Causes of interscan variability of coronary artery calcium measurements at electron-beam CT

RATIONALE AND OBJECTIVES: The authors performed this study to investigate the causes of interscan variability of coronary artery calcium measurements at electron-beam computed tomography (CT). MATERIALS AND METHODS: Two sets of electron-beam CT scans were obtained in 298 consecutive patients who underwent electron-beam CT to screen for coronary artery calcium. Interscan variations of coronary artery calcium characteristics and the effects of heart rate, electrocardiographic (ECG) triggering method, image noise, and coronary motion on interscan variability were analyzed. RESULTS: The interscan mean variabilities were 21.6% (median, 11.7%) and 17.8% (median, 10.8%) with the Agatston and volumetric score, respectively (P < .01). Variability decreased with increasing calcification score (34.6% for a score of 11-50 and 9.4% for a score of 400-1,000, P < .0001). The absolute difference in Agatston score between scans was 44.1 +/- 95.6. The correlation coefficient between the first and second sets of scans was 0.99 (P < .0001). Lower interscan variability was found in younger patients (<60 years), patients with stable heart rates (heart rate changing less than 10 beats per minute during scanning), patients with no visible coronary motion, and those with an optimal ECG triggering method (P < .05 for all). Results of multivariate logistic analysis showed that changes in calcium volume, mean attenuation, and peak attenuation were significant predictors of interscan variability and caused the interscan variations of the coronary artery calcium measurements (r2 = 0.83, P < .0001). CONCLUSION: Coronary calcification at electron-beam CT varies from scan to scan. Volumetric scoring and optimal ECG triggering should be used to reduce interscan variability. Baseline calcium score and interscan variability must be considered in the evaluation of calcium progression.     

Variability of repeated coronary artery calcium measurements by 16-MDCT with retrospective reconstruction

OBJECTIVE: High reproducibility on coronary calcium scoring is an important factor in monitoring the progression of coronary atherosclerosis. The purposes of this study were, using a 16-MDCT scanner with retrospective reconstruction, to compare the effects of thin-slice images and overlapping image reconstruction on the reproducibility of coronary calcium scoring and to compare 16-MDCT with electron beam CT (EBCT). MATERIALS AND METHODS: Fifty patients underwent two sequential examinations using both EBCT and MDCT. For MDCT, images were reconstructed from the same raw data using the following thicknesses and increments (thickness/increment): 1.25 mm/1.25 mm, 2.5 mm/2.5 mm, and 2.5 mm/1.25 mm. The Agatston, volume, and mass scores were calculated on four pairs of image sets. Statistical analysis was performed to determine significant differences in interscan variability among image acquisition protocols and among measurement algorithms. RESULTS: Overlapping reconstructed images (thickness/increment, 2.5 mm/1.25 mm) obtained on a 16-MDCT scanner showed the lowest variability (mean, 13%; median, 10%) when compared with the Agatston score. CONCLUSION: The use of 16-MDCT with overlapping reconstruction by retrospective reconstruction, yielding low variability of coronary artery calcium measurement on two sequential scans, has an advantage over EBCT in monitoring the progression of atherosclerosis.     

Effect of the reconstruction window obtained at the isovolumic relaxation period on the image quality in electrocardiographic-gated 16-multidetector-row computed tomography coronary angiography studies

