Other modalities

Question 1

How does voxel affect resolution?

Answer 1

smaller voxel = higher resolution

Question 2

what are the advantages of CT?

Answer 2

• Images bone and soft tissue.
• Differentiate different tissues.
• Head injury – can bone and brain.
• Speed (compared MRI).
• Multi-planar (manipulate, reconstruct images)
• Cost and availability usually cheaper (compared to MRI).

Question 3

What are disadvantages of CT?

Answer 3

• Patient radiation dose
• Dose for head – 2mSv
• Often requires intravenous contrast to distinguish tissues (iodine based, allergy)
• Artefact (metallic objects, amalgam in head and neck).
• Expensive in comparison with plain radiography.

Question 4

What elements does MRI involve?

Answer 4

protons (water
magnetic field
radiofrequency pulses

Question 5

How is an MRI taken?

Answer 5

Patient is placed in a magnetic field where water protons are aligned. Another magnetic field is applied at an angle and then removed. The protons oscillate/ resonate back to their original position. This resonance is measured by the computer.

Question 6

what colour is cortical bone and dental hard tissues in an MRI and why?

Answer 6

Black - as not much water present

Question 7

what colour is pathology in MRI?

Answer 7

bright

Question 8

what are advantages of MRI?

Answer 8

• No ionising radiation
• Excellent for viewing soft tissue, cancellous bone, infection, infiltration cortex breach.
• Multi-planar

Question 9

What are disadvantages of MRI?

Answer 9

• Multiple contraindications – pacemakers, artificial heart valves, surgical clips particularly intra-cerebral aneurysm clips, 1st trimester pregnancy.
• FB within eyes/ orbits.
• Danger of strong magnetic fields – might clear your bank card!
• Units need to be away from car parks and other facilities.
• Scan times can be quite long and noisy.
• Claustrophobia.

Question 10

What are the uses for ultrasound?

Answer 10

neck swelling
salivary glands
blood flow
guidance for biopsy/ drainage

Question 11

what are the advantages of ultrasound?

Answer 11

• No ionising radiation
• No known harmful effects
• Ideal for superficial soft tissue structures.
• Multi-planar
• Operator dependant
• Real time images
• Blood flow
• Can be used to guide fine needle aspirate or biopsies.

Question 12

what are disadvantages of ultrasound?

Answer 12

• Operator dependant
• Difficult to interpret.
• Superficial tissues
• Cannot penetrate bone.

Question 13

how does radioisotope scanning work?

Answer 13

Inject isotopes which are unstable and decay emitting radioactive particles or radiation.

Question 14

how is isotope selected in RS?

Answer 14

according to tissue being imaged

Question 15

how is increased activity seen in RS?

Answer 15

radioactive compound concentrated in target tissue

Question 16

how are radioactive emissions detected in RS?

Answer 16

by gamma camera

Question 17

What isotope is used for radioisotope scanning?

Answer 17

technetium

Question 18

why is technetium used in RS?

Answer 18

• Short half-life (6 hours) ensures lower patient dose.
• Easily available
• Can be bound easily to different substances.

Question 19

When would RS be used?

Answer 19

• Salivary gland function
• Condylar growth in mandibular asymmetry
• Thyroid
• Bone metastases
• Osteomyelitis.

Question 20

what are problems with nuclear medicine imaging?

Answer 20

• Poor resolution
• Appearances not specific and may not be able to distinguish between different pathological processes.
• Radiation dose.

Question 21

what is PET CT?

Answer 21

Images are acquired with both technologies at the same time and superimposed on each other. The radio-active contrast can be given orally, inhaled or into a vein, depending on what is being investigated.
- Shows areas where cells are more active than normal.

Question 22

when is PET CT used?

Answer 22

• Diagnosing cancer
• Cancer staging
• Radiotherapy planning
• Assess how affective treatment has been.
• Distinguish between active disease and scarring following treatment.