentration, derived from the iodine-based material-decomposition image and the iodine concentration ratio (IC_ratio) between AP and PVP, were obtained. Statistical analyses {two-sample t test, One-factor analysis of variance, and area under the receiver operating characteristic curve (A [z])} were performed.

Results

The mean normalized iodine concentration (NIC) (0.5 ± 0.12) during PVP in the control group was significantly higher than that in the study group (0.4 ± 0.10 on average, 0.4 ± 0.08 for Class A, 0.4 ± 0.15 for Class B, and 0.4 ± 0.06 for Class C) (All p < 0.05). Within the cirrhotic liver group, the mean NIC for Class C during the AP (0.1 ± 0.05) was significantly higher than NICs for Classes A (0.1 ± 0.06) and B (0.1 ± 0.03) (Both p < 0.05). The IC_ratio in the study group (0.4 ± 0.15), especially for Class C (0.5 ± 0.14), was higher than that in the control group (0.3 ± 0.15) (p < 0.05).The combination of NIC and IC_ratio showed high sensitivity and specificity for differentiating healthy liver from cirrhotic liver, especially in Class C cirrhotic liver.

Conclusion

Spectral CT Provides a quantitative method with which to analyze the cirrhotic liver, and shows the potential value in the classification of liver cirrhosis.     

双低对比剂联合能谱CT成像技术在门静脉成像中的应用研究

目的 探讨双低对比剂联合能谱CT成像技术在门静脉成像中的应用价值,并评价其辐射剂量.方法 搜集行肝脏门静脉CT扫描的患者72例,均采用宝石能谱CT进行扫描.随机分为两组,A组为双低对比剂联合单能量成像组,共36例;B组为常规组,共36例.A组使用低浓度对比剂碘克沙醇,浓度为270 mgI/ml,低对比剂总量(按1.2 ml/kg体重计算).采用能谱扫描模式,80 kVp和140 kVp电压快速切换,通过原始数据重组出最佳单能量图像.B组使用常规对比剂碘海醇,浓度为350 mgI/ml,常规对比剂总量(按1.5ml/kg体重计算).采用螺旋扫描模式,120 kVp混合能量,得到门静脉图像.比较两组图像中门静脉主干的CT值、信噪比(SNR)、对比噪声比(CNR)及噪声,通过这些客观参数来评价图像质量,由2名高年资放射科医师采用双盲法对图像质量进行主观评分,并比较两组图像的CT容积剂量指数(CTDI)、剂量长度乘积(DLP)及有效辐射剂量(ED).对所得的数据使用SPSS 19.0统计软件进行统计学分析.结果 A组对比剂总量为(84.43±11.17) ml,B组对比剂总量为(93.50±9.53) ml,A组明显低于B组(P＜0.01).A组门静脉CT值及CNR分别为(226.65±17.99) HU、5.83 ±1.64,B组门静脉CT值及CNR分别为(195.01±23.98)HU、4.00±1.64,A组门静脉CT值及CNR明显高于B组(P＜0.01).两组中门静脉SNR、图像噪声及主观评分差异无统计学意义(P＞0.05).A组中CTDI、DLP及ED分别为(10.32 ±2.22) mGy、(264.54±57.44) mGy·cm、(4.50±0.98) mSv,B组中CTDI、DLP及ED分别为(13.20±2.35) mGy、(363.89±75.40) mGy·cm、(6.19±1.28) mSv,A组中CTDI、DLP及ED明显低于B组(P＜0.01).结论 在门静脉CT血管成像中,使用低总量、低浓度对比剂联合能谱CT单能量成像技术,在获得满足临床需求图像的同时,不仅有效地减少了对比剂的用量及提高图像的SNR,还降低了辐射剂量,具有在临床广泛推广的价值.     

Contrast Media in Abdominal Computed Tomography: Optimization of Delivery Methods

Objective

To provide a systematic overview of the effects of various parameters on contrast enhancement within the same population, an animal experiment as well as a computer-aided simulation study was performed.

