Figure 1
Study pipeline. A) DWI were pre-processed and then their native and flipped orientations (contralateral to the upper limb with highest preoperative tremor severity) were used to compute response functions separately for each acquisition scheme for the basis of single-shell 3-tissue constrained spherical deconvolution. B) Native and flipped white matter FOD images were used to compute study-specific templates. Fixel metrics (FD, FC (Δd indicating change in diameter) and FDC) were computed and harmonised according to acquisition scheme using neuroCombat. C) DBS stimulation volumes were reconstructed for each patient. D) Tractograms were generated from each white-matter FOD template. Dentato-rubro-thalamic tracts were reconstructed to extract FDC metrics. Whole-brain and stimulation-seeded general linear models were used to model associations of preoperative tremor severity and postoperative tremor change, respectively. Abbreviations: dentato-rubro-thalamic, DRT (decussating, dec.; non-decussating, non-dec.); deep brain stimulation, DBS; cerebrospinal fluid, CSF; diffusion-weighted imaging, DWI; fiber cross-section, FC; fiber density, FD; fiber density and cross-section, FDC; fiber orientation distribution, FOD; grey matter, GM; primary motor cortex, M1; response function, RF; volume of tissue activation, VTA; white matter, WM.
Table 1
Demographic and clinical information.
| DT | ET/ETp | p-VALUE | |
|---|---|---|---|
| Age (years) | 60.1 ± 13.5; 62 | 69 ± 6.7; 69.5 | 0.02* |
| Disease duration (years) | 26.1 ± 11.62; 27 | 28.1 ± 15.4; 27.5 | 0.673 |
| Sex (F: N; %) | 5; 32 | 7; 39 | 0.915† |
| Preoperative UL severity (left + right) | 35 ± 8.3; 31 | 35.8 ± 8.4; 35 | 0.967 |
| Postoperative UL severity (left + right) | 19.5 ± 11; 16 | 18 ± 6.6; 19.5 | 0.711 |
| Follow-up duration (months) | 12.2 ± 3.7; 12 | 13.1 ± 4.7; 12 | 0.719 |
| Postoperative change (%) | 50.1 ± 35.8; 62.4 | 55.6 ± 19.1; 56.3 | 0.782 |
| Stimulation amplitude (left + right; mA) a | 3.4 ± 0.6; 3.3 | 3.4 ± 0.5; 3.3 | 0.962 |
[i] Note. Values are presented as mean ± standard deviation; median, except sex which is presented as the number, and percentage of females. a Values reflect only the active electrode for patients presenting with unilateral configuration at follow-up. * Indicates statistical significance. † Indicates χ2 test. Abbreviations: dystonic tremor, DT; essential tremor, ET; female, F; upper limb; UL.
Figure 2
Clinical and demographic results. A) Pre-post raw upper limb severity scores for both DT and ET groups. B) The postoperative percent change scores of upper limb severity for both DT and ET groups. C) Correlations of age and preoperative tremor severity for DT (left) and ET (right). D) Correlations of age and postoperative percent change scores of upper limb severity for DT (left) and ET (right). * Indicates statistical significance (p < 0.05).
Figure 3
DT and ET group electrode renderings (A; B) and stimulation volume N-maps (C; D). A) electrodes are displayed for DT (blue) and ET (orange) groups from axial (left) and coronal views. B) Electrodes for each group on the left hemisphere (LH) and right hemisphere (RH). C) N-maps are displayed from sagittal (left panels) and axial (right panels) views with corresponding MNI152NLin2009bAsym co-ordinates and panel orientations. Colour bars on the right indicate the number of patient stimulation overlaps for a given voxel. Renderings and outlines show the VIM (green), VOp (black) and zona incerta (white) defined from the DBS Intrinsic Template atlas [52], a manually curated atlas of subcortical structures, superimposed on an ultra-high resolution (100 µm) 7T MRI template in MNI152NLin2009bAsym space [53]. Abbreviations: anterior, A; lateral, L; left hemisphere, LH; medial, M; posterior, P; right hemisphere, RH; superior, S.
Figure 4
Fixels with associations of increased FD and FDC changes with increased preoperative tremor severity in patients with essential and dystonic tremor. Fixels are displayed as consecutive coronal (A) and sagittal (B) sections. The colour bar indicates the t-value for each fixel. From left to right (C): Short range connections (sagittal), long range connections (coronal) and a magnification of non-decussating and decussating cerebello-thalamo-cortical tracts. Abbreviations: anterior, A; lateral, L; medial, M; superior, S.