1H MRSI AT 7T USING AN INTERLEAVED NARROW-BAND PRESS SEQUENCE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 1H MRSI at 7T using an interleaved narrow-band PRESS sequence with spatial-spectral adiabatic refocusing pulses Proton magnetic resonance spectroscopic imaging (1H MRSI) is a useful technique for measuring metabolite levels in vivo, with Choline (Cho), Creatine (Cr) and N-Acetyl-Aspartate (NAA) being the most prominent MRS-detectable brain biochemicals of interest. 1H MRSI at very high fields, such as 7T, offers the advantages of higher SNR and improved spectral resolution. However, major technical challenges associated with high-field systems, such as increased chemical shift localization (CSL) error as well as B1 and B0 inhomogeneity, degrade the performance of conventional 1H MRSI sequences. To address these problems, we have developed a Position Resolved Spectroscopy (PRESS) sequence with adiabatic spatial-spectral (SPSP) refocusing pulses, to acquire multiple narrow spectral bands in an interleaved fashion. The adiabatic SPSP pulses can be overdriven by a factor of 1.6 before reaching the peak RF amplitude limits for our 7T whole body magnet, providing magnetization profiles that are largely invariant over the 40% B1 variation measured for our 7T head coil. Additionally, there is negligible CSL error since the transmit frequency is adjusted for each spectral band. In vivo 1H MRSI data was obtained from the brain of a normal volunteer using a standard PRESS sequence and the interleaved narrow-band PRESS sequence with adiabatic refocusing pulses. In comparison with conventional PRESS, this new approach generated high quality spectra from an appreciably larger region of interest and achieved higher overall SNR.