16-MDCT Coronary Angiography Shim et al. 16-MDCT Coronary Angiography Sung Shine Shim 1 Yookyung Kim Soo Mee Lim Received December 1, 2003; accepted after revision June 1, 2004. 1 All authors: Department of Radiology, Ewha Womans University MokDong Hospital, 911-1 MokDong YangCheon- Ku, Seoul 158-710, South Korea. Address correspondence to Y. Kim (yookkim@ewha.ac.kr). AJR 2005;184:649 654 0361 803X/05/1842 649 American Roentgen Ray Society Improvement of Image Quality with ß-Blocker Premedication on ECG-Gated 16-MDCT Coronary Angiography OBJECTIVE. The objective of our study was to assess the effect of β-blockers on image quality of ECG-gated 16-MDCT coronary angiography. MATERIALS AND METHODS. Coronary CT angiography was performed in two groups: group 1, 24 volunteers (mean age, 50 years; mean heart rate, 69 beats per minute [bpm]; range, 47 97 bpm); and group 2, 15 patients with current ischemic heart disease (mean age, 54 years; mean heart rate, 54 bpm; range, 48 69 bpm) who were premedicated with 20 40 mg of oral propranolol 1 hr before the study. CT scans were obtained on a 16-MDCT scanner with a 12 0.75 mm collimation and 420-msec rotation using nonionic contrast material (80 ml; injection rate, 4 ml/sec). Images were reconstructed at 30 80% of the cardiac cycle in increments of 5%. Image quality of the following eight coronary segments was assessed by two radiologists in consensus: left main coronary artery; proximal and middle segments of the left anterior descending () and left circumflex () coronary arteries; and the proximal, middle, and distal segments of the right coronary artery (). Image quality was assessed, using a 5-point grading scale, as grades 1 5. Images assessed as grade 4 or 5 were considered to be of diagnostically acceptable quality. RESULTS. In group 1, grade 4 or 5 image quality was achieved for visualization of 92% of the left main coronary arteries; 96% of the proximal coronary arteries; 88% of the middle, proximal, and middle coronary arteries; 83% of the proximal s; 58% of the middle s; and 96% of the distal s. In group 2, this level of image quality was achieved in 100% of the left main coronary arteries, proximal and middle arteries, and proximal arteries; 87% of the middle arteries; and 93% of the proximal, middle, and distal s. CONCLUSION. Reduction of heart rates with β-blocker premedication improves the image quality of CT coronary angiography, especially in terms of the visualization of the right coronary artery. DCT with retrospective ECG gating and IV injection of contrast M agent has recently been introduced as a method for the noninvasive visualization of coronary artery stenoses [1 5]. However, image quality has proven to be insufficient for the reliable detection of coronary stenoses in a substantial number of cases. In such cases, images of subjects with high heart rates often render coronary segments unassessable, and coronary arteries are frequently affected by motion artifacts [1 3]. Also, a patient s heart rate during scanning critically influences image quality [4, 5]. Schroeder et al. [4] found that the best vessel visibility was obtained in patients with a heart rate of less than 65 beats per minute (bpm) using a single-phase image reconstruction and 4-MDCT, and they advised that heart rates be lowered before MDCT coronary angiography. Therefore, we investigated whether image quality would improve on CT coronary angiography with the routine administration of an oral β-blocker before 16- MDCT. Materials and Methods Patients and Premedication Twenty-four volunteers and 15 patients with current ischemic heart disease (18 men, 21 women) who underwent CT coronary angiography at our institution between January 2003 and July 2003 were enrolled in our study. The study was approved by the hospital ethics committee, and written informed consent was obtained from all subjects before they were included in the study. The 24 volunteers had AJR:184, February 2005 649
