Imaging, infection, inflam and ca Flashcards
Scientific basis of PET
- Type of molecular imaging
- Uses radionuclides that decay by positron emission.
- Proton -> neutron + positron
- Can be used for absolute quantitation but requires arterial samples
- Gamma rays emitted indirectly by a PET radionuclide are introduced into the body on a biologically active molecule
- A 3D image can be seen by a PET-CT
Ideal isotope for labelling
- Need short half-life, similar to length of examination
- Needs to be a gamma emitter
- Should be readily available at hosp. site
- Can be easily bound to pharmaceutical component
- Easy to prepare
- Examples: F18, is commonly used. C11 is used for prostate
Scientific basis for MRI
- Strong magnetic field aligns protons in the body in one direction
- Radiofrequency pulse displaces protons and images created by displaying time taken for protons to ‘relax’ back to original alignment
Indications for MRI-specific contrast agents
- Excellent bone and soft tissue detail
- Vessel can be demonstrated
- Brain, spine and MSK
- Abdo and pelvis
- Cardiac imaging
Contraindications for MRI-specific contract agents
- Claustrophobic and noisy
- Motion artefact
- Cannot image patients with pacemakers, aneurysm clips unless they’re compatible with an MRI
Example of contrast agent used in MRI
- Gadolinium DTPA
- IV contrast medium, causes changes in local magnetic field and alters tissue signal
- Vascular lesion and some tumours can be more easily seen
Patient safety issue specific to MRI
- Pacemakers, aneurysm clips
- Projectile risk, metal in room being pulled over and hitting patient
- Claustrophobia and discomfort
Clinical applications of imaging for diagnosis
- Make initial diagnosis
- Stage disease
- Monitor response to treatment
- Evaluate residual mass after treatment: always going to be residual mass. It’s just whether it’s cancerous or scar tissue
- Assess when there is concern of relapse
Pros and cons of population screening with radiological testing
- Should detect disease at an early stage where treatment can alter outcome
- Test should cause no harm
- High sensitivity/specificity
- Benefit to individual and population should outweigh cost
Guidelines used judicious use of imaging
ALARA, as low as reasonably possible
- Ensure whether examination is necessary
- Need enough clinical infor for appropriate protocol
- Minimise repeat examination
Detection of gamma radiation and production of digital image by gamma camera
Gamma ray is emitted from the patient, image crystal produces flashes of light
This is displayed as an image
Detection of gamma radiation and production of digital image by PET
- Dual head gamma camera
- PET tracers emit positrons that annihilate with electron that cause 2 gamma photons to be emitted in opposite directions
Detection of gamma radiation and production of digital image by SPECT
- Gamma cameras rotate around area of interest
- Also uses a radionuclide tracer
- Tracers in SPECT emit gamma radiation which is measured directly and gets a 3D image
- Used in brain, cardiac and lung
Currency of radiation
- Emission energy - keV
- PET scans 50-300 keV
Examples of diseases you can diagnose
- Inflammation: rhematoid arthritis, aortitis (tram tract activity in scnas), ulcerative colitis
- You can also stage a tumour
