Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT

European Radiology, Jun 2002

High reproducibility is a key requirement for coronary calcium scoring in follow-up examinations. We investigated the inter-examination reproducibility of calcium scoring with retrospectively ECG-gated multisection spiral CT (MSCT). Fifty patients were examined twice with MSCT. Slices were reconstructed with retrospective ECG gating in the diastolic phase with 3-mm slice width and up to 125-ms temporal resolution. We calculated the Agatston score, calcium volume with and without isotropic interpolation, and calcium mass, and derived the mean and median variability. We investigated the change of variability with use of 3-mm non-overlapping and overlapping increments (2, 1.5, 1 mm). Use of overlapping increment results in considerably reduced interscan variability. We observed a minimum mean variability of 12% and a minimum median variability of 9% for the Agatston score. For volume and mass quantification we obtained a minimum mean variability of 7.5% and a minimum median variability of 5%. Multisection spiral CT enables coronary calcium quantification with high reproducibility in follow-up examinations mainly founded on image data with reduced partial-volume errors due to overlapping increment.

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Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT

B. Ohnesorge T. Flohr R. Fischbach A. F. Kopp A. Knez S. Schrder U. J. Schpf A. Crispin E. Klotz M. F. Reiser C. R. Becker 0 1 2 3 0 A.F. Kopp Department of Clinical Radiology, University of Tbingen , Hoppe-Seyler-Strasse 3, 72076 Tbingen, Germany 1 U.J. Schpf A. Crispin M.F. Reiser C.R. Becker Department of Clinical Radiology, Grosshadern Clinic, University of Munich , Marchioninistrasse 15, 81377 Munich, Germany 2 A. Knez Department of Cardiology, Grosshadern Clinic, University of Munich , Marchioninistrasse 15, 81377 Munich, Germany 3 R. Fischbach Department of Clinical Radiology, University of Mnster , 48149 Mnster, Germany High reproducibility is a key requirement for coronary calcium scoring in follow-up examinations. We investigated the interexamination reproducibility of calcium scoring with retrospectively ECG-gated multisection spiral CT (MSCT). Fifty patients were examined twice with MSCT. Slices were reconstructed with retrospective ECG gating in the diastolic phase with 3-mm slice width and up to 125-ms temporal resolution. We calculated the Agatston score, calcium volume with and without isotropic - interpolation, and calcium mass, and derived the mean and median variability. We investigated the change of variability with use of 3-mm nonoverlapping and overlapping increments (2, 1.5, 1 mm). Use of overlapping increment results in considerably reduced interscan variability. We observed a minimum mean variability of 12% and a minimum median variability of 9% for the Agatston score. For volume and mass quantification we obtained a minimum mean variability of 7.5% and a minimum median variability of 5%. Multisection spiral CT enables coronary calcium quantification with high reproducibility in follow-up examinations mainly founded on image data with reduced partial-volume errors due to overlapping increment. Electron-beam CT scanning (EBCT) has been established as a non-invasive imaging modality for the detection and quantification of coronary calcium by using the Agatston scoring algorithm [1]. With EBCT scanning, typically 3-mm thick slices are acquired contiguously with prospective ECG triggering in mid-diastole and an exposure time of 100 ms per slice. An effective radiation exposure of approximately 0.9 mSv was reported for this protocol [2]. The amount of coronary calcification may be used as a marker for the total atherosclerotic plaque burden [3]. Variable amounts of calcification may indicate regression or progression of atherosclerosis and coronary artery disease (CAD) [4]. The normal progression of coronary calcification is approximately represented by 1427% (average 24%, [5]) increase of the calcium score per year that may be enhanced up to 3348% for patients with significant coronary disease [6, 7]. Various studies have shown that progression of coronary calcification is decelerated (<10% per year) in patients under statin therapy [8]. For reliable monitoring of the progression of coronary disease via measurement of coronary calcification, the error between successive examinations must be considerably smaller than the expected change of calcified plaque burden; thus, high accuracy and reproducibility of the calcium score measurement with interscan variability below 10% are crucial for reliable detection of small changes within a reasonable follow-up interval. The interscan reproducibility of EBCT scanning has been shown to have poor to fair values ranging from 14 to 51% mean variability depending on scan technique and scoring method [4, 9, 10]. High variability is particularly present for small amounts of calcification. Recently, alternative quantitative volumetric scoring methods have been developed that have improved interscan reproducibility [11]. Partial-volume errors introduced by contiguous acquisition with 3-mm slice width, long breathhold times of 2540 s, and image artifacts due to inconsistent ECG triggering for arrhythmic heart rates have been identified as the main variability factors [2]. Recently, mechanical multi-slice CT systems (MSCT) with simultaneous acquisition of four slices, 0.5-s scanner rotation, and 125-ms maximum temporal resolution provided by special reconstruction algorithms have become available for cardiac CT scanning [12, 13]. The first studies have shown a high correlation of MSCT with prospectively ECG-triggered acquisition and 250-ms effective exposure time compared with EBCT for the detection of coronary calcification using the Agatston- and volumetric scoring methods [14]; however, it has also been shown that a higher degree of coronary motion artifacts may be present with MSCT due to reduced temporal resolution with 250-ms effective exposure time. Multislice CT with retrospective ECG gating enables continuous volume coverage with acquisition of overlapping slices and substantially faster volume coverage compared with ECG triggering. Phantom studies and experimental patient studies have shown that non-overlapping sequential scanning is an (...truncated)


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B. Ohnesorge, T. Flohr, R. Fischbach, A. Kopp, A. Knez, S. Schröder, U. Schöpf, A. Crispin, E. Klotz, M. Reiser, C. Becker. Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT, European Radiology, 2002, pp. 1532-1540, Volume 12, Issue 6, DOI: 10.1007/s00330-002-1394-2