Vivek Buch, Postdoctoral Faculty Sponsor
Multisite thalamic recordings to characterize seizure propagation in the human brain.
Brain : a journal of neurology
Neuromodulation of the anterior nuclei of the thalamus (ANT) has shown to be efficacious in a subset of patients with refractory focal epilepsy. One important uncertainty is to what extent thalamic subregions other than the ANT could be recruited more prominently in the propagation of focal onset seizures. We designed the current study to simultaneously monitor the engagement of the ANT, mediodorsal (MD) and pulvinar (PUL) nuclei during seizures in patients who could be candidates for thalamic neuromodulation. We studied 11 patients with clinical manifestations of presumed temporal lobe epilepsy (TLE) undergoing invasive stereo-encephalography (sEEG) monitoring to confirm the source of their seizures. We extended cortical electrodes to reach the ANT, MD and PUL nuclei of the thalamus. More than one thalamic subdivision was simultaneously interrogated in nine patients. We recorded seizures with implanted electrodes across various regions of the brain and documented seizure onset zones (SOZ) in each recorded seizure. We visually identified the first thalamic subregion to be involved in seizure propagation. Additionally, in eight patients, we applied repeated single pulse electrical stimulation in each SOZ and recorded the time and prominence of evoked responses across the implanted thalamic regions. Our approach for multisite thalamic sampling was safe and caused no adverse events. Intracranial EEG recordings confirmed SOZ in medial temporal lobe, insula, orbitofrontal and temporal neocortical sites, highlighting the importance of invasive monitoring for accurate localization of SOZs. In all patients, seizures with the same propagation network and originating from the same SOZ involved the same thalamic subregion, with a stereotyped thalamic EEG signature. Qualitative visual reviews of ictal EEGs were largely consistent with the quantitative analysis of the corticothalamic evoked potentials, and both documented that thalamic nuclei other than ANT could have the earliest participation in seizure propagation. Specifically, pulvinar nuclei were involved earlier and more prominently than ANT in more than half of the patients. However, which specific thalamic subregion first demonstrated ictal activity could not be reliably predicted based on clinical semiology or lobar localization of SOZs. Our findings document the feasibility and safety of bilateral multisite sampling from the human thalamus. This may allow more personalized thalamic targets to be identified for neuromodulation. Future studies are needed to determine if a personalized thalamic neuromodulation leads to greater improvements in clinical outcome.
View details for DOI 10.1093/brain/awad121
View details for PubMedID 37137813
Banding-free balanced SSFP cardiac cine using frequency modulation and phase cycle redundancy.
Magnetic resonance in medicine
PURPOSE: To develop a method for banding-free balanced SSFP cardiac cine imaging in a single breath-hold.METHODS: A frequency modulation scheme was designed for cardiac applications to eliminate the time normally required for steady-state stabilization between multiple phase-cycled acquisitions. Highly undersampled acquisitions were reconstructed using a model-based reconstruction that exploits redundancy both over time and between phase cycles. Performance of the methods was evaluated using both retrospective and prospective undersampling in scans with and without frequency modulation from four subjects.RESULTS: The proposed methods enabled balanced SSFP cardiac cine with three effective phase cycles in only 10 heartbeats. Images acquired with frequency modulation and with standard phase cycling were of similar quality. The combination of temporal and inter-acquisition similarity constraints reduced errors by approximately 45% compared to enforcing similarity constraints over time alone.CONCLUSIONS: In off-resonance conditions that preclude the acquisition of single-acquisition balanced SSFP, phase cycling can eliminate the dark bands in balanced SSFP cine cardiac imaging at the expense of some SNR efficiency. The proposed techniques permit these types of acquisitions in a single breath-hold.
View details for DOI 10.1002/mrm.27815
View details for PubMedID 31228278
Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.
Magnetic resonance in medicine
2018; 79 (6): 2944–53
To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing.A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects.Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets.Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
View details for PubMedID 28994486