Introduction to Advanced Imaging
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List the different types of advanced imaging
- Computed tomography (CT)
- Magnetic Resonance Imaging (MRI)
What advantage does CT have over radiography?
It avoids superimposition of structures
What structures is CT good for imaging?
Skeleton and lungs
What safety considerations must be taken into account with CT?
Describe how a CT image is generated
X-ray beam passes through the patient and strikes detectors. The X-ray tube and detectors rotate around the patient so a cross sectional image is generated.
What is CT windowing?
When you adjust the display settings to highlight different tissues - this allows multiple organs to be assessed on a single image.
Why is CT a better choice for imaging CNS trauma than MRI?
As CT takes 10mins whereas MRI takes 45mins. This is better in unstable patients.
What structures is MRI excellent for imaging?
Soft tissues i.e. the CNS
What safety considerations must be taken into account with MRI?
There is no ionising radiation but MRI uses a very strong magnet which can pose a major safety hazard - no metal must be taken into the room.
Describe how an MRI image is generated
Body is placed in a magnetic field with a strong receiver coil. Protons align with magnetic field. Electromagnetic pulse moves protons from alignment with main field. As protons relax back to main field, the change in signal is detected by receiver coil. Image is generated.
Describe the difference between T1 and T2 weighted images
Fluid appears hypo intense on T1 weighted images whereas it appears hyper intense on T2 weighted images.
What is fluoroscopy?
'Real time' radiography
What is fluoroscopy useful for?
Swallowing disorders, tracheal collapse, vascular diseases. Also good for placement of pacemakers, catheters, etc.
What area of vet med is scintigraphy commonly used in?
Equine medicine - usually to diagnose lameness
What does scintigraphy show?
Tissue activity rather than absolute anatomy
Describe the process of scintigraphy
Radioactive material is injected into the blood stream. This is bound to a tracer which localises it to specific tissues. The radiation is detected by a gamma camera. Increased tissue activity shows up as increased radio-activity of that tissue.
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