BY THORALF NIENDORF, PH.D., GABRIELE A. KROMBACH, M.D., AND DANIEL K. SODICKSON, PH.D., M.D.
Prof. Niendorf is chair of ultrahigh field MRI at the Charité - University Medicine and director of the Ultrahigh Field MR Facility at the Max-Delbrueck Center for Molecular Medicine, both in Berlin. Prof. Krombach is an applied professor of radiology and head of clinical MRI in the radiology department at RWTH Aachen, University Hospital, in Aachen, Germany. Prof. Sodickson is an associate professor of radiology, vice chair of research, and director of the Center for Biomedical Imaging in the radiology department at New York University Langone Medical Center.
Cardiovascular MR imaging has become a valuable diagnostic modality. The need for speed and efficiency when imaging cardiovascular structures has helped to drive the development of rapid imaging techniques and advanced MR hardware.
The growing availability of high-field MRI systems is now prompting interest in 3T cardiovascular MRI. The move from 1.5T to 3T means a doubling in signal-to-noise ratio. Subsequent gains in contrast-to-noise ratio, imaging speed, and efficiency can be translated into added diagnostic value.
Many of the high-field cardiovascular MRI applications earn the moniker of “advanced techniques.” High-field cardiovascular MRI has been regarded as one of the most challenging MR applications owing to practical obstacles associated with magnetic field inhomogeneities, radiofrequency nonuniformities across the heart, and RF power deposition constraints.
CVMR is an area in which 3T imaging boasts a number of advantages over 1.5T. Gains in spatial and temporal resolution can be invested in streamlining structural and functional cardiovascular imaging and can also be used to facilitate targeted tissue characterization and improve access to physiological information.
ADDED VALUE
First-pass contrast-enhanced MR angiography is a particularly appealing candidate for high-field CVMR. Contrast between blood vessels and background tissue on 3T images is superior to that on images acquired at 1.5T.
High-field MRA thrives on turning SNR into speed to capture the arterial phase of contrast enhancement. The benefits of high-field MRA may be exploited to increase anatomic coverage or spatial resolution within a given imaging time. This allows comprehensive scanning of any target vessel territory, while avoiding the frequently encountered difficulty of truncated anatomy. Continuous volumetric, time-resolved MRA can also be performed with temporal resolution that would be unattainable at 1.5T (i.e., two to four seconds). This makes it possible to evaluate contrast dynamics or to distinguish arterial from venous phases without substantially sacrificing the spatial resolution.
High-field imaging may also open up new clinical territory. The extension of MRA to include submillimeter spatial resolution imaging of tiny peripheral vessels (Figure 1), for example, may allow MRI to replace digital subtraction angiography for vessel flow and assessment prior to bypass surgery.1 This approach has been impossible at 1.5T.
