CORRESPONDENCE: RESEARCH CORRESPONDENCE
Noninvasive Coronary Angiography With a Prototype 256-Row Area Detector Computed Tomography System Comparison With Conventional Invasive Coronary Angiography
Sadako Motoyama, MD, PhD*,
Hirofumi Anno, MD, PhD,
Masayoshi Sarai, MD, PhD,
Takahisa Sato, MD, PhD,
Yoshihiro Sanda, MD,
Yukio Ozaki, MD, PhD,
Teruhito Mochizuki, MD, PhD,
Kazuhiro Katada, MD, PhD and
Hitoshi Hishida, MD, PhD
* Department of Cardiology, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan (Email: sadakom{at}fujita-hu.ac.jp).
To the Editor: Since the initial reports describing the usefulness of computed tomography angiography (CTA) with 4-row multislice compute tomography (MSCT) for the examination of the coronary arteries, the number of detector rows has been further increased. Now, 256-row area detector CT (256-row CT) has been developed, and a prototype system has been installed at our institution. The diagnostic accuracy of coronary CTA with 256-row CT for the evaluation of stenoses was compared with that of conventional invasive coronary angiography (CAG) in this study.
The subjects were 10 patients (6 men and 4 women, mean age 69 ± 10 years) with suspected coronary artery disease who were examined by invasive CAG and who underwent coronary CTA with 256-row CT within 2 weeks before or after CAG during the period from January to April 2006. All patients showed sinus rhythm. The coronary arteries were divided into 15 segments according to the American Heart Association classification. Evaluation focused on coronary arteries 1.5 mm or more in lumen diameter. Regions containing stents and stenotic lesions for which percutaneous coronary intervention (PCI) had been performed within the preceding 2 weeks were excluded from the evaluation. The presence of stenoses of 50% or more was investigated with coronary CTA and invasive CAG, and the results were compared. Before the start of this clinical study, approval was obtained from our institution’s ethics review board and informed consent to participate in the study was obtained from each patient.
The system used was a prototype 256-row CT scanner with an overall detector width of 128 mm (256 x 0.5 mm) (1,2), meaning that a range of 128 mm can be covered in a single rotation of the X-ray tube, and it is therefore not necessary to employ helical scanning. The scanning protocol for coronary CTA was a 3-s dynamic scan without electrocardiography (ECG) gating, a tube voltage of 135 kV, a tube current of 330 mA, and a scan speed of 0.5 s/rotation. First, 50 ml of contrast medium was injected intravenously at 4.0 ml/s, then a mixture of 10 ml of contrast medium and 10 ml of saline solution was injected at 4.0 ml/s, and finally a 20-ml saline flush was injected at 4.0 ml/s. Images were reconstructed by the retrospective ECG-gated half-scan reconstruction method with a single cardiac cycle or by the segmented reconstruction method with multiple cardiac cycles. Each coronary artery segment was visually evaluated in curved multiplanar reformation and cross-sectional images by 2 investigators who were blinded to the results of invasive CAG. Conventional invasive CAG images were acquired with standard methods. The images were evaluated by 2 investigators who were blinded to the results of 256-row CT imaging.
Representative cases are shown in Figure 1. In the 10 patients, 108 coronary artery segments were investigated. The heart rate during scanning ranged from 51 to 76 beats/min (mean ± SD, 60.5 ± 7.9 beats/min), with the heart rate variation ranging from 0 to 7 beats/min. Ten regions were found to be difficult to evaluate, owing to extensive calcification. No regions were found to be difficult to evaluate because of discontinuities caused by motion artifacts or banding artifacts. In invasive CAG studies, 15 stenoses were identified in 7 patients. Compared with CAG for the detection of significant stenotic lesions, the sensitivity, specificity, and positive and negative predictive values of 256-row CT were 100% (15 of 15), 89% (83 of 93), 60% (15 of 25), and 100% (83 of 83), respectively, when severe calcification was assumed to be stenosis. When severe calcification was excluded, the sensitivity, specificity, and positive and negative predictive values were 100% (11 of 11), 95% (83 of 87), 73% (11 of 15), and 100% (83 of 83), respectively.
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Figure 1 Case 1
The heart rate during scanning was 65 to 66 beats/min. The images were reconstructed by half-scan reconstruction with 1 cardiac cycle. (A) A stenosis is demonstrated in right coronary artery (RCA) #2 by invasive coronary angiography. (B) A computed tomography curved multiplanar reformation image shows a stenosis at the corresponding location. (C) The stenosis can also be identified in the volume-rendered image. (D) A cross-sectional image shows a stenosis at the corresponding location. Ao = aorta; LAD = left anterior descending coronary artery.
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These results are comparable to those that have been obtained for 64-row CT, which has been reported to have a sensitivity of 73% to 94% and a specificity of 95% to 97% (3). The technical limitations of the prototype 256-row CT system are: 1) a slower rotation speed (0.5 s/rotation); 2) the inability to perform prospective ECG-gated scanning; and 3) the lack of an ECG dose modulation function, as has already been implemented in current 64-row CT systems. Therefore the temporal resolution is lower than that of a 64-row CT system. Nevertheless, no blood vessels were found to be difficult to evaluate because of discontinuities caused by motion artifacts or banding artifacts, and the diagnostic accuracy was comparable to that of 64-row CT. One of the reasons was that the data acquisition time was shorter and, as a result, variations in heart rate were minimized. In case 1, motion artifacts due to inadequate breath-holding were observed in the images reconstructed by segmented reconstruction with 3 cardiac cycles. However, images reconstructed by half-scan reconstruction did not show motion artifacts. Therefore, 256-row CT has the potential to respond flexibly to arrhythmias and variations in heart rate and is also suitable for examining patients who cannot hold their breath. Another reason for the favorable results was that isophasic images (i.e., images with no temporal differences in the longitudinal direction) were obtained, because helical scanning was not employed, and therefore the coronary arteries were depicted with good continuity visually in the longitudinal direction. Recently, dual-source CT systems have been introduced. Such CT systems are equipped with 2 sets of X-ray tubes and detectors, allowing images to be acquired at a temporal resolution of 83 ms with the half-scan reconstruction method (4,5). Because multiple cardiac cycles are needed to depict the coronary arteries when helical scanning is employed, it is likely that 256-row CT will have advantages in terms of the continuity of coronary artery images. However, dual-source CT is considered to have the advantages of higher temporal resolution and increased stability. It is therefore anticipated that a system that incorporates the advantages of both systems will be developed as further advances are made in CT technologies. In this study, we performed 3-s dynamic scanning without ECG dose modulation. The effective dose/scan calculated from the simulation results was 33.3 mSv, which is higher than the average effective dose of 14.2 mSv for a 64-row CT system at our institution. With 256-row CT, imaging in the Z-axis direction in the same time phase is possible in a single scan without the need to employ helical scanning. Therefore, if prospective ECG gated scanning could be performed in combination, a reduction in the exposure dose to 3 to 4 mSv should be possible.
It is expected that an ECG-gated scan function and exposure dose reduction functions will be available in commercial products. The scan speed should be improved to the same level as that of a 64-row CT system by the time the system reaches the market. Because the number of subjects in this study was small (10 patients), owing to the short evaluation period, when the 256-row CT system becomes commercially available with these functions provided, it will be necessary to evaluate its diagnostic capabilities in a larger number of patients.
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References
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