Photostimulable Phosphor (Psp)
PSP stand for “Photo Stimulable phosphor”. Computed Radiography uses very equipment similar to conventional radiography except that in place of an x-ray film to create the image,an Imaging Plate (IP) is used. The Imaging Plate is positioned in a special cassette and placed under the body part or object to be examined and the x-ray exposure is made. The imaging plate is run through a special laser scanner or CR Reader that reads and digitizes the image.
COMPUTERIZED RADOGRAPHY CASSETTE
- Fluorinated polymer material – Protective layer
- Barium fluorohalide crystal doped with europium (BaFl:Eu)- Phosphor Layer
- Polyethylene terephthalate (PET)-Base
- Lead – Backing Layer
Phosphor layer is composed of barium fluorohalide crystal doped with europium. Europium acts as an activator. It changes the chemical structure of phosphor to trap the electrons on x-ray exposure.
Europium is present in very small amounts and is responsible for the storage property of PhotostimulableLumniscence(PSL).
LAYERS OF AN IP
Protective layer, Phosphor layer, Reflecting layer, Base, Antistatic layer, backing layer
CROSS-SECTIONAL VIEW OF AN IMAGING PLATE
SEQUENCE OF EVENTS
- EXPOSE- results into x-ray induced image forming a signal
- STIMULATE- stimulation of latent image results from the interaction of laser beam with PSP
- READ- light signal emitted after stimulation is detected and measured
- ERASE- before reuse, any residual metastable electrons is moved to ground state by an intense light.
Computed radiography uses a medium to capture the x-ray energy and produces a digital image. CR generally involves the use of a cassette that houses the imaging plate, to record the image. CR system is reliable and is low cost conversion of multiple x-ray equipment’s into digital format. The Imaging Plate is reusable and thousands of exposures can be made on it.
Key words: Photostimulablelumniscence, Europium, Imaging Plate, PACS, DICOM, Photo Multiplier Tube
By:- Mr. Binoo
Department of Radiology
Uttaranchal (P.G.) College of Biomedical Sciences and Hospital