Fast magnetic resonance thermal imaging using dynamic updating of spiral interleaves

Magnetic resonance imaging is a useful tool for providing information on temperature changes in tissue during thermal therapy. The current work investigates the effects of dynamically updating an interleaved spiral acquisition with reduced field of view data to increase the temporal resolution of a typical temperature sensitive scan without loss of in-plane spatial resolution. Phase-difference images from an interleaved gradient-echo spiral acquisition were used to monitor temperature changes in ex vivo porcine kidney during high-intensity focused ultrasound sonications. Original data was collected using an 8 interleave spiral sequence and varying the order of acquisition of the interleaves. Different dynamic update strategies were investigated by re-ordering raw image data and reconstructing intermediate images after updating only specified interleaves. Measurements of the phase-difference image noise and changes in the phase-difference at the focus due to temperature were compared with the original 8 interleave acquisition data. Results conclude that this method of dynamically updating k-space data provides a significant increase in temporal resolution of the sequence without affecting in-plane spatial resolution or slice efficiency. This technique is advantageous over other reduced k-space acquisition methods that compromise in the effective in-plane spatial resolution, such as keyhole imaging.