CT - Mod 2: Quiz

Compare and Contrast WINDOW WIDTH and WINDOW LEVEL. What does each one determine?

Window width (WW) is the range of CT numbers displayed in the CT image and is represented by a gray scale. It determines the maximum umber os shades of gray that can be displayed on a CT monitor. It also determines how much contrast appears in the image. Window level (WL) is the center/midpoint of the range of CT numbers. It determines how bright the image appears. A low WL makes the image appear brighter, and a high WL makes the image appear darker.

A region of interest (ROI) is a tool used in CT scanning. Describe what a ROI does and how it helps the radiologist.

A ROI is a CT tool that can "circle" an area of interest on an image and obtain a CT number. That number helps the radiologist identify a specific tissue and obtain statistical information

Explain how CONVENTIONAL AXIAL SCANNING differs from HELICAL SCANNING.

Axial scanning is often referred to as "step and shoot" and is time consuming. During axial scanning, the tube starts and stops as it rotates around the patient. After the data is acquired during a single revolution, the table is moved to the next position and the process is repeated for the duration of the scan until the prescribed anatomy is covered. This type of scanning is still used for brain imaging. Helical scanning involves continuous movement of the x-ray tube as the table moves through the gantry. The beam races a helical, or spiral, path around the patient, allowing much faster scan times compared to axial scanning. Large amounts of data can be collected during each scan and can typically be completed in one breath hold.

When might a HALF-SCANNING technique be used? What does it improve?

Half-scanning techniques are used to reduce the appearance of motion in a CT scan from involuntary movement such as a beating heart. The half-scan mode is beneficial simply because it shortens the scan time considerably and improves temporal resolution

Name TWO reasons why COLLIMATION (both pre and post patient collimators) is so important in CT imaging

Reduces scatter radiation, improves contrast resolution, improves image quality, improves axial resolution

A "scout image" is necessary for every CT scan. List two other terms that may be used instead of "scout"

Scanogram pilot topogram survey

When the x, y, and z planes (length, width, and height) are equal, the volume data set is a. isotropic b. linear c. anisotropic d. rectangle-shaped

a. isotropic

The mathematical unit that describes shades of gray on a CT image is called a. a voxel unit b. matrix unit c. a Hounsfield unit d. none of these

c. a Hounsfield unit

Which of the following is associated with a 3D representation of tissue volume? a. matrix b. pixel c. voxel d. sampling

c. voxel

Name FOUR components in the GANTRY PORTION of the CT imaging system

x-ray tube, detector array, high-voltage generator, patient-support couch, cooling system