Magnetic resonance angiography: A comparison of techniques and applications in dogs and humans

Abstract

SummaryMagnetic resonance angiography (MRA) is a non-invasive imaging technique for visualising blood vessels and blood flow. The first half of this article is a literature review of the three basic MRA techniques: Timeof-flight (TOF) angiography, phase-contrast angiography and contrast-enhanced angiography. Physical principles, technical requirements, investigated parameters, advantages and disadvantages of the methods, and the correlation between application of contrast medium and time of examination are discussed. Subsequent processing of the MR images using “maximum intensity projection“ (MIP) provided a threedimensional image of the vascular architecture and improved the anatomical orientation; however, MIP was shown to sometimes cause additional diagnostic pitfalls. Therefore, the original slices should always be consulted in addition to the MIP. The second half of this article describes the application of the different MRA methods in veterinary medicine and compares the results with MRA in human medicine. A total of 15 dogs with clinical signs that warranted further work-up using MRA, and 20 human patients requiring MRA, were included in the study. Five healthy dogs served as controls. The vascular architecture in dogs was compared with that in human patients, and the images were scrutinized for lesions that corresponded to the clinical signs. An abnormal vascular architecture was identified in eight dogs with a portosystemic shunt, which allowed targeted surgical intervention. Aneurysms, thrombi and stenoses were seen in images from human patients. Comparison of the vascular architecture in humans and dogs allowed the anatomic identification and evaluation of the visualised blood vessels in the dog. Magnetic resonance imaging is still a relatively new technique in veterinary medicine and appears to be a promising diagnostic tool for a number of disorders as the availability of high-field MRI in veterinary clinics increases.