Multiple image quality metrics are currently available to assess target detectability in photoacoustic images. Common metrics include contrast, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR). The generalized contrast-to-noise ratio (gCNR) is a relatively new image quality metric to assess the probability of photoacoustic target detectability. This paper demonstrates the applicability of gCNR to assess photoacoustic image quality using simulated and experimental images created with delay-and-sum (DAS), short-lag spatial coherence (SLSC), generalized coherence factor weighting combined with DAS (GCF+DAS), and minimum variance (MV) beamforming. Images were created from data acquired with a fixed light source with output energy values increasing from 2 mJ to 35 mJ. The gCNR converged to 0.93, 0.98, 0.99, and 0.85 for DAS, SLSC, GCF+DAS, and MV beamforming, respectively, at energies of approximately 20, 10, 10, and 20 mJ, respectively. These results indicate that gCNR has the potential to determine the minimum laser energy needed to maximize the detectability of a photoacoustic target for any given image formation method.
Many cardiac interventional procedures (e.g., radiofrequency ablation) require fluoroscopy to navigate catheters in veins toward the heart. However, this image guidance method lacks depth information and increases the risks of radiation exposure for both patients and operators. To overcome these challenges, we developed a robotic visual servoing system that maintains visualization of segmented photoacoustic signals from a cardiac catheter tip. This system was tested in two in vivo cardiac catheterization procedures with ground truth position information provided by fluoroscopy and electromagnetic tracking. The 1D root mean square localization errors within the vein ranged 1.63 − 2.28 mm for the first experiment and 0.25 − 1.18 mm for the second experiment. The 3D root mean square localization error for the second experiment ranged 1.24 − 1.54 mm. The mean contrast of photoacoustic signals from the catheter tip ranged 29.8 − 48.8 dB when the catheter tip was visualized in the heart. Results indicate that robotic-photoacoustic imaging has promising potential as an alternative to fluoroscopic guidance. This alternative is advantageous because it provides depth information for cardiac interventions and enables enhanced visualization of the catheter tips within the beating heart.