| Outcome/accomplishment:
Researchers at the NSF-funded Biomimetic MicroElectronic Systems (BMES)
Engineering Research Center (ERC) explored parameters around which it is
acceptable to use Magnetic Resonance Imaging (MRI) scans for imaging of
patients who have retinal prosthesis implants. They determined that it
is possible, in principle, to administer MRIs to retinal implant wearers
and obtain accurate results, safely.
Impact/benefits: Because
of this research at BMES, which is headquartered at the University of Southern
California (USC), we now have a greater understanding of how MRI scanning
affects retinal implants and vice versa. This is important because of the
large population of blind individuals who could potentially benefit from
the still-developing technology of retinal implants.
Explanation/ background:
MRI is commonly used to diagnose patients' health problems by providing
visual feedback of abnormalities within the body. However, MRIs can't
be used with patients who have certain neural stimulators—for instance,
cochlear implants or deep brain stimulation devices—as these devices do
not safely interact with the magnetic fields produced by MRIs. However,
investigators established through animal testing that it is possible to
scan patients implanted with a retinal prosthesis as long as precautions
are taken to minimize radio interference between the MRI machine and the
implanted device.
Two of the chief concerns
are: radio frequency interference that can corrupt the MRI results; and
MRI fields that can disrupt the radio frequency communication between an
external camera and the implanted retinal stimulator. Investigators
determined that these issues could be avoided by turning off the retinal
implant's radio frequency link when the MRI was actively scanning.
Several levels of MRI interaction
were investigated. First, investigators showed that MRI fields did not
damage the retinal implant and that the implant did not generate heat or
force when subjected to MRI fields. Argus II implants were placed
in “phantoms”—specially designed objects meant to stand in for humans during
MRI performance tests. At both 1.5T and 3.0T (T stands for Tesla,
indicating magnet strength), the implants remained fully functional and
showed little chance of tissue damage resulting from someone being scanned
while wearing an Argus II.
Investigators also showed
that an observed artifact, a visual inaccuracy in the MRI-produced image,
was 4 cm or less, and resulted from interference of an inactive implant
in the animal used for scanning tests. The images produced showed
that in humans, it will be possible to accurately image the visual cortex
areas; those areas are at the back of the head, well outside the <4cm
artifact produced in the area of the retinal implant. |
