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
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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
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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)