Peaks in the beta band of the human subthalamic nucleus: a case for low beta and high beta activity.

OBJECTIVE: Peaks in the beta band of local field potentials (LFPs) may serve as a biological feedback signal for closed-loop deep brain stimulation (DBS) in Parkinson's disease (PD). However, the specific frequency of such peaks and their response to DBS and to different types of movement remains uncertain. In the present study, the authors examined the abundance of discernible peaks in the beta band and the effect of different types of movement and DBS on these peaks. METHODS: Subthalamic nucleus LFPs were analyzed from 38 patients with PD in a frequency range between 10 and 35 Hz, as well as the impact of movement (gait, hand movements) and electrical stimulation on these peaks. The position of the electrode segments from which LFPs were recorded was computed. RESULTS: The authors found a bimodal distribution of peaks in the beta band with discernible high- (27 Hz) and low-frequency (15 Hz) peaks. Movement of either hand had no significant effect on these peaks, whereas walking significantly reduced high-frequency beta peaks but not the peaks in the low beta band. Stimulation caused an amplitude-dependent suppression of both peaks. CONCLUSIONS: DBS suppresses LFP beta peaks of different frequencies, whereas beta suppression caused by movement is dependent on the type of movement and frequency of the peak. These results will support the investigation of distinct LFP spectra for the application of closed-loop DBS.

Neurogeriatrics-a vision for improved care and research for geriatric patients with predominating neurological disabilities.

Geriatric medicine is a rapidly evolving field that addresses diagnostic, therapeutic and care aspects of older adults. Some disabilities and disorders affecting cognition (e.g. dementia), motor function (e.g. stroke, Parkinson's disease, neuropathies), mood (e.g. depression), behavior (e.g. delirium) and chronic pain disorders are particularly frequent in old subjects. As knowledge about these age-associated conditions and disabilities is steadily increasing, the integral implementation of neurogeriatric knowledge in geriatric medicine and specific neurogeriatric research is essential to develop the field. This article discusses how neurological know-how could be integrated in academic geriatric medicine to improve care of neurogeriatric patients, to foster neurogeriatric research and training concepts and to provide innovative care concepts for geriatric patients with predominant neurological conditions and disabilities.

Analyzing the co-localization of substantia nigra hyper-echogenicities and iron accumulation in Parkinson's disease: A multi-modal atlas study with transcranial ultrasound and MRI.

BACKGROUND: Transcranial B-mode sonography (TCS) can detect hyperechogenic speckles in the area of the substantia nigra (SN) in Parkinson's disease (PD). These speckles correlate with iron accumulation in the SN tissue, but an exact volumetric localization in and around the SN is still unknown. Areas of increased iron content in brain tissue can be detected in vivo with magnetic resonance imaging, using quantitative susceptibility mapping (QSM). METHODS: In this work, we i) acquire, co-register and transform TCS and QSM imaging from a cohort of 23 PD patients and 27 healthy control subjects into a normalized atlas template space and ii) analyze and compare the 3D spatial distributions of iron accumulation in the midbrain, as detected by a signal increase (TCS+ and QSM+) in both modalities. RESULTS: We achieved sufficiently accurate intra-modal target registration errors (TRE<1 mm) for all MRI volumes and multi-modal TCS-MRI co-localization (TRE<4 mm) for 66.7% of TCS scans. In the caudal part of the midbrain, enlarged TCS+ and QSM+ areas were located within the SN pars compacta in PD patients in comparison to healthy controls. More cranially, overlapping TCS+ and QSM+ areas in PD subjects were found in the area of the ventral tegmental area (VTA). CONCLUSION: Our findings are concordant with several QSM-based studies on iron-related alterations in the area SN pars compacta. They substantiate that TCS+ is an indicator of iron accumulation in Parkinson's disease within and in the vicinity of the SN. Furthermore, they are in favor of an involvement of the VTA and thereby the mesolimbic system in Parkinson's disease.

Bioccipital Lobe Hypoperfusion and Anton's Syndrome Resolution with Intravenous Thrombolysis.

BACKGROUND: Anton's syndrome is a rare neurological disorder characterized by a combination of visual anosognosia and confabulation of visual experience, most often seen after bilateral ischemic damage to the posterior occipital cortex. CASE REPORT: We report the first case of an acute synchronous P2 occlusion as confirmed by multiparametric computed tomography (CT) including perfusion. After the administration of Recombinant tissue plasminogen activator (rtPA), Anton's syndrome completely resolved. CONCLUSION: Multiparametric CT imaging may aid in quickly proving the underlying stroke in Anton's syndrome, especially helpful considering the discrepancy between the patient's perception and clinical examination results.

