Computed Tomography: Scan Modes, Image Quality Flashcards
What is Topograms?
Done prior to CT scanning to select the position of scan regions
X-ray tube is kept in a fixed angular position
What is the result of Topogram?
Digital survey radiograph with low spatial resolution
What happens in a sequential CT?
after scanning a single slice over 360
the patient is transported for a defined distance or scan increment
What continues to require the capability for single slice sequential scanning?
Dynamic CT and interventional CT
What are the scan parameters generally used?
Kilovoltage: from 80 kVp to 140 kVp
Tube current: from 10 mA to 800 mA
Slice thickness S: from 0.5 mm to 10 mm
Scan time per 360o rotation: 0.3 s - 2 s
Number of simultaneous slices M: 1 to 128
Scan increment: arbitrary, mostly equal to total slice collimation M x S
Scan range: 1 to 100 cm
What is dynamic CT used to record?
Temporal changes in the attenuation characteristics of the object examined
What is dynamic CT used for in the clinical applications?
Assessment of contrast medium dynamics in various body regions
What is the process of dynamic CT typically?
- A representative slice, or M slices for multi-slice scanners are selected
- Contrast medium is adminstered
- The selected slices are scanned repeatedly
What does the time interval between scans depend on?
physiological process to be examined and the type of contrast medium
How are monitoring interventions by CT done?
in real time with continuous scanning of a slice or a number of slices (for multi-slice CT) with the fastest possible reconstruction and presentation of images
What is performed under CT guidance?
- Biopsies
- Drainage’s
- Numerous other therapeutic interventions
What allows for data acquisition for entire head or chest?
Transition from fan beam geometry to cone beam geometry
What is the principal problem inherent in cone beam geometry?
details in the object are projected onto different detector rows for different projection angles, depending on their distance from the central plane
What allows the assessment of vascular anatomy and pathology, but not of soft tissues, which exhibit low contrast?
3D cone beam CT angiography
What does spiral scans encompass?
many rotations of the tube-detector system, while the patient is transported continuously through the gantry.
