Combination of multichannel single-voxel MRS signals using generalized least squares

Abstract

Purpose: To propose using the generalized least square (GLS) algorithm for combining multichannel single-voxel magnetic resonance spectroscopy (MRS) signals.

Materials and methods: Phantom and in vivo brain MRS experiments on a 7 T scanner equipped with a 32-channel receiver coil, as well as Monte Carlo simulations, were performed to compare the coefficient of variation (CV) of the GLS method with those of two recently reported spectral combination methods.

Results: Compared to the two existing methods, the GLS method significantly reduced CV values for the simulation, phantom, and in vivo experiments.

Conclusion: The GLS method can lead to improved precision of peak quantification.

Fig. 1

Comparisons of precision and lack of bias of the three spectral combination methods using Monte Carlo simulations. a: One combined spectrum computed using the GLS method for the first simulation experiment. There were no input baseline errors in the multichannel FIDs except random noise with 1/noise = 25 which was in an arbitrary unit. The same arbitrary unit was used in both simulation experiments. b: CV of the Cr peak area as a function of 1/noise for the first simulation experiment. c: Normalized Cr peak area as a function of 1/noise for the first simulation experiment. d: CV of the Cr peak area as a function of 1/noise for the second simulation experiment, in which a constant baseline error being equal to 2% of the NAA peak amplitude in the most sensitive channel was added to the simulated spectrum of each channel. e: Normalized Cr peak area as a function of 1/noise for the second simulation experiment.

Fig. 2

One combined spectrum of the phantom computed using the GLS method, where 32-channel data from the first acquisition were used. Voxel size = 2 × 2 × 2 cm³, TR = 2.5 s, TE₁ = 37 ms, TE₂ = 63 ms, spectral width = 4000 Hz, number of samples = 2048, number of acquisitions = 128.

Fig. 3

Two combined spectra, one for each scan, of the first normal volunteer computed using the GLS method. Each combined spectrum was computed using the 32-channel data from the first acquisition. Voxel size = 3 × 3 × 3 cm³, TR = 2.5 s, TE₁ = 37 ms, TE₂ = 63 ms, spectral width = 4000 Hz, number of samples = 2048, number of acquisitions = 128.

Fig. 4

Three combined spectra, one for each scan, of the second normal volunteer computed using the GLS method. Voxel size = 3 × 3 × 3 cm³, TE₁ = 37 ms, TE₂ = 63 ms, spectral width = 4000 Hz, number of samples = 2048, number of acquisitions = 128. For the first and second scans, no OVS was applied and TR = 2.5 s. For the third scan, OVS with six slabs were added to the pulse sequence and TR = 4.3 s.