Shim et al. risk factors of coronary heart disease including hypertension or diabetes mellitus but did not have any record of past or current coronary heart disease, and the 15 patients were admitted to our hospital because of acute chest pain and had a diagnosis of ischemic heart disease based on ECG and laboratory findings. The latter group of 15 patients underwent CT within 3 days after admission. Conventional coronary angiography performed in this group within 2 days after CT coronary angiography revealed coronary artery stenoses of more than 70% in seven patients, 30 70% in two patients, and less than 30% in three patients; normal finding were seen in the remaining three patients. Echocardiographic and MDCT assessments of left ventricular wall motion showed mild hypokinesia in four of the 15 patients (septum in three, posterior wall in one) and moderate hypokinesia in one patient (posterior wall). The study participants were divided into two groups: group 1, the 24 volunteers, did not take β- blocker premedication, and group 2, the 15 patients with suspected coronary artery disease, received β- blocker premedication. The mean age of the study participants was 49.6 ± 14.7 (SD) years (range, 23 79 years) in group 1 and 54.0 ± 11.5 years (range, 38 70 years) in group 2. Group 2 patients received 20 mg propranolol (Pranol, Deawoong) 1 hr before scanning, and those who showed a persistent high heart rate of greater than 65 bpm after receiving 20 mg of oral propranolol received an additional 20 mg. One patient who showed the highest heart rate more than 65 bpm on ECG after premedication with 40 mg of oral propranolol was excluded from this study. In all subjects, heart rates were evaluated on ECG during CT. In group 1, the mean heart rate was 68.4 ± 13.6 bpm (range, 47 97 bpm), and the mean individual heart rate variation during scanning was 13.1 ± 14.8 bpm (range, 3 64 bpm). The number of patients who showed a highest heart rate of less than 65 bpm was six. In group 2, the mean heart rate was 54.0 ± 6.7 bpm (range, 48 69 bpm), and the mean individual heart rate variation during scanning was 5.8 ± 4.0 bpm (range, 2 15 bpm). In group 2, the mean heart rate before β-blocker premedication was determined using ECG records from examinations performed 1 3 days before CT. The mean heart rate before β-blocker premedication in group 2 was 80.3 ± 18.6 bpm (range, 66 139 bpm). No patient had severe chronic obstructive pulmonary disease or asthma, in which β-blocker use is contraindicated. In all volunteers and patients with suspected coronary artery disease, the MDCT examination was successfully completed without complications. To compare the two groups in terms of heart rates, we applied the Mann-Whitney U test. MDCT Protocol CT scans were obtained using a 16-MDCT scanner (SOMATOM Sensation, Siemens Medical Solutions), and volume data sets were acquired with 12 0.75 mm collimation, a gantry rotation time of 420 msec, a table feed of 2.8 mm per 360 rotation, and an effective tube current time product of 400 mas at a tube voltage of 120 kv. Coronary vessel enhancement was achieved with a bolus of 80 ml of nonionic contrast material (iohexol, Omnipaque 300, Nycomed) injected through an 18-gauge catheter into an antecubital vein at a flow rate of 4 ml/sec and followed by a 40-mL saline flush at 4 ml/sec. CT scans were obtained from the carina to the diaphragm face of the heart during a single breath-hold. Reconstruction was performed for 30 80% of the cardiac cycle in increments of 5% using retrospective ECG gating and commercially available cardiac reconstruction software (Syngo, version A50A or A60, Siemens Medical Solutions). A partial scan reconstruction technique was used for image reconstruction. In patients with heart rates of less than 65 bpm, a single-sector reconstruction was performed with a temporal resolution of 210 msec. If the heart rate increased to more than 65 bpm, the current reconstruction software switched from single-sector reconstruction to multisector reconstruction, which provided a temporal resolution of 105 msec. Image Analysis We analyzed 11 different