Coronary calcium screening with dual-source CT: reliability of ungated,high-pitch chest CT in comparison with dedicated calcium-scoring CT

Purpose

To investigate the reliability of ungated, high-pitch dual-source CT for coronary artery calcium (CAC) screening.

Materials and methods

One hundred and eighty-five smokers underwent a dual-source CT examination with acquisition of two sets of images during the same session: (a) ungated, high-pitch and high-temporal resolution acquisition over the entire thorax (i.e., chest CT); (b) prospectively ECG-triggered acquisition over the cardiac cavities (i.e., cardiac CT).

Results

Sensitivity and specificity of chest CT for detecting positive CAC scores were 96.4 % and 100 %, respectively. There was excellent inter-technique agreement for determining the quantitative CAC score (ICC = 0.986). The mean difference between the two techniques was 11.27, representing 1.81 % of the average of the two techniques. The inter-technique agreement for categorizing patients into the four ranks of severity was excellent (weighted kappa?=?0.95; 95 % CI 0.93–0.98). The inter-technique differences for quantitative CAC scores did not correlate with BMI (r?=?0.05, p?=?0.575) or heart rate (r?=?–0.06, p?=?0.95); 87.2 % of them were explained by differences at the level of the right coronary artery (RCA: 0.8718; LAD: 0.1008; LCx: 0.0139; LM: 0.0136).

Conclusion

Ungated, high-pitch dual-source CT is a reliable imaging mode for CAC screening in the conditions of routine chest CT examinations.

Key points

? CAC is an independent risk factor for major cardiac events.? ECG-gated techniques are the reference standard for calcium scoring.? Great interest is directed toward calcium scoring on non-gated chest CT examinations.? Reliable calcium scoring can be obtained with dual-source CT in a high-pitch mode.

     

Impact of radiation dose and iterative reconstruction on pulmonary nodule measurements at chest CT: a phantom study

PURPOSE

We aimed to identify the impact of radiation dose and iterative reconstruction (IR) on measurement of pulmonary nodules by chest computed tomography (CT).

METHODS

CT scans were performed on a chest phantom containing various nodules (diameters of 3, 5, 8, 10, and 12 mm; +100, −630 and −800 HU for each diameter) at 80, 100, 120 kVp and 10, 20, 50, 100 mAs (a total of 12 radiation dose settings). Each CT was reconstructed using filtered back projection, iDose⁴, and iterative model reconstruction (IMR). Thereafter, two radiologists measured the diameter and attenuation of the nodules. Noise, contrast-to-noise ratio and signal-to-noise ratio of CT images were also obtained. Influence of radiation dose and reconstruction algorithm on measurement error and objective image quality metrics was analyzed using generalized estimating equations.

RESULTS

The 80 kVp, 10 mAs CT scan was not feasible for the measurement of 3 mm sized simulated ground-glass nodule (GGN); otherwise, diameter measurement error was not significantly influenced by radiation dose (P > 0.05). IR did not have a significant impact on diameter measurement error for simulated solid nodules (P > 0.05). However, for simulated GGNs, IMR was associated with significantly decreased relative diameter measurement error (P < 0.001). Attenuation measurement error was not significantly influenced by either radiation dose or reconstruction algorithm (P > 0.05). Objective image quality was significantly better with IMR (P < 0.05).

