Download Quantitative assessment of left ventricular function with dual

Eur Radiol (2008) 18: 570–575
DOI 10.1007/s00330-007-0767-y
S. Busch
T. R. C. Johnson
B. J. Wintersperger
N. Minaifar
A. Bhargava
C. Rist
M. F. Reiser
C. Becker
K. Nikolaou
Received: 12 May 2007
Revised: 3 August 2007
Accepted: 28 August 2007
Published online: 2 October 2007
# European Society of Radiology 2007
S. Busch and T. Johnson contributed equally
to this study.
S. Busch (*) . T. R. C. Johnson .
B. J. Wintersperger . N. Minaifar .
A. Bhargava . C. Rist . M. F. Reiser .
C. Becker . K. Nikolaou
Department of Clinical Radiology,
University of Munich,
Marchioninistr. 15,
81377 Munich, Germany
e-mail: [email protected]
Tel.: +49-89-70953620
Fax: +49-89-70958832
CARD IAC
Quantitative assessment of left ventricular
function with dual-source CT in comparison
to cardiac magnetic resonance imaging:
initial findings
Abstract Cardiac magnetic resonance imaging and echocardiography
are currently regarded as standard
modalities for the quantification of left
ventricular volumes and ejection
fraction. With the recent introduction
of dual-source computedtomography
(DSCT), the increased temporal resolution of 83 ms should also improve
the assessment of cardiac function in
CT. The aim of this study was to
evaluate the accuracy of DSCT in the
assessment of left ventricular functional parameters with cardiac magnetic resonance imaging (MRI) as
standard of reference. Fifteen patients
(two female, 13 male; mean age 50.8±
19.2 years) underwent CT and MRI
examinations on a DSCT (Somatom
Definition; Siemens Medical Solutions, Forchheim, Germany) and a
3.0-Tesla MR scanner (Magnetom
Trio; Siemens Medical Solutions),
respectively. Multiphase axial CT images were analysed with a semiautomatic region growing algorithms
(Syngo Circulation; Siemens Medical
Solutions) by two independent
blinded observers. In MRI, dynamic
cine loops of short axis slices were
evaluated with semiautomatic contour
detection software (ARGUS; Siemens
Medical Solutions) independently by
two readers. End-systolic volume
(ESV), end-diastolic volume (EDV),
ejection fraction (EF) and stroke volume (SV) were determined for both
modalities, and correlation coefficient,
systematic error, limits of agreement
and inter-observer variability were
assessed. In DSCT, EDV and ESV
were 135.8±41.9 ml and 54.9±
29.6 ml, respectively, compared with
132.1±40.8 ml EDV and 57.6±
27.3 ml ESV in MRI. Thus, EDV was
overestimated by 3.7 ml (limits of
agreement −46.1/+53.6), while ESV
was underestimated by 2.6 ml (−36.6/
+31.4). Mean EF was 61.6±12.4% in
DSCT and 57.9±9.0% in MRI, resulting in an overestimation of EF by
3.8% with limits of agreement at
−14.7 and +22.2%. Rank correlation
rho values were 0.81 for EDV (P=
0.0024), 0.79 for ESV (P=0.0031)
and 0.64 for EF (P=0.0168). The
kappa value of inter-observer variability were amounted to 0.85 for
EDV, ESV and EF. DSCT offers the
possibility to quantify left ventricular
function from coronary CT angiography datasets with sufficient diagnostic
accuracy, adding to the value of the
modality in a comprehensive cardiac
assessment. The observed differences
in the measured values may be due to
different post-processing methods and
physiological reactions to contrast
material injection without betablocker medication.
Keywords Cardiac function .
Coronary angiography . Computed
tomography
571
Introduction
The evaluation of global left ventricular function with endsystolic and end-diastolic volumes and especially ejection
fraction and myocardial mass is diagnostically important in
multiple cardiac diseases. So far, parameters of cardiac
function are routinely assessed with echocardiography or
magnetic resonance imaging (MRI) with excellent temporal and spatial resolution. MRI is regarded as standard of
reference in dynamic imaging and functional assessment of
the myocardium [1]. But also computed tomography (CT)
is gaining increasing importance in cardiac imaging, especially with the improved temporal resolution of dual-source
CT (DSCT) of about 83 ms [2]. Apart from the high clinical
potential of non-invasive coronary CT angiography with its
capability to reliably rule out significant coronary artery
disease, the technique’s inherent sharp depiction of the
endocardial contours and the improving temporal resolutions of new scanner generations also makes it possible to
quantify ventricular function, adding to the value of the
modality in a comprehensive cardiac assessment. The
purpose of this study was to evaluate the assessment of left
ventricular function parameters with DSCT with reference
to MRI.
