Real-Time and Interactive MRI

Free of ionizing radiation, unlike x-ray, CT, and PET, MRI is recognized as an ideal tool to monitor and control interventions. Its advantages include a superior spatial resolution and soft tissue contrast to help delineate tissue abnormality and the ability to provide cross-sectional images in any orientation. It is also able to noninvasively monitor temperature changes, making it ideal for monitoring energy deposition during thermal ablation. To leverage these advantages in various types of interventions, a number of groups have made and continue to make efforts to exploit MRI in the operating room. Interventional MRI differs from diagnostic MRI in its interactive and real-time nature whereby the progress of intervention is instantly visualized by the physician as feedback. To this end, imaging parameters may often require adjustment so that position and orientation of the imaging plane track the locations of needles and catheters or movement of a focal lesion during a procedure. Since there are trade-offs to be made in image contrast, signal-to-noise ratio, spatial resolution, and temporal resolution when choosing MRI techniques, they must be carefully selected depending on their purpose. In this chapter, we review a wide range of imaging techniques that enable interactive and real-time MRI for interventional guidance.