The use of 64-slice multidetector computed tomography (64-MDCT) offers a number of advantages in the evaluation of head and neck trauma in the emergency department—as in the case of the 37-year-old woman imaged above—according to Dr. Osamu Sakai, director of head and neck imaging at Boston Medical Center where 64-MDCT is used in the level I trauma center.
Several images can be acquired simultaneously with 64-MDCT, allowing for faster scans in trauma cases and resulting in earlier therapy and reduced mortality. In addition, 64-MDCT reduces motion artifacts, sharpening multiplanar images and 3D reconstructions.
Thinner slices can be achieved with 64-MDCT, meaning that voxels approach the same size in all dimensions (isotropy). Isotropic voxels allow cross-sectional images to be reconstructed in arbitrary planes, allowing physicians to choose the best views. In addition, spatial resolution with 64-MDCT is in the submillimeter range. Increased resolution decreases partial volume effect caused by having more than one tissue type within the voxel. Partial volume effect results in voxels with average radiodensities of all of the tissue types present in the voxel and may thus be hard to interpret.
For CT angiography (CTA), 64-MDCT's faster scans result in less venous contamination, the superimposition of venous structures on the image that can occur when scanning times are slower because contrast material has time to reach the veins. While scan delay time after intravenous contrast injection is unchanged, the total dose of contrast may be reduced. Requests for CTA have increased dramatically since the introduction of 64-MDCT, according to Dr. Sakai, also of Boston University. CTA using 64-MDCT is now a first-line study for patients with suspected vascular injury and subarachnoid hemorrhage because faster scan times reduce artifacts, such as venous contamination.
The woman imaged above was ejected from her vehicle as the result of a collision, resulting in multiple skull base fractures. Volume-rendering CTA demonstrates an intact circle of Willis (images g and h). Volume-rendering CT venography reveals thrombosed distal right transverse and sigmoid sinuses and jugular bulb/vein (left image).
“Almost all stable patients with penetrating injuries, fractures of skull base and cervical spine, or other clinically suspected vascular injuries undergo CTA with 64-MDCT at our institution,” wrote Dr. Sakai and his colleagues in a poster presented at the 2006 annual meeting of the American Society of Neuroradiology.
Finally, 64-MDCT can “unfuse” or retrospectively produce thinner axial images provided there are sufficient raw data. Abnormalities that aren't picked up on routine 5-mm sections can pop out when reviewed at 1.25-mm or 0.625-mm thickness and spacing, providing additional information to physicians and can be crucial when trauma is not clinically suspected, according to Dr. Sakai.