Dissertation Defence: Pulse Sequence Design for Fast and Flexible Sodium Magnetic Resonance Imaging
March 13 at 9:30 am - 1:30 pm
Jason Reich, supervised by Dr. Rebecca Feldman, will defend their dissertation titled “Pulse Sequence Design for Fast and Flexible Sodium Magnetic Resonance Imaging” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Medical Physics.
An abstract for Jason Reich’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.
Abstract
Sodium (23Na) magnetic resonance imaging can be used to obtain information pertaining to tissue viability that is complementary to that of routine clinical hydrogen (1H) MRI. Imaging 23Na is technically challenging due to its low in-vivo signal-to-noise ratio and rapid transverse relaxation. Three-dimensional (3D) ultrashort echo time (UTE) sequences, often used for 23Na MRI, involve whole-volume acquisitions that have required scan times of 10-34 min. Two-dimensional (2D) UTE sequences can be used to image a reduced number of slices, but scan times have remained long, ranging 2-10 min per slice.
This dissertation explores the design of 2 novel pulse sequences that combine simultaneous multi-slice and UTE techniques to reduce scan times for 23Na MRI. (1) The power independent of number of slices presaturated UTE (PINS-UTE) sequence uses a prepulse to saturate wide regions of magnetization so that a non-selective pulse can be used to simultaneously excite 3 slices. (2) The differential multi-block presaturated UTE (δMB-UTE) uses a prepulse to saturate 2 blocks of magnetization so that a non-selective pulse can be used to excite the surrounding magnetization. By subtracting acquisitions with shifted saturation blocks, four simultaneous slices can be imaged. Both sequences are first implemented for 1H MRI, then modified for 23Na MRI.
The δMB-UTE sequence enabled the rapid imaging of a reduced through-plane field-of-view with both 1H and 23Na MRI. Images obtained with the PINS-UTE sequence exhibited signal variation due to unwanted signal between the slices. For 23Na MRI, the scan times required by the PINS-UTE and δMB-UTE sequences are expected to be 12x shorter than those of 2D UTE sequences. Compared to current 3D UTE sequences for 23Na MRI, the scan time of the PINS-UTE sequence is expected to be 1.75x longer, while the scan time of the δMB-UTE sequence is expected to be comparable. For both sequences, greater acceleration relative to 3D UTE sequences may be achieved when fewer slices are of interest or high in-plane resolution is desired.
The sequences introduced in this dissertation may enable the integration of 23Na MRI into clinical protocols and support studies of diseases such as multiple sclerosis, stroke, and cancer.