OBJECTIVE: To evaluate whether images obtained during the reconstruction window responding to the isovolumic relaxation period could be used for rapid and easy postprocessing. METHODS: One hundred ten consecutive patients with suspected coronary artery disease who had previously had a multidetector computed tomography (MDCT) scan for imaging coronary arteries were enrolled in this study. The age of the patients was 59 +/- 13 years (range: 33-78 years), and 77 (70%) were male. Multidetector computed tomography was performed on a 16-detector-row computed tomography scanner during 1 breath hold (16-24 seconds). Seven different sets of images reconstructed at every 10% of the R-R interval from 30% to 90% for contrast-enhanced scans at levels containing the first several centimeters of the left and right coronary arteries were analyzed. The best of these reconstruction windows were then compared with the images reconstructed at the isovolumic relaxation period, which is the last portion of the T wave at the end of the systole, where there is not any change in ventricular volume, which causes stepladder artifacts. The step artifact was classified as excellent, good, or poor. Image quality was assessed by 2 radiologists who were not aware of each other's interpretation. RESULTS: According to the routinely used reconstructions, there were 76 patients with excellent image quality, 28 with good image quality, and 6 with poor image quality. For the period of isovolumic relaxation, there were 74 patients with excellent image quality, 25 with good image quality, and 11 with poor image quality. CONCLUSION: If one begins image analysis with the isovolumic relaxation period reconstruction window, spending less time for postprocessing analyses, good image quality can be obtained such as with other good reconstruction windows.     

Variability of repeated coronary artery calcium measurements by 1.25-mm- and 2.5-mm-thickness images on prospective electrocardiograph-triggered 64-slice CT

High reproducibility on coronary artery calcium scoring is a key requirement in monitoring the progression of coronary atherosclerosis. The purpose of this prospective study is to assess the reproducibility of 1.25-mm- and 2.5-mm-thickness images on prospective electrocardiograph-triggered 64-slice CT with respect to 2.5-mm-thickness images on spiral overlapping reconstruction. One hundred patients suspected of coronary artery disease were scanned twice repeatedly, both on prospective electrocardiograph-triggered step-and-shoot and retrospective electrocardiograph-gated spiral scans. Using 1.25-mm-thickness collimation, 1.25-mm- and 2.5-mm-thickness image sets on prospective scans and 2.5-mm-thickness image sets with 1.25-mm increment (overlapping) on retrospective scans were obtained. Coronary artery calcium scores, interscan variability and interobserver variability were evaluated. The mean interscan variability in coronary artery calcium measurement on 1.25-mm prospective/2.5-mm prospective/2.5-mm overlapping retrospective scans were Agatston: 10%/18%/12%, volume: 10%/12%/10% and mass: 8%/13%/11% for observer 1 and Agatston: 8%/14%/10%, volume: 7%/9%/10% and mass: 7%/10%/9% for observer 2, respectively. The mean interobserver variability was 5% to 14%. In conclusion, prospective electrocardiograph-triggered 64-slice CT using the 1.25-mm prospective scan shows the lowest variability. The 2.5-mm prospective scan on volume or mass scoring shows variability of around 10%, comparable to 2.5-mm-thickness spiral overlapping reconstruction images.     

Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT

High reproducibility is a key requirement for coronary calcium scoring in follow-up examinations. We investigated the inter-examination reproducibility of calcium scoring with retrospectively ECG-gated multisection spiral CT (MSCT). Fifty patients were examined twice with MSCT. Slices were reconstructed with retrospective ECG gating in the diastolic phase with 3-mm slice width and up to 125-ms temporal resolution. We calculated the Agatston score, calcium volume with and without isotropic interpolation, and calcium mass, and derived the mean and median variability. We investigated the change of variability with use of 3-mm non-overlapping and overlapping increments (2, 1.5, 1 mm). Use of overlapping increment results in considerably reduced interscan variability. We observed a minimum mean variability of 12% and a minimum median variability of 9% for the Agatston score. For volume and mass quantification we obtained a minimum mean variability of 7.5% and a minimum median variability of 5%. Multisection spiral CT enables coronary calcium quantification with high reproducibility in follow-up examinations mainly founded on image data with reduced partial-volume errors due to overlapping increment.     

