Radiology

Question 1

What are the pros and cons of X-rays?

Answer 1

• X-rays are good at showing things that are surrounded by black air eg lung cancer.
• X-rays are good at showing things that are surrounded by white bone eg fractures.
• X-rays are good at showing things that destroy white bone eg bone cancer.
• To be visible on a simple x-ray, an abnormality must be of very different density to the tissue that surrounds it and unfortunately, a lot of pathology, especially that affecting soft tissues, is of similar density to its surroundings and isn’t shown by simple X-rays.

Question 2

What are contrast studies?

Answer 2

Liquids containing dense elements like barium or iodine can block x-rays. By putting these into the spaces between tissues, the tissue outlines become visible. This is called a contrast study.

Question 3

Describe CT scans

Answer 3

• CT is a sophisticated way of using x-rays to produce images.
• It is more able than radiographs to distinguish between tissues of similar density and is often used to show soft tissue pathology.
• It has superior contrast resolution compared to a radiograph

Question 4

What are the disadvantages to CT?

Answer 4

CT gives large doses of ionising radiation.

Soft tissues of similar density still cannot be distinguished by CT and CT cannot resolve bone marrow disease.

Question 5

4 advantages and 3 disadvantages of ultrasound?

Answer 5

• Ultrasound has high spatial resolution which is useful in imaging MSK soft tissue structures e.g. tendons and muscles.
• Body fluids readily transmit ultrasound whereas solid structures within the fluid reflect it.
• This allows abnormal fluid collections to be well shown by ultrasound as the surrounding tissues reflect more sound and contrast with the black fluid
• Soft tissues with different acoustic properties are well differentiated by ultrasound e.g. soft tissue tumours.
• Bone blocks US, so it can’t see the brain, the spinal canal, inside joints or assess bone marrow.
• Gas blocks US, so ‘windy’ patients are difficult to assess and gas containing structures like the lungs or bowel can’t be assessed.
• Very fat patients make poor US subjects.

Question 6

Although MRIs provide the best images, what are the disadvantages?

Answer 6

• Time spent in the scanner can be very long and it is not possible to get all patients to lie still for this length of time.
• Some patients find the machine too claustrophobic or simply may not be suitable due to metal implants etc in their body.
• MRI is also very expensive.