Single Fiber Perfusion Phantom for OpticalCoherence Tomography

Petra Podlipna1,2 and Radim Kolar1,2

1International Clinical Research Center - Center of Biomedical Engineering, St. Anne’s University Hospital Brno,Pekarska 53, 656 91 Brno, Czech Republic

2Department of Biomedical Engineering, Faculty of Electrical Engineering and Communication, Brno University ofTechnology, Technicka 3058/10, 616 00, Brno, Czech Republic

podlipna@phd.feec.vutbr.cz

Abstract: This paper presents the successful construction of perfusion flow phantom and itsbasic experiment with optical coherence tomography. It is created from polypropylene hollowfiber with porous walls and gold nanoparticles solution is used as a flowing medium.© 2013 Optical Society of America

OCIS codes: 170.4500, 170.3880, 350.4990

1. Introduction

Optical coherence tomography (OCT) is promising imaging method. It produces high-resolution cross-sectional im-ages using near-infrared light. Basically, it maps the local reflectivity of scattering samples, for example living tissues.It is able to visualize the morphology and in special cases also physiology (Doppler OCT imaging, polarization-sensitive OCT, etc.). [1–3]

Since the introduction of OCT in 1991 [1], applications of OCT have spread into various areas of research and alsoclinical practice and many enhancements have been presented. The first clinical application emerged in ophthalmologyand OCT became accepted as a clinical standard in this field. Nowadays, OCT is becoming an important instrument inclinical cardiology. [2]

As the OCT is quickly developing area, there is need for tissue simulating phantoms with determined properties fortesting new approaches and technologies. Current papers describe various types of tissue phantoms for OCT [4] fromsimple Intralipid solutions [5, 6] to a multilayer tissue phantom with embedded capillary system [7]. However, to thebest of our knowledge, this is the first attempt to create a perfusion phantom. This paper presents the construction ofperfusion flow phantom for optical coherence tomography. A basic experiment for verification of the phantom functionis also described.

2. Materials and Methods

The fundamental part of created phantom is polypropylene hollow fiber with porous walls. Pores size is irregular inthe range of tens to hundreds of nanometers. This fiber is embedded in glass capillary with 1 mm inner diameter and170µm wall thickness (see detail in Fig. 1) to provide acceptable volume of outer environment of the fiber. Both endsof capillary are sealed with beeswax. The inner volume of the glass capillary was filled with distilled water throughthe fiber. Before filling, pores of the fiber had to be activated by pure ethanol, which was subsequently washed out bywater. The fiber is connected with syringe pump by silicon tube. During OCT measurements, constant flow rate 0.2 mlper minute was set.

For this experiment, Swept Source OCT system (Thorlabs, OCS1300SS, center wavelength 1325 nm) was used.In contrast to the original approach described in [1], this system acquire the depth information from the sample bysweeping a narrow linewidth laser through a broad optical bandwidth [8]. The complete scheme of experimental setupis shown in Figure 1.

The solution of gold nanorods was used to test their transport through the permeable membrane. Gold nanorods(Sigma-Aldrich, 716839) are in a form of colloidal suspension with water in concentration 30µg ml−1. Their declaredproportions are 10 nm diameter and 45 nm length. Generally, gold nanorods are widely used for various biomedical ap-plications, from imaging to therapeutical applications. They are very promising due to their tunable optical propertiesand good biocompatibility [9–11].

Fig. 1. Scheme of experimental setup. Detail on the right shows hollow fiber embedded in waterfilled glass capillary.

Before the experiment, the fiber must be activated to remove the air and make the fiber hydrophilic. The flow ofpure ethanol and its flow through the fiber membrane was scanned by OCT, see Figure 2 for illustration.

At the start of the measurement, hollow fiber and glass capillary were filled with distilled water. Then pumpingof gold nanorods solution had started and capillary was being continuously scanned by OCT. Except from imageextraction from raw data obtained from OCT device, no extra processing was performed on the data.

3. Results

Obtained tomographical images are shown in Figure 2. The left image shows the state in the middle of the ethanol flowcurrently activating pores. The specific shapes in the image are caused by mixing the ethanol with water due to theirdifferent refractive indices. In the middle image the initial state with both fiber and capillary filled only with water isdisplayed. The last image shows the state after several minutes of gold nanorods solution pumping is displayed. Thegold nanoparticles were visible as small moving dots inside and also outside the hollow fiber. Due to high flow ratethrough the fiber, there is only small number of dots visible inside the hollow fiber. Details in each corner of imagesin Figure 2 shows the difference between pre- and post-pumping state better.

Fig. 2. Semi-permeable hollow fiber embedded in glass capillary imaged by OCT. From left: fiberfilled with pure ethanol for pores activation, fiber and capillary filled with distilled water, fiber filledwith gold nanorods solution. Details in corners have enhanced contrast.

4. Conclusion

In this paper, we have presented, to the best of our knowledge, the first perfusion phantom for optical coherencetomography. For this phantom, the polypropylene hollow fiber with porous walls was used and embedded in glasscapillary filled with distilled water as an outer environment. The testing of created phantom was performed by pumpingthe gold nanorods solution through the fiber. Above described results are very promising. We have proved that thefiber is permeable for used gold nanorods which are frequently declared as possible contrast agents for OCT andthis permeability can be displayed by OCT. This opens the broad area of research. Our future work will be focused onimprovement of experiment equipment to provide more comfortable work and also on finding other suitable substancesthat will be able to permeate through fiber wall and detected by OCT. Next step then will include quantitative detectionof this permeate, determination of perfusion curves and estimation of perfusion parameters under different conditions.

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