A Single-Motor system for 3D Spiral Photoacoustic and Ultrasound Imaging of Rectal Cancer In Vivo

Colorectal cancer is the 3rd most prevalent cancer in the United States. Photoacoustic imaging reveals vascular contrast of the tumor and can be used to assess and predict treatment response of rectal cancer patient undergoing radiation and neoadjuvant therapy. A compact and portable endorectal acoustic resolution photoacoustic microscopy and ultrasound (ARPAM/US) system was developed and translated to clinics for patient evaluation. The current system utilizes hollow shaft motor, connected to the imaging head for 360o clockwise and anticlockwise rotation to acquire 2D images. Each rotation provides co-registered photoacoustic and ultrasound B-scan images with 1000 A-lines in one second. The characterization of the system with a 7um carbon fiber revealed the axial resolution for ultrasound and photoacoustics to be 35µm and 72µm, and the lateral resolution of 122 µm and 116 µm respectively. Currently, 4 patients have been imaged in-vivo with the hand-held probe in an ongoing clinical trial. We show an in vivo ARPAM/US imaging example to demonstrate the performance of the current system. However, even operated by steady hands of surgeons, it is challenging to acquire 3D images for better visualization of rectal tumors. We designed and implemented a novel 3D imaging probe. The proposed single motor design utilizes a unique rotation and translation coupler design. A =-28 threaded shaft facilitates translation of 0.9mm per rotation with over 2cm translation limit. The images can be stitched together to generate 3D spiral images of co-registered ultrasound and photoacoustics for better visualization of the tumor.