CT Image Production
Interpolation
Estimating an unknown value when surrounding values are known
If rotation time is decreased what other parameter should be changed to maintain image quality?
Increase mA
What is the primary reason for decreasing the detector thickness for CTA
Increase spatial resolution
Shifting the center of a Sagittarius image changes the coordinates to which two data sets?
Y-axis & Z-axis
What process prevents star-like artifact from appearing of CT images
Back-projection filter
Blood HU
+39 hu
A single "view" acquired during a scan is also called a:
Projection
Fat
-52 hu
What is the main difference between image production of CT vs Xray?
Projections are compiled into a 3D volume of data
During axial scanning, what two variables determine the total amount of anatomical coverage per tube rotation
# of activated detector rows Thickness of activated detector rows
What axis position changes while moving through the axial set of data (superior to inferior)
Z-axis (longitudinal)
What is the pitch of the scan Acquisition thickness: 20 Detector rows: 20 Rotation time: 0.8s Tube current: 250 mA Table movement: 10 mm
1 Beam width=detector rows x acquisition thickness Pitch=table movement / beam width
What is a common kVp setting used in CT?
120 kVp
Calculate the total beam width of a scan using 32 detector rows, 0.5 mm detectors, 100 mA, 140 kVp
16 mm (32 rows X 0.5mm/row)
"8-slice scanner" refers to a system that has
8 detector rows
Compared to general radiography, CT X-ray tubes require
A larger heat capacity
The signal produced by a CT detector is an
Analog electrical signal (detector capture remnant X-ray photons & produce an electrical signal proportional to the number of photons they received)
What portions of a patient receive radiation exposure during CT
Any portion within the gantry
The specific process that accelerates electrons in an X-ray tube
Application of voltage (kVp)
What is the relationship between acquisition thickness and spatial resolution?
As acquisition thickness increases, spatial resolution decreases
What acquisition mode collects a series of adjacent axial sections
Axial Scanning
Describe the flow of electrons through an X-ray tube
Cathode To anode (The cathode is the same as the filament, the source of electrons -. The anode is the target +.)
The width of the xray beam is controlled by
Collimation
Where is raw data stored
Computer system
Which component of the CT imaging system is responsible for creating reconstructed image data?
Computer system (Last step in the data transformation process)
What is the result of the change: 0.625mm X 16 rows to 1.25mm X 8 rows
Decreased pt dose
Compare protocols using a pitch of 0.73 vs 0.87. The pitch of 0.87 will result in what two differences
Decreased scan time Decreased pt dose
Helical scanning is preferred over axial for what three reasons?
Decreased scan time Improved IV contrast timing Improved post-processing
X-ray tubes in CT are most similar to which other modality
Diagnostic radiography
Slice interval
Distance from the start of one slice to the start of the next slice
If mA is decreased by a factor of 2, how is the pt radiation dose changed if all other factors remain the same
Dose is decreased by 2
What is the orientation of the X-axis
Extends horizontally across the scanner Represents data coordinates from Lt to Rt
During helical scanning if the table moves a greater distance than the beam width, the pitch will be
Greater than 1
The principal advantage of thin detector rows is
Higher spatial resolution
How is data from the SFOV used during image production?
Image reconstruction
An increase of which exposure factors would increase the total # of xray photons exposing the detectors? (Three)
Increased mA (total # of photons produced) Increased kVp (penetration ability) Increased Rotation Time (longer exposure)
Which of the following effects can occur when mA is increased? (Three)
Increased pt dose Increased beam intensity Increased exposure of detector elements
The inner rows of a non-uniform detector array have the advantage of
Increased spatial resolution
Increasing the mA & kVp will usually result in: (two)
Increases pt dose Decreased image noise
What technical change is expected to increase penetrating ability of an X-ray beam
Increasing kVp
A pitch of 0.79 will result in
Overlap in scan data
The process of assigning a specific level of edge enhancement is controlled by: (3)
Reconstruction algorithms Reconstruction filters Reconstruction kernels
Iterative Reconstruction
Reduces pt dose Increases image quality
What two algorithms are most useful for viewing soft tissue changes around the cranium
Smoothing algorithm Standard algorithm
Production of X-rays in CT requires (three)
Source of electrons Mean of rapidly accelerating electrons Means of rapidly deceleration of electrons
Convolution
The mathematical filtration of CT data to enhance the appearance of specific tissue types
Under what two circumstances would it be impossible to retro missing anatomy
The original SCAN data has been deleted from the computer system The missing anatomy was outside the original SFOV
Pitch
The ratio of the table movement to beam width
The sequential acquisition mode is described as
The table only moves between exposures
Acquisition thickness refers to:
The thickness of active detector rows
Physical components located inside the CT Gary typically include (two)
X-ray tube High voltage generator
