Magnetic Resonance Pulse Sequences for Fluorine-19

Cellular therapy is the transplantation of live cells or a cell population in a patient for the treatment of complex diseases. The success of cellular therapy will rely heavily on delivering the cells to their targeted organs or areas of interest. Magnetic resonance imaging (MRI) has the ability to noninvasively track the transplanted cells to ensure they are in the desired destination. Unlike other MRI contrast agents, fluorine-19 has the ability to provide unambiguous cell tracking for two reasons: Fluorinated agents are more readily inert and will not be metabolized quickly so their movement progression can be monitored Additionally, ^(19)F has a limited background MR signal so resulting images will yield positively labeled cells, thus providing successful cell tracking and quantification of cells.

The primary objective of this work was to enable the study of ^(19)F MRI on the Siemens MAGNETOM Verio scanner located at the Texas A&M Institute for Preclinical Studies (TIPS) facility at Texas A&M by making the necessary scanner modifications and pulse sequence adaptions. A ^(19)F/^(1)H dual tuned surface coil was purchased from RAPID Biomedical and was used throughout this work. Additionally, pulse sequence modifications to a spin echo sequence and a spoiled gradient echo (called fast low angle shot or FLASH) were made to enable scanning at the fluorine-19 resonant frequency.

A series of experiments were performed with the goal of finding the optimal parameters for each sequence. It was found that the spin density, as compared with the T1 and T2 weighted images, resulted in the highest SNR for the spin echo sequence. The FLASH sequence with a small flip angle, low TE, and high TR provided the larger signal for the fluorine-19 images. Additionally, a large voxel size for both sequences provided a detectable and quantifiable signal for this type of functional imaging.

T cells were labeled with ^(19)F and imaged to determine sensitivity and labeling efficiency. The goal of this ex vivo study was to obtain a reliable and quantifiable signal and image to be the basis for future in vivo studies. With the completion of this project, Texas A&M Institute for Preclinical Studies will be equipped with the software and knowledge to perform multinuclear MR imaging, specifically of ^(19)F.