Radiopharmaceuticals, Radiation, & Radiographic Contrast Agents Flashcards
1
Q
Element
A
- The smallest amount of a substance that exhibits the properties of that substance
- Grouped by the # of protons in each atom, and are arranged in the Periodic Table
2
Q
Radioactivity
A
- The process by which the nucleus of an unstable atom loses energy by emitting ionizing radiation
- Radioactive elements have nuclear imbalance (# protons/neutrons)
3
Q
Nuclide
A
- Term used to describe any atom by referencing the nucleus mass and energy
- # on top is mass
- # on bottom is atomic
- mass # = protons + neutrons
4
Q
Isotope
A
- Term used to describe elements with the same nucleus and the same # of protons but varying numbers of neutrons
5
Q
Radioactive Transformation
A
- Process by which a radioactive unstable element transforms to a less unstable or more stable element
6
Q
Curie (Ci) - unit of measure
A
- 3.7 x 10^10 nuclear transformations per second or disintegrations per second (dps)
7
Q
Becquerel (Bq) - unit of measure
A
- 1 Becquerel is equivalent to 1 disintegration per second
- 1 mCi = 37 MBq = 3.7x10^7 Bq
8
Q
Radioactive Half-life (T1/2)
A
- The time required for a radionuclide to decay to 50% of its original radioactivity
- Or, the time required for 50% of the radioactive atoms to decay
9
Q
Decay Constant
A
- Each radionuclide has a characteristic Decay Constant (λ)
- (λ) = ln2 / T1/2
- Large decay constant = small half-life = radionuclide decays rapidly
- Small decay constant = big-half life = radionuclide decays slowly
10
Q
Activity and Decay Constant
A
- Relationship between activity (A) and decay constant (λ) is:
A = λN / (3.7 x 10^10)
11
Q
Decay Equation
A
- Used to predict the radioactivity at any time once one knows the original radioactivity
- Nt = (N0)e^-λt
- Nt = # of un-decayed atoms at time (t)
- N0 = original # of un-decayed atoms at time = 0
12
Q
Radiation Decay Types
A
- Alpha particles, beta particles and gamma rays are emitted from the nuclei of the radioactive atoms
- X rays are generated as electrons from higher orbitals fall down into lower orbitals
13
Q
Alpha particles
A
- Helium nucleus = 2 neutrons + 2 protons; charge of +2
- Emitted from nuclei of radioactive atoms
- Transfer energy in very short distances (50-90 um in tissue)
- Shielded by paper or layer of skin
- Primary damage from internal exposure to tissues (bone, kidney, liver, lung, spleen)
14
Q
Beta Particles
A
- Small, electrically charged particle w/a negative charge (negatron, electron) or a positive charge (positron)
- Ejected from nuclei of radioactive atoms
- Emitted with kinetic energy
- Shielded by low-density materials, such as plastic or wood (penetration 0.2-1.3 cm)
- Can cause tissue damage - skin burns
15
Q
Gamma Photons
A
- Electromagnetic photons or radiation
- Emitted from nuclei of radioactive atoms
- Emitted w/kinetic energies related to radioactive source
- Highly penetrating
- High-density shielding required: Lead, Tungsten, Concrete
- External radiation hazards
16
Q
X Rays
A
- Overlap w/gamma-rays in wavelength
- Electromagnetic photons or radiation
- Produced from orbital electrons of radioactive atoms
- Emitted w/various energies & wavelengths
- Highly penetrating
- High-density shielding required: Lead, Tungsten, Concrete
- External radiation hazards
17
Q
Auger Electrons
A
- Small electrically charged particle w/a negative charge
- Ejected from orbital electrons of radioactive atoms
- Relatively lower kinetic energies than B-particles
18
Q
Radiation
A
Particles or waves of energy emitted from unstable atoms
19
Q
Radioactive Contamination
A
Radioactive material usually in any undesired location
20
Q
Radiation Dose
A
- The amount of radiation absorbed by body tissue
- Typically, it is measured in rad (radiation absorbed dose)
- 1 rad = 100 ergs energy / 1g of tissue
- 1 Gray (gy) = 100 rad
- Gy is the international unit of absorbed dose
21
Q
Effect of Ionizing Radiation on Living Cells
A
1) Injured cells repair themselves
2) Cells die and are replaced
3) Cells incorrectly repair themselves resulting in a biophysical change (i.e. cancer)
- Exposure to ionizing radiation can cause damage to DNA and ultimately increases lifetime risk of developing cancer
22
Q
Tissue Sensitivity
A
