Frequency domain analysis of the photoacoustic (PA) radio frequency signals can potentially be used as a tool for characterizing microstructure of absorbers in tissue. This study investigates the feasibility of analyzing the spectrum of multiwavelength PA signals generated by excised human prostate tissue samples to differentiate between malignant and normal prostate regions. Photoacoustic imaging at five different wavelengths, corresponding to peak absorption coefficients of deoxyhemoglobin, whole blood, oxyhemoglobin, water and lipid in the near infrared (NIR) (700 nm – 1000 nm) region, was performed on freshly excised prostate specimens taken from patients undergoing prostatectomy for biopsy confirmed prostate cancer. The PA images were co-registered with the histopathology images of the prostate specimens to determine the region of interest (ROI) corresponding to malignant and normal tissue. The calibrated power spectrum of each PA signal from a selected ROI was fit to a linear model to extract the corresponding slope, midband fit and intercept parameters. The mean value of each parameter corresponding to malignant and adjacent normal prostate ROI was calculated for each of the five wavelengths. The results obtained for 9 different human prostate specimens, show that the mean values of midband fit and intercept are significantly different between malignant and normal regions. In addition, the average midband fit and intercept values show a decreasing trend with increasing wavelength. These preliminary results suggest that frequency analysis of multispectral PA signals can be used to differentiate malignant region from the adjacent normal region in human prostate tissue.
Prostate cancer is the second leading cause of death in American men after lung cancer. The current screening
procedures include Digital Rectal Exam (DRE) and Prostate Specific Antigen (PSA) test, along with Transrectal
Ultrasound (TRUS). All suffer from low sensitivity and specificity in detecting prostate cancer in early stages. There is a
desperate need for a new imaging modality. We are developing a prototype transrectal photoacoustic imaging probe to
detect prostate malignancies in vivo that promises high sensitivity and specificity. To generate photoacoustic (PA)
signals, the probe utilizes a high energy 1064 nm laser that delivers light pulses onto the prostate at 10Hz with 10ns
duration through a fiber optic cable. The designed system will generate focused C-scan planar images using acoustic lens
technology. A 5 MHz custom fabricated ultrasound sensor array located in the image plane acquires the focused PA
signals, eliminating the need for any synthetic aperture focusing. The lens and sensor array design was optimized
towards this objective. For fast acquisition times, a custom built 16 channel simultaneous backend electronics PCB has
been developed. It consists of a low-noise variable gain amplifier and a 16 channel ADC. Due to the unavailability of 2d
ultrasound arrays, in the current implementation several B-scan (depth-resolved) data is first acquired by scanning a 1d
array, which is then processed to reconstruct either 3d volumetric images or several C-scan planar images. Experimental
results on excised tissue using a in-vitro prototype of this technology are presented to demonstrate the system capability
in terms of resolution and sensitivity.
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