Issues and design solutions associated with performing MRI scans on patients with active implantable medical devices

Magnetic Resonance Imaging (MRI) has become one of medicine's most important diagnostic tools. However, due to patient safety concerns, MRI is contraindicated by both device and MRI equipment manufacturers for patients with active implanted medical devices (AIMDs). The primary concern is overheating of implanted leadwires due to currents induced from the powerful RF fields of the MRI scanner. In pacemaker patients, heating of myocardial tissue has caused increase in pacemaker capture threshold and in some cases complete loss of capture (inability to pace). Permanent damage to an implantable cardioverter defibrillator and at least one patient death and another with severe burns along the wires of deep brain electrodes have also been reported. The authors, with pacemaker leadwires placed in a "worse case" MRI scan condition, have measured distal tip leadwire temperatures of up to 57 degrees C (more than sufficient to cause tissue damage). Another risk is localized myocardial ablation which could result in changes in the action potential vector during atrial/ventricular contraction. However, in contrast to reports of problems, there have been several recent anecdotal reports of MRI scans being safely performed on non-pacemaker dependent patients under highly controlled conditions. Proper diagnosis, treatment and management of a number of life threatening diseases such as cancer, neurological and brain disorders are made possible by MRI. Accordingly, the physician, with informed patient consent, must sometimes ignore the legal contraindications, weigh the risk factors, and go ahead and perform an MRI on an AIMD patient. This paper quantifies the attendant risks of performing MRI on AIMD patients and discusses means of mitigating certain hazards such as leadwire overheating including the performance a new leadwire distal tip resonant bandstop filter chip (MRI Chip) which presents a high impedance at the MRI pulsed RF frequency.