Materials and Methods

In an animal experiment, single-level dynamic CT through the liver was performed at 5-second intervals just after the injection of contrast medium for 3 minutes. Combinations of three different amounts (1, 2, 3 mL/kg), concentrations (150, 200, 300 mgI/mL), and injection rates (0.5, 1, 2 mL/sec) were used. The CT number of the aorta (A), portal vein (P) and liver (L) was measured in each image, and time-attenuation curves for A, P and L were thus obtained. The degree of maximum enhancement (Imax) and time to reach peak enhancement (Tmax) of A, P and L were determined, and times to equilibrium (Teq) were analyzed. In the computed-aided simulation model, a program based on the amount, flow, and diffusion coefficient of body fluid in various compartments of the human body was designed. The input variables were the concentrations, volumes and injection rates of the contrast media used. The program generated the time-attenuation curves of A, P and L, as well as liver-to-hepatocellular carcinoma (HCC) contrast curves. On each curve, we calculated and plotted the optimal temporal window (time period above the lower threshold, which in this experiment was 10 Hounsfield units), the total area under the curve above the lower threshold, and the area within the optimal range.

Results

A. Animal Experiment: At a given concentration and injection rate, an increased volume of contrast medium led to increases in Imax A, P and L. In addition, Tmax A, P, L and Teq were prolonged in parallel with increases in injection time The time-attenuation curve shifted upward and to the right. For a given volume and injection rate, an increased concentration of contrast medium increased the degree of aortic, portal and hepatic enhancement, though Tmax A, P and L remained the same. The time-attenuation curve shifted upward. For a given volume and concentration of contrast medium, changes in the injection rate had a prominent effect on aortic enhancement, and that of the portal vein and hepatic parenchyma also showed some increase, though the effect was less prominent. A increased in the rate of contrast injection led to shifting of the time enhancement curve to the left and upward. B. Computer Simulation: At a faster injection rate, there was minimal change in the degree of hepatic attenuation, though the duration of the optimal temporal window decreased. The area between 10 and 30 HU was greatest when contrast media was delivered at a rate of 2-3 mL/sec. Although the total area under the curve increased in proportion to the injection rate, most of this increase was above the upper threshould and thus the temporal window was narrow and the optimal area decreased.

Conclusion

Increases in volume, concentration and injection rate all resulted in improved arterial enhancement. If cost was disregarded, increasing the injection volume was the most reliable way of obtaining good quality enhancement. The optimal way of delivering a given amount of contrast medium can be calculated using a computer-based mathematical model.     

多层螺旋CT头颈部低剂量对比剂血管成像的可行性研究

目的 探讨16排多层螺旋CT低剂量对比剂头颈部血管成像的可行性。资料与方法 30例头颈部CT血管成像(CTA)分为3组．采用不同的对比剂量：100ml、80ml和60ml。根据原始图像和最大强度投影(MIP)重建像评价3组病例颈部动脉、颅内动脉的显示程度、静脉充盈程度以及伪影;并测量动脉内对比剂的浓度。结果 颈动脉、椎动脉及颅内动脉在3组病例中均清晰显示．显示程度评分上3组间无统计学差异。静脉充盈程度和伪影的主观评分亦无显著性差异。3组动脉内的对比剂浓度均维持在较高的水平,统计学无显著性差异。结论 16排多层螺旋CT头颈部血管成像使用低剂量对比剂可以满足临床需要。     

体部CT和磁共振学会双能量CT白皮书(上)

体部CT和磁共振学会于2016年末陆续推出了双能量CT系列白皮书,这是该学会首次推出的关于双能量CT专家共识之系列白皮书。本文主要介绍该白皮书系列的第一和第二部分。第一部分描述了双能量CT的基本技术原理和术语,第二部分主要介绍双能量CT的辐射剂量和碘对比剂的敏感性。