CONCLUSION

Nodule measurements were not affected by radiation dose except for 3 mm simulated GGN on 80 kVp, 10 mAs dose setting. However, for GGNs, IMR may help reduce diameter measurement error while improving image quality.Recently, the National Lung Screening Trial demonstrated that three annual low-dose computed tomography (CT) screenings (cumulative average effective dose, 4.5 mSv) resulted in a 20% relative mortality reduction of lung cancer in comparison with chest radiographs for individuals at high risk of lung cancer (1, 2). Despite the great advantage of low-dose CT screenings, one of the biggest considerations must be radiation exposure.Currently, there are several techniques known to reduce radiation exposure from chest CT (3, 4). Modification of the tube current is the simplest method of radiation dose reduction and has been a mainstay of chest CT imaging for radiation dose reduction (5). As lowering radiation dose is often accompanied by increased noise in CT images reconstructed with the conventional filtered back projection (FBP) algorithm (6), noise-reducing iterative reconstruction (IR) algorithms have also become available. At present, all major CT vendors have their own unique IR techniques (6). A novel IR algorithm, iterative model reconstruction (IMR) (Philips Healthcare), was developed recently and this knowledge-based IR incorporates system optics as well as data statistics and image statistics.For clinical application of these IR algorithms in conjunction with reduced radiation dose, the feasibility of lesion characterization and radiologic measurements are fundamental prerequisites. Nodule measurements should be performed equally well without significant variability between low-dose IR-applied CT images and standard-dose CT reconstructed with FBP. This is of great significance since the management of small incidentally-detected pulmonary nodules, especially ground-glass nodules (GGNs), differs based on nodule size and their changes over follow-up examinations (7). Manual measurements of nodule diameter on chest CT of various radiation doses from standard to ultra-low doses have been studied previously; however, the effect of IR algorithms were not considered in those investigations (8, 9). In addition, considering the fuzzy, ill-defined border of GGNs and the fact that GGNs are usually followed-up with low-dose CT, advantage of IR for the measurement of GGNs is clearly expected. Nevertheless, IR has not been highlighted for evaluating GGNs to date.In this study, we hypothesized that the accuracy of manual nodule measurement would be potentially affected by various radiation dose settings and reconstruction algorithms such as iDose⁴ (Philips Healthcare) and IMR. We suspected that the measurement of GGNs would be particularly influenced by the variables. Therefore, we performed modeling analysis using an anthropomorphic chest phantom with simulated nodules.     

Radiation dose reduction in chest CT: a review

OBJECTIVE: This article aims to summarize the available data on reducing radiation dose exposure in routine chest CT protocols. First, the general aspects of radiation dose in CT and radiation risk are discussed, followed by the effect of changing parameters on image quality. Finally, the results of previous radiation dose reduction studies are reviewed, and important information contributing to radiation dose reduction will be shared. CONCLUSION: A variety of methods and techniques for radiation dose reduction should be used to ensure that radiation exposure is kept as low as is reasonably achievable.     

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、     

Low dose contrast CT for transcatheter aortic valve replacement assessment: Results from the prospective SPECTACULAR study (spectral CT assessment prior to TAVR)

BackgroundComputed tomographic angiography (CTA) based planning for transcatheter aortic valve replacement (TAVR) is essential for reduction of periprocedural complications. Spectral CT based imaging provides several advantages, including better contrast/signal to noise ratio and increased soft tissue contrast, permitting better delineation of contrast filled structures at lower doses of iodinated contrast media. The aim of this prospective study was to assess the initial feasibility of a low dose iodinated contrast protocol, utilizing monoenergetic 40 keV reconstruction, using a dual-layer CT scanner (DLCT) for CTA in patients undergoing TAVR planning.Methods116 consecutive TAVR patients underwent a gated chest and a non-gated CTA of the abdomen and pelvis. 40 keV virtual monoenergetic images (VMI) were reconstructed and compared with conventional polychromatic images (CI). The proximal aorta and access vessels were scored for image quality by independent experienced cardiovascular imagers.ResultsProximal aortic image quality as assessed by signal to noise (SNR) and contrast to noise ratio (CNR), were significantly better with 40 keV VMI relative to CI (SNR 14.65 ± 7.37 vs 44.16 ± 22.39, p < 0.001; CNR 15.84 ± 9.93 vs 59.8 ± 40.83, p < 0.001). Aortic root dimensions were comparable between the two approaches with a bias towards higher measurements at 40 keV (Bland Altman). SNR and CNR in all access vessel segments at 40 keV were substantially better (p < 0.001 for all peripheral access vessel segments) with comparable image quality.Conclusion40 keV VMI with low dose contrast dose spectral imaging is feasible for comprehensive preprocedural evaluation of access vessels and measurements of aortic root dimensions in patients undergoing TAVR.     

