Postexercise Lactate Clearance, T₂ Relaxation, and J-Modulation in Human Skeletal Muscle Measured With Double-Quantum...

¹H MRS lactate measurements are potentially valuable for studying energy metabolism in working skeletal muscle, but some technical obstacles need to be overcome. Spectral filtering to isolate the lactate signal from overlapping lipid resonances shows promise. We report a novel sequence with 3D localisation and a CH-selective double quantum filter (DQF) which enables dynamic postexercise single-shot measurement of cellular lactate T₂ and clearance kinetics.

Using a two-channel ¹H transceiver coil at 7 T we applied a localized CH-selective DQF sequence to postexercise calf muscle in 11 subjects. In one leg acquisitions with constant and incrementing T_E were interleaved to measure lactate decrease and T₂. In the other the CH-selective sequence was interleaved with the nonselective variant.

Postexercise DQF shows lactate clearly in 4 s single-shot spectra. Fitting was able to separate lactate concentration kinetics from T₂ and J-modulation: clearance t_1/2 = 162 ± 42 s and T₂ = 138 ± 20 ms (mean ± SD); the scalar coupling constant fitted from time evolution was J = 16.6 ± 0.8 Hz, closely matching J = 16.5 ± 1.3 Hz derived from spectral splitting. Direct comparison showed 2.3 ± 0.9 times higher signal with the new CH-selective sequence.

The new sequence improved lactate detection, enabling quantification from single shots postexercise with time resolution similar to ³¹P MRS. Measuring clearance and relaxation time constants of intramuscular lactate lays the groundwork for future absolute quantification and studies of intra- and extracellular lactate compartmentation based on dipolar coupling differences.