Matthew Dwayne Bucknor MD, Presenter: Nothing to Disclose

Viola Rieke PhD, Abstract Co-Author: Nothing to Disclose

Thomas M. Link MD, PhD, Abstract Co-Author: Research Grant, General Electric Company Research Grant, InSightec Ltd

Mark William Wilson MD, Abstract Co-Author: Nothing to Disclose

Sharmila Majumdar PhD, Abstract Co-Author: Nothing to Disclose

Maythem Saeed DVM, PhD, Abstract Co-Author: Nothing to Disclose

To evaluate hyperacute structural changes (<1 hour) on MR and CT imaging following MR guided high-intensity focused ultrasound (MRgHIFU) in a swine femoral bone model as a function of number of focal spot zones and energy per focus, for a given target volume.

Experimental procedures received approval from the institutional committee on animal research. MRgHIFU was used to create two thermal lesions (distal and proximal) in the right femur of 8 pigs, while the left femur was used as a control. Each target was subjected to either 4 (n=4) or 6 (n=4) sonications within similar treatment volumes. The energy dosed to the distal target was higher than the proximal target (419±19 J versus 324±17 J). On real-time MR thermometry, the temperature rise adjacent to target bone was quantified. HIFU lesions were imaged using multiple MRI sequences (3.0T) and 64-slice CT, with and without contrast, before and after treatment. 

MRgHIFU created focal hypoenhanced lesions measuring on average 2.1 cm in maximum craniocaudal dimension. Interestingly, within similar prescribed treatment volumes, the use of 6 as opposed to 4 sonications increased the depth of the transverse intramedullary hypoenhanced zone, measuring up to 6.5 mm versus 2.9 mm, respectively (p<0.001). T2-weighted MRI demonstrated the tissue edema surrounding the sonicated targets, while Gd-enhanced images delineated the hypoenhanced ablation zone. Furthermore, the difference in energy dosing between the distal and proximal targets corresponded to a temperature rise of 70±5 °C distally and 60±5 °C proximally. However, there was no significant difference in the immediate post-contrast hypoenhanced foci on MRI between distal and proximal lesions (p>0.05). CT imaging failed to demonstrate morphological abnormalities with and without contrast media. 

The number of focal sonications plays a crucial role in the depth of treatment within the targeted bone. MR thermometry provided precise thermal dose maps. Unlike CT, T2-weighted and contrast enhanced MR demonstrated the hyperacute structural changes in the femur and surrounding soft tissue.

Sonication number and energy dose during MRgHIFU of bone can be selected to precisely control ablation zone size, allowing for more effective and better-tolerated treatment of focal bone lesions.

Bucknor, M, Rieke, V, Link, T, Wilson, M, Majumdar, S, Saeed, M, MR-guided High-intensity Focused Ultrasound Ablation of the Femoral Bone: MRI and CT Evaluation of Structural Changes.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13028092.html