Advantages of spiral CT AYMAN OSAMA

In spiral CT there is continuous patient advancement during constant X-ray source rotation. This results in volume acquisition of data from which retrospective image reconstruction of individual slices is generated. This provides two major advantages: speed and flexibility in slice increment and plane.

Slip-ring gantry system Slip-ring gantry system. The major technological advancements that enable for spiral CT are improvements in X-ray tubes and the introduction of slip-ring technology. In slip-ring system, power within the gantry is not transmitted with a cable, but rather through stationary rings allowing for continuous rotation.

Pitch = (number of 360° tube rotations: table speed) Pitch = (number of 360° tube rotations: table speed). Usually, pitch of 1 is used, which denotes 1 rotation while the table moves 1 mm/sec. Increasing the table speed, decreases the pitch , increasing the length of the spiral set, but also adversely affecting the sensitivity profile of the section.

Collimation and incrementation Collimation and incrementation. The collimation is set before scanning, and affects the spiral set length.

Advantages 1- Short exam times. For example, the chest or abdomen can be examined within 1-2 breathholds. This improves patient comfort and throughput; allows for scanning in various phases of contrast enhancement, and decreases motion artifacts

2- Vascular visibility. Allows for vascular imaging in arterial, venous and equilibrium phases as well as 2D and 3D CT-Angiography.

3- Parenchymal organ enhancement - Liver; biphasic scanning. Scanning in the arterial (hepatic artery) phase,increases sensitivity in detecting hypervascular primary and metastatic tumors, which may appear isodense on dynamic scanning. Scanning in early portal phase, increases sensitivity detecting the more common metastatic lesions which may become isodense in the equilibrium or delayed phases.

Pancreas. Increased sensitivity in detecting small adenocarcinomas and islet cell tumors, seen in the arterial phase as hypodense or hyperdense areas respectively, and becoming isodense in the portal and later phase. kidneys. Study in arterial, venous and excretory phase. Lung there is preliminary evidence the malignant pulmonary nodules enhance in early phases greater than the benign ones. Also evaluation of pulmonary varix of AVM.

4- Retrospective imaging -Variable incrementation of images (e. g 4- Retrospective imaging -Variable incrementation of images (e.g., 8-mm-thick images obtained every 8, 4, or 1 mm): Improves sensitivity in lesion detection in lung (pulmonary nodules) and liver (metastases). Requires raw data. - Multiplanar images: coronal, sagittal, oblique. - Curved (traced) reformations: generate planar displays of curvilinear structures (e.g., along the course of the splenic artery, or a small bowel loop). - 3D imaging: Skeletal (maxillofascial, spinal, hip and other fractures) Parenchymal (e.g. organs, tumors) may improve volumetric measurements ,Vascular (CT-Angiography).

5- Decrease in the amount of IV contrast needed for equivalent studies done with dynamic scanning