Materials and methods
Fifteen patients (two female, 13 male, age 50.8±19.2 years)
were prospectively included in the study. Ethics committee
approval had been obtained prior to patient recruitment, and
all patients gave informed written consent. CT and MRI
scans of each patient were acquired within 1 week (4±
3 days).
Coronary CTA scans were performed with a DSCT scanner (Somatom Definition; Siemens, Forchheim, Germany).
The mean heart rate was 80±14 beats/min. Beta-blockers
were not administered in preparation for the scan. Collimation was 64×0.6 mm, rotation time 0.33 s, tube potential
120 kV and current 580 mAs. Contrast material (Ultravist,
370 mgI/ml; Bayer Schering, Berlin, Germany) was injected intravenously according to a body weight adapted
regimen with a volume of 1.25 ml/kg and the flow rate
tailored to an injection time of 20 s. Bolus tracking in the
ascending aorta with a threshold of 100 HU was used for
timing. A saline flush of 100 ml was routinely applied. The
entire volume of the heart was acquired within 8–9 s in one
breath-hold with simultaneous recording of the electrocardiographic trace. A medium soft convolution kernel
(B26f) was used for image reconstruction at a slice thickness of 1 mm with 1 mm increment. The use of narrower
slices was not possible for multiphase reconstructions due
to memory restrictions. Multiphase datasets were reconstructed at 5% steps from early systole (0% of the RR
interval) to the late diastole (95% of the RR interval),
resulting in 20 phases of the cardiac cycle.
MRI was performed on a 3-T MRI system (Magnetom
Trio; Siemens, Erlangen, Germany) with a 12-element
cardiac array coil. Heart rates were 65±15/min. Localizer
images were obtained in three planes to identify the long
axis of the left ventricle. Dynamic cine loops of long and
short axis views were acquired with steady-state free precession (SSFP) techniques at 8-mm slice thickness and
1.4×1.8 mm in-plane resolution with a temporal resolution
of 42 ms (TR 3.2 ms, TE 1.4 ms, flip angle 54–60°). The
left ventricle was covered with subsequent short axis slices
from base to apex with a 2-mm gap [3]. Twenty phases
were acquired per cardiac cycle. The image data was acquired within a total of 10–15 s breath-hold time.
DSCT and MRI datasets were evaluated by two experienced radiologists unaware of the results of each other.
A semiautomated software tool (Syngo Circulation on a
Multi Modality Workplace; Siemens, Forchheim, Germany)
was applied for the evaluation of the CT datasets (Fig. 1).
The software uses a region growing algorithm that quantifies
the volume of voxels with densities between 150 and 300
HU [4]. The mitral valve and the anteroseptal region had to
be marked manually. This procedure had to be done twice,
for the endsystolic and for the enddiastolic phase of the RR
interval. The software then traced the left ventricular wall
automatically in long-axis views, excluding papillary muscles and trabeculae with the option to correct the contours
manually, if necessary. Ejection fraction (EF), end-systolic
volume (ESV), end-diastolic volume (EDV) and stroke
volume (SV) were calculated automatically. For the evaluation of MRI, a standard software tool (ARGUS; Siemens,
Forchheim, Germany) was used to quantify functional parameters from dynamic short axis cine loops. The software
requires an initial definition of endocardial and epicardial
contours in at least one slice and the assignment of endsystolic and end-diastolic frames. The software then offers a
semi-automatic contour propagation into the other slices, but
extensive manual correction of these contours is usually
necessary to match the lines to the actual left ventricular
wall. From the contour data, the software similarly
quantifies EF, ESV, EDV and the SV. Hence, papillary
muscles were included in the blood pool of the left ventricle
in this evaluation.
