Using low cost and small size light emitting diodes (LED) as the alternative illumination source for photoacoustic (PA) imaging has many advantages, and can largely benefit the clinical translation of the emerging PA imaging technology. Here, we present our development of LED-based PA imaging integrated with B-mode ultrasound. To overcome the challenge of achieving sufficient signal-to-noise ratio by the LED light that is orders of magnitude weaker than lasers, extensive signal averaging over hundreds of pulses is performed. Facilitated by the fast response of the LED and the high-speed driving as well as the high pulse repetition rate up to 16 kHz, B-mode PA images superimposed on gray-scale ultrasound of a biological sample can be achieved in real-time with frame rate up to 500 Hz. The LED-based PA imaging could be a promising tool for several clinical applications, such as assessment of peripheral microvascular function and dynamic changes, diagnosis of inflammatory arthritis, and detection of head and neck cancer.

Photoacoustic spectrum analysis at either 1200 nm or 532 nm can allow differentiation of fatty from normal liver tissue in a mouse model by showing the microstructural changes associated with lipid and hemoglobin in the liver tissue. PurposeTo investigate the use of photoacoustic (PA) spectrum analysis (PASA) to identify microstructural changes corresponding to fat accumulation in mouse livers ex vivo and in situ.Materials and MethodsThe laboratory animal protocol for this work was approved by the university committee on use and care of animals. Six mice with normal livers and six mice with fatty livers were examined ex vivo with a PA system at 1200 nm, and nine similar pairs of mice were examined at 532 nm. To explore the feasibility of this technique for future study in an in vivo mouse model, an additional pair of normal and fatty mouse livers was scanned in situ with an ultrasonographic (US) and PA dual-modality imaging system. The PA signals acquired were analyzed by using the proposed PASA method. Results of the groups were compared by using the Student t test.ResultsProminent differences between the PASA parameters from the fatty and normal mouse livers were observed. The analysis of the PASA parameters from six normal and six ...

By using our dual-modality system enabling simultaneous real-time ultrasound (US) and photoacoustic (PA) imaging of human peripheral joints, we explored the potential contribution of PA imaging modality to rheumatology clinic. By performing PA imaging at a single laser wavelength, the spatially distributed hemoglobin content reflecting the hyperemia in synovial tissue in metacarpophalangeal (MCP) joints of 16 patients were imaged, and compared to the results from 16 healthy controls. In addition, by performing PA imaging at two laser wavelengths, the spatially distributed hemoglobin oxygenation reflecting the hypoxia in inflammatory joints of 10 patients were imaged, and compared to the results from 10 healthy controls. The statistical analyses of the PA imaging results demonstrated significant differences (p < 0.001) in quantified hemoglobin content and oxygenation between the unequivocally arthritic joints and the normal joints. Increased hyperemia and increased hypoxia, two important physiological biomarkers of synovitis reflecting the increased metabolic demand and the relatively inadequate oxygen delivery in affected synovium, can both be objectively and non-invasively evaluated by PA imaging. The proposed dual-modality system has the potential of providing additional diagnostic information over the traditional US imaging approaches and introducing novel imaging biomarkers for diagnosis and treatment evaluation of inflammatory arthritis.

This study investigates the feasibility of characterizing the microstructures within a biological tissue by analyzing the frequency spectrum of the photoacoustic signal from the tissue. Hypotheses are derived from theoretical analyses on the relationships between the dimensions/concentrations of the photoacoustic sources within the region-of-interest and the linear model fitted to the power spectra of photoacoustic signals. The hypotheses are validated, following the procedures of ultrasound spectrum analysis, by simulations and experiments with phantoms fabricated by embedding the polyethylene microspheres in porcine gelatin, indicating that photoacoustic spectrum analysis could be a potential tool for characterizing microstructures in biological samples.

Photoacoustic tomography (PAT) offers structural and functional imaging of living biological tissue with highly sensitive optical absorption contrast and excellent spatial resolution comparable to medical ultrasound (US) imaging. We report the development of a fully integrated PAT and US dual-modality imaging system, which performs signal scanning, image reconstruction, and display for both photoacoustic (PA) and US imaging all in a truly real-time manner. The back-projection (BP) algorithm for PA image reconstruction is optimized to reduce the computational cost and facilitate parallel computation on a state of the art graphics processing unit (GPU) card. For the first time, PAT and US imaging of the same object can be conducted simultaneously and continuously, at a real-time frame rate, presently limited by the laser repetition rate of 10 Hz. Noninvasive PAT and US imaging of human peripheral joints in vivo were achieved, demonstrating the satisfactory image quality realized with this system. Another experiment, simultaneous PAT and US imaging of contrast agent flowing through an artificial vessel, was conducted to verify the performance of this system for imaging fast biological events. The GPU-based image reconstruction software code for this dual-modality system is open source and available for download from http://sourceforge.net/projects/patrealtime.

With the capability of assessing high resolution optical contrast in soft tissues, photoacoustic imaging (PAI) can offer valuable structural and functional information of human joints, and hold potential for diagnosis and treatment monitoring of inflammatory arthritis. Recent studies have demonstrated that PAI can map 2D and 3D morphology of the cartilage, synovium, vascularity, and bone tissue in human peripheral joints. Initial trials with patients affected by inflammatory arthritis have also suggested that PAI can detect the hemodynamic properties in articular tissues as well as their changes due to active inflammation. This review focuses on the recent progress in technical development of PAI for human musculoskeletal imaging and inflammation detection. PAI can provide non-invasive and non-ionizing serial measurements for monitoring of therapeutic interventions with the potential for higher sensitivity than existing imaging modalities such as ultrasound. However, further investigation is needed to validate the value of PAI in rheumatology clinical settings.