Yoshiaki Morita1, Mitsuhiro Tsuritani2, Naoaki Yamada1, Yoshiaki Watanabe1, Tatsuya Nishii1, Atsushi Kono1, Jun Yoshimatsu2, and Tetsuya Fukuda1
1Department of Radiology, National Cerebral and Cardiovascular Center, Suita, Osaka, Japan, 2Department of Perinatology and Gynecology, National Cerebral and Cardiovascular Center, Suita, Osaka, Japan
Synopsis
Volumetric analysis of the fetal heart by ultrasound (US) in congenital heart disease is often
difficult due to its complex anatomy and US-specific artifacts. We implemented
the real-time cine sequence without ECG triggering and the post-processing
technique (PhyZiodynamics), which enabled noise reduction and interpolation
based on motion coherence. Fetal MRI using real-time cine imaging allowed for
detailed functional assessment in both ventricles and showed acceptable levels
of correlation with both the prenatal and postnatal US findings, suggesting
that this technique is a promising diagnostic tool for functional assessment of
congenital cardiovascular abnormalities.
Introduction
The current gold standard in fetal cardiac imaging is the
use of ultrasound (US). However, accurate volumetric analysis of both ventricles
is often difficult in cases with congenital heart disease due to complex anatomy
and US specific artifacts. Furthermore, US has the disadvantages of a limited
acoustic window and observer dependency.
Fetal MRI has recently become a viable tool for
evaluating the fetal cardiovascular system. 1,2 One of the main issues in evaluating fetal cardiac
function via cine imaging is gating the acquisition to the fetal ECG. Notably,
the ECG triggering method for a fetus is not yet clinically available at all
hospitals. Purpose
In this study, we performed fetal MRI using real-time
cine imaging without ECG triggering and the post-processing technique
(PhyZiodynamics), which enable noise reduction and interpolation based on motion
coherence, and evaluated the feasibility of fetal MRI for functional assessment
of the fetal heart for congenital heart disease.Methods
Prenatal cardiac MRIs on 18 pregnant women
carrying fetuses with congenital heart
disease were performed on a 1.5 T clinical machine (MAGNETOM Sonata, Siemens AG
Healthcare Sector, Erlangen, Germany).
Before cardiac MR examination, the fetal
heart rate was measured via cardiotocography, and the detected heart rate was
used as an R-R interval of simulated ECG in real-time cine imaging.
Both the transverse and short-axis planes
were acquired using a real-time multi-slice True-FISP cine sequence (TE/TR=1.3/2.6msec,
flip angle 50°, FOV 200mm, matrix 192×154, slice thickness 4 mm) without ECG triggering of a fetal
heartbeat. The length of real-time scanning was adjusted to two times the R-R
interval (decided before MRI) using a simulated ECG.
With use of the post-processing technique, which enabled noise reduction and interpolation
based on motion coherence (PhyZiodynamics; Zio station 2 software, Ziosoft Inc., Japan), the
effective temporal resolution was 37 msec.
The left ventricular volume was analyzed from
the
short axis plane, and the right
ventricular volume was analyzed from the transverse axis plane by two experienced observers via manual
tracing of the endocardial border using Siemens Argus software. CMR findings were compared with prenatal and
postnatal echocardiography.Results
In
all fetal images acquired from the real-time cine sequence, myocardial
contraction of both ventricles was visualized well (Figure 1).
Table 1 showed
the mean end-diastolic volume (EDV), end-systolic volume (ESV), and ejection
fraction (EF) via real-time cine imaging. LVEF based on fetal MRI and prenatal and postnatal US
correlated well; prenatal US was r=0.73, and postnatal US was r=0.84 (Figure 2). LVEFs obtained by an MRI
tended to be lower than those obtained with US. EDV on the fetal MRI and
ventricular internal dimension in diastole (VDd) on the postnatal US also
correlated well; LV was r=0.64, and RV was r=0.80 (Figure 3).
Intra-
and inter-observer variability for EDV, ESV, and EF in both ventricles were
sufficiently small in real-time True-FISP cine imaging.Discussion
Our
results demonstrated that real-time cine imaging without real ECG triggering
allows detailed functional assessment in both ventricles and shows acceptable
levels of correlation with both the prenatal and postnatal US findings.
In
this study, we used the novel post-processing
technique PhyZiodynamics, which tracks the movement of individual voxels
through space and time based on the non-rigid registration between phases (Figure 4). This voxel-to-voxel mapping
of information enables the employment of additional algorithms that reduce
noise, improve motion coherence, and measure function. 3 With use of this
application, non-linear interpolation between registered voxels can generate
increased phase data from the original cine data set.
EFs
were systematically lower when obtained with an MRI than with US; however, this
might have been due to the different techniques employed. A previous study in a
cardiac porcine model of known volume showed that cine MRI yielded the most
precise volumetry by using methods
similar to those used in our study, particularly for the right ventricle, which
has a more complex anatomy.
4 Therefore, we
believe that cine MRI has the potential to evaluate more accurate functional
assessment compared with other modalities such as US.Conclusion
Fetal
CMR using real-time cine imaging is a promising diagnostic tool for functional assessment
of congenital cardiovascular abnormalities.Acknowledgements
No acknowledgement found.References
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Brown HA PhyZiodynamics® A Revolutionary Approach for Post-Processed Noise
Reduction, Motion Coherence, and Functional Analytics. 2010 Ziosoft, Inc.
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