14. Introduction To Clinical Imaging

Question 1

Describe the process of echocardiography.**

Answer 1

A type of ultrasound scan that is able to visualise the four chambers of the heart, assess muscular contraction and direction of blood flow all in real-time.

Easily obtained by placing the ultrasound probe between the patient’s ribs and sometimes placing a probe down the oesophagus.

Question 2

Describe the process of coronary angiography.*

Answer 2

• A catheter is inserted in a peripheral artery (e.g. femoral artery) via a hollow needle.
• The catheter is threaded all the way to the aortic root and then into the coronary vasculature (blood vessels that supply and drain the heart)
• A radiopaque dye is injected into each of the coronary roots.
• A simple 2D radiography of the heart is taken. The area reached by the dye shows a darker colour? Because it does not allow the penetration of X-rays.

Question 3

Main advantages and disadvantages of MRI

Answer 3

Advantages:
- Non-invasive as ionising radiation is not used. No radiation damage to patients.
- Can be used on pregnant women. ALTHOUGH, care is advised as there are still certain unknowns.
- Highly detailed. Good for looking at soft tissue injuries, e.g. ligament and tendon, CNS or PNS

Disadvantages:
- Not useful for parts where there is little water, e.g. bones, as it is reliant on H+ ions.
- Strong electromagnetic forces interact with metallic objects. Caution is advised. Patients with implants and devices must be thoroughly worked up before being scanned.
- Expensive and so rare.
- Takes a lot of time to perform.
- Highly uncomfortable for patients as they have to be immobile during the whole procedure. Can be very claustrophobic.

Question 4

Main advantages and disadvantages of ultrasound.

Answer 4

Advantages:
- Cheap and portable.
- No risk of ionising radiation. HOWEVER, some theorised unknowns of the effect of high frequency waves.
- Good at looking what’s inside an empty hollow organ.

Disadvantages:
- Highly user dependent.
- Drastically limited by external factors, e.g. patients BMI.
- Little diagnostic value when used in a part surrounded by tissues of high echogeniticity.

Question 5

Main advantages and disadvantages of plain radiography.

Answer 5

Advantages:
- Simple, cheap and quick.

Disadvantages:
- Ionising radiation (can be prevented by metal suits). Not advised to use on pregnant women.
- 2D so pathologies can be easily missed if obstructed by areas of higher density.
- Not effective for soft tissues (MRI), hollow organs (ultrasound) or the neurological system (MRI).

Question 6

Main advantages and disadvantages of CT scans

Answer 6

Advantages:
- 3D imaging
- Quick
- Highly available

Disadvantages:
- Large amounts of ionising radiation. Not advised to use on pregnant women.
- Difficulty producing an accurate image for soft tissues, e.g. muscles, ligaments and tendons.