Monitoring of tissue coagulation during thermotherapy using optoacoustic technique

Abstract

In this paper we have applied the laser optoacoustic technique for real time noninvasive monitoring of thermal damage in tissues. Changes in tissue optical properties during coagulation were detected by measuring and analysing amplitude and temporal characteristics of optoacoustic signals. Coagulation of liver, myocardium and prostate was induced by interstitial continuous wave Nd : YAG laser irradiation of the samples or by conductive heating. Real time detection of thermally-induced changes in optical properties was performed with sensitive wide-band acoustic transducers. Combination of optoacoustic and diffuse reflectance technique was applied for determination of tissue optical properties: effective attenuation, total diffuse reflectance, reduced scattering coefficient and absorption coefficient. The optical properties did not change up to temperature of coagulation (about 53°C) and sharply increased during heating up to 70°C. Monitoring of the expansion of interstitial coagulation front within freshly excised canine tissues was performed in real time with spatial resolution of about 0.6 mm. The results of our study suggest that this technique can potentially be used for real time precise thermotherapy of malignant and benign lesions at depths of the order of the centimetre.

Integration of photoacoustic imaging and high-intensity focused ultrasound

“…The increase in the amplitude of photoacoustic signals after HIFU treatment is consistent with previous results. 16,17 The increase in the amplitude of photoacoustic signals after HIFU can be attributed to a combination of several factors. Notably, the Grüneisen parameter is affected by tissue coagulation.…”

“…15 PAI has demonstrated to be capable of monitoring thermal lesions generated by HIFU or other means. 16,17 A study for PAI guidance of HIFU has also been proposed with the application of a time-reversal technique. 18 Currently, PAI and HIFU are performed by two separate systems.…”

Red blood cell as a universal optoacoustic sensor for non-invasive temperature monitoring

“…[14][15][16] The presence of temperature dependent optoacoustic response (ThOR) measured from biological solutions, cells, and tissues provided the foundation for pioneering efforts in non-invasive temperature monitoring since over a decade ago. 17,18 Recent progress in this field of science demonstrated close correlation between local optoacoustic image intensity and temperature in tissue mimicking phantoms, [7][8][9][10]15,19 possibility to enhance the technique by combining laser optoacoustic and thermoacoustic sensing, 20 and optoacoustic temperature measurements in microscopy mode. 21,22 However, when considering in vivo applications, sample-to-sample and spatial variations of Gr€ uneisen parameter for different tissues negate all the advantages of the current methods, including high precision of the obtained temperature calibration curves.…”

Two-dimensional spatiotemporal monitoring of temperature in photothermal therapy using hybrid photoacoustic–ultrasound transmission tomography

“…For use of the method in this situation, the relationship between SOS and temperature during coagulation should be investigated. Since our method allows hybrid imaging, as mentioned earlier, we can use PAs to monitor changes in tissue optical properties caused by coagulation 24,25 and then use the SOS-temperature relations that apply in this regime. Finally, from the perspective of preclinical and clinical measurements, the proposed method is suited for objects, which lend themselves to the acquisition of multiple PA projections in a tomographic geometry.…”