Acceptable implants identified for 7-T MRI scanners

Twenty patient implants have been deemed acceptable in subjects referred for 7-T MRI procedures, according to a study published in the February issue of the American Journal of Roentgenology.

The advent of 7-T MRI systems has brought numerous advancements for neurologic applications through its increased strength of the static magnetic field. However, this elevation in strength means safety concerns for subjects with metallic implants or other objects.

"[T]he presence of metallic items is currently a contraindication for 7-T MRI examinations because of presumed adverse interactions with the static magnetic field and MRI-related heating. Unfortunately, restrictions such as these preclude a large subset of volunteer subjects as well as patients—in particular, patients with conditions currently of interest for investigation at 7 T,” wrote lead author Adrienne N. Dula, of the Vanderbilt University Medical Center in Nashville, Tenn., and colleagues.

The researchers evaluated MRI issues for 28 different metallic implants and other objects in association with a 7-T MR system using translational attraction and torque. The items investigated included two aneurysm clips, one hemostatic clip, seven vascular implants, eight orthopedic implants, eight biopsy tissue markers, and two miscellaneous objects.

Eight of the 28 items revealed magnetic field interactions at levels that could pose risks to human subjects, such as compression hip screws, plates, lag screws, hip stems, access ports, and clips. Though the two aneurysm clips showcased heating, the temperature did not rise above 1°C. The remaining 20 objects did not exhibit significant magnetic qualities at 7-T.

“This information has important significance for screening patients referred for MRI procedures at 7 T because it indicates that some individuals and patients with certain implants and devices can undergo examinations at this very high field strength,” wrote Dula and colleagues.