Influence of heart rate on coronary calcium scores: a multi-manufacturer phantom study

To evaluate the influence of heart rate on coronary calcium scores (CCS) using a dynamic phantom on four high-end computed tomography (CT) systems from different manufacturers. Artificial coronary arteries were moved in an anthropomorphic chest phantom at linear velocities, corresponding to <?60, 60–75 and >?75 beats per minute (bpm). Data was acquired with routinely used clinical protocols for CCS on four high-end CT systems (CT1–CT4). CCS, quantified as Agatston and mass scores were compared to reference scores at <?60 bpm. Influence of heart rate was assessed for each system with the cardiac motion susceptibility (CMS) Index. At increased heart rates (>?75 bpm), Agatston scores of the low mass calcification were similar to the reference score, while Agatston scores of the medium and high mass calcification increased significantly up to 50% for all CT systems. Threefold CMS increases at >?75 bpm in comparison with <?60 bpm were shown. For medium and high mass calcifications, significant differences in CMS between CT systems were found. Heart rate substantially influences CCS for high-end CT systems of four major manufacturers, but CT systems differ in motion susceptibility. Follow-up CCS CT scans should be acquired on the same CT system and protocol, and preferably with comparable heart rates.     

Influence of iterative image reconstruction on CT-based calcium score measurements

Iterative reconstruction techniques for coronary CT angiography have been introduced as an alternative for traditional filter back projection (FBP) to reduce image noise, allowing improved image quality and a potential for dose reduction. However, the impact of iterative reconstruction on the coronary artery calcium score is not fully known. In 112 consecutive stable patients with suspected coronary artery disease, the coronary calcium scores were assessed. Comparisons were made between the Agatston, volume and mass scores obtained with traditional FBP, and by using adaptive statistical iterative reconstruction (ASIR). A significant reduction of the Agatston score, volume score and mass score was observed for ASIR when compared to FBP, with median differences of resp. 26, 5 mm³ and 1 mg. Using the ASIR reconstruction, the number of patients with a calcium score of zero increased by 13 %. Iterative CT reconstruction significantly reduces the Agatston, volume and mass scores. Since the calcium score is used as a prognostic tool for coronary artery disease, caution must be taken when using iterative reconstruction.     

Very small calcifications are detected and scored in the coronary arteries from small voxel MDCT images using a new automated/calibrated scoring method with statistical and patient specific plaque definitions

A negative (zero) Agatston coronary calcium score (CCS) by current methods confers a very low risk for hard coronary events during the next years. However, controversy remains on how to use a negative score since some hard events still occur. We report on a new method with improved detection sensitivity for very small calcifications with the potential to more confidently rule out early atherosclerotic disease. Seventy-eight (78) patients with negative Agatston scores by conventional methods with 2.5 mm slices were selected from routine GE 64 MDCT scans. Each scan was reconstructed a second time from the same data to create 0.625 mm isotropic voxels. The 2.5 mm images were manually scored by the usual Agatston method using the GE SmartScore? software. Both the 2.5 and 0.625 mm image sets were scored with a new automated and calibrated method (N-vivo?, Image Analysis). The software automatically computes dual scoring thresholds that are statistically defined and specific for each patient, scanner, and scan. The images were hybrid calibrated by simultaneous scanned phantoms in combination with in vivo blood/muscle references. The output reported the calibrated mass scores along with the number of plaques using 18 pt, 3-D connectivity criteria. A CCS Test phantom with known CaHA microspheres was used to validate the method. Twenty-three percent (18 of 78) of the patients with negative Agatston scores by the conventional method scored positive for coronary calcifications by the N-vivo method. The number of small plaques scored per patient varied from 1 to 4. One patient with a single small calcification suffered a hard coronary event during the CT scan. All of the detected plaques were located in the proximal heart. The conventional CCS method misclassified 23% of these patients as having negative coronary calcium scores. The N-vivo automated scoring method with small voxel CT images increased the detection sensitivity of small calcifications with no increase in radiation dose. Detection of small coronary calcified plaques occult to conventional scoring methods may increase the negative predictive power of calcium scoring and may improve plaque composition analysis.     

