Computed tomography (CT) and magnetic resonance imaging (MRI) are now routinely used in the diagnostic investigation of spinal diseases. Both CT and MRI offer significant advantages over survey radiographs and myelography. The overall diagnostic sensitivity of MRI is superior to CT, and as such MRI can be used to image the vast majority of spinal disorders, with few exceptions (eg. spinal trauma caused by gunshot). Routine survey radiographs are always recommended before proceeding with advanced imaging because the area of interest may be more specifically localized, thus reducing scanning time, and severe spinal/ osseous lesions, such as hemivertebrae or discospondylitis, may be identified without the need of advanced imaging studies. In general, CT provides superior spatial resolution and is better suited for imaging bone. Slice thicknesses as thin as 1 to 1.5 mm are possible in almost all available CT units. Thinner slice acquisitions (submillimeter) are possible with newer, multidetector systems. For CT this is a distinct advantage over MRI, for which such thin slice acquisitions are not currently possible because of decreases in SNR as slice thicknesses decrease. Other advantages of CT over MRI are decreased cost, fewer maintenance requirements and associated expense, and rapidity of imaging. Imaging patients under sedation is now possible with some of the newer scanners because of their rapid scan times. CT can be used to successfully guide needle aspirations or biopsies once a lesion is localized, but this is not generally done with MRI guidance because of prolonged imaging times and the inability to use metal implements for tissue sampling. MR provides superior contrast resolution and is better suited for imaging soft tissues, such as the spinal cord, nerve roots, and intervertebral discs. Images can be acquired in multiple planes whereas CT images can only be acquired in one plane (typically transverse). Although CT images can be reformatted into any plane desirable, including 3-dimensional, the image detail is slightly reduced on reformatted as compared with acquired images. The quality and conspicuity of the reformatted images is a factor of acquisition slice thickness; the thinner the slices acquired, the better the detail on reformatted images. Whereas myelography is still often used in conjunction with CT of the spine, this is not necessary with MRI because of the ability to alter tissue contrast by applying different acquisition sequences. Thus, the associated morbidity risk often accompanying myelography is avoided.