0.2 - Nuclear Medicine Flashcards
What is the tracer theory in nuclear medicine?
radioactive compounds participate in physiologicl process just as the nonradioactive counterparts would
What is radiolabelling?
- a substance is labeled with radionuclides in its chemical composition
- the radionuclides emit radiation as they decay so they can be visualised in biochemical processes to gather information
What are radiopharmaceuticals?
- radiopharmaceuticals = radioisotopes + specific compound
- the specific compound is target-specific (organ, tissue, cell or molecule specific), determining where the radiopharmaceutical will go and act and this is useful for functional imaging
- provides the ability to quantify biochemical processes and differentiate abnormal tissue from normal tissue
What are radioactive isotopes?
- radioactive isotopes have unstable nuclei
- there is an excess amount of energy due to a decreased or increased number of neutrons, resulting in radioactive decay
What are isotopes?
the number of protons remains the same but there is a different number of neutrons, thus changing the mass number
What are the types of radioactive decay?
- proton deficiency: beta decay (β-particle + γ-radiation)
- excess protons:
- positron emission (annihilation + 2γ photons)
- electron capture (characteristic X-ray emission) - large nuclei: alpha radiation (α-particle)
What are the types of ionizing radiation?
- particle radiation: α, β or positron
- electromagnetic radiation: γ, X-ray
- almost all types of radioactive decays is accompanied by γ-rays
What are the in vivo diagnostic methods in nuclear medicine?
- SPECT, gamma emitting isotopes (ie. Tc99, I123, In111-indium)
- PET (ie. F18, Ga68-gallium, C11)
What are the therapeutic isotopes in nuclear medicine?
alpha and beta emitting isotopes
ie. I131, Lu177 (lutetium), Ra223 (radium)
What are the physical and chemical properties of Technetium-99m?
physical
- pure γ radiation
- half life = 6h
- γ energy = 140keV for optimal detection
chemical
- huge number of radiopharmaceuticals are labelled with Tc
What are the instruments used for gamma-emitting isotopes?
- gamma (planar) camera
- single photon emission computed tomography (SPECT)
Overview of gamma (planar) camera
- one detector head for gamma emitting radioisotopes
- planar imaging
- 2D summation image
Overview of SPECT
- single photon emission computed tomography
- gamma emitting radioisotopes
- cross-sectional imaging with one or more detector heads that have a rotational motion
- multi-directional projection images
- computerised reconstruction: cross-sectional images, 2D tomographic images in 3 planes, 3D
What are the types of planar imaging of gamma emitting radioisotopes?
- static study: after injecting the radiopharmaceutical, an equilibrium state is reached in which the distribution does not change over time (acquisition)
- dynamic study: after injecting the radiopharmaceutical the different phases of a process can be recorded/visualized (metabolic, excretion etc. - short acquisition time)
What modalities are used to detect positron emitting isotopes?
- PET
- Hybrid imaging techniques
Overview of PET
- positron emission tomography
- positron and electron collide resulting in annihilation that produces 2 γ photons at a 180° angle, which are detected by a detector ring
- cross-section tomographic images with multi-directional projection or computerised reconstruction (cross-sectional, 2D in 3 planes, 3D)
What is the difference between PET and SPECT?
- physical properties of tracers: PET emits a double-photon, SPECT emits a single photon
- sensitivity: PET is more sensitive that SPECT due to no collimator
- resolution: PET=4mm ; SPECT=10mm
- quantification: both PET and SPECT are quantifiable
Why is PET/SPECT (nuclear medicine) more advantageous compared to CT (radiography)?
highly sensitive
- highest functional sensitivity
- functional abnormality can be detected before anatomical abnormalities
- high biological contrast b/w normal and abnormal tissue
high specificity
- radiopharmaceuticals specifically accumulate at pathological tissues
metabolic information
- differentiation between non-viable (necrotic) and viable tumor is possible
What is CT (radiography) like compared to PET/SPECT (nuclear medicine)?
- lower specificity
- high resolution
- morphologic information (anatomy)
- localization and extent of the disease
- short acquisition time
What are the disadvantages of PET/SPECT (nuclear medicine)?
- lower resolution
- lack of precise localization
- longer acquisition time
What is hybrid imaging?
- combines the advantages of PET/SPECT and CT (or MRI)
- The use of two modalities in one device, so the imaging is done one after the other in the same position
- CT has a role in localization, attenuation correction and increasing specificity
What are examples of some conventional nuclear medicine scans?
- bone scintigraphy
- thyroid scintigraphy
- dynamic renal scintigraphy
- nuclear cardiology
- neuroendocrine tumor detection
Overview of bone scintigraphy
- Tc 99m-diphosphonate is absorbed by the bones according to osteoblast activity
- almost all bone diseases cause increased osteoblast activity
- very sensitive to detect lesions in the bone before X-ray (if bone scan is positive it indicates bone metastasis even if X-ray is negative)
- it is not specific (ie. fractures, inflammation, primary bone tumors, metastases)
What are the indications for bone scintigraphy?
- bone metastases: can detect mets 6 months before it is seen on X-ray
- diagnosis, staging and follow-up
- whole body imaging
- lower sensitivity in cold (osteolytic) lesions - other
- primary bone tumors
- fractures
- prosthesis loosening
- osteomyelitis
- arthritis
