1H-MRS of hepatic fat using short TR at 3T: SNR optimization and fast T2 relaxometry

To increase the signal-to-noise ratio (SNR) efficiency of hepatic fat signals in proton magnetic resonance spectroscopy (1H MRS) at 3 T, in order to improve the quantitation of hepatic fat and allow fast, single breath-hold T2 relaxometry of hepatic water and fat.

Since the T1 of lipid protons is relatively short, we hypothesized that it could be possible to increase the lipid SNR efficiency by choosing a TR shorter than that typically employed (≥1.5 s). The lipid SNR per unit-time was calculated using published values of lipid (CH2)n protons' T1 at 3 T. 1H MRS PRESS spectra were acquired from VOIs located in the right lobe of the liver in 28 healthy volunteers. At the short TR of 0.6 s, fast T2 relaxometry with the acquisition of 16 echo times (30, 40, ..., 180 ms), was performed in a single breath-hold measurement using a modified PRESS sequence.

Good agreement was observed between simulated and experimental data, with the shortening of TR to 0.6 s yielding an ~50% SNR improvement of hepatic lipid (CH2)n resonances, compared to the SNR at TR=2 s. The T2 relaxation time of water and lipid (CH2)n protons at 3 T was 25.8±1.1 ms and 55.4±3.9 ms, respectively, across five healthy volunteers.

The short-TR approach allows for an improved SNR efficiency of lipids and for fast T2 relaxometry of hepatic water and fat, with a detailed coverage of the T2 relaxation decay curve, within a single breath-hold experiment.