Simulation and Experiment of Ghost Imaging-OCT Target Imaging in

Scattering Media

Decai Huyan

, Nofel Lagrosas

and Tatsuo Shiina

Graduate School of Science and Engineering, Chiba University, Chiba-shi, Japan

Keywords:

OCT, Ghost Imaging, Scattering Media.

Abstract:

Conventional optical coherence tomography (OCT) target imaging is easily affected by scattering media and

gets error results in optical properties about transmittance and absorbance of the target. We propose a new

system for this problem by combining the Ghost Imaging(GI) technique and OCT on the measurement path.

Even if the modulated images by scatterers under its low signal-to-noise ratio, the GI technique can recon-

struct the images in the situation. Our system uses a single detector in the 2D dimensions to get the target

images in the scattering media by getting rid of the modulation. In this paper, we introduce the concept and

demonstrate the experimental method of Ghost Imaging-OCT, we call GI-OCT. We get the same shape in the

binarized images by comparing the GI-OCT experimental image with corrected modulation and the original

image without modulation. In the simulation we obtained the PSNR value of 47dB at 10% noise rate. In the

experiment we got the PSNR value of 18.89dB.The results prove our system is helpful for target imaging in

the scattering media.

1 INTRODUCTION

Optical coherence tomography (OCT) is an imag-

ing technique that can produce high-resolution to-

mographic images using a non-contact, non-invasive

method on a non-homogeneous medium(Huang et al.,

1991). Based on the principle of low coherence inter-

ference, OCT combines reﬂected light from the mea-

surement and reference paths to recover the optical

property distribution of an object at a depth direction.

OCT systems have been used in commercial cases and

have achieved great success in ophthalmology by pro-

viding detailed images from the inner retina. It has

recently been used to diagnose cases in cardiology

and dermatology(Gambichler et al., 2005). Moreover,

OCT is also used in many biomedical multilayer scat-

tering media, such as organs and skin(Spaide et al.,

2018). This imaging technique is very important in

early skin cancer detection and others.

This paper aims to detect no modulation target im-

age in a scattering media. This modulation repre-

sents the scattering in the OCT image. No modula-

tion means the OCT image is without the scattering.

https://orcid.org/0000-0002-2490-0439

https://orcid.org/0000-0002-8672-4717

https://orcid.org/0000-0001-9292-4523

In OCT measurements in scattering media, the tar-

get signal is always affected due to light attenuation

and scattering in the scattering media as the measured

light propagates in the depth direction. Such scat-

tering attenuation of the OCT signal can be reduced

by multi-angle incidence measurement and increas-

ing the number of measurements. However, in un-

known scattering media, these methods cannot elim-

inate the inﬂuence of the media on the target signal.

The scattering media may change the direction of the

measured light and cause a time delay. This makes it

difﬁcult to get an accurate shape of the target and to

obtain an adequate image of the target in the scatter-

ing media.

Ghost imaging (GI) techniques have attracted at-

tention because they distinguish between signal and

noise. GI has been used in many ﬁelds since the

publication of the paper ”ghost imaging using a sin-

gle detector”(Bromberg et al., 2009). In this paper,

they presented that a single probe can illuminate a

sample with different patterns of light multiple times,

and reconstructed an image based on the relationship

between the reﬂected light total intensity and the il-

luminated light pattern. We propose a new method

to obtain target images in scattered media by com-

bining Ghost Imaging and TimeDomain-OCT (GI-

OCT)(Huyan et al., 2022). The proposed method

Huyan, D., Lagrosas, N. and Shiina, T.

Simulation and Experiment of Ghost Imaging-OCT Target Imaging in Scattering Media.

DOI: 10.5220/0011677400003408

In Proceedings of the 11th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2023), pages 67-73

ISBN: 978-989-758-632-3; ISSN: 2184-4364

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

in this paper can reconstruct images even when the

signal-to-noise ratio is low due to scattering, using the

ability of GI. By using this method, target images can

be obtained without scattering effects.

