Photoacoustic Tomography (PAT)

Ovarian Cancer

Of all the gynecological cancers, ovarian cancer registers the highest mortality rate, standing out as the ninth most common type of cancer and the fifth deadliest cancer in the US. Ovarian cancer occurs in the ovary cells; cells responsible for female reproduction and the production of progesterone and estrogen in women. Cancer starts when the cells in the ovary start multiplying uncontrollably to form a tumor. This tumor spreads to the rest of the body.

Photoacoustic Tomography (PAT)

It is commonly known termed as thermoacoustic tomography. It is one of the latest trends in medical imaging modality that combines ultrasound and optical techniques for cancer screening while avoiding the application of excising tissue or ionizing radiation. The tissue is exposed to a laser beam that causes it to expand. This expansion creates a broadband ultrasound signal that works on a reflection concept (Alqasemi et al. 2013). Measurements are taken on some different positions. The ultrasound is the input that helps in the image reconstruction to produce maps indicating the absorbed optical densities.

Various research groups have developed different photoacoustic imaging probes. One of the probes is configured to deliver light to the tissue while the other probe serves with the ultrasound transducer. For this research, the probes used to measure between a few and a hundred microns. The probes have a small diameter hence have a limitation at the end to preserve them. Fiber bundled probes, on the other hand, are wider and are more flexible (Jiang 2015).  Although they also apply to the photoacoustic imaging, their size makes them unfavorable for transvaginal ultrasound probes. They device normally have a higher light loss during transmission.

Optical Fiber-based Transvaginal Photoacoustic/ Ultrasound Imaging Probe

It incorporates a special design for the detection of ovarian cancer. It includes a much improved light delivery system, it is cheap and has a longer robust period of work.  The light delivery part is made up of light coupling optics, a transducer sheath with highly reflecting aluminum on the inside and multi-mode optical fibers around the ultrasound transducer (Stack & David 2009). The aluminum covering on the inside facilitates the reflection and transportation of light. The probe’s design considers output power efficiency and light fluence as the key factors.

Although the probe fluence level and energy efficiency levels are favorable for transvaginal photoacoustic, the probe still applies to other endoscopic designs. During the design of the probe, the researchers considered two critical parameters. These parameters affect the rate of light penetration into the tissues. One of the parameters is the light output efficiency, for a given power level. The other is the fluence of the tissue surface. It is highly recommended to set it on a high output efficiency at the probe to improve the SNR of the image. Also, the fluence of the probe should be kept at an optimal level as it can harm the patient.

The probe has a connection to an automated image collection system that receives and analyzes the appropriate signals through the transducer. It outlays the picture on a monitor instantly (Wang, Molly & Quing 2015). Moreover, the system is equally capable of detecting and processing co-register echo and pulse ultrasound imaging. By this capability, it is possible to obtain both the functional and morphological information from the ovarian tissues.

From research (EX VIVO), the photoacoustic images taken using the probe produced images showing a clear distinction between network and blood vascular, absent in normal ovaries, making the probe the most suitable for the characterization of ovarian tissue.  

The output light beams should be configured to maintain a high production efficiency on the probe, and an excellent fluence under the MPE. For the research and design of the probe, aluminum was the perfect internal coating due to its low-cost value and high reflective properties. Alternatively, the silver foil can also replace aluminum for the same purpose in the future.

 

Work Cited

Alqasemi, Umar, Patrick D. Kumavor, Hai Li, Alexander A. Oraevsky, Behnoosh Tavakoli, Lihong V. Wang, Yi Yang, and Quing Zhu. “Transvaginal Photoacoustic Imaging Probe and System Based on a Multiport Fiber-Optic Beamsplitter and a Real Time Imager for Ovarian Cancer Detection.” 8581 (2013). Print.

Jiang, Huabei. Photoacoustic Tomography., 2015. Print.

Stack, M S, and David A. Fishman. Ovarian Cancer. New York: Springer, 2009. Print

Wang, Tianheng, Molly Brewer, and Quing Zhu. “An Overview of Optical Coherence Tomography for Ovarian Tissue Imaging and Characterization.” Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology. 7.1 (2015): 1-16. Print.

 

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