Chapter 5: Methods Of Data Acquisition Flashcards
- Are the initial images in all CT studies, are
similar to conventional radiographs. - Are acquired while the tube remains in a
stationary position, and the table moves
through the scan field. - The image quality is lower than of a
conventional radiograph.
LOCALIZER
- indicate whether the patient is placed head- first or feet-first, supine or prone.
- ensures correct image annotations.
Correct Directional Input
- Also known as Axial Scanning, Conventional Scanning, Serial Scanning or Sequence Scanning. The original CT scanning method.
STEP AND SHOOT SCANNING
- This occurs when slices
taken at different times do not align due to
breathing variations.
Misregistration
- high resolution imaging of small structure.
- Cardiac studies
Axial Scans
- faster scans for trauma patients.
Helical Scans
- Also known as spiral scanning or continuous scanning
- This combines a rotating x-ray tube, constant x-ray output and uninterrupted table movement.
HELICAL SCANNING
- the true thickness of reconstructed slices.
EFFECTIVE SLICE THICKNESS
- interpolation can cause effective slice
thickness to exceed the collimator-selected
value.
Slice Thickness Blooming
– the relationship between table movement and x-ray beam width.
Pitch
-represents slice thickness and image sharpness.
SSP
– actual thickness of the physical slice of tissue during scanning
Slice Thickness
– is the reconstructed image that is displayed
Image Thickness
- Was introduced in 2006, this system includes 2 x-ray tubes and two detector arrays in a single gantry.
- Increased scan speed (very useful in cardiac imaging)
- Dual energy imaging
DUAL-SOURCE CT
is a type of X-ray CT that uses a photon-counting detector to record the energy of each X-ray photon. This technology can produce images with higher resolution, better contrast, and fewer artifacts than
conventional C
Photon-counting computed tomography (PCCT)
- Is used in the 3rd and 4th generation CT-
scanners. - One row of detectors aligned in the Z axis,
detector width approximately 15mm - Uses a fan beam geometry
- Collimator used for slice thickness control
- Slice thickness is less than the detector width
(>10mm) - A very straight forward simple design
- Cost effective, lower complexity compared
to the MDCT
SINGLE-DETECTOR ROW SYSTEMS
- Uses multiple rows of detectors, enabling
multiple slices per gantry rotation. - Started with 4 to 64 rows, modern scanners can have as much as 320 (TOSHIBA Aquilon)
- Faster scanning time, broader Z axis
coverage. - Uses a cone shaped beam.
MULTIDETECTOR ROW SYSTEMS (MDCT)
– equal detector size in all rows
Uniform Array
- Central rows are thinner for higher resolution, peripheral rows are wider.
- Improved image quality in different body
regions - reduced rad dose
Adaptive Array
Applications of MDCT
Axial Scans
Helical Scans
- Eliminates the interscan delay found in
traditional axial CT. - Introduced In the late 1980’s
- Optimized the use of iodinated contrast
agents, reduced motion artifacts, volumetric data acquisition.
Helical scanning
- slices are parallel, data are collected slice by slice with stationary table positions.
Axial Scans
- continuous x-ray output with smooth table movement, slices are slightly angeled
resembling the rungs of a spring.
Helical Scans
- Adjust the slant and blur caused by
continuous table movement, 360 deg LI and 180 deg LI.
HELICAL INTERPOLATION
: table moves one slice thickness per
rotation
Pitch = 1
: Faster table speed, less overlap, lower radiation dose
Pitch > 1
: Slower table speed, overlapping slices, higher radiation dose
Pitch < 1
