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Transcript

References

Skills

* In CR, most cassettes have the same speed; however, there are special extremity or chest cassettes that produce greater resolution.

* These are typically 100 relative speed.

* Great care must be taken when converting to a CR system from a film/screen system to adjust technical factors to reflect the new speed.

The Reader

Preprocessing, Processing and Forwarding the Image

With CR systems, no chemical processor or darkroom is necessary.

Cassette is fed into a reader:

Removes the imaging plate

Scans it with a laser, releasing the stored electrons

Erasing the Image

* Once the imaging plate has been read, the signal is sent to the computer.

* Image is preprocessed.

* A monitor displays the image so that the technologist can do the following:

- Review the image

- Manipulate it if necessary (postprocessing)

- Send it to the quality control station and ultimately to the picture archiving and communications system (PACS)

SocialErasing the ImageErasingErasing the Ima

- The process of reading the image returns most of electrons to a lower energy state.

- Reading effectively removes the image from the plate.

- Imaging plates are extremely sensitive to scatter radiation.

- Plates should be erased to prevent a buildup of background signal.

The Laser

- Plates should be run at least once a week under an erase cycle to remove background radiation and scatter.

- Erasure mode allows the surface of imaging plate to be scanned without recoding generated signal.

Systems automatically erase the plate by flooding it with light to remove any electrons still trapped after the initial plate reading.

- Cassettes should be erased before use if the last time of erasure is unknown.

SPEED

Laser stands for light amplification by stimulated emission of radiation.

Laser creates and amplifies a narrow, intense beam of coherent light.

Speed

The Computed Radiography Cassette, Imaging Plate, and Reader

- Spatial resolution refers to the amount of detail present in any image.

- Phosphor layer thickness and pixel size determines resolution in CR.

- The thinner the phosphor layer is, the higher resolution.

- Film/screen radiography resolution at its best is limited to 10 line pairs per millimeter (lp/mm).

- CR resolution is 2.55 lp/mm to 5 lp/mm, resulting in less detail

* In conventional radiography, speed is determined by the size and layers of crystals in the film and screen.

I* n CR, speed is not exactly the same because there is no intensifying screen or film.

* The phosphors emit light according to the width and intensity of the laser beam as it scans the plate, resulting in a relative speed that is roughly equivalent to a 200-speed film/screen system.

Spatial Resolution

- CR dynamic range, or the number of recorded densities, is much higher, and lack of detail is difficult to discern.

- More tissue densities on the digital radiograph are seen, giving the appearance of more detail.

Lesser

Spatial Resolution

* CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser.

* For example, Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200, hence the speed number.

Reader

For example, an anteroposterior knee radiograph typically does not show soft tissue structures on the lateral aspects of the distal femur or proximal tibia or fibula.

An anteroposterior knee digital image shows not only the soft tissue but also the edge of the skin. This is due to the wider dynamic recording range and does not mean that there is additional detail.

DR.RHAMAH

PREPARED BY :

Objectives

BEDOOUR ALANAZI

ENT9AR ALANAZI

Cassette & Imaging Plate

MEASHAL ALANAZI

FA6MAH ALSHEKH

* Describe the basic construction of a computed radiography cassette.

* Describe the construction of a computed radiography imaging plate.

* Identify the various layers of the imaging plate.

* Describe the purpose of each layer of the imaging plate.

Experience

Imaging Plate

ALAA AAWAYLI

FAI ALZAHRANI

Computed Radiography

Construction

Image recorded on a thin sheet of plastic known as the imaging plate

Consists of several layers:

Protective layer: a very thin, tough, clear plastic for protection of the phosphor layer

Phosphor, or active, layer

A layer of photostimulable phosphor that “traps” electrons during exposure

.

City, State

Email Address

Telephone

Cassette

Looks like a film/screen cassette

Durable, lightweight plastic

Backed by aluminum

No intensifying screens

Antistatic material

Explain the process of photostimulation in the imaging plate.

Describe the process of laser beam formation.

Explain the process of reading the imaging plate.

Compare conventional radiographic screen and film speed to computed radiography systems.

Discuss how an image is erased from the imaging plate.

also called cassette based radiography and it is the digital acquisition modality that uses storage phosphor plates to produce projection images.

CR requirements:

The CR cassettes.

Phosphor plates.

The CR readers.

Technologist quality control workstation.

Means to view the images, either a printer or a viewing station.

Reflective layer: a layer that sends light in a forward direction when released in the cassette reader

May be black to reduce the spread of stimulating light and the escape of emitted light.

Conductive layer: a layer of material that will absorb and reduce static electricity

Color layer: Newer plates may contain a color layer, located between the active layer and the support that absorbs the stimulating light but reflects emitted light.

Support layer: a semirigid material that gives the imaging sheet some strength

Backing layer: a soft polymer that protects the back of the cassette

Interests

Education

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