Maximizing dose reductions with cardiac CT

Multidetector computed tomography has come a long way in a short time, quickly becoming a standard tool in the cardiac imaging armamentarium. The promise of plaque imaging, combined with both anatomical visualization and stenosis detection, has made this a preferred first line test of many cardiologists and radiologists. This test is well suited to rule out coronary artery disease (obstruction) and still diagnosing subclinical plaque, with may be a good target for anti-atherosclerotic therapies. There has been recent criticism against CT imaging, and cardiac CT specifically, due to the high radiation doses that being employed. New advances have allowed for dramatic dose reductions. These include more routinely performed methods such as dose modulation, and newer methods such as prospective gating or minimizing the field of view. This paper will review the different applications to reduce cardiac CT radiation doses to nominal levels, potentially expanding the applications of cardiac CT by removing one of the biggest barriers.     

Radiation exposure and dose reduction measures in cardiac CT

Noninvasive visualization of the heart by CT is highly accurate and useful, but its association with ionizing radiation and the potential risk of cancer induction has raised concerns. Dose-saving algorithms, new CT scanners, and scanning techniques have been developed to effectively reduce the amount of radiation exposure without deterioration of image quality. Furthermore, additional strategies for dose reduction can be pursued in daily practice following the ALARA (as low as reasonably achievable) principle. However, there still is a high additional dose-saving potential in a consequent application of dose reduction measures, and we recommend individually adapted scan protocols to obtain cardiac CT studies with optimal diagnostic image quality and lowest possible radiation dose.     

Low kVp imaging for dose reduction in dual-source cardiac CT

With the widespread application of cardiac CT has come increasing concern over the effects of radiation dose associated with this exam. Dual source CT provides a number of methods for dose reduction in helical ECG-gated cardiac CT studies. This article discusses several of these methods, with a particular emphasis on low kVp scanning, which can be applied in a large percentage of patients.     

Low kVp imaging for dose reduction in dual-source cardiac CT

With the widespread application of cardiac CT has come increasing concern over the effects of radiation dose associated with this exam. Dual source CT provides a number of methods for dose reduction in helical ECG-gated cardiac CT studies. This article discusses several of these methods, with a particular emphasis on low kVp scanning, which can be applied in a large percentage of patients.     

多层螺旋CT主动脉低剂量与常规剂量扫描的对照研究

目的探讨主动脉低剂量扫描的可行性及不同体重条件下满足诊断的最低mA量。方法研究分两步，初步筛选58例扫描70例次各种可疑主动脉病变或术后随访病例，随机抽取10例为常规剂量350mA扫描，低剂量组按体重分为〈65kg，65～75kg，〉75kg三组，分别采用管电流为50、100、150mA，其余扫描参数同常规剂量组；记录单次加权CT剂量指数（weighted CT dose index，CTDIvol）、扫描长度和平均剂量长度乘积（dose length produce，DLP）。对不同低剂量组的主动脉图像满足诊断率进行比较，并进行统计学处理。第二步筛选60例各种夹层动脉瘤，针对不同体重组采用高一个50mA等级的低剂量扫描（100、150、200mA），记录并分析相应CTDIvol和DLP，评价图像质量及满足诊断率。结果初步研究采用50、100、150mA的CTDIvol仅为常规剂量350mA的11．3％、29．0％和42．7％，各组DLP值与常规剂量组相比均有统计学意义（P〈0．001），但50mA组的诊断符合率仅为60％。第二步研究采用100、150、200mA的CTDIvol为常规剂量的29．0％、42．7％和57．3％，各低剂量组DLP与常规剂量组两两比较差异均有统计学意义（P〈0．001），且各组满足诊断率均达到100％。轴位及各种三维重建图像显示良好。结论适当的主动脉低剂量扫描可以替代常规剂量扫描。夹层动脉瘤应采用略高于其他主动脉病变的管电流。低剂量200mA可普遍适用于各主动脉病变的扫描成像与正确诊断。     

Low radiation dose protocol in cardiac CT with 100 kVp: usefulness of display preset optimization

