The success of deep brain stimulation (DBS) is dependent on the accurate placement of electrodes in the operating room (OR). However, due to intraoperative brain shift, the accuracy of pre-operative scans and pre-surgical planning are often degraded. To compensate for brain shift, we created a finite element bio-mechanical brain model that updates preoperative images by assimilating intraoperative sparse data from the brain surface or deep brain targets. Additionally, we constructed an artificial neural network (ANN) that leveraged a large number of ventricle nodal displacements to estimate brain shift. The machine learning method showed potential in incorporating ventricle sparse data to accurately compute shift at the brain surface. Thus, in this paper, we propose using this machine learning model to estimate brain atrophy at deep brain targets such as the anterior commissure (AC) and the posterior commissure (PC). The ANN consists of an input layer with nine hand-engineered features, such as the distance between the deep brain target and the ventricle node, two hidden layers and an output layer. This model was trained using eight patient cases and tested on two patient cases.
The success of deep brain stimulation (DBS) depends upon the accurate surgical placement of electrodes in the OR. However, the accuracy of pre-operative scans is often degraded by intraoperative brain shift. To compensate for brain shift, we developed a biomechanical brain model that updates preoperative images by assimilating intraoperative sparse data from either the brain surface or deep brain structures. In addition to constraining the finite element model, surface sparse data estimates model boundary conditions such as the level of cerebrospinal fluid (CSF). As a potentially cost-effective and safe alternative to intraoperative imaging techniques, a machine learning method was proposed to estimate surface brain atrophy by leveraging a large number of ventricle nodal displacements. Specifically, we constructed an artificial neural network (ANN) that consisted of an input layer with 9 hand-engineered features such as the surface-to-ventricle nodal distance. The multilayer perceptron was trained using 132,000 nodal pairs from eleven patient cases and tested using 48,000 from four cases. Results showed that in a testing case, the ANN estimated an overall surface displacement of 8.79 ± 0.765 mm to the left and 8.26 ± .455 mm to the right compared to the ground truth (10.36 ± 1.33 mm left and 7.40 ± 1.40 mm right). The average prediction error of all four testing cases was less than 2 mm. With further development and evaluation, the proposed method has the potential of supplementing the biomechanical brain model with surface sparse data and estimating boundary parameters.
Brain shift is a confounder to the accuracy of electrode lead placement during deep brain stimulation (DBS) surgery. Model based image updating method can compensate for brain shift with high efficiency and accuracy. A key element to achieving clinically accepted accuracy using our biomechanical brain model is designating rigorous boundary conditions (BCs) that define general physics of the model. In this retrospective study, we searched for a set of six optimal BCs such as gravitational direction and level of CSF for our model to simulate accurate brain shift in DBS lead placement surgery. Specifically, we conducted 9072 trials of brain shift simulation with varying boundary conditions and deep brain sparse data for three training cases and applied these parameters to three testing cases for evaluation. The optimal set of parameters was determined based on lowest target registration error (TRE) evaluated at five deep brain landmarks near the subthalamus area. We show that simulations with optimal BCs compensated 61.28% and 50.06% of brain shift on average in two of the three testing cases where large brain deformation occurred and 26.5% in one testing case of small brain shift. In comparison, optimal BCs delivered consistent and accurate prediction of brain shift at all deep brain landmarks in both training and testing cases whereas default sets of BCs produced similar results at some landmarks but underperformed for the rest. With only deep brain sparse data and a set of optimal BCs, our biomechanical brain model can achieve significant brain shift compensation in DBS cases and Its clinical utility will be examined in surgical cases in future OR.
