Chapter 5 - Cassette-Based Image Acquisition

Quantum mottle or Quantum noise

When insufficient light is produced, the image is grainy, a condition known as…?

Grid frequency

Refers to the number of grid lines per centimeter or lines per inch.

between 80 and 152 lines/in

What’s the typical grid frequency?

Grid ratio

It’s the relationship between the height of the lead strips and the space between the lead strips

6:1

What’s a proper grid ratio for mobile radiography?

12:1

What’s a proper grid ratio for departmental grids?

parallel and focused

Most grids chosen by radiography departments are…?

Parallel grids

They are less critical to beam centering but should not be used at distances less than 48 inches.

Focused grids

They consist of lead strips angled to coincide with the diversion of the x-ray beam and must be used within specific distances using a precisely centered beam.

Collimation

It’s the reduction of the area of beam that reaches the patient through the use of two pairs of lead shutters encased in a housing attached to the x-ray tube.

Shuttering

What do you call postexposure image manipulation where a black background can be added around the original collimation edges, virtually eliminating the distracting white or clear areas?

Exposure indicator number

What is the result of converting light into a signal for calculating exposure?

Exposure Index (IE)

What does Kodak (Rochester, NY) use as the exposure indicator?

logarithm of the median exposure (lgM)

What’s the term for exposure indicator in an Agfa (Mortsel, Belgium) system?

Histogram

It is a graphic representation of the numerical tone values of an x-ray exposure.

automatic data recognition

With this, the image recording range is automatically determined.

semiautomatic mode

In this mode, the latitude value of the histogram is fixed, and only a small reading area is used.

semiautomatic mode

This mode is especially useful for examinations of the odontoid, L5/S1 spot film, sinuses, and any other tightly collimated examinations.

semiautomatic mode

When using this mode, pre- cautions must be taken to carefully center the part to be examined. This mode is not recommended for high absorption objects such as prostheses.

multiple manual mode

In this mode, the area of interest is selected by the technologist, and the image is derived from the selected areas imaged in semiautomatic mode.

fixed mode

In this mode, the user selects the exposure index, or sensitivity I number, and the value of the latitude from a menu.

fixed mode

This mode is useful when imaging cross-table hips, C7-T1 lateral view of the cervical spine, any body part with a lot of metal, and parts that cannot be centered

Artifacts

These are any undesirable densities on the processed image other than those caused by scatter radiation or fog.

1. imaging plate artifacts

2. plate reader artifacts

3. image processing artifacts

4. printer artifacts

What are four common types of artifacts?

Imaging Plate Artifacts

As imaging plate ages, it becomes prone to cracks from the action of removing and replacing the imaging plate within the reader.

Cracks

It appears as areas of lucency on the image

Plate Reader Artifacts

The intermittent appearance of extraneous line patterns can be caused by problems in the plate reader’s electronics.

Printer Artifacts

Fine white lines may appear on the image because of debris on the mirror in the laser printer.

Underexposure

produces quantum mottle

overexposure

It affects contrast.

Operator errors

It can also create artifacts.