To evaluate the radiation dose and image quality of 100 kVp cardiac CT, and the effects of display setting optimization. We randomly assigned 100 patients undergoing cardiac CT to one of following two protocols. Fifty patients underwent our conventional protocol with 120 kVp, and the other 50 patients underwent our low radiation dose protocol with 100 kVp. We compared effective dose (ED); CT number, image noise, and contrast noise ratio (CNR) of ascending aorta at 120 and 100 kVp protocol. We also performed quantitative analysis and qualitative analysis for bitmap image of 120, 100 kVp, and display preset optimization for 100 kVp images. The estimated ED was 48 % lower with the 100 kVp protocol than the 120 kVp protocol (2.8 vs. 5.5 mSv, p < 0.01). There is no significant difference in the CNR between 100 and 120 kVp protocol (18.5 ± 3.6 vs. 18.6 ± 3.8, p = 0.84). Display preset optimization significantly improved image quality of 100 kVp cardiac CT, and there is no significant difference in qualitative analysis and quantitative analysis between 100 kVp scan with optimized display preset and 120 kVp scan (p > 0.05). The 100 kVp scanning with optimized display preset offers almost same image quality at cardiac CT of thin adults under 48 % decreased radiation dose.     

Coronary CT angiography with low radiation dose

With the introduction of 64-slice CT and dual-source CT technology, coronary CT angiography (CCTA) has emerged as a useful diagnostic imaging modality for the noninvasive assessment of coronary heart disease. Recently, the risks associated with ionizing radiation on CT have raised serious concerns. The main concern of exposure to ionizing radiation is the potential risk of cancer. CCTA involves much higher radiation dose with the advances in the spatial and temporal resolution of cardiac CT. Currently, various dose-saving algorithms, such as ECG (electrocardiography)-based dose modulation, reduced tube voltage, and prospective ECG gating, high-pitch helical scanning are available to lower radiation exposure during cardiac CT. Therefore, careful selection of CT scanning protocols is needed to keep the radiation exposure ‘as low as reasonably achievable (ALARA)’. In this review we will discuss the radiation dose safety issues, the measurement of radiation dose and current use of dose-saving techniques in CCTA.     

基于容积CT剂量指数、剂量长度乘积及体型特异性剂量估算评估儿童CT辐射剂量

目的 观察以容积CT剂量指数(CTDIvol)与体型特异性剂量估算(SSDE)所评估的儿童CT辐射剂量差异，分析CTDIvol和剂量长度乘积(DLP)对于儿童CT辐射管控的价值。方法 回顾性分析3 247例患儿，其中1 238例接受头颅CT检查，1 152例接受胸部CT检查，857例接受腹盆部CT检查；记录年龄、CTDIvol及DLP,计算有效直径(De)、水当量直径(Dw)、转换因子(f)及基于Dw的SSDE(SSDE_Dw)。比较CTDIvol与SSDE_Dw在不同年龄段儿童CT检查中的差异，观察其评估CT辐射剂量的效能；建立CTDIvol、DLP、f与年龄及De的回归模型，观察其用于儿童CT辐射管控的价值。结果 头颅、胸部及腹盆部CTDIvol与SSDE_Dw差异均有统计学意义(P均<0.001)。随年龄和De增高，CTDIvol和DLP增加(R²为0.76～0.93)而f减小(R²为0.74～0.99)。结论 相比CTDIvol,以SSDE_Dw评估...     

Validity of the size-specific dose estimate in adults undergoing coronary CT angiography: comparison with the volume CT dose index

