Study of the Optical Properties of Biological Tissues Quantitative

Assessment Possibility using Spatial-Frequency

Domain Imaging

Alexander V. Kolpakov, Yuliya V. Ivanova, Svetlana A. Yushina and Anastasia S. Semenova

Department of Biomedical Technical Systems, Bauman Moscow State Technical University,

2-nd Baumanskaya str., 5/1, Moscow, Russia

Keywords: Optical Properties, Biological Tissues, Spatial-frequency Domain Imaging, Spectrophotometry, Optical

Imaging, Quantitative Assessment.

Abstract: The paper is devoted to the study of the possibility of using spatial-frequency domain imaging (SFDI)

technology in the tasks of visualizing neurovascular structures in the brain tissue during endosurgical

intervention, as well as the detection and objective quantitative assessment of lesions in the tissues of the

oral cavity. As a result of the initial stage of experimental studies in vivo, it was shown that SFDI allows

tracking the dynamics of optical parameters of tissues as a result of changes in blood filling and is

potentially applicable for detecting subsurface optical inhomogeneities in tissues.

1 INTRODUCTION

In recent decades, optical imaging has become

increasingly important in the field of medicine and

biology. The use of biological tissues optical

properties is widely used: from fundamental

research to obtain new knowledge about biological

processes to screening and numerical assessment of

the pathological processes stage.

The interest in optical methods is the result of

their unique property - non-invasiveness. The

sources of optical contrast are two main physical

phenomena - absorption and scattering of photons in

tissue.

One of the technologies for studying the optical

properties of tissue is the spatial frequency domain

imaging (SFDI). The main advantage of SFDI is the

ability to separate absorption and scattering effects

in the formation of optical contrast.

As a result of research in recent years, a number

of laboratories have shown the possibility of

visualizing the distribution and objective

quantitative assessment of the optical properties of

biological tissues using SFDI (Applegate, 2020;

Svaasand et al., 1999; Cuccia et al., 2019; Svaasand

et al., 1994; Cuccia et al., 2009; Hielscher et al.,

1975; Groenhuis et al., 1983; O'Sullivan et al., 2012;

Gioux et al., Carole et al., 2019).

At present, on the basis of the Department of

Biomedical Technical Systems of the Bauman

Moscow State Technical University, studies of SFDI

are being carried out, the purpose of which is to

determine the possibility of using SFDI in a number

of areas of medicine, in particular:

- in neurosurgery to solve the problem of

visualizing neurovascular structures in the

brain tissue during endosurgical intervention.

The hypothesis being tested is that due to the

peculiarity of SFDI, namely, due to the

possibility of separating with its help the

contribution of absorption and scattering to the

total attenuation of backscattered radiation,

there is the possibility of separate visualization

of blood vessels, as more absorbing structures,

and nerves, as more dissipative;

- in dentistry for visualization and quantitative

assessment at an early stage of inflammatory

processes, as well as erosive and ulcerative

lesions. The difference in the values of the

absorption and scattering coefficients of

intact and affected tissues of the oral cavity

can be hypothetically determined using SFDI

and used in the system for automatic

detection and control of the dynamics of

inflammatory and precancerous processes in

the tissues of the oral cavity at an early stage.

Kolpakov, A., Ivanova, Y., Yushina, S. and Semenova, A.

Study of the Optical Properties of Biological Tissues Quantitative Assessment Possibility using Spatial-Frequency Domain Imaging.

DOI: 10.5220/0010969300003123

In Proceedings of the 15th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2022) - Volume 1: BIODEVICES, pages 317-321

ISBN: 978-989-758-552-4; ISSN: 2184-4305

317

As a result of previously conducted research at

the Department of Biomedical Technical Systems:

- proved that the problem of detecting blood

vessels and cranial nerves during endoscopic

removal of tumors of the base of the skull can

be solved using the methods of automatic

detection of blood vessels and cranial nerves

based on methods of multispectral image

analysis and quantitative spectrophotometry

with local sensing in red and near infrared

(hereinafter - RNIR) wavelength ranges

(Safonova et al., 2019; Safonova et al., 2020;

Safonova et al., 2019; Safonova et al., 2019;

Safonova et al., 2019).

Under the conditions of the stand experiment the

possibility of detecting blood vessels located in the

tissues of the brain at a depth of up to 3 mm using

images of the red and near infrared range confirmed

(Kolpakov et al., 2021).

The possibility of visualization of the oral cavity

soft and hard tissues structure using radiation of the

near infrared wavelength range by diaphanoscopy has

been proven, as well as the possibility of detecting

lesions in the oral cavity tissues using visualization in

the near infrared range (Kolpakov et al., 2016).

SFDI is a new quantitative imaging technique, a

broadband diffuse optical technique that can separate

the effects of absorption and scattering and therefore

approximately determine the number of

chromophores in tissues. The method can be used to

measure the concentrations of tissue components

such as oxyhemoglobin, deoxyhemoglobin, lipids,

and water (Applegate et al., 2020).

Spatial frequency domain imaging consists of

projecting a two-dimensional (2-D) light pattern,

usually in the form of a harmonic periodic grating

(HPG), and analyzing the effect of multiple

scattering and absorption in tissue on the amplitude

of attenuated radiation, backscattered or past. In this

case, the amplitude of the attenuated radiation is

considered as a function of the spatial frequency of

the pattern.

