High-field magnetic resonance investigations of prostate cancer: Development of imaging techniques and radiofrequency coils.

摘要

The purpose of this thesis is to develop new techniques for magnetic resonance imaging (MRI) and spectroscopic imaging (MRSI) of the prostate at high field strengths for the detection of prostate cancer. Each of these techniques involves the design of radiofrequency (RF) coils and pulse sequences to address the specific challenges encountered at high field strengths. First, a pair of external transceive surface coil arrays are described for MR imaging of the prostate at 4.0 Tesla. It is shown that by manipulating the relative phases of the array elements, it is possible to induce constructive interference of the transmit fields in the prostate, thereby reducing the effects of RF shading. In addition, MRSI of the prostate is demonstrated in a human volunteer using the external transceive phased array, without the use of an endorectal coil.;To improve transmitter efficiency at high field regardless of patient size, an endorectal coil was developed to act as both a transmitter and receiver. The heating distribution surrounding the endorectal transmitter was determined through electromagnetic field simulations, as well as temperature measurements in a beef tissue phantom. Based on these results, the safe operating limit of the coil was determined. Using the transceive endorectal coil in conjunction with localization by adiabatic selective refocusing (LASER), in-vivo MRSI data were acquired from a patient with biopsy proven prostate cancer. In this experiment, gradient-modulated, offset-independent adiabatic (GOIA) pulses were used to achieve very sharp, uniform localization in the presence of a non-uniform transmit field.;Finally, a novel technique is described to enable in-vivo quantitative sodium imaging of the mouse prostate at 9.4 Tesla. A dual-tuned proton/sodium radiofrequency coil is described, and used to acquire high-resolution proton and sodium images of the mouse prostate. The tissue sodium concentration was estimated by fitting pixel intensifies to a linear model based on two sodium reference vials of known concentrations. The average prostate sodium concentration was measured in five healthy mice. A high concentration of sodium was observed in the mouse prostate, making it clearly visible in sodium images.;Keywords. Magnetic Resonance Imaging, Magnetic Resonance Spectroscopic Imaging, Prostate Cancer, Citrate, Choline, Creatine, Localized Spectroscopy, Variable Rate Selective Excitation, Gradient-Modulated Offset-Independent Adiabatic Pulses, Radiofrequency Coils, Transceive, Receive-only, Phased-Array, Endorectal Transmitter, Dual-Tuned RF Coil, Quantitative Sodium MRI.;To improve reception sensitivity, a receive-only endorectal coil was designed for use in combination with the external transceive surface coil array described above. Using this new coil configuration, in-vivo MRSI data were acquired from a patient with biopsy proven prostate cancer. It is shown that variable-rate selective excitation (VERSE) can successfully be used to reduce the peak B1 and SAR required for spectroscopic localization, while maintaining acceptable off-resonance selection profiles.