A new method for temperature-field reconstruction during ultrasound-monitored cryosurgery using potential-field analogy.

The current study aims at developing computational tools in order to gain information about the thermal history in areas invisible to ultrasound imaging during cryosurgery. This invisibility results from the high absorption rate of the ultrasound energy by the frozen region, which leads to an apparent opacity in the cryotreated area and a shadow behind it. A proof-of-concept for freezing-front estimation is demonstrated in the current study, using the new potential-field analogy method (PFAM). This method is further integrated with a recently developed temperature-field reconstruction method (TFRM) to estimate the temperature distribution within the frozen region. This study uses prostate cryosurgery as a developmental model and trans-rectal ultrasound imaging as a choice of practice. Results of this study indicate that the proposed PFAM is a viable and computationally inexpensive solution to estimate the extent of freezing in the acoustic shadow region. Comparison of PFAM estimations and experimental data shows an average mismatch of less than 2 mm in freezing-front location, which is comparable to the uncertainty in ultrasound imaging. Comparison of the integrated PFAM + TFRM scheme with a full-scale finite-elements analysis (FEA) indicates an average mismatch of 0.9 mm for the freezing front location and 0.1 mm for the lethal temperature isotherm of -45 °C. Comparison of the integrated PFAM + TFRM scheme with experimental temperature measurements show a difference in the range of 2 °C and 6 °C for selected points of measurement. Results of this study demonstrate the integrated PFAM + TFRM scheme as a viable and computationally inexpensive means to gain information about the thermal history in the frozen region during ultrasound-monitored cryosurgery.

Characterization of a CMOS sensing core for ultra-miniature wireless implantable temperature sensors with application to cryomedicine.

In effort to improve thermal control in minimally invasive cryosurgery, the concept of a miniature, wireless, implantable sensing unit has been developed recently. The sensing unit integrates a wireless power delivery mechanism, wireless communication means, and a sensing core-the subject matter of the current study. The current study presents a CMOS ultra-miniature PTAT temperature sensing core and focuses on design principles, fabrication of a proof-of-concept, and characterization in a cryogenic environment. For this purpose, a 100 µm × 400 µm sensing core prototype has been fabricated using a 130 nm CMOS process. The senor has shown to operate between -180°C and room temperature, to consume power of less than 1 µW, and to have an uncertainty range of 1.4°C and non-linearity of 1.1%. Results of this study suggest that the sensing core is ready to be integrated in the sensing unit, where system integration is the subject matter of a parallel effort.

Temperature field reconstruction for minimally invasive cryosurgery with application to wireless implantable temperature sensors and/or medical imaging.

There is an undisputed need for temperature-field reconstruction during minimally invasive cryosurgery. The current line of research focuses on developing miniature, wireless, implantable, temperature sensors to enable temperature-field reconstruction in real time. This project combines two parallel efforts: (i) to develop the hardware necessary for implantable sensors, and (ii) to develop mathematical techniques for temperature-field reconstruction in real time-the subject matter of the current study. In particular, this study proposes an approach for temperature-field reconstruction combining data obtained from medical imaging, cryoprobe-embedded sensors, and miniature, wireless, implantable sensors, the development of which is currently underway. This study discusses possible strategies for laying out implantable sensors and approaches for data integration. In particular, prostate cryosurgery is presented as a developmental model and a two-dimensional proof-of-concept is discussed. It is demonstrated that the lethal temperature can be predicted to a significant degree of certainty with implantable sensors and the technique proposed in the current study, a capability that is yet unavailable.