2 DIFFERENT OF

CONVENTIONAL OCT AND

GI-OCT

Unlike conventional OCT, the OCT probe light from

GI-OCT does not focus on a point but illuminates the

light on an area, as in full ﬁeld-OCT(FF-OCT). This

method can take two-dimensional images with a sin-

gle probe. FF-OCT enables imaging of target dis-

tribution because the camera directly takes a cross-

sectional two-dimensional image perpendicular to the

optical axis. However, FF-OCT cannot obtain tar-

get distribution without the effect of scattering. FF-

OCT uses a megapixel camera to achieve cellular-

level imaging. Each pixel in an FF-OCT image is a

point measurement of the target, the same as conven-

tional OCT(Vabre et al., 2002).

For ease of understanding, we show the target

(scattered sample) in the scattering media in two parts

on the OCT measurement. The former is the scat-

ter layer before the light hits the target, and the latter

is the target layer. When measuring the target layer

in the scatter media with conventional OCT, a three-

dimensional image can be constructed by changing

the reference light path (A scan) and orthogonal mo-

tion of the probe (B scan) as shown in Figure 1(a).

However, the reﬂected signal does always have scat-

tering from the scatter layer, so the target layer dis-

tribution had modulated by scattering. For example,

when measuring the optical properties (transmittance

and absorbance) of a target layer with OCT, the dis-

tribution of the front scatter layer may change the di-

rection of the light or delay the received signal of the

target layer due to scattering. As a result, the modu-

lated image of the optical properties of the target layer

is detected.

Figure 1(b) illustrates the concept of GI-OCT, in

which GI-OCT probe light passes through an ex-

pander and spatial light modulator (SLM), and the

generated light patterns illuminate the target layer be-

hind the scatter layer. Reﬂected light from the tar-

get and scatter layers are focused on a point detec-

tor. The A-scan signal of GI-OCT is a series of light

intensities separated in the depth direction for each

light illuminated pattern. Every A-scan signal can be

separated as the sum of the illuminate pattern inten-

sities for each layer distribution with the axial resolu-

tion of OCT. After repeated measurements with dif-

ferent light patterns, the correlation between those il-

luminated patterns and the sum of interference inten-

sities of each separated layer is calculated by using

the GI method to obtain each layer distribution. Each

separated layer is reconstructed in a multilayer sam-

ple(3D).

Compared to conventional OCT measurements,

GI-OCT acquires a two-dimensional image in the

plane perpendicular to the optical axis with a sin-

gle detector. Light misalignment to other directions

and time delay in scattering media can be simultane-

ously summed and detected as OCT interference sig-

nals. The misalignment and delay are constructed as a

scatter layer distribution. The target layer distribution

and the former scattering layer distribution can be re-

constructed using the same procedure. By the scatter

layer distribution, the optical properties of the target

layer can be corrected, and the target distribution is

obtained without the scatter layer effects.

3 EXPERIMENT

Figure 3(a) shows the GI-OCT experiment setup.

The GI-OCT uses the superluminescent diodes (SLD)

light source with a central wavelength of 860 nm,

Gaussian distribution, and an axial resolution of

10.1µm. The reference path consists of a steady ro-

tating motor and a ﬁxed mirror to complete the axial

scanning (A-scan)(Shiina et al., 2003). The measure-

ment path of GI-OCT has the optical probe, which

is composed of a collimator and two lenses to make

the beam diameter expand. The DMD chip (DLP2000

DMD) is placed in the measurement area. The sample

is set between the DMD chip and the optical probe.

There is a matrix corresponding to 640 × 360

and a total size of 4.84 × 2.72mm micromirrors ar-

ranged inside the DMD chip. Each mirror size is

7.56 × 7.56 µm, and the deﬂection angle is ±12 de-

grees on the diagonal axis, divided into ”on” and ”off”

states. Then, the DMD chip in our experiments is ori-

ented towards the vertical optical axis 12 degree to

obtain the reﬂected light from the DMD. DMD chips

are rotated 45 degrees counterclockwise in the verti-

cal plane against the optical axis to make the diagonal

axis vertical too. Moreover, the DMD is tilted 12 de-

gree against the optical axis when the micromirrors

state is ”on”. Because of these tilts, this DMD ori-

entation causes a series of interference signals in the

time domain, as shown in Fig 3(b). In GI-OCT ex-

periment, the DMD chip displays 10 × 10 speckles

patterns in the area, which is 2 × 2mm in size.

