智能期相联合SSF技术改善冠状动脉CTA图像运动伪影

目的:评价智能期相选择(Smart phase)和自动追踪冻结(Snap-Shot-Freeze, SSF)技术联合应用在前门控冠状动脉CT血管成像(Coronary CT angiography, CCTA)改善图像运动伪影中的价值。方法:94例疑似心血管疾病的患者行CCTA检查。所有患者图像均采用smart phase、SSF及smart phase+SSF两种技术联合进行后处理。将原始图像(A组)、smart phase图像(B组)、SSF图像(C组)和smart phase+SSF图像(D组)导入GE AW4.6工作站。对四组患者冠状动脉三大分支(右冠状动脉、左前降支及左旋支)图像质量进行主观评价(5分法)和测量每组图像主动脉根部及前胸壁肌肉CT值和标准差,并计算图像的噪声(Noise,N)、信噪比(Signal-to-noise ratio,SNR)和对比噪声比(Contrast-to-noise ratio,CNR)和比较。结果:经smart phase处理后,A组冠状动脉三大分支图像评分均得到了明显提高(P<0.05)。经SSF矫正的A组和B组冠状动脉三大分支图像质量评分均得到明显提高(P<0.05)。Smart Phase联合SSF技术得到的图像评分在所有组中评分最高,与其他组均存在显著差异(P<0.05)。结论:Smart phase联合SSF技术可明显改善前门控CCTA图像运动伪影,值得临床推广应用。     

Infant Cardiac CT Angiography with 64-Slice and 256-Slice CT: Comparison of Radiation Dose and Image Quality Using a Pediatric Phantom

Background

The aims of this study were to investigate the image quality and radiation exposure of pediatric protocols for cardiac CT angiography (CTA) in infants under one year of age.

Methodology/Principal Findings

Cardiac CTA examinations were performed using an anthropomorphic phantom representing a 1-year-old child scanned with non-electrocardiogram-gated (NG), retrospectively electrocardiogram-gated helical (RGH) and prospectively electrocardiogram-gated axial (PGA) techniques in 64-slice and 256-slice CT scanners. The thermoluminescent dosimeters (TLD) were used for direct organ dose measurement, while dose-length product and effective mAs were also used to estimate the patient dose. For image quality, noise and signal-to-noise-ratio (SNR) were assessed based on regions-of-interest drawn on the reconstructed CT images, and were compared with the proposed cardiac image quantum index (CIQI). Estimated dose results were in accordant to the measured doses. The NG scan showed the best image quality in terms of noise and SNR. The PGA scan had better image quality than the RGH scan with 83.70% dose reduction. Noise and SNR were also corresponded to the proposed CIQI.

Conclusions/Significance

The PGA scan protocol was a good choice in balancing radiation exposure and image quality for infant cardiac CTA. We also suggested that the effective mAs and the CIQI were suitable in assessing the tradeoffs between radiation dose and image quality for cardiac CTA in infants. These results are useful for future implementation of dose reduction strategies in pediatric cardiac CTA protocols.     

256 层CT 冠状动脉造影低剂量技术联合应用的临床价值

目的:探讨前瞻性心电门控扫描、低管电压结合迭代重建算法在256层螺旋CT冠脉造影中的应用价值。方法:回顾性分析行256层螺旋CT冠状动脉成像(CCTA)、体质量指数正常的受检者130例。常规剂量组(A组)50例:应用回顾性心电门控扫描模式,管电压120 kv;低剂量组(B组)80例,心率70次/分者50例,心率≧70次/分者30例:应用前瞻性心电门控扫描模式,管电压100 kv。B组患者原始数据分别应用迭代算法(Idose3)重建及标准滤波反投影法(FBP)重建。比较A、B两组的有效辐射剂量,对各组客观图像质量及主观图像质量进行统计学分析。结果:A、B两组平均有效辐射剂量分别为(15.34±3.89)、(1.43±0.12)m Sv。B组患者应用迭代重建图像噪声降低,差异有统计学意义(P0.05)。应用FBP重建,B组图像噪声高于A组,两者比较差异有统计学意义(P0.05)。各组主观图像质量评分差异无统计学意义(P0.05)。结论:前瞻性心电门控低千伏扫描模式联合迭代重建算法在提供满足诊断的冠状动脉CTA图像的同时,辐射剂量降幅高达90.6%。心率70次/分-85次/分的患者也可行256层CT前门控扫描,降低管电压造成的图像噪声增加可以通过迭代重建弥补。     