A baseline study for detection of Parkinson's disease with 3D-transcranial sonography and uni-lateral reconstruction.

INTRODUCTION: TCS is a well-established technique for diagnosis of Parkinson's disease (PD). Volumetric 3D-TCS is a promising complementary approach for objective acquisition and analysis, in particular for less experienced sonographers. This study provides baselines for Parkinson detection (sensitivity and specificity), cutoff values and inter-rater agreement in 3D-TCS. METHODS: We performed 3D-TCS in 52 subjects (healthy controls and PD) bilaterally, and reconstructed in 3D space uni-laterally. Ipsi-lateral hyperechogenicities in the substantia nigra are manually segmented slice-by-slice in the 3D volume by two raters at different experience levels. ROC threshold analysis is performed and compared on features representing 3D volume and axial cross-sections (2.5D) of hyperechogenicities. Pearson correlation and intra-class correlation coefficients were evaluated for assessment of inter-rater agreement. RESULTS: 50 subjects were included. Both raters achieved high classification accuracy with 2.5D/3D features extracted from 3D-TCS volumes (best results sensitivity/specificity/cut-off per rater: 84.6%/88.9%/25.0mm2; 77.8%/88.9%/95.9mm3). The inter-rater agreement in 3D was high (ICC(A,1) = 0.777, p < 10-3), the classification performance of both sonographers was statistically not significantly different. CONCLUSION: The study presents first baseline values for uni-lateral 3D-TCS examination, and finds no disadvantage of uni-lateral reconstructions compared to previous bi-lateral fusion. Volumetric 3D-TCS has potential for a high inter-rater agreement and accuracy in detection of PD, in particular for sonographers with less experience.

Subthalamic oscillatory activity and connectivity during gait in Parkinson's disease.

Local field potentials (LFP) of the subthalamic nucleus (STN) recorded during walking may provide clues for determining the function of the STN during gait and also, may be used as biomarker to steer adaptive brain stimulation devices. Here, we present LFP recordings from an implanted sensing neurostimulator (Medtronic Activa PC + S) during walking and rest with and without stimulation in 10 patients with Parkinson's disease and electrodes placed bilaterally in the STN. We also present recordings from two of these patients recorded with externalized leads. We analyzed changes in overall frequency power, bilateral connectivity, high beta frequency oscillatory characteristics and gait-cycle related oscillatory activity. We report that deep brain stimulation improves gait parameters. High beta frequency power (20-30 Hz) and bilateral oscillatory connectivity are reduced during gait, while the attenuation of high beta power is absent during stimulation. Oscillatory characteristics are affected in a similar way. We describe a reduction in overall high beta burst amplitude and burst lifetimes during gait as compared to rest off stimulation. Investigating gait cycle related oscillatory dynamics, we found that alpha, beta and gamma frequency power is modulated in time during gait, locked to the gait cycle. We argue that these changes are related to movement induced artifacts and that these issues have important implications for similar research.

Typical features of Parkinson disease and diagnostic challenges with microdeletion 22q11.2.

OBJECTIVE: To delineate the natural history, diagnosis, and treatment response of Parkinson disease (PD) in individuals with 22q11.2 deletion syndrome (22q11.2DS), and to determine if these patients differ from those with idiopathic PD. METHODS: In this international observational study, we characterized the clinical and neuroimaging features of 45 individuals with 22q11.2DS and PD (mean follow-up 7.5 ± 4.1 years). RESULTS: 22q11.2DS PD had a typical male excess (32 male, 71.1%), presentation and progression of hallmark motor symptoms, reduced striatal dopamine transporter binding with molecular imaging, and initial positive response to levodopa (93.3%). Mean age at motor symptom onset was relatively young (39.5 ± 8.5 years); 71.4% of cases had early-onset PD (<45 years). Despite having a similar age at onset, the diagnosis of PD was delayed in patients with a history of antipsychotic treatment compared with antipsychotic-naive patients (median 5 vs 1 year, p = 0.001). Preexisting psychotic disorders (24.5%) and mood or anxiety disorders (31.1%) were common, as were early dystonia (19.4%) and a history of seizures (33.3%). CONCLUSIONS: Major clinical characteristics and response to standard treatments appear comparable in 22q11.2DS-associated PD to those in idiopathic PD, although the average age at onset is earlier. Importantly, treatment of preexisting psychotic illness may delay diagnosis of PD in 22q11.DS patients. An index of suspicion and vigilance for complex comorbidity may assist in identifying patients to prioritize for genetic testing.