Comparison of ordinal versus Agatston coronary calcification scoring for cardiovascular disease mortality in community-living individuals

Coronary artery calcification (CAC) by the Agatston method predicts cardiovascular disease (CVD), but requires cardiac gated computed tomography (CT) scans, a procedure not covered by most insurance providers. An ordinal CAC score (scored 0–12 based on artery number and extent of calcification involvement) can be measured on standard chest CTs. However, the correlation of ordinal and Agatston CAC scores and their relative association with CVD mortality is uncertain, which we sought to determine. Nested case–control study. Community-living individuals undergoing “whole body” CT scans for preventive medicine. 4,544 consecutive patients with CT scans, were followed from 2000 to 2009. We selected cases who died of CVD (n = 57) and age, sex, and CT slice-thickness matched each case to three controls (N = 171). Cardiac gated 3 mm chest CTs and non-gated 6 mm standard chest CTs. CVD death over 9 years follow-up. The intra- and inter-reader kappa for the ordinal CAC score was 0.90 and 0.76 respectively. The correlation of Agatston and ordinal CAC scores was 0.72 (p < 0.001). In models adjusted for traditional CVD risk factors, the odds of CVD death per 1 SD greater CAC was 1.66 (1.03–2.68) using the ordinal CAC score and 1.57 (1.00–2.46) using the Agatston score. A simple ordinal CAC score is reproducible, strongly correlated with Agatston CAC scores, and provides similar prediction for CVD death in predominantly Caucasian community-living individuals.     

Dose reduction for coronary calcium scoring with hybrid and model-based iterative reconstruction: an ex vivo study

Purpose To determine the influence of dose reduction on coronary calcium scoring using hybrid and model-based iterative reconstruction (IR) techniques. Methods Fifteen ex vivo hearts were scanned in a phantom representing an average adult person at routine dose and three levels of dose reduction; 27, 55 and 82 % reduced-dose, respectively. All images were reconstructed using filtered back-projection (FBP), hybrid IR (iDose⁴, levels 1, 4 and 7) as well as model-based IR iterative model reconstruction (IMR, levels 1, 2 and 3). Agatston, mass and volume scores found with iDose⁴ and IMR were compared to FBP reconstruction (routine dose) as well as objective image quality. Results With FBP calcium scores remained unchanged at 82 % reduced dose. With IR Agatston scores differed significantly at routine dose, using IMR level 3 and iDose⁴ level 7, and at 82 % reduced dose, using IMR levels 1–3 and iDose⁴ level 7. The maximum median difference was 5.3 %. Mass remained unchanged at reduced dose levels while volume was significantly lower at 82 % reduced dose with IMR (maximum median difference 5.0 %). Objective image quality improved with IR, at 82 % reduced dose the CNR of iDose⁴ level 7 was similar to the reference dose CNR, and IMR levels 1–3 resulted in an even higher CNR. Conclusion Calcium scores were not affected by radiation-dose reduction with FBP and low levels of hybrid IR. Objective image quality increased significantly using hybrid and model-based IR. Therefore low level hybrid IR has the potential to reduce radiation-dose of coronary calcium scoring with up to 82 %.     

Reproducibility of two coronary calcium quantification algorithms in patients with different degrees of calcification

Purpose: To evaluate the reproducibility of coronary calcium quantification algorithms by electron beam CT (EBT) in patients with different amounts of calcified plaque using the conventional (Agatston) score and an area score and to demonstrate a potential application of these results for evaluation of follow-up scans. Methods: In 50 consecutive patients, the conventional calcium score (CCS = Agatston score) and the area score (AS) were summed for each artery and patient. Data were analyzed in four groups according to degrees of calcification: 0 (absent–minimal): CCS 0–9, I (mild): CCS 10–99, II (moderate): CCS 100–399, III (severe): CCS 400. We determined and compared the reproducibility for each algorithm within and among groups. Results: Median percent reproducibility improved with increasing amounts of calcified plaque for the CCS and the AS (p = 0.002 and p = 0.004, respectively). We demonstrate how these reproducibility values can be used to evaluate long-term follow-up studies. The reduction of median reproducibility per patient using the AS vs. the CCS was 32% (13 vs. 19%, respectively). On a vessel-by-vessel basis, the reduction of median reproducibility was 7% (24.3 vs. 22.6%, CCS vs. AS, p < 0.02), which was attributable to a 45% reduction in reproducibility in arteries with mild scores (46.1 vs. 25.5%, CCS vs. AS, p < 0.005). Conclusion: The AS has an improved reproducibility compared with the CCS, especially in patients with small amounts of coronary calcifications which may prove clinically useful. Different reproducibility values in different degrees of calcification can be used for an individual assessment of changes in amounts of coronary calcification.     

