| The development of noninvasive methods for characterizing mammographically indeterminate lesions represents an active area of current research in medical imaging. In particular, much research effort is being directed toward the development of new techniques for measuring tumour blood flow. This thesis consists of experiments designed to evaluate the use of a magnetic resonance imaging technique called Intravoxel Incoherent Motion (IVIM) to produce microvascular flow images of breast lesions.;The first phase of this thesis addresses the underlying biological question of whether malignancies can be distinguished from benign lesions on the basis of microvessel density. Histological techniques were used to stain for blood vessels on archival breast biopsy tissue. Vessel distributions in invasive carcinomas were compared to those in fibroadenomas, a class of commonly occurring benign lesion. There was no significant difference in numbers of microvessels between the fibroadenomas and carcinomas in our study; however, vessels were concentrated around the boundaries of invasive carcinomas, whereas, in fibroadenomas, they were more uniformly distributed.;A second major focus of this thesis is the evaluation of IVIM in an animal tumour model. Quantitative diffusion measurements using the gold-standard Pulsed Gradient Spin Echo (PGSE) sequence were performed. Measured diffusion coefficients were specific for viable and for necrotic tumour in our model. These results show promise for using diffusion-weighted imaging to noninvasively follow tumour response to therapy. However, further studies using the PGSE technique revealed that the high sensitivity of this sequence to macroscopic motions such as patient respiratory motion will likely prevent its use for IVIM measurements of tumour blood flow in vivo.;The third phase of the thesis was the design and construction of a breast gradient coil set to be used as a hardware add-on for a clinical MR scanner. The high gradient efficiencies of these coils will provide images with better spatial resolution than can currently be achieved clinically, and additionally, will provide large motion-sensitizing gradients that facilitate diffusion and flow imaging. Moreover, the availability of large readout gradients enables imaging using fast, motion-insensitive techniques such as echo-planar imaging. |