We prepare a sample with the target in the scatter-

PHOTOPTICS 2023 - 11th International Conference on Photonics, Optics and Laser Technology

Figure 1: Setup of (a) a conventional OCT, that produces the target image with scattering inﬂuence. (b) GI-OCT, that produces

the scatter image that can be used to generate the target image without the scattering inﬂuence. The difference between (a)

and (b) is the presence of the beam expander and SLM in the GI-OCT setup.

ing media, and it has two layers: the ﬁrst layer is the

scatter layer, and the second layer is the target layer.

Both layers are painted with water-based pigments on

a slide glass. The target layer has the character ”F”,

and the scatter layer was half-covered on the diagonal

axis with paint. The water-based pigment adhered to

the slide glass uniformly, and the pigment attenuation

rate was 53%.

In our experiments, we set the DMD chip in the

GI-OCT measurement area, and the reﬂected light

from the DMD chip passes through the sample and

returns to the probe. With this setup, the concept of

GI-OCT about eliminating modulation becomes clear.

Because the DMD chip is located in the measurement

area, its reﬂection efﬁciency is high, resulting in more

stable light intensity. This setup eliminates the inﬂu-

ence from many different layers and focuses on re-

constructing the target layer with one scattering layer.

However, we used four separate experiments for

this experimental design to achieve our purpose. Ex-

periment 1: OCT beam distribution measurement (not

any layers); Experiment 2: target layer measurement;

Experiment 3: scatter layer measurement; Experi-

ment 4: target layer overlapping scatter layer mea-

surement.

4 SIMULATION

To validate our proposed GI-OCT technique, we per-

formed simulation experiments on the reconstruction

of target imaging. First, we explain the evaluation

method for the quality of the reconstructed image,

which is the peak signal-to-noise ratio (PSNR) used

for comparing the reconstructed of original image. It

approximates human perception of reconstruction im-

age quality and is calculated using Eq.(1).

PSNR = 10 · log

(

MAX

MSE

) (1)

MSE is the mean squared error of the original and

reconstructed picture. MAX is the maximum possible

pixel value in the image. In an 8-bit image, accep-

tance values for the PSNR in the original and recon-

structed pictures should be over 30 dB to achieve a

higher reconstruction quality.

In the OCT measurements, the quality of the OCT

image is degraded by noise, due to the slight move-

ment of the sample, limited light bandwidth, phase

aberrations of propagating beam, the aperture of the

detector, and multiple scattering within the coherence

length. So we evaluate noise inﬂuence on the recon-

structed image.

We implemented multiple GI methods, includ-

ing computational ghost imaging (CGI), differential

Simulation and Experiment of Ghost Imaging-OCT Target Imaging in Scattering Media

Figure 2: The steps of GI-OCT measurement: light pattern from the probe and SLM illuminates the sample to obtain the

intensity of the OCT signal (intensity vs time graph) which can be calculated together with the pattern to produce the GI-OCT

result. The matrices show the visualization of calculation process.

Figure 3: (a) Experiment set-up of GI-OCT. (b) The DMD micromirrors reﬂected signals in the time domain.

ghost imaging (DGI), pseudo-inverse ghost imaging

(PGI), and differential pseudo-inverse ghost imaging

(DPGI), to determine which one was appropriate for

GI-OCT.(Ferri et al., 2010; Zhang et al., 2014) CGI

is the calculation of pattern and light intensity, DGI

is the difference between pattern and light intensity,

PGI is the inverse matrix calculation of pattern and

light intensity, and DPGI is the inverse matrix differ-

ence between pattern and light intensity. Between 90

and 1500 OCT measurements, we set noise at 10%

of signal intensity in the OCT simulation (signal to

noise ratio ≈ 10%). The simulation results with noise

effects of reconstruction image quality are shown in

Figure 4. The noise is the random value on each pat-

tern in the gradation −25 ∼ 25, which is 10% image

value in the 8 bits image.