宝石能谱CT GSI成像和常规成像在上腹部应用价值的对比研究

目的:探讨宝石能谱CT GSI扫描模式在上腹部检查中降低辐射剂量和优化图像质量的可行性及应用价值。方法:选择2016年9月至2016年12月期间我院40例拟行上腹部三期增强的患者,根据扫描模式将患者分为A组和B组,每组20例。A组患者采用宝石能谱CT常规扫描模式行螺旋扫描,管电压120 Kvp及自动毫安管电流,确定NI值为10。B组患者采用GSI模式行三期增强扫描收集门脉期图像。回顾性自适应统计迭代重建(ASIR)70kev单能量图像,应用ASIR Review工具收集0到100%ASIR的CT值、噪声值,计算图像信号噪声比(SNR)。记录各组剂量报告中CT剂量容积指数(CTDI vol)及剂量长度乘积(DLP),并计算有效剂量(ED),采用图像质量主观评分对图像进行评价。结果:B组CT值、噪声值及SNR均高于A组(P0.05),B组CTDIvol、DLP和ED均显著低于A组(P0.05);随着ASIR升高,SNR升高,但是图像质量主观评分先升高后降低。当ASIR为50%时,图像质量最高,不同ASIR的CT值、噪声值之间的差异无统计学意义(P0.05)。结论:宝石能谱CT GSI扫描模式的效果明显优于螺旋扫描,同时在降低图像噪声的前提下选择50%ASIR,可保障图像质量。     

Automatic exposure control at single- and dual-heartbeat CTCA on a 320-MDCT volume scanner: Effect of heart rate,exposure phase window setting,and reconstruction algorithm

PurposeTo investigate whether electrocardiogram (ECG)-gated single- and dual-heartbeat computed tomography coronary angiography (CTCA) with automatic exposure control (AEC) yields images with uniform image noise at reduced radiation doses.Materials and methodsUsing an anthropomorphic chest CT phantom we performed prospectively ECG-gated single- and dual-heartbeat CTCA on a second-generation 320-multidetector CT volume scanner. The exposure phase window was set at 75%, 70–80%, 40–80%, and 0–100% and the heart rate at 60 or 80 or corr80 bpm; images were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR, adaptive iterative dose reduction 3D). We applied AEC and set the image noise level to 20 or 25 HU. For each technique we determined the image noise and the radiation dose to the phantom center.ResultsWith half-scan reconstruction at 60 bpm, a 70–80% phase window- and a 20-HU standard deviation (SD) setting, the imagenoise level and -variation along the z axis manifested similar curves with FBP and IR. With half-scan reconstruction, the radiation dose to the phantom center with 70–80% phase window was 18.89 and 12.34 mGy for FBP and 4.61 and 3.10 mGy for IR at an SD setting SD of 20 and 25 HU, respectively. At 80 bpm with two-segment reconstruction the dose was approximately twice that of 60 bpm at both SD settings. However, increasing radiation dose at corr80 bpm was suppressed to 1.39 times compared to 60 bpm.ConclusionAEC at ECG-gated single- and dual-heartbeat CTCA controls the image noise at different radiation dose.     

不同剂量64排CT增强扫描结合三维重建在胃癌应用中的图像质量研究

目的:研究不同剂量64排CT增强扫描结合三维重建在胃癌应用中的图像质量。方法:90例胃癌行胃部64层螺旋CT三期增强扫描患者后根据管电压设置分成A、B、C三组:A组120KV、B组100KV、C组80KV。通过轴位图像结合三维重建(VR、MPR和MIP等)分析不同剂量下螺旋CT扫描结合三维重建图像诊断质量。结果:A、B两组的图像清晰度的差异无统计学意义(P0.05),A、B组剂量加权指数降低率的差异具有统计学意义,A、C两组间图像清晰度及剂量加权指数降低率的差异具有统计学意义(P0.05),B、C组两项差异具有统计学意义。结论:适当调整MSCT的剂量,可以获得与常规MSCT剂量完全相同的图像而且可以降低辐射。     

Reduced Radiation Exposure for Face Transplant Surgical Planning Computed Tomography Angiography

Objective

To test the hypothesis that wide area detector face transplant surgical planning CT angiograms with simulated lower radiation dose and iterative reconstruction (AIDR3D) are comparable in image quality to those with standard tube current and filtered back projection (FBP) reconstruction.

