Unit 3 Direct Radiography (DR)

Question 1

What are 2 different terms used to describe DR?

Answer 1

-Flat panel detector technology
-Cassetteless

Question 2

What is the big difference between CR and DR?

Answer 2

• One-step process: Capture, process, display image within x-ray unit itself
• Images display within 2-3 seconds (CR takes up to 90 seconds)

Question 3

DR Advatages

Answer 3

• Lower patient doses (lower mAs)
• Speed and efficiency
• Higher quality images
• Wide exposure latitude (room for error)

Question 4

DR Disadvantages

Answer 4

• 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

Question 5

What is the main difference between direct conversion and indirect conversion DR

Answer 5

Indirect conversion uses a scintillator(converts x-rays to light)

Question 6

Direct vs Indirect conversion

Answer 6

-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

Question 7

Which type of DR demonstrates better spatial resolution and why?

Answer 7

-Direct, because light is not needed

Question 8

What is the active component in Direct Capture DR?

Answer 8

Amorphous selenium

Question 9

What is a DEL?

Answer 9

Part of the DR detector that captures the latent image, converts it to an electronic form, and transfers the signal to the ADC

Question 10

Describe the steps in image acquisition for Direct Conversion DR

Answer 10

1. 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)
2. X-rays interact with Amorphous Selenium and ionize the atoms
3. Electrons are collected and stored by the capacitor
4. TFT Switch turns on in sequence and sends the electrons out to the ADC

Question 11

Image Quality: Detective Quantum Efficiency

Answer 11

how sensitive the DEL is to x-ray exposure

DQE: 0.3-0.7 = 30%-70%

Question 12

Larger DEL means

Answer 12

More sensitive = Less mAs needed

Question 13

Smaller DEL means

Answer 13

Less sensitive = More mAs needed

Question 14

IMAGE QUALITY: Fill Factor

Answer 14

% of DEL that is coated in active component

• Higher FF = Better Image detail
• Lower FF = Worse Image detail

Question 15

What 2 requirements are needed for Indirect Conversion DR?

Answer 15

-Scintilator
-Photodetector

Uses a scintillator to convert x-rays to light that is then converted to electron signal by a photodetector

Question 16

Other parts of Indirect Conversion DR

Answer 16

-TFT(Thin Flat Transistor)
-Charged-Couple device(CCD)
-Complementary metal oxide semiconductor(CMOS)

Question 17

What are two common materials used for scintillation in Indirect Conversion DR?

Answer 17

-Gadolinium Oxysulfide: Reduced spatial resolution due to light spread
-Cesium lodide: Reduced light spread due to crystal arrangement = improved resolution

Question 18

INDIRECT DR IMAGE ACQUISITION: TFT

Answer 18

Used to capture, store, and transmit the electronic signal to the computer for processing

Question 19

INDIRECT DR IMAGE ACQUISITION: CCD

Answer 19

Question 20

INDIRECT DR IMAGE ACQUISITION: CMOS

Answer 20

Question 21

INDIRECT DR IMAGE ACQUISITION

Answer 21

Question 22

CCD vs CMOS

Answer 22

Charged Coupled Device
• More expensive
• More durable
• Improved image quality

Complemtary Metal Oxide Semiconductor
• Less expensive
• Less sensitive to light
• Reduced Image quality

Question 23

COMMON ARTIFACTS IN DIGITAL IMAGING: Quantum Mottle:

Answer 23

Low SNR

Question 24

COMMON ARTIFACTS IN DIGITAL IMAGING: Ghost Images

Answer 24

incomplete erasure of a CR cassette

Question 25

COMMON ARTIFACTS IN DIGITAL IMAGING: Scratches/Dust on IP

Answer 25

white lines, specks or artifacts on the image

Question 26

COMMON ARTIFACTS IN DIGITAL IMAGING: Damage to DEL

Answer 26

drop out artifacts

Question 27

CR vs DR Indirect vs DR Direct

Answer 27