Purpose: Transvaginal ultrasound (TVUS) is a widely used real-time and non-invasive imaging technique for fetal and maternal care. It can provide structural and functional measurements about the fetal brain, such as blood vessel diameter and blood flow. However, it lacks certain biochemical estimations, such as hemoglobin oxygen saturation (SO2), which limits its ability to indicate a fetus at risk of birth asphyxia. Photoacoustic (PA) imaging has been steadily growing in recognition as a complement to ultrasound (US). Studies have shown PA imaging is capable of providing such biochemical estimations as SO2 at relatively high penetration depth (up to 30 mm).
Approach: In this study, we have designed and developed a multi-modal (US, PA, and Doppler) endocavity imaging system (ECUSPA) around a commercialized TVUS probe (Philips ATL C9-5).
Results: The integrated system was evaluated through a set of in-vitro, ex-vivo, and in-vivo studies. Imaging of excised sheep brain tissue demonstrated the system’s utility and penetration depth in transfontanelle imaging conditions. The accuracy of using the spectroscopic PA imaging (sPA) method to estimate SO2 was validated by comparing sPA oximetry results with the gold standard measurements indicated by a blood gas analyzer. The ability of US and Doppler to measure moving blood volume was evaluated in-vivo. Spectral unmixing capabilities were tested using fluorophores within sheep brains.
Conclusion: The developed system is a high resolution (about 200 μm at 30 mm depth), real-time (at 30 Hz), and quantitative (SO2 estimation error <10 % ) imaging tool with a total diameter less than 30 mm, making it suitable for intrapartum applications such as fetal and maternal diagnostics.
Given that breast cancer is the second leading cause of cancer-related deaths among women in the United States, it is necessary to continue improving the sensitivity and specificity of breast imaging systems that diagnose breast lesions. Photoacoustic (PA) imaging can provide functional information during in vivo studies and can augment the structural information provided by ultrasound (US) imaging. A full-ring, all-reflective, illumination system for photoacoustic tomography (PAT) coupled to a full-ring US receiver is developed and tested. The US/PA tomography system utilizes a cone mirror and conical reflectors to optimize light delivery for PAT imaging and has the potential to image objects that are placed within the ring US transducer. The conical reflector used in this system distributes the laser energy over a circular cross-sectional area, thereby reducing the overall fluence. This, in turn, allows the operator to increase the laser energy achieving better cross-sectional penetration depth. A proof-of-concept design utilizing a single cone mirror and a parabolic reflector is used for imaging cylindrical phantoms with light-absorbing objects. For the given phantoms, it has been shown that there was no restriction in imaging a given targeted cross-sectional area irrespective of vertical depth, demonstrating the potential of mirror-based, ring-illuminated PAT system. In addition, the all-reflective ring illumination method shows a uniform PA signal across the scanned cross-sectional area.
Due to the high rate of gynecologic cancers among females, obtaining structural, functional, and molecular information from reproductive organs can potentially reveal diseases at their early stages of development . In this study, we aimed to develop a miniaturized phased-array ultrasound (US) and photoacoustic (PA) endoscope for potential imaging gynecologic cancer. The developed endoscope is built around a phased-array US transducer coupled to a fiber optic light delivery system. In particular, the proposed endoscope consists of a 64-element phased array US transducer, coupled to a light delivery system that includes six fiber optics. The probe dimensions allow for utilizing this device for imaging various types of gynecologic cancers in which the probe can become close to the pathologic tissue. Given the small imaging aperture, adaptive beamforming was developed to reconstruct co-registered US and PA images in 90-degrees sector scan format. The developed endoscope was tested in a set of tissue-mimicking phantom studies to determine its characteristics and its ability to form form co-registered volumetric US and PA images. In addition, spectroscopic PA (sPA) imaging of biocompatible, folate conjugated dye was tested to demonstrate the possibility of using the developed endoscope in imaging PA molecular contrast agents.
Among various types of cancer, breast cancer is considered to be the most common that affects thousands of women all over the world. Several imaging tools are being used for breast cancer detection and diagnosis. Mammography and B-mode ultrasound (US) are the primary screening tools for breast lesions. However, mammography is limited with low sensitivity especially in women with dense breasts, who appear to be at higher risk of breast cancer. Additionally, the B-mode US suffers from low specificity in the differential diagnosis of breast lesions. Therefore, it is clinically significant to develop screening techniques that could eliminate previous limitations. Photoacoustic (PA) has been showing potential for early stage detection and staging breast cancer due to its unique abilities to acquire functional and molecular information of the breast lesions. We have developed an optimized US and PA tomography system, which uses custom designed all reflective based optics to create an omnidirectional ring-shaped beam to illuminate a cross-section of the breast tissue and acquire thegenerated acoustic waves by using a full-ring US transducer. The developed PA tomography (PAT) system can potentially make a more uniform illumination of the breast tissue and more importantly enhance the imaging depth. In this study, development of the full-ring illumination and the results of our initial feasibility US/PA tests are presented.
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