Download Quantification of left ventricular function and mass in heart transplant

Eur Radiol (2008) 18: 1784–1790
DOI 10.1007/s00330-008-0949-2
Gorka Bastarrika
Maria Arraiza
Carlo N. De Cecco
Stefano Mastrobuoni
Matias Ubilla
Gregorio Rábago
Received: 4 November 2007
Accepted: 22 February 2008
Published online: 20 May 2008
# European Society of Radiology 2008
G. Bastarrika (*) . M. Arraiza .
C. N. De Cecco . S. Mastrobuoni .
M. Ubilla . G. Rábago
Department of Radiology, Clínica
Universitaria, Universidad de Navarra,
Avenida Pío XII, 36,
31008 Pamplona, Spain
e-mail: [email protected]
Tel.: +34-948-255400
Fax: +34-948-296500
G. Bastarrika . M. Arraiza .
C. N. De Cecco . S. Mastrobuoni .
M. Ubilla . G. Rábago
Department of Radiology, Universita’
di Roma “Sapienza”–Ospedale Sant’
Andrea,
Rome, Italy
CARD IAC
Quantification of left ventricular function
and mass in heart transplant recipients using
dual-source CT and MRI: initial clinical
experience
G. Bastarrika . M. Arraiza .
C. N. De Cecco . S. Mastrobuoni .
M. Ubilla . G. Rábago
Department of Cardiovascular Surgery,
Clínica Universitaria, Universidad de
Navarra,
Pamplona, Spain
Abstract The purpose of this study
was to compare LV function and mass
quantification derived from cardiac
dual-source CT (DSCT) exams with
those obtained by MRI in heart transplant recipients. Twelve heart transplant
recipients who underwent cardiac
DSCT and MRI examination were
included. Double-oblique short-axis
8-mm slice thickness images were
evaluated. Left ventricular ejection
fraction, end-diastolic volume, endsystolic volume, stroke volume, cardiac
output and myocardial mass were
manually assessed for each patient by
two blinded readers. A systematic
overestimation of all left ventricular
Introduction
Allograft rejection and arterial hypertension after orthotopic cardiac transplantation are well known factors that may
provoke changes in the function and mass of the
transplanted heart [1]. Accurate quantification of left
ventricular volumes, ejection fraction and myocardial
mass is essential for patient management. So far, in routine
clinical practice assessment of these parameters is
performed with echocardiography. Magnetic resonance
volumes by DSCT when compared
with MRI was observed. Mean difference was 16.58±18.61 ml for EDV, 4.9
4± 6.84 ml for ESV, 11.64±13.58 ml
for SV and 5.73±1.14 l/min for CO.
Slightly lower values for left ventricular
ejection fraction with DSCT compared
with MRI were observed (mean difference 0.34±3.18%, p=0.754). Correlation between DSCT and MRI for left
ventricular mass was excellent (rho =
0.972). Bland and Altman plots and
CCC indicated good agreement between DSCT and MRI left ventricular
function and mass measurements. The
interobserver correlation was good. In
conclusion, DSCT accurately estimates
left ventricular ejection fraction, volumes and mass in heart transplant
recipients.
Keywords Dual-source computed
tomography (DSCT) . Heart function .
Cardiac mass . Heart transplantation
imaging (MRI) is considered the standard of reference for
the functional evaluation of the left ventricle [2–5].
Retrospectively ECG-gated multidetector CT (MDCT)
is increasingly being used for cardiac imaging. MDCT
allows accurate non-invasive evaluation of coronary arteries and depiction of significant coronary artery stenoses in
patients with suspicion of coronary artery disease [6–8].
