Other modalities Flashcards
How does voxel affect resolution?
smaller voxel = higher resolution
what are the advantages of CT?
- 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).
What are disadvantages of CT?
- 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.
What elements does MRI involve?
protons (water
magnetic field
radiofrequency pulses
How is an MRI taken?
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.
what colour is cortical bone and dental hard tissues in an MRI and why?
Black - as not much water present
what colour is pathology in MRI?
bright
what are advantages of MRI?
- No ionising radiation
- Excellent for viewing soft tissue, cancellous bone, infection, infiltration cortex breach.
- Multi-planar
What are disadvantages of MRI?
- 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.
What are the uses for ultrasound?
neck swelling
salivary glands
blood flow
guidance for biopsy/ drainage
what are the advantages of ultrasound?
- 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.
what are disadvantages of ultrasound?
- Operator dependant
- Difficult to interpret.
- Superficial tissues
- Cannot penetrate bone.
how does radioisotope scanning work?
Inject isotopes which are unstable and decay emitting radioactive particles or radiation.
how is isotope selected in RS?
according to tissue being imaged
how is increased activity seen in RS?
radioactive compound concentrated in target tissue
how are radioactive emissions detected in RS?
by gamma camera
What isotope is used for radioisotope scanning?
technetium
why is technetium used in RS?
- Short half-life (6 hours) ensures lower patient dose.
- Easily available
- Can be bound easily to different substances.
When would RS be used?
- Salivary gland function
- Condylar growth in mandibular asymmetry
- Thyroid
- Bone metastases
- Osteomyelitis.
what are problems with nuclear medicine imaging?
- Poor resolution
- Appearances not specific and may not be able to distinguish between different pathological processes.
- Radiation dose.
what is PET CT?
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.
when is PET CT used?
- Diagnosing cancer
- Cancer staging
- Radiotherapy planning
- Assess how affective treatment has been.
- Distinguish between active disease and scarring following treatment.
