Thus, it is not widely used due to its poor resolution and being operator dependent. The iUS’s images, however, are of poor quality and user dependent with a cumbersome reconstruction of the navigation view. Studies have shown its usefulness in localizing deep-seated vascular lesions such as cavernomas and metastasis. Recent advances have yielded promising results with 3-D ultrasound that uses shear waves as opposed to longitudinal waves, linear regression analysis shows that it correlates better with preoperative MRIs. The iUS is more widely available and less costly. The main modalities include intraoperative ultrasound (iUS), intraoperative magnetic resonance imaging (iMRI), and intraoperative computed tomography (iCT) scanner. The surgical community did not reach a consensus on whether navigation alone improved outcomes in surgery but recognized there was a need for a more accurate solution which was addressed by the real-time images provided by intraoperative imaging modalities. The brain shift phenomenon can occur in the cortex and deep brain structures which may result in damage to eloquent areas of the brain, for example, in glioma surgery. This renders the images in the navigation system incorrect and can make surgery inaccurate. This occurs due to a distortion of brain tissue with several studies documenting surgical manipulation of brain tissue, tissue swelling, and loss of cerebrospinal fluid and use of brain retractors as a cause of this dynamic spatiotemporal event which is time dependent. in 1986, this limits the correlation surgeons can achieve between preoperative image and intraoperative anatomy. The significant limitation of navigation, however, is the presumption that the brain and skull are rigid structures, but during surgery due to the phenomenon of brain shift described by Kelly et al. New navigation systems give approximately 2 mm of accuracy. The system calibrates preoperative images to the intraoperative coordinate system of the patient using a transformation matrix creating a link between preoperative imaging and anatomical structures giving surgeons a 3-D orientation of the position of the region of interest. The navigation system in surgery produces the tip of a pointer on an image. This complexity can be attributed to the complicated anatomy of the brain that has fascinated neurosurgeons and anatomists alike. Conventionally, image-guided neuronavigation systems have helped localize complex lesions in the brain. Intraoperative imaging modalities are important tools in the armamentarium of modern neurosurgeons as these greatly have helped overcome the challenges faced by traditional neuronavigation systems.
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