Presentations

The inhomogeneous magnetization transfer (ihMT) technique has shown myelin sensitivity, and is understood to be dependent on power and the dipolar relaxation time parameter, T_1D, which is longer in myelinated tissues. Implementation of ihMT can be adapted to provide a smaller, but non-negligible signal from other, relatively short T_1D tissues. Simulations showed a measurable ihMT signal, achieved from fixed low duty cycle MT preparations with high B₁ pulses, decayed with pulse width at a rate dependent on T_1D. Thus short, high B₁ pulses were implemented to acquire ihMT data from ex-vivo samples of rat heart, kidney, and tail tendon, demonstrating the feasibility of short T_1D imaging.

Perfusion imaging is a promising application for hyperpolarized tracers, as they provide high signal with no endogenous background. Hyperpolarized 13C labeled tert-butanol is a freely diffusible perfusion agent with long T1 and T2 relaxation times in vivo. Prior work has shown that tert-butanol can be polarized to 5-10% using dynamic nuclear polarization through addition of glycerol as a glassing agent. Here we investigate a formulation based on a water/sucrose/tert-butanol mixture that yields a 1.6-fold improvement in polarization, and illustrate its use in 3D cerebral perfusion imaging in rats.

The inhomogeneous magnetization transfer (ihMT) technique provides a myelin-sensitive signal and has been applied for 3D acquisition in the steady-state. Sequences applied in a segmented fashion, following some magnetization preparation, provide an advantage of allowing insertion of additional modules, e.g. motion correction. An ihMT acquisition in the style of the magnetization-prepared rapid gradient-echo sequence was designed based on considerations of safety, hardware and optimizing the ihMT signal. Whole brain 3D ihMT data with 2.4mm isotropic resolution was achieved in 6-7mins. IhMT ratios between 15-20% were measured in white matter areas, and were not significantly modified by inclusion of a prospective motion correction module.