Materials and Methods

The sinograms from 320-detector row CT angiography of four clinical candidates for face transplantation were processed utilizing standard FBP, FBP with simulated 75, 62, and 50% tube current, and AIDR3D with corresponding dose reduction. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured at muscle, fat, artery, and vein. Image quality for each reconstruction strategy was assessed by two independent readers using a 4-point scale.

Results

Compared to FBP, the median SNR and CNR for AIDR3D images were higher at all sites for all 4 different tube currents. The AIDR3D with simulated 50% tube current achieved comparable SNR and CNR to FBP with standard dose (median muscle SNR: 5.77 vs. 6.23; fat SNR: 6.40 vs. 5.75; artery SNR: 43.8 vs. 45.0; vein SNR: 54.9 vs. 55.7; artery CNR: 38.1 vs. 38.6; vein CNR: 49.0 vs. 48.7; all p-values >0.19). The interobserver agreement in the image quality score was good (weighted κ = 0.7). The overall score and the scores for smaller arteries were significantly lower when FBP with 50% dose reduction was used. The AIDR3D reconstruction images with 4 different simulated doses achieved a mean score ranging from 3.68 to 3.82 that were comparable to the scores from images reconstructed using FBP with original dose (3.68–3.77).

Conclusions

Simulated radiation dose reduction applied to clinical CT angiography for face transplant planning suggests that AIDR3D allows for a 50% reduction in radiation dose, as compared to FBP, while preserving image quality.     

自由呼吸状态下冠状动脉CT血管成像的可行性研究

目的:探讨自由呼吸状态下冠状动脉CT血管成像(Coronary CT Angiography, CCTA)的可行性。方法:收集187例疑似冠心病患者,所有患者均行CCTA检查,其中108例采用传统屏气法扫描,79例采用自由呼吸法扫描。扫描采用前门控预估法(Auto Gating)测得冠脉扫描期相,设置扫描范围和参数(准直宽度256×0.625、224×0.625、192×0.625,球管转速0.28 s,kV100,智能管电流,噪声指数25)。对比剂浓度为370 mg I/m L,注药量为0.86 m L/kg,注药时间维持12 s。由2名高年资放射科医师对冠状动脉图像采用5分法评分。测量升主动脉根部(冠状动脉左主干开口水平)和胸壁肌肉的CT值及标准差,计算图像的信噪比和对比噪声比。结果:自由呼吸状态下右冠状动脉(Right coronary artery, RCA)、左前降支(Left ascending artery, LAD)、左旋支(Left circumflex artery, LCx)的优良血管率分别为46.5%(87/187)、51.9%(97/187)及48.7%(91/187);屏气状态下RCA、LAD、LCx的优良血管率分别为32.6%(61/187)、36.4%(68/187)及36.9%(69/187),两组之间无统计学差异(Fisher值分别为6.94、1.54、0.81,P均0.05)。采用自由呼吸和屏气状态下CCTA检查的主动脉CT值、噪声、SNR和CNR均无统计学差异(P均0.05)。结论:采用超宽探测器CT,自由呼吸法CCTA可完全取代传统屏气法CCTA检查,从而降低受检者的配合难度,提高工作效率。     

Selection of optimal cardiac phases for ECG-triggered coronary CT angiography in pediatrics

