Objective: Focusing precision in tcMRgFUS tractotomy depends on the ability of the treatment system to compensate for acoustic field distortions induced by the patient skull.

Background: The cerebello-thalamic tract (CTT) is our target of choice for the treatment of essential or dystonic tremor. The orientation of the CTT in the target volume based on anatomical studies (Ref: Morel: stereotactic atlas of human thalamus) in the sagittal projection is about 60 to 65° relative to the ACPC line and in the coronar projection about 40 to 45° relative to the intersection of coronar and midsagittal plane.

Methods: We report on our preliminary experience in 8 CTT tractotomies. The final thermal lesion at the focal point has the shape of an ellipsoid. The angle of the main axis was measured in relation to the ACPC line (sagittal view) and the midsagittal line (coronar view) using BrainLab software, and compared with direction of CTT. Focusing precision was evaluated on MRI 48 hours po. by comparing the coordinates of focal point to the 3 dimensional coordinates of thermal lesion. The lesion size and orientation was then compared in two groups of 4 patients each. In group 1, the desired therapeutic response could be achieved while keeping the acoustic focus at the original target position during the whole treatment; in group 2, the acoustic focus had to be electronically steered away from the original target position to compensate for inadequate therapeutic response.

Results: MRgFUS intervention resulted in a prompt suppression of the tremor in the extremity contralateral to the site of intervention in all 8 patients at the end of procedure. Group1: lesions are 180mm3 in average and show a good alignment of their main axis with the orientation of CTT. Group 2: Average lesion size was 310 mm3 and there is a clear misalignment between main lesion axis and CTT. Correlation between lesion volume and sagittal angle: Pearson r= 0.81; p=0,0015. The focal point is excentric to the centre of lesion. There is a predominant thermal spread in superior and anterior direction.

Conclusions: We observed qualitatively a correlation between the alignment of the effected lesion with the targeted neuronal tract and the lesion size required to achieve the desired therapeutic effect. Future work will aim at better understanding and predicting the lesion orientation to adapt planning procedures accordingly.

« Back to 2016 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/focusing-precision-and-lesion-size-in-cerebello-thalamo-tractotomy-by-mr-imaging-guided-high-intensity-focused-ultrasound-mrgfus/