Quantification of coronary artery calcium with multi-detector row CT: assessing interscan variability with different tube currents pilot study

PURPOSE: To assess the interscan variability of coronary artery calcium as measured with different tube currents and quantification methods in prospective electrocardiography (ECG)-gated multi-detector row CT. MATERIALS AND METHODS: Thirty-three subjects who were asymptomatic for coronary heart disease underwent prospective ECG-gated, subsecond multi-detector row CT of the heart. Each subject underwent two consecutive CT examinations, the first with a dose of either 40 mAs (n = 18) or 80 mAs (n = 15) and the second with a dose of 150 mAs. Calcium volume and calcium score were calculated. Pearson correlation coefficient was computed between the calcium scores of high- and low-dose examinations. Interscan variability in these measurements (ie, the absolute percentage difference) was compared between the examinations with 40-150 mAs and those with 80-150 mAs by using an independent sample t test. In addition, the interscan variabilities of calcium scores between vessels were evaluated with repeated measures of analysis of variance. The interscan variabilities between calcium score and volume measurement were also compared with paired t tests. RESULTS: Twenty-seven of 33 subjects had coronary artery calcium deposits on both CT scans. Five subjects had no calcium deposit on either scan. One subject had calcium deposits on only one scan. The total calcium score between the high- and low-dose scans was highly correlated (r = 0.98) and was not significantly different (P =.58). The interscan variability of calcium score showed no significant difference with respect to subject (P =.25) or vessel (P =.84). The interscan variability of the calcium volume measurement was significantly lower than that of the calcium score with respect to both the subject (P <.01) and the vessel (P <.01). CONCLUSION: A dose of 40 mAs appears adequate for quantifying coronary artery calcium at multi-detector row CT. Interscan variability of multi-detector row CT is substantially reduced by using the calcium volume method.     

Advances in cardiac imaging with 16-section CT systems

RATIONALE AND OBJECTIVES: The authors present advances in electrocardiographically (ECG) gated cardiac spiral scanning with recently introduced 16-section computed tomographic (CT) equipment. MATERIALS AND METHODS: The authors discuss the technical principles of ECG-gated cardiac scanning. They give an overview on system properties and on the detector design. They describe ECG-gated scan- and image-reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose. They discuss key parameters for image quality and present simulation and phantom studies and they give preliminary values for the patient dose. RESULTS: An extension of the adaptive cardiac volume reconstruction for ECG-gated spiral CT provides adequate image quality for up to 16 sections. With the smallest reconstructed section width (about 0.83 mm) and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a transverse resolution phantom independent of the heart rate. For coronary CT angiography, the influence of transverse resolution is most pronounced for coronary segments that are only slightly tilted relative to the scan plane. In this case, visualization of stents and plaques is considerably improved with 1.0-mm or smaller section width. For 0.42-second gantry rotation time, temporal resolution reaches its optimum (105 msec) at a heart rate of 81 beats per minute. Effective patient dose for the standard protocols recommended by the manufacturer ranges from 0.45 mSv (male) for ECG-triggered calcium scoring to 7.1 mSv (male) for high-resolution ECG-gated coronary CT angiography. With ECG pulsing, the dose is reduced by 30%-50% depending on the patient's heart rate. CONCLUSION: Clinical experience will be needed to evaluate fully the potential of 16-section technology for cardiac imaging.     

Evidence for lower variability of coronary artery calcium mineral mass measurements by multi-detector computed tomography in a community-based cohort--consequences for progression studies