Qualitative postural control differences in Idiopathic Parkinson's Disease vs. Progressive Supranuclear Palsy with dynamic-on-static platform tilt.

OBJECTIVES: We aimed to assess whether postural abnormalities in Progressive Supranuclear Palsy (PSP) and Idiopathic Parkinson's Disease (IPD) are qualitatively different by analysing spontaneous and reactive postural control. METHODS: We assessed postural control upon platform tilts in 17 PSP, 11 IPD patients and 18 healthy control subjects using a systems analysis approach. RESULTS: Spontaneous sway abnormalities in PSP resembled those of IPD patients. Spontaneous sway was smaller, slower and contained lower frequencies in both PSP and IPD as compared to healthy subjects. The amount of angular body excursions as a function of platform angular excursions (GAIN) in PSP was qualitatively different from both IPD and healthy subjects (GAIN cut-off value: 2.9, sensitivity of 94%, specificity of 72%). This effect was pronounced at the upper body level and at low as well as high frequencies. In contrast, IPD patients' stimulus-related body excursions were smaller compared to healthy subjects. Using a systems analysis approach, we were able to allocate these different postural strategies to differences in the use of sensory information as well as to different error correction efforts. CONCLUSIONS: While both PSP and IPD patients show abnormal postural control, the underlying pathology seems to be different. SIGNIFICANCE: The identification of disease-specific postural abnormalities shown here may be helpful for diagnostic as well as therapeutic discriminations of PSP vs. IPD.

Quantification of gait parameters with inertial sensors and inverse kinematics.

Measuring human gait is important in medicine to obtain outcome parameter for therapy, for instance in Parkinson's disease. Recently, small inertial sensors became available which allow for the registration of limb-position outside of the limited space of gait laboratories. The computation of gait parameters based on such recordings has been the subject of many scientific papers. We want to add to this knowledge by presenting a 4-segment leg model which is based on inverse kinematic and Kalman filtering of data from inertial sensors. To evaluate the model, data from four leg segments (shanks and thighs) were recorded synchronously with accelerometers and gyroscopes and a 3D motion capture system while subjects (n = 12) walked at three different velocities on a treadmill. Angular position of leg segments was computed from accelerometers and gyroscopes by Kalman filtering and compared to data from the motion capture system. The four-segment leg model takes the stance foot as a pivotal point and computes the position of the remaining segments as a kinematic chain (inverse kinematics). Second, we evaluated the contribution of pelvic movements to the model and evaluated a five segment model (shanks, thighs and pelvis) against ground-truth data from the motion capture system and the path of the treadmill. RESULTS: We found the precision of the Kalman filtered angular position is in the range of 2-6° (RMS error). The 4-segment leg model computed stride length and length of gait path with a constant undershoot of 3% for slow and 7% for fast gait. The integration of a 5th segment (pelvis) into the model increased its precision. The advantages of this model and ideas for further improvements are discussed.

Spatial constraints evoke increased number of steps during turning in Parkinson's disease.

OBJECTIVE: Turning and limitations to step length were shown to trigger progressive shortening of steps, which can lead to freezing of gait. By reducing the base area in which the turn had to take place, we aimed to evaluate the contribution of spatial constraints on 360° axial turns in people with Parkinson's disease with and without freezing. METHODS: We evaluated 40 patients with and without freezing and 16 age-matched healthy subjects. We assessed clinical data, and used body-worn inertial sensors to describe stepping and turn duration of 360° in quadratic squares of different sizes marked on the floor. RESULTS: We found that, when subjects had to perform turns in smaller as compared to larger squares, this spatial constraint strongly affected the turning behavior, i.e. increased the number of steps, and the duration of turns. However, turning was significantly more impaired in patients as compared to controls, and patients with freezing were significantly worse as patients without freezing. CONCLUSION: Our data show that spatial constraint during axial turning has the potential to deteriorate stepping performance, especially in patients reporting freezing of gait. SIGNIFICANCE: The size of the base area needs to be defined in any item or scale that makes diagnostic use of turning.

MR imaging differentiation of Fe2+ and Fe3+ based on relaxation and magnetic susceptibility properties.

