Photoacoustic tomography for imaging the prostate: a transurethral illumination probe design and application

Min Ai,Shuo Tang,Septimiu E Salcudean,Robert Rohling,Jong-In Youn,Purang Abolmaesumi

doi:10.1364/boe.10.002588

Abstract

In vivo imaging of prostate cancer with photoacoustic tomography is currently limited by the lack of sufficient local fluence for deep tissue penetration and the risk of over-irradiation near the laser-tissue contact surface. We propose the design of a transurethral illumination probe that addresses those limitations. A high energy of 50 mJ/pulse is coupled into a 1000-µm-core diameter multimode fiber. A 2 cm diffusing end is fabricated, which delivers light in radial illumination. The radial illumination is then reflected and reshaped by a parabolic cylindrical mirror to obtain nearly parallel side illumination with a doubled fluence. The fiber assembly is housed in a 25 Fr cystoscope sheath to provide protection of the fiber and maintain a minimal laser-tissue contact distance of 5 mm. A large laser-tissue contact surface area of 4 cm2 is obtained and the fluence on the tissue surface is kept below the maximum permissible exposure. By imaging a prostate mimicking phantom, a penetration depth of 3.5 cm at 10 mJ/cm2 fluence and 700 nm wavelength is demonstrated. The results indicate that photoacoustic tomography with the proposed transurethral probe has the potential to image the entire prostate while satisfying the fluence maximum permissible exposure and delivering a high power to the tissue.

Highlights

Prostate cancer (PCa) is the most common cancer and the second leading cause of cancer deaths among North American men [1]
Digital rectal examination (DRE) is limited by a low overall sensitivity (37%) [3] and prostatespecific antigen (PSA) is limited by a low specificity (36%) [4]
When multi-parametric MRI (mpMRI) is available, it can be fused with US in order to guide some of the biopsy sampling to areas that appear suspicious on mpMRI [8]

Summary

Introduction

Prostate cancer (PCa) is the most common cancer and the second leading cause of cancer deaths among North American men [1]. Digital rectal examination (DRE) and serum prostatespecific antigen (PSA) are the current techniques for early detection of PCa. Upon a suspicious DRE and/or a high PSA reading, a transrectal ultrasound (TRUS) guided systematic random biopsy is performed [2]. Various magnetic resonance imaging (MRI) techniques have been investigated for detecting PCa and show a consistently higher accuracy than conventional ultrasound (US) [7]. Unavoidable movements of the prostate affect the US-MRI registration and lead to biopsy localization error [9,10]. Regardless of the techniques, since not all prostate tissue is sampled, there could be underestimation of the Gleason score which is related to PCa aggressiveness used in PCa patient management [6]

Methods

Findings

Discussion

Conclusion