PurposeThe use of coronary computed tomography angiography (CCTA) in children remains limited by patient’s irradiation, and motion artefacts impairing image quality. Triggering the acquisition at the appropriate moment, and acquiring only necessary components of the cardiac cycle could overcome these limitations. Yet, optimal cardiac intervals to perform CCTA as a function of heart rate (HR) have not yet been addressed in pediatrics.MethodsFifty children with coronary artery anomalies underwent a CCTA on a wide-coverage single-beat CT scanner. Multiple phases from 25% to 85% of the R-R interval were acquired and reconstructed with 10% increments. Two radiologists independently assessed motion artifacts on each cardiac phase using a 4-point semi-quantitative scale.ResultsAt patient level, the best phase for acquisition was found in diastole for patients with HR ≤ 75 bpm and in systole for patients with HR > 85 bpm. At coronary segments and structures level, median optimal phases were reported at 70%, 80%, 47%, 50%, and 54% of the R-R interval for patients with HR ≤ 60, 61–75, 86–100, 101–130, and >130 bpm respectively. For patients with HR between 76 and 85 bpm, no clear trend could be observed. Optimal acquisition durations represented 10% (2 phases), 20% (3 phases), 50% (multiphase), 20% (3 phases), and 10% (2 phases) of the R-R interval for patients with HR ≤ 60, 61–75, 76–100, 101–130, and >130 bpm, respectively.ConclusionsOptimal positioning and duration of CCTA acquisition intervals were investigated as a function of children’s HR, to reduce motion artifacts and patient’s irradiation.     

多层螺旋CT Flash Spiral模式老年冠状动脉成像的图像质量及影响因素分析

目的:探讨老年多层螺旋CT Flash Spiral模式和Spiral模式的冠状动脉动脉成像质量及其影响因素。方法:选择我院2010年1月~2012年12月行多层螺旋CT冠状动脉成像老年患者186例,根据心率和心律将患者分为两组:A组98例行Flash Spiral模式扫描;B组88例行Spiral模式扫描,对两组扫描的冠状动脉分别做图像后处理。比较两组患者的一般情况、图像质量评分及辐射剂量,并统计分析心率变异性对图像质量的影响。结果:两组患者在年龄、性别构成、体重指数(BMI)、钙化积分方面差异无统计学意义(均P0.05);在心率、心率变异性方面,A组明显低于B组,差异有统计学意义(均P0.05);两组患者图像质量评分、图像噪声及对比信噪比(CNR)相比较,差异均无统计学意义(均P0.05);不可诊断节段基于血管节段评价A组和B组分别为1.98%和2.21%,基于患者评价分别为8.16%和6.82%,差异无统计学意义(均P0.05);A组扫描时间、容积CT剂量指数(CTDIvol)、剂量长度乘积(DLP)、单位有效剂量(ED)小于B组,差异有统计学意义(均P0.05);心率变异性10次/min患者冠状动脉图像质量明显低于心率变异性5~10次/min和≤5次/min(P0.05)。结论:采用多层螺旋CT Flash Spiral模式扫描老年冠状动脉成像质量与Spiral模式接近,但有效辐射剂量明显减少。心率变异性是影响老年患者Flash Spiral模式扫描图像质量的重要因素。     

Dose optimization in cardiac CT

Rapid progress in the field of Cardiac CT is fostered by the advances in CT scanner technology as well as multiple clinical trials demonstrating its role in coronary artery disease and other indications like congenital heart disease, pulmonary vein assessment and pre transcatheter aortic valve replacement. The cardiovascular imager today is responsible for delivering diagnostic image quality while striking a balance with optimized radiation dose. Radiation dose is the result of multiple scanner and patient related factors. Achieving a justifiable radiation dose according to the ALARA principle requires an adept understanding of the factors affecting radiation dose. We review different scan factors and their effect on radiation dose and present strategies for radiation dose optimization in cardiac CT.     

Generating and using patient-specific whole-body models for organ dose estimates in CT with increased accuracy: Feasibility and validation

The estimation of patient dose using Monte Carlo (MC) simulations based on the available patient CT images is limited to the length of the scan. Software tools for dose estimation based on standard computational phantoms overcome this problem; however, they are limited with respect to taking individual patient anatomy into account. The purpose of this study was to generate whole-body patient models in order to take scattered radiation and over-scanning effects into account. Thorax examinations were performed on three physical anthropomorphic phantoms at tube voltages of 80 kV and 120 kV; absorbed dose was measured using thermoluminescence dosimeters (TLD). Whole-body voxel models were built as a combination of the acquired CT images appended by data taken from widely used anthropomorphic voxel phantoms. MC simulations were performed both for the CT image volumes alone and for the whole-body models. Measured and calculated dose distributions were compared for each TLD chip position; additionally, organ doses were determined.MC simulations based only on CT data underestimated dose by 8%–15% on average depending on patient size with highest underestimation values of 37% for the adult phantom at the caudal border of the image volume. The use of whole-body models substantially reduced these errors; measured and simulated results consistently agreed to better than 10%.This study demonstrates that combined whole-body models can provide three-dimensional dose distributions with improved accuracy. Using the presented concept should be of high interest for research studies which demand high accuracy, e.g. for dose optimization efforts.     

