Chikako Fujioka

Prospective versus Retrospective ECG-gated 64-Detector Coronary CT Angiography: Assessment of Image Quality, Stenosis, and Radiation Dose

PURPOSE To show that prospective electrocardiographically (ECG)-triggered coronary computed tomographic (CT) angiography (hereafter, prospective CT angiography) is at least as effective as retrospective ECG-gated coronary CT angiography (hereafter, retrospective CT angiography). MATERIALS AND METHODS Institutional review committee approval and informed consent were obtained. Sixty patients with heart rates of less than 75 beats per minute who were referred for coronary CT angiography were enrolled. Both prospective and retrospective CT angiography were performed with a 64-detector scanner. Data acquisition times were recorded. Two independent cardiac radiologists evaluated subjective image quality (1, excellent; 4, poor) and severity of stenosis (0% occlusion, 1%-49% occlusion, 50%-75% occlusion, and >75% occlusion) with the 17-segment American Heart Association classification model. Discrepancies were settled by consensus. Effective radiation doses of prospective and retrospective CT angiography were calculated with volume CT dose index. Data regarding acquisition time and radiation exposure for prospective and retrospective CT angiography were compared. The Student t test was performed, and kappa statistics were calculated. RESULTS Mean data acquisition time of prospective CT angiography was shorter than that of retrospective CT angiography (5.6 seconds +/- 1.1 [standard deviation] vs 6.7 seconds +/- 1.1, respectively; P < .01). Consensus-determined image quality in coronary artery branches was similar between prospective CT angiography and retrospective CT angiography (1.15 vs 1.13, respectively; P = .992). Excellent agreement between prospective CT angiography and retrospective CT angiography was observed in the detection of significant (>or=50% occlusion) coronary artery stenoses per segment (kappa = 0.882) and in the grading of stenoses per patient (kappa = 0.829). Calculated effective dose with prospective CT angiography was 79% lower than that with retrospective CT angiography (4.1 mSv +/- 1.8 vs 20.0 mSv +/- 3.5, respectively; P < .001). CONCLUSION Prospective CT angiography can reduce radiation dose below that of retrospective CT angiography with dose modulation, while maintaining image quality and the ability to assess luminal obstructions in patients with heart rates of less than 75 beats per minute.

Radiation Dose, Image Quality, Stenosis Measurement, and CT Densitometry Using ECG-Triggered Coronary 64-MDCT Angiography : A Phantom Study

OBJECTIVE The purpose of this study was to compare prospective ECG-triggered and retrospective ECG-gated coronary 64-MDCT angiography as to radiation dose, image quality, accuracy of stenosis measurement, and CT densitometry. MATERIALS AND METHODS Coronary artery models (n = 3) with different plaque densities (approximately 50, approximately 110, and approximately 1,000 H) on a cardiac phantom were scanned in variable heart rate sequences (n = 14) with both prospective ECG-triggered and retrospective ECG-gated scanning. Radiation dose, image quality graded by motion and stairstep artifacts (grade 1, excellent, to grade 4, poor, with grades 1 and 2 defined as satisfactory), accuracy of stenosis measurement (area; 18%, 50%, and 82%), and CT densitometry of plaques (soft, approximately 50; and intermediate, approximately 110 H) were compared between the two protocols using the Mann-Whitney U test and repeated measures. RESULTS The radiation dose of prospective ECG-triggered CT angiography (CTA) (3.0 mSv) was lower than that of retrospective ECG-gated CTA (11.7-13.0 mSv) when the same tube current (mA) and voltage (kVp) were used in both methods. Prospective ECG-triggered CTA images were assigned a satisfactory quality rating in stable heart rate up to 75 beats per minute (bpm) when using the minimal X-ray exposure time. In this range, there were no significant differences in stenosis measurement (p = 0.17) and CT densitometry (p = 0.93) between the two protocols. CONCLUSION Prospective ECG-triggered coronary 64-MDCT has the potential to reduce radiation exposure while maintaining the diagnostic performance of retrospective ECG-gated coronary 64-MDCT.

Soft and Intermediate Plaques in Coronary Arteries: How Accurately Can We Measure CT Attenuation Using 64-MDCT?