PURPOSE: To compare the measurement variability for coronary artery calcium (CAC) measurements using mineral mass compared with a modified Agatston score (AS) or volume score (VS) with multi-detector CT (MDCT) scanning, and to estimate the potential impact of these methods on the design of CAC progression studies. MATERIALS AND METHODS: We studied 162 consecutive subjects (83 women, 79 men, mean age 51 +/- 11 years) from a general Caucasian community-based cohort (Framingham Heart Study) with duplicate runs of prospective electrocardiographically-triggered MDCT scanning. Each scan was independently evaluated for the presence of CAC by four experienced observers who determined a "modified" AS, VS and mineral mass. RESULTS: Of the 162 subjects, CAC was detected in both scans in 69 (42%) and no CAC was detected in either scan in 72 (45%). Calcium scores were low in the 21/162 subjects (12%) for whom CAC was present in one but not the other scan (modified AS < 20 in 20/21 subjects, mean AS 4.6 +/- 1.9). For all three quantification algorithms, the inter- and intraobserver correlation were excellent (r > 0.96). However, the mean interscan variability was significantly different between mineral mass, modified AS, and VS (coefficient of variation 26 +/- 19%, 41 +/- 28% and 34 +/- 25%, respectively; p < 0.04), with significantly smaller mean differences in pair-wise comparisons for mineral mass compared with modified AS (p < 0.002) or with VS (p < 0.03). The amount of CAC but not heart rate was an independent predictor of interscan variability (r = -0.638, -0.614 and -0.577 for AS, VS, and mineral mass, respectively; all p < 0.0001). The decreased interscan variability of mineral mass would allow a sample size reduction of 5.5% compared with modified AS for observational studies of CAC progression and for randomized clinical trials. CONCLUSION: There is significantly reduced interscan variability of CAC measurements with mineral mass compared with the modified AS or VS. However, the measurement variability of all quantification methods is predicted by the amount of CAC and is inversely correlated to the extent of partial volume artifacts. Moreover, the improvement of measurement reproducibility leads to a modest reduction in sample size for observational epidemiological studies or randomized clinical trials to assess the progression of CAC.     

Noninvasive visualization of coronary arteries using contrast-enhanced multidetector CT: influence of heart rate on image quality and stenosis detection

OBJECTIVE: Although multidetector CT (MDCT) with retrospectively ECG-gated image reconstruction has been shown to permit noninvasive visualization of the coronary arteries, the 125-250 msec required for image acquisition frequently causes motion artifacts. We investigated the influence of a patient's heart rate on the presence of motion artifacts and on accuracy of stenosis detection on contrast-enhanced MDCT. MATERIALS AND METHODS: In 100 patients, MDCT was performed, and ECG-gated cross-sectional images were retrospectively reconstructed. From the 10 data sets obtained for each patient (reconstructed at 0-90% of the cardiac cycle in increments of 10%), we chose the best data set for every coronary artery. The images of the arteries were evaluated for occurrence of artifacts and the presence of high-grade stenosis (diameter reduction exceeding 70%) or occlusions. MDCT results were compared with coronary angiographic findings. RESULTS: Of the 400 coronary arteries, 115 (29%) could not be evaluated because of motion artifacts (n = 84) or other reasons (n = 31). Overall, 51 (49%) of 104 stenoses were revealed on MDCT. For detecting stenosis in those arteries that we could evaluate, MDCT had a sensitivity of 91% (51 of 56 stenoses detected) and a specificity of 89%. As the heart rate increased, the number of arteries that could be evaluated decreased, and overall sensitivity for stenosis detection decreased from 62% (heart rate < or = 70 beats per minute) to 33% (heart rate > 70 beats per minute). CONCLUSION: MDCT can reveal coronary stenoses, but the usefulness of MDCT as an aid in accurately evaluating stenoses decreases as a patient's heart rate increases.     

重组相位窗对16层螺旋CT冠状动脉成像图像质量的影响

目的:探讨不同重组相位窗对16层螺旋CT冠状动脉成像质量的影响。方法:对28例健康体检者采用回顾性心电门控的16层螺旋CT冠状动脉成像,将其扫描原始数据分别按45%、55%、65%、70%、75%、85%R-R间期的不同相位的横断面进行重组。结果:左主干在6个R-R时相均显示良好;左前降支在70%R-R时相的重组图像质量最佳;左回旋支及右冠状动脉在75%R-R时相的重组图像质量最佳,整体图像在75%R-R时相的重组图像质量最佳。结论:重组相位窗对多层螺旋CT冠状动脉成像图像质量有重要影响作用。     

Three-dimensional coronary MR angiography performed with subject-specific cardiac acquisition windows and motion-adapted respiratory gating

