Hybrid CMUT Array Achieves 0.271 mm Median Error in MRI-Free CT-to-Ultrasound Skull Registration for tFUS

{"The study tested four registration modes on a CT-derived skull surface with 25 poses incorporating 10 mm lateral offsets and ±5 degree rotations. Therapeutic pulse-echo data from the sparse array were combined with high-resolution plane-wave images from the integrated US-Cross CMUT sub-array. Fused mode outperformed therapeutic-only and imaging-only approaches by jointly minimizing surface-matching residuals and local feature alignment, reducing sensitivity to element placement noise modeled with five radial seeds.","Transcranial focused ultrasound already treats essential tremor and is expanding to Alzheimer’s and depression trials, yet current workflows require preoperative MRI plus optical tracking to align CT skull models with the array. Eliminating MRI removes a costly step, reduces patient burden, and avoids coordinate-transform errors. The CMUT integration allows the same hardware to both deliver therapy and acquire the registration data, potentially shortening setup from 30–45 minutes to under 10 minutes in future clinical use.","The main limitation is reliance on simulated Field II data with idealized noise; real skull heterogeneity, tissue attenuation, and array manufacturing tolerances remain untested. A prospective cadaver or first-in-human study with optical ground-truth tracking and at least 30 independent registrations would be required to confirm sub-millimeter accuracy holds in vivo before regulatory consideration for non-MRI-guided procedures."}