title: Feasibility of Structural and Functional MRI Acquisition with Unpowered Implants in Argus II Retinal Prosthesis Patients: A Case Study.
abstract: OBJECTIVE
  Magnetic resonance imaging (MRI) can measure the effects of vision loss and recovery on brain function and structure. In this case study, we sought to determine the feasibility of acquiring anatomical and functional MRI data in recipients of the Argus II epiretinal prosthesis system.
  
  
  METHODS
  Following successful implantation with the Argus II device, two retinitis pigmentosa (RP) patients completed MRI scans with their implant unpowered to measure primary visual cortex (V1) functional responses to a tactile task, whole-brain morphometry, V1 cortical thickness, and diffusion properties of the optic tract and optic radiation. Measurements in the subjects with the Argus II implant were compared to measurements obtained previously from RP patients and sighted individuals.
  
  
  RESULTS
  The presence of the Argus II implant resulted in artifacts that were localized around the patient's implanted eye and did not extend into cortical regions or white matter tracts associated with the visual system. Structural data on V1 cortical thickness and the retinofugal tract obtained from the two Argus II subjects fell within the ranges of sighted and RP groups. When compared to the RP and sighted subjects, Argus II patients' tactile-evoked cross-modal functional MRI (fMRI) blood oxygen level-dependent (BOLD) responses in V1 also fell within the range of either sighted or RP groups, apparently depending on time since implantation.
  
  
  CONCLUSIONS
  This study demonstrates that successful acquisition and quantification of structural and functional MR images are feasible in the presence of the inactive implant and provides preliminary information on functional changes in the brain that may follow sight restoration treatments.
  Successful MRI and fMRI acquisition in Argus II recipients demonstrates feasibility of using MRI to study the effect of retinal prosthesis use on brain structure and function.
authors.affiliation: Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA.
authors.forename: Samantha I
authors.initials: SI
authors.lastname: Cunningham
authors.affiliation: Laboratory of Neuro Imaging, USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Shi
authors.affiliation: USC Eye Institute, University of Southern California, Los Angeles, CA, USA.
authors.forename: James D
authors.initials: JD
authors.lastname: Weiland
authors.affiliation: USC Eye Institute, University of Southern California, Los Angeles, CA, USA ; Department of Ophthalmology and Visual Sciences, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Paulo
authors.initials: P
authors.lastname: Falabella
authors.affiliation: USC Eye Institute, University of Southern California, Los Angeles, CA, USA.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Olmos de Koo
authors.affiliation: Kellogg Eye Center, University of Michigan, Ann Arbor, MI, USA.
authors.forename: David N
authors.initials: DN
authors.lastname: Zacks
authors.affiliation: Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA ; Department of Psychology, University of Southern California, Los Angeles, CA, USA.
authors.forename: Bosco S
authors.initials: BS
authors.lastname: Tjan
keywords: MRI; dMRI; fMRI; retinal prothesis; retinitis pigmentosa