Abstract
.Opto-acoustic imaging involves using light to produce sound waves for visualizing blood in biological tissue. By using multiple optical wavelengths, diagnostic images of blood oxygen saturation and total hemoglobin are generated using endogenous optical contrast, without injection of any external contrast agent and without using any ionizing radiation. The technology has been used in recent clinical studies for diagnosis of breast cancer to help distinguish benign from malignant lesions, potentially reducing the need for biopsy through improved diagnostic imaging accuracy. To enable this application, techniques for mapping oxygen saturation differences within tissue are necessary. Using biologically relevant opto-acoustic phantoms, we analyze the ability of an opto-acoustic imaging system to display colorized parametric maps that are generated using a statistical mapping approach. To mimic breast tissue, a material with closely matching properties for optical absorption, optical scattering, acoustic attenuation, and speed of sound is used. The phantoms include two vessels filled with whole blood at oxygen saturation levels determined using a sensor-based approach. A flow system with gas-mixer and membrane oxygenator adjusts the oxygen saturation of each vessel independently. Datasets are collected with an investigational Imagio® breast imaging system. We examine the ability to distinguish vessels as the oxygen saturation level and imaging depth are varied. At depth of 15 mm and hematocrit of 42%, a sufficient level of contrast to distinguish between two 1.6-mm diameter vessels was measured for an oxygen saturation difference of . In addition, an oxygenated vessel was visible at a depth of 48 mm using an optical wavelength of 1064 nm, and a deoxygenated vessel was visible to a depth of 42 mm with 757 nm. The results provide insight toward using color mapped opto-acoustic images for diagnosing breast cancer.
Highlights
Structural and functional information pertaining to total hemoglobin concentration and blood oxygen saturation can be visualized with OA, while morphological and anatomical information can be obtained with ultrasound
We have presented a method for characterizing colorized OA image maps that display spatial information regarding relative blood oxygen saturation and hemoglobin in tissue
In the polyvinyl chloride plastisol (PVCP) phantom, it was measured that distinguishing the two vessels required a sO2 difference of 4.6%, when imaged at 15 mm depth and at 42% hematocrit
Summary
Over the past 25 years, a growing community of researchers, clinicians, and device manufacturers have been investigating and developing translational opto-acoustic (OA) imaging technologies with the aim of improving clinical care for several diseases.[1,2,3,4,5,6] For breast cancer diagnosis, one promising technique is OA imaging combined with ultrasound (OA/US).[7,8,9,10,11,12,13,14,15,16,17,18,19,20] Combining OA with ultrasound is advantageous because each modality provides information that is complementary to the other. Structural and functional information pertaining to total hemoglobin concentration (ctHb) and blood oxygen saturation (sO2 ) can be visualized with OA, while morphological and anatomical information can be obtained with ultrasound. In conventional ultrasound, which is commonly used to assess and characterize breast masses, there is large overlap between benign and malignant image features, which results in false-positive cases that must be confirmed with subsequent biopsy.[21,22,23] OA can provide functional information about the metabolism of tumors by imaging blood and vascular structure, OA involves several physical principles that make it ideally suited for diagnostic breast imaging. Due to the composition of breast tissue, scattered light can penetrate to a depth of several centimeters, which is suitable for clinical applications
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