The results of DSCT with reference to MRI were
evaluated with linear regression analysis and Bland-Altman
plots including mean differences and limits of agreement.
Bland-Altman plots were generated seperately for EDV,
ESV, SV and EF. The absolute differences between
respective DSCT and MRI values were documented and
tested for significance with the Wilcoxon test for paired
samples. Inter-observer variability was quantified with the
calculation of Cohen’s kappa. Values were interpreted as
follows: kappa <0.20: poor agreement; 0.21–0.40: fair
572
Fig. 1 Use interface of Syngo
Circulation software for functional evaluation of the left
ventricle. a Matching the mitral
valve and the left ventricular
blood pool. b Marking the
anterorseptal region. c, d The
defined epi- and endoocardial
contours of the software voxelbased with possibitity to correct
manually and the 3D figure of
the calculated volume
agreement; 0.41–0.60: moderate agreement; 0.61–0.80:
good agreement, and 0.81–1.00: very good agreement.
Results
In all fifteen patients, left ventricular contour detection was
feasible in both, the MRI and CT examinations. Using
DSCT, mean EDV was 135.8±41.9 ml, versus 132.1±
40.8 ml EDV in MRI. Mean ESV was 54.9±29.6 ml in
DSCT and 57.6±27.3 ml in MRI, and mean SV was 80.9±
20.9 ml in DSCT and 74.5±18.1 ml in MRI (Table 1). Left
ventricular ejection fraction amounted to 61.6±12.4% in
DSCT and 57.9±9.0% in MRI. Bland-Altman plots (Fig. 2)
show an overestimation of EF in DSCT by 3.8% with limits of
agreement at −14.7 and 22.2%. EDV and SV were also
minimally overestimated by DSCT, with respective values of
3.7 (−46.1/53.6) ml and 6.4 (−30.8/43.5) ml. ESV was under-
Table 1 Mean, standard deviation, absolute difference, P value of Wilcoxon test, Spearman rho for rank correlation with P value and limits
of agreement for parameters of left ventricular function in DSCT and MRI
EDV (ml)
ESV (ml)
SV (ml)
EF (%)
DSCT
MRI
Difference
Wilcoxon P Regression equation Spearman rho P
135.8±41.9
54.9±29.6
80.9±20.9
61.6±12.4
132.1±40.8
57.6±27.3
74.5±18.1
57.9±9.0
3.7±25.4
−2.6±17.3
6.4±18.9
3.8±9.4
0.68
0.11
0.22
0.14
Y ¼ 25:5 þ 0:83X
Y ¼ 4:1 þ 0:88X
Y ¼ 33:8 þ 0:63X
Y ¼ 9:1 þ 0:91X
0.81
0.79
0.36
0.64
0.0024
0.0031
0.1763
0.0168
Limits of agreement
−46.1–53.6
−36.6–31.4
−30.8–43.5
−14.7–22.2
573
Fig. 2 Results of Bland-Altman
plot analysis for EDV, ESV, SV
and EF as assessed in DSCT and
MRI. The diagrams indicate the
difference versus the mean values (drawn through) of both
modalities and ±1.96-fold standard deviations (dashed lines)
estimated in DSCT by 2.6 ml (−36.6/31.4). Spearman rank
correlation showed significant correlations between DSCT
and MRI for ejection fraction (rho 0.64, P=0.0168), for EDV
(rho 0.81, P=0.0024), for ESV (rho 0.79, P=0.0031) and nonFig. 3 Scatter plot with regression slope and 95% confidence
intervals (dashed lines) for
EDV, ESV, SV and EF
significant correlation for SV (rho 0.36, P=0.1763) (Fig. 3).
With respective P values of 0.68, 0.11, 0.22 and 0.14 for EDV,
ESV, SV and EF, none of the observed differences were
statistically significant in the Wilcoxon test. Inter-observer
574
variability in EF, EDV and ESV measurements for both
imaging modalities showed a kappa of 0.85, indicating a very
good agreement.
Discussion
The functional cardiac parameters are important for therapy
planning of congestive heart failure and decision making in
patients suffering from coronary heart disease, e.g. before
bypass surgery. This functional information is usually derived from other diagnostic procedures than CT, i.e. echocardiography or projection X-ray ventriculography, despite
their limited accuracy and precision compared with MRI [5].