OBJECTIVE The objective of this study was to validate the accuracy of 64-MDCT densitometry of soft and intermediate plaques. MATERIALS AND METHODS Acrylonitrile-butadiene-styrene resin (47 H) and acrylic (110 H) were used to simulate soft and intermediate plaques, respectively, in coronary artery models (diameters of 3 and 4 mm). The variable parameters were heart rate (50, 65, 80, and 95 beats per minute), reconstruction algorithm (half and segmentation), coronary artery enhancement (150, 250, 350, and 450 H), CT densitometry site (arterial lumen or center), shape of plaque (D-shaped, centric, and eccentric), and level of stenosis due to plaque (25%, 50%, and 75% of arterial diameter). Measured CT attenuation values of soft and intermediate plaques were compared for different combinations of parameters. Repeated measures analysis of variance, Wilcoxons signed rank, Mann-Whitney U, and Kruskal-Wallis tests were used for statistical analyses. RESULTS For measuring soft plaque, CT densitometry was accurate at low heart rates with the use of a half reconstruction algorithm (p < 0.01) on intracoronary artery enhancement of 250 H (p < 0.01). For both soft and intermediate plaques, the densitometry measurements near the arterial lumen were overestimated and higher than those at the center (p < 0.01). For plaques that were 50% or more of the arterial diameter, accurate CT densitometry was possible. CONCLUSION Coronary artery enhancement has a significant impact on 64-MDCT densitometry measurements of coronary artery plaques, especially of soft plaques. A large plaque size, densitometry performed not near the arterial lumen but at the center of the plaque, intracoronary enhancement of 250 H, and a low heart rate increase the accuracy of plaque densitometry.

Variability of Repeated Coronary Artery Calcium Measurements on Low-Dose ECG-Gated 16-MDCT

OBJECTIVE High reproducibility on coronary artery calcium (CAC) scoring is a key requirement in monitoring the progression of coronary atherosclerosis. Retrospective ECG-gated helical CT has been shown to be superior to prospective gating helical CT in the reproducibility of CAC measurements. However, it brings with it a high level of radiation exposure. The purpose of this study was to compare low- and standard-dose protocols in the variability of CAC scores and in image quality, thereby assessing the feasibility of low-dose retrospective ECG-gated helical CT in CAC measurements. SUBJECTS AND METHODS Eighty-six patients with CAC were scanned using a tube current setting of 100 mA once and then a tube current setting equivalent to the patients body weight twice. CAC scores (Agatston and volume) and interscan variability were evaluated. The mean and SD of the CT attenuation values in regions of interest in the aorta were measured, and the value (mean + 2 x SD) was obtained. RESULTS A high correlation of log(10) (Agatston score + 1) was observed between sequential helical CT scans (r = 0.998). The variability in CAC measurements ranged from 11% to 12% for both the Agatston and volume scores. With the tube current equivalent to body weight, the value (mean + 2 x SD) did not exceed a CT attenuation value of 130 H. CONCLUSION Low-dose retrospective ECG-gated helical CT-yielding low variability and achieving the level of image quality needed to measure CAC-can be used to monitor patients with coronary atherosclerosis.

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.

Survey of Aorta and Coronary Arteries With Prospective ECG-Triggered 100-kV 64-MDCT Angiography

OBJECTIVE The purpose of this study was to investigate the feasibility of prospective ECG-triggered axial 64-MDCT angiography of the aorta and coronary arteries performed at a tube voltage of 100 kV. SUBJECTS AND METHODS Thirty patients with a heart rate less than 75 beats/min who were referred for aortic CT angiography were enrolled. The image quality of the ascending aorta, aortic valve, and coronary arteries was evaluated for motion artifacts. Contrast enhancement (mean attenuation) was measured in the ascending aorta, descending aorta, and bifurcation of the aorta. Aortic valve and coronary artery lesions were surveyed. RESULTS Acceptable image quality was achieved in 100% (30/30) of cases for the ascending aorta, 97% (29/30) of cases for the aortic valve, and 98% (442/452) of coronary arterial segments. Contrast enhancement was greater than 200 HU and was satisfactory (ascending aorta, 379 +/- 80 HU; descending aorta, 354 +/- 72 HU; bifurcation, 355 +/- 96 HU). Lesions found in the aortic valve were plaque (n = 16) and bicuspid valve (n = 1) and in the coronary arteries were > or = 50% luminal stenosis (n = 5), plaque (n = 21), myocardial bridge (n = 12), and anomalous origin (n = 1). The effective radiation dose was estimated to be 7.5 +/- 1.7 mSv. CONCLUSION For patients with a heart rate less than 75 beats/min, prospective ECG-triggered axial CT angiography at a tube voltage of 100 kV has the potential to provide clinically relevant information about the aorta and coronary arteries with low radiation exposure.