PURPOSE: The aim of this study is to evaluate the MR imaging behavior of ferrous (Fe2+) and ferric (Fe3+) iron ions in order to develop a noninvasive technique to quantitatively differentiate between both forms of iron. METHODS: MRI was performed at 3 T in a phantom consisting of 21 samples with different concentrations of ferrous and ferric chloride solutions (between 0 and 10 mmol/L). A multi-echo spoiled gradient-echo pulse sequence with eight echoes was used for both T 2* and quantitative susceptibility measurements. The transverse relaxation rate, R 2* = 1/T 2*, was determined by nonlinear exponential fitting based on the mean signals in each sample. The susceptibilities, χ, of the samples were calculated after phase unwrapping and background field removal by fitting the spatial convolution of a unit dipole response to the measured internal field map. Relaxation rate changes, ΔR 2*(c Fe), and susceptibility changes, Δχ(c Fe), their linear slopes, as well as the ratios ΔR 2*(c Fe) / Δχ(c Fe) were determined for all concentrations. RESULTS: The linear slopes of the relaxation rate were (12.5 ± 0.4) s-1/(mmol/L) for Fe3+ and (0.77 ± 0.09) s-1/(mmol/L) for Fe2+ (significantly different, z test P < 0.0001). The linear slopes of the susceptibility were (0.088 ± 0.003) ppm/(mmol/L) for Fe3+ and (0.079 ± 0.006) ppm/(mmol/L) for Fe2+. The individual ratios ΔR 2*/Δχ were greater than 40 s-1/ppm for all samples with ferric solution and lower than 20 s-1/ppm for all but one of the samples with ferrous solution. CONCLUSION: Ferrous and ferric iron ions show significantly different relaxation behaviors in MRI but similar susceptibility patterns. These properties can be used to differentiate ferrous and ferric samples.

Neck Vibration Proprioceptive Postural Response Intact in Progressive Supranuclear Palsy unlike Idiopathic Parkinson's Disease.

Progressive supranuclear palsy (PSP) and late-stage idiopathic Parkinson's disease (IPD) are neurodegenerative movement disorders resulting in different postural instability and falling symptoms. IPD falls occur usually forward in late stage, whereas PSP falls happen in early stages, mostly backward, unprovoked, and with high morbidity. Postural responses to sensory anteroposterior tilt illusion by bilateral dorsal neck vibration were probed in both groups versus healthy controls on a static recording posture platform. Three distinct anteroposterior body mass excursion peaks (P1-P3) were observed. 18 IPD subjects exhibited well-known excessive response amplitudes, whereas 21 PSP subjects' responses remained unaltered to 22 control subjects. Neither IPD nor PSP showed response latency deficits, despite brainstem degeneration especially in PSP. The observed response patterns suggest that PSP brainstem pathology might spare the involved proprioceptive pathways and implies viability of neck vibration for possible biofeedback and augmentation therapy in PSP postural instability.

Postural Stabilization Differences in Idiopathic Parkinson's Disease and Progressive Supranuclear Palsy during Self-Triggered Fast Forward Weight Lifting.

Progressive supranuclear palsy (PSP) and late-stage idiopathic Parkinson's disease (IPD) are neurodegenerative movement disorders resulting in different postural instability and falling symptoms. IPD falls occur usually forward in late stage, whereas PSP falls happen in early stages, mostly backward, unprovoked, and with high morbidity. Self-triggered, weighted movements appear to provoke falls in IPD, but not in PSP. Repeated self-triggered lifting of a 0.5-1-kg weight (<2% of body weight) with the dominant hand was performed in 17 PSP, 15 IPD with falling history, and 16 controls on a posturography platform. PSP showed excessive force scaling of weight and body motion with high-frequency multiaxial body sway, whereas IPD presented a delayed-onset forward body displacement. Differences in center of mass displacement apparent at very small weights indicate that both syndromes decompensate postural control already within stability limits. PSP may be subject to specific postural system devolution. IPD are susceptible to delayed forward falling. Differential physiotherapy strategies are suggested.

Hypometric anticipatory postural adjustments in dystonia are not affected by deep brain stimulation of globus pallidus internus.

