Deuterium echo‐planar spectroscopic imaging (EPSI) in the human liver in vivo at 7 T

Abstract

To demonstrate the feasibility of deuterium echo-planar spectroscopic imaging (EPSI) to accelerate 3D deuterium metabolic imaging in the human liver at 7 T. Methods: A deuterium EPSI sequence, featuring a Hamming-weighted k-space acquisition pattern for the phase-encoding directions, was implemented.Three-dimensional deuterium EPSI and conventional MRSI were performed on a water/acetone phantom and in vivo in the human liver at natural abundance. Moreover, in vivo deuterium EPSI measurements were acquired after oral administration of deuterated glucose. The effect of acquisition time on SNR was evaluated by retrospectively reducing the number of averages. Results:The SNR of natural abundance deuterated water signal in deuterium EPSI was 6.5% and 5.9% lower than that of MRSI in the phantom and in vivo experiments, respectively. In return, the acquisition time of in vivo EPSI data could be reduced retrospectively to 2 min, beyond the minimal acquisition time of conventional MRSI (of 20 min in this case), while still leaving sufficient SNR. Three-dimensional deuterium EPSI, after administration of deuterated glucose, enabled monitoring of hepatic glucose dynamics with full liver coverage, a spatial resolution of 20 mm isotropic, and a temporal resolution of 9 min 50 s, which could retrospectively be shortened to 2 min. Conclusion:In this work, we demonstrate the feasibility of accelerated 3D deuterium metabolic imaging of the human liver using deuterium EPSI. The acceleration obtained with EPSI can be used to increase temporal and/or spatial resolution, which will be valuable to study tissue metabolism of deuterated compounds over time.

Interleaved trinuclear MRS for single‐session investigation of carbohydrate and lipid metabolism in human liver at 7T

“…The most substantial difference in intensity is observed for the TMA peak at 3.2 ppm, which appears to be even larger in this subject than expected based on T 2 times from the literature 21 ( T 2 = 32 ms, expected 23% signal loss from 6 versus 14 ms T E ). Comparison of VAPOR WS with water elimination by MC indicates that water signal removal was usually more effective with VAPOR, but that the water reference acquired with MC can be useful for compensation of motion‐induced phase and frequency variation, though this feature is mostly relevant for very small VOIs 49–60 and here for subjects with low fat content. Comparison of spectra acquired in breath‐holds versus those obtained with rhythmic breathing indicates that both acquisition schemes are viable, but that the latter provided more stable and robust results in most subjects.…”

“…It even allowed depth resolved Glc dynamics to be obtained. However, without doubt, use of an echo‐planar readout for one spatial direction would be beneficial 56 to increase either the temporal or spatial resolution, which would be particularly important to define a portal vein input function for metabolic modeling. At the current resolution it is not possible to clearly distinguish between hepatocellular and vascular glucose contributions on a macroscopic, let alone mesoscopic, scale.…”

A silent echo‐planar spectroscopic imaging readout with high spectral bandwidth MRSI using an ultrasonic gradient axis

“…4,5 Therefore, several approaches exist that try to accelerate the MRSI acquisition, such as by shortening or removing suppression pulses and reducing the TR, 6,7 applying parallel-imaging methods, [8][9][10] or by using simultaneous spatial-spectral encoding (SSE). [11][12][13][14][15] SSE accelerates MRSI by applying specific gradient waveforms during the FID, which increases the spatial encoding per TR. However, the time needed for this spatial encoding limits the spectral bandwidth of SSE methods when compared with phase-encoded MRSI and other acceleration approaches.…”