title: Effects of Near-Infrared Light on Cerebral Bioenergetics Measured with Phosphorus Magnetic Resonance Spectroscopy.
abstract: OBJECTIVE
  Cerebral photobiomodulation (PBM) improves mood and cognition. Cerebral metabolic enhancement is a mechanism proposed to underlie PBM effects. No PBM studies to date have applied phosphorus magnetic resonance spectroscopy (31P MRS), which can be used to assess metabolic intermediates such as phosphocreatine (PCr) and adenosine triphosphate, the latter of which is elevated by PBM. Accordingly, we used 9.4 Tesla31P MRS to characterize effects of single and repeat cerebral PBM treatments on metabolism. PBM was delivered to healthy adult beagles in the form of transcranial laser treatment (TLT) at a wavelength of 808 nm, which passes safely through the skull and activates cytochrome C oxidase, a mitochondrial respiratory chain enzyme.
  
  
  METHODS
  Isoflurane-anesthetized subjects (n = 4) underwent a baseline31P MRS scan followed by TLT applied sequentially for 2 min each to anterior and posterior cranium midline locations, to irradiate the dorsal cortex. Subjects then underwent31P MRS scans for 2 h to assess acute TLT effects. After 2 weeks of repeat TLT (3 times/week), subjects were scanned again with31P MRS to characterize effects of repeat TLT.
  
  
  RESULTS
  TLT did not induce acute31P MRS changes over the course of 2 h in either scan session. However, after repeat TLT, the baseline PCr/β-nucleoside triphosphate ratio was higher than the scan 1 baseline (p < 0.0001), an effect attributable to increased PCr level (p < 0.0001).
  
  
  CONCLUSIONS
  Our findings are consistent with reports that bioenergetic effects of PBM can take several hours to evolve. Thus, in vivo31P MRS may be useful for characterizing bioenergetic effects of PBM in brain and other tissues.
authors.affiliation: 1 McLean Imaging Center , McLean Hospital, Harvard Medical School, Belmont, Massachusetts.
authors.forename: Dionyssios
authors.initials: D
authors.lastname: Mintzopoulos
authors.affiliation: 1 McLean Imaging Center , McLean Hospital, Harvard Medical School, Belmont, Massachusetts.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Gillis
authors.affiliation: 2 LumiThera, Inc. , Poulsbo, Washington.
authors.forename: Clark E
authors.initials: CE
authors.lastname: Tedford
authors.affiliation: 1 McLean Imaging Center , McLean Hospital, Harvard Medical School, Belmont, Massachusetts.
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Kaufman
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000528:radiation effects; D004195:Disease Models, Animal; D004285:Dogs; D004734:Energy Metabolism / Q000528:radiation effects*; D005260:Female; D028022:Low-Level Light Therapy / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010759:Phosphorus Isotopes; D011897:Random Allocation; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared
chemical_list: D010759:Phosphorus Isotopes
keywords: adenosine triphosphate; cerebral metabolism; cytochrome C oxidase; low-level laser therapy; major depression; near-infrared light; phosphocreatine; phosphorus magnetic resonance spectroscopy; photobiomodulation