CT Basics
What plan are CT images initially generated in?
A transverse (axial) image perpendicular to the long axis of the body.
Which CT generation used a pencil beam and a single detector?
First-generation CT.
In helical CT, what two movements occur simultaneously during scanning?
Tube rotation and couch movement.
Pixels represent 2D information. What does the 3D equivalent represent?
A voxel.
What does CTDIvol represent?
The CT output intensity per volume (mGy).
Which two planes are commonly reconstructed from axial CT data?
Coronal and sagittal planes.
What major advantage did second-generation CT scanners offer?
Increased speed due to multiple detectors and fan beam.
What is detector binning used to adjust?
Slice thickness.
What happens to pixel size if matrix size increases but FOV stays constant?
Pixel size decreases.
What is DLP and how is it calculated?
Dose Length Product = CTDIvol × scan length.
What CT component solves thousands of equations to reconstruct the image?
The computer (microprocessor or array processor)
What artifact is specifically associated with third-generation CT scanners?
Ring artifacts from detector malfunctions.
What does pitch represent in helical CT?
The relationship between couch movement and beam width.
What HU value corresponds to water?
0 HU.
Does increasing kVp always increase dose in CT?
No—higher kVp increases penetration, allowing lower mAs and possibly reducing dose.
What does attenuation depend on when forming CT projections
Mass density and effective atomic number.
Which generation uses stationary detectors arranged in a full circle?
Fourth-generation CT.
What is the consequence of increasing pitch above 1.0?
Lower patient dose but decreased z-axis resolution.
Window width controls the number of HUs displayed; what does window level control?
The brightness/midpoint HU.
What effect does pitch > 1.0 have on patient dose?
Decreases dose.
What is the process of superimposing projection data to form an image called?
Back projection (with filtering applied).
What technology allowed continuous rotation and made helical CT possible?
Slip-ring technology.
What unique reconstruction challenge does MSCT introduce due to wide beams?
The cone-beam effect requiring special reconstruction algorithms.
What function is used to evaluate spatial resolution by plotting fidelity vs frequency?
Modulation Transfer Function (MTF).
What factor causes additional rotations beyond planned length, increasing dose?
Overranging.