Published on March 20, 2014
Dr. Muhammad bin zulfiqar PGR-1 SIMS/ SHL.
Basics of Digital Language
5 Byte The basic unit of binary coded information Kilobyte—210 – 1024 bites Megabyte—1024 times1024bites
Performance parameters Pixel: Smallest complete sample of an image. Has a varied set of tones in shades of white/ black/grey. Expressed in binary codes (bits). Size of the pixel : Smaller the size , better resolution. CR- 50 to 200 microns, DR- 100 to 200 microns, DM- 50 to 100 microns. Gray Scale: Shades of Gray in between pure black and pure white. Bit Depth: No of shades to define each pixel ,measured as no of bits. Larger the depth, incr gray scale and large file size.
Spatial Resolution: finer details, diff objects in an image. Depends on sampling frequency and no of pixels. expressed in lp/mm. Contrast Resolution: Color or gray scale differentiation. Indicate the no of shades of grey that a detector can capture. File Size. Performance Parameters(contd..)
DIGITAL PROJECTION RADIOGRAPHY COMPUTED RADIOGRAPHY (CR) DIGITAL RADIOGRAPHY (DR)
11011101 CR X-RAYS CR PLATE SCANNER
DETECTORS 11011101 DR X-RAYS
Computed Radiography (CR) Been around since 1980-81 Uses same radiographic equipment No change in X-ray machine Uses an imaging plate Contains a photostimulator phosphor Need a cassette reader Images can be sent to a PACS
Computed Radiography (CR) Re-usable metal imaging plates replace film & cassette Uses conventional bucky & x-ray equipment
CR SYSTEM COMPONENTS CASSETTES (phosphor plates) ID STATION IMAGE PREVIEW STATION DIGITIZER VIEWING STATION
CASETTE CONSTRUCTION LIGHTWEIGHT ALUMINUM PLASTIC STEEL FRAME FRONT PANEL MADE OF LOW ATTENUATION CARBON FIBER
PROTECTIVE LAYER PHOSPHOR LAYER ANTI-HALO & REFLECTIVE LAYER BASE BACKING LAYER
PHOSPHOR LAYER BASE Ba FX: Eu +2 PET- POLYETHYLENE TERAPHTALATE PROTECTIVE LAYER FLUORINATED POLYMER MATERIAL PROTECTS PHOSPHOR LAYER
ANTI-HALO LAYER + REFLECTIVE LAYER PREVENTS LASER FROM PASSING THROUGH. REFLECTED LIGHT FROM PHOSPHOR IS ALLOWED TO PASS. BACKING LAYER PROTECTS THE BASE FROM DAMAGE.
REMOTE OPERATOR PANEL
Add module code number and lesson title 29
Add module code number and lesson title 30 The principle of PSP Excitation Storage Emission CB Trap ADC PMT
Higher Energy Electron State Lower Energy Electron State - - - - - - - - - - - - - - - - - - - - - - - - - - - X-Ray Photon - Photon pumps electron to higher energy state
Add module code number and lesson title 36 (Images courtesy of AFGA) PSP digitizer Casette and PSP Workstation
Reading Imaging Plate Reader scans plate with laser Laser releases electrons trapped in high energy states Electrons fall to low energy states Electrons give up energy as visible light Laser Beam Higher Energy Elect ron St at e Lower Energy Elect ron St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - Lower Energy Electron State
Reader scans plate with laser light using rotating mirror Film pulled through scanner by rollers Light given off by plate measured by PM tube & recorded by computer Reading Imaging Plate
Conventional CR Scanning
25% OF STORED ENERGY WITHIN 8 HOURS
CR PLATE CR SCANNER/READER CR AFTER EXPOSURE IS INSERTED INTO CR SCANNER
CR Exposure & Readout
PM TUBE AMPLIFIER ADC LASER LIGHT GATE
PLATE & F-CENTERS LASER 633 nm PHOTOSTIMULABLE LUMINESCENCE 390-400 nm
After read-out, plate erased using a bright light Plate can be erased virtually without limit Plate life defined not by erasure cycles but by physical wear
IMAGE DISPLAY Typical image plate can be reused thousands of times
CR Resolution Small cassettes have better spatial resolution Smaller pixels More pixels / mm
PICTURE DESTINATION -PACS
CR CHARACTERISTIC CURVE VERY WIDE LATITUDE CR SYSTEMS LESS RADIOGRAPH REPEATS
Much greater latitude than screen/film Plate responds to many decades of input exposure under / overexposures unlikely Computer scale inputs exposure to viewable densities Unlike film, receptor separate from viewer
CHARACTERISTIC CURVE LATITTUDE OF CR LATITTUDE OF FILM
IMAGE CAN BE SALVAGED WITH CR 500% OVEREXPOSURE 80% UNDEREXPOSURE USE ADEQUATE KVP
HARD COPY GENERATED IN LASER PRINTER
CR SYSTEM EFFICIENCY CHARACTERISTIC QDE- QUANTUM DETECTION EFFICIENCY NO NEED FOR SCREENS QDE: THE MEASURE OF THE EFFICIENCY OF CR SYSTEM TO CONVERT REMNANT X-RAYS TO USEFUL IMAGE SIGNAL QDE PATIENT DOSE
Receptor provides direct digital output No processor / reader required Images available in < 15 seconds Much less work for technologist
PACS and DICOM THE ROLE OF PACS : A Picture Archiving and Communication System (PACS) aims to replace conventional analogue film and paper clinical request forms and reports with a completely computerized electronic network whereby digital images are viewed on monitors in conjunction with the clinical details of the patient and the associated radiological report displayed in electronic format. The ROLE OF DICOM: Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a picture archiving and communication system (PACS). The different devices come with DICOM conformance statements which clearly state the DICOM classes they support. DICOM has been widely adopted by hospitals .
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