In vivooptoacoustic temperature imaging for image-guided cryotherapy of prostate cancer

Abstract

The objective of this study is to demonstrate in vivo the feasibility of optoacoustic temperature imaging during cryotherapy of prostate cancer. We developed a preclinical prototype optoacoustic temperature imager that included pulsed optical excitation at a wavelength of 805 nm, a modified clinical transrectal ultrasound probe, a parallel data acquisition system, image processing and visualization software. Cryotherapy of a canine prostate was performed in vivo using a commercial clinical system, Cryocare CS, with an integrated ultrasound imaging. The universal temperature-dependent optoacoustic response of blood was employed to convert reconstructed optoacoustic images to temperature maps. Optoacoustic imaging of temperature during prostate cryotherapy was performed in the longitudinal view over a region of 30 mm (long) × 10 mm (deep) that covered the rectum, the Denonvilliers fascia, and the posterior portion of the treated gland. The transrectal optoacoustic images showed high-contrast vascularized regions, which were used for quantitative estimation of local temperature profiles. The constructed temperature maps and their temporal dynamics were consistent with the arrangement of the cryoprobe and readouts of the thermal needle sensors. The temporal profiles of the readouts from the thermal needle sensors and the temporal profile estimated from the normalized optoacoustic intensity of the selected vascularized region showed significant resemblance, except for the initial overshoot, that may be explained as a result of the physiological thermoregulatory compensation. The temperature was mapped with errors not exceeding ±2 °C (standard deviation) consistent with the clinical requirements for monitoring cryotherapy of the prostate. In vivo results showed that the optoacoustic temperature imaging is a promising non-invasive technique for real-time imaging of tissue temperature during cryotherapy of prostate cancer, which can be combined with transrectal ultrasound-the current standard for guiding clinical cryotherapy procedure.

Photoacoustic Imaging in Gastroenterology: Advances and Needs

“…with the optical absorption coefficient μ a , the local optical fluence F, and the dimensionless Grüneisen parameter Γ representing thermoelastic efficiency of the medium. The Grüneisen parameter is temperature sensitive and depends on the volumetric thermal expansion coefficient (β), the speed of sound (V l ) for longitudinal waves, and the specific heat capacity at constant pressure (C p ) [19,20]. In the tissue, a rise of temperature ΔT ~ 10 −3°C generates a pressure wave of p ~ 1 kPa.…”

Optoacoustic image formation approaches—a clinical perspective

“…Intravascular access is also possible, and dedicated probes can find important applications such as the characterization of human coronary atherosclerosis [12,150,166,167]. Potentially important diagnostic feature of the OA method is its high sensitivity to temperature variations as well as ability to spectrally differentiate coagulated tissues, which can be employed for monitoring ablation procedures and other thermal interventions [168][169][170][171][172][173].…”

Photoacoustic image-guided interventions

“…PAI enabled visualization of blood vessels 66,67,77 during surgeries and temperature 70 monitoring during therapies using the endogenous contrast agent hemoglobin for contrast enhancement. Image guidance is critical in guiding fetal surgeries such as anastomoses photocoagulation.…”

“…by only using endogenous agents; (9) great optical contrast that highlights blood vessels; and (10) easily incorporated into the current operating environment with no laborious efforts. 1,3,53–72…”