OBJECTIVE: In coronary MR angiography, data are conventionally accepted in only short and fixed periods of the cardiac and respiratory cycles. We hypothesized that a more flexible and subject-specific approach to cardiac and respiratory gating may shorten scanning times while maintaining image quality. SUBJECTS AND METHODS: We implemented an acquisition technique that uses subject-specific acquisition windows in the cardiac cycle and a motion-adapted gating window for respiratory navigator gating. Cardiac acquisition windows and trigger delays were determined individually from a coronary motion scan. Motion-adapted gating used a 2-mm acceptance window for the central 35% of k-space and a 6-mm window for the outer 65% of k-space. In 10 subjects, three-dimensional coronary MR angiograms of the right and left coronary systems were acquired with this technique (the "adaptive technique") as well as a conventional acquisition method, and the scanning times and image quality were compared. The adaptive technique was then applied prospectively to 40 patients who underwent coronary radiographic angiography. RESULTS: Scanning times with the adaptive technique were reduced by a factor of 2.3 for the right coronary artery and by a factor of 2.2 for the left coronary artery system compared with the conventional technique, mainly because we were able to use longer subject-specific acquisition windows in patients with low heart rates. Subjective and objective measurements of image quality showed no significant differences between the two techniques. Prospective evaluation of MR angiograms yielded a sensitivity and specificity of 74.3% and 88.2%, respectively, to detect significant coronary artery stenoses. CONCLUSION: Coronary MR angiography with subject-specific acquisition windows and motion-adapted respiratory gating reduces scanning times while maintaining image quality and provides high diagnostic accuracy for the detection of coronary artery stenosis.     

Assessment of left ventricular function with 16- and 64-slice multi-detector computed tomography

BACKGROUND: Important to the risk stratification and management of cardiac patients is the assessment of left ventricular function (LVEF), thus imaging modalities which can provide both anatomical and functional data is desirable. Electrocardiographic (ECG) gated multi-detector computed tomographic (MDCT) images may provide accurate assessment of LV ejection fraction, volume and dimensions but have shown systemic errors in the past due to slow gantry rotation speed. METHODS: Between May 2004 and January 2005, 306 patients underwent ECG-gated cardiac CT studies at the Massachusetts General Hospital. Patients with available CT data sets and a recent (within 3 months) ECHO and/or SPECT perfusion imaging were included in the study. ECG-gated data sets were acquired either with a 16-slice or with a 64-slice MDCT. Functional MDCT data sets were reconstructed in 10 cardiac phases (5-95%) with 1.5mm slices. Images were processed and interpreted by two observers blinded to ECHO and SPECT results. RESULTS: A total of 69 patients had MDCT and ECHO or SPECT within 3 months (33 had 16-slice and 36 had 64-slice MDCT). There was fair correlation between LVEF measured by 16-slice MDCT and 'ECHO or SPECT' (62+/-10% vs. 62+/-10%; r=0.56). There was poor correlation between LVEF measured by 16-slice MDCT and ECHO (64+/-10% vs. 59+/-11%; r=0.26) and there was good correlation between LVEF measured by 16-slice MDCT and SPECT (62+/-11% and 64+/-9%, respectively; r=0.76). There was very good correlation between LVEF measured by 64-slice MDCT and 'ECHO or SPECT' (57+/-15% vs. 58+/-13%; r=0.86). There was very good correlation between LVEF measured by MDCT and ECHO (56+/-14% vs. 54+/-15%; r=0.89) and between LVEF measured by 64-slice MDCT and SPECT (60+/-13% and 60+/-14%, respectively; r=0.90). CONCLUSION: The assessment of LVEF and LV dimensions with 64-slice MDCT provide values which are similar to those obtained by echocardiography and Tc-99m gated SPECT. The accuracy of the 64-slice MDCT with a gantry rotation speed of 330ms (when compared to ECHO and SPECT) may be superior to that of the 16-slice MDCT at 420ms gantry rotation.     