BACKGROUND: Dystonia is a movement disorder with patterned, directional, and often sustained muscle contractions that produce abnormal postures or repetitive movements. Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is an effective and safe treatment for medically refractory dystonia. However, recent studies reported gait problems, gait freezing and falls in patients treated with DBS. Because these symptoms may point to deficient gait initiation processes, we systematically assessed the anticipatory postural adjustments (APAs) prior to stepping in dystonia patients with GPi-DBS. METHODS: Thirteen patients with focal/segmental dystonia under GPi-DBS and twelve healthy control subjects were included in the study. Data were collected using pressure sensitive sensors and APAs were studied by centre of pressure measures. We compared APAs of both groups and analysed the influence of GPi-DBS on APAs in patients. RESULTS: Medio-lateral and antero-posterior COP displacements, total COP path, maximal APA velocity and 1st step length were all smaller in patients for both ON (p=0.006, p=0.018, p=0.002, p=0.016, p=0.04) and OFF (p=0.001, p=0.01, p=0.001, p=0.03, p=0.024) condition compared to healthy subjects. GPi-DBS did not change APA parameters in patients. CONCLUSIONS: Observations that APAs are impaired in dystonia and are at the same time not affected by the stimulation current are compatible with the assumption that APAs and dystonic symptoms may rely on distinct networks, possibly within the same cortical and basal ganglia structures. With no effect of stimulation on APAs it is unlikely that this would be a mechanism of impaired balance in the patients after the surgery.

Diagnostic accuracy of whole-brain CT perfusion in the detection of acute infratentorial infarctions.

INTRODUCTION: Although the diagnostic performance of whole-brain computed tomographic perfusion (WB-CTP) in the detection of supratentorial infarctions is well established, its value in the detection of infratentorial strokes remains less well defined. We examined its diagnostic accuracy in the detection of infratentorial infarctions and compared it to nonenhanced computed tomography (NECT), aiming to identify factors influencing its detection rate. METHODS: Out of a cohort of 1380 patients who underwent WB-CTP due to suspected stroke, we retrospectively included all patients with MRI-confirmed infratentorial strokes and compared it to control patients without infratentorial strokes. Two blinded readers evaluated NECT and four different CTP maps independently for the presence and location of infratentorial ischemic perfusion deficits. RESULTS: The study was designed as a retrospective case-control study and included 280 patients (cases/controls = 1/3). WB-CTP revealed a greater diagnostic sensitivity than NECT (41.4 vs. 17.1 %, P = 0.003). The specificity, however, was comparable (93.3 vs. 95.0 %). Mean transit time (MTT) and time to drain (TTD) were the most sensitive (41.4 and 40.0 %) and cerebral blood volume (CBV) the most specific (99.5 %) perfusion maps. Infarctions detected using WB-CTP were significantly larger than those not detected (15.0 vs. 2.2 ml; P = 0.0007); infarct location, however, did not influence the detection rate. CONCLUSION: The detection of infratentorial infarctions can be improved by assessing WB-CTP as part of the multimodal stroke workup. However, it remains a diagnostic challenge, especially small volume infarctions in the brainstem are likely to be missed.

Gait recording with inertial sensors--How to determine initial and terminal contact.

Lightweight inertial sensors are increasingly used for recording of gait in medicine, rehabilitation and sport. Several distinct events during the gait cycle such as heel-strike or toe-off have to be detected in the data obtained from these sensors. We re-investigated the correlation between the data of shank-mounted gyroscopes and three reference systems, namely accelerometers, pressure-sensitive soles and a motion capture system in a group of 14 young healthy men. We confirmed that the heel strike corresponds to a trough in the gyroscope curve, as several previous reports have stated. However, the toe-off moment clearly did not coincide with another trough of the gyroscope trace, as had been assumed in the past. The heel-off moment was reliably at 51% of the step cycle, irrespective of gait velocity, in our data. These findings are crucial for gait recording systems which aim to assess the temporal as well as spatial descriptors of human gait.

Crossed cerebellar diaschisis in patients with acute middle cerebral artery infarction: Occurrence and perfusion characteristics.

