Abstract
Noninvasive photobiomodulation therapy (PBMT) of spinal cord disease remains speculative due to the lack of evidence for whether photobiomodulatory irradiances can be transcutaneously delivered to the spinal cord under a clinically acceptable PBMT surface irradiation protocol. We developed a flexible nine-channel photodetection probe for deployment within the spinal canal of a cadaver dog after hemilaminectomy to measure transcutaneously transmitted PBMT irradiance at nine sites over an eight-cm spinal canal length. The probe was built upon a 6.325-mm tubular stem, to the surface of which nine photodiodes were epoxied at approximately 1cm apart. The photodiode has a form factor of 4.80 mm×2.10 mm×1.15 mm (length×width×height). Each photodiode was individually calibrated to deliver 1V per 7.58 μW/cm2 continuous irradiance at 850nm. The outputs of eight photodiodes were logged concurrently using a data acquisition module interfacing eight channels of differential analog signals, while the output of the ninth photodiode was measured by a precision multimeter. This flexible probe rendered simultaneous intraspinal (nine-site) measurements of transcutaneous PBMT irradiations at 980nm in a pilot cadaver dog model. At a surface continuous irradiance of 3.14 W/cm2 applied off-contact between L1 and L2, intraspinal irradiances picked up by nine photodiodes had a maximum of 327.48 μW/cm2 without the skin and 5.68 μW/cm2 with the skin.
Highlights
Photobiomodulation therapy (PBMT),[1] previously termed lowlevel light therapy,[2] has shown safe and potentially beneficial therapeutic outcomes for conditions including stroke[3] and wounds that resist conventional treatments.[4]
We report the development of a flexible ninechannel probe, ∼80-mm long, for deployment in the spinal canal of large cadaver dogs after hemilaminectomy and demonstrate simultaneous intraspinal light irradiance quantification at nine sites under surface light irradiation
The spinal canal extending from ∼T10 to L6 vertebral sections was exposed
Summary
Photobiomodulation therapy (PBMT),[1] previously termed lowlevel light therapy,[2] has shown safe and potentially beneficial therapeutic outcomes for conditions including stroke[3] and wounds that resist conventional treatments.[4]. The transcranial light transmission of 0.00114% in this dog cadaver agreed with transcranial light transmission at 5-cm depth in human cadavers.[1] It is, perhaps possible to deliver PBMT light to the spinal cord level at a dose that has shown the potential of improving human cerebral conditions[13] at a clinically safe surface irradiation protocol. The use of a single photodiode sensor challenges the localization of the probe once deployed intraspinally, the consistency of multisite measurements on any subject, and the reproducibility of inter-subject evaluation that are all parametric to the feasibility of noninvasive PBMT of the spinal cord under a clinically acceptable surface light irradiation protocol. The probe had nine fiber-optical diffusers (FODs) as auxiliary sensors for relative scaling of the light irradiations reaching the nine PDs at low light irradiance conditions
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