In vivo cryoablation of prostate tissue with temperature monitoring by optoacoustic imaging

Abstract

Cryoablation of prostate cancer is an FDA approved clinical procedure, which involves repetitive rapid cooling of a lesion to lethal temperatures of -40C and below. The major drawback of the technique is the insufficient control over the fast thermal processes that may result in severe complications (impotence, incontinence, perforation of the rectal wall) and morbidity. The developed optoacoustic imaging technique provides non-invasive real-time temperature mapping of tissue adjacent to prostate and enables more efficient control over the procedure, which is necessary to reduce side effects and accelerate the physician's learning curve. In these studies we successfully demonstrated real-time transrectal optoacoustic imaging during prostate cryoablation in live canine model focused on optoacoustic thermography of the rectal wall within the depth of 1cm. Our method utilized previously discovered universal thermal dependence of the normalized optoacoustic response of blood. Nanosecond-pulse radiation of Ti-Sapphire laser tuned to the isosbestic point of hemoglobin (802±3 nm) was delivered via fiberoptic illuminators assembled on both sides of the linear array of the 128-channel transrectal ultrasound probe. Temperature readouts at discrete locations inside and nearby prostate were also performed using standard transperineal needle sensors. The effect of homeostasis on optoacoustic imaging in live tissue was examined during cooling and shown to be significant only within the range of ±1.5C in respect to the body temperature. Accuracy of in vivo optoacoustic temperature measurements was determined as ±2C for the range of temperature from +35 to -15C, which is more than sufficient for tracking the essential isotherms in the course of clinical procedures.

Advanced optoacoustic methods for multiscale imaging of in vivo dynamics

“…Thus, the signal amplitude can be modulated by changing the temperature in the sample. This effect has been exploited for non-invasive temperature monitoring in clinical procedures involving radiofrequency ablation [264], high-intensity focused ultrasound (HIFU) [265], cryoablation [266] or laser-induced thermotherapy (LITT) [267]. At the microscopic level, temperature changes in individual cells can be measured with an accuracy of 0.2°C [257].…”

“…Similarly, optoacoustics has also been used to monitor HIFU [265], and radiofrequency ablation [264], where multispectral imaging has also been used to identify spectral changes associated with tissue coagulation. Temperature monitoring during the cryoablation of a canine model of prostate cancer has been performed with an accuracy of 2°C for a temperature range from 35 to −15°C [266]. …”

Thermal memory based photoacoustic imaging of temperature

“…However, taking ratiometric measurements at different temperatures, conventional PA thermometry can only measure the relative changes in tissue temperature, assuming that the optical properties of the tissue do not change when the temperature changes [28]. To determine the absolute temperature in tissue, ex vivo calibrations of tissues with known optical properties have to be performed by measuring the relative changes in PA signals at multiple reference temperatures [20–25]. The calibration-based PA thermometry has achieved a relatively high accuracy of ∼0.6°C on homogenous phantoms and have been applied in monitoring photothermal therapy [23, 24] and cryoablation of prostate tissue [25].…”

“…To determine the absolute temperature in tissue, ex vivo calibrations of tissues with known optical properties have to be performed by measuring the relative changes in PA signals at multiple reference temperatures [20–25]. The calibration-based PA thermometry has achieved a relatively high accuracy of ∼0.6°C on homogenous phantoms and have been applied in monitoring photothermal therapy [23, 24] and cryoablation of prostate tissue [25]. However, the calibration process using a thermal coupler in deep tissue is extremely challenging if possible at all in practical applications.…”

Deep-tissue temperature mapping by multi-illumination photoacoustic tomography aided by a diffusion optical model: a numerical study

“…Thus, by measuring the changes in PA signals at different temperatures over time, the ratiometric change in the PA signals as a function of temperatures can be obtained by fitting the data to a linear model. 2,8,9,12 These ratiometric methods can obtain an accuracy of ∼0.1°C in relative temperature mapping and have been used in photothermal therapy, 10,13 cryoablation of prostate tissue, 14 and development of gold nanorods. 7 However, these ratiometric methods are based on the photoacoustic microscopy systems and mostly work only in superficial depths.…”