Coronary artery imaging with 64-slice computed tomography from cardiac surgical perspective☆

Invasive coronary angiography (ICA) is still considered the method of choice for the diagnosis and then assessment of severity of coronary artery stenoses. However, the cost-extensive technique is associated with the danger of the invasive procedure and the inconvenience for the patient. Already the previous 16-slice CT scanner showed in multiple studies 1–3 promising results, but the incomplete evaluation of the coronary artery tree made its use in clinical routine impossible. 64-Slice computed tomography (CT) recently has been introduced with high expectations. It provides an increased spatial and temporal resolution compared to the previous scanner models. The new kind of imaging technique provides isotropic voxels down to 0.4 mm3 with a maximum temporal resolution of 83 ms 4. It is generally the rule that cardiovascular surgeons themselves analyse the ICA in addition to the cardiologists prior to bypass surgery. When 64-slice CT would be intended to complement or even replace ICA, CT image analysis prior to surgery should be consequently also performed by the operating surgeon. The goal of this study was to investigate the diagnostic accuracy of 64-slice CT with regard to coronary artery stenoses for preoperative planning of coronary artery bypass grafting (CABG) when image analysis is performed by cardiovascular surgeons. The results of 64-MSCT were compared to routine results of coronary angiography. 64-Slice CT was performed in addition to ICA in 50 elective patients (39 male, 11 female, age 66 ± 8 years) in sinus rhythm. These patients were divided in a study group of 40 patients (34 males, 6 females) and a control group of 10 patients (5 males, 5 females). The study group included patients with coronary artery disease (CAD); the control group consisted only of patients with valve disease and inconspicuous coronaries. As cardiovascular risk factors of all examined patients were evaluated: smoking, obesity, hypertension, diabetes mellitus and high blood cholesterol. Risk factors of the study group: Smoking → 37/40 patients Obesity → 16/40 patients Hypertension (RR ≥ 140/90 mmHg) → 16/40 patients Diabetes mellitus → 8/40 patients High blood cholesterol → 37/40 patients One patient of the study group had no cardiovascular risk factors. Risk factors of the control group: Smoking → 4/10 patients Obesity → 3/10 patients Hypertension (RR ≥ 140/90 mmHg) → 7/10 patients Diabetes mellitus → 1/10 patients High blood cholesterol → 2/10 patients Two patients of the control group had no cardiovascular risk factors. In the study group, 40 patients had CAD diagnosed by coronary angiography. The control group consisted of patients suffering from valve disease only, which was diagnosed preoperatively by transthoracic echocardiography: Five patients with aortic stenosis → aortic valve replacement One patient with combined aortic stenosis and insufficiency → aortic valve replacement One patient with aortic insufficiency → aortic valve replacement Three patients with mitral insufficiency → mitral valve reconstruction Coronary angiography therefore was normal. Patients with arrhythmia, allergy to iodinated contrast media, and renal insufficiency (serum creatinine > 120 mmol/l) were already during patient selections excluded from the study. The local ethics committee approved the study protocol and written informed consent was obtained from all patients. According to the standard techniques, a conventional selective coronary angiography on a Philips Integris Allura 9 Biplanesystem was performed. The contrast medium (Ultravist, Schering) consumption including the levogram averaged 140 ml. 5F diagnostic catheters (Cordis, Johnson the circumflex branch (CX) in a proximal and distal segment; the left main (LM), the diagonal branch 1 (D1) of the LAD and the first marginal branch of the CX (1st marg.) were considered as being independent segments. If the diameter reduction was >50%, the accordant vessel segment was scored as being significantly stenosed. Coronary arteries with diameter as large as 1.5 mm were analysed including those vessels distal to an occlusion. All CT scans were performed on a 64-slice scanner with a 0.37 s rotation time (Somatom Sensation 64, Siemens, Forchheim, Germany). No additional beta-blockers were administered prior to CT. A bolus of 80 ml iodixanol (Visipaque 320 mgI/ml, Amersham Health, Buckinghamshire, UK) was injected into an antecubital vein at a flow rate of 5 ml/s, followed by a 50 ml saline chasing bolus. Start delay was defined by bolus tracking in the ascending aorta and scan start was automatically initiated 5 s after reaching the threshold (140 Hounsfield Units, HU). After that, scanning was performed from the tracheal bifurcation to the diaphragm using the following parameters: X-ray tube potential 120 kV, effective tube current 500–680 mAs, detector collimation 32 mm × 0.6 mm, table feed 9.2 mm/rotation, and pitch 0.24. Depending on the individual anatomy, the field-of-view was fitted to the cardiac size in each patient (211 ± 19 mm; range, 182–268 mm). We used retrospective electrocardiographic (ECG) gating for optimal heart phase selection 23. The implemented adaptive cardio volume approach was used for data reconstruction. Depending on the heart rate throughout the examination, axial slices were reconstructed synchronized to the ECG by a single sector (≤65 beats per minute bpm) or two-sector algorithm (>65 bpm) using data from one or two consecutive heartbeats 4,22. When necessary, R-wave indicators were manually repositioned to improve the quality of synchronization. Images were reconstructed in 5% intervals of the cardiac cycle to allow assessment of coronary arteries at that cardiac phase with minimal vessel motion. Slices with a thickness of 1 mm (increment 0.8 mm) and a medium soft-tissue reconstruction kernel (B30f) were used for evaluating coronary arteries. The whole dataset was saved in the picture archiving and communicating system of the hospital (PACS) and was transferred for image analysis to a dedicated workstation (Second Wizard, Siemens) equipped with a 4D software (Syngo Argus, Siemens). The CT image presentation to the cardiovascular surgeons was performed by a radiologist. Each evaluation started with a 3D reconstruction of the heart in the volume rendering technique (VRT) (Fig. 1A). This technique provides an overview about the courses of the arteries, possible occlusions or opacified adjacent structures. Thereafter, each segment was analysed in a plane parallel and orthogonal to the course of the artery. For improved visualization of crucial locations, the techniques of multi-planar reformations (MPR) and maximum intensity projections (MIP) were used, Fig. 1B–E. Combinations of all techniques (3D heart models and 2D images in two planes) enabling different views of the interior and exterior surface of the coronary arteries optimise the image evaluation. VRT image of the LAD (A). MIP image in an oblique sagittal (B, arrow) and oblique transverse (C, arrow) plane. MPR parallel (D, arrow) and orthogonal (E, circle) to the vessel. In combination of these techniques, a non-calcified significant stenosis in the middle segment of the LAD is evaluable. Analysis of the coronary artery stenoses by CT was accomplished in the same pattern as mentioned above for ICA. Two blinded and independent readers from the clinic for cardiovascular surgery without any knowledge of the patient's medical history and of the results from ICA investigated the CT scans with regard to hemodynamically significant stenoses using the same evaluation criteria like ICA. Segments with a diameter down to 1.5 mm including those distal to occlusions were analysed. A significant stenosis was defined as vessel lumen constriction more than 50%. Also, the same classification – 11 segments of the coronary vessel system – already described for the evaluation of the ICA was used for the analysis of CT. The type of stenosing plaque was defined as being calcified, mixed (calcified and non-calcified fractions), and non-calcified. Since intravascular ultrasound was not applied, no differentiation of plaque qualities could be performed with ICA. Image quality of 64-slice CT was defined as follows: Reliable analysis: optimal diagnostic image quality and conditions for evaluation by both readers Unreliable analysis: reduced diagnostic image quality and limited conditions for evaluation by readers Not assessable: strongly reduced image quality with no possibility for analysis by the readers Different reasons for image quality degradation were defined as follows: Strong vessel wall calcifications (Fig. 2A) Motion artefacts (Fig. 2B) Small vessel diameter (Fig. 2C) Illustrations of image limitations. Strong calcifications in the middle segment of the LAD demonstrated in an oblique MIP (A, arrow). Motion artefacts prevent any image analysis (B). Small vessel diameter starting in the middle segment makes detailed evaluation difficult (C, circle). This study investigated the diagnostic accuracy of 64-slice CT for detection of coronary artery stenoses in ≥1.5 mm diameter segments. The location and number of significant stenoses were documented and compared with the results from ICA, the latter of which was considered the standard of reference. Images of the coronary arteries from CT and ICA of both groups (pathologic/non-pathologic coronary vessels) were evaluated by two blinded cardiovascular surgeons. The concordance between the both reviewers for diagnosing significant coronary artery stenosis was calculated by the Cohen's kappa-value 6 and appraised by the instructions of Landis and Koch 7. Sensitivity, specificity, negative and positive predictive value were calculated for the group of patients with excellent image quality and for all patients together (including reduced and not assessable image quality) and between the group of CAD patients and the group of valve disease. Quantitative variables were expressed as mean ± standard deviation and categorical variables as frequencies or percentages. ICA and 64-slice CT were successfully performed in all 50 patients without complications. Eleven segments in each patient and consequently a total of 550 segments in all 50 patients were analysed. The mean heart rate during the CT scan was 65 ± 11 bpm with a range of 38–89 bpm. The overall CT scan time was approximately 12 s (range 10–13 s) and the mean total time for the examination was less than 13 min (range 8–14 min). The inter-observer agreement between the two readers for the detection of significant coronary artery stenoses with both imaging modalities was excellent (kappa-value of 0.93 for CT and 0.95 for ICA). ICA demonstrated CAD in 80% (40/50) of the patients with at least one significant stenosis. In the 20% (10/50) patients with valvular disease, stenosis-free coronary arteries were identified. In 23% (129/550) of these segments, hemodynamically