Coronary artery calcium scoring on low-dose prospective electrocardiographically-triggered 64-slice CT.

RATIONALE AND OBJECTIVES The purpose of this prospective study was to assess image noise and variability in repeated coronary artery calcium (CAC) scoring on low-dose prospective electrocardiographically-triggered 64-slice multidetector computed tomography. MATERIALS AND METHODS Patients (n = 115) suspected of having coronary artery disease were scanned twice, using a tube current of 10 x body mass index mA. The standard deviation (SD) of the computed tomographic value in the ascending aorta and (mean + 2 x SD) were obtained. Repeated CAC scores (Agatston, volume, and mass) were measured by two observers, and the interscan and interobserver variability were determined. RESULTS The mean tube current used was 246 +/- 36 mA. The mean tube current-time product and mean estimated effective dose were 57 +/- 8 mA and 0.9 +/- 0.2 mSv, respectively. The SD and (mean + 2 x SD) computed tomographic values in the ascending aorta were 16 +/- 3 and 75 +/- 10 Hounsfield units, respectively. Repeated CAC scores were correlated (r(2) = 0.995-0.998). The interscan variability for observer 1 and observer 2, respectively, were 13% and 13% for Agatston score, 12% and 11% for volume, and 11% and 11% for mass. The interobserver variability for scan 1 and scan 2, respectively, were 3% and 3% for Agatston score, 5% and 3% for volume, and 3% and 3% for mass. CONCLUSION Low-dose prospective electrocardiographically-triggered 64-slice multidetector computed tomography shows low interscan and interobserver variability on CAC scoring while maintaining low image noise.

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.

In vitro measurement of CT density and estimation of stenosis related to coronary soft plaque at 100 kV and 120 kV on ECG-triggered scan

PURPOSE The purpose of the study was to compare 100 kV and 120 kV prospective electrocardiograph (ECG)-triggered axial coronary 64-detector CT angiography (64-MDCTA) in soft plaque diagnosis. MATERIALS AND METHODS Coronary artery models (n = 5) with artificial soft plaques (-32 HU to 53 HU at 120 kV) with three stenosis levels (25%, 50% and 75%) on a cardiac phantom (mimicking slim patients environment) were scanned in heart rates of 55, 60 and 65 beats per minute (bpm). Four kinds of intracoronary enhancement (205 HU, 241 HU, 280 HU and 314 HU) were simulated. The soft plaque density and the measurement error of stenosis (in percentage), evaluated by two independent observers, were compared between 100 kV and 120 kV. The radiation dose was estimated. RESULTS Interobserver correlation of the measurement was excellent (density; r = 0.95 and stenosis measure; r = 0.97). Neither the density of soft plaque nor the measurement error of stenosis was different between 100 kV and 120 kV (p = 0.22 and 0.08). The estimated radiation doses were 2.0 mSv and 3.3 mSv (in 14 cm coverage) on 100 kV and 120 kV prospective ECG-triggered axial scans, respectively. CONCLUSION The 100 kV prospective ECG-triggered coronary MDCTA has comparable performance to 120 kV coronary CTA in terms of soft plaque densitometry and measurement of stenosis, with a reduced effective dose of 2 mSv.

Coronary artery calcium scoring on different 64-detector scanners using a low-tube voltage (80 kVp).

PURPOSE The aim of this study was to compare the calcium score and reproducibility of coronary artery calcium scores obtained on the four kinds of 64-detector computed tomography (CT) scanners using standard (120 kVp) and low tube voltage (80 kVp) scan techniques. MATERIALS AND METHODS We scanned 80 and 120 kVp on all scanners. We calculated Agatston, volume, and mass scores for coronary artery calcium scoring on each scanner and compared the coefficients of variation of the calcium scores to evaluate reproducibility of among CT scanners. RESULTS The averages of the total mean Agatston score, total mean volume score, and total mean mass score at 80 kVp/120 kVp were 798.9/683.8, and 627.2/567.3, and 157.1/156.7, respectively. The total mean mass score was almost constant irrespective of the tube voltage. The total mean coefficients of variation for the four CT scanners were lower at 80 than 120 kVp (4.1% vs. 10.2% [total mean Agatston score], 3.2% vs. 9.6% [total mean volume score], and 3.2% vs. 9.4% [total mean mass score]). CONCLUSION Use of the low tube voltage technique can reduce variations in the coronary artery calcium scores obtained on different CT scanners.