We screened 195 consecutive patients scheduled for ICA because of suspected CAD or suspected progress of a known CAD for participation in the present study. All patients were listed for ICA because of typical chest pain or positive stress tests.
Seventeen (9%) patients declined to participate, 47 (24%) patients had contraindications, and for eight (4%) patients no scan time was available. Of the 195 patients, 124 (64%) were enrolled in this study. The local ethics committee had approved the study protocol and all patients gave informed consent. Exclusion criteria were defined as irregular heart rate, contraindications to iodinated contrast media, and increased serum creatinine concentrations > 133 μmol/l. All patients underwent MDCT one day before ICA. Patients with heart rates > 65 beats/min were given additional β blockade.
MDCT was performed with a 16 detector slice computed tomograph (Sensation 16 Speed 4D, Siemens Medical Solutions, Forchheim, Germany) with a newly developed tube (Straton, Siemens Medical Solutions), 370 ms rotation time, and 16 slices read out simultaneously in the cardiac mode. The scan protocol was as follows: native vessels were scanned without contrast medium to determine the total calcium burden of the coronary tree (16 × 1.5 mm collimation, table feed 3.8 mm/rotation, tube current 133 mA at 120 kV). To evaluate the circulation time, 20 ml of contrast medium (20 ml at 4 ml/s, 400 mg iodine/ml, Imeron 400; Altana Pharma, Constance, Germany) and a chaser bolus of 20 ml saline were administered in an antecubital vein. The contrast enhanced scan of the coronary arteries was acquired with the following protocol: 80 ml intravenous contrast agent followed by 20 ml chaser bolus (50 ml at 4.0 ml/s, then 30 or 50 ml at 2.5 ml/s), 16 × 0.75 mm collimation, table feed 3.8 mm/rotation, tube current 650 mA at 120 kV. Computed tomography started at the aortic root cranial to the coronary ostia and stopped at the diaphragm caudally of all cardiac structures. ECG pulsing with reduced tube current during systole was recorded during all scans to minimise radiation exposure.
Axial images were reconstructed by the standard built-in ECG gated half scan reconstruction algorithm (temporal resolution 185 ms, slice thickness 1.0 mm, increment 0.5 mm, kernel B 30 f). The reconstruction window was set to start at 60%; in case of motion artefacts an additional test series reconstructing single slices in 5% steps ranging from 20–75% relative to the RR interval was adopted. Examples of images are shown in figs 1 and 2.
Figure 1 Exclusion of coronary artery disease in a patient. (A) Curved multiplanar reconstruction of the left anterior descending artery. (B) Curved multiplanar reconstruction of the left circumflex artery. (C) (more ...)
Figure 2 Patient with severe calcifications (140 mg calcium hydroxyapatite) in projection on the left anterior descending artery with a tight stenosis (arrows) between two calcified plaques immediately after the delivery (more ...)
MDCT image interpretation
Two reviewers, blinded to the results of ICA and to all clinical information, evaluated the MDCTs in a joint reading. Data were analysed on an offline workstation for postprocessing (Leonardo, Siemens, Forchheim, Germany). Coronary calcifications were assessed on native scans and quantified by determining the total calcium mass expressed in mg of calcium hydroxyapatite.
Contrast enhanced MDCT angiograms were investigated by the use of axial slices and 4 mm thin slab maximum intensity projections in axial and double oblique orientation adapted to the specific anatomy of the vessel.
Image quality was classified as excellent (no motion artefacts present), good (minor motion artefacts present), moderate (substantial motion artefacts present but luminal assessment regarding significant stenosis still possible), heavily calcified (vessel lumen obscured by calcification), or blurred (no luminal assessment of significant stenosis possible).
The readers assessed significant lesions with a diameter stenosis
50%. Results were documented separately for 13 coronary segments from each patient according to a modified American Heart Association classification with 13 segments (right coronary artery, segments 1–4; left main, segment 5; left anterior descending coronary artery, segments 6–10; left circumflex artery, segments 11–13).
The clinical diagnosis based on MDCT was considered to be correct if MDCT ruled out any significant lesion > 50% or MDCT detected correctly at least one significant lesion > 50% that was detected by ICA.
Quantitative coronary angiography
ICA was performed with standard techniques one day after the MDCT. All angiograms were evaluated by one blinded independent observer by quantitative coronary analysis (Philips Medical Systems, Einthoven, the Netherlands). The projection with the most severe degree of diameter stenosis was used for evaluation. Lesions with a diameter stenosis > 50% were considered to be significant.
ICA was regarded as the reference standard for the detection of significant lesions. MDCT results were compared on a segmental basis, for each vessel and each patient. If a segment contained more than one lesion, the most severe lesion determined the diagnostic accuracy of the assessment. Categorical data were presented with absolute frequencies and percentages. Continuous variables are shown as mean (SD). Data were analysed with Prism 3.0 (GraphPad Software Inc, San Diego, California, USA).