Prashant Nair, Ariel Roguin, 204
“Magnetic Resonance Imaging in patients with ICDs and Pacemakers”
Image quality:
Though lot of studies have been done to determine whether the devices are fully MR imaging-
compatible (function appropriately and without significant image distortion) very little is known
about the fact whether these device are MR-safe (function appropriately in the MR environment
but distort the image) or may not be usable in an MR scanner44,45. Image artifacts and RF noise
can be caused by the presence implanted devices in the MR environment which are in or near the
imaging field of view (such as implants or surface electrodes). These materials produce their own
characteristic static magnetic field that can perturb the relationship between position and
frequency essential to accurate image reconstruction. If the object has a magnetic susceptibility
that is significantly different from that of tissue, distortion will result. Primary concerns with
image artifact and noise include the production of a void where anatomical information is needed
as well as the production of artifacts that may be misdiagnosed as pathology. Schueler et al45
have offered an assessment of image quality according to four criteria: geometric distortion;
susceptibility-induced artifact; warping artifact; and bending, warping, or obliteration of image
contours.
Most artifacts from pacemakers and leads result in local image distortion, signal voids, or
increased noise. In an in vitro study26 in a dog model using the clinical scanning protocols this
issue was addressed and image distortion was analyzed by measuring the area where there was a
void in the MR image. The distortion was analyzed at the level of the heart and at the level of the
device. Artifacts due to the devices and leads were observed in some MR sequences and less in
others. Most of the distortion was dependent on scan protocol and image plane: Fast Spin Echo
and FIESTA sequences had significant distortion. Fast Gradient Recalled Echo, Tagging and
FSPGR sequences, however, yielded good images. Larger artifacts were observed in image
planes roughly parallel to the planes defined by the device itself. Most distortion was at a
distance of 10-15 cm around the device generator. The authors concluded that image distortion
was dependent on the imaging plane and protocol used. Most image distortion was in the area
adjacent to the device generator. Therefore, organs visualization beyond this distance, such as
knees, lower spine, liver or brain, will not be affected by the presence of the pacemaker or ICD.
Summary:
Most researchers in the field agree that although several hundreds of patients with
implanted devices underwent safe MR scan - this does not conclude that MR imaging in patients
with pacemakers or ICDs is indeed safe. According to the FDA’s definition, today’s ICDs are
not “MR Safe” nor “MR compatible”. Because of the small size of the series and limited to few
manufacturers one cannot conclude that MR imaging can deliberately be performed routinely in
Pacemaker/ICD patients without risk. Further study is required to better understand the
interaction between pacemakers and ICD systems and the effects of MR imaging.
Ultimately, a truly “MR safe” ICD system will need to be developed. Nevertheless, one
should be encouraged, and like the experience with pacemakers, the initial encouraging reports of
MR imaging in ICD patients reported only a small series.
Like pacemaker patients, ICD patients should not be considered for MR scan unless
appropriate precautions are undertaken and then only when other avenues to acquire clinically
relevant imaging data have been explored. Should MR imaging be considered in a patient with
an implantable device, appropriate consultation with a qualified cardiologist or
electrophysiologist is strongly advised so that patients can be adequately screened and correctable
physiologic abnormalities (e.g. hypoxia, electrolyte abnormalities, etc.) can be addressed prior to
MR imaging. The patient must not be pacemaker/ICD dependent. The clinician needs to
document in the chart, that MR imaging is crucial to the management of the patient. No other
imaging can be expected to provide an alternative or has been unsuccessfully tried. The patient or
family will sign a preprinted consent form explaining potential adverse reactions, invalidation of
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 197-209 (2005)