双源CT冠状动脉成像辐射剂量的优化

目的：探讨使用更窄的曝光时间窗对双源CT冠状动脉成像图像质量和辐射剂量的影响。方法：选择心律稳定、配合屏气在本院行冠状动脉CTA检查者共360例,按心率及扫描方案随机分为5组：当心率＜65次/分时,行回顾性心电门控扫描,用70％-80％曝光时间窗成像冠状动脉（A组）;窄窗方案根据前瞻性心电门控平扫所获得的最佳时相,选择此时相为中心总长1％作为曝光时间窗,行前瞻心电性门控冠状动脉成像（B组）。当心率≥65次/时,行回顾性心电门控扫描,常规使用30％-80％曝光时间窗成像冠状动脉（C组）;窄窗方案根据前瞻性心电门控平扫所获得的最佳时相,以此时相为中心选择总长10％的曝光时间窗,分别用前瞻性心电门控（D 组）和低剂量回顾性心电门控行冠状动脉成像（E组）;分别计算各组平均有效辐射剂量以及冠状动脉图像质量（4分制评分）,并作统计学分析。结果：A 组[（8．11±1．54）mSv]和B组[（3．63±0．82）mSv],C 组[（10．56±2．51）mSv]和 D 组[（4．42±1．16）mSv],D 组[（4．42±1．16）mSv]和E组[（5．43±1．14）mSv]的辐射剂量相比较均有统计学差异（P＜0．05）,采用窄窗方案前瞻性心电门控技术的辐射剂量最少;而各组间图像质量,均无统计学差异（P＞0．05）。结论：前瞻性心电门控通过平扫获得最佳时相,当心率＜65次/分时,选择曝光总长1％的时间窗,而当心率≥65次/分时,选择曝光总长10％的时间窗,能获得高质量的、满足诊断要求的图像,并可有效地降低辐射量。     

Variation of the coronary calcium score depending on image reconstruction interval and scoring algorithm

RATIONALE AND OBJECTIVES: To evaluate the reconstruction interval dependent bandwidth of the coronary calcium score, considering different methods of image reconstruction and quantification of coronary calcifications. MATERIALS AND METHODS: Seventy-five patients underwent coronary calcium scoring by use of retrospectively ECG-gated multislice spiral CT. In all patients overlapping and nonoverlapping image reconstruction was performed every 10% of the RR-interval. Coronary calcium score was calculated for every reconstructed image series using the Agatston score and a volumetric scoring method. In 25 patients the analysis was performed twice to determine the reconstruction interval dependent intraobserver variability. RESULTS: For nonoverlapping image reconstruction the median of the calcium score determined by the Agatston method ranged from 125.8 to 216.2 and from 166.9 to 211.7 for the volumetric scoring method. For overlapping image reconstruction the corresponding values ranged from 91.6 to 160.5 for the Agatston score and 128.3 to 175.3 for the volumetric calcium score. Reconstruction interval dependent median (mean) variation of the coronary calcium score ranged from 24.1 (45.5)% for nonoverlapping image reconstruction using the Agatston score to 17.5 (25.2)% utilizing a volumetric calcium score with overlapping image reconstruction. There was no statistical significant (P< 0.05) difference between the different methods. Intraobserver variability for the different image reconstruction intervals ranged from 0.78% to 21.51%. The least intraobserver variability was found for overlapping image reconstruction during the diastole using the volumetric scoring method. CONCLUSIONS: Diastolic image reconstruction at 50% or 60% of the RR-interval is recommendable for retrospectively ECG-gated multislice spiral CT. Volumetric calcium scoring and overlapping image reconstruction are beneficial to reduce the variation of the coronary calcium score.     