sets of images reconstructed at 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, and 80% of the cardiac cycle in each patient. Image data were transferred to a computer workstation (Wizard, Siemens Medical Solutions) and displayed using a multiplanar reformation (multiplanar reconstruction) technique. Two radiologists analyzed all the images in consensus for the visibility of the coronary arteries. The image data of groups 1 and 2 were intermixed, and the observers did not know the group assignment or heart rate of the patients when assessing the images. Segmental evaluation of the coronary arteries was performed according to the American Heart Association classification, which differentiates among 15 segments (Fig. 1); we assessed eight of these 15 coronary segments: the left main coronary artery; the proximal and middle segments of the left anterior descending () and left circumflex () coronary arteries; and the proximal, middle, and distal segments of the right coronary artery (). A 5-point scale was used. Image quality in each coronary segment reconstructed at each trigger delay was scored as follows: 5, no motion artifacts; 4, minor artifacts (mild blurring); 3, moderate artifacts (moderate blurring without discontinuity); 2, severe artifacts (doubling or discontinuity in the course of the coronary segments); or 1, unassessable (vessel structures not differentiable) (Fig. 2). A score of 4 or higher was considered acceptable in terms of image quality. The number of patients with an acceptable image quality in each coronary segment was calculated and compared between the two groups. Results All subjects had a sinus rhythm on ECG during CT. The use of the β-blocker in group A B Fig. 1. Drawings show segmental anatomy (segments indicated by numbers) according to American Heart Association classification. A, Drawing shows lateral view of right coronary artery (). B, Drawing shows right anterior oblique view of left coronary artery with left main (LM), left anterior descending (), and left circumflex () arteries. 650 AJR:184, February 2005
16-MDCT Coronary Angiography Fig. 2. CT coronary angiograms show middle segment of right coronary artery; each illustrates different grade of image quality. A, Image shows little motion artifact (grade 5). B, Image shows mild blurring of vascular margin (grade 4). C, Image shows moderate blurring of vascular margin (grade 3). D, Image shows doubling and discontinuity in course of coronary segments (grade 2). E, Image shows vessel structure is not visible. 2 patients in our study significantly reduced the heart rate during scanning (mean, 80.3 ± 18.6 bpm without β-blocker vs 54.0 ± 6.7 bpm with β-blocker; p < 0.0001), and group 2 had a significantly lower mean heart rate than group 1 (54.0 ± 6.7 bpm vs 68.4 ± 13.6 bpm; Mann-Whitney U test, p = 0.001) (Fig. 3). Coronary artery stenosis was detected in one of the group 1 volunteers and in 13 of the group 2 patients on CT coronary angiography. Of all the coronary segments, 86.3% showed acceptable image quality in group 1 and 95.8% A B C in group 2. Focusing on an acceptable score for each coronary segment in more than one of 30 80% cardiac cycle reconstruction images in the two groups, we evaluated the patients with acceptable image quality. The results are summarized in Table 1 and are illustrated in Figure 1. Acceptable image quality of each segment except the middle was obtained in 83.3 96.1% of group 1 and 87.4 100.0% of group 2. Acceptable image quality of the middle was obtained in 58.3% of group 1 and 93.3% of group 2 (Table 1 and Fig. 4). D The optimal reconstruction window in the cardiac cycle for the best image quality in the and left main,, and arteries was 60 65% in both groups (Tables 2 and 3). Acceptable image quality of each coronary segment except the middle in image reconstruction at 60% was achieved in 50.0 70.8% of group 1 and 80.0 100.0% of group 2. Acceptable image quality of the middle in image reconstruction at 60% was obtained in 33.3% of group 1 and 80.0% if group 2 (Table 4). E AJR:184, February 2005 651
