Ms. Alice K. Ding Profile

Alice K. Ding

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Proceedings Article | 4 April 2022 Paper

Controllability of the vagus nerve using directed electrode stimulation

Brianna Jacobson, Alice Ding, Ma Luo, Kyvia Pereira, Michael Miga

Proceedings Volume 12034, 120342H (2022) https://doi.org/10.1117/12.2612783

KEYWORDS: Nerve, Electrodes, Axons, Action potentials, 3D modeling, Surgery, Finite element methods, Tissues, Platinum, Nervous system

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Vagus nerve stimulation (VNS), commonly used to reduce seizures in patients with epilepsy, is a promising therapeutic treatment for a number of health issues. Current VNS apparatuses employ a helical electrode design, which stimulates the nerve with no anatomical specificity. The efficacy and breadth of VNS therapy could be improved by targeting stimulation to specific regions of the nerve. A mock electrode was built around a morphologically accurate finite element model of the vagus nerve. Electric currents were injected into the nerve model, and a nodal activating function was used to determine which axons would initiate action potentials. Electrode configurations and stimulation settings were adjusted to target specific fascicles until optimal activation was achieved. Results indicated that small, proximal electrodes could stimulate targeted regions while avoiding activation of off-target axons. Injection of negative current perpendicular to the positive stimulus also proved to refine spatial stimulation, allowing for the activation of deep fascicles with minimal side-effects. While an understanding of the fascicular anatomy of the vagus nerve is still being explored, the preliminary results of this study corroborate the concept of selectively targeting regions of the nerve with electrical stimulation in order to treat specific patient needs. The computational process presented in this work could be employed as a planning tool prior to the geometrical design and surgical implantation of VNS devices.

Proceedings Article | 15 February 2021 Poster + Presentation + Paper

Modeling the effects of bipolar helical cuff electrodes in vagus nerve stimulation

Alice Ding, Ma Luo, Michael Miga

Proceedings Volume 11598, 115982H (2021) https://doi.org/10.1117/12.2582182

KEYWORDS: Tumors, Tumor growth modeling, Nerve, Electrodes, Therapeutics, Rigid registration, Microwave radiation, Magnetic resonance imaging, Transplantation, Liver

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While mainly used for reducing seizures in epileptic patients, vagus nerve stimulation (VNS) has been implied to be capable of treating various other diseases. However, the therapeutic extent and control of neuromodulation for these conditions are still uncertain and are limited by the ability to predict neural activation responses upon targeting certain fascicles. Generally, VNS is administered through a bipolar helical cuff electrode implanted around the left vagus nerve. The electrode delivers pulses of electricity to the nerve to recruit axons. This work focuses on predicting percent activation and regions of activation based on different adjustable factors such as injected current amplitude and pulse width of stimuli and the activated region of the electrode. To achieve, a simplified finite element model was created using cylindrical geometries as nerve components with an addition of helical cuff electrodes. All of these components were encased in surrounding tissue with assumed properties similar to adipose. Electric potential distribution in the model was processed with an activating function defined along the axonal length which estimates the injected current at the nodes of Ranvier (NoR). These values were then enforced in the neuron simulation as a current clamp approximation applied at the NoR and the likelihood of an action potential was determined. Presence of action potentials were then detected to determine which axons were recruited in VNS. This preliminary work determined that electrode configurations can target specific fascicles in the nerve while amplitudes and pulse widths of stimuli contribute to the percentage of the nerve activated. This demonstrates the ability for patient-specific control over targeting fascicles. Additionally, this work presents initial steps to improving the model by using histological data to create a geometric-specific approach.

Proceedings Article | 16 March 2020 Presentation + Paper

Image data-driven thermal dose prediction for microwave ablation therapy

Alice Ding, Jon Heiselman, Michael Miga

Proceedings Volume 11315, 113151G (2020) https://doi.org/10.1117/12.2550550

KEYWORDS: Tumors, Liver, Image registration, Computed tomography, Rigid registration, Microwave radiation, Tissues, Optical tracking, Image segmentation

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Because many patients diagnosed with hepatocellular carcinoma are not eligible for liver transplantation or resection, there has been a great deal of interest in developing locoregional therapies such as thermal ablation. One such thermal ablation therapy is microwave ablation. While benefits have been gained in the management of disease, local recurrence in locoregional therapies is still very common and represents a significant problem. One suggested factor is the presence of soft tissue deformation which is thought to compromise image-to-physical targeting of diseased tissue. This work focuses on presenting a hepatic phantom with an embedded mock tumor target and studying the effects of deformation on ablation when using image-to-physical rigid and non-rigid alignment approaches. While being deformable, the hepatic phantom was designed to enable optical visibility of the ablation zone with target lesion visibility in CT images post-treatment using albumin, agar, formaldehyde, and water constituents. Additionally, a physical mock tumor target phantom was embedded in the hepatic liver phantom and contained CT contrast agent for the designation of lesion prior to mock intervention. Using this phantom, CT scans and sparse-surface data were collected to perform rigid and nonrigid registrations. The registrations allowed for the navigation of the ablation probe to the center of the mock lesions using a custom-built guidance system; this was then followed by microwave ablation treatments. Approximately 96.8% of the mock lesion was ablated using nonrigid registration to guide delivery while none of the mock lesion was ablated using the rigid alignment for guidance, i.e. a completely missed target. This preliminary data demonstrates an improvement in the accuracy of target ablation using a guidance system that factors in soft tissue deformation.

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