CT of the pancreas: comparison of image quality and pancreatic duct depiction among model-based iterative,adaptive statistical iterative,and filtered back projection reconstruction techniques

The purpose of this study is to compare CT images of the pancreas reconstructed with model-based iterative reconstruction (MBIR), adaptive statistical iterative reconstruction (ASiR), and filtered back projection (FBP) techniques for image quality and pancreatic duct (PD) depiction. Data from 40 patients with contrast-enhanced abdominal CT [CTDIvol: 10.3 ± 3.0 (mGy)] during the late arterial phase were reconstructed with FBP, 40% ASiR–FBP blending, and MBIR. Two radiologists assessed the depiction of the main PD, image noise, and overall image quality using 5-point scale independently. Objective CT value and noise were measured in the pancreatic parenchyma, and the contrast-to-noise ratio (CNR) of the PD was calculated. The Friedman test and post-hoc multiple comparisons with Bonferroni test following one-way ANOVA were used for qualitative and quantitative assessment, respectively. For the subjective assessment, scores for MBIR were significantly higher than those for FBP and 40% ASiR (all P < 0.001). No significant differences in CT values of the pancreatic parenchyma were noted among FBP, 40% ASiR, and MBIR images (P > 0.05). Objective image noise was significantly lower and CNR of the PD was higher with MBIR than with FBP and 40% ASiR (all P < 0.05). Our results suggest that pancreatic CT images reconstructed with MBIR have lower image noise, better image quality, and higher conspicuity and CNR of the PD compared with FBP and ASiR.     

KARL-3D迭代重建及MAC重建技术在CT检查中去金属植入物伪影的临床应用价值

目的探讨KARL-3D迭代重建及去金属伪影(MAC)重建技术在CT检查中去金属植入物伪影的临床应用价值。方法收集105例体内有金属植入物患者的CT扫描数据,对扫描图像进行FBP常规重建、KARL-3D迭代重建及MAC重建。以金属伪影影响最严重的区域作为感兴趣区(ROI),比较三组ROI的CT值、噪声值(SD)、信噪比(SNR)、对比噪声比(CNR)和主观评分。结果三组图像的CT值、SD、SNR、CNR和主观评分比较,差异均具有统计学意义(P<0.05),其中SD值(SD1与SD2)的排序为FBP组>KARL-3D迭代组>MAC组;余三项指标(SNR1,SNR2和CNR)排序均为FBP组相似文献   

CT predictors of post-procedural aortic regurgitation in patients referred for transcatheter aortic valve implantation: an analysis of 105 patients

