Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_16_3270 - Endocavity Ultrasound and Photoacoustic Imaging to Evaluate Cervical Cancer Oxygenation: Preliminary Ex Vivo Results

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Endocavity Ultrasound and Photoacoustic Imaging to Evaluate Cervical Cancer Oxygenation: Preliminary Ex Vivo Results
M. Dziemianowicz1, M. M. Dominello2, J. W. Burmeister2, M. Basij1, Y. Yan1, and M. Mehrmohammadi1; 1Wayne State, Detroit, MI, 2Department of Oncology, Wayne State University School of Medicine, Detroit, MI

Purpose/Objective(s): Hypoxia is a common feature of cervical cancer and may have a significant impact on the efficacy of radiotherapy. Current modalities for measuring tumor hypoxia such as BOLD MRI and PET-based hypoxia tracers are cumbersome, expensive, and thus not well suited for routine clinical use. Photoacoustic (PA) imaging is an ultrasound (US)-based modality that is capable of imaging hemoglobin oxygen saturation in tissues and blood vessels. In this study, we describe preliminary measurements using a miniaturized phased-array US/PA endoscope that can image through the cervical canal and assess tissue oxygenation.

Materials/Methods: The endoscope consists of a 64-element phased array US transducer, operated between 5 and 8 MHz. It is coupled to a light delivery system and has a total diameter less than 4.2 mm. The light delivery design yields aligned and overlapped ultrasound and light beams required for PA imaging. Given the small imaging aperture, an adaptive beamforming technique was developed to reconstruct co-registered US and PA images in a 90-degree sector format. Acquired US and PA signals were used to reconstruct real-time co-registered images. Ex vivo validation for the blood oxygenation (SO2) measurement involved development of a blood-gas exchange system, to induce different blood SO2 levels in heparinized sheep’s blood between 46%-100%. Spectroscopic PA (sPA) imaging was performed to evaluate measure blood SO2 and sPA measurements were validated using a blood gas analyzer.

Results: The US/PA endoscope was tested in acquiring volumetric (3D) images of tissue-mimicking phantoms, simulating the imaging through the cervical canal. Co-registration of US and PA imaging demonstrate axial and lateral resolutions of 580 μm and 1.31 mm (at 25 mm depth) respectively. Analysis of PA oximetry compared with the blood gas analyzer showed high correlation (R2=0.87), demonstrating the accuracy of sPA imaging in noninvasive measurement of hemoglobin oxygenation over a broad range of SO2 variation (46-100%). While more imaging depth characterization studies are required, we anticipate that PA imaging in a clinical in vivo setting will be effective to a depth of 15 mm.

Conclusion: This study demonstrates the feasibility of developing a miniaturized US/PA endoscope, accurately measuring tissue oxygenation using sPA, and achieves high-resolution volumetric co-registered US and PA imaging in cervical canal mimicking phantoms. This modality has the potential to provide a convenient, minimally-invasive, and less-expensive approach to measuring tumor hypoxia that may be more suited to clinical practice than available imaging techniques. Current work is focused on developing a technique to co-register the available PA and US imaging with treatment planning scans, which would allow incorporation of hypoxia data into brachytherapy treatment planning for cervical cancer.

Author Disclosure: M. Dziemianowicz: None. M.M. Dominello: None. J.W. Burmeister: Research Grant; NIH. Board Member; SDAMPP. Chair, Radiation Oncology Physics Exam Committee; American Board of Radiology. M. Basij: None. Y. Yan: None.

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