Performance validation of improved photoacoustic / ultrasound superposed imaging system for evaluation of diabetic neuropathy

We developed a Photoacoustic (PA) imaging system which could be realized the fusion of PA and conventional Ultrasound (US) image. The prototype PA system for clinical study had comprised a 755 nm laser light source, and a 9 MHz US linear array probe. We successfully observed median and sural nerve bundles with US image, and PA images of blood vessels around and in that nerve bundles in the clinical study for diabetic patients. We applied this experimental design and concept to evaluate diabetic neuropathy, most common microvascular complication, to patients with type 2 diabetes. As results of the preliminary clinical trials, we found two technological challenges to overcome. The first technological challenge is to improve nerve bundle US image quality by higher frequency detection. The second challenge is to change the wavelength of laser light in order to clarify the relation between PA signal intensity and clinical staging of diabetic neuropathy. Owing to these technical challenges, the system was extended to a combination of 1064 nm and 12 MHz US linear array probe. We verified the performance of the extended prototype PA system compared with the previous system using a specially designed rabbit hypoxia model. Histologic examination was confirmed by a fusion image of PA image from sciatic nerve vessel and US morphologic image. We also performed preliminary clinical study to patients with type 2 diabetes and patient with amputation leg. The extended photoacoustic / ultrasound superposed imaging system succeed in the visualization of the nerve bundle and its internal and external blood vessels clearly. PA imaging was shown to be useful for prediction of risk of foot amputation and early detection of diabetic neuropathy.