IMAGING LAB MPHY 487
DIGITAL RADIOGRAPHY
Mohammad Esmael Alsulimane B.Sc, M.Sc
Medical Physics Lecturer - Physics Department
All Rights Reserved:
Some information and figures in this presentation are collection from presentations who's name are listed below.
Dr. Omar A. Al-Amoudi
Consultant Medical Physicist and Head of Medical Physics Section King Fahd Armed Forces Hospital, Jeddah
Gwenda Harris
Film Screen Imaging Computed Radiography / Digital Radiography IMAGE RECEPTOR SYSTEMS.
www.coastalxray.com.au www.varian.com
Contents
• X – Ray Image Formation
• Conventional Radiography
• Digital Radiography
X – Ray Image Formation
Electron Source
Evacuated Path for Electron Acceleration
Target Electrode
External Energy Source to Accelerate the Electrons
X – Ray Image Formation
X – Ray Image Formation
• The tube housing protects the tube and
provides shielding to prevent leakage radiation.
• The housing contains an oil bath to
provide electrical insulation and help cool the tube.
• An evacuated glass is used to surround
the anode & cathode assembly to prevent the electrons from colliding with gas (air) molecules.
• X-rays exit through a window in the tube housing.
X – Ray Image Formation
• The X-ray tube contains a negatively charged cathode containing the filament that serves as the source of electrons that are accelerated towards the anode to produce X-rays.
• The filament is usually made of coiled tungsten wire.
• The focusing cup surrounds the filament(s) and helps direct and focus the electron beam towards the anode target.
X – Ray Image Formation
X – Ray Image Formation
•Without the focusing cup, the electron beam would be
spread beyond the anode because the mutual electrostatic repulsion among the electrons.
•With a focusing cup, which is negatively charged, the beam is condensed and directed to the desired area of the anode
Conventional Images
❖ Conventional radiographic imaging systems have worked well for over a century providing better diagnostic images.
❖ However, conventional radiographic images (Screen-film) have limitations.
Limitation of Conventional Imaging
❖
Once image is obtained, very little can be done to enhance the information content
❖
Noise inherent in these images which degrade contrast resolution
❖
film processor problems, film processor QA, time consuming
❖
Can be viewed only in single geographic location at a time
❖
can’t visualize the image immediately
❖
Only available as a hard copy film
Digital Radiography
❖ Energy from x-rays is absorbed by the digital detector and transformed into electrical charges.
❖ Electrical charges are recorded, digitized and quantified into a gray scale that represents the amount of x-ray energy deposited on the detector.
❖ Post processing software is needed for organizing the raw data into clinically meaningful image.
❖ Images are sent to archive and linked to the patient demographic information .
❖ Sent to workstation for review.
Digital Radiography
Various Types of Digital Detectors
Indirect DR \ Create visible light photons from x-rays with scintillator then produce electrons with photodiodes typically lower spatial resolution than direct DR and lower dose efficiency than direct DR due to limiting the phosphor thickness so as not to adversely impact spatial resolution.
Direct DR \ Create electrons from absorbed x-rays, typically higher spatial resolution than indirect DR and higher dose efficiency than indirect DR due to electric field lines constraining electron lateral drift.
Digital Indirect Radiography
Principles of CR Radiography
o A storage Phosphor plate is placed inside of CR cassette.
o Most storage Phosphor is made from BaFBr Compound, Eu Activated
o Laser beam scans the storage phosphor screen to acquire the analog image data (signal)
o After exposure and scanning, the Phosphor plate is ERASED by exposing to bright light exposure within the digitizer
o The previous data removed and the plate is ready to be exposed
again
CR helps in portable radiography: where the tight exposure limits of SF are hard to achieve.
Screen Film Images
Computed
Radiography Images
Digital Direct Radiography
• DR used to describe total electronic imaging capturing.
• Eliminates the need for an image plate altogether.
• uses a transistor receiver.
• Captures and converts x-ray energy directly into digital signal.
• Seen immediately on monitor then sent to PACS.
DR VS CR
CR DR
Characteristics
Need cassette imaging plate No need cassette
transistor receiver Physics Principles
Image need time to view Image view directly
Speed
Less resolution and need more dose to same image quality Good resolution
Image Quality
Less sensitive More Sensitive its mean lower
radiation dose sensitivity
Old model Modern model
Model
Shaper Costly
Cost
