Approaches to MR angiography

Measurement of the geometric parameters of the aortic bifurcation from magnetic resonance images

This paper presents a method for measuring arterial geometry in vivo using MRI. The approach was validated using MR images of three perfused compliant casts of human aortic bifurcations whose geometry was known. Preliminary human studies demonstrated the reproducibility of the technique. The approach was applied to 20 normal individuals to study the effects of age, race, and gender on the geometry of the aortic bifurcation. The results show that older people tend to have a smaller bifurcation angle, lower planarity, and larger angular asymmetry than younger people. Asians have larger bifurcation angles than whites. The bifurcation of males is more asymmetric than that of females. These results may have implications regarding the heritability of arterial geometry, the similarities of cardiovascular risk within families, and differences in risk among groups.

New directions in medical imaging of cancer. Magnetic resonance methods and single photon emission computed tomography

Magnetic resonance methods and single photon emission computed tomography (SPECT) are developing technologies that provide both functional and anatomic information. Their role in the diagnosis and monitoring of cancer is the subject of current clinical research. Magnetic resonance imaging (MRI) delineates organs and tissue heterogeneities using differences in the relaxation parameters of water and fat protons; both protons and other nuclei can be imaged or studied by magnetic resonance spectroscopy (MRS) to provide information on the state of naturally occurring or infused molecules. SPECT quantifies the distribution of radiolabeled agents in tissues and organs; labeled monoclonal antibodies provide highly specific imaging of tumors. Spatial resolution is the limiting technologic factor. Proton MRI provides the highest current resolution, better than 1 mm in vivo in deep tissues, whereas the resolution of MRS and SPECT is limited to several cubic centimeters. Recent advances in these technologies have significantly increased their specificity and ability to detect small, deep lesions.