Investigation of factors affecting hypothermic pelvic tissue cooling using bio-heat simulation based on MRI-segmented anatomic models

Abstract

This study applied a simulation method to map the temperature distribution based on magnetic resonance imaging (MRI) of individual patients, and investigated the influence of different pelvic tissue types as well as the choice of thermal property parameters on the efficiency of endorectal cooling balloon (ECB). MR images of four subjects with different prostate sizes and pelvic tissue compositions, including fatty tissue and venous plexus, were analyzed. The MR images acquired using endorectal coil provided a realistic geometry of deformed prostate that resembled the anatomy in the presence of ECB. A single slice with the largest two-dimensional (2D) cross-sectional area of the prostate gland was selected for analysis. The rectal wall, prostate gland, peri-rectal fatty tissue, peri-prostatic fatty tissue, peri-prostatic venous plexus, and urinary bladder were manually segmented. Pennes’ bioheat thermal model was used to simulate the temperature distribution dynamics, by using an in-house finite element mesh based solver written in Matlab. The results showed that prostate size and periprostatic venous plexus were two major factors affecting ECB cooling efficiency. For cases with negligible amount of venous plexus and small prostate, the averaged temperature in the prostate and neurovascular bundles could be cooled down to 25°C within 30 minutes. For cases with abundant venous plexus and large prostate, the temperature could not reach 25°C at the end of 3 hours cooling. Large prostate made the cooling difficult to propagate through. The impact of fatty tissue on cooling effect was small. The filling of bladder with warm urine during the ECB cooling procedure did not affect the temperature in the prostate or NVB. In addition to the 2D simulation, in one case a 3D pelvic model was constructed for volumetric simulation. It was found that the 2D slice with the largest cross-sectional area of prostate had the most abundant venous plexus, and was the most difficult slice to cool, thus it may provide a conservative prediction of the cooling effect. This feasibility study demonstrated that the simulation tool could potentially be used for adjusting the setting of ECB for individual patients during hypothermic radical prostatectomy. Further studies using MR thermometry are required to validate the in silico results obtained using simulation.

Feasibility study of a novel rectal cooling system for hypothermic radical prostatectomy in a swine model

“…The development of novel rectal tube cooling systems based on the concept of hypothermia combined with an improved surgical technique may help to improve surgical outcomes. Other research groups compared postoperative outcomes using similar designs of endorectal cooling tubes to maintain hypothermia in the pelvic cavity or around the lesions [ 5 8 17 18 19 20 21 ]. Our group quantitatively analyzed anatomical structures in the pelvic cavity using preoperative magnetic resonance imaging (MRI) and applied these data to the design of a multi-lumen balloon catheter.…”

Hypothermic Cooling Measured by Thermal Magnetic Resonance Imaging; Feasibility and Implications for Virtual Imaging in the Urogenital Pelvis

“…As simulation study by Lin et al 16 addresses the computational issues when building a virtual MRI model of endorectal cooling. Virtual studies are needed to address inherent cooling challenges of variable prostate volumes, venous plexus, ‘cold’ sink effect of blood flow, and tissue thermal properties.…”

Numerical simulation of temperature variations in a canine knee joint during therapeutic heating

“…Since then, several alternative heat transfer models have been developed providing a quantitative analysis of the complex phenomenon of heat transfer in living tissues [12]. Since the publication of the heat transfer equation, due to its great simplicity and the ability to predict the temperature distribution reasonably well, the Pennes equation has been widely used for the analysis of a range of heat transfer phenomena in living tissues [13][14][15].…”