We aimed to investigate the overall prevalence and possible factors influencing the occurrence of crossed cerebellar diaschisis after acute middle cerebral artery infarction using whole-brain CT perfusion. A total of 156 patients with unilateral hypoperfusion of the middle cerebral artery territory formed the study cohort; 352 patients without hypoperfusion served as controls. We performed blinded reading of different perfusion maps for the presence of crossed cerebellar diaschisis and determined the relative supratentorial and cerebellar perfusion reduction. Moreover, imaging patterns (location and volume of hypoperfusion) and clinical factors (age, sex, time from symptom onset) resulting in crossed cerebellar diaschisis were analysed. Crossed cerebellar diaschisis was detected in 35.3% of the patients with middle cerebral artery infarction. Crossed cerebellar diaschisis was significantly associated with hypoperfusion involving the left hemisphere, the frontal lobe and the thalamus. The degree of the relative supratentorial perfusion reduction was significantly more pronounced in crossed cerebellar diaschisis-positive patients but did not correlate with the relative cerebellar perfusion reduction. Our data suggest that (i) crossed cerebellar diaschisis is a common feature after middle cerebral artery infarction which can robustly be detected using whole-brain CT perfusion, (ii) its occurrence is influenced by location and degree of the supratentorial perfusion reduction rather than infarct volume (iii) other clinical factors (age, sex and time from symptom onset) did not affect the occurrence of crossed cerebellar diaschisis.

Visual cues combined with treadmill training to improve gait performance in Parkinson's disease: a pilot randomized controlled trial.

OBJECTIVE: To evaluate the effects of visual cues combined with treadmill training on gait performance in patients with Parkinson's disease and to compare the strategy with pure treadmill training. DESIGN: Pilot, exploratory, non-blinded, randomized controlled trial. SETTING: University Hospital of Munich, Germany. SUBJECTS: Twenty-three outpatients with Parkinson's disease (Hoehn and Yahr stage II-IV). INTERVENTIONS: Patients received 12 training sessions within five weeks of either visual cues combined with treadmill training (n = 12) or pure treadmill training (n = 11). MAIN MEASURES: Outcome measures were gait speed, stride length and cadence recorded on the treadmill. Functional tests included the Timed Up and Go Test, the Unified Parkinson's Disease Rating Scale and the Freezing of gait-questionnaire. Assessments were conducted at baseline, after the training period and at two months follow-up. RESULTS: After the training period (n = 20), gait speed and stride length had increased in both groups (p ⩽ 0.05). Patients receiving the combined training scored better in the Timed Up and Go Test compared with the patients receiving pure treadmill training (p ⩽ 0.05). At two months follow-up (n = 13), patients who underwent the combined training sustained better results in gait speed and stride length (p ⩽ 0.05) and sustained the improvement in the Timed Up and Go Test (p ⩽ 0.05). CONCLUSIONS: This pilot study suggests that visual cues combined with treadmill training have more beneficial effects on gait than pure treadmill training in patients with a moderate stage of Parkinson's disease. A large-scale study with longer follow-up is required.

3D transcranial ultrasound as a novel intra-operative imaging technique for DBS surgery: a feasibility study.

PURPOSE: Intra-operative image guidance during deep brain stimulation (DBS) surgery is usually avoided due to cost and overhead of intra-operative MRI and CT acquisitions. Recently, there has been interest in the community towards the usage of non-invasive transcranial ultrasound (TCUS) through the preauricular bone window. In this work, we investigate, for the first time, the feasibility of using 3D-TCUS for imaging of already implanted DBS electrodes. As a first step towards this goal, we report imaging methods and electrode localisation errors outside of the operating room on eight previously operated DBS patients. METHODS: We evaluate the feasibility of using 3D-TCUS by registering volumes to pre-operative T1-MRI. US-MRI registration is achieved through a two-step point-based approach. First, a rough surface scan of the subjects' skin surface in 3D-TCUS space is registered to a segmented skin-surface point cloud from MRI. Next, we perform a refinement using rigid registration of multiple pairs of manually marked anatomical landmarks. We validate against post-operative CT scans which are also registered to pre-operative MRI. RESULTS: Qualitative results are given in form of 3D reconstruction examples at 2.5 and 3.5 MHz TCUS image frequency, overlaid on pre-operative T1-MRI and post-operative CT. Quantitative evaluation is performed by reporting the accuracy of electrode tip localisation at 2.5 and 3.5 MHz after our US-MRI approach. As a baseline, we also report RMSE errors for pairs of anatomical landmarks in pre-operative MRI and 3D-TCUS. CONCLUSION: Multiple image examples show the appearance and quality of 3D-TCUS scans, depending on the bone window. Overall accuracy of anatomic point pairs lies on the order of 3.2 mm, using our registration approach. Compared to this baseline, electrode tip localisation in 3D-TCUS has a mean accuracy on the order of 4.8 mm and a precision on the order of 2.3 mm. While insufficient at first glance, we argue why these results are promising nonetheless. Our work motivates further future work in improved TCUS scanning, advanced TCUS-MRI registration and computer-aided electrode detection in 3D-TCUS.