Comparison of transrectal photoacoustic, Doppler, and magnetic resonance imaging for prostate cancer detection

Transrectal ultrasonography (TRUS) is the most popular imaging modality for diagnosing and treating prostate cancer. TRUS-guided prostate biopsy is mandatory for the histological diagnosis of patients with elevated serum prostate specific antigen (PSA), but its diagnostic accuracy is not satisfactory due to TRUS's low resolution. As a result, a considerable number of patients are required to undergo an unnecessary repeated biopsy. Photoacoustic imaging (PAI) can be used to provide microvascular network imaging using hemoglobin as an intrinsic, optical absorption molecule. We developed an original TRUS-type PAI probe consisting of a micro-convex array transducer with an optical illumination system to provide superimposed PAI and ultrasound images. TRUS-type PAI has the advantage of having much higher resolution and greater contrast than does Doppler TRUS. The purpose of this study was to demonstrate the clinical feasibility of the transrectal PAI system. We performed a clinical trial to compare the image of the cancerous area obtained by transrectal PAI with that obtained by TRUS Doppler during prostate biopsy. The obtained prostate biopsy cores were stained with anti-CD34 antibodies to provide a microvascular distribution map. We also confirmed its consistency with PAI and pre-biopsy MRI findings. Our study demonstrated that transrectal identification of tumor angiogenesis under superimposed photoacoustic and ultrasound images was easier than that under TRUS alone. We recognized a consistent relationship between PAI and MRI findings in most cases. However, there were no correspondences in some cases.