CT的基本知识PPT.ppt

COMPUTED TOMOGRAPHY (CT);Who invented CT ?;CT is a computerised X-ray technique. It?uses electronic systems connected to a computer to capture and process the signals from x-rays that have passed through the body and construct a cross-sectional pictures from the patient on a television screen or monitor. ;人; Scanning gantry Scanner table Computer Displayer Memory storage and Camera, etc;X-ray tube;;Differences in linear attenuation coefficients among tissues are responsible for CT image contrast. Ct number: X-ray attenuation value in the CT image expressed in Hounsfield unit (HU). ;CT number of different tissues; 2000 or more HU are resolved by CT, only 16 gray-scales can be resolved by human eyes，so window technique of image must be used Window width, the range of CT number used in image Window level: the center of used CT numbers in image Proper window width and window level are essential for CT imaging;WL 50 WW 100 ;★ WW=100,WL=50;;;;liver +50 （WL）;Remember: Always use suitable WW and WL in order to clearly observe the structures you want to see .;2.3 Classification of CT; Conventional CT;Spiral CT;Multi-slice spiral CT;;Multi-slice CT enables a wide range of clinical applications from 3D to perfusion imaging to CT fluoroscopy ;;2.4 Examination methods of CT;Plain scan;Conventional contrast-enhanced scan;Plain scan;Plain scan;Arterial phase;Nodular enhancement appears in the rim of the lesion(A)，showing similar density with blood vessel. With the time passing by, enhancement spreads to the center and fill the whole lesion(C);CT Myelography involves opacification of the subarachnoid space by injection of contrast media and followed by CT scanning. Currently, only non-ionic iodinated contrast material is recommended for intrathecal injection.;CT myelography;Axial and sagittal reformation images show excellent bone detail and the outline of the subarachnoid space. ;; Target scan of vertebrae;;5. High resolution CT (HRCT) A CT technique using thin col