Cardiac computed tomography (CT) allows accurate and detailed analysis of the anatomy of the aortic root and valve, including quantification of calcium. We evaluated the correlation between different CT parameters and the degree of post-procedural aortic regurgitation (AR) after transcatheter aortic valve implantation (TAVI) using the balloon-expandable Edwards Sapien prosthesis. Pre-intervention contrast-enhanced dual source CT data sets of 105 consecutive patients (48 males, mean age 81 ± 6 years, mean logEuroSCORE 34 ± 13 %) with symptomatic severe aortic valve stenosis referred for TAVI using the Edwards Sapien prosthesis (Edwards lifesciences, Inc., CA, USA) were analysed. The degrees of aortic valve commissural calcification and annular calcification were visually assessed on a scale from 0 to 3. Furthermore, the degree of aortic valve calcification as quantified by the Agatston score, aortic annulus eccentricity, aortic diameter at the level of the sinus of valsalva and at the sinotubular junction were assessed. Early post-procedural AR was assessed using aortography. Significant AR was defined as angiographic AR of at least moderate degree (AR ≥ 2). Visual assessment of the degree of aortic annular calcification as well as the Agatston score of aortic valve calcium correlated weakly, yet significantly with the degree of post-procedural AR (r = 0.31 and 0.24, p = 0.001 and 0.013, respectively). Compared to patients with AR < 2, patients with AR ≥ 2 showed more severe calcification of the aortic annulus (mean visual scores 1.9 ± 0.6 vs. 1.5 ± 0.6, p = 0.003) as well as higher aortic valve Agatston scores (1,517 ± 861 vs. 1,062 ± 688, p = 0.005). Visual score for commissural calcification did not differ significantly between both groups (mean scores 2.4 ± 0.5 vs. 2.5 ± 0.5, respectively, p = 0.117). No significant correlation was observed between the degree of AR and commissural calcification, aortic annulus eccentricity index or aortic diameters. The extent of aortic valve annular calcification, but not of commissural calcification, predicts significant post-procedural AR in patients referred for TAVI using the balloon-expandable Edwards Sapiens prosthesis.     

The feasibility of sub-millisievert coronary CT angiography with low tube voltage,prospective ECG gating,and a knowledge-based iterative model reconstruction algorithm

We evaluated the feasibility of sub-millisievert (mSv) coronary CT angiography (CCTA) using low tube voltage, prospective ECG gating, and a knowledge-based iterative model reconstruction algorithm. Twenty-four non-obese healthy subjects (M:F 13:11; mean age 50.2 ± 7.8 years) were enrolled. Three sets of CT images were reconstructed using three different reconstruction methods: filtered back projection (FBP), iterative reconstruction (IR), and knowledge-based iterative model reconstruction (IMR). The scanning parameters were as follows: step-and-shoot axial scanning, 80 kVp, and 200 mAs. On the three sets of CT images, the attenuation and image noise values were measured at the aortic root. The signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) were calculated at the proximal right coronary artery and the left main coronary artery. The qualitative image quality of the CCTA with IMR was assessed using a 4-point grading scale (grade 1, poor; grade 4, excellent). The mean radiation dose of the CCTA was 0.89 ± 0.09 mSv. The attenuation values with IMR were not different from those of other reconstruction methods. The image noise with IMR was significantly lower than with IR and FBP. Compared to FBP, the noise reduction rate of IMR was 69 %. The SNR and CNR of CCTA with IMR were significantly higher than with FBP or IR. On the qualitative analysis with IMR, all included segments were diagnostic (grades 2, 3, and 4), and the mean image quality score was 3.6 ± 0.6. In conclusion, CCTA with low tube voltage, prospective ECG gating, and an IMR algorithm might be a feasible method that allows for sub-millisievert radiation doses and good image quality when used with non-obese subjects.     

Image quality of CT angiography with model-based iterative reconstruction in young children with congenital heart disease: comparison with filtered back projection and adaptive statistical iterative reconstruction

