title: Lamina-specific functional MRI of retinal and choroidal responses to visual stimuli.
abstract: OBJECTIVE
  To demonstrate lamina-specific functional magnetic resonance imaging (MRI) of retinal and choroidal responses to visual stimulation of graded luminance, wavelength, and frequency.
  
  
  METHODS
  High-resolution (60 × 60 μm) MRI was achieved using the blood-pool contrast agent, monocrystalline iron oxide nanoparticles (MION) and a high-magnetic-field (11.7 T) scanner to image functional changes in the normal rat retina associated with various visual stimulations. MION functional MRI measured stimulus-evoked blood-volume (BV) changes. Graded luminance, wavelength, and frequency were investigated. Stimulus-evoked fMRI signal changes from the retinal and choroidal vascular layers were analyzed.
  
  
  RESULTS
  MRI revealed two distinct laminar signals that corresponded to the retinal and choroidal vascular layers bounding the retina and were separated by the avascular layer in between. The baseline outer layer BV index was 2-4 times greater than the inner layer BV, consistent with higher choroidal vascular density. During visual stimulation, BV responses to flickering light of different luminance, frequency, and wavelength in the inner layer were greater than those in the outer layer. The inner layer responses were dependent on luminance, frequency, and wavelength, whereas the outer layer responses were not, suggesting differential neurovascular coupling between the two vasculatures.
  
  
  CONCLUSIONS
  This is the first report of simultaneous resolution of layer-specific functional responses of the retinal and choroid vascular layers to visual stimulation in the retina. This imaging approach could have applications in early detection and longitudinal monitoring of retinal diseases where retinal and choroidal hemodynamics may be differentially perturbed at various stages of the diseases.
authors: Research Imaging Institute, University of Texas Health Science Center, San Antonio, Texas, USA.
authors: Yen-Yu I
authors: YY
authors: Shih
authors: Bryan H
authors: BH
authors: De la Garza
authors: Eric R
authors: ER
authors: Muir
authors: William E
authors: WE
authors: Rogers
authors: Joseph M
authors: JM
authors: Harrison
authors: Jeffrey W
authors: JW
authors: Kiel
authors: Timothy Q
authors: TQ
authors: Duong
mesh_terms: D000818:Animals; D001810:Blood Volume; D002829:Choroid / Q000098:blood supply / Q000502:physiology*; D003287:Contrast Media / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D052203:Ferrosoferric Oxide / Q000008:administration & dosage; D008279:Magnetic Resonance Imaging; D008297:Male; D053758:Nanoparticles / Q000008:administration & dosage; D010775:Photic Stimulation / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow; D012160:Retina / Q000502:physiology*; D012171:Retinal Vessels / Q000502:physiology
chemical_list: D003287:Contrast Media; C499827:monocrystalline iron oxide nanoparticle; D052203:Ferrosoferric Oxide