Francois Cornelis MD, Presenter: Nothing to Disclose

Bruno Quesson, Abstract Co-Author: Research grant, Koninklijke Philips Electronics NV

Chrit T. W. Moonen PhD, Abstract Co-Author: Research grant, Koninklijke Philips Electronics NV

Nicolas Grenier MD, Abstract Co-Author: Nothing to Disclose

To quantitatively evaluate in vivo they thermal properties of the kidney from non destructive local heatings induced by MR guided HIFU. Temperature images were analyzed with the Bio Heat Transfer (BHT) model to derive absorption coefficient (α), thermal diffusivity (D) and perfusion (wb), following the method proposed by Dragonu et al. [NMR Biomed. 2009].

Forty-two HIFU heatings (120W, 20s) were performed in the kidney of  6 pigs (60kg body weight) under general anaesthesia. Arterial flow was modulated by insertion of an angioplasty balloon in the aorta under MRI guidance (1.5 Tesla scanner, Philips HIFU prototype). Real-time volumetric MR thermometry (PRF method) was performed using a multi-slice single shot EPI gradient-echo sequence (TE/TR=29/80 ms, 300x300 FOV, 112x112 matrix). For each time point, the spatial integration of the temperature rise inside the acquired volume was performed and the resulting thermal load (Eth(t)) curve was fitted to extract wb and α, using the BHT model. D was determined from the analysis of the spatial spread of temperature during the cooling period with a 2D Gaussian fitting routine of the temperature maps in the central slice. The thermal dose maps were also computed (Sapareto equation) for estimation of potential tissue damage.

In presence of a normal arterial flow, Eth(t) decreased exponentially during the cooling period, whereas it remained constant when the balloon was inflated, in corcordance with the BHT model. A linear dependence in time of variance of the Gaussian function was observed. Absorption (a=9.23+/-1.67 mm³.K/J) and thermal diffusivity (D=0.27+/-0.17 mm²/s) were found independent from flow, whereas perfusion was significantly reduced (normal flow =0.06+/-0.02 vs blocked flow =0.009+/-0.007 ml.ml/s, p <0.0001) when the balloon was inflated. No pixels reached the lethal thermal dose.

An excellent correspondence was observed between the BHT model and experimental in vivo data obtained on the kidney, showing that this model is relevant to describe temperature changes in vivo during HIFU heating. This method could therefore help in improving the sonication strategy for the HIFU tretament of perfused organs.

This method provides a non invasive way to quantitatively determine the tissue thermal parameters and could therefore help in improving the sonication strategy for the HIFU treatment.

Cornelis, F, Quesson, B, Moonen, C, Grenier, N, In Vivo Characterization of Tissue Thermal Properties of the Kidney by HIFU Local Hyperthermia under MR Thermometry and Modulation of the Arterial Flow.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9000415.html