Alejandro Santos Diaz1, Alireza Akbari1, and Michael Noseworthy1,2,3
1School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada, 2Imaging Research Centre, St Joseph's Healthcare, Hamilton, ON, Canada, 3Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada
Synopsis
Long acquisition time due to the low sensitivity
is one of the main constrains for using 31P MRSI on a regular basis. Different
methods have been proposed to accelerate the acquisition showing advantages and
limitations. In this work we present for the first time an in vivo experiment
using flyback-Echo Planar Spectroscopic Imaging readout and compare it with the
traditional fidCSI sequence. Results suggest that the technique might be
suitable for clinical applications.Purpose
Phosphorus Magnetic Resonance Imaging (31P-MRSI)
is capable of assessing high energetic metabolites like phosphocreatine (PCr) within
human tissue. The main limitation for its use on a regular basis is the long
acquisition time required due to the limited sensitivity. The latest efforts to
address this issue while preserving as much SNR as possible have focused on
using a GRAPPA acquisition scheme [1] and the compressed sensing approach for
traditional spatial localization techniques [2], [3]. In a previous comparison of fast spectroscopic
imaging methods [4], flyback-Echo Planar Spectroscopic Imaging
(EPSI) showed to be very robust and insensitive to timing errors, making it a
worthy choice. Our group previously reported the implementation of 31P-EPSI using a flyback readout [5], tested in a phantom and showed reliable data
to be used in vivo. The purpose of this study was to test the mentioned
sequence in human calf muscle.
Methods
Experiments were performed using a 3T GE MR750
scanner (GE Healthcare, Milwaukee, WI) and a home designed/built 31P-tuned
(51.705 MHz) 7.62cm(3 inch) surface coil tuned specifically for calf muscle Flyback
echo planar gradients (Fig. 1) were designed to achieve 2 cm resolution, over a
24 cm field of view (FOV) (i.e. 12x12 matrix) using a spectral bandwidth of
1302 Hz, slice thickness = 4cm and TR = 1500 ms. In order to produce the full
spectral bandwidth coverage, acquisitions were interleaved twice. 31P-EPSI
data using 4, 8 and 16 averages were compared to same data acquired using
pulse-acquire (fidCSI) sequence. Acquisition time and SNR of the PCr peak were
measured. Reconstructed data was first interpolated in order to fit a
rectilinear grid an then phase corrected [6]. No line broadening was applied in this
preliminary analysis.
Results
The sequence was capable of achieving a 6x acceleration when
compared to regular fidCSI for NEX=8. The phosphorus images, created as the
area under the PCr peak and resized (interpolated for display), correlated well
spatially with both the anatomical reference and the CSI data (Fig. 1). Table 1 summarizes the SNR and scan times for all acquisitions.
Discussion
Our in vivo results are consistent with what was
previously reported using phantoms [5]. The sequence tested in this work
appears to be reliable alternative to routine fidCSI, achieve fast 31P-MRSI
data in applications with relatively low spectral bandwidth.
Acknowledgements
To CONACYT for the scholarship granted, CVU: 304930.
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