Computed Tomography (CT) Basics Flashcards

Which artifact in CT appears as alternating bright and dark bands radiating from high-density structures and is caused by insufficient sampling?

Answer: Streak artifact

Streak artifacts appear as bright and dark bands radiating from high-density objects (e.g., metal implants, dense bone) and result from insufficient projection data or beam hardening at those locations.

In multidetector CT (MDCT), the detector array configuration that allows simultaneous acquisition of multiple thin slices per rotation is called:

Answer: Multi-row detector array

MDCT uses multi-row detector arrays with multiple rows of detectors, allowing simultaneous acquisition of multiple slices per gantry rotation, dramatically increasing scan speed.

Which reconstruction method is used in modern CT to reduce image noise and patient dose compared to filtered back projection (FBP)?

Answer: Iterative reconstruction (IR)

Iterative reconstruction (IR) algorithms repeatedly refine the image by comparing the reconstructed image to the original projection data, achieving lower noise at the same or lower dose than FBP.

The spatial resolution of a CT system is characterized by its ability to resolve small, high-contrast objects and is quantified using:

Answer: Modulation transfer function (MTF) or line pair per centimeter (lp/cm)

Spatial resolution in CT is measured by MTF (modulation transfer function) or in line pairs per centimeter (lp/cm) using bar phantoms, indicating the finest detail the system can resolve.

Isotropic voxels in CT imaging are desirable because they:

Answer: Have equal dimensions in all three planes, enabling high-quality multiplanar reformations in any direction

Isotropic voxels have equal x, y, and z dimensions, so multiplanar reformations (MPR) in coronal, sagittal, or oblique planes have the same resolution as the original axial images.

The gantry in a CT scanner houses the x-ray tube and detector array. The typical gantry rotation time for a modern CT scanner is:

Answer: 0.27–0.5 seconds per rotation

Modern CT scanners achieve gantry rotation times of approximately 0.27–0.5 seconds per 360° rotation, enabling rapid scanning and cardiac CT capability.