Feasibility of MDCT to assess global ventricular function
using coronary MDCT datasets in this group of subjects
has been proved [9–11]. In heart transplant recipients
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MDCT has also shown its ability to detect significant
coronary artery stenoses compared with invasive coronary
angiography [12, 13]. A recent study demonstrates that 64row MDCT may permit detection of coronary allograft
vasculopathy [14]. However, due to several factors,
including high heart rates, obesity and post-surgical
changes, heart transplant recipients represent a challenge
for MDCT cardiac imaging [15]. MDCT scanners have a
limited temporal resolution, often requiring beta-blocker
premedication to obtain high quality cardiac exams [11,
16]. These limitations may cause inaccuracies when
determining cardiac volumes with MDCT. Dual-source
computed tomography (DSCT) provides a high constant
temporal resolution of 83 ms independent of the heart rate
[17]. Hence, this technology might possibly improve
accuracy and reliability of LV function and mass assessment [17]. Recently quantitative assessment of LV function
with DSCT has been evaluated [18]. The role of this
technique in heart transplant recipients has not been
evaluated yet.
In this study we compared LV function and mass
quantification derived from cardiac DSCT exams with
those obtained by MRI as the reference standard in patients
who underwent orthotopic cardiac transplantation.
Materials and methods
Patient population
Twelve consecutive heart transplant recipients referred for
exclusion of coronary allograft vasculopathy underwent
retrospectively ECG-gated contrast-enhanced DSCT. In all
subjects additional cardiac MR examination was performed
within 1 month before the DSCT examination. Standard
exclusion criteria for MDCT coronary angiography and
MRI were applied. All patients were in sinus rhythm and
had normal renal function (creatinine <1.4 mg/dl). Patients
with arrhythmia (more than four premature beats per
minute or atrial fibrillation), hemodynamic instability,
known allergy to iodated contrast media or renal failure
(creatinine <1.4 mg/dl) were excluded from the study.
Patients with MR unsafe ferromagnetic objects, referring
claustrophobia or pacemaker or AICD implantation were
also excluded. No beta blockers were employed prior to the
scan to lower the heart rate. Written informed consent was
obtained from all patients. The study protocol was
approved by the institutional review board.
DSCT image acquisition protocol and image
reconstruction
Retrospectively ECG-gated coronary CT angiography
exams were performed with a DSCT scanner (Somatom
Definition, Siemens Medical Solutions, Forchheim, Ger-
many) at end inspiration. Scanning direction was craniocaudal from above the origin of the coronary arteries to the
end of the diaphragm. Mean acquisition time was 8 s. Tube
voltage of 120 kV and current of 410 mAs for both tubes
were employed. Detector collimation was 32×0.6 mm,
slice acquisition 64×0.6 mm by means of a z-flying focal
spot [19] and gantry rotation time 0.33 ms. The pitch was
variable (0.3–0.45) and automatically adapted to the heart
rate. Full tube current was administered between 30 and
80% of the cardiac cycle by means of automatic tube
current modulation (ECG pulsing) technique. Cardiac
exams were performed after continuous injection of
70 ml of contrast material (Iomeron 400, Iomeprol, Bracco
s.p.a, Milan, Italy) via an antecubital vein at a flow rate of
5 ml/s followed by 50 ml chaser saline flush using a dualhead power injector (CT Stellant, Medrad Inc., Indianola,
PA). Data acquisition was triggered using the bolus
tracking technique with the region of interest placed into
the aorta with a threshold of 100 HU.
A mono-segment reconstruction algorithm that uses data
from a quarter rotation of both detectors was employed for
retrospective image reconstruction [17]. Double-oblique
short-axis orientation images encompassing the whole
heart were reconstructed with section thickness of 8 mm
and no interslice gap. Medium smooth convolution kernel
(B26f) and image matrix of 512×512 pixels were used.
Image series were directly reconstructed from the raw data
in 5% steps throughout the entire cardiac cycle (0–95% of
the R-R interval) resulting in 20 phases per cardiac cycle.
No manual ECG-editing was performed. All DSCT
images were suitable for analysis. Reconstructed images
were transferred to an external workstation (Leonardo,
Siemens Medical Solutions) equipped with a dedicated
cardiac post-processing software tool (Argus, Siemens
Medical Solutions).