64层螺旋CT不同剂量扫描对活动性继发性肺结核患者诊断价值、图像质量和辐射剂量的影响

目的:研究64层螺旋CT不同剂量扫描对活动性继发性肺结核患者诊断价值、图像质量和辐射剂量的影响,旨在为临床活动性继发性肺结核患者提供更为安全有效的检查方案。方法:将我院从2018年1月2020年1月收治的100例活动性继发性肺结核患者纳入研究。对所有患者分别进行低剂量(40 m A)以及常规剂量(120 m A)扫描和薄层重建。比较不同剂量扫描的诊断准确率、影像学表现、图像质量以及辐射参数、患者满意度。结果:64层螺旋CT低剂量扫描与常规剂量扫描诊断活动性继发性肺结核的准确率分别为92.00%、93.00%,两者比较差异无统计学意义(P>0.05)。低剂量扫描及常规剂量扫描在空洞、钙化灶、实变、磨玻璃密度影及树芽征发生率方面对比差异均无统计学意义(P>0.05)。低剂量扫描及常规剂量扫描在扫描图像质量、薄层重建图像质量方面对比差异均无统计学意义(P>0.05)。低剂量扫描各项扫描辐射参数均低于常规剂量扫描,差异有统计学意义(P<0.05)。低剂量扫描的患者满意度高于常规剂量扫描的患者(P<0.05)。结论:64层螺旋CT不同剂量扫描对活动性继发性肺结核患者的诊断价值及生成的图像质量相近,但低剂量扫描可有效降低辐射剂量,从而在一定程度上增加扫描的安全性,使患者满意度提升。     

Dose profiles for lung and breast regions at prospective and retrospective CT coronary angiography using optically stimulated luminescence dosimeters on a 64-detector CT scanner

PurposeThe purpose of our study was to acquire dose profiles at critical organs of lung and breast regions using optically stimulated luminescence (OSL) dosimeters; assess the actual radiation dose delivered at retrospective and prospective computed tomography coronary angiography (CTCA).Materials and methodsUsing a chest CT phantom we applied a prospectively-gated step-and-shoot- and a retrospectively-gated helical mode on a 64-detector row CT scanner. Retrospective scan mode was used with and without electrocardiogram (ECG) based tube current modulation. OSL dosimeters were used to measure dose profiles. In the both scan modes we acquired dose profiles and determined the mean and maximum dose in left lung and in left breast regions.ResultsIn prospective mode, the mean dose was 21.53 mGy in left lung- and 23.59 mGy in left breast region. With respect to the retrospective mode, the mean dose with tube current modulation was 38.63 mGy for left lung- and 46.02 mGy for left breast region, i.e. 0.56 and 0.55 times lower than the mean dose without modulation.ConclusionThe OSL dosimeter is useful for measurement of the actual radiation dose along z-axis at lung and breast regions in the prospective and the retrospective CTCA.     

Self-Navigation with Compressed Sensing for 2D Translational Motion Correction in Free-Breathing Coronary MRI: A Feasibility Study

Purpose

Respiratory motion correction remains a challenge in coronary magnetic resonance imaging (MRI) and current techniques, such as navigator gating, suffer from sub-optimal scan efficiency and ease-of-use. To overcome these limitations, an image-based self-navigation technique is proposed that uses “sub-images” and compressed sensing (CS) to obtain translational motion correction in 2D. The method was preliminarily implemented as a 2D technique and tested for feasibility for targeted coronary imaging.

Methods

During a 2D segmented radial k-space data acquisition, heavily undersampled sub-images were reconstructed from the readouts collected during each cardiac cycle. These sub-images may then be used for respiratory self-navigation. Alternatively, a CS reconstruction may be used to create these sub-images, so as to partially compensate for the heavy undersampling. Both approaches were quantitatively assessed using simulations and in vivo studies, and the resulting self-navigation strategies were then compared to conventional navigator gating.