To retrospectively evaluate the image quality of CT angiography (CTA) reconstructed by model-based iterative reconstruction (MBIR) and to compare this with images obtained by filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR) in newborns and infants with congenital heart disease (CHD). Thirty-seven children (age 4.8 ± 3.7 months; weight 4.79 ± 0.47 kg) with suspected CHD underwent CTA on a 64detector MDCT without ECG gating (80 kVp, 40 mA using tube current modulation). Total dose length product was recorded in all patients. Images were reconstructed using FBP, ASIR, and MBIR. Objective image qualities (density, noise) were measured in the great vessels and heart chambers. The contrast-to-noise ratio (CNR) was calculated by measuring the density and noise of myocardial walls. Two radiologists evaluated images for subjective noise, diagnostic confidence, and sharpness at the level prior to the first branch of the main pulmonary artery. Images were compared with respect to reconstruction method, and reconstruction times were measured. Images from all patients were diagnostic, and the effective dose was 0.22 mSv. The objective image noise of MBIR was significantly lower than those of FBP and ASIR in the great vessels and heart chambers (P < 0.05); however, with respect to attenuations in the four chambers, ascending aorta, descending aorta, and pulmonary trunk, no statistically significant difference was observed among the three methods (P > 0.05). Mean CNR values were 8.73 for FBP, 14.54 for ASIR, and 22.95 for MBIR. In addition, the subjective image noise of MBIR was significantly lower than those of the others (P < 0.01). Furthermore, while FBP had the highest score for image sharpness, ASIR had the highest score for diagnostic confidence (P < 0.05), and mean reconstruction times were 5.1 ± 2.3 s for FBP and ASIR and 15.1 ± 2.4 min for MBIR. While CTA with MBIR in newborns and infants with CHD can reduce image noise and improve CNR more than other methods, it is more time-consuming than the other methods.     

A novel iterative reconstruction algorithm allows reduced dose multidetector-row CT imaging of mechanical prosthetic heart valves

Multidetector-row CT is promising for prosthetic heart valve (PHV) assessment but retrospectively ECG-gated scanning has a considerable radiation dose. Recently introduced iterative reconstruction (IR) algorithms may enable radiation dose reduction with retained image quality. Furthermore, PHV image quality on the CT scan mainly depends on extent of PHV artifacts. IR may decrease streak artifacts. We compared image noise and artifact volumes in scans of mechanical PHVs reconstructed with conventional filtered back projection (FBP) to lower dose scans reconstructed with IR. Four different PHVs (St. Jude, Carbomedics, ON-X and Medtronic Hall) were scanned in a pulsatile in vitro model. Ten retrospectively ECG-gated CT scans were performed of each PHV at 120 kV, 600 mAs (high-dose CTDI_vol 35.3 mGy) and 120 kV, 300 mAs (low-dose CTDI_vol 17.7 mGy) on a 64 detector-row scanner. Diastolic and systolic images were reconstructed with FBP (high and low-dose) and the IR algorithm (low-dose only). Hypo- and hyperdense artifact volumes were determined using two threshold filters. Image noise was measured. Mean hypo- and hyperdense artifact volumes (mm³) were 1,235/5,346 (high-dose FBP); 2,405/6,877 (low-dose FBP) and 1,218/5,333 (low-dose IR). Low-dose IR reconstructions had similar image noise compared to high-dose FBP (16.5 ± 1.7 vs. 16.3 ± 1.6, mean ± SD, respectively, P = 1.0). IR allows ECG-gated PHV imaging with similar image noise and PHV artifacts at 50% less dose compared to conventional FBP in an pulsatile in vitro model.     

基于模型及自适应统计迭代重建优化儿童腹部低剂量CT血管造影图像质量

目的 评价基于模型的迭代重建（MBIR）及自适应统计迭代重建（ASIR）优化100 kV儿童腹部CT血管造影（CTA）图像质量的价值。方法 对55例患儿行100 kV低剂量腹部CTA,分别采用MBIR、100% ASIR、80% ASIR、60% ASIR、40% ASIR及滤过反向投影（FBP）算法重建为6组图像,评价图像质量,包括图像噪声、大动脉（LA）及小动脉（SA）显示能力;对比各级动脉CT值及标准差（SD）,计算信噪比（SNR）及对比噪声比（CNR）。结果 图像噪声主观评分及LA评分以MBIR图像最高,ASIR次之,FBP图像质量最差;SA评分以MBIR图像最佳,FBP次之;随权重提升,ASIR图像评分逐渐降低,100% ASIR最低（P均<0.05）。MBIR图像SD最低,其SNR及CNR明显高于其他图像（P均<0.05）。结论 MBIR可明显提高儿童低剂量CTA图像质量,100% ASIR仅可提高图像显示LA能力。     

