Bio

Professional Education


  • Doctor of Philosophy, Arizona State University, Biomedical Engineering (2019)
  • Bachelor of Engineering, Southern Medical University (First Military Medical University), Biomedical Engineering (2013)

Stanford Advisors


Publications

All Publications


  • Evaluation of magnetohydrodynamic effects in magnetic resonance electrical impedance tomography at ultra-high magnetic fields MAGNETIC RESONANCE IN MEDICINE Minhas, A. S., Chauhan, M., Fu, F., Sadleir, R. 2019; 81 (4): 2264–76

    Abstract

    Artifacts observed in experimental magnetic resonance electrical impedance tomography images were hypothesized to be because of magnetohydrodynamic (MHD) effects.Simulations of MREIT acquisition in the presence of MHD and electrical current flow were performed to confirm findings. Laminar flow and (electrostatic) electrical conduction equations were bidirectionally coupled via Lorentz force equations, and finite element simulations were performed to predict flow velocity as a function of time. Gradient sequences used in spin-echo and gradient echo acquisitions were used to calculate overall effects on MR phase images for different electrical current application or phase-encoding directions.Calculated and experimental phase images agreed relatively well, both qualitatively and quantitatively, with some exceptions. Refocusing pulses in spin echo sequences did not appear to affect experimental phase images.MHD effects were confirmed as the cause of observed experimental phase changes in MREIT images obtained at high fields. These findings may have implications for quantitative measurement of viscosity using MRI techniques. Methods developed here may be also important in studies of safety and in vivo artifacts observed in high field MRI systems.

    View details for DOI 10.1002/mrm.27534

    View details for Web of Science ID 000462092100005

    View details for PubMedID 30450638

    View details for PubMedCentralID PMC6373455

  • Functional magnetic resonance electrical impedance tomography (fMREIT) sensitivity analysis using an active bidomain finite-element model of neural tissue MAGNETIC RESONANCE IN MEDICINE Sadleir, R. J., Fu, F., Chauhan, M. 2019; 81 (1): 602–14

    Abstract

    A direct method of imaging neural activity was simulated to determine typical signal sizes.An active bidomain finite-element model was used to estimate approximate perturbations in MR phase data as a result of neural tissue activity, and when an external MR electrical impedance tomography imaging current was added to the region containing neural current sources.Modeling-predicted, activity-related conductivity changes should produce measurable differential phase signals in practical MR electrical impedance tomography experiments conducted at moderate resolution at noise levels typical of high field systems. The primary dependence of MR electrical impedance tomography phase contrast on membrane conductivity changes, and not source strength, was demonstrated.Because the injected imaging current may also affect the level of activity in the tissue of interest, this technique can be used synergistically with neuromodulation techniques such as deep brain stimulation, to examine mechanisms of action.

    View details for DOI 10.1002/mrm.27351

    View details for Web of Science ID 000454009000049

    View details for PubMedID 29770490

    View details for PubMedCentralID PMC6239993

  • The effect of potassium chloride on Aplysia Californica abdominal ganglion activity BIOMEDICAL PHYSICS & ENGINEERING EXPRESS Fu, F., Chauhan, M., Sadleir, R. 2018; 4 (3)
  • Direct detection of neural activity in vitro using magnetic resonance electrical impedance tomography (MREIT) NEUROIMAGE Sadleir, R. J., Fu, F., Falgas, C., Holland, S., Boggess, M., Grant, S. C., Woo, E. 2017; 161: 104–19

    Abstract

    We describe a sequence of experiments performed in vitro to verify the existence of a new magnetic resonance imaging contrast - Magnetic Resonance Electrical Impedance Tomography (MREIT) -sensitive to changes in active membrane conductivity. We compared standard deviations in MREIT phase data from spontaneously active Aplysia abdominal ganglia in an artificial seawater background solution (ASW) with those found after treatment with an excitotoxic solution (KCl). We found significant increases in MREIT treatment cases, compared to control ganglia subject to extra ASW. This distinction was not found in phase images from the same ganglia using no imaging current. Further, significance and effect size depended on the amplitude of MREIT imaging current used. We conclude that our observations were linked to changes in cell conductivity caused by activity. Functional MREIT may have promise as a more direct method of functional neuroimaging than existing methods that image correlates of blood flow such as BOLD fMRI.

    View details for DOI 10.1016/j.neuroimage.2017.08.004

    View details for Web of Science ID 000415673100010

    View details for PubMedID 28818695

    View details for PubMedCentralID PMC5696120

  • Temperature- and frequency-dependent dielectric properties of biological tissues within the temperature and frequency ranges typically used for magnetic resonance imaging-guided focused ultrasound surgery INTERNATIONAL JOURNAL OF HYPERTHERMIA Fu, F., Xin, S., Chen, W. 2014; 30 (1): 56–65

    Abstract

    This study aimed to obtain the temperature- and frequency-dependent dielectric properties of tissues subjected to magnetic resonance (MR) scanning for MR imaging-guided focused ultrasound surgery (MRgFUS). These variables are necessary to calculate radio frequency electromagnetic fields distribution and specific radio frequency energy absorption rate (SAR) in the healthy tissues surrounding the target tumours, and their variation may affect the efficacy of advanced RF pulses.The dielectric properties of porcine uterus, liver, kidney, urinary bladder, skeletal muscle, and fat were determined using an open-ended coaxial probe method. The temperature range was set from 36 °C to 60 °C; and the frequencies were set at 42.58 (1 T), 64 (1.5 T), 128 (3 T), 170 (4 T), 298 (7 T), 400 (9 T), and 468 MHz (11 T).Within the temperature and frequency ranges, the dielectric constants were listed as follows: uterus 49.6-121.64, liver 44.81-127.68, kidney 37.3-169.26, bladder 42.43-125.95, muscle 58.62-171.7, and fat 9.2327-20.2295. The following conductivities were obtained at the same temperature and frequency ranges: uterus 0.5506-1.4419, liver 0.5174-0.9709, kidney 0.8061-1.3625, bladder 0.6766-1.1817, muscle 0.8983-1.3083, and fat 0.1552-0.2316.The obtained data are consistent with the temperature and frequency ranges typically used in MRgFUS and thus can be used as reference to calculate radio frequency electromagnetic fields and SAR distribution inside the healthy tissues subjected to MR scanning for MRgFUS.

    View details for DOI 10.3109/02656736.2013.868534

    View details for Web of Science ID 000330708100008

    View details for PubMedID 24417349