Nuclear Medicine Flashcards
How does nuclear medicine differ from normal imaging?
Provides physiological info of organ/tissue
Uses INTERNAL source of radiation (not external)
What are the basic principles of nuclear medicine?
- Radiopharmaceutical/radionuclide (radioactive substance is attached to METABOLICALLY active substance)
- The radioactive substance decays and emits Gamma radiation + detected
What are the 3 types of decay?
Beta minus decay
Beta plus decay
Gamma decay
What are the advantages of technetium 99?
- reduced radiation exposure as short half life and pure gamma emission
- cheap and easy to produce
- easily binds to pharmaceuticals
- can be attached to many pharmaceuticals - WIDE RANGE of target organs
What can technetium 99m be used for?
SPECT (single photon emission CT)
V/Q scan (PE)
Gated cardiac pool imaging (multi gated acquisition imaging) to evaluate LV function
Bone scintigraphy (for metabolically abnormal bone)
Sentinel node imaging (breast)
What is technetium 99m labelled with in: bone scintigraphy Sentinel node imaging Gated cardiac blood pool imaging V/Q scan SPECT (single photon emission CT)
Phosphate
Sulphur
RBC
DTPA inhaled (n.b. Can use xenon instead of technetium 99) and MAA injection (macroaggregated serum albumin_
Sestamibi (uptake proportional to mycoardial blood flow) or exametazine (brain blood flow)
What radioactive tracer does PET scanning use?
FDG: F-18 labelled deoxyglucose
How does PET scanning work?
FDG undergoes BETA + decay which releases positrons
Positrons react with electrons and reads 2 gamma radiation in opposite directions
Detectors of PET scanner measure the gamma rays
A ring containing multiple gamma cameras is used to detect gamma in all directions (they interact with gamma cameras 180 degrees from them) to pinpoint where gamma radiation is released and create an image
What are the applications of PET?
1) diagnose and monitor Ca
2) detect mets (picks up smaller
3) assess response to Ca Rx
4) functional imaging of neurodegenerative and psychiatric conditions
5) cardiac imaging: MI (myocardial cells use glucose when damaged) or assess whether Tx or bypass needed
NOT STAGING (use PET-CT)
also Hashefi et al discusses the non-cancer use of PET: OP, OA, interstitial lung disease, chronic pain syndromes, granulomatous disease (sarcoid + crohn’s)
Why is PET useful in MI?
Damaged myocardial cells utilise glucose rather than fatty acids and so these cells take up FDG used in PET –> thus areas of myocardial damage show up as hot spots
What is PET-CT useful for?
- Cancer staging!!!!!
- Also imaging/assessing primary malignancies (esp bone)
- response to CTx
- early detection if recurrence of malignancy suspected
- research
- future role in myocardial assessment
- future role in neuroimaging (psych [depression] and organic illnesses)
Give some contraindications and disadvantages for PET-CT?
- HF (pt has to lie down for long time)
- DM
- pregnancy
Disadvantages:
Pts considered radioactive (isolated, can’t be exposed to kids and pregnant women, HUMAN WASTE radioactive)
Fast for 4-6hrs
Must sit quietly for 1hr while radionuclide circulates
What is SPECT? How does it work?
What are the advantages over PET?
Single photon emission CT
- Tracer (eg T99) introduced to pt
- Release gamma
- Gamma cameras rotate around pt
- Creates 3D images
Adv: cheaper and tracers have longer half life than FDG
What tracer/radionuclide is used in PET?
FDG
What are the uses of SPECT?
Summary: SPECT is used for BLOOD FLOW/vasculature
Most common: 1. Dx/monitor heart disease (myocardial perfusion)
- Bone disorders
- GI bleeds
- Research roles (e.g. Evaluating blood flow patterns in psych/organic neuro disorders) - using exametazine
How is SPECT used to assess myocardial perfusion?
1) T99m attached to sestamibi which is taken up by mitochondria in myocardial cells
2) rate of uptake is proportional to perfusion/blood flow
3) images taken at rest and exercise
How can SPECT be used in brain imaging in psych and organic neuro disorders?
Evaluate the cerebral blood flow patterns!
T99m attached to exametazime (crosses BBB)
How would you use SPECT to measure blood flow to the brain?
Technetium99 attached to examelazine
In VQ scan what is T99 labelled with?
Inhaled: DTPA
Injected: macro-aggregated albumin
What is T99 labelled with in SPECT to measure cardiac perfusion?]
What about for brain blood flow?
Sestimibi (taken up by mitochondria –> rate uptake proportional to blood flow)
Exametazine (think - sounds like an anti-epileptic)
What can T99 be labelled with?
SPECT (blood supply: heart perfusion): sestamibi T99
SPECT (brain perfusion): exametazine
Sentinel node imaging: T99 w/ sulfur
Bone scintigraphy: phosphate w/ T99
Cardiac gated blood pool imaging: T99 w/ RBCs
VQ scan: injected T99 w/ MAA (macroaggregated albumin) + inhaled T99/xenon w/ DTPA
What type of decay does PET scan undergo?
Positron emission tomography
Undergoes beta plus decay: excess protons –> POSITRON released –> annihilates electron –> 2 gamma rays emitted in opposite directions
What are the disadvantages of PET?
Expensive + short half life (image quickly), can’t use in certain pts (e.g. DM for FDG PET)
How can nuclear medicine be used to image the heart?
- SPECT (myocardial perfusion) - T99 w/ setsamibi
- FDG PET (damaged myocardium)
- Cardiac gated blood pool imaging - T99 w/ RBCs
Give some non-neoplastic roles of PET-CT?
Not from paper
Myocardial assessment (FDG PET - damaged myocardium) Future role in functional neuroimaging