MRI image acquisition protocol
MRI was performed using a 1.5-T MRI system (Magnetom
Symphony with quantum gradients; maximum gradient
amplitude 30 mT/m; slew rate, 125 mT/m/s, Siemens
Medical Solutions, Erlangen, Germany) with a fourelement phased array coil. After localizer images were
obtained, dynamic 8–12 contiguous short axis cine loops
covering the entire left ventricle were acquired using a
steady-state free precession (SSFP) sequence. The following parameters were employed: TR: 3.09 ms, TE: 1.3 ms,
flip angle: 80, matrix: 156×192, field of view: 260–
280×325–375 mm. In-plane resolution was 1.7×1.7 mm
and temporal resolution varied from 25–50 ms. Slice
thickness was 8 mm. No interslice spacing was used.
Twenty-five phases were acquired per cardiac cycle using
retrospective gating. All MRI images were suitable for
analysis. Reconstructed images were transferred to the
same external workstation.
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DSCT and MRI data analysis
DSCT and MRI images were assessed, in duplicate, by two
blinded readers. For quantitative evaluation of cardiac
parameters, slices from the base of the heart to the apex
were analyzed. The base of the left ventricle was defined as
the most basal slice surrounded by at least 50% myocardium in all cardiac phases [20] and the apex as the last slice
with a visible lumen along the entire cardiac cycle. In each
patient end-diastolic and end-systolic phases were visually
determined and manually marked by the observers as the
images showing the largest and smallest LV cavity areas,
respectively. Endocardial and epicardial borders of the left
ventricle were manually traced on serial short axis slices at
end-systolic and end-diastolic phases using Argus software
(Fig. 1). Papillary muscles and trabeculations were
excluded from the volumetric analysis and included in
myocardial mass quantification. Left ventricular ejection
fraction (EF), end-diastolic volume (EDV), end-systolic
volume (ESV), stroke volume (SV), cardiac output (CO),
and myocardial mass were calculated for all patients using
the Simpson’s method. This method consists of summing
the endo- and epicardial area of all end-diastolic and endsystolic images and multiplying the result by the slice
thickness. Left ventricular mass was calculated as the
Fig. 1 DSCT (upper row) and
MRI (lower row) images of a
51-year-old heart transplant recipient. End-diastolic (a, c) and
end-systolic images with manually traced endo-and epicardial
borders are shown
difference between endo- and epicardial volumes at enddiastole multiplied by myocardial density (1.05 g/ml).
Statistical analysis
All data are summarized as mean ± standard deviation. A
Wilcoxon test for paired samples was employed to
calculate differences in left ventricular parameters for
respective DSCT and MRI values. For linear correlation
analysis the Spearman rank correlation coefficient (rho)
was determined. Correlation was defined as poor (rho=0);
minimal (rho=0.1–0.40), moderate (rho=0.41–0.60), good
(rho=0.61–0.80) and excellent (rho=0.81–1.0). To assess
the degree of agreement between the results of DSCT and
MRI for each pair of left ventricular values Bland and
Altman plots including mean differences and limits of
agreement [21] were generated. Concordance-correlation
coefficient (CCC) was also calculated for each measured
variable and to assess interobserver variability [22]. The
CCC can range from 0 to 1, with a CCC of zero
representing no agreement and a CCC of 1 meaning
perfect reliability. A p-value of 0.05 or less was considered
statistically significant. Data analysis was performed using
commercially available statistical softwares (MedCalc,
1787
Version 9.3.0.0. MedCalc Software; Mariakerke, Belgium,
and SPSS for Windows, version 13.0/SPSS Inc., Chicago,
IL).
Results
Patient population
Twelve consecutive patients underwent cardiac DSCT and
MRI. The study population was predominantly male (11
men, 1 woman) with a mean age of 63.92±11.81 years (age
range 36–77). The mean time from transplantation to study
enrolment was 10.42±5.06 years (range: 4.5–19.8 years).
The mean heart rate was 88.42±11.86 bpm during DSCT
(range: 71–109 bpm) and 87.5±12.19 bpm during MRI
(range: 64–114 bpm) (p=0.97, NS).
Left ventricular function and mass
In all patients cardiac DSCT and MRI exams were
successfully performed without complications. All studies
were of adequate quality for function and mass assessment
allowing optimal manual segmentation of the left ventricle.
