Lecture 6

Question 1

What are the main benefits of utilising digital imaging? (provide 3)

Answer 1

1. Don’t have to store films
2. Improved radiographic appearance
3. More flexibility with over/under exposure
4. Image processing
5. More rapid image production
6. Dispense with wet processing

Question 2

Differentiate between CR and DR:

Answer 2

Computed radiography (CR):

• Utilises a cassette loaded with image plate simmilar to cassette
• Compatible with existing X-ray tables

Digital radiography (DR):

• No casette is used
• Panel detector

Question 3

Breifly explain the difference between indirect detection and direct detection:

Answer 3

Indirect detection:

• Screen reacts with X-rays to produce light ⇒ each element is read out ⇒ read out is in form of an electronic signal

Direct detection:

• Electrons released after X-ray directly strikes a photoconductor (Selenium) ⇒ electrons and collected by each element ⇒ read out in the form of an electronic signal

Question 4

Which system has better spatial resolution digital images or film screen combinations?

Answer 4

• Film screen combinations have better spatial resolution

Question 5

What has better contrast resolution - digitial imaging or film screen combinations?

Answer 5

• All digital imaging systems have better contrast resolution than film screens

Question 6

Breifly explain on digital images how an objective and a subjective measure of image quality control can be made:

Answer 6

Objective assesment:

• Exposure indices

Subjective assesment:

• Double the image size
• No pixelation = good
• Multiple dots = underexposure
• Evaluate for anatomic clipping = overexposure

Question 7

Below is an example of anatomy clipping what is the cause of this defect:

Answer 7

Overexposure