Short echo spectroscopic imaging of the human brain at 7T using transceiver arrays

• Published in: Magnetic resonance in medicine Vol. 62; no. 1; pp. 17 - 25
• Main Authors: Avdievich, N.I., Pan, J.W., Baehring, J.M., Spencer, D.D., Hetherington, H.P.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.07.2009
• Subjects: Biomarkers, Tumor - analysis; Brain; Brain - metabolism; Brain Neoplasms - diagnosis; Brain Neoplasms - metabolism; Equipment Design; Equipment Failure Analysis; Glutamic acid; Glutamic Acid - analysis; Head; human brain; Humans; Image Enhancement - instrumentation; Inversion; Lipids; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Spectroscopy - instrumentation; Magnetics - instrumentation; N.M.R; Neuroimaging; oligodendroglioma; Oligodendroglioma - diagnosis; Oligodendroglioma - metabolism; Reproducibility of Results; Sensitivity and Specificity; short echo spectroscopic imaging; transceiver arrays; Transducers
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.21970

Recent advances in magnet technology have enabled the construction of ultrahigh‐field magnets (7T and higher) that can accommodate the human head and body. Despite the intrinsic advantages of performing spectroscopic imaging at 7T, increased signal‐to‐noise ratio (SNR), and spectral resolution, few studies have been reported to date. This limitation is largely due to increased power deposition and B1 inhomogeneity. To overcome these limitations, we used an 8‐channel transceiver array with a short TE (15 ms) spectroscopic imaging sequence. Utilizing phase and amplitude mapping and optimization schemes, the 8‐element transceiver array provided both improved efficiency (17% less power for equivalent peak B1) and homogeneity (SD(B1) = ±10% versus ±22%) in comparison to a transverse electromagnetic (TEM) volume coil. To minimize the echo time to measure J‐modulating compounds such as glutamate, we developed a short TE sequence utilizing a single‐slice selective excitation pulse followed by a broadband semiselective refocusing pulse. Extracerebral lipid resonances were suppressed with an inversion recovery pulse and delay. The short TE sequence enabled visualization of a variety of resonances, including glutamate, in both a control subject and a patient with a Grade II oligodendroglioma. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.