Size-specific dose estimate (SSDE) takes into account the patient size but remains to be fully validated for adult coronary computed tomography angiography (CCTA). We investigated the appropriateness of SSDE for accurate estimation of patient dose by comparing the SSDE and the volume CT dose index (CTDI_vol) in adult CCTA. This prospective study received institutional review board approval, and informed consent was obtained from each patient. We enrolled 37 adults who underwent CCTA with a 320-row CT. High-sensitivity metal oxide semiconductor field effect transistor dosimeters were placed on the anterior chest. CTDI_vol reported by the scanner based on a 32-cm phantom was recorded. We measured chest diameter to convert CTDI_vol to SSDE. Using linear regression, we then correlated SSDE with the mean measured skin dose. We also performed linear regression analyses between the skin dose/CTDI_vol and the body mass index (BMI), and the skin dose/SSDE and BMI. There was a strong linear correlation (r = 0.93, P < 0.001) between SSDE (mean 37 ± 22 mGy) and mean skin dose (mean 17.7 ± 10 mGy). There was a moderate negative correlation between the skin dose/CTDI_vol and BMI (r = 0.45, P < 0.01). The skin dose/SSDE was not affected by BMI (r = 0.06, P > 0.76). SSDE yields a more accurate estimation of the radiation dose without estimation errors attributable to the body size of adult patients undergoing CCTA.     

320排CT高管电压在低剂量扫描中的应用

目的探讨管电压对320排CT颅脑扫描辐射剂量及图像质量的相关影响,优化CT低剂量扫描参数。方法随机把60例颅脑平扫受检者分成3组,每组20例。分别以100kV,400mAs、120kV,220mAs和135kV,160mAs进行扫描。记录不同管电压扫描的辐射剂量长度乘积（DLP）,测量扫描所得图像中豆状核和丘脑区的CT值标准差,并由两位副主任医师对图像质量进行盲法评分,对比分析不同管电压CT扫描的辐射剂量及图像质量。结果3组辐射剂量长度乘积（OLP）100kV组为601．7mGy,120kV组为551．0mGy,135kV组为533．8mCy,135kV组明显低于100kV组。3组图像质量差异无统计学意义（P〉0．05）,结论高管电压颅脑CT扫描,有助于降低扫描辐射剂量。     

低剂量宽体探测器CT一站式心脏成像评价复杂先天性心脏病婴幼儿左心功能

目的 探讨低剂量宽体探测器CT（Revolution CT）一站式心脏成像评价复杂性先天性心脏病（CCHD）婴幼儿左心功能的价值。方法 采用Revolution CT对45例CCHD患儿行心脏全期相增强扫描,计算获得左心室收缩末期容积（LVESV）、左心室舒张末期容积（LVEDV）、左心室每搏输出量（LVSV）和左心室射血分数（LVEF）,并与二维超声心动图（2D-ECHO）所测相同指标进行比较分析。比较高危组（n=26）与低危组（n=19）患儿Revolution CT左心功能各指标的差异,以二元Logistic回归分析左心功能指标与病情轻重程度的关系。记录并计算患儿接受的有效辐射剂量（ED）。结果 Revolution CT所测LVESV、LVEDV及LVSV均高于2D-ECHO（P均<0.05）,LVEF低于2D-ECHO（P=0.003）。Revolution CT与2D-ECHO所测LVESV、LVEDV、LVSV及LVEF之间均呈正相关（r=0.800、0.830、0.871、0.708,P均<0.001）。高危组与低危组间Revolution CT所测LVESV、LVEDV和LVSV差异有统计学意义（P均<0.05）,LVEF差异无统计学意义（P=0.395）,且Logistic回归分析显示LVESV、LVEDV及LVSV是高危CCHD的危险因素（P均<0.05）。患儿接受的ED为0.30（0.26,0.35）mSv。结论 Revolution CT可在较低辐射剂量下实现解剖结构与心功能测量的一站式成像,对于CCHD术前评估、术式选择和预后判断均有重要价值。     

借助CT图像评价心脏左右斜位摄影体位

目的 借助ＣＴ图像分析心脏斜位摄影体位的正确性,进一步加强质量控制。方法 将８０例胸部ＣＴ图像按胸厚分为〉２０ｃｍ和〈２０ｃｍ两组经数码相机输入计算机,ＣＴ图像通过计算机处理后得到一组参考数值;并以此分析８０例心脏斜位的摄影体位。结果 １．体形对测量脊柱与前后胸壁比值影响不大。右前斜位两组不同胸厚的平均值均为１．３９～１．４０,左前斜位胸厚〉２０ｍｃ组平均值为１．５０～１．５５,胸厚〈２０ｍｃ组平均值为１．５０～１．５４;２．不符要求的斜位片中,右前斜位主要以角度偏大为主,共８例（１０％）;左前斜位以角度偏小为主,共１１例（１３．８％）。结论 通过测量心脏斜位片脊柱与前后胸壁比值。能评价心脏斜位片摄影体位正确性。     