In Figure 4, starting with the number of measure-

ments from 200 to 1500, the DPGI results are the best,

and the PSNR value is beyond the acceptance value

of 30 dB at the 800 measurements. PSNR’s values

of PGI, DGI and CGI are all below 30dB. It can be

Figure 4: PSNR values derived from GI simulation with

10% noise.

concluded that the DPGI has the best reconstruction

efﬁciency for our OCT application.

As shown in Figure 5, we simulated the scatter and

target layers in the experiment. Based on the experi-

ment, we used a 10 × 10 pixel resolution in this simu-

lation. Figure 5 (a) shows the simulated scatter layer.

PHOTOPTICS 2023 - 11th International Conference on Photonics, Optics and Laser Technology

To simplify the calculation and to easily distinguish

the effect of the scatter layer, we masked 1/4 of the

area as a scatter layer. Figure 5 (b) shows the target

layer obtained from the photograph of the letter ’T’.

By loading a photograph with the letter ’T’ and resiz-

ing it to 10 × 10 pixel image. Because the OCT beam

is expanded in the GI-OCT measurement, causing the

light intensity distribution affects the target result, we

added the OCT beam to the simulation experiment, as

shown in Figure 5 (c). By using the DPGI method

on the 800 measurements with 10% random noise,the

image from the GI-OCT measurement is obtained and

shown in Figure 5 (d). Figure 5 (d) shows the image

of target layer overlapping the scatter layer and OCT

beam distribution with 10% random noise.

Figure 5: Simulation images. (a)scatter image. (b)light dis-

tribution. (c)target image. (d)overlaps (a), (b) and (c).

After correcting layer by layer with Figure 5 (d),

we obtain the results of GI-OCT, as shown in Fig-

ure 6. Figure 6 (a) shows the simulation results after

correcting the OCT beam distribution. This result is

corrected in Figure 5 (d) using the OCT beam distri-

bution in Figure 5 (c). Figure 6 (b) shows the result of

the corrected target layer, which can be successfully

identiﬁed as the letter ’T’. By calculating the PSNR

value for the reconstructed image in Figure 6 (b) with

the original image in Figure 5 (b), we get 47dB, which

is acceptable. Not only that, but we also reconstructed

the scatter layers and obtained Figure 6 (c). The re-

constructed scatter layers have the same distribution

as the original scatter layers in Figure 5 (c). Mean-

while, the OCT beam distribution(Figure 6c) is also

reconstructed with the same result of Figure 5 (c).

Figure 6: Simulation results. (a)target and scatter image

corrected light distribution. (b)target image corrected scat-

ter effect. (c)scatter image. (d)light distribution.

5 RESULTS

The distribution of the OCT beam, target layer, scat-

ter layer, and the target layer overlapping the scatter

layer was obtained from Experiments 1, 2, 3, and 4,

respectively.

Figure 7: The results of GI-OCT. (a) target layer distribution

overlapped beam distribution. (b) target layer distribution

overlapped beam distribution and scatter layer distribution.

Figure 7 (a) is the target layer distribution. It is

the result overlapped with the OCT probe beam dis-

tribution. A diagonal stroke can be seen from right

upper to left bottom, similar to the vertical stroke of

the character ”F”. It is difﬁcult to identify the two

horizontal strokes of the character ”F.”. Figure 7 (b)

is target layer overlapped by the scatter layer. This

result have the OCT probe beam and the scatter layer

distributions, too. No stroke of the character ”F” can

be recognized.

We normalize each image of GI-OCT results from

four experiments. First, we remove the OCT beam

distribution from the target layer distribution to ob-

tain Figure 8 (a). One stroke on the diagonal and two

vertical strokes can be clearly identiﬁed, forming the

Simulation and Experiment of Ghost Imaging-OCT Target Imaging in Scattering Media

character ”F”. We also remove the scatter distribution

from the target layer overlapped by the scatter layer

distribution to obtain Figure 8 (b). And this process

has recovered the OCT beam distribution.

