Prof. Dr. med. Frank K. Wacker

Interventional MRI - why is it not clinical reality - yet!

(Montag, 15.05 Uhr, Schinkelsaal)

Frank Wacker

With the increasing use of diagnostic MRI over the last decades a growing interest for MR guidance of interventional procedures became evident. Technical improvements such as short magnet bores, improved magnet homogeneity, better gradient performance and new data sampling and reconstruction techniques have helped to introduce real time MR-guidance into the clinical arena. The clinical necessity to use this imaging technology for procedure guidance stems from unique advantages of MRI such as excellent soft tissue contrast, unique functional as well as structural information, flexible image plane adjustments and lack of ionizing radiation exposure.

However, well established interventional imaging techniques such as x-ray fluoroscopy for vascular procedures and CT and ultrasound for percutaneous needle based interventions show a remarkable progress as well. Angiography systems in specifically designed suites that are tailored for interventions, CT scanners with interventional modes and in-room display, and ultrasound machines with interactive device guidance are examples for systems that are far ahead of MRI in terms of dedication for procedure guidance. In addition, progress with image fusion, real time registration and overlay techniques help to augment 2D techniques such as fluoroscopy or ultrasound with information from previously acquired MRI images thus closing the gap between MR augmented guidance and true MRI guidance.

In some arenas, however, MRI guidance is a clinical reality. Examples include MRI guided breast biopsy, biopsies and injections for musculoskeletal lesions and prostate biopsies. With most of these applications MRI is the only modality that visualizes the lesion making it an obvious choice for targeting. There are other reasons for MRI guidance such as lack if radiation, which, based on the ALARA principle, should play an important role especially in patients, who are sensitive to radiation exposure. There are other theoretical benefits of MRI such as the ability to visualize heat distribution during thermal tumor ablation that are not thoroughly studied in the clinical arena. This is highly disappointing, because many in the field feel that MRI guidance would facilitate a more targeted and precise tumor ablation that could increase local tumor control as well as overall survival.

Even with obvious and well accepted benefits of MRI guidance, the number of MRI guided procedures remains relatively low in the clinical realm. Poor access to the patient in the magnet, lack of MR safe devices, safety issues with ferromagnetic material and workflow challenges make true MRI guided procedures somewhat challenging. This is in stark contrast to the tailored workflow in dedicated, procedure friendly interventional suites. In addition, MRI suites constitute a high capital investment. Many hospital administrators think that return on investment is much easier to achieve with diagnostic procedures and do not value the medical benefit of MRI guided procedures.

It will require a continuous effort of physicians, engineers and physicists to generate and improve the tools and knowledge necessary to perform MRI guided procedures. Theoretical benefits of MRI guidance that are well known from phantom and animal studies need to be translated into clinical reality by means of well-designed studies, preferably multi center trials. However, advancement of other, sometimes less complex image guidance techniques will not come to rest, making this a challenging task.

Prof. Dr. Frank Wacker
Direktor des Instituts für diagnostische und interventionelle Radiologie, Medizinische Hochschule Hannover