The multi-slices obtained from the spiral or helical CT is used to reconstruct the three- dimensional images. Multi-slice spiral CT uses multiple arrays of detectors and can be used to image larger volumes in a given time, or to image a given volume in a shorter scan time, compared to single-slice spiral CT. The collimated X-ray beam can also be made thinner, giving higher quality three-dimensional scans. In multislice CT scanning, the effective slice thickness is dictated by the dimensions of the individual detectors, rather than the collimated X-ray beam width. Fan beam reconstruction techniques, in combination with linear interpolation methods, are used in multispiral CT. A typical three-dimensional CT image will be as in Fig 4.22.
. The MRI and CT images are used in neurosurgery for planning the surgery and also used in image guidance systems. The 3D models are formed from these imaging techniques and a better understanding of the pathology and the best possible surgical approach can be made possible. Spiral CT angiography yields enough topographical information for the accurate planning of stereotactic surgery for brain lesions. The intra operation MRI also helps in reducing the mistakes in the surgery. The three-dimensional imaging can also be used for training the novice neurosurgeons.