Shim et al. Heart Rate (bpm) 80 70 60 50 40 30 Group 1 Group 2 Fig. 3. Box-and-whisker plot shows influence of concurrent β-blocker therapy on mean heart rate in beats per minute (bpm). Difference between groups is significant (unpaired Student s t test, p < 0.0001). Study Subjects (%) 100 80 60 40 20 0 LM p- m- p- m- Coronary Segment p- m- d- Fig. 4. Bar graph shows percentage of volunteers (black bars), who did not receive β-blocker therapy, and percentage of patients (white bars), who did receive β-blocker therapy, with acceptable image quality in image reconstruction at 30 80% of cardiac cycle. LM = left main coronary artery, p = proximal, m = middle, d = distal, = left anterior descending artery, = left circumflex artery, = right coronary artery. TABLE 1 Patients with Acceptable Image Quality in Each Coronary Segment Coronary Segment Group Proximal Middle Proximal Middle Proximal Middle Distal 1 (n = 24) 92.0 96.1 88.2 88.2 88.2 83.3 58.3 96.1 2 (n = 15) 100 100 100 100 87.4 93.0 93.0 93.0 Note. Data are percentages of the patients with a score of 4 or higher in more than one of 30 80% cardiac cycle reconstruction images. = left anterior descending, = left circumflex, = right coronary artery. Discussion Since the introduction of MDCT as a noninvasive tool for the depiction of coronary arteries, the clinical value of CT coronary angiography has been the subject of several studies. MDCT with retrospective ECG gating and the IV injection of contrast agent permits the visualization of the coronary artery lumen and the detection of stenoses [1 3]. However, previous MDCT investigations have revealed two major limitations: coronary artery motion frequently is not sufficiently suppressed, and stenosis assessment is thus often impaired in the presence of coronary calcification [4 6]. Giesler et al. [5] reported that even though they selected the optimal reconstruction window for individual coronary arteries, motion artifacts could not be prevented in the images of 21% of coronary arteries. Therefore, a useful approach might be to limit the use of MDCT for coronary artery visualization to patients with low heart rates or to use pharmacologic intervention (e.g., β-blockers) during scanning to enhance image quality. Recently, Schroeder et al. [4] found it advisable to lower patient heart rate to less than 65 bpm before performing CT coronary angiography to achieve satisfactory image quality. In our study, patients who received β-blocker therapy showed significantly lower heart rates than those who did not; the mean reduction achieved was approximately 26 bpm. Recent studies in which CT coronary angiography was performed using 4-MDCT have shown that accurate evaluation of coronary segments is possible in 71 74% of patients [4, 5]. Ropers et al. [7] analyzed 144 coronary arteries on 16-MDCT and found that 96% of coronary arteries were assessable in patients with a heart rate below 60 bpm. In our study, the image quality of CT coronary angiography using 16-MDCT was found to be improved by β-blocker therapy, which produced 95.8% diagnostically acceptable coronary segments versus 86.3% without β- blocker therapy. Our study showed and arteries are significantly more prone to motion artifacts than the left main and arteries. Increased motion artifacts in and arteries, particularly at higher heart rates, may be due to the close proximity of both coronary arteries to the atrium, which is reactivated during the early diastolic phase [2, 8, 9]. Giesler et al. [5] reported that 48% of s show a degraded image quality, and Schroeder et al. [4] reported lower visibilities 652 AJR:184, February 2005
