Methods and apparatus for near infrared spectroscopy
A system for performing near infrared spectroscopy (NIRS) monitors tissue oxygenation and/or hemodynamics. The system comprises a sensor coupled to a controller and/or processing device. The sensor comprises a light source which is operable to emit light of various distinct wavelengths and a detector which is operable to collect corresponding backscattered light.
1 . A near infrared spectroscopy (NIRS) sensor comprising:
a body having a dorsal face, a ventral face, and proximal and distal ends, the body supporting a light source and a photodetector in a spaced apart relationship, the light source operative to emit light from the ventral face of the body and the photodetector operative to detect light incident on the ventral face of the body and to generate an output signal;
a flexible flap extending laterally from the body along opposed first and second sides of the body; and
a NIRS controller comprising electronic circuits connected to control the light source to emit light of different wavelengths at different times wherein the NIRS controller is configured to control the light source to emit light of each of five distinct wavelengths, λ1 to λ5, in a sequence and to sample the output signal of the photodetector in coordination with the operation of the light sources to obtain a sequence of light intensity readings each of the light intensity readings corresponding to one of the wavelengths and the NIRS controller is configured to drive each of a plurality of light emitters of the light source with a corresponding driving signal wherein the corresponding driving signals for different ones of the light emitters vary in one or more of waveform, duty cycle, amplitude, and frequency.
2 . The NIRS sensor according to claim 1 wherein the flap extends between the first and second sides around the distal end of the body.
3 . The NIRS sensor according to claim 1 wherein the flap has a thickness that is less than a thickness of the body.
4 . The NIRS sensor according to claim 1 wherein the flap has a thickness in the range of 0.2 mm to 0.4 mm.
5 . The NIRS sensor according to claim 1 wherein a material of the flap extends continuously across the dorsal face of the body and encapsulates the light source and the photodetector.
6 . The NIRS sensor according to claim 5 wherein the flap comprises a flexible mesh.
7 . The NIRS sensor according to claim 1 wherein the flap is formed with a curvature such that a ventral face of the flap is concave and has a cylindrical geometry.
8 . The NIRS sensor according to claim 1 wherein the flap is wider at the distal end of the body and tapers in width along the body toward the proximal end of the body.
9 . The NIRS sensor according to claim 8 wherein a profile of a perimeter of the flap is teardrop shaped.
10 . The NIRS sensor according to claim 8 wherein a perimeter of the flap has a convex portion adjacent to the distal end of the body that joins onto concave tapering portions on both sides of the body.
11 . The NIRS sensor according to claim 10 comprising grooves in the flap that extend along both sides of the body.
12 . The NIRS sensor according to claim 1 wherein the flap is formed with shallow grooves that extend along both sides of the body on the dorsal face of the flap.
13 . The NIRS sensor according to claim 1 wherein a portion of the body between the light source and the photodetector is opaque to the light emitted by the light source and blocks direct transmission of light from the light source to the photodetector and the light source is operative to emit light having wavelengths in the range of 600 nm to 1000 nm.
14 . The NIRS sensor according to claim 1 wherein the light source comprises a plurality of light emitters, the plurality of light emitters each emit a different one of a plurality of wavelengths of light, the plurality of wavelengths of light are distributed around an isosbestic point, and the plurality of wavelengths includes one or more wavelengths above the isosbestic point and one or more wavelengths below the isosbestic point.
15 . The NIRS sensor according to claim 14 wherein the plurality of wavelengths includes two or more wavelengths selected from 660±10 nm, 730±10 nm, 810±10 nm, 850±10 nm, and 940±10 nm.
16 . The NIRS sensor according to claim 1 wherein the light source is spaced apart from the photodetector by a first distance in the range of 5 mm to 20 mm, the photodetector is a first photodetector and the NIRS sensor comprises a second photodetector spaced apart from the light source, the second photodetector operative to detect light incident on the ventral face of the body, and the second photodetector is spaced apart from the light source by a second distance in the range of 1½ to 2 times the first distance.
17 . The NIRS sensor according to claim 1 wherein the dorsal surface of the body is formed with a plurality of recesses and the recesses comprise a row of shallow dimples.
18 . The NIRS sensor according to claim 1 comprising a cable connected to the proximal end of the body, wherein the cable comprises first electrical conductors connected to drive the light source and second electrical conductors connected to carry an output signal from the photodetector and the cable comprises a sheath enclosing the first and second conductors, the first conductors run within a first electrically conductive shield inside the sheath and the second conductors run within a second electrically conductive shield inside the sheath.
19 . The NIRS sensor according to claim 1 comprising a trans-amplifier within the body and connected to convert a current signal output by the photodetector to a voltage signal.