The mean left ventricular ejection fraction, left ventricular volumes and left ventricular mass are summarized in
Table 1. Overall values were within normal limits. The
mean EF assessed on DSCT was 68.19±4.52%, wheareas
the mean EF estimated from MRI was 68.53±2.853%. Left
ventricular volumetric measurements as determined with
DSCT showed a mean EDV of 113.47±24.37 and a mean
ESV of 35.43±6.42 ml, whereas MRI revealed a mean
EDV of 96.88±20.71 ml and a mean ESV of 30.49±
6.82 ml. The mean SV calculated from DSCT was 78.02±
20.35 ml and the mean SV estimated from MRI was
66.37±14.79 ml. The mean CO derived from DSCT was
6.83±1.99 l/min, wheareas the mean CO estimated from
MRI was 5.73±1.14 l/min. There was good correlation
between DSCT and MRI measurements of left ventricular
function parameters except for the end-systolic volume for
which correlation was minimal (rho=0.392). A systematic
overestimation of all left ventricular volumes by DSCT
when compared with MRI was observed (Table 1). BlandAltman analysis demonstrated a trend toward DSCT
resulting in slightly lower values for left ventricular
ejection fraction compared with MRI (mean difference
0.34±3.18%).
Mean left ventricular mass as determined with DSCT
was 120.29±34.45, whereas the mean left ventricular mass
estimated from MRI was 116.08±27.35 g. This difference
was not statistically significant (p>0.05). Spearman rank
correlation between DSCT and MRI for left ventricular
mass was excellent (rho=0.972).
Bland and Altman plots and CCC indicated good
agreement between DSCT and MRI left ventricular function and mass measurements (Fig. 2). Results are shown in
Table 1.
The interobserver agreement for left ventricular parameters by means of DSCT was 0.74 (0.33 to 0.92) for EF,
0.90 (0.73 to 0.97) for EDV, 0.87 (0.66 to 0.95) for ESV,
0.88 (0.69 to 0.96) for SV, 0.83 (0.56 to 0.94) for CO, and
0.92 (0.79 to 0.97) for left ventricular mass. The
interobserver agreement was 0.50 (0.15 to 0.73) for EF,
0.91 (0.74 to 0.97) for EDV, 0.84 (0.66 to 0.93) for ESV,
0.79 (0.51 to 0.91) for SV, 0.78 (0.43 to 0.93) for CO, and
0.68 (0.30 to 0.87) for left ventricular mass using MRI.
Discussion
The main finding of this study is that DSCT provides
accurate measurements of left ventricular ejection fraction,
volumes and mass in orthotopic heart transplant recipients.
Recent reports have emphasized the potential of MDCT to
evaluate coronary arteries and measure cardiac function
within a single exam [9–11]. However, as heart transplant
recipients represent a challenge for cardiac MDCT imaging, only few papers focus on the role of 64-row MDCT
scanners in determining coronary allograft vasculopathy
and assessing cardiac function [12, 13, 15]. High resting
heart rates and the absence of response to oral beta-blocker
Table 1 Differences in left ventricular function and mass quantification as determined by DSCT and MRI
EF (%)
EDV (ml)
ESV (ml)
SV (ml)
CO (l/min)
Mass (g)
DSCT
MRI
P value
rho value
Bland- Altman
CCC
68.19±4.52
113.47±24.37
35.43±6.42
78.02±20.35
6.83±1.99
120.29±34.45
68.53±2.853
96.88±20.71
30.49±6.82
66.37±14.79
5.73±1.14
116.08±27.35
0.754
0.015
0.034
0.019
0.015
0.308
0.641*
0.701*
0.392
0.769*
0.776*
0.972*
-0.34 (-2.37 /1.68)
16.58 (4.76 /28.40)
4.94 (0.59 /9.29)
11.64 (3.01 /20.27)
1.10 (0.31 /1.89)
4.21 (-3.68 /12.10)
0.64
0.51
0.36
0.57
0.56
0.91
(0.25–0.85)
(0.09–0.78)
(-0.11–0.69)
(0.18–0.81)
(0.24–0.77)
(0.77–0.97)
Data are presented as mean ± SD. EF: ejection fraction; EDV: end-diastolic volume; ESV: end-systolic volume; SV: stroke volume; CO:
cardiac output; mass: myocardial mass. CCC: concordance correlation coefficient.
