Potentials and Limitations of Directional Deep Brain Stimulation: A Simulation Approach.

BACKGROUND: Directional leads are increasingly used in deep brain stimulation. They allow shaping the electrical field in the axial plane. These new possibilities increase the complexity of programming. Thus, optimized programming approaches are needed to assist clinical testing and to obtain full clinical benefit. OBJECTIVES: This simulation study investigates to what extent the electrical field can be shaped by directional steering to compensate for lead malposition. METHOD: Binary volumes of tissue activated (VTA) were simulated, by using a finite element method approach, for different amplitude distributions on the three directional electrodes. VTAs were shifted from 0 to 2 mm at different shift angles with respect to the lead orientation, to determine the best compensation of a target volume. RESULTS: Malpositions of 1 mm can be compensated with the highest gain of overlap with directional leads. For larger shifts, an improvement of overlap of 10-30% is possible, depending on the stimulation amplitude and shift angle of the lead. Lead orientation and shift determine the amplitude distribution of the electrodes. CONCLUSION: To get full benefit from directional leads, both the shift angle as well as the shift to target volume are required to choose the correct amplitude distribution on the electrodes. Current directional leads have limitations when compensating malpositions >1 mm; however, they still outperform conventional leads in reducing overstimulation. Further, their main advantage probably lies in the reduction of side effects. Databases like the one from this simulation could serve for optimized lead programming algorithms in the future.

Previous Musical Experience and Cortical Thickness Relate to the Beneficial Effect of Motor Synchronization on Auditory Function.

Auditory processing can be enhanced by motor system activity. During auditory-motor synchronization, motor activity guides auditory attention and thus facilitates auditory processing through active sensing. Previous research on enhanced auditory processing through motor synchronization has been limited to easy tasks with simple stimulus material. Further, the mechanisms and brain regions underlying this synchronization are unclear. We investigated the effect of motor synchronization on auditory processing with naturalistic, musical auditory material in a discrimination task. We further assessed how previous musical training and cortical thickness of specific brain regions relate to different aspects of auditory-motor synchronization. We conducted an auditory-motor experiment in 139 adults. The task involved melody discrimination and beat tapping synchronization. Additionally, 68 participants underwent structural MRI. We found that individuals with better auditory-motor synchronization accuracy showed improved melody discrimination, and that melody discrimination was better in trials with higher tapping accuracy. However, melody discrimination was worse in the tapping than in the listening only condition. Longer previous musical training and thicker Heschl's gyri were associated with better melody discrimination and better tapping synchrony. Post hoc analyses furthermore pointed to a possible moderating role of frontal regions. Our results suggest that motor synchronization can enhance auditory discrimination abilities through active sensing, but that this beneficial effect can be counteracted by dual-task inference when the two tasks are too challenging. Moreover, prior experience and structural brain differences influence the extent to which an individual can benefit from motor synchronization in complex listening. This could inform future research directed at development of personalized training programs for hearing ability.

Accelerated 3D-GRASE imaging improves quantitative multiple post labeling delay arterial spin labeling.

PURPOSE: To investigate the impact of accelerated, single-shot 3D-GRASE acquisition on quantitative arterial spin labeling (ASL) with multiple and single post-labeling delay (PLD) in terms of perfusion-weighted SNR per unit scan time (TSNRPW ) and quantification accuracy. METHODS: Five subjects were scanned on a 3T MRI scanner using the pseudo-continuous arterial spin labeling (PCASL) technique with a 3D-GRASE imaging sequence capable of parallel imaging acceleration. A 3-inversion pulse background suppression was simulated and implemented in the sequence. Three time-matched single PLD measurements, a segmented one without acceleration, 1 with conventional GRAPPA, and 1 with CAIPIRINHA sampling, were used to compare TSNRPW . Three time-matched multiple PLD measurements with the identical imaging parameters were additionally evaluated (no acceleration vs. CAIPIRINHA sampling vs. CAIPIRINHA sampling with doubled number of PLDs). Cerebral blood flow and arterial transit time fit uncertainties were compared and used as a quality measure. RESULTS: The single PLD measurements show an 11% TSNRPW increase using CAIPIRINHA sampling instead of GRAPPA sampling, while the non-accelerated scan exhibits 35% higher TSNRPW compared to the GRAPPA scan. However, taking advantage of the increased number of averages for multiple PLD acquisitions, a 14%/16% (gray matter) and 34%/36% (white matter) reduction of CBF fit uncertainty is observed with CAIPIRINHA sampling (6 PLDs/12 PLDs) compared to no acceleration. CONCLUSION: Accelerated single-shot 3D-GRASE with PCASL allows for smaller quantification uncertainties than time-matched segmented acquisitions. Corresponding single-shot acquisitions with acceptable blurring and no intra-volume motion render state-of-the-art ASL methods in a clinically feasible time possible.

Improving perfusion quantification in arterial spin labeling for delayed arrival times by using optimized acquisition schemes.

OBJECTIVE: The improvement in Arterial Spin Labeling (ASL) perfusion quantification, especially for delayed bolus arrival times (BAT), with an acquisition redistribution scheme mitigating the T1 decay of the label in multi-TI ASL measurements is investigated. A multi inflow time (TI) 3D-GRASE sequence is presented which adapts the distribution of acquisitions accordingly, by keeping the scan time constant. MATERIAL AND METHODS: The MR sequence increases the number of averages at long TIs and decreases their number at short TIs and thus compensating the T1 decay of the label. The improvement of perfusion quantification is evaluated in simulations as well as in-vivo in healthy volunteers and patients with prolonged BATs due to age or steno-occlusive disease. RESULTS: The improvement in perfusion quantification depends on BAT. At healthy BATs the differences are small, but become larger for longer BATs typically found in certain diseases. The relative error of perfusion is improved up to 30% at BATs>1500ms in comparison to the standard acquisition scheme. CONCLUSION: This adapted acquisition scheme improves the perfusion measurement in comparison to standard multi-TI ASL implementations. It provides relevant benefit in clinical conditions that cause prolonged BATs and is therefore of high clinical relevance for neuroimaging of steno-occlusive diseases.