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Photoacoustic (PA) imaging, which is a hybrid emerging soft tissue imaging technique, can be potentially used for efficient detection of soft tissue characterization. PA imaging offers optical absorption property based contrast which can be utilized to detect various tissue pathologies at the early stage. Although pure optical imaging also offers optical property based contrast, unlike PA imaging it cannot maintain good resolution at significant depth inside the tissue due to significant scattering of light inside soft tissue. In this study, a dual mode photoacoustic microscopy and ultrasound (US) imaging system will be assembled for in vivo breast imaging. Breast cancer is one of the most common malignancies among women globally. Early and efficient detection of breast cancer can potentially reduce the number of breast cancer induced deaths as well as lead to better prognosis and breast cancer management of the patients. Although PA imaging can provide useful functional information about soft tissue for efficient detection of the malignant lesion, it cannot provide sufficient anatomical cues for localization of the detected lesion. For localization of malignant tumor already detected by the PA imaging, US imaging is required. The proposed Photoacoustic microscopy system will employ a high energy nanosecond Nd:YAG laser of wavelength 1064 nm to generate the PA waves which will be detected using a single element focused 7.5 MHz ultrasound transducer. Once assembled, detail characterization of the PA microscopy system will be performed. 2D point spread function (PSF) of the PA microscopy system will be measured using point targets [lead pencil/steel wires with small radius] in the water bath. Using the same target in the water bath, 2D PSF corresponding to pulse echo US imaging will also be determined. From the 2D PSF, the axial resolution and lateral resolution corresponding to both PA as well as US imaging will be computed. For acquiring the 2D PSF, the point targets will be scanned along lateral direction using a linear stage. For measuring the sensitivity of the system, special purpose phantoms, in which point targets will be embedded at different depths, will be created. Using these phantoms, which will simulate the optical as well as ultrasound properties of soft tissue, the sensitivity of the system will be measured at different depths. For computing sensitivity at different depths, the corresponding signal to noise ratio will be computed from the acquired PA data. Once the characterization of the system is completed, phantoms simulating the optical as well as ultrasound properties of the human breast with malignant lesion will be prepared and experiments will be performed to acquire PA as well as US data of the phantoms.
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