Results

Sub-images reconstructed using CS showed a lower artifact level than sub-images reconstructed without CS. As a result, the final image quality was significantly better when using CS-assisted self-navigation as opposed to the non-CS approach. Moreover, while both self-navigation techniques led to a 69% scan time reduction (as compared to navigator gating), there was no significant difference in image quality between the CS-assisted self-navigation technique and conventional navigator gating, despite the significant decrease in scan time.

Conclusions

CS-assisted self-navigation using 2D translational motion correction demonstrated feasibility of producing coronary MRA data with image quality comparable to that obtained with conventional navigator gating, and does so without the use of additional acquisitions or motion modeling, while still allowing for 100% scan efficiency and an improved ease-of-use. In conclusion, compressed sensing may become a critical adjunct for 2D translational motion correction in free-breathing cardiac imaging with high spatial resolution. An expansion to modern 3D approaches is now warranted.     

Feasibility Study of Using Gemstone Spectral Imaging (GSI) and Adaptive Statistical Iterative Reconstruction (ASIR) for Reducing Radiation and Iodine Contrast Dose in Abdominal CT Patients with High BMI Values

Purpose

To prospectively investigate the effect of using Gemstone Spectral Imaging (GSI) and adaptive statistical iterative reconstruction (ASIR) for reducing radiation and iodine contrast dose in abdominal CT patients with high BMI values.

Materials and Methods

26 patients (weight > 65kg and BMI ≥ 22) underwent abdominal CT using GSI mode with 300mgI/kg contrast material as study group (group A). Another 21 patients (weight ≤ 65kg and BMI ≥ 22) were scanned with a conventional 120 kVp tube voltage for noise index (NI) of 11 with 450mgI/kg contrast material as control group (group B). GSI images were reconstructed at 60keV with 50%ASIR and the conventional 120kVp images were reconstructed with FBP reconstruction. The CT values, standard deviation (SD), signal-noise-ratio (SNR), contrast-noise-ratio (CNR) of 26 landmarks were quantitatively measured and image quality qualitatively assessed using statistical analysis.

Results

As for the quantitative analysis, the difference of CNR between groups A and B was all significant except for the mesenteric vein. The SNR in group A was higher than B except the mesenteric artery and splenic artery. As for the qualitative analysis, all images had diagnostic quality and the agreement for image quality assessment between the reviewers was substantial (kappa = 0.684). CT dose index (CTDI) values for non-enhanced, arterial phase and portal phase in group A were decreased by 49.04%, 40.51% and 40.54% compared with group B (P = 0.000), respectively. The total dose and the injection rate for the contrast material were reduced by 14.40% and 14.95% in A compared with B.

Conclusion

The use of GSI and ASIR provides similar enhancement in vessels and image quality with reduced radiation dose and contrast dose, compared with the use of conventional scan protocol.     

管电压对下肢CT血管成像辐射剂量及图像质量的影响研究

目的:研究管电压对下肢CT血管成像辐射剂量及图像质量的影响。方法:选取2016年1月-2017年10月于我院行下肢CT血管成像的患者102例,将其以随机数字表法均分成观察组与对照组,每组51例。对照组管电压取120kV,观察组管电压取80kV,其他扫描参数相同。分别比较两组辐射剂量情况、客观图像质量以及主观图像质量情况。结果:观察组CT剂量指数(CTDIvol)、计量长度乘积(DLP)、有效辐射剂量(ED)水平均明显低于对照组,差异均有统计学意义(P0.05)。观察组腹主动脉、髂总动脉、股动脉、腘动脉、胫前动脉、胫后动脉、腓动脉CT值以及图像噪声均明显高于对照组,差异均有统计学意义(P0.05),两组动脉对比噪声比(CNR)和信噪比(SNR)比较差异无统计学意义(P0.05)。观察组血管阶段显示评分、血管细节分支显示评分均明显高于对照组,而血管边缘锐利度评分明显低于对照组,差异均有统计学意义(P0.05)。结论:下肢CT血管成像采用80kV管电压扫描可有效降低患者所接受的辐射剂量,且能获取较为满意的图像,值得临床推广应用。     

A Monte Carlo simulation for the estimation of patient dose in rest and stress cardiac computed tomography with a 320-detector row CT scanner

