Integrated detection scheme for fast blood flow measurement
Disclosed are various embodiments for integrated diffuse correlation spectroscopy. A first control signal can be sent to a switch to cause an integrator to integrate a current from a photodiode. An integrated current can be received from the integrator, and a data signal can be sent to a computing device based at least in part on the integrated current. A second control signal can be sent to a switch to cause the integrator to cease integrating the current from the photodiode.
1. A system for tissue blood flow measurement, comprising:
a photodiode configured to output a photodiode current based at least in part on a plurality of photons received by the photodiode, the plurality of photons being diffused through tissue illuminated by a light source;
an integration circuit configured to output an integrated current based at least in part on the photodiode current, the integrated current integrating a plurality of instantaneous photodiode intensity currents; and
a first computing device comprising a processor and a non-transitory computer-readable medium, the non-transitory computer-readable medium having stored instructions which, when executed by the processor, cause the processor to at least:
receive a representation of the integrated current from the integration circuit;
calculate a first photon intensity value corresponding to the representation of the integrated current; and
provide the first photon intensity value to a second computing device, to estimate tissue blood flow dynamics.
2. The system of claim 1 , wherein the photodiode operates in a photovoltaic mode such that the photodiode current flows from an anode of the photodiode to a cathode of the photodiode.
3. The system of claim 1 , wherein the integration circuit comprises an operational amplifier and a resistor-capacitor circuit.
4. The system of claim 1 , wherein the integrated current is a function of a time of integration.
5. The system of claim 1 , wherein the integrated current is defined as:
I
t
(
T
)
=
1
T
∫
0
T
i
(
t
)
dt
,
where IV) is the integrated current, t is a measurement time, Tis a time of integration, and i(t) is an instantaneous photodiode current at the measurement time, the instantaneous photodiode current being among the plurality of instantaneous photodiode intensity currents.
6. The system of claim 1 , wherein the integration circuit comprises an enable switch, and
wherein the instructions, when executed by the processor, further cause the processor to:
send a first control signal to the enable switch in the integration circuit, the first control signal causing the enable switch to be closed and the integration circuit to begin outputting the integrated current.
7. The system of claim 6 , wherein the integration circuit further comprises an operational amplifier, and
wherein the enable switch is electrically coupled with the photodiode and the operational amplifier.
8. The system of claim 6 , wherein the integration circuit further comprises a reset switch, and
wherein the instructions, when executed by the processor, further cause the processor to:
send a second control signal to the enable switch and the reset switch in the integration circuit, the second control signal causing the enable switch to be open, the reset switch to be closed, and the integration circuit to be reset.
9. The system of claim 8 , wherein the integration circuit further comprises an operational amplifier and a resistor-capacitor circuit electrically,
wherein the operational amplifier, the resistor-capacitor circuit, and the reset switch are electrically coupled in parallel.
10. The system of claim 6 , wherein the instructions, when executed by the processor, further cause the processor to:
before sending the first control signal, receive a dark current, wherein the dark current comprises a leakage current that flows through the photodiode;
calculate a second photon intensity corresponding to the dark current; and
correct a dark current noise in the integrated current based on the second photon intensity.
11. The system of claim 10 , wherein to correct the dark current noise in the integrated current, the instructions, when executed by the processor, further cause the processor to:
subtract the second photon intensity from the first photon intensity value.
12. The system of claim 1 , further comprising a voltage-controlled current source,
wherein the instructions, when executed by the processor, further cause the processor to at least send a drain control signal to the voltage-controlled current source for suppressing non-fluctuating DC current to the integration circuit, the drain control signal specifying a value of an input voltage for the voltage-controlled current source.
13. The system of claim 12 , wherein the voltage-controlled current source comprises an operational amplifier and a metal-oxide-semiconductor field effect transistor.
14. A method for tissue blood flow measurement, comprising:
receiving, by an integration circuit, a plurality of photons from a photodiode, the plurality of photons being diffused through tissue illuminated by a light source;
integrating, by the integration circuit, a plurality of instantaneous photodiode intensity currents based on the plurality of photons to produce an integrated current;
receiving, by an first computing device, a representation of the integrated current;
calculating, by the first computing device, a first photon intensity corresponding to the representation of the integrated current; and
providing, by the first computing device, the first photon intensity to a second computing device to estimate tissue blood flow dynamics.
15. The method of claim 14 , wherein the integrated current is defined as:
I
t
(
T
)
=
1
T
∫
0
T
i
(
t
)
dt
,
where it( 1 ) is the integrated current, t is a measurement time, T is a time of integration, and i(t) is an instantaneous photodiode current at the measurement time, the instantaneous photodiode current being among the plurality of instantaneous photodiode intensity currents.
16. The method of claim 14 , further comprising:
sending, by the first computing device, a first control signal to an enable switch in the integration circuit, the first control signal causing the enable switch to be closed and the integration circuit to begin outputting the integrated current.
17. The method of claim 16 , further comprising:
sending a second control signal to the enable switch and a reset switch in the integration circuit, the second control signal causing the enable switch to be open, the reset switch to be closed, and the integration circuit to be reset.
18. The method of claim 16 , further comprising:
before sending the first control signal, receiving, by the first computing device, a dark current, wherein the dark current comprises a leakage current that flows through the photodiode;
calculate by the first computing device, a second photon intensity corresponding to the dark current; and
correct by the first computing device, dark current noise in the integrated current based on the second photon intensity.
19. The method of claim 18 , wherein correcting the dark current noise in the integrated current comprising:
subtracting the second photon intensity from the first photon intensity.
20. The method of claim 14 , further comprising:
sending, by the first computing device, a drain control signal to a voltage-controlled current source for suppressing non-fluctuating DC current to the integration circuit, the drain control signal specifying a value of an input voltage for the voltage-controlled current source.