Karl迭代重建技术对低剂量CT定量评估婴幼儿肺密度及肺容积的影响

目的 观察Karl迭代重建技术对低剂量CT定量评估婴幼儿肺密度及肺容积的影响。方法 纳入100例临床疑诊呼吸系统疾病的婴幼儿,将其随机分为低剂量（LD）组及常规剂量（RD）组各50例;采集肺部平扫CT图像,对LD组分别以滤波反投影（FBP）算法及Karl 1、3、5、7、9级迭代重建技术重建图像,对RD组以FBP算法重建。记录2组有效剂量（ED）,测量并比较各重建图像中的全肺平均肺密度（MLD）和全肺容积（LV）的差异,以及支气管分叉水平的主动脉、竖脊肌、胸腺、前胸壁皮下脂肪噪声值（SD）平均值及图像质量主观评价的差异。结果 LD组ED较RD组下降84.44%。FBP重建图像中,LD组MLD和主观评分均低于RD组（P均<0.01）,其LV和SD均高于RD组（P均<0.01）。LD组内Karl 1、3、5、7、9级重建图像中的MLD、LV、SD和主观评分差异均有统计学意义（P均<0.05）;随Karl迭代等级升高,MLD逐渐升高、LV和SD则逐渐减低,Karl 7级与Karl 1级间各指标差异均有统计学意义（P均<0.05）,主观评分以Karl 5级最高。LD组Karl 5级重建图像的MLD和主观评分均高于LD组FBP重建图像（P均<0.05）而低于RD组FBP重建图像（P<0.05）;LV和SD均低于LD组FBP重建图像（P均<0.01）,而高于RD组FBP重建图像（P<0.01）。结论 低剂量定量CT可能低估婴幼儿MLD而高估其LV;Karl迭代重建技术能提高CT定量分析的准确性、降低图像噪声、提高图像质量,尤以Karl 5级迭代重建图像质量最佳。     

Impact of knowledge-based iterative model reconstruction on myocardial late iodine enhancement in computed tomography and comparison with cardiac magnetic resonance

We evaluated the image quality and diagnostic performance of late iodine enhancement computed tomography (LIE-CT) with knowledge-based iterative model reconstruction (IMR) for the detection of myocardial infarction (MI) in comparison with late gadolinium enhancement magnetic resonance imaging (LGE-MRI). The study investigated 35 patients who underwent a comprehensive cardiac CT protocol and LGE-MRI for the assessment of coronary artery disease. The CT protocol consisted of stress dynamic myocardial CT perfusion, coronary CT angiography (CTA) and LIE-CT using 256-slice CT. LIE-CT scans were acquired 5 min after CTA without additional contrast medium and reconstructed with filtered back projection (FBP), a hybrid iterative reconstruction (HIR), and IMR. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed. Sensitivity and specificity of LIE-CT for detecting MI were assessed according to the 16-segment model. Image quality scores, and diagnostic performance were compared among LIE-CT with FBP, HIR and IMR. Among the 35 patients, 139 of 560 segments showed MI in LGE-MRI. On LIE-CT with FBP, HIR, and IMR, the median SNRs were 2.1, 2.9, and 6.1; and the median CNRs were 1.7, 2.2, and 4.7, respectively. Sensitivity and specificity were 56 and 93% for FBP, 62 and 91% for HIR, and 80 and 91% for IMR. LIE-CT with IMR showed the highest image quality and sensitivity (p?<?0.05). The use of IMR enables significant improvement of image quality and diagnostic performance of LIE-CT for detecting MI in comparison with FBP and HIR.     

