Short-lag spatial coherence beamforming of photoacoustic images for enhanced visualization of prostate brachytherapy seeds

Abstract

Abstract:Prostate brachytherapy, administered by implanting tiny radioactive seeds to treat prostate cancer, currently relies on transrectal ultrasound imaging for intraoperative visualization of the metallic seeds. Photoacoustic (PA) imaging has been suggested as a feasible alternative to ultrasound imaging due to its superior sensitivity to metal surrounded by tissue. However, PA images suffer from poor contrast when seeds are distant from the light source. We propose a transperineal light delivery method and investigate the application of a short-lag spatial coherence (SLSC) beamformer to enhance low-contrast photoacoustic signals that are distant from this type of light source. Performance is compared to a conventional delay-and-sum beamformer. A pure gelatin phantom was implanted with black ink-coated brachytherapy seeds and the mean contrast was improved by 3-25 dB with the SLSC beamformer for fiber-seed distances ranging 0.6-6.3 cm, when approximately 10% of the receive aperture elements were included in the short-lag sum. For fiber-seed distances greater than 3-4 cm, the mean contrast-to-noise ratio (CNR) was approximately doubled with the SLSC beamformer, while mean signal-to-noise ratios (SNR) were mostly similar with both beamformers. Lateral resolution was decreased by 2 mm, but improved with larger short-lag values at the expense of poorer CNR and SNR. Similar contrast and CNR improvements were achieved with an uncoated brachytherapy seed implanted in ex vivo tissue. Results indicate that the SLSC beamformer has potential to enhance the visualization of prostate brachytherapy seeds that are distant from the light source.

Identification and removal of laser-induced noise in photoacoustic imaging using singular value decomposition

“…As with wavelet denoising [15, 20], SVD could also be used to reduce residual noise, for instance by performing a second truncation of the singular value matrix in which diagonal elements of the singular value matrix that are below a certain threshold are zeroed [15–17]. Examples of artifact reduction methods that have recently shown promise include localised vibration tagging [11], short-lag spatial coherence weighting [12, 21,22], and synthetic aperture PA-guided focused US [13]. …”

Spatial Angular Compounding ofPhotoacoustic Images

“…To evaluate the quality of compounded PA images, contrast, CNR, and SNR were computed with normalized envelope-detected data as follows [8], [14]: $$\text{Contrast}=\frac{{\mu }_s-{\mu }_n}{{\mu }_n}$$ $$\text{CNR}=\frac{\mid {\mu }_s-{\mu }_n\mid }{{\sigma }_n}$$ $$\text{SNR}=\frac{{\mu }_s}{{\sigma }_n}$$ where, μ s represents the average value of the image intensities in the selected PA signal ROI surrounding the maximum signal intensity and μ n and σ n represent the average and standard deviation, respectively, of image intensities in the background noise ROI. The size of the ROIs were fixed to 4.2 mm in the lateral dimension and 1.0 mm in the axial dimension.…”

“…In addition, motion-based approaches were implemented to reduce artifacts in PA [15], [25] and US images [26] requiring deformation of the target relative the probe, which is not always feasible. Unlike previous methods which rely on signal amplitudes, the short-lag spatial coherence (SLSC) beamformer, which was originally developed for US images [27], [28], creates images based on spatial coherence, and it triples the effective penetration depth in photoacoustic images with no frame averaging required [14], [17], [29]. It may also be weighted by amplitude-based images to reduce clutter and provide spectroscopic information [30].…”

Thermoacoustic contrast of prostate cancer due to heating by very high frequency irradiation

“…Several groups have applied photoacoustic imaging to studies of brachytherapy seeds in tissue phantoms (Harrison and Zemp, 2011, Kuo et al, 2012, Su et al, 2011. Poor depth penetration of optical radiation may require transurethral light delivery and highly optimized reconstruction (Lediju Bell et al, 2013), however. In vivo studies of the canine prostate have also been performed (Wang et al, 2010, Patterson et al, 2010.…”