Zero echo time imaging-based skull density ratio for high-intensity focused ultrasound

Purpose To evaluate whether skull density ratio (SDR) estimates required for high-intensity focused ultrasound (HIFU) treatment of tremor can be accurately derived from zero echo time (ZTE) magnetic resonance images (MRI) by comparing them with measurements from computed tomography (CT) scans using an intensity profile-based approach.Materials and methods Fifty-seven patients with essential tremor (n = 44), Parkinson’s disease (PD) tremor (n = 10), both (n = 1) or uncategorized tremor-dominant disease (n = 2), underwent ZTE imaging before a neuro-HIFU treatment. Skull attenuation estimates, i.e. skull density ratios, were calculated from ZTE and CT images using the developed in-house SDR calculation pipeline and compared with the vendor-provided benchmark SDR values. To statistically evaluate the linear relationships between the datasets, Pearson correlation coefficients (r) and their corresponding p-values were calculated. A novel ZTE-based SDR inclusion threshold was derived.Results A statistically significant positive correlation (r = 0.96, p< 0.0001) was detected between the CT-derived SDRs and the benchmark values, indicating that the in-house pipeline achieved high accuracy. Statistically significant positive correlation (r = 0.80, p< 0.0001) between the benchmark SDR values and the ZTE-derived SDR values was detected. A novel ZTE-based inclusion threshold of 0.51–0.53 was suggested.Conclusions To our knowledge, this research was the first to take an intensity-profile-based approach when comparing high-resolution ZTE images and CT scans for skull density ratio calculation. The findings of this study support the possibility of the zero echo time sequence being validated for clinical use.