Alternative Imaging Modalities

Question 1

What other modalities are available for imaging?

Answer 1

• MRI
• ultrasound
• nuclear medicine (radio-isotope scanning)
• combination of modalities including PET

Question 2

What are the advantages of CT scanning?

Answer 2

• images bone and soft tissue
• differentiate different tissues
• head injury - can see bone and brain
• speed compared to MRI
• multi-planar - manipulate, reconstruct images
• cost and availability usually cheaper than MRI

Question 3

Disadvantages of CT scanning?

Answer 3

• patient radiation dose
• dose for head ~ 2mSv
• often requires IV contrast to distinguish tissues (iodine based –> allergy)
• artefacts (metallic objects, amalgam in head and neck)
• expensive in comparison to plain radiography

Question 4

Advantages of MRI scanning?

Disadvantages:

Answer 4

• no ionising radiation
• excellent for viewing soft tissue, cancellous bone: changes in marrow, infection, infiltration, cortex breach
• multi-planar

Disadvantages:

• multiple contraindications: pacemaker, artificial heart valves, surgical clips, 1st trimester of pregnancy
• FB with the eyes/orbits
• danger of strong magnetic field
• units need to be away from car parks and other facilities
• availability and cost of scanning
• scan times can be long and noisy
• claustrophobia

Question 5

Advantages of ultrasounds:

Disadvantages?

Answer 5

• no ionising radiation, no known harmful effects
• ideal for superficial soft tissue structures
• multi-planar
• operator dependent
• real time images
• blood flow
• can be used as a guide for fine needle aspirate or biopsies

Disadvantages:

• operator dependent
• difficult to interpret
• superficial tissues
• cannot penetrate bone

Question 6

When could ultrasound be used?

Answer 6

• neck swelling
• salivary glands
• blood flow
• guidance for biopsies/drainage