Figure 8: GI-OCT reconstructed images. (a) target layer

distribution without beam distribution. (b) corrected tar-

get layer distribution without beam distribution and scatter

layer distribution.

Figure 9: GI-OCT-reconstructed images with binarization

of (a) original target layer image, (b) corrected target layer

image.

Figure 8 (b) shows the same distribution of the

character ”F” as show in Figure 8 (a). We regard

Figure 8 (a) as the original distribution of the target

layer image, and Figure 8 (b) as the target layer image

obtained after correction by scattering effects. The

PSNR of the corrected target layer image in Figure

8 (b) is calculated to be 18.08 dB with the original

target layer image in Figure 8 (a).

With an appropriate threshold value, binarization

can result in Figures 9 (a) and (b) from Figures 8 (a)

and (b). They have an identical distribution, and their

PSNR is 160 dB. Moreover, we quantify the average

stroke lengths of the character ”F” in Figure 9 (c) and

estimate the error rate to evaluate our experimental

results. The error rate is the ratio of the stroke length

of the reconstructed image to the length of the orig-

inal target stroke. In Figure 9 (c), the length of the

upper horizontal is 1.14 mm, the middle horizontal is

1.17mm, and the vertical stroke is 1.83 mm, and the

widths of these strokes are 0.36mm. As compared

to Figure 9 (a) and (b), we get the average length

of the upper horizontal, middle horizontal, and ver-

tical strokes, and their stroke widths are 0.98mm,

1.12mm, 1.70mm and 0.28 mm, and the error rates

are 14.0%, 4.2%, 7.1% and 22.2%, respectively. Er-

rors in stroke lengths and widths are smaller than

0.2mm.

Figure 10: The intensity error percentages between (a) the

original target layer compared with uniform distribution.

(b) the corrected target layer compared with uniform dis-

tribution. The uniform distribution is the binanirized ideal

image in Fig.9.

As a result of the GI reconstruction, the target

layer’s total transmission can be adjusted to reorder

the target’s actual transmittance distribution. In our

experiment, the original target layer’s total transmis-

sion is 47%. And the total transmission of the cor-

rected target layer is 47%, too. So we rearranged the

transmission distribution in Figure 8 (a) and (b). The

average transmission deviations in Figure 8 (a) and

(b) are 20.0% and 14.8%, respectively. The deviation

of each pixel is compared to an ideal uniform target

layer distribution, as shown in Figure 9. The vertical

coordinate is the deviation percentage of each pixel

with the mean transmission. The horizontal coordi-

nate indicates the pixel of the character from top to

bottom in Figure 8 (a) and (b). This indicates that

the solidiﬁcation of the pigment is not uniform. Due

to the limitation of the number of measurements and

not 100% reproducibility of the pattern intensity, the

target distribution is not completely consistent, so the

transmission deviation trends are partly consistent in

Figure 10. This deviation trend can be interpreted as

the actual target transmittance distribution.

6 CONCLUSION

Our research aims to eliminate the scattering inﬂu-

ence of scattering media on the target layer’s optical

properties, for which we propose a new method called

GI-OCT. We simulated the measurement of a target

layer affected by a scatter layer and added the effect

of the OCT beam and noise during the measurement.

The GI-OCT measurement method was used to ob-

tain a target layer without the scattering effects. A

PSNR value of 47 dB was obtained for the original

PHOTOPTICS 2023 - 11th International Conference on Photonics, Optics and Laser Technology

and corrected image by correcting the effects of the

OCT beam and noise.

In the experiment, we successfully reconstruct the

target layer distribution without scattering inﬂuence

by using the GI technique to the OCT measurement

path in a two-dimensional area. In the lower number

of measurements, the PSNR value of our results is

18.08dB, but the target layer of character ”F” can be

identiﬁable. In the binarized images, we successfully

acquired the target shapes without scattering effects

and obtained the PSNR value of 160dB. The quanti-

tative target length obtained an error smaller than the

resolution, which is 0.2mm.

Our next step is to work on the scattering effects

on image reconstruction in ﬂowing scatter.

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Simulation and Experiment of Ghost Imaging-OCT Target Imaging in Scattering Media