Cognosensors Remote : Developing an NIR Imaging Model to Map Brain Function
Prasheel Lillaney Project Advisor: Dr. Britton Chance
Introduction
Goal: Develop an untethered system for detection of oxygenation and blood volume levels in the pre-frontal cortex.
Use oxygenation and blood volume information to tell us about subject behavior
Why untethered? Eliminates nervousness and
misleading signals
Experimental Setup
Laser
= 805 nm
Subject
(Phantom)
Detector
(PMT)
1-2 M
Processing of Signal
Basic PrincipleConvert photons from laser into an electrical signal Processing of signal is based on TCSPC (Time Correlated Single Photon Counting) Develop processing system- determine absorption coefficient (a)
Standard Single Photon Counting System
One source / One detector model at the moment Solved problem of trigger signal not being accepted by SPC board Some concern with grounding issues with the Hamamatsu R5600U PMT
SPC Experimental Setup
Laser Frequency varied from 15 MHz to 40 MHz Attenuators used are identical (anywhere from 1 dB to over 40 dB attenuation Amplifiers used not identical
SPC Experimental Results 1
Trials 1,2,3 for Phantom 1 (a = 0.02 cm )
Trial 1 Trial 2 Trial 3
-1
70000 60000 50000 40000 30000 20000 10000 0 500
Photon C ounts
Trials done with PMT/Subject distance at 60 cm Trial 3 done with subject position altered to increase reflection
Enhanced Log Plot (Data points 575-625)
Trial 1 4.4 LOG P hoton Counts 4.2 4 3.8 3.6 3.4 3.2 3 0 y = -0.016x + 4.2878 R2 = 0.9706 Linear (Trial 1)
550 600 Time Increment (1024=50ns)
650
Trials 1,2,3 for Phantom 1 (a = cm 0.02 )
Trial 1 Trial 2 Trial 3
-1
LO G Ph o to n Co u n ts
5 4.5 4 3.5 3 2.5 500 550 600 650
10
20
30
40
50
Time Increment (1024=50ns)
Time Increment (1024=50ns)
SPC Experimental Results 2
Remote Trial Demonstrating Seperation of Specular and Photon Migration
3.6 3.4 LOG Photon Counts 3.2 3 2.8 2.6 2.4 0 100 200 300 400 500 600 700 800 900 Time Increment (1024=50ns)
Possible separation of reflection and diffuse photon signals? Possible artifact from PMT.
Trial 1
4 3.8 LOG Photon Counts
LOG Photon Counts 4 3.8 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2 400
Trial 2
3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2 400 500 600 Time Increment (1024=50ns) 700 800 \
500
600 Time Incremenet (1024=50ns)
700
800
Box Car System
Reference: Chance, B.
Initial Box Car Results
Voltage Peak to Peak (mV) vs Frequency (MHz)
600 Voltage (mV) 500 400 300 200 100 0 0 1 2 3 Frequency (MHz) 4 5 6
Response from 1-gated integrator and pulse generator. Voltage decreased as frequ...