significant stenoses were detected. Three-vessel disease was diagnosed in 42% (21/50), two-vessel disease in 32% (16/50) and one-vessel disease in 6% (3/50) of the patients. With 64-slice CT, a complete evaluation of all segments was possible in 77% (39/50) of the patients, whereas in 23% (11/50) the image quality of at least one segment was estimated as being limited but still diagnostic or being completely not assessable. Image quality of 92% (506/550) of the segments was rated as being excellent and thus reliable for diagnosis. In 5% (27/550) of the segments, the evaluation was rated as being limited but still diagnostic, so that the two surgeons would have taken the responsibility for a diagnosis. In 3% (17/550) of the segments, both readers were not able to do any approximation, so that they were rated not assessable. Fig. 3 gives an overview about the evaluation of all segments by the two readers with 64-slice CT. Percentages of complete and incomplete analysis of 550 segments in 50 patients. Subdivision for evaluation in reliable analysis, limited analysis, and not assessable segments. Strong vessel wall calcification, motion artefacts, and small vessel diameter were the reasons for a limited or not assessable quality of 64-slice CT, with the most frequent cause of 50% (22/44) being massive vessel wall calcification which caused beam hardening artefacts followed by motion artefacts in 34% (15/44) (Table 1). Reasons for reduced image quality according to the distribution in different branches Thirty-nine percent (17/44) of reduced reliability affected the RCA, 41% (18/44) the LAD including D1 and 20% (9/44) the CX including 1st marginal branch. Five percent (6/150) of all RCA segments were considered not reliable due to motion artefacts and 4% (4/150) due to strong vessel wall calcifications. Two segments (middle and distal) were not assessable because of artefacts caused by a pacemaker lead in the right atrium. Three percent (6/200) of the LAD segments including D1 were not reliable because of strong vessel wall calcifications and 5% (10/200) because of motion artefacts. In the MSCT evaluation, a three-vessel disease was present in 32% (16/50), a two-vessel disease in 42% (21/50), a one-vessel disease in 8% (4/50) and no vessel disease in 18% (9/50). With ICA, 128 significant stenosis were detected, 111 of them were also identified with 64-slice CT (sensitivity 86%). Four hundred and four of the 422 disease-free segments in the ICA were found with CT (specificity 96%). Nineteen false-positive and 14 false-negative findings of CT were found. In addition, three significant lesions were missed with CT in unassessable segments and were thus classified as The positive predictive value was and the negative predictive value was In the segments that were rated reliable by the the increased to and the to Nineteen diagnosis were made 8 Also, the positive and negative predictive increased to and in In the 40 patients with at least one significant stenosis was identified with 64-slice CT. All analysed segments of the patients with valvular disease were percent of the evaluated segments were excluded a significant stenosis. In one segment was found a significant stenosis with CT, whereas the ICA wall but in 9 of the 10 patients with valvular disease, CAD could be excluded by CT, whereas in one patient with an inconspicuous ICA an one-vessel disease was found with CT. With 64-slice CT, of all significant coronary lesions were non-calcified. percent of the significant stenoses were mixed and had at least one whereas of them were completely The different demonstrated in Fig. of stenosing as with 64-slice CT. Fig. 5 a non-calcified significant stenosis in the distal segment of the both the VRT image as as ICA showed a significant no analysis of the plaque quality was possible (Fig. and MPR and the MIP a non-calcified plaque could be identified (Fig. and In this an of the distal RCA at the of the stenosis was performed (Fig. The of the showed no calcifications but cholesterol of a significant stenosis in the VRT image (A, circle) and ICA (B, circle) in the distal segment of the MPR (C, arrow) and oblique MIP (D, images a non-calcified stenosis and of the distal RCA at the of stenosis Fig. 6 a significant in the The MPR the stenosis in the middle segment of the RCA in the and orthogonal plane (Fig. and also which were not with ICA. in the middle segment of the RCA demonstrated in the VRT image (A, arrow) and ICA (B, circle). of a stenosis in MPR images parallel (C, arrow) and orthogonal (D, arrow) to the vessel. CT in addition a which was not with ICA (C, The of a new CT scanner with improved spatial and temporal resolution slices per rotation an of image quality that allow a more evaluation of coronary artery stenosis. The models and 16-slice CT showed for detection of significant stenoses of and This study has for the first time that 64-slice CT image and diagnosis of significant stenosis by cardiovascular surgeons is with a high diagnostic a of the to the above mentioned studies is not due to in imaging and patient the of and of for those segments with image quality in study a The were when including all segments into the analysis reaching a of and a of We analysed all arteries a diameter whereas previous studies were limited to segments with a diameter of mm the of not assessable segments in study was 3% and was thus This is even more not administered additional beta-blockers or to heart and to the diameter of the coronary