Value of cardiac CT in patients with heart failure

Multidetector CT (MDCT) with 64-slice capability continues to gain momentum for cardiovascular imaging. Beyond images of coronary arteries, it also provides reliable information on left ventricular structure and function, cardiac venous anatomy, the pulmonary venous system, and right ventricular function—all aspects important in the management of heart failure patients. Potential unique applications in heart failure include cardiac dyssynchrony evaluation, assessing cardiomyopathies, and posttransplant annual follow-up. This review details the multiple applications and limitations of MDCT in the heart failure population, including comparison with other commonly used imaging modalities such as echocardiography and MRI.     

多层螺旋CT低剂量对比剂肺动脉成像

目的评价低剂量对比剂多层螺旋CT肺动脉造影(CTPA)的成像技术及图像质量。方法应用多层螺旋CT对24名疑似肺栓塞的病人行CTPA检查,对比剂总量为20ml(300mgI/ml)。以单层动态增强扫描所测时间-密度曲线的峰值时间为扫描延迟时间,对比剂注射速率5.5ml/s,数据采集时间2~3s;另随机选择24例常规对比剂剂量(50ml)CT-PA检查影像作为对照组,影像质量按5级行盲法评价。结果试验组5级图像占34%,4级37%,3级29%,未见1级、2级。对照组5级25%,4级34%,3级41%,未见1级、2级。结论20ml的对比剂可使患者肺动脉各级分支显影,并且达到诊断要求。     

Strategies for cardiac CT imaging

We review the scanning techniques for cardiac CT imaging with single slice and multislice scanners. Combined with prospective triggering for transaxial scanning and retrospective gating for helical scanning the potential advantages and the basic limitations are discussed. Based on those theoretical considerations, the major conclusion is that high resolution data sets with isotropic spatial resolution can be acquired with quadslice, spiral scanning, only. First clinical results support this conclusion.     

Similar postprandial glycemic reductions with escalation of dose and administration time of American ginseng in type 2 diabetes

OBJECTIVE: We previously demonstrated that 3 g American ginseng (AG) reduced postprandial glycemia (PPG) in type 2 diabetic individuals. We investigated whether further reductions can be achieved with escalation of dose and time of AG administration. RESEARCH DESIGN AND METHODS: Ten type 2 diabetic patients (6 men, 4 women; age 63+/-2 years; BMI 27.7+/-1.5 kg/m2; HbA1c 7.3+/-0.3%) were randomly administered 0 g (placebo) or 3, 6, or 9 g ground AG root in capsules at 120, 80, 40, or 0 min before a 25-g oral glucose challenge. Capillary blood glucose was measured before ingestion of AG or placebo and at 0, 15, 30, 45, 60, 90, and 120 min from the start of the glucose challenge. RESULTS: Two-way analysis of variance (ANOVA) demonstrated that treatment (0, 3, 6, and 9 g AG) but not time of administration (120, 80, 40, or 0 min before the challenge) significantly affected PPG (P<0.05), with significant (P = 0.037) interaction for area under the curve (AUC). Pairwise comparisons showed that compared with 0 g (placebo), 3, 6, or 9 g significantly (P<0.05) reduced AUC (19.7, 15.3, and 15.9%, respectively) and incremental glycemia at 30 min (16.3, 18.4, and 18.4%, respectively), 45 min (12.5, 14.3, and 14.3%, respectively), and 120 min (59.1, 40.9, and 45.5%, respectively). However, pairwise comparisons showed no differences between the 3-, 6-, or 9-g doses and any of the times of administration. CONCLUSIONS: AG reduced PPG irrespective of dose and time of administration. No more than 3 g AG was required at any time in relation to the challenge to achieve reductions. Because these reductions included glycemia at the 2-h diagnostic end point, there may be implications for diabetes diagnosis and treatment.