Methods
Participants and study criteria
7 patients with ET (right hand, 5 males and 2 females), with a mean age of 63 ± 4.24 years underwent successful unilateral tcMRgFUS VIM nucleus thalamotomy. The inclusion criteria were age 22 years or more (male or female); diagnosis of ET by neurologists or neurosurgeons specialized in movement disorders according to relevant diagnostic criteria; history of oral administration of antitremor drugs, medically intractable manifestations such as poor response to medications, and intolerance to medications due to adverse reactions; good communication skills; a postural or intention tremor score for the dominant hand/arm of two or more as assessed by the clinical rating scale for tremor (CRST); functional disorders in daily life due to ET (a score of ≥2 for any item in Part C of the CRST); capability to receive computed tomography (CT) and magnetic resonance imaging (MRI) examinations and an appropriate skull density ratio; agreement on enrollment by two study staff after assessment.
The exclusion criteria were as follows: severe functional disorders in the heart, liver, kidney, or blood coagulation; alcohol or drug abuse; active infection or compromised immunity; history of intracranial hemorrhage, cerebrovascular disease, brain tumor, epilepsy, or other brain diseases; other neurodegenerative diseases; intolerance to holding the supine position for a long time; obvious cognitive impairments; mental illnesses or history of mental illnesses; pregnancy or lactation; previous deep brain stimulation or stereotactic ablation; injection of kreotoxin in the arm, neck, or face within five months before baseline; an overall skull density ratio of 0.3 (± 0.05) or less (calculated by cranial CT); other incompatible conditions contraindications for CT or MRI examinations. Both fNIRS and CRST scores were determined after pharmacokinetic depletion of oral drugs in vivo.
The study was approved by the Ethics Committee of the Chinese Peoples Liberation Army General Hospital (Ethics Committee Approval No.: 2018 LUNSHEN No. 021, 2018 LUNSHEN No. 021-1), and written informed consent was obtained from all participants.
Clinical assessment
The CRST was used to assess tremor symptoms before and after treatment. The CRST is divided into three parts: Part A to assess resting state, postural, and intention tremors; Part B related to the functional assessment during writing and pouring liquids; and Part C to assess life and social activity dysfunction. The scale is designed with a total score of 160; the higher the score, the more severe the tremor. The scoring was performed by two experienced neurologists.
Functional imaging experiment
The patients underwent fNIRS during a finger-to-nose task (both hands, two separate tasks) and dominant hand (right) writing task 24 h before treatment and 1 month after treatment. The patients were prompted to switch from resting state to performing the task. A 3-min break was allowed between resting and task performing states. Participants were informed of the motion tasks they had to complete before each experiment.
fNIRS data acquisition
A 52-channel continuous wave fNIRS system (ETG-4100 Optical Topography System; Hitachi Medical Co., Japan) with a sampling rate of 10 Hz was used to collect the optical absorption of near infrared light at two wavelengths (695 nm and 830 nm) from seven patients. We aimed to primarily measure cortical activation in the dorsolateral prefrontal cortex, primary motor area, primary somatosensory area, and premotor and supplementary area. The setup of the optode probe is shown in Figure 1.
Statistical analysis of fNIRS signal
We used NIRS-SPM version 4.1[14] to calculate the activation maps of oxyhemoglobin (OxyHb) which has been reported to be the most sensitive indicator of regional cerebral blood flow[15] and to have a robust correlation with the BOLD signal[16, 17] .Individual analysis of fNIRS data started with the modified Beer –Lambert law in order to transfer optical density variation to the changes in concentration of OxyHb[18]. Spatial registration of channel locations was conducted based on the real coordinates of references(i.e., nasion, the pre auricular points anterior to the left and right ears, inion, Cz), optodes, and channels obtained from the 3D digitizer. After data preparation, a high-pass filter method (wavelet minimum description length detrending algorithm) was employed for the tasks of pointing to the nose with the right hand and writing to eliminate the existing global drifts of optical signal measurements due to respiration, vasomotion, blood pressure variation, movements during the experiments, instrumental instability, or other experimental errors[19] . Then, a low-pass filter (hemodynamic response function) was used in order to smooth the data to attenuate high frequency components. Next, a general linear model were used to compute parameter estimates, that is, task-related β-values as the model’s weights:
Y represents a N × M matrix of the measured fNIRS data after preprocessing (N means the number of time points; while M means the number of channels); X represents a N × W design matrix composed by W-regressors; β represents a W × M regression coefficients matrix indicating the contribution of each regressor to Y; ε represents a N × M error matrix that was not able to explain by the model.
For the fNIRS group analysis, a one sample t-test was applied on the task-related β value for each channel across all the ET patients so as to calculate the activation difference between each task and the corresponding resting state condition. To avoid false positives because of multichannel comparison, p values were corrected by false discovery rate (p-value corrected by false discovery rate [FDR] < 0.05). Next, t-test maps of the activation increase which were smoothed using the spline methodwere generated using the plotTopoMap tool (http://www.alivelearn.net/wp-content/uploads/2011/04/plottopomap.m).
We visualized all the t-test results using the nirs2img function in the xjview toolbox to convert the t-test values of each channel to its corresponding Montreal Neurological Institute coordinates on an image file (http://www.alivelearn.net/xjview8/). Then, we applied the BrainNet Viewer toolbox (http://www.nitrc.org/projects/bnv/) [20] to project the channel position with its t-test value to the cortical surface using that image file. Finally, for those channels with a significant activation increase after one-sample t-test, we used two sample paired t-tests to compare task-related β values after tcMRgFUS with the task-related β values before tcMRgFUS.
Correlation analysis between brain activity and clinical manifestations
In order to examine the relationship between brain activity and clinical manifestations, for those channels with significant activation increase, Spearman's rank correlation coefficient (ρ) was calculated between the task related β value after tcMRgFUS treatment minus the task related β value before tcMRgFUS treatment (Δβ) and the score change between CRST testing before and after tcMRgFUS treatment (|ΔCRST-B|). CRST testing after treatment was measured twice: one month after tcMRgFUS treatment, and again three months after tcMRgFUS treatment.