Proton T1ρ‐dispersion imaging of rodent brain at 1.9 T

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Abstract
Detection of H217O with proton T1ρ-dispersion imaging holds promise as a means of quantifying metabolism and blood flow with MRI. However, this technique requires a priori knowledge of the intrinsic T1ρ dispersion of tissue. To investigate these properties, we implemented a T1ρ imaging sequence on a 1.9-T Signa GE scanner. A series of T1ρ images for different locking frequencies and locking durations were obtained from rat brain in vivo and compared with 5 % (wt/vol) gelatin phantoms containing different concentrations of 17O ranging from .037 % (natural abundance) to 2.0 atom%. Results revealed that, although there is considerable T1ρ-dispersion in phantoms doped with H217O, the T1ρ of rat brain undergoes minimal dispersion for spin-locking frequencies between .2 and 1.5 kHz. A small degree of T1ρ dispersion is present below .2 kHz, which we postulate arises from natural-abundance H217O. Moreover, the signal-to-noise ratios of T1ρ-weighted images are significantly better than comparable T2-weighted images, allowing for improved visualization of tissue contrast. We have also demonstrated the feasibility of proton T1ρ-dispersion imaging for detecting intravenous H217O on a live mouse brain. The potential application of this technique to study brain perfusion is discussed.