In vivo proton observed carbon edited (POCE) ¹³C magnetic resonance spectroscopy of the rat brain using a volumetric transmitter and receive‐only surface coil on the proton channel

Abstract

A convenient and sensitive platform to study energy metabolism and neurotransmitter cycling is presented. Magn Reson Med 79:628-635, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Minimum echo time PRESS‐based proton observed carbon edited (POCE) MRS in rat brain using simultaneous editing and localization pulses

“…Ideally, the 12.6‐ms PRESS‐POCE sequence used for comparisons would have also utilized Mao refocusing pulses; however, the TE of the sequence would require to be extended to ∼15 ms (due to higher R‐valued Mao pulses relative to Hermite pulses: 6200 Vs 3400) to accommodate the nonsimultaneous and pulses. The 12.6‐ms PRESS‐POCE sequence in its current state provides good sensitivity and localization, as described in a previous study for in vivo POCE‐MRS. Therefore, the SEAL‐PRESS sequence was compared against this unmodified 12.6‐ms PRESS‐POCE sequence, with the primary intention of validating editing efficiency of SEAL.…”

“…Figures b through c illustrates 1D spatial profiles for the refocusing pulse directions (left–right and anteroposterior) obtained with the SEAL‐PRESS and 12.6‐ms PRESS‐POCE sequences, for which sharper profiles were obtained for the SEAL‐PRESS sequence due to the use of Mao pulses. Furthermore, near‐uniform nutation in the region of interest is seen due to the homogenous field generated with the 1 H volumetric transmitter …”

“…Performance of the SEAL‐PRESS sequence was compared against a previously described PRESS‐POCE sequence (TR = 4000 ms, TE = 12.6 ms, TE 1 = 2.6 ms, TE 2 = 10 ms, SW = 6.0 kHz, and 1502 points) in which was also a HS pulse (length = 1.4 ms, BW [99% inversion efficiency] = 7.7 kHz) applied ms before the final echo, hereafter referred to as the 12.6‐ms PRESS‐POCE sequence. Comparisons between the 2 sequences were made, primarily to evaluate and validate carbon editing in phantom and in vivo, for the proposed SEAL scheme relative to a classical carbon‐editing scheme used on the 12.6‐ms PRESS‐POCE sequence.…”

“…A few notable approaches to localized, J‐difference edited POCE‐MRS reported in the literature are as follows: 1) Employ a pulse on alternate scans centered ms before the final echo. This type of editing is seen in point resolved spectroscopy (PRESS) localized POCE and localization by adiabatic spin‐echo refocusing (LASER) POCE sequences. However, POCE via this scheme typically necessitates the final echo to be >10 ms to accommodate 2 nonsimultaneously employed and pulses and the ms delay.…”

“…LASER‐POCE sequences reported have TE >22 ms, primarily due to the requirement for 3 pairs of ∼1 ms adiabatic full passage (AFP) pulses and an ∼10 ms final echo; however, the effects of homonuclear J‐evolution and diffusion are minimized for LASER‐POCE due to the Carr‐Purcell spin‐echo character of the sequence, and chemical shift displacements are minimal due to the high bandwidth (BW) AFP pulses (relative to purely amplitude modulated pulses) used. PRESS‐POCE sequences have been implemented with TE < 16 ms, which is an attractive alternative to LASER and multi‐shot ISIS‐based implementations, provided that a spatially homogenous field is present.…”