Simultaneous detection of metabolite concentration changes, water BOLD signal and pH changes during visual stimulation in the human brain at 9.4T

Abstract

This study presents a method to directly link metabolite concentration changes and BOLD response in the human brain during visual stimulation by measuring the water and metabolite signals simultaneously. Therefore, the metabolite-cycling (MC) non-water suppressed semiLASER localization technique was optimized for functional 1H MRS in the human brain at 9.4 T. Data of 13 volunteers were acquired during a 26:40 min visual stimulation block-design paradigm. Activation-induced BOLD signal was observed in the MC water signal as well as in the NAA-CH3 and tCr-CH3 singlets. During stimulation, glutamate concentration increased 2.3 ± 2.0% to a new steady-state, while a continuous increase over the whole stimulation period could be observed in lactate with a mean increase of 35.6 ± 23.1%. These increases of Lac and Glu during brain activation confirm previous findings reported in literature. A positive correlation of the MC water BOLD signal with glutamate and lactate concentration changes was found. In addition, a pH decrease calculated from a change in the ratio of PCr to Cr was observed during brain activation, particularly at the onset of the stimulation.

Measurement of glucose metabolism in the occipital lobe and frontal cortex after oral administration of [1-13C]glucose at 9.4 T

“… 30 with optimizations of the spoiling, phase cycling and crushers later described by Dorst et al. 25 (TE/TR = 24/5000 ms, 64 averages (Ave), acquisition time = 512 ms, bandwidth = 8000 Hz, sequence duration = 5.67 min). A water-reference signal (Ave = 16) as well as a macromolecular spectrum 31 , 32 (TR = 8 s, Ave = 32) were taken from the same voxel.…”

“…Raw MRS data were processed with in-house-written code in Matlab (version 2016a; MathWorks, Natick, MA) as described in detail before 25 , 30 , 31 , 33 and here summarized: (1) replace the data points after 250 ms with zeros; (2) frequency and phase alignment; (3) MC subtraction for the metabolite spectra and the macromolecular data; (4) averaging; (5) eddy current correction using the MC water signal; (6) combine coils using a singular value decomposition method; (7) peak alignment to the NAA signal or the water signal for the water data; (8) removing residual water signal using HSVD for the spectral data; and (9) truncation at 150 ms with subsequent zero filling.…”

“…All measurements were performed using a 9.4 T wholebody MR scanner (Magnetom, Siemens Healthineers, Erlangen, Germany). A home-built 4-channel surface coil was used for the measurement in the occipital lobe 24 as it is described in Dorst et al 25 and an 8-channel Tx/16-channel Rx volume coil in 3-loop surface transmit mode was used for the voxel in the frontal cortex. 26 More details about the coil setup can be found in the Supplementary Material and Figure S1.…”

“…First-order and second-order B 0 shimming were performed using FAST(EST)MAP, 27 and then a voxel-based power calibration was executed. 28,29 The spectra were measured using a short TE 1H MC-semiLASER sequence; details can be found in Giapitzakis et al 30 with optimizations of the spoiling, phase cycling and crushers later described by Dorst et al 25 (TE/TR ¼ 24/5000 ms, 64 averages (Ave), acquisition time ¼ 512 ms, bandwidth ¼ 8000 Hz, sequence duration ¼ 5.67 min). A water-reference signal (Ave ¼ 16) as well as a macromolecular spectrum 31,32 (TR ¼ 8 s, Ave ¼ 32) were taken from the same voxel.…”

“…Raw MRS data were processed with in-house-written code in Matlab (version 2016a; MathWorks, Natick, MA) as described in detail before 25,30,31,33 and here summarized: (1) replace the data points after 250 ms with zeros; (2) frequency and phase alignment;…”