16-MDCT Coronary Angiography TABLE 2 Coronary Segment TABLE 3 Coronary Segment Percentage of Patients with Acceptable Image Quality in Each Coronary Segment Relative to the Cardiac Cycle in Group 1 Cardiac Cycle (%) 30 35 40 45 50 55 60 65 70 75 80 25.0 16.7 12.5 25.0 29.2 41.7 70.8 70.8 70.8 54.2 41.7 coronary artery Proximal 25.0 16.7 16.7 20.8 29.2 45.8 70.8 62.5 54.2 37.5 37.5 Middle 25.0 16.7 12.5 25.0 29.2 41.7 62.5 62.5 70.8 29.2 29.2 Proximal 20.8 12.5 8.3 8.3 29.2 41.7 66.7 70.8 62.5 29.2 8.3 Middle 20.8 12.5 12.5 0 29.2 37.5 66.7 62.5 50.0 20.8 12.5 Proximal 25.0 16.7 12.5 4.2 16.7 41.7 50.0 41.7 37.5 8.3 12.5 Middle 20.8 8.3 12.5 4.2 8.3 20.8 33.3 33.3 12.5 0 0 Distal 16.7 45.8 29.2 20.8 16.7 58.3 58.3 58.3 33.3 12.5 16.7 Note. Data are percentages of the patients with a score of grade 4 or 5. Percentage of Patients with Acceptable Image Quality in Each Coronary Segment Relative to the Cardiac Cycle in Group 2 Cardiac Cycle (%) 30 35 40 45 50 55 60 65 70 75 80 33.3 33.3 26.7 53.3 73.3 100 100 100 100 66.7 73.3 coronary artery Proximal 13.3 26.7 26.7 40.0 73.3 93.3 100 100 80.0 53.3 33.3 Middle 0 33.3 33.3 46.7 73.3 80.0 100 100 93.3 66.7 46.7 Proximal 13.3 33.3 13.3 40.0 73.3 80.0 93.3 100 93.3 46.7 13.3 Middle 13.3 26.7 26.7 33.3 66.7 80.0 86.7 86.7 86.7 46.7 6.7 Proximal 40.0 26.7 13.3 26.7 33.3 80.0 80.0 66.7 53.3 13.3 6.7 Middle 33.3 26.7 6.7 13.3 26.7 60.0 80.0 86.7 60.0 13.3 6.7 Distal 40.0 40.0 40.0 46.7 40.0 73.3 80.0 60.0 40.0 20.0 6.7 Note. Data are percentages of the patients with a score of grade 4 or 5. TABLE 4 Percentage of Patients with Acceptable Image Quality in Image Reconstruction at 60% of Cardiac Cycle Coronary Segment Group Proximal Middle Proximal Middle Proximal Middle Distal 1 (n = 24) 70.8 70.8 62.5 66.7 66.7 50.0 33.3 58.3 2 (n = 15) 100 100 100 93.3 86.7 80.0 80.0 80.0 Note. Data are percentages. = left anterior descending, = left circumflex, = right coronary artery. for arteries (77.7%) and s (64.9%) than for the left main (100%) and (82.3%) arteries. In our study, the middle segment of the in particular showed the highest incidence of motion artifact among the coronary segments in the non-β-blocker group and the most prominent improvement of image quality with β-blocker therapy. We looked at each segment of the different vessels individually because the patterns of movement are evidently unequal throughout the complete arterial tree. Proximal segments usually showed higher image quality than middle or distal segments, and middle segments of the showed the lowest image quality, because of the presence of motion artifacts. In our study, we reconstructed images at an increment of 5% instead of 10% because increments of 10% for the position of the image reconstruction window might be too long to detect subtle differences. The results of our study indicate that the best-quality images are obtained at 60 65% of the cardiac cycle. We evaluated coronary segments displayed using the multiplanar reconstruction technique on a workstation. CT coronary imaging then showed that the higher-quality images were obtained on transverse scans. That transverse scans are less susceptible to motion artifacts, whereas the other imaging planes, even at low heart rates, often tend to depict nonexisting vascular discontinuances or nonexisting wall irregularities. Our study is limited by the small number of patients. In addition, group 2 consisted of patients with suspected coronary artery disease, whereas group 1 was a volunteer group who did not have a history of coronary artery diseases. Decreased cardiac wall motion due to myocardial infarction might have had improved coronary visibility on CT coronary angiography in group 2. However, we think that the change of cardiac wall motion did not greatly influence the improvement of image quality in comparison with the decrease of heart rates in our study. In conclusion, our study indicates that CT coronary angiography using 16-MDCT with β-blocker administration produces images of diagnostically acceptable quality in almost all coronary segments and that the large number of unassessable right coronary arteries, due to motion artifacts, is markedly reduced by β- blocker premedication. Thus, administration of an agent such as β-blocker is necessary before CT coronary angiography to achieve the best image quality. AJR:184, February 2005 653
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