使用自适应统计迭代重建技术降低胸部CT辐射剂量:一项初步研究

目的在一组采用不同的管电流时间乘积(40～150mAs)的CT检查中,比较自适应统计迭代重建技术(ASIR)和滤波反向投影技术(FBP)重建获得影像的病灶显示能力及影像质量。材料与方法在这项经机构审查委员会批准,符合HIPAA标准的研究中,共有23例病人接受了CT     

64排螺旋CT在线剂量调节技术在胸部CT扫描中的应用价值

目的探讨64排螺旋CT在线剂量调节技术（4D CARE Dose）在胸部CT扫描中的应用价值。方法选择我院2011年6月进行胸部螺旋CT扫描的患者60例,按体重分级后随机分为实验组和对照组,对照组使用固定曝光参数扫描,实验组使用自动曝光控制参数扫描,分别记录每次扫描的CT容积剂量指数（CTDI vol）,对比分析,并运用SPSS 13.0软件进行统计学分析（可信度为95%）。结果在图像质量满足临床影像诊断的前提下,运用4D CARE Dose剂量调节的容积剂量指数（实验组）,体重65kg以下组最小剂量3.62mGy,最大剂量6.42mGy;体重65-75kg组最小剂量4.89mGy,最大剂量8.43mGy;体重75kg以上组最小剂量6.37mGy,最大剂量10.22mGy。固定扫描参数的容积剂量指数（对照组）体重65kg以下组剂量6.68mGy;体重65-75kg组剂量9.32mGy;体重75kg以上组剂量12.08mGy。结论胸部螺旋64排螺旋CT扫描时,运用在线剂量调节技术（4D CARE Dose）与固定扫描条件相比,患者接受辐射剂量明显降低。     

Influence of difference in cross-sectional dose profile in a CTDI phantom on X-ray CT dose estimation: a Monte Carlo study

The longitudinal dose profile in a computed tomography dose index (CTDI) phantom had been studied by many researchers. The cross-sectional dose profile in the CTDI phantom, however, has not been studied. It is also important to understand the cross-sectional dose profile in the CTDI phantom for dose estimation in X-ray CT. In this study, the cross-sectional dose profile in the CTDI phantom was calculated by use of a Monte Carlo (MC) simulation method. A helical or a 320-detector-row cone-beam X-ray CT scanner was simulated. The cross-sectional dose profile in the CTDI phantom from surface to surface through the center point was calculated by MC simulation. The shape of the calculation region was a cylinder of 1-mm-diameter. The length of the cylinder was 23, 100, or 300 mm to represent various CT ionization chamber lengths. Detailed analyses of the energy depositions demonstrated that the cross-sectional dose profile was different in measurement methods and phantom sizes. In this study, we also focused on the validation of the weighting factor used in weighted CTDI (CTDI _w ). As it stands now, the weighting factor used in CTDI _w is (1/3, 2/3) for the (central, peripheral) axes. Our results showed that an equal weighting factor, which is (1/2, 1/2) for the (central, peripheral) axes, is more suitable to estimate the average cross-sectional dose when X-ray CT dose estimation is performed.     