新一代基于模型的迭代重建在低剂量上腹部CT中的应用

目的 比较自适应统计迭代重建（ASIR）、常规基于模型的迭代重建（MBIRc）、新一代基于模型的迭代重建（MBIRn）中优化低密度对比设置的MBIR_NR403种算法对低剂量上腹部CT图像质量的影响。方法 采用CT扫描静止状态下水模,比较0.625 mm层厚时滤波反投影算法（FBP）、ASIR、MBIRc和MBIR_NR40的空间分辨率和密度分辨率。1年内接受2次腹部增强CT扫描受检者60例,初次检查采用常规辐射剂量（噪声指数=10）扫描,FBP重建。复查时采用低辐射剂量方案（噪声指数=20）扫描,分别采用标准算法ASIR、MBIRc和MBIR_NR40三种方法重建为0.625 mm层厚的图像后进行对比分析。测量皮下脂肪、背部肌肉、肝脾实质CT值和噪声,计算以皮下脂肪为背景的肝脾实质CNR,采用单因素方差分析比较各重建算法噪声和CNR。由2名放射科医师以常规剂量FBP重建为基础,采用半定量目测评分法盲法进行噪声和细节结构、病变边缘清晰度评分,比较主观评分差异,评价观察者间一致性。结果 体模研究提示MBIRc空间分辨率最高,MBIR_NR40密度分辨率最高。临床研究显示初次检查剂量长度乘积（DLP）为（368.03±146.25） mGy·cm,有效剂量（ED）为（5.52±2.19） mSv;复查时DLP为（93.18±41.21） mGy.cm,ED为（1.40±0.62） mSv,分别下降约74.68%和74.64%。MBIR_NR40重建图像肌肉、脂肪噪声低于MBIRc、ASIR重建和常规剂量FBP重建（P均<0.05）。MBIR_NR40重建图像肝脾CNR大于MBIRc、ASIR重建和常规剂量FBP重建（P均<0.05）。2名放射科医师主观评分一致性优良。低剂量MBIR_NR40主观图像噪声最低、显示上腹部细节结构和病变边缘特征最清晰,优于MBIRc,MBIRc优于常规剂量FBP,低剂量ASIR最差,差异均有统计学意义（P均<0.05）。结论 减少辐射剂量约75%低剂量上腹部成像时,MBIR重建图像质量优于ASIR、MBIRc重建图像及常规剂量FBP图像。     

Reliability analysis of visual ranking of coronary artery calcification on low-dose CT of the thorax for lung cancer screening: comparison with ECG-gated calcium scoring CT

Coronary artery calcification (CAC) is frequently detected on low-dose CT (LDCT) of the thorax. Concurrent assessment of CAC and lung cancer screening using LDCT is beneficial in terms of cost and radiation dose reduction. The aim of our study was to evaluate the reliability of visual ranking of positive CAC on LDCT compared to Agatston score (AS) on electrocardiogram (ECG)-gated calcium scoring CT. We studied 576 patients who were consecutively registered for health screening and undergoing both LDCT and ECG-gated calcium scoring CT. We excluded subjects with an AS of zero. The final study cohort included 117 patients with CAC (97 men; mean age, 53.4 ± 8.5). AS was used as the gold standard (mean score 166.0; range 0.4–3,719.3). Two board-certified radiologists and two radiology residents participated in an observer performance study. Visual ranking of CAC was performed according to four categories (1–10, 11–100, 101–400, and 401 or higher) for coronary artery disease risk stratification. Weighted kappa statistics were used to measure the degree of reliability on visual ranking of CAC on LDCT. The degree of reliability on visual ranking of CAC on LDCT compared to ECG-gated calcium scoring CT was excellent for board-certified radiologists and good for radiology residents. A high degree of association was observed with 71.6 % of visual rankings in the same category as the Agatston category and 98.9 % varying by no more than one category. Visual ranking of positive CAC on LDCT is reliable for predicting AS rank categorization.     

The impact of a new model-based iterative reconstruction algorithm on prosthetic heart valve related artifacts at reduced radiation dose MDCT