- Radiosensitivity is the relative susceptibility of cells to radiation damage
- Factors increasing cell sensitivity to radiation: high division rate, high metabolic rate, undifferentiated, well-nourished
23
Q
Radiography
A
- The traditional image receptor is a cassette that contains a fluorescent screen and a piece of photographic film
- X-rays cause the screen to glow
- The light exposes the film
- Modern image receptors are now digital
24
Q
4 Tissue Densities
A
1) Bone
2) Soft tissue
3) Fat
4) Air
25
X-ray Contrast Agents
- Contrast agents are used to highlight features that would normally not be seen
- Materials are used which are radio-opaque
- Administration may be oral, rectal, IV injection or retrograde into the bladder and ureters
- Barium-based agents are often used for GI studies
- Iodine-based agents are used in IV studies
- VERY VISCOUS (needs to be warmed up)
26
Computed Tomography
- This array of data can be used to form "slices" in any orientation
- Advantage of CT is a large volume of the body can be sampled at one time
27
Nuclear Medicine
- The radiopharmaceutical biodistribution is determined by the physiologic procceses occurring within the patient
- Images are acquired of the biodistribution
- Image physiology rather than anatomy
28
Single Photon Emission Computed Tomography (SPECT)
- Nuclear medicine equivalent of CT
- Detectors rotate around the patient
- Typical acquisition time is 10-45 minutes
29
Positron Emission Tomography (PET)
- The positron is the anti-particle of the electron
- When a positron and an electron meet, they undergo annihilation
- Each particle is entirely converted into energy, which takes the form of 2 photons moving in opposite directions
30
Radiopharmaceutical
Chemical substance that contains radioactive atoms and is suitable for administration to humans for diagnosis or treatment of disease
31
Ideal Properties of DIAGNOSTIC Isotopes
- Readily Available (7 days a week)
- Low production costs
- Short t1/2 (hours)
- Good physical properties: γ-rays for imaging
- No particulate emissions
- Allows for high specific activity labeling
- Reproducible chemistry
- Candidates: 99mTc, 111In, 18F, 68Ga
32
Ideal Properties of THERAPEUTIC Isotopes
- Readily Available (7 days a week)
- Low production costs
- Physical T1/2 matched to biological application
- Good physical properties (alpha/beta/auger particles for therapy and gamma/x photons for imaging)
- Dose rate and range in tissue: LET = ∆E/∆X
- Allow high specific activity labeling
- Reproducible chemistry
- Candidates: 177Lu, 90Y, 131I, 188Re
33
Properties that Influence Renal and Hepatic Excretion
- Molecular Weight
- -- MW >10^5 = hepatic
- -- MW <10^3 = renal; <68,000 glomerular filtration
- Lipophilicity (Octanol-Water Partition Coefficient)
- -- Lipophilic (Octanol) = favors hepatic
- -- Water Solubility = favors renal
- Charge
- -- Hepatic = +/- or Neutral = All
- --- Renal = Neutral or +1
34
Optimum Dose of Radiopharmaceutical
- Allows acquisition of the desired info with the least amount of radiation dose or exposure to the patient
- Half-life
- Radiation type
- Energy
35
Cyclotron Production of Radionuclides
- Charged particle accelerator
- 18O (p,n) 18F (PET Imaging)
- 111Cd (p,n) 111In (SPECT Imaging)
36
18F-FDG
- 18F-FDG most widely used PET radiopharmaceutical
- (18F) Fluoro-2-deoxy-D-glucose
- 18F-FDG is made by nucleophilicsubstitution of 18F-for OH-group at 2
37
18F-FDG Metabolism
- Like glucose,18F-FDG is transported into the cell
- 18F-FDG undergoes glycolysis (Phosphorylization)
- Further metabolism requires -OH group in the C-2 position
- 18F-FDG cannot undergoglycolysis. It hits a metabolic “dead end”and is retained in the cell
38
18F-FDG PET Distribution
- Some tissues selectively use glycolytic metabolism
- Need higher metabolism than surrounding tissues (want high target:background)
- 18F-FDG is used to image:
–Cancer
–Infection
–Brain metabolism
–Myocardial Ischemia
–Trauma
39
9 Domains Encompassing Nuclear Pharmacy Practice:
1. Procurement and storage
2. Radiopharmaceutical preparation
3. Quality assurance
4. Radiopharmaceutical dispense
5. Radiopharmaceutical distribution
6. Health and safety
7. Provision of drug information and consultation
8. Monitoring patient outcomes
9. Research and development
