Unit 3 Direct Radiography (DR) Flashcards
What are 2 different terms used to describe DR?
-Flat panel detector technology
-Cassetteless
What is the big difference between CR and DR?
• One-step process: Capture, process, display image within x-ray unit itself
• Images display within 2-3 seconds (CR takes up to 90 seconds)
DR Advatages
• Lower patient doses (lower mAs)
• Speed and efficiency
• Higher quality images
• Wide exposure latitude (room for error)
DR Disadvantages
• Detectors are large and cumbersome
• High initial cost
• Cannot be used with standard x-ray equipment
• Detectors are not as durable as CR and are expensive
What is the main difference between direct conversion and indirect conversion DR
Indirect conversion uses a scintillator(converts x-rays to light)
Direct vs Indirect conversion
-Direct:
• More expensive
• Improved spatial resolution
• No light is needed
• No light = No loss of information
-Indirect:
• Requires a scintillator and photodetector
• Less expensive
• Some light photons will be lost and not converted to electrical signal
• Reduced spatial resolution
Which type of DR demonstrates better spatial resolution and why?
-Direct, because light is not needed
What is the active component in Direct Capture DR?
Amorphous selenium
What is a DEL?
Part of the DR detector that captures the latent image, converts it to an electronic form, and transfers the signal to the ADC
Describe the steps in image acquisition for Direct Conversion DR
- An electric charge is applied to the detector to activate the semiconductor when plate is turned on
* Detector and x-ray unit must be CONNECTED (wireless) - X-rays interact with Amorphous Selenium and ionize the atoms
- Electrons are collected and stored by the capacitor
- TFT Switch turns on in sequence and sends the electrons out to the ADC
Image Quality: Detective Quantum Efficiency
•how sensitive the DEL is to x-ray exposure
•how effectively an imaging system converts incident X-ray photons into a usable image signal, taking into account both signal and noise
DQE: 0.3-0.7 = 30%-70%
Larger DEL means
More sensitive = Less mAs needed
Smaller DEL means
Less sensitive = More mAs needed
IMAGE QUALITY: Fill Factor
% of DEL that is coated in active component
• Higher FF = Better Image detail
• Lower FF = Worse Image detail
What 2 requirements are needed for Indirect Conversion DR?
-Scintilator
-Photodetector
Uses a scintillator to convert x-rays to light that is then converted to electron signal by a photodetector
Other parts of Indirect Conversion DR
-TFT(Thin Flat Transistor)
-Charged-Couple device(CCD)
-Complementary metal oxide semiconductor(CMOS)
What are two common materials used for scintillation in Indirect Conversion DR?
-Gadolinium Oxysulfide: Reduced spatial resolution due to light spread
-Cesium lodide: Reduced light spread due to crystal arrangement = improved resolution
INDIRECT DR IMAGE ACQUISITION: TFT
Used to capture, store, and transmit the electronic signal to the computer for processing
INDIRECT DR IMAGE ACQUISITION: CCD
INDIRECT DR IMAGE ACQUISITION: CMOS
INDIRECT DR IMAGE ACQUISITION
CCD vs CMOS
Charged Coupled Device
• More expensive
• More durable
• Improved image quality
Complemtary Metal Oxide Semiconductor
• Less expensive
• Less sensitive to light
• Reduced Image quality
COMMON ARTIFACTS IN DIGITAL IMAGING: Quantum Mottle:
Low SNR
COMMON ARTIFACTS IN DIGITAL IMAGING: Ghost Images
incomplete erasure of a CR cassette
COMMON ARTIFACTS IN DIGITAL IMAGING: Scratches/Dust on IP
white lines, specks or artifacts on the image
COMMON ARTIFACTS IN DIGITAL IMAGING: Damage to DEL
drop out artifacts
CR vs DR Indirect vs DR Direct
What does a scintilator do
converts x-rays to light
