This research aims to improve the MRI-based diagnosis of prostate cancer, by utilizing a new MRI endorectal assembly that can improve MRI specificity and sensitivity. A novel Endorectal assembly includes a tetrahedron array of positional tracking coils, and a mechanism for compressing the prostate. The tetrahedron array provides motion compensation and magnetic field correction. The assembly enables segmented Diffusion-weighted EPI (DW-EPI) imaging with reduced distortion. A Strain imaging sequence utilizes prostate compression to differentiate tumor from normal tissue. The applications are tested in a 12-dog cohort, including 8 with prostate cancer.
The Specific Aims are:
AIM #1 : Develop endorectal coils with integrated tetrahedron tracking coils. The new Endorectal coils will be built and tested. We add a tetrahedron-shaped array of four micro-coils. This array is kept folded during rectal insertion, so as not to occupy additional footprint, with a mechanism for expansion before use. A water-driven compression mechanism pressurizes a balloon in the assembly, delivering a short-duration compression of the prostate. Outcome measures are tracking SNR and motion correction accuracy.
AIM #2 : Develop DW-EPI sequences with integrated prospective motion compensation. We will develop a segmented DW-EPI sequence which utilizes the tracking tetrahedron (AIM 1) for positional and phase correction. Prostate single-shot DW-EPI suffers from geometric distortions, due to non-uniform magnetic-fields. Our solution utilizes reduced-distortion segmented EPI, which require corrections for motion and for phase changes, provided by the tracking array and transferred in real-time to the pulse sequence. Outcome measures are the spatial distortion reduction vs. efficiency cost, as observed in dogs with prostate cancer.
AIM #3 : Develop MRI strain sequences using hydraulic prostate compression. We will develop, optimize and test in dogs, a DENSE [Displacement Encoding with Stimulated Echo] strain pulse sequence which uses the Endorectal coil (AIM 1). Strain imaging will utilize short-duration balloon-induced compression to determine the prostate's elastic response (compliance). The tracking coils will be used to trigger the sequence during periods when respiratory motion is small. Outcome measures will be the strain SNR in the prostate, the CNR between tumor and normal tissues, the effects of respiration, and the scan's temporal efficiency.
Prostate cancer is the US's largest cancer by incidence, and 2nd largest by mortality1, 2. MRI's role is increasing, as seen in the major increases in prostate MRI procedures2. Initially, MRI diagnosis/staging was primarily based on soft-tissue contrast3-6 but it is increasingly apparent that higher specificity/sensitivity resides in micro-structural contrast, as seen with perfusion7 or diffusion8.
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