Due to the improved temporal resolution of 83 ms,
DSCT can be regarded as a promising method to acquire
functional left ventricular parameters as a complementary
information that can be a determined from coronary CT
angiography datasets non-invasively and without the need
for additional contrast agent or radiation exposure [2]. The
required post-processing has become easier and less timeconsuming and can be expected to be implemented into
routine clinical care soon [6]. In previous CT scanner
generations, a certain heart rate limit had to be observed to
reliably obtain diagnostic images, and pharmacological
modulation was required in many patients [7, 8]. In this
study, diagnostic examination could be obtained in DSCT
without lowering patients’ heart rates. Thus, no betablockers were used in all 15 patients before DSCT.
Similar to other studies [9, 10], we observed only very
small non-significant systematic differences in ESV and
EDV and high correlation coefficients especially for EDV
and EF, so that we can confirm the linear relationship
between both volumetric imaging techniques. Sugeng et al.
[11] described false-low EF values in CT, while we observed a slight overestimation. Sugeng et al. [11] discussed
the possibility that the injection of large volume of iodine
contrast agent could provoke a change in preload and could
cause a negative inotropic effect, but the Frank Starling
mechanism may also cause our opposite observation. In
further studies beta-blockers were used to lower the heart
rate, which has been postulated to be responsible for
reduced EF values in CT examinations [12]. We did not
modulate heart rates with beta-blockers for the CT
examination, and the Bainbridge reflex triggered by atrial
stretch receptors may cause increased sympathetic input
with positive chronotropic effect, which is also supported
by the high heart rates observed in our study group at CT
examination compared to those at MRI. The trend to higher
injection rates in CT may then cause a stronger inotropic and
chronotropic effect and may explain higher values for EF
and SV in CT studies compared to values acquired in MRI.
Another explanation for the observed intermodality differences is the visualisation of endocardial borders and the
exclusion or inclusion of trabeculae into the left ventricular
blood pool. We used two different semiautomatic software
tools for the evaluation, in CT a tool which is based on a
volumetric region-growing algorithm, and in MRI a software
tool that calculates the volumes from short-axis slices by
multiplying the area of the manually drawn contour with the
slice distance. Although not observed in other studies [13,
14], this may explain that there is an underestimation of the
volume in systole, while there is an overestimation in diastole, because trabeculae can cause an actual underestimation
of end-diastolic volumes in MRI as they reduce the diameter
of the endocardial contour, while the region growing
algorithm counts bright pixels between the trabeculae as
blood pool in CT. In systole, the effect should be smaller
because the trabeculae lie closely adjacent to each other so
that there is only a very small volume between trabeculae. Of
course, the depiction of the trabeculae will depend on a high
contrast opacification of the ventricular blood pool. Papillary
muscles were excluded from the ventricular blood pool by
the density-based region-growing algorithm in CT and
included into the blood pool contour in MRI. Although this
has been shown to cause significant differences [15], this
systematic error should be equal in systole and diastole.
The number of acquired phases in DSCT and MRI were
equal for the range of heart rates in our patients, so there
should not be an effect that causes differences in the
identification of end-systolic and end-diastolic phases. Our
observation that DSCT reliably displays the left ventricular
wall with a clear contour and without steps confirms that
the temporal resolution is sufficient for functional evaluation. The temporal resolution of CT does not seem to be the
crucial factor here because the inaccurate definition of endsystole would result in false-high end-systolic volumes and
thus decrease ejection fraction, and our results show a small
opposite systematic error. This may be regarded as an
indication that the increased temporal resolution of DSCT
solves the problem of earlier CT scanner generations, in
which the inadequate temporal resolution and the inflicted
inaccurate match of end-systole caused false-high volumes
and false-low ejection fraction measurements [16].
The observed non-significant differences between functional parameters acquired in CT and MRI [17, 18] may be
caused by physiological effects due to rapid contrast material
injection and the absence of beta-blocker medication in CT. In
summary, a sufficient evaluation of the left ventricular function and wall motion is feasible with CT angiography datasets
acquired for the examination of the coronary arteries, thus
adding a comprehensive functional aspect to the static morphological assessment in CT and possibly rendering the modality a one-stop shop similar to MRI for some indications [6].
575
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