In MR-guided focused ultrasound (FUS) thalamotomy for essential tremor, the ablation hotspot seen in MR thermography is spatially displaced from the true target because heating changes the proton resonance frequency, producing both a chemical-shift-like spatial offset and a shift of the k-space center. This work introduces a two-step correction: first, a pixel-by-pixel spatial correction using the measured field map around the focus removes the roughly 1 mm displacement from field gradients; second, a temperature-induced echo-time (TE) variation map compensates the k-space-center offset that biases the apparent focus location. Applied together, the corrections lower the mean temperature error from -0.11 to -0.05 C relative to chemical-shift correction alone, improving the accuracy of targeting the ablation focus during treatment.
Purpose: To adjust the location of the ablation focus by correcting the spatial discrepancy induced by temperature changes between the target coordinate and the hotspot as seen in MR thermography. …