Accurate surgical placement of electrodes is essential to successful deep brain stimulation (DBS) for patients with neurodegenerative diseases such as Parkinson’s disease. However, the accuracy of pre-operative images used for surgical planning and guidance is often degraded by brain shift during surgery. To predict such intra-operative target deviation due to brain shift, we have developed a finite-element biomechanical model with the assimilation of intraoperative sparse data to compute a whole brain displacement field that updates preoperative images. Previously, modeling with the incorporation of surface sparse data achieved promising results at deep brain structures. However, access to surface data may be limited during a burr hole-based procedure where the size of exposed cortex is too small to acquire adequate intraoperative imaging data. In this paper, our biomechanical brain model was driven by deep brain sparse data that was extracted from lateral ventricles using a Demon’s algorithm and the simulation result was compared against the one resulted from modeling with surface data. Two patient cases were explored in this study where preoperative CT (preCT) and postoperative CT (postCT) were used for the simulation. In patient case one of large symmetrical brain shift, results show that model driven by deep brain sparse data reduced the target registration error(TRE) of preCT from 3.53 to 1.36 and from 1.79 to 1.17 mm at AC and PC, respectively, whereas results from modeling with surface data produced even lower TREs at 0.58 and 0.69mm correspondingly; However, in patient case two of large asymmetrical brain shift, modeling with deep brain sparse data yielded the lowest TRE of 0.68 from 1.73 mm. Results in this study suggest that both surface and deep brain sparse data are capable of reducing the TRE of preoperative images at deep brain landmarks. The success of modeling with the assimilation of deep brain sparse data alone shows the potential of implementing such method in the OR because sparse data at lateral ventricle can be acquired using ultrasound imaging.
Deep brain stimulation (DBS) electrode placement is a burr-hole procedure for the treatment of patients with neuro- degenerative disease such as Parkinson’s disease, essential tremor and dystonia. Accurate placement of electrodes is the key to optimal surgical outcome. However, the accuracy of pre-operative images used for surgical planning are often degraded by intraoperative brain shift. To compensate for intraoperative target deviation, we have developed a biomechanical model, driven by partially sampled displacements between pre- and postCT, to estimate a whole brain displacement field based on which updated CT (uCT) can be generated. The results of the finite element model depend on sparse data, as the model minimizes the difference between model estimates and sparse data. Existing approaches to extract sparse data from brain surface are typically geometry or feature-based. In this paper, we explore a geometry- based iterative closest point (ICP) algorithm and a feature-based image registration algorithm, and drive the model with 1) geometry-based sparse data only, 2) feature-based sparse data only, and 3) combined data from 1) and 2). We assess the model performance in terms of model-data misfit, as well as target registration errors (TREs) at the anterior commissure (AC) and posterior commissure (PC). Results show that the model driven by the geometry-based sparse data reduced the TREs of preCT from 1.65mm to 1.26 mm and 1.88 mm to 1.58 mm at AC and PC, respectively by compensating majorly along the direction of gravity and the longitudinal axis, whereas feature-based sparse data contributed to the compensation along the lateral direction at PC.
The success of deep brain stimulations (DBS) heavily relies on the accurate placement of electrodes in the operating room (OR). However, the pre-operative images such as MRI and CT for surgical targeting are degraded by brain shift, a combination of brain movement and deformation. One way to compensate for this intra-operative brain shift is to utilize a nonlinear biomechanical brain model to estimate the whole brain deformation based on which an updated MR can be generated. Due to the variability of deformation in both magnitude and direction among different cases, partially sampled intraoperative data (e.g., O-arm, CT) of tissue motion is critical to guide the model estimation. In this paper, we present a method to extract the sparse data by matching brain surface features from pre- and post-operative CTs, followed by the reconstruction of the full 3d-displacement field based on the original spatial information of these 2d points. Specifically, the size and the location of the sparse data were determined based on the pneumocephalus in the post-operative CT. The 2D CT-encoded texture maps from both pre-and post-operative CTs were then registered using Demons algorithm. The final 3d-displacement field in our one-patient-example shows an average lateral shift of 1.42mm, and a shift of 10.11mm in the direction of gravity. The results presented in this work have shown the potential of assimilating the sparse data from intra-operative images into the pipeline of model-based image guidance for DBS in the future.
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