arteries. study was a high for CAD and had a large of coronary artery wall which is image quality of coronary CT. In addition, this with patients a high of the coronary artery disease have in an of the of MSCT to coronary stenoses. A patient selection the of these results to clinical for the heart in study from to reconstruction intervals to the cardiac cycle were performed enabling an individual choice of the phase with minimal vessel motion for each This to a reduction of motion artefacts for most of the arteries and therefore the reliable assessment of segments with heart A still of coronary artery CT is the on a sinus which makes coronary artery evaluation in patients with impossible. In the most segments image quality was evaluation was still possible and was considered 3% were rated as being completely not evaluable. In contrast to CT, to 32% of the coronary segments had to be excluded from the analysis due to reduced image quality with CT and 16-slice CT this a and is not only by improved time but also by the that the scan time is significantly this more and motion artefacts of the patient. In strong calcifications were a for the analysis of coronary arteries in temporal spatial and of volume of 64-slice CT compared to previous CT scanner lesions with and coronary still the accuracy of coronary angiography. These cause beam hardening and volume artefacts in the of image reconstruction with and the assessment of and coronary lesions is in vessels and at the of the lumen on the size and type studies to investigate the of the for evaluation of patients with previous In this study, calcifications caused artefacts and thus lumen visualization in 4% of all analysed segments in 50% of the limited and segments. the all false-positive significant stenoses with CT were with ICA as wall ICA the of the lumen provides less about wall or plaque For and of plaque or lumen intravascular ultrasound is considered the method of We were able to the quality of the stenosing plaque without to as standard to these However, the of 16-slice CT for plaque quality diagnosis was already demonstrated in different previous studies In study of the were non-calcified. than of all significant stenoses had a and of them were In addition, were not or only as wall with ICA which could be a potential for using 64-slice CT as preoperative planning in patients coronary in invasive (Fig. of the and of CT image and image evaluation. the is not only for the protocol and quality and of the CT examination but also for the image and evaluation. The a of images that could lead to an evaluation of the in this study the cardiovascular surgeon. This of images could be the for the excellent inter-observer agreement of both readers (kappa-value of because all images were to them by the same radiologist. In addition, the and of the This is a to ICA the study be analysed by different independent of the cardiologists because used. a protocol for data and image evaluation of coronary arteries with 64-slice CT is and should be the of studies in When the and including the of 64-slice CT in clinical could be as follows: The image could be a diagnostic in patients with or cardiovascular risk factors. 64-Slice CT could be able to as a to significant For ICA is performed at present for patients than 50 with a valve disease to even when is no clinical of coronary In these would be more for the patients to a CT scan without being to the of ICA. of coronary arteries in to and of significant stenosis or vessel wall as as an course of the arteries could to and the in invasive the is on the and an improved in patients on could to the coronary arteries, evaluation of arteries and ascending aorta for planning the in of and be performed in the same CT of the aortic and mitral valve is the same CT examination to and calcifications or It is not clinical coronary artery CT in when evaluating patients with 64-slice CT provides with regard to a spatial and temporal resolution and to an increased and volume the of patients with and factors as strong vessel wall calcifications and motion artefacts which all cause a image 64-slice CT as a imaging technique to ICA but replace in clinical routine at this potential as a be compared with as conventional and In the coronary CT be used to with multiple risk factors and to a would for CT to replace We should not have the goal completely to replace the coronary angiography at the We should a for the For diagnostic examination of an patient with risk factors for cardiac disease, in the the of the CT is not A patient without any risk factors and should be an diagnostic for a coronary artery disease then in the 64-MSCT is the for evaluation of or patients without any risk factors and a mitral insufficiency or an aortic then also the use of MSCT of coronary angiography is the For preoperative planning the MSCT could be in the a to the invasive techniques, and for with the which in the coronary angiography. If a distal or then for planning the 64-MSCT should the the for for for patients with high and to have the 64-MSCT is a choice than the coronary angiography. For those of that this one replace diagnostic angiography to a of and that to do one of these scans in each mean the MSCT to one patient and the The examination not a It with down the patient and is 10 The image reconstruction is a more time but is also improved with the min to an image reconstruction for an overview and possible evaluation of This has been by the of in and Image of the