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Medical Imaging > 0.2 - Nuclear Medicine > Flashcards

0.2 - Nuclear Medicine Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the tracer theory in nuclear medicine?

A

radioactive compounds participate in physiologicl process just as the nonradioactive counterparts would

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2
Q

What is radiolabelling?

A
  • 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
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3
Q

What are radiopharmaceuticals?

A
  • 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
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4
Q

What are radioactive isotopes?

A
  • 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
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5
Q

What are isotopes?

A

the number of protons remains the same but there is a different number of neutrons, thus changing the mass number

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6
Q

What are the types of radioactive decay?

A
  • 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)
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7
Q

What are the types of ionizing radiation?

A
  • particle radiation: α, β or positron
  • electromagnetic radiation: γ, X-ray
    - almost all types of radioactive decays is accompanied by γ-rays
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8
Q

What are the in vivo diagnostic methods in nuclear medicine?

A
  • SPECT, gamma emitting isotopes (ie. Tc99, I123, In111-indium)
  • PET (ie. F18, Ga68-gallium, C11)
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9
Q

What are the therapeutic isotopes in nuclear medicine?

A

alpha and beta emitting isotopes

ie. I131, Lu177 (lutetium), Ra223 (radium)

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10
Q

What are the physical and chemical properties of Technetium-99m?

A

physical
- pure γ radiation
- half life = 6h
- γ energy = 140keV for optimal detection

chemical
- huge number of radiopharmaceuticals are labelled with Tc

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11
Q

What are the instruments used for gamma-emitting isotopes?

A
  • gamma (planar) camera
  • single photon emission computed tomography (SPECT)
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12
Q

Overview of gamma (planar) camera

A
  • one detector head for gamma emitting radioisotopes
  • planar imaging
  • 2D summation image
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13
Q

Overview of SPECT

A
  • 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
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14
Q

What are the types of planar imaging of gamma emitting radioisotopes?

A
  • 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)
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15
Q

What modalities are used to detect positron emitting isotopes?

A
  • PET
  • Hybrid imaging techniques
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16
Q

Overview of PET

A
  • 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)
17
Q

What is the difference between PET and SPECT?

A
  • 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
18
Q

Why is PET/SPECT (nuclear medicine) more advantageous compared to CT (radiography)?

A

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

19
Q

What is CT (radiography) like compared to PET/SPECT (nuclear medicine)?

A
  • lower specificity
  • high resolution
  • morphologic information (anatomy)
  • localization and extent of the disease
  • short acquisition time
20
Q

What are the disadvantages of PET/SPECT (nuclear medicine)?

A
  • lower resolution
  • lack of precise localization
  • longer acquisition time
21
Q

What is hybrid imaging?

A
  • 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
22
Q

What are examples of some conventional nuclear medicine scans?

A
  • bone scintigraphy
  • thyroid scintigraphy
  • dynamic renal scintigraphy
  • nuclear cardiology
  • neuroendocrine tumor detection
23
Q

Overview of bone scintigraphy

A
  • 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)
24
Q

What are the indications for bone scintigraphy?

A
  • 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
25
Q

What is thyroid scintigraphy?

A
  • Tc99m-pertechetate iv. is taken up by Na-I symporters in thyroid cells just as iodine would be taken up
  • detect iodine uptake to map thyroid function
  • main indications: function of nodules, differential diagnosis of hyperthyroidism, ectopic thyroid tissue
  • Tc-uptake = iodine uptake (quantification)
26
Q

What is dynamic renal scintigraphy?

A
  • radiopharmaceutical is emptied by glomerular filtration and tubular secretion
  • renal function and urinary flow can be investigated
  • way and time of urine emptying can be followed
27
Q

What is nuclear cardiology used for?

A
  • myocardial perfusion scintigraphy
  • investigation of relative perfusion distribution
  • radiopharmaceutical uptake in the myocardium is proportional to blood flow
  • can detect ischemic heart disease (atherosclerotic narrowing of coronary vessels leads to reduced perfusion during activity)
28
Q

Nuclear imaging of neuroendocrine tumors

A
  • functional diagnosis with the visualization of molecular properties of neuroendocrine tumors
  • target: tumor-specific
  • theranostics: diagnosis and treatment of tumors using pharmaceuticals
    - tumors overexpressing somatostatin receptors are treated while normal cells remain intact

Medical Imaging (17 decks)

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