Terahertz Reflection Imaging of Paraffin-embedded Human Breast

Cancer Samples: Some First Results

Mohamed Boutaayamou, Delphine Cerica and Jacques G. Verly

Department of Electrical Engineering and Computer Science, University of Liège, Liège, Belgium

Keywords: Terahertz Imaging, Breast Cancer, Paraffin-embedded Sample, Terahertz Absorbance.

Abstract: Several studies have shown that terahertz (THz) pulsed imaging has the potential of identifying the margins

of human breast cancer in paraffin-embedded tissue samples. Before using this technique for the assessment

of cancer margins during breast-conserving surgery, it is important to study the validity and reproducibility

of previously published results. In the present paper, we describe some first results in the characterization of

paraffin-embedded human breast cancer tissue through THz reflection imaging based on measurements

provided by a newly acquired THz time-domain spectrometer. First, we measured the THz reflection impulse

response of these samples using this spectrometer. Second, we processed, for one selected breast cancer tissue

sample, the recorded data to generate preliminary images of (1) several maps of parameters extracted in the

time- and frequency-domains, and (2) a map of the absorbance.

1 INTRODUCTION

One of the promising application of terahertz pulsed

imaging (TPI) is the characterization of biological

tissues, where terahertz (THz) means 10

Hz. In

particular, TPI has shown potential for identifying

human breast cancer during breast-conserving

surgery (Fitzgerald et al., 2006; Yu et al., 2012).

A key issue with this surgery is the more than 20%

rate of re-operation after postoperative

histopathological analysis of the cancer resection

margins (Jacobs, 2008). This rate results from the

current lack of accurate intraoperative cancer margins

assessment tools.

As a member of the TERA4ALL project consortium

that aims to promote THz technology applications

across the Walloon Region of Belgium, our group

investigates the use and validation of TPI in breast

cancer margins assessment, in the context of reducing

the re-operation rate of a breast-conserving surgery.

Previous studies (Fitzgerald et al., 2006; Ashworth

et al., 2009; Hassan et al., 2012; Bowman et al., 2017)

have already presented promising results of significant

contrast between normal and cancerous breast tissues

when TPI is applied to freshly excised or dehydrated

paraffin-embedded (PE) samples.

Although the water content of the tissue has been

shown to contribute significantly to the tissue’s optical

properties in the THz range, it has been suggested that

the interaction of THz radiation with this tissue may also

be sensitive to other factors, such as the tissues structure,

the cell density, and the presence of certain proteins

(Fitzgerald et al., 2006). These factors could explain

why imaging contrast between different tissue regions

can also be demonstrated for dehydrated samples

(Bowman et al., 2017).

In this paper, we describe some first results in the

characterization of PE human breast cancer tissue

samples through TPI in reflection mode using

measurements obtained by a newly acquired THz

time-domain (TD) spectrometer (Fig. 1).

Figure 1: Picture of the THz time-domain spectrometer

TeraPulse 4000 (TeraView Ltd, Cambridge, UK).

There are two motivations for the choice of

considering these samples for this first stage of

research. First, they are easy to obtain (from

biobanks), to carry, and to store. Second, additional

testing on PE human breast cancer samples would be

200

Boutaayamou, M., Cerica, D. and Verly, J.

Terahertz Reﬂection Imaging of Parafﬁn-embedded Human Breast Cancer Samples: Some First Results.

DOI: 10.5220/0009163302000203

In Proceedings of the 13th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2020) - Volume 2: BIOIMAGING, pages 200-203

ISBN: 978-989-758-398-8; ISSN: 2184-4305

required in order (1) to investigate the reproducibility

of previously published results, (2) to potentially

improve the methodology used to obtain these results,

and (3) to provide a better understanding of the origin

of contrast in TPI without the presence of water in the

tissue samples.

2 EXPERIMENT & METHOD

PE human breast tissue samples of various

thicknesses (10, 20, 30, and 50 µm), containing both

normal and cancerous regions, were provided by the

Biobank of the University Hospital of Liège

(Biothèque Hospitalo-Universitaire de Liège). The

present study was approved by the local ethics

committee of the University of Liège, Liège, Belgium

(Ref: 2017/175).

We used the THz TD spectrometer TeraPulse

4000 (TeraView Ltd, Cambridge, UK) to record the

impulse response (IR) of theses samples in open air

(Fig. 1). The experimental setup is schematically

represented in Fig. 2.

Figure 2: Schematic diagram of the experimental setup used

to measure the reflection THz IR of the sample.

The samples were mounted on glass slides. Thus, we

used the THz TD spectrometer in reflection mode as

THz radiation is strongly attenuated in glass. Prior to

scanning each sample, the reference IR (i.e., no sample

in the THz beam) was recorded from a gold-coated

alignment mirror (not shown in Fig. 1).

A sample of interest was then scanned point-by-

point in two orthogonal directions characterized by x-

and y-coordinates using a mapper unit (not shown in

Fig. 1). The scanning produced at each scan point a

full IR (signal), referred to as the measurement at this

point. The spatial scan step was 200 µm in each

direction. In addition, we used the TeraPulse software

to apply a fast Fourier transform (FFT) to the IR

obtained at each scan point, yielding the associated

frequency response (FR).

