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Computed Radiography

Cassette-based digital imaging is the digital acquisition modality that uses storage phosphor plates to produce projection images. It can be used in standard radiographic rooms just like film/screen.

1.) CR cassettes
2.) Phosphor Plates
3.) CR reader

The use of CR requires?

1.) Cassette
2.) Imaging Plate (IP)
3.) Computed Radiography Reader
4.) Optical Components
5.) Computer Control

What are the basic components of a CR system?


It consists of a durable, lightweight plastic material. A light-proof container that protects an imaging plate from light and handling and is backed by a thin sheet of aluminum that absorbs x-rays.

Imaging Plate

It is housed in a cassette. The material must have the ability to store and release the image information in a usable form.

Barium Fluorohalide Bromides and Iodides with Europium Activators

The most common phosphor with characteristics favorable for CR is?

1.) Storage Phosphors Screen
2.) Photostimulable Imaging Plates

IP screens are also called?

Computed Radiography Reader

The cassette is fed into this that removes the imaging plate and scans it with a laser to release the stored electrons.


Source of stimulating light.

Beam Shaping Optics

It keeps the laser beam constant size, shape, speed and intensity.

Light Collecting Optics

Emitted light from the IP, is channeled into a funnel like fiber optic collection assembly and is directed at the photodetector, photomultiplier tube (PMT) photodiode (PD) or charge-coupled device (CCD).

Optical Filters

It filters the light before photodetection occurs.


It receives light from the fiber optic collection assembly, and transmits a time-varying analog signal to a computer system.

1.) Protective Layer
2.) Phosphor or Active Layer
3.) Reflective Layer
4.) Conductive Layer
5.) Color Layer
6.) Support Layer
7.) Conductor Layer
8.) Light Shield Layer
9.) Backing Layer

What are the layers of the imaging plate?

Protective Layer

A very thin, tough, clear plastic that protects the phosphor layer.

Phosphor or Active Layer

Holds the Photostimulable phosphor (PSP), which is the active component in the plate.

Reflective Layer

It sends light in a forward direction when released in the cassette reader. This layer may be black to reduce the spread of stimulating light and the escape of emitted light.

Conductive Layer

The material in this layer absorbs and reduces static electricity.

Color Layer

It is located between the active and support layers of the IP that absorbs the stimulating light but reflects emitted light.

Support Layer

A semi-rigid material that gives the imaging sheet some strength and a base on which to coat the other layers.

Conductor Layer

It grounds the plate to eliminate electrostatic problems and absorb light to increase sharpness.

Light Shield Layer

It prevents light from erasing data on the imaging plate or leaking through the backing, decreasing the spatial resolution.

Backing Layer

A soft polymer that protects the back of the cassette.

Photostimulable Luminescence

It is defined as light produced by a phosphor (active layer) when struck by light or x-ray photons. It occurs following x-ray exposure. However, it also occurs some time later when exposed to a different light source (laser beam).


The ___________ of the laser beam affects the spatial resolution of the CR system.

Raster Pattern

Scanning of the IP by a laser occurs in a ____ as the plate is fed through the processor.


It is largely automatic in digital.


It is performed to optimize the appearance of the image for purpose of better detecting pathology.


It is the process of labeling the image.

Window and Level

Expands the digital grayscale to visible.


This improves visualization and spatial resolution.

Image Flip and Image Inversion

Reorients image presentation and makes white black and black white.

Subtraction (DSA)

Improves image contrast.

Pixel Shift

Registering the image to correct for patient motion.

Region of Interest (ROI)

Determines average pixel value in quantitative imaging.


Various computed radiography images receptors is different for each manufacturer.

0.1, 100

Exposure sensitivity of the imaging plate ranges from __ mR up to maximum of __ mR.

Exposure Indicator

In order to evaluate the exposure for CR image, most manufacturers have an ______ that provides information on the average amount of radiation used for an image.


_____ uses a sensitive number (S number) that is related to the amount of amplification required by the PM tube to adjust the digital image.


______ CR indicator system is called the exposure index, which is directly proportional to the radiation striking the IP.


_____ system uses a log median exposure (LgM), it compares the exposure level of an image to a baseline established for the department.

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