Multi-detector CT of the chest: influence of dose onto quantitative evaluation of severe emphysema: a simulation study

PURPOSE: Quantitative evaluation of the lung parenchyma might be impaired or unreliable by use of reduced-dose CT protocols. Aim of the study was to define the threshold where reduced dose has significant impact on quantitative emphysema parameters. MATERIALS AND METHODS: Thirty patients with severe centrilobular emphysema underwent multidetector computed tomography (120 kV, 150 mAs). Original CT raw data were simulated using 10 mAs settings (10-100 SIMmAs). Quantitative analysis provided lung volume, emphysema volume, emphysema index, mean lung density, and 4 emphysema volume classes. Simulated low-dose results were compared with original acquisition. RESULTS: Emphysema index showed no clinical relevant variation down to 30 SIMmAs. The large emphysema volume class was significantly different below 50 SIMmAs. The intermediate and small classes showed an overproportional variation below 50 SIMmAs. CONCLUSIONS: Dose reduction down to 30 SIMmAs is possible for clinical routine. Settings below 50 SIMmAs significantly alter the in-detailed 3-dimensional emphysema quantification.     

Colonic perforation at CT colonography: assessment of risk in a multicenter large cohort

PURPOSE: To assess retrospectively the incidence, clinical features, and treatment of colonic perforation at computed tomographic (CT) colonography in a large multicenter cohort. MATERIALS AND METHODS: The study was performed in accordance with the institutional ethics committees' requirements of a retrospective review in each of the participating centers, and no informed consent was required. A review of all patients who underwent CT colonography between January 2001 and December 2004 in 11 medical centers representing more than 95% of studies performed in a single country was performed to determine the rate of colorectal perforation. Data about patient demographics and patient- and procedure-related risk were recorded. Information about the location of the perforation, its likely mechanism, and treatment was collected. Analysis included calculation of rates of colonic perforation and surgical treatment and of 95% confidence intervals. RESULTS: A total of 11 870 CT colonographic studies were performed in 6837 (57.6%) men and 5033 (42.4%) women (mean age, 59.9 years; range, 38-90 years) with seven cases of colorectal perforation, yielding a risk rate of 0.059% (one of 1696 studies; 95% confidence interval: one of 974, 971 of 6537). The mean age of the patients with perforation was 77.8 years. Six (84%) of seven cases of perforation occurred in symptomatic patients at high risk for colorectal neoplasia, and one (16%) occurred in an asymptomatic average-risk patient. All studies were performed after insufflation of room air. Six (84%) cases of perforation occurred in patients in whom a rectal tube was inserted, and in five of them, a balloon was inflated. Five (71%) cases of perforation occurred in the sigmoid colon; and two (29%), in the rectum. Four (57%) patients (one in 2968 patients; 95% confidence interval: 1.5 in 10 000, 14.7 in 10 000) required surgical treatment. Possible factors that contributed to perforation were left inguinal hernia containing colon (n = 4), severe diverticulosis (n = 3), and obstructive carcinoma (n = 1). CONCLUSION: Perforation of the colon and rectum is a rare complication of CT colonography. Older age and underlying concomitant colonic disease were present in patients with perforation.     

Low-dose nonenhanced helical CT of renal colic: assessment of ureteric stone detection and measurement of effective dose equivalent

PURPOSE: To evaluate a low-dose, nonenhanced helical computed tomographic (CT) protocol in the detection of ureteric stones and measure the associated effective dose equivalent (H(E)) of radiation. MATERIALS AND METHODS: Sixty patients suspected of having renal colic and referred by emergency department physicians underwent nonenhanced helical CT with 7-mm collimation and a 2:1 pitch and then conventional intravenous urography (IVU). The two studies were prospectively and independently interpreted. The diagnostic accuracy of CT for ureteric stone detection was determined by comparing the scans with the IVU images and with a combination of clinical, surgical, and other imaging findings. The radiation risk from typical CT and IVU examinations (five images) was measured in terms of H(E) and compared with the estimated risk from two previously reported CT protocols. RESULTS: CT correctly depicted 36 of 37 ureteric stones, and one false-positive case was recorded, for a sensitivity of 97%, specificity of 96%, and accuracy of 97%. The H(E) for our CT protocol was determined to be 2.8 mSv, which is about double that for IVU and about 75% and 50% of that for two previously reported CT protocols. CONCLUSION: Our low-dose CT protocol is superior to IVU and clinically adequate for diagnosis of renal colic.