Stereotactic navigational systems are being incorporated into an increasing number of neurosurgical procedures. Preoperatively acquired 3D images are used for planning the procedure, and are also employed in intraoperative navigations to help localize and resect brain lesions. However, as the operation progresses, multiple factors contribute to changes that limit the accuracy of the navigation based on pre-operative images alone. Our method to correct for brain shift involves the use of ultrasound intraoperatively to update patient specific pre-operative MRI scans using a physics based dynamic model. To validate the imaging and modeling process, a phantom was designed that simulates the brain and its shifting patterns resulting from several of the clinical factors present during a brain operation. MRI and ultrasound datasets were acquired for several permutations of phantom parameters. Deformation algorithms were then applied to the phantom data to demonstrate the efficacy of this approach as a method to effectively update the pre-operatively acquired MRI data during an operation.