A pilot study of photoacoustic imaging system for improved real-time visualization of neurovascular bundle during...

Photoacoustic imaging, a noninvasive imaging based on optical excitation and ultrasonic detection, enables one to visualize the distribution of hemoglobin and acquire a map of microvessels without using contrast agents. We examined whether it helps visualize periprostatic microvessels and improves visualization of the neurovascular bundle.

We developed a photoacoustic imaging (PAI) system with a hand-held probe combining optical illumination and a conventional linear array ultrasound probe. In experiments with a phantom model, it was able to visualize vessels with diameters as small as 300 μm within a depth of 10 mm. We also developed a TRUS type probe for our photoacoustic imaging system and used it to intraoperatively monitor periprostatic tissues in seven patients with clinically organ-confined prostate cancer who were undergoing non-nerve-sparing retropubic radical prostatectomy. Images of periprostatic tissues from resected prostatectomy specimens were also obtained using the linear photoacoustic probe, and the consistency of the microvessel distribution and co-existence of nerve fibers was examined by double immunostaining of paraffin-embedded sections with anti-CD31 and anti-S-100 antibodies.

Intraoperative monitoring of periprostatic tissues with the TRUS photoacoustic probe showed substantial signals on the posterolateral surface of the prostate and clearly demonstrated the location and extent of the neurovascular bundle better than does TRUS alone. Photoacoustic images of the periprostatic tissues in resected specimens also showed substantial signals that were especially strong on the posterolateral surface of the prostate. Nerve fibers were closely co-localized with periprostatic microvessels and the pattern of their distribution was consistent with that of PAI signals.

The intraoperative photoacoustic imaging located the microvascular complex in the neurovascular bundle. Moreover, the neurovascular bundle was easier to identify by PAI than by TRUS alone, suggesting that PAI could be helpful in nerve-sparing radical prostatectomy.