Overlapping cross-sections significantly improve the reproducibility of coronary calcium measurements by electron beam tomography: a phantom study

PURPOSE: We conducted phantom studies to investigate whether overlapping cross-sections and volumetric scoring would significantly improve interscan reproducibility of electron beam tomography (EBT) for coronary artery calcium quantification. METHOD: Fifteen phantoms simulating various amounts of coronary calcification were scanned in five different positions with a slice thickness of 3.0 mm and a table feed of 3.0, 2.5, and 2.0 mm. For the conventional "Agatston score" and a "volume score" (total volume of calcified lesions), interscan variabilities were compared between the three image acquisition protocols. RESULTS: Agatston score variability was significantly lower for the 2.0 mm table feed than for the 3.0 or 2.5 mm table feed (3.0 mm: 22.9 +/- 10.3%; 2.5 mm: 13.6 +/- 8.2%; 2.0 mm: 8.9 +/- 5.5%). Volume score variability was significantly lower for 2.5 and 2.0 mm table feed than for 3.0 mm table feed (3.0 mm: 21.7 +/- 11.0%; 2.5 mm: 10.9 +/- 5.9%; 2.0 mm: 9.8 +/- 5.9%). CONCLUSION: Overlapping cross-sections, especially in combination with volumetric scoring, significantly improved interscan reproducibility of EBT calcium quantification in a phantom study.     

Effect of varying slice thickness on coronary calcium scoring with multislice computed tomography in vitro and in vivo

OBJECTIVES: To compare coronary calcium scoring results (calcium volume, calcium mass, Agatston score, and number of lesions) of different slice thicknesses using a 16-slice CT (MSCT) scanner. MATERIALS AND METHODS: A nonmoving anthropomorphic thorax phantom with calcium cylinders of different sizes and densities was scanned 30 times with repositioning applying a standardized retrospectively ECG-gated MSCT (SOMATOM Sensation 16; Siemens, Forchheim, Germany) scan protocol: collimation 12 x 0.75 mm, tube voltage 120 kV, effective tube current time-product 133 mAs(eff). Fifty patients (29 male; age 57.2 +/- 8.4 years) underwent a nonenhanced scan applying the same scan protocol. Two image sets (effective slice thicknesses 3 mm and 1 mm) were reconstructed at 60% of the RR interval. Image noise was measured in both studies. Calcium volume, calcium mass and Agatston score were calculated using a commercially available software tool. RESULTS: Due to increased image noise in thinner slices, calcium scoring in all scans was performed applying a scoring threshold of 350 HU. In the phantom study, 1-mm slices showed significantly higher scoring results in respect to calcium volume (+8.2%), calcium mass (+12.5%), and Agatston score (+5.3%) (all P < 0.0001). In the patient study, 27 patients had coronary calcifications in 3-mm slices, and 31 patients had coronary calcifications in 1-mm slices. Thinner slices showed significantly higher scoring results in respect to volume (+47.1%), mass (+47.2%), and Agatston score (+29.7%) (all P < 0.0001). CONCLUSIONS: When comparing 3-mm and 1-mm slices in coronary calcium scoring in MSCT, thinner slices lead to significantly increased scoring results.     

多排螺旋CT心电门控技术对肺静脉口径的研究

目的 利用多排螺旋CT(MDCT)心电门控技术评价1个心动周期内肺静脉口径的变化.方法 前瞻性收集25例利用回顾性心电门控技术进行扫描的检查者,进行10个时相的肺静脉重建.首先在横断位同一层面上测量出右下肺静脉(RIPV)各个时相的口径,得出其最大值及最小值所对应的2个时相,然后在这2个时相下运用多种后处理技术重建4条肺静脉,最后分别测量其口径最大值与最小值并进行统计学分析.结果 横断面上右下肺静脉最大值出现在35%时相(16.21±2.53),最小值出现在85%时相(13.29±2.11);4条肺静脉口径在35%时相的最大值与85%时相最小值比较具有统计学意义(P<0.01).结论 MDCT心电门控技术可以更准确描述肺静脉口径,在1个心动周期内肺静脉口径呈现周期性变化.     

Coronary artery calcification scoring by prospectively triggered multidetector-row computed tomography: is it reproducible?

