Abstract:
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Purpose: Signal-to-noise ratios (SNR) and resolution are critical factors in the application of proton MR spectroscopic imaging (MRSI) to the human brain. It is expected that these factors will be enhanced by the use of high magnet field strengths and sensitive, phased-array receiver coil systems. This abstract reports the development of phased-array proton MRSI on a 3.0T whole body MR system, and compares SNR and resolution to volume head coil acquisitions at 1.5T.
Methods and Materials: Scans were performed on 1.5T and 3.0T MR scanners (Intera-NT; Philips Medical System, The Netherlands). At 3.0T, signal reception was performed using a prototype 8-element phased-array head coil (MRI Devices) interfaced to 6 receiver channels. All RF pulses were transmitted using the Philips body coil. Testing of sequences was performed on a phantom (containing neurochemicals at physiological concentrations), and on the brains of normal human volunteers. Two multi-slice protocols were developed (TR/TE 1600/140 msec) based on either 3/4 FOV 2D MRSI (scan time 15 minutes) using uniform sensitivity reconstruction with optimum SNR, or 1/2 FOV 2D MRSI (scan time 10 minutes) with SENSE reconstruction. Both protocols required B1 maps for MRSI reconstruction. SNR and spectral resolution was compared between scans.
Results: MRSI SNR was improved between 55% (central region) to 142% (periphery) with at 3.0T with the phased array coil to compared to the volume head coil at 1.5T. Spectral resolution was also improved; NAA linewidths were 0.04+/-0.01ppm at 3.0T versus 0.06+/-0.01ppm at 1.5T. However, artifacts from peri-cranial lipid signals were larger using the phased-array head coil.
Conclusion: Phased-array MRSI at 3.0T shows improvements in SNR and resolution as expected compared to volume head coils at 1.5T. Because metabolite T2 and T2* relaxation times decrease with increasing field strength, these improvements depend on the use of short echo times and optimum adjustment of field homogeneity.
Barker DPhil, P,
Proton MR Spectroscopic Imaging at 3.0T with Phased-Array Coils. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3108423.html