2 MATERIALS AND METHODS

2.1 Stand for SFDI Research

To study the possibility of using SFDI, an

experimental stand is required. Currently, scientists

from Boston University (Applegate et al., 2020)

have created an openSFDI guide to create such a

stand from publicly available components

(hereinafter - the stand).

The stand contains three main modules: a

lighting module, a spatial modulation subsystem and

an image registration module (Figure 1).

Figure 1: The complete stand (off State). LED – light-

emitting diodes; CL - collimating lenses; DCM – dichroic

mirrors; AL - achromatic lens; P - linear polarizers; M –

guiding mirror; C - camera; DMD - digital micromirror

device.

An example of generating a lighting pattern is

shown in Figure 2. The object under study must be

placed in the illumination area.

Figure 2: Registration of the template (HPG) at the stand.

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The programming of the controller with the

spatial modulator DMD was carried out in

accordance with the instructions for the openSFDI

system (Applegate et al., 2020).

To generate lighting patterns and register the

resulting images, we used software based on the

LabView platform, developed by a research group

from Boston University (Applegate et al., 2020).

The assembled stand allows image registration at

wavelengths of 660 and 850 nm at various spatial

radiation modulation frequencies.

The processing of experimental results in the

general case for SFDI technology consists of four

stages:

- demodulation over three images at the same

spatial frequency: with phases of 0, 120 and

240 degrees,

- calibration to separate the instrument

response function (IRF or MTF

system

) from the

response function of the test sample,

- determination of the diffuse reflection

coefficient of the recorded sample,

- determination of the optical characteristics of

the recorded sample as a result of solving the

inverse problem: from the known values of

the diffuse reflection coefficient R

at two (or

more) spatial frequencies, the values of the

optical parameters of the object are

determined, which satisfy the radiation

transfer equation.

Figure 3 shows images with phases of 0, 120 and

240 degrees, obtained at the stand, as well as the

result of demodulation of these images. From three

images obtained in three phases, as a result of

demodulation, one image is obtained without stripes.

2.2 Initial Experimental Study

In order to initially test the possibility of measuring

the dynamics of biological tissues optical parameters

using SFDI, an experiment was carried out on the

assembled stand, during which the change in the

absorption and scattering coefficients on the surface

of the back of the volunteer's palm was monitored

during the change in the blood volume of the hand

using an occlusive cuff.

In the course of the experiment, the cuff was put

on a few centimeters above the bend of the subject's

elbow, and SFDI images of the back of the hand

were registered (Figure 4) at radiation wavelengths

of 660 and 850 nm in the non-occluded mode, in

venous oclussion mode (cuff pressure values 90 and

110 mm. Hg) and arterial occlusion mode (cuff

pressure value 220 mm Hg).

Figure 3: Images of the object taken at the stand.

a) -c ) Illumination with a spatial frequency of

0.5 mm

-1

, with phases of 0 °, 120 ° and 240 °;

d) result of demodulation.

Study of the Optical Properties of Biological Tissues Quantitative Assessment Possibility using Spatial-Frequency Domain Imaging

319

Figure 4: Scheme of SFDI images registration in an

experiment with an occlusal cuff: the area of registration is

marked with a red rectangle.

The registered images were used to determine

the values of the absorption and reduced scattering

coefficients averaged over the selected area.

3 RESULTS AND DISCUSSION

As a result of the initial work, a stand for

researching the SFDI technology was assembled.

The performance of the stand is confirmed by

obtaining a high-quality demodulated image.

The experimental dependences of the absorption

and reduced scattering coefficients on the pressure in

the occlusal cuff, obtained as a result of the

experiment, are shown in Figure 5.

The extrema of the values of the absorption and

reduced scattering coefficients were registered in the

mode of venous occlusion, corresponding to the

maximum blood filling of the investigated area. This

observation corresponds to the hypothetical

dynamics of the optical properties of the studied

tissues under the conditions of the experiment. Thus,

as a result of the analysis of the obtained

experimental dependences, it was found that the

SFDI technology makes it possible to adequately

monitor the dynamics of optical parameters of

tissues as a result of changes in blood filling and is

potentially applicable for the detection of subsurface

optical inhomogeneities in tissues, such as blood

vessels, inflammation foci.

To determine the accuracy of tissues optical

parameters SFDI measurements, it is required to

conduct a series of measurements on a larger sample

of subjects, as well as to develop SFDI metrological

support, including sets of measures, and methods for

verifying the results of SFDI measurements.

Figure 5: Parameters of absorption and scattering obtained

during the experiment on the stand: a) the value of the

absorption coefficient of the palm, depending on the

pressure in the cuff; b) the value of the reduced scaterring

coefficient of the palm depending on the pressure in the

cuff.

In the course of further work, it is planned:

- verification of the obtained experimental

dependences of the results of SFDI

measurements on the pressure in the occlusal

cuff on a larger number of subjects;

- verification of the results of SFDI

measurements using phase modulation

spectrophotometry;

- carrying out research at the stand in order to

determine the best values of the radiation and

registration parameters of the SFDI system

for the possibility of using it in the tasks of

visualizing neurovascular structures in the

brain tissue during endosurgical intervention,

detecting lesions in the tissues of the oral

cavity;

- development of metrological support for

SFDI systems;

- development, manufacture and clinical

testing of prototypes of SFDI systems for

visualization of neurovascular structures in

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the brain tissue during endosurgical

intervention, detection and objective

numerical assessment of lesions in the tissues

of the oral cavity.

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