*p<0.05
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Fig. 2 Bland-Altman plots
show the agreement between
DSCT and MRI. Plots for left
ventricular ejection fraction
(EF), end-diastolic volume
(EDV), end-systolic volume
(ESV), stroke volume (SV),
cardiac output (CO) and LV
mass (MASS) are presented
premedication by heart transplant recipients have limited
the widespread employment of MDCT for coronary
imaging in this population [15]. On the other hand, when
comparing cardiac function parameters obtained with
MDCT with respect to MRI, results are inconsistent [11,
23, 24]. This inconsistency might be due to the common
practice of giving beta blockers when performing cardiac
MDCT exams [25–27], which may artificially reduce the
heart rate and thus affect estimation of cardiac parameters
[11, 28].
Dual-source CT allowed for robust cardiac image quality
in our heart transplant recipient series, which was not
influenced by their high resting heart rates (mean 88.42±
11.86 bpm, range: 71–109 bpm). Optimal image quality
permitted accurate evaluation of left ventricular volumes
and mass in all subjects, with good agreement with respect
to data obtained from MRI. Even if the difference was not
statistically significant, a tendency to underestimate the
ejection fraction was found in this series. Results presented
herein support findings of similar studies performed with
MDCT [11, 29–31], but interestingly, differ from recently
reported data using a DSCT scanner [18]. In their study
Busch at al. [18] found non-significant differences between
functional parameters acquired with DSCT and MRI.
According to the authors, this might be due to the
Bainbridge reflex produced by rapid contrast material
injection causing increased sympathetic input in a study
population that did not receive pre-scan beta-blocker
therapy. As our study population consisted of subjects in
whom the sympathetic reflex is inhibited, the cited positive
1789
chronotropic effect presumably may not be so intense. We
also found overestimation of the end-systolic volume
probably due to the fact that temporal resolution of DSCT
(83 ms) still remains lower than that of MRI (40 ms).
According to our results, correlation between DSCT and
MRI data was good for all cardiac function parameters
except for the end-systolic volume (rho =0.392). The
Bland-Altman analysis showed acceptable limits of agreement and minimal bias, suggesting that data derived from
DSCT may be used as an estimate of left ventricular
parameters. As already demonstrated by previous studies
[32, 33], we also observed equivalent quantification of left
ventricular mass with DSCT and MRI (mean difference
4.21±12.42 g, p=0.308], supporting the fact that threedimensional techniques do not depend on limitations
imposed by geometric assumptions [34, 35]. This issue is
of particular interest in heart transplant recipients, in whom
post-surgical changes, the different orientation of the
transplanted heart, the inadequate acoustic window, the
remodeling process, and the potential foreshortening of
the left ventricular apex [34, 35] may limit accurate
quantification of cardiac parameters by routinely employed
diagnostic tools, such as echocardiography [36].
Our study has several limitations. First, a small cohort of
heart transplant recipients was included. Second, patients
did not undergo cardiac DSCT and MRI on the same day,
but were clinically stable, no allograft rejection was
demonstrated at the time of study, and their therapy
remained unchanged. Third, the number of acquired phases
in DSCT and MRI differed. This might cause differences in
the identification of end-systolic and end-diastolic phases.
Nevertheless, limits of agreement between DSCT and MRI
were acceptable.
In conclusion, our findings reveal that DSCT accurately
estimates left ventricular ejection fraction, volumes and
mass in heart transplant recipients. We observed that DSCT
tends to overestimate left ventricular volumes when
compared with MRI. One advantage of DSCT is the fact
that clinicians may use this technique for a one-stop-shop
evaluation of the heart in heart transplant recipients without
the need of additional radiation exposure or contrast
administration.
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