To assess the impact of hybrid iterative reconstruction (IR) and novel model-based iterative reconstruction (IMR) and dose reduction on prosthetic heart valve (PHV) related artifacts and objective image quality. One transcatheter and two mechanical PHVs were embedded in diluted contrast-gel, inserted in an anthropomorphic phantom and imaged stationary with retrospectively ECG-gated computed tomography. Eight acquisitions were obtained of each PHV at 120 kV, 600 mAs (routine), 300 and 150 mAs (reduced dose). Data were reconstructed with filtered back projection (FBP), IR and IMR. Hypodense and hyperdense artifact volumes were quantified using two threshold filters. Signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were calculated. Artifact volumes differed significantly between reconstruction algorithms for all PHVs (P < 0.005). Compared to FBP, IR decreased overall hypodense and hyperdense artifact volumes; at 150 mAs by 53 and 20 % (IR) and 67 and 23 % (IMR), respectively and significantly increased SNR and CNR at all doses (P < 0.012). Even at reduced dose, IMR resulted in higher image quality than routine dose FBP and IR. Iterative reconstruction and particularly IMR significantly reduce PHV-related artifacts and improve objective image quality in non-pulsatile conditions, even in reduced-dose images. Also, this study suggests that IMR allows for more radiation dose reduction in comparison to hybrid IR while maintaining high image quality.     

FBP、ASiR和VEO三种重建算法对常规剂量胸部CT图像质量的影响

目的探讨滤波反投影(FBP)、自适应统计迭代重建技术(ASiR)和基于模型的迭代重建算法(MBIR,商品名"VEO")三种重建技术对常规剂量胸部薄层CT图像质量的影响。方法应用能谱CT对15例成年患者行胸部增强CT扫描,扫描条件:100kVp,自动毫安,噪声指数15,螺距0.984∶1,球管转速0.4秒/圈。分别用FBP、50%ASiR(50%比例ASiR和FBP混合以降低噪声)和VEO三种重建算法对原始数据行0.625mm薄层重建,测量图像噪声及胸主动脉与背部肌肉的对比噪声比(CNR),并对3组图像分别进行质量评分,然后行对比分析。结果FBP、50%ASiR和VEO三组图像的噪声分别为24.30±3.55、17.11±2.55及11.69±1.74,50%ASiR和VEO组图像噪声分别较FBP组降低29.59%和51.89%(P均<0.01);胸主动脉与背部肌肉的CNR FBP、50%ASiR和VEO三组图像分别为10.56±3.05、15.15±3.88及21.69±5.62,50%ASiR和VEO组图像CNR较FBP组分别提高43.47%和105.40%(P均<0.01);图像质量主观评分FBP、50%ASiR和VEO三组图像分别为4.03±0.72、4.63±0.41及5.75±0.25,50%ASiR和VEO组图像较FBP组分别提高14.89%和42.68%(P均<0.01)。结论与FBP重建算法比较,在相同剂量条件下,50%ASiR和VEO能显著降低胸部CT图像噪声并提高图像质量;其中VEO重建算法降噪及提高图像质量效果更为显著。     

Small calcified coronary atherosclerotic plaque simulation model: minimal size and attenuation detectable by 64-MDCT and MicroCT

Zero calcium score may not reflect the absence of calcifications as small calcifications could be missed. This study aimed to evaluate minimal size and minimal attenuation of coronary calcifications detectable by computed tomography (CT) and to determine the minimal spatial resolution required for detecting calcification onset. Using open source CT simulation software, CTSim^?, several 50%-stenotic coronary artery phantoms were designed with 5?μm resolution, realistic morphology and tissue-specific Hounsfield Unit (HU) values. The plaque had an attenuation resembling fibrous plaque and contained a single calcification. X-ray projections were simulated with settings resembling non-contrast-enhanced 64 multi detector-row CT (64-MDCT). Scanning and reconstruction were simulated with spatial resolution of a 64-MDCT (0.4mm) and of a MicroCT (48?μm). Starting from a single calcium granule, the calcification was simulated to grow in size and attenuation until it could be detected using clinically accepted calcium determination scheme on MicroCT and 64-MDCT images. The smallest coronary calcifications detectable at MicroCT and 64-MDCT, which had a realistic attenuation (?1,024 to 3,072?HU), were of 25?μm and 215?μm diameter, respectively. The area was overestimated 7.7 and 8.8 times, respectively. Calcifications with smaller size need to have an unrealistically high attenuation to be detectable by 64-MDCT. In conclusion, 64-MDCT is only able to detect coronary calcifications with minimal diameter of 215?μm. Consequently, early onset of calcification in coronary plaque will remain invisible when using CT and a zero calcium score can not exclude the presence of coronary calcification.