Giovanna Nordio1, Radhouene Neji2, Karl Kunze2, Rene Botnar1, and Claudia Prieto1
1Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, 2MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom
Synopsis
In this study we investigate the
feasibility of a 3D turbo spin-echo imaging technique with variable flip angle
combined with an undersampled Cartesian variable density trajectory (3D
TSE-VDCASPR) for efficient whole-heart black-blood imaging. Data from five healthy subjects are acquired with the proposed 3D TSE-VDCASPR and the
conventional 3D TSE with Cartesian GRAPPA. The proposed imaging 3D TSE-VDCASPR
imaging technique allows for comparable black-blood imaging, with the advantage
of reduce nominal scan time (4.6±1 vs 8.1±1.6 minutes ± seconds). Future work
will investigate more advanced motion compensation and image reconstruction
techniques in order to achieve predictable and fast scan time.
Introduction
Black-blood imaging suppresses blood signal, allowing the
visualization of the vessel walls and the morphology of the heart. Recently, 3D turbo spin-echo (TSE) imaging
techniques with variable flip angle [1] have been proposed for the
visualization of the aortic vessel wall and whole-heart anatomy, allowing
free-breathing acquisition with high image resolution [2-3]. However, 3D TSE can
be quite challenging due to prolonged scan time and image artefacts due to
insufficient blood nulling. In this study, we investigate the feasibility of a
3D TSE imaging sequence with variable flip angle combined with an undersampled Cartesian
variable density trajectory for efficient whole-heart black-blood imaging. The
proposed imaging sequence is compared with conventional 3D TSE in five healthy
subjects.Methods
Five healthy subjects were examined on a 1.5T
MR system (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany) using a 3D
turbo spin-echo prototype imaging sequence with Cartesian sampling and GRAPPA
reconstruction (3D TSE) and a Cartesian variable density trajectory with spiral
profile order (3D TSE-VDCASPR) [4] with iterative SENSE reconstruction [ref].
The imaging parameters used for the T1 weighted 3D TSE sequence were: coronal
orientation, image resolution of 1x1x2mm3, FOV = 320x320x110, echo
train length = 35, echo spacing = 3.3 ms, echo time = 17 ms, number of
averages = 2, ECG triggered with end-systolic image acquisition, fat
suppression = SPIR, resulting in an acquisition window of 116 ms. The 3D TSE
sequence uses a 90˚ slice-selective RF excitation followed by non-selective
refocusing RF pulses with variable flip angles. A diaphragmatic navigator with
a gating window of 5mm and a tracking factor of 0.6 was used for respiratory
motion compensation for both sequences. To reduce free induction decay (FID)
artefacts, the sampling points were acquired twice (two averages) and then
averaged together prior the final image reconstruction [5]. The 3D TSE-VDCASPR data
were acquired with an acceleration factor of 3.8 and reconstructed offline
using iterative SENSE (It-SENSE), while the conventional 3D TSE data were
acquired with Cartesian GRAPPA acceleration of 2 right-left (RL) and
reconstructed directly on the scanner.Results
Figure 2 shows the images
acquired with the conventional 3D TSE imaging sequence and the proposed 3D TSE-CASPR
for two representative subjects. After It-SENSE reconstruction, the delineation
of the myocardial and vessels borders is sharper in the 3D TSE-VDCASPR images. 3D
TSE-VDCASPR achieves comparable image quality to the conventional 3D TSE
imaging sequence. However, the nominal scan time of 3D TSE-VDCASPR was
considerably lower than that of the conventional 3D TSE approach (4.6±1 vs 8.1±1.6
minutes ± seconds). Figure 3 shows the 3D TSE-CASPR images reformatted in three
different orientations (sagittal, transversal and coronal) for a representative
subject.Conclusions
The combination of variable flip
angle 3D TSE imaging with a variable density Cartesian trajectory allows for black-blood
imaging of the whole-heart in a reduced scan time. Future works will
investigate the use of more advance motion compensation and reconstruction
techniques in order to achieve predictable and faster scan time.Acknowledgements
This work was supported by the following grants: BHF 1)
PG/18/59/33955, EPSRC 2) EP/P032311/1; 3) EP/P007619/1; and the Wellcome/EPSRC
Centre for Medical Engineering (WT 203148/Z/16/Z).References
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