Helical and Multislice CT
- 1. HELICAL AND MULTISLICE CT Prepared by: Manoj Bhatta B.Sc.MIT, 1st batch Gandaki Medical College THRC
- 2. HELICAL CT A technique where by the patient is transported continuously through the gantry while data are acquired continuously during several 360 degrees scans. Also k/a spiral or volume CT. Slice by slice CT Spiral/helical CT
- 3. Advantages of helical CT Increased speed a study. Exact continuity of images. Less slice misregistration. Less motion artifact. Need for less contrast medium. Availability of volumetric data.
- 4. Advances of spiral CT over conventional CT 1. Slip ring device 2. More efficient tube cooling 3. Increased milliampere capability 4. Smoother table movement 5. Software adjustment for table movement 6. Efficient detectors
- 5. Slip-ring technology Is one of the important parts of spiral CT machines. Serves as a connection of the gantry rotating part and the fixed portion of the power line and the signal line.
- 7. Adjustment in reconstruction algorithm Interpolation algorithm • Estimation of a unknown value between known values is called interpolation. • Estimation of a unknown value beyond known values is called extrapolation.
- 9. Pitch: relation of table speed to slice thickness Pitch= Table feed * time per rotation of 360 collimation Pitch= Table feed , if it is a 1 sec scan. collimation
- 10. Limitations Requires very cooperative patient. Costly machine and X-ray tube. Loss of image resolution because of the interpolation required to process data.
- 11. Multislice CT (MSCT) or Multi-detector CT (MDCT) Uses multiple parallel detectors instead of a single detector array. And hence greater volume of patient is scanned in a single rotation
- 12. Advantages of MSCT over single slice Same acquisition in shorter time. Improved z-axis resolution. Reduced artifacts. Increased coverage per rotation. Reduced overall tube loading. More information available for the radiologists. Possibility of new applications.