Figure 3: Picture of a 50 µm-thick sample.

Figure 4: Example of a recorded IR of the sample, in red,

and the recorded reference IR (using a gold-coated

alignment mirror), in blue.

In this paper, we consider the results from the

50 µm-thick sample shown in Fig. 3. Fig. 4 shows an

example of (1) a recorded reflected THz IR from the

surface of this sample and (2) the corresponding

reference IR.

We extracted several parameters both from the IR

recorded directly in the TD and from the FR

computed in the frequency-domain (FD). These

parameters are described later.

For each TD (respectively FD) parameter, we

assigned the parameter value at each measurement

point to a pixel in an image in order to create a THz

TD (respectively FD) image of this parameter.

We obtained the preliminary THz images by

assigning the following TD and FD parameters to each

pixel (corresponding to a measurement point):

• The normalized amplitude of the sample IR at a

given optical delay 𝑡



, i.e.,

𝐸



𝑡





max



|𝐸



𝑡





, (1)

where

𝐸





𝑡



is the amplitude of the IR (at the

measurement point of interest (Fig. 4)).

Computer

THz receiver

THz emitter

Sample

Optical delay line

Femtosecond

pulsed laser

Terahertz Reﬂection Imaging of Parafﬁn-embedded Human Breast Cancer Samples: Some First Results

201

• The normalized peak-to-peak amplitude of the

sample IR (Fig. 4), i.e.,

𝐸





−𝐸





max



|𝐸





−𝐸





(2)

• The normalized magnitude of the sample FR at a

given frequency 𝑓, i.e.,

𝐴

𝑝𝑖𝑥𝑒𝑙



𝑓



max



|𝐴

𝑝𝑖𝑥𝑒𝑙



𝑓



(3)

where

𝐴





𝑓



is the magnitude of the sample FR (at

a given measurement point of interest).

• The absorbance of the sample at a given

frequency 𝑓, is calculated using the Beer-

Lambert relation, i.e.,

−log





𝐴

𝑝𝑖𝑥𝑒𝑙



𝑓



𝐴

𝑟𝑒𝑓

𝑝𝑖𝑥𝑒𝑙



𝑓





(4)

where 𝐴







𝑓



is the magnitude of the reference FR

(obtained from the reference IR).

3 RESULTS & DISCUSSION

Figures 5-8 depict preliminary THz reflection images

of the aforementioned TD and FD parameters for the

50 µm-thick PE sample. These parameters are given

in arbitrary units ([a.u.]) or without units in the case

of the absorbance ([-]).

Figure 5: THz TD image obtained using the normalized

amplitude of the IR at optical delay 𝑡



of 9 ps, as defined

by Eq. (1).

Contrasted regions in the images allow one to

distinguish (1) areas of the glass slide with and

without a sample, (2) paraffin alone versus excised

PE tissue areas, and (3) some defects associated with

the sample (such as cracks and regions where the

paraffin had detached from the glass slide).

In addition, one can observe, in the images,

interesting contrasted regions that may correlate with

different types of tissue inside the excised tissue area.

A rigorous comparison with a histopathological

analysis is required before drawing any conclusion on

the potential meaning of these contrasted regions.

Figure 6: THz TD image obtained using the normalized

peak-to-peak amplitude of the IR, as defined by Eq. (2).

Figure 7: THz FD image obtained using the normalized

magnitude of the FR at 2.5 THz, as defined by Eq. (3).

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202

Figure 8: THz FD image of absorbance at 1 THz, as defined

by Eq. (4).

4 CONCLUSION & FUTURE

WORK

This paper shows preliminary THz images generated

from the THz reflection IR of excised PE human

breast cancer tissue samples on glass slides,

experimentally measured in open air using a newly

acquired THz TD spectrometer. Although contrasted

regions were identified, one would need to further

interpret these images by comparing them to the

results of a histopathological analysis.

Future work includes (1) the use of the THz TD

spectrometer with water-free (nitrogen-purged)

sample compartment for future measurements, (2) the

validation of contrasted regions by correlation with a

histopathological analysis, (3) the use of a different

sample slide material with low THz absorption

coefficient allowing TPI in transmission mode, (4)

TPI of fresh animal tissue and of fresh tissue

phantoms to characterize the optical properties of

these materials in the THz range before testing

valuable freshly-excised human breast cancer

samples, and (5) the development of signal-

processing algorithms dedicated to the assessment of

breast tumor margins.

ACKNOWLEDGEMENTS

This work was performed as part of the project

TERA4ALL which is funded by European Regional

Development Fund (ERDF) and Wallonia.

ABBREVIATIONS

The following abbreviations are used in this paper:

TPI Terahertz pulsed ima

THz Terahertz, 1 THz=10

Hz.

PE Paraffin-embedded.

TD Time-domain.

FD Frequenc

-domain.

IR Impulse response.

FR Frequenc

response.

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Terahertz Reﬂection Imaging of Parafﬁn-embedded Human Breast Cancer Samples: Some First Results

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