Differential dose responses of transcranial focused ultrasound at brain regions indicate causal interactions.

We have previously shown that focused ultrasound (FUS) pulses in low pressure range exerted bidirectional and brain state-dependent neuromodulation in the nonhuman primate somatosensory cortices by fMRI. Here we aim to gain insights about the proposed neuron selective modulation of FUS and probe feedforward versus feedback interactions by simultaneously quantifying the stimulus (FUS pressures: 925, 425, 250 kPa) and response (% BOLD fMRI changes) function at the targeted area 3a/3b and off-target cortical areas at 7T. In resting-state, lowered intensities of FUS resulted in decreased fMRI signal changes at the target area 3a/3b and off-target area 1/2, S2, MCC, insula and auditory cortex, and no signal difference in thalamic VPL and MD nuclei.

A reduced aperture allows for transcranial focus localization at lower pressure.

Localizing the focus during transcranial focused ultrasound procedures is important to ensure accurate targeting of specific brain regions and interpretation of results. Magnetic resonance acoustic radiation force imaging uses the displacement induced by the ultrasound focus in the brain to localize the beam, but the high pressure required to displace brain tissue may cause damage or confounds during subsequent neuromodulatory experiments. Here, reduced apertures were applied to a phased array transducer to generate comparable displacement to the full aperture but with 20% lower free field pressure.

Conditional Vasospasm-Free Survival Following Aneurysmal Subarachnoid Hemorrhage.

Background: Following aneurysmal subarachnoid hemorrhage (SAH), patients are monitored closely for vasospasm in the intensive care unit. Conditional vasospasm-free survival describes the risk of future vasospasm as a function of time elapsed without vasospasm. Conditional survival has not been applied to this clinical scenario but could improve patient counseling and intensive care unit use.

Impact of postoperative dexamethasone on survival, steroid dependency, and infections in newly diagnosed glioblastoma patients.

Background: We examined the effect of dexamethasone prescribed in the initial 3 postoperative weeks on survival, steroid dependency, and infection in glioblastoma patients.

Methods: In this single-center retrospective cohort analysis, we electronically retrieved inpatient administration and outpatient prescriptions of dexamethasone and laboratory values from the medical record of 360 glioblastoma patients. We correlated total dexamethasone prescribed from postoperative day (POD) 0 to 21 with survival, dexamethasone prescription from POD30 to POD90, and diagnosis of an infection by POD90.

Bidirectional and state-dependent modulation of brain activity by transcranial focused ultrasound in non-human primates.

Transcranial focused ultrasound (FUS) stimulation under MRI guidance, coupled with functional MRI (fMRI) monitoring of effects, offers a precise, noninvasive technology to dissect functional brain circuits and to modulate altered brain functional networks in neurological and psychiatric disorders. Here we show that ultrasound at moderate intensities modulated neural activity bi-directionally. Concurrent sonication of somatosensory areas 3a/3b with 250 kHz FUS suppressed the fMRI signals produced there by peripheral tactile stimulation, while at the same time eliciting fMRI activation at inter-connected, off-target brain regions.

Hyperoxemia and Cerebral Vasospasm in Aneurysmal Subarachnoid Hemorrhage.

Background: Cerebral vasospasm is a major contributor to disability and mortality after aneurysmal subarachnoid hemorrhage. Oxidation of cell-free hemoglobin plays an integral role in neuroinflammation and is a suggested source of tissue injury after aneurysm rupture. This study sought to determine whether patients with subarachnoid hemorrhage and cerebral vasospasm were more likely to have been exposed to early hyperoxemia than those without vasospasm.

Considerations for ultrasound exposure during transcranial MR acoustic radiation force imaging.

The aim of this study was to improve the sensitivity of magnetic resonance-acoustic radiation force imaging (MR-ARFI) to minimize pressures required to localize focused ultrasound (FUS) beams, and to establish safe FUS localization parameters for ongoing ultrasound neuromodulation experiments in living non-human primates. We developed an optical tracking method to ensure that the MR-ARFI motion-encoding gradients (MEGs) were aligned with a single-element FUS transducer and that the imaged slice was prescribed at the optically tracked location of the acoustic focus. This method was validated in phantoms, which showed that MR-ARFI-derived displacement sensitivity is maximized when the MR-ARFI MEGs were maximally aligned with the FUS propagation direction.

Volumetric MRI thermometry using a three-dimensional stack-of-stars echo-planar imaging pulse sequence.

Purpose: To measure temperature over a large brain volume with fine spatiotemporal resolution.

Methods: A three-dimensional stack-of-stars echo-planar imaging sequence combining echo-planar imaging and radial sampling with golden angle spacing was implemented at 3T for proton resonance frequency-shift temperature imaging. The sequence acquires a 188x188x43 image matrix with 1.

Snapshot MR technique to measure OEF using rapid frequency mapping.

Magnetic resonance (MR)-based oxygen extraction fraction (OEF) measurement techniques that use blood oxygen level-dependent (BOLD)-based approaches require the measurement of the R2' decay rate and deoxygenated blood volume to derive the local oxygen saturation in vivo. We describe here a novel approach to measure OEF using rapid local frequency mapping. By modeling the MR decay process in the static dephasing regime as two separate dissipative and oscillatory effects, we calculate the OEF from local frequencies measured across the brain by assuming that the biophysical mechanisms causing OEF-related frequency changes can be determined from the oscillatory effects.

RAZER: a pulse sequence for whole-brain bolus tracking at high frame rates.

Purpose: To introduce a pulse sequence that obtains whole-brain perfusion measurements at 1.7 mm isotropic voxel resolution by dynamic susceptibility contrast MRI bolus tracking despite using a temporal resolution of 10.3 s: RAdial kZ-blipped 3D GRE-echo-planar imaging (GRE-EPI) for whole-brain pERfusion (RAZER).