Cerebral blood flow (CBF) imaging using arterial spin labeling (ASL)

ASL is a noninvasive technique to measure CBF by using magnetically labeled arterial blood water as an endogenous tracer. A main research direction at LOFT is development and translation of advanced ASL techniques. In particular, pseudo-continuous ASL (pCASL) with background suppressed (BS) 3D GRASE sequence showed great promise in perfusion imaging of acute stroke and brain tumor (Figs. 1-3, thumbnail link to Gallery). Pediatric perfusion imaging using ASL is a main area of applications and is funded by NIMH R01 and ARRA. In a pilot project funded by UCLA Alzheimer’s Disease Research Center (ADRC), we are comparing ASL with positron emission tomography (PET) in mild cognitive impairment and early Alzheimer’s disease patients. Ongoing developments at LOFT include vessel-encoded ASL in chronic stroke and moya moya disease. We are also comparing ASL with dynamic susceptibility contrast (DSC) perfusion MRI and digital subtraction angiography (DSA) in stroke patients. In collaboration with Beijing MRI center at Chinese Academy of Sciences, we are developing ultrahigh field ASL at 7T (Fig. 4).

Pediatric Template of Brain Perfusion

As a major neuroscience application, we are collecting both cross-sectional and longitudinal ASL perfusion MRI data from typical developing children aged 7 to 17. These data will be used to construct a developmental template of brain function based on baseline CBF and perfusion responses to working memory tasks. This project is funded by NIMH and ARRA. We are also part of the C-MIND project to study the development of brain function from infants to adolescents using ASL and BOLD fMRI (https://research.cchmc.org/c-mind/) funded by NICHD.
Pediatric Template of Brain Perfusion released: http://figshare.com/articles/The_Pediatric_Template_of_Brain_Perfusion_PTBP_/923555

Arterial transit time and water permeability mapping using diffusion weighted perfusion MRI

Another research direction at LOFT is to develop diffusion-weighted (DW) ASL perfusion MRI to separate labeled signals in the arterial, capillary and tissue compartments, thereby allowing estimate of arterial transit time (a technique termed FEAST) and water permeability across the blood-brain barrier (BBB). We are applying FEAST in chronic stroke and moya moya patients. In addition, we are collaborating with Dr. Timothy Duong at Univ of Texas Health Science Center at San Antonio (UTHSCSA) to perform BBB water permeability measures in non-human primates (NHP) (Fig. 5&6, thumbnail link to Gallery).

Time-resolved 4D dynamic MR angiography (dMRA) and cerebral blood volume (CBV) mapping

A recent development at LOFT is to perform time-resolved 4D dynamic MRA (dMRA) by combining ASL with segmented multiphase TrueFISP readout – a technique termed TrueSTAR (TrueFISP based spin tagging with alternating radiofrequency). This 4D dMRA technique provides millisecond (50-100ms) temporal resolution and millimeter (1-4mm3) spatial resolution, and is useful in delineating dynamic blood flow through arteriovenous malformation (AVM). Further developments include improving the imaging speed of TrueSTAR using radial acquisition, HYPR, compressed sensing (CS) and parallel imaging. We are also developing algorithms to quantify cerebral blood volume (CBV) using TrueSTAR.
(thumbnail link to videos in ppt)

Functional MRI with high spatiotemporal resolution

At LOFT, we are interested in developing alternative pulse sequences for BOLD and perfusion based fMRI that offer millisecond (a few 100ms) temporal resolution and millimeter (1-5mm3) spatial resolution. These alternative pulse sequences include GRASE and TrueFISP etc. in conjunction with radial trajectories and parallel acquisition. Compared to conventional gradient-echo EPI, these alternative methods offer improved coverage of brain regions affected by field inhomogeneity effects, such as the orbitofrontal cortex. The high temporal resolution is beneficial for event-related fMRI and resting state fMRI to filter out physiological noise. Recently, we have applied simultaneous multislice (SMS) or multiband imaging techniques in ASL and steady state free precession (SSFP) sequences to achieve highly accelerated fMRI without geometric distortion or banding artifacts.

Perfusion MRI in body organs and rodents

Currently, we are expanding research interests from human brain to body organs such as myocardium, kidney, skeletal muscle. In collaboration with Dr. Hongyu An at Univ of North Carolina at Chapel Hill, we are developing rodent perfusion imaging at 7 and 9.4T using continuous and pseudo-continuous ASL.
(Fig. 7-9, thumbnail link to Gallery).

Imaging of Neuromodulation

We are developing novel imaging techniques for mapping neuromodulation effects using transcranial electric stimulation (TES) and deep brain stimulation (DBS), including MR mapping of electric currents based on the Ampere’s law and neuromodulation induced hemodynamic effects using BOLD and ASL imaging. These techniques can be applied for verifying target engagement and to guide the application of neuromodulation techniques such as transcranial direct current stimulation (tDCS) in clinical populations.
Watch Mayank Jog presentation at BrainSTIM symposium of OHBM meeting 2015 in Hawaii. Youtube link