Abstract
Metabolic imaging of the human brain by in-vivo magnetic resonance spectroscopic imaging (MRSI) can non-invasively probe neurochemistry in healthy and disease conditions. MRSI at ultra-high field (≥ 7 T) provides increased sensitivity for fast high-resolution metabolic imaging, but comes with technical challenges due to non-uniform B0 field. Here, we show that an integrated RF-receive/B0-shim (AC/DC) array coil can be used to mitigate 7 T B0 inhomogeneity, which improves spectral quality and metabolite quantification over a whole-brain slab. Our results from simulations, phantoms, healthy and brain tumor human subjects indicate improvements of global B0 homogeneity by 55%, narrower spectral linewidth by 29%, higher signal-to-noise ratio by 31%, more precise metabolite quantification by 22%, and an increase by 21% of the brain volume that can be reliably analyzed. AC/DC shimming provide the highest correlation (R2 = 0.98, P = 0.001) with ground-truth values for metabolite concentration. Clinical translation of AC/DC and MRSI is demonstrated in a patient with mutant-IDH1 glioma where it enables imaging of D-2-hydroxyglutarate oncometabolite with a 2.8-fold increase in contrast-to-noise ratio at higher resolution and more brain coverage compared to previous 7 T studies. Hence, AC/DC technology may help ultra-high field MRSI become more feasible to take advantage of higher signal/contrast-to-noise in clinical applications.
Highlights
Metabolic imaging of the human brain by in-vivo magnetic resonance spectroscopic imaging (MRSI) can non-invasively probe neurochemistry in healthy and disease conditions
The characteristic negative peak of 2HG obtained for double spin-echo TE1/TE2 = 58/20 ms is clearly visible at 2.25 ppm for linewidths up to 0.1 ppm (Fig. 1A,C,D)
The quality parametric maps (SNR, Cramer-Rao lower bound (CRLB), FWHM) show an increase in mean signal to noise ratio (SNR) by 9–35%, a decrease of mean CRLB by 18–21%, and a decrease of mean linewidth by 17–37% for 2 SHbox + AC/DCbrain compared to 2 SHbox
Summary
Metabolic imaging of the human brain by in-vivo magnetic resonance spectroscopic imaging (MRSI) can non-invasively probe neurochemistry in healthy and disease conditions. Our results from simulations, phantoms, healthy and brain tumor human subjects indicate improvements of global B0 homogeneity by 55%, narrower spectral linewidth by 29%, higher signal-to-noise ratio by 31%, more precise metabolite quantification by 22%, and an increase by 21% of the brain volume that can be reliably analyzed. Magnetic resonance spectroscopic imaging (MRSI) at ultra-high field (≥ 7 T) has the potential to map the neurochemistry of the human brain with high spatial resolution and fast acquisition t imes[1]. This may be possible due to the increase in sensitivity[2] with the strength of the static magnetic field B0. Human MR scanners are equiped with spherical harmonics shimming, which in clinical configuration include up to eight shim channels for first and second order spherical harmonics, with some 7 T research systems equipped with a few 3rd-order SH shim coils
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