Optimize micro-MRI for preclinical cancer imaging of solid tumors.

Measurement of tumor volume with MRI is complicated by two problems. The first is the scale. Since the mouse is 3000 times smaller than human, spatial resolution must be appropriately scaled; however if the voxels are 3000 times smaller, the signal will be concomitantly weaker. Sensitivity in preclinical imaging has been addressed through the use of higher magnetic field (7-15 T), specialized radio frequency (rf) coils, and novel imaging methods. But these modifications introduce new sources of variability for contrast compared to the clinical domain; T1 increases and T2 decreases at higher field. Susceptibility increases at higher field. Balancing these many tradeoffs for clinically analogous optimal preclinical protocols is a non-trivial effort. The second major problem is the biology.

What do we mean by “size” of tumor?
Messiou et al [56] have highlighted this problem in the specific context of imaging sarcomas during treatment. Size, determined from T1 weighted (W) image, may differ from size defined on T2 or with contrast , after radiation treatment as necrosis, fibrosis, edema, and vascular integrity change. We will adapt their clinical protocol to the following preclinical protocol: i) T1W; T2W; T1 with contrast enhancement (Magnevist); ii) T1W with fat saturation; iii) We will include diffusion weighted (DW) and apparent diffusion coefficient (ADC) images as supplemental images as in [56].  Although DW-MR images and ADC calculations are not being performed in the clinical sarcoma trial associated with this project, there is considerable interest in the use of DW-MR for drug development and clinical monitoring of cancer.  Therefore, in this project we will also collect DW-MR data to begin to standardize its use in mouse models.