Skeletal Scintigraphy Flashcards
(49 cards)
is an intrinsic characteristic of each radionuclide
physical half-life (T 1/2)
- T 1/2 is given by the expression
radionuclide decay constant ____, where ____ is the radionuclide decay constant
0.693
Most radiopharmaceuticals are also cleared from organs by _____.
various physiologic processes
Biologic clearance of material (radioactivity) from the body can be modeled as being ______
exponential
- The biologic clearance will be characterized by a _____
biologic half-life (Tb)
The _____ of a radionuclide in any organ encompasses both radioactive decay and biologic clearance.
effective half-life (Te)
Effective half-lives must always be ____ than the physical or biologic half-life.
shorter
The relation between T 1/2, Tb, and Te is
1/Te = 1/Tb, + 1/T 1/2
When the biologic half life is much longer than the physical half-
life, the effective half-life is ____
equal to the physical half-life
When the physical half-life is much longer than the biologic half life, the effective half-life is ___
equal to the biologic half-life
is an active, constantly
changing organ.
skeleton
The skeleton is made up of
inorganic calcium
hydroxyapatite crystal,
Ca1(PO4)6(OH)2, and an organic matrix
of collagen and blood vessels
An ideal radiopharmaceutical for skeletal scintigraphy must be:
- Inexpensive
- Stable
- Rapidly localized to bone
- Quickly cleared from the background soft tissues
- Must have favorable imaging and dosimetry characteristics
The combination o f technetium-99m,
desirable for gamma camera imaging, with members of the phosphate family met these parameters in ____
Tc-99m hydroxymethylene diphosphonate (Tc-99m HMDP or HDP) and Tc-99m methylene diphosphonate (Tc-99m MDP).
is more commonly used agent showing extensive skeletal detail
Tc-99m MDP
Incomplete labeling may occur if air is introduced into the vial causing
stannous ion hydrolysis
from the technetium generator eluate may lead to colloid formation, which can accumulate in the reticuloendothelial system of organs, such as the liver.
Excess alumina
Tc-99m MDP should be used within ____ of preparation or radiopharmaceutical breakdown may also yield
2 to 3 hours
Tc-99m MDP binding occurs by
_____ in the hydroxyapatite mineral component of the osseous matrix.
chemisorption
_____ is seen in areas of
reduced or absent blood flow or infarction.
Decreased activity
Approximately ____ of the dose is localized to the bone, with the remainder excreted by the kidneys.
50%
Images are typically taken at ___ to balance the need for background clearance with the relatively short 6-hour half-life of Tc-99m and patient convenience.
2 to 4 hours
The half-life of Tc-99m effectively limits
imaging to within approximately ____ of injection.
24 hours
The dosimetry provided assumes a
____
2-hour voiding cycle
