Chapter 12 - Computed Radiography

Define computed radiography (CR).

a digital imaging technique that uses a cassette-based system

Computed Radiography is also known as?

Photostimulable Phosphor (PSP) Imaging

True or False: CR is a form of digital radiography.

True

IP stands for…?

imaging plate

PSL stands for…?

photostimulable luminescence

The ________ image is the image that is invisible just after the exposure.

latent

After 8 hours, how much of the energy is lost percentage-wise from the latent image if not processed immediately?

25%

The ________ image is the visible image after processing.

manifest

What are the 7 layers that compose the Imaging Plate?

1. Protective layer

2. Phosphor layer

3. Reflective layer

4. Conductive layer

5. Support layer

6. Light shielding layer

7. Backing layer

What type of scan is it when the laser moves across the imaging plate (IP)?

fast scan

What type of scan is it when the imaging plate moves through the reader?

slow scan

__________ is an activator in the photostimulable phosphor.

europium

What is used to convert small amounts of light into amplified electric signals?

photomultiplier tube

ADC stands for…?

analog to digital converter

The ____________ identifies all intensities (gray/black/white) on the IP in the form of a graph on which the X-axis is the pixel value or brightness level, and the Y-axis is the number of pixels for each exposure.

histogram

True or False: High energy (high kVp) gives a narrower histogram (less shades of gray) and low energy gives a wider histogram (more shades of gray).

False;

higher energy = wider histogram (more shades of gray)

lower energy = narrower histogram (less shades of gray)

A _______________ is a preset curve that maps pixel values to display brightness.

Look Up Table (LUT)

The ___________________ is the measure of the amount of exposure received by the image receptor.

Exposure Index (EI)

True or False: The Exposure Index is not a measure of radiation dose to the patient.

True

Computed radiography imaging produces ____________ gray levels.

10,000

True or False: Following the laser stimulation of the photostimulable phosphor, the excited electrons are mostly stabilized.

True

What is the name of the device that is needed to transfer the latent image within the image plate to a viewable digital radiograph?

imaging plate reader/digitizer

True or False: With computed radiography, the contrast can be changed.

False; the contrast is constant regardless of radiation exposure

__________ is prevented by flooding the erased imaging plate with bright light.

ghosting

True or False: The diameter of the laser beam determines the spatial resolution of the CR imaging system.

True

(smaller beam diameter = higher spatial resolution)

The principal source of of noise on a radiographic image is __________________.

scatter radiation

The source of the stimulating light in Computed Radiography (CR) is a ______.

laser

Which layer of the computed radiography imaging plate prevents unwanted light and background radiation from affecting the unprocessed latent image?

light-shield layer

Which layer of the computed radiography imaging plate is responsible for creating the latent image from the transmitted X-ray photons exiting the patient?

phosphor layer

The phosphor layer of the computed radiography imaging plate is composed of?

barium fluorohalides and europium activators

An X-ray photon is absorbed by the phosphor layer of a computed radiography plate through what type of interaction?

photoelectric interaction

What are the four principal characteristics of any medical image?

1. Spatial resolution

2. Contrast resolution

3. Noise

4. Artifacts

True or False: Electronic noise from the computer can cause image noise.

True

True or False: Sampling and quantization are not two processes of analog-to-digital conversion (ADC).

False; they are both processes of analog-to-digital conversion.

SP stands for…?

storage phospor

PMT stands for…?

photomultiplier tube

SPS stands for…?

storage phosphor screen