PurposeTo estimate organ dose and effective dose for patients for cardiac CT as applied in an international multicenter study (CORE320) with a 320-Detector row CT scanner using Monte Carlo (MC) simulations and voxelized phantoms. The effect of positioning of the arms, off-centering the patient and heart rate on patient dose was analyzed.MethodsA MC code was tailored to simulate the geometry and characteristics of the CT scanner. The phantoms representing the adult reference male and female were implemented according to ICRP 110. Effective dose and organ doses were obtained for CT acquisition protocols for calcium scoring, coronary angiography and myocardial perfusion.ResultsFor low heart rate, the normalized effective dose (E) for cardiac CT was higher for female (5.6 mSv/100 mAs) compared to male (2.2 mSv/100 mAs) due to the contribution of female breast tissue. Averaged E for female and male was 11.3 mSv for the comprehensive cardiac protocol consisting of calcium scoring (1.9 mSv); coronary angiography including rest cardiac perfusion (5.1 mSv) and stress cardiac perfusion (4.3 mSv). These values almost doubled at higher heart rates (20.1 mSv). Excluding the arms increased effective dose by 6–8%, centering the patient showed no significant effect. The k-factor (0.028 mSv/mGy.cm) derived from this study leads to effective doses up to 2–3 times higher than the values obtained using now outdated methodologies.ConclusionMC modeling of cardiac CT examinations on realistic voxelized phantoms allowed us to assess patient doses accurately and we derived k-factors that are well above those published previously.     

CT检查中造影剂不良反应的预防、处理及对影像学检查 的影响分析

目的：在CT 等医学影像检查过程中,常需要应用造影剂。在造影剂的使用常常发生不良反应,掌握不良反应的发生率,减少 或减轻患者的不良反应,能够使CT 增强扫描顺利进行,提高检查安全性。方法：搜集我院2011 年10 月至2012 年9 月间的1500 例CT 造影增强检查患者,包括冠状动脉CT 血管成像（冠脉CTA）、头部CT 血管成像（头CTA）、肝脏增强、泌尿系三维成像 （CTU）以及双下肢血管成像（双下肢CTA）,进行造影剂的不良反应类型、造影剂药物剂量、注射速度等统计分析,总结造成不良 反应发生的因素及处理方法。结果：不良反应的类型包括发热、呕吐、荨麻疹、面色潮红、局部疼痛、流泪、血压下降、喉头水肿、休 克等。使用非离子型造影剂出现不良反应者85 例,占5.67 %。其中轻度反应65 例,占4. 33%;中度反应16 例,占1.06%;重度4 例,占0. 27 %。结论：在CT 增强扫描过程中,造影剂的用量及注射速度与不良反应的发生有相关性。ＣＴ 检查过程总应该认真 执行操作流程,密切观察病人情况,积极防治,正确处理,将造影剂不良反应降低到最低程度,使患者更加安全。     

Low dose computerized tomography examinations of coronary occlusive disease

Background: The aim of this study was to present an original technique of low-dose coronary computerized tomographyangiography (CCTA) for the evaluation and early diagnosis of coronary occlusive disease (COD) and to compare from this technique of CCTA with those resulting from the latest conventional angiography and multidetector computerized tomography units. Methodology: The study included 820 CCTA exams of patients with COD (average age 61 +/? 7 years), with a follow-up exam in 204 male (39%) and 62 female (20%) patients with hemodynamically insignificant coronary occlusion. Exams were performed using a 64-slice computerized tomography (CT) unit using electrocardiography (ECG)-triggering and individual settings (voltage of the x-ray tube and effective tube-current) based on each patient’s body mass index. Exponential dose for each exam was defined. Results:There was a statistically significant progression in the number of patients in whom occlusion of one of 3 coronary arteries occurred in hemodynamically significant occlusive disease (occlusion of more than 50% of lumen) — 60 of 204 males and 12 of 62 females (p<0.0001 and p<0.001). The mid-effective radiation dose during CCTA exams was 1.9+/-0.7mSv (range of 0.9 to 3.9 mSv). Conclusion: Prospective ECG-triggering allowed for low-dose CCTA exams while still enabling high diagnostic accuracy in evaluating patients with COD. The technique used in this study resulted in 2 times less the exponential dose than conventional angiography.