The absence of ionizing radiation is one of the main arguments in favor of interventional MRI, but even fervent supporters of this technology appreciate the many practical difficulties involved in providing real-time MR image guidance. Despite this, the potential benefits suggest that today’s interventional toy could still become the routine tool of tomorrow.

The term “interventional MRI” covers a broad spectrum of procedures, ranging from straightforward biopsies to more complex cardiovascular repairs. To reflect this, a special focus session at ECR 2009 covered a wide variety of clinical applications, with an emphasis on the future.

Following the increased availability of MR mammography, some imaging clinics now use MRI to guide the biopsy of suspicious lesions in the breast. Providing MR-based breast imaging or even screening without this interventional capacity simply does not make sense, said Prof. Dr. Arno Bücker, who chaired the session.

“If you perform MRI and you see a lesion on the images that was not visible on x-ray mammography, you need a way to localize and biopsy that lesion under MRI guidance,” said Bücker, a professor of radiology at Saarland University Hospital in Homburg, Germany.

Interest in MR-guided endovascular interventions is also growing. MRI has been used to guide puncture in the bile duct and renal system during percutaneous cholangiography with drainage and percutaneous nephrostomy. The modality is then used to control localization of the catheter and guidewire.

MRI can visualize both the vessel wall and surrounding tissue when imaging vessels with atherosclerotic plaque. Animal experiments have shown almost all cardiovascular interventions to be feasible, including the catheterization and stenting of coronary arteries, according to Prof. Gabrielle Krombach, a professor of radiology at Aachen University Hospital in Germany.

Emerging ablative techniques that use focused ultrasound may benefit from MR guidance as well. In addition to guiding the therapeutic probe, MRI can visualize the effects of tissue heating in real-time, improving safety and efficacy. No other imaging modality offers this dual benefit.

In spite of these innovations, many routine image-guided interventions are currently performed under x-ray fluoroscopy, especially vascular procedures. One reason is the lack of MR-compatible instruments. Making instruments that can be used safely inside an operational MR system means more than just selecting nonmagnetic materials, said Michael Bock, Ph.D., head of the interventional MRI research group at the German cancer research center (DKFZ) in Heidelberg.