Fast pulsatile blood flow measurement in deep tissue through a multimode detection fiber

Abstract

Significance: Noninvasive in vivo fast pulsatile blood flow measurement in deep tissue is important because the blood flow waveform is correlated with physiological parameters, such as blood pressure and elasticity of blood vessels. Compromised blood flow may cause diseases, such as stroke, foot ulcer, and myocardial ischemia. There is great clinical demand for a portable and cost-effective device for noninvasive pulsatile blood flow measurement.

Aim: A diffuse-optics-based method, diffuse speckle pulsatile flowmetry (DSPF), was developed for fast measurement (∼300 Hz) of deep tissue blood flow noninvasively. To validate its performance, both a phantom experiment and in vivo demonstration were conducted.

Approach: Over the past two decades, single-mode fibers have been used as detection fibers in most diffuse-optics-based deep tissue blood flow measurement modalities. We used a multimode (MM) detection fiber with a core size of 200 μm for diffused speckle pattern detection. A background intensity correction algorithm was implemented for speckle contrast calculation. The MM detection fiber helped to achieve a level of deep tissue blood flow measurement similar to that of conventional modalities, such as diffuse correlation spectroscopy and diffuse speckle contrast analysis, but it increases the measurement rate of blood flow to 300 Hz.

Results: The design and implementation of the DSPF system were introduced. The theory of the background intensity correction for the diffused speckle pattern detected by the MM fiber was explained. A flow phantom was built for validation of the performance of the DSPF system. An in vivo cuff-induced occlusion experiment was performed to demonstrate the capability of the proposed DSPF system.

Conclusions: An MM detection fiber can help to achieve fast (∼300 Hz) pulsatile blood flow measurement in the proposed DSPF method. The cost-effective device and the fiber-based flexible probe increase the usability of the DSPF system significantly.

Keywords: deep tissue blood flow; diffuse correlation spectroscopy; diffuse speckle contrast analysis; laser speckle.

Fig. 1

(a) Schematic of a DCS system. APD, avalanche photodiode; C, correlator for $G_2(\tau )$ calculation (it could be a hardware correlator or software correlator). (b) Schematic of a fiber-based DSCA system.

Fig. 2

Illustration of the speckle pattern correction process. Around 6000 frames of speckle images (acquisition rate of 300 fps) are averaged to generate the background intensity profile. Then, the following raw CCD images will be divided by this background to obtain the corrected speckle pattern.

Fig. 3

Schematic of the flow phantom experimental setup for DSPF system. Laser source is delivered by an MM fiber into the phantom. Another MM fiber with a core size of $200\mu \mathrm{m}$ is used for detection at a distance of 15 mm to the source fiber. The other side of the detection fiber is inserted into a camera, without the lens, touching the CCD sensor. An example of the corrected speckle image is displayed beside the CCD. The area used for $1/K^2$ calculation is marked by a yellow square.

Fig. 4

(a) Flow waveforms measured by DSPF system at different pumping rates. When the pumping rate becomes faster, the averaged flow measurement reading increases and the pinching frequency of the rollers also increases. (b) Averaged flow measurement at each flow rate. (c) Averaged pinching frequency at each flow rate. Pinching frequency is calculated from the peak-to-peak intervals of the raw flow waveform (Video 1, 3 MB, MP4 [URL: https://doi.org/10.1117/1.JBO.25.5.055003.1]).

Fig. 5

Simultaneous measurement of DSPF (blue) and PPG (orange) waveforms. Both (a) brachial artery (s–d separation: 15 mm and laser power: 4 mW) and (b) right prefrontal cortex (s–d separation: 25 mm and laser power: 20 mW) measurements are demonstrated. The exposure time of the CCD camera was 2 ms. The corresponding measurement locations are indicated on the left (Video 2, 980 KB, MP4 [URL: https://doi.org/10.1117/1.JBO.25.5.055003.2]).

Fig. 6

(a) Blood flow measurement of a healthy subject’s thumb during an arm-cuff-induced occlusion experiment. (b) Zoom-in view of the pulsatile blood flow waveform during baseline. (c) Zoom-in view of the pulsatile blood flow waveform during recovery.