The objective of this study was to measure the interobserver and interscan variation of coronary artery calcium scores using multidetector-row computed tomography (MDCT). Seventy-five patients underwent 2 sequential MDCT scans for coronary artery calcification. Each patient's score was separately measured by 3-blinded radiologists. Scores were treated as discrete and continuous data, and independent statistical analysis was performed on all results. There was a high proportion of interscan and inter-reader concordance for the presence of coronary calcium (range, 0.893-0.973) and for its quantity (range, 0.936-0.988). Overall, prospectively triggered multidetector-row calcium scoring is reproducible though there is more variation in those patients with already high scores. There is no need to scan patients twice at the same sitting.     

Variability of repeated coronary artery calcium scoring and radiation Dose on 64- and 16-slice computed tomography by prospective electrocardiographically-triggered axial and retrospective electrocardiographically-gated spiral computed tomography: a phantom study

RATIONALE AND OBJECTIVES: We sought to compare coronary artery calcium (CAC) scores, the variability and radiation doses on 64- and 16-slice computed tomography (CT) scanners by both prospective electrocardiographically (ECG)-triggered and retrospective ECG-gated scans. MATERIALS AND METHODS: Coronary artery models (n = 3) with different plaque CT densities (approximately 240 Hounsfield units [HU], approximately 600 HU, and approximately 1000 HU) of four sizes (1, 3, 5, and 10 mm in length) on a cardiac phantom were scanned three times in five heart rate sequences. The tube current-time products were set to almost the same on all four protocols (32.7 mAs for 64-slice prospective and retrospective scans, 33.3 mAs for 16-slice prospective and retrospective scans). Slice thickness was set to 2.5 mm to keep the radiation dose low. Overlapping reconstruction with a 1.25-mm increment was applied on the retrospective ECG-gated scan. RESULTS: The CAC scores were not different between the four protocols (one-factor analysis of variance: Agatston, P = .32; volume, P = .19; and mass, P = .09). Two-factor factorial analysis of variance test revealed that the interscan variability was different between protocols (P < .01) and scoring algorithms (P < .01). The average variability of Agatston/volume/mass scoring and effective doses were as follows: 64-slice prospective scan: 16%/15%/11% and 0.5 mSv; 64-slice retrospective scan: 11%/11%/8% and 3.7 mSv; 16-slice prospective scan: 20%/18%/13% and 0.6 mSv; and 16-slice retrospective scan: 16%/15%/11% and 2.9 to 3.5 mSv (depending on the pitch). CONCLUSION: Retrospective ECG-gated 64-slice CT showed the lowest variability. Prospective ECG-triggered 64-slice CT, with low radiation dose, shows low variability on CAC scoring comparable to retrospective ECG-gated 16-slice CT.     

Potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT

OBJECTIVE: The potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT was evaluated using Agatston, volume, and mass scoring algorithms. SUBJECTS AND METHODS: Fifty-six patients were imaged twice using an identical prospectively ECG-triggered sequential scanning protocol. The Agatston, volume, and mass scores were computed by two observers independently. In addition, a patient's total Agatston score was referenced to an age- and sex-stratified database to determine a percentile ranking. Interscan, interobserver, and intraobserver variability and the resultant impact on patients' risk stratifications were assessed. RESULTS: Significant interscan differences were found for all mean coronary calcium scores (Wilcoxson's signed rank test, p <0.0001). Although the median percentage of interscan variability was low for all scoring methods, the interquartile range was wide, indicating significant variability in the data. Median scores (lower quartile-upper quartile) for observers 1 and 2, respectively, were as follows: Agatston, 5% (0-79%) and 6% (0-83%); volume, 12% (0-51%) and 12% (0-57%); and mass, 14% (0-57%) and 14% (0-58%). Interobserver and intraobserver differences between mean calcium scores were not significant, and consequently, lower interobserver and intraobserver variabilities (narrow interquartile ranges of 0-5%) were observed for all scores. Despite significant interscan differences in calcium scores, the percentile ranking assigned to the two scans differed in only 13% of patients. Interobserver differences resulted in a change in the percentile ranking in 7-9% of patients, whereas intraobserver differences caused a change in only 5% of patients. CONCLUSION: The accuracy of sequential MDCT for coronary calcium quantification is sufficient in most cases for stratification of patient risk.