To investigate a link between the appearance of photoacoustic imaging (PAI) and microvasculature in prostate cancer and to assess the feasibility of PAI for angiogenesis imaging in prostate cancer.

We have developed a PAI system equipped with a transrectal ultrasound (TRUS)-type probe. Three patients who underwent PAI just before prostate biopsy and subsequently underwent radical prostatectomy were included. The PAI appearance was retrospectively reviewed, and in each patient, 4 representative areas were selected: 1 with high PAI signal intensity, 1 with low PAI signal intensity, 1 peripheral to the index tumor, and 1 inside the index tumor. The correlation of PAI intensity with 3 microvascular parameters—microvascular density, total vascular area (TVA), and total vascular length (TVL)—assessed by CD34-immunostaining in resected specimens was analyzed.

In all 3 patients the PAI intensity, TVA, and TVL in areas with high-intensity PAI signals were significantly higher than those in areas with low-intensity PAI signals, suggesting that PAI appearance describes the distribution of microvasculature in prostatic tissue correctly. All index tumors showed a ring-like PAI appearance consisting of a peripheral area of high signal intensity completely or partially surrounding an area with low signal intensity. The PAI intensity, TVA, and TVL in the periphery of the index tumors were significantly higher than those inside of the index tumors.

The intensity of PAI signals might reflect the microvascularity in normal prostatic tissues and index tumors. PAI could be a novel modality for imaging prostate cancer angiogenesis.