Skeletal Scintigraphy Flashcards
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
Radiopharmaceuticals a r e
administered to pregnant women
only if
clearly needed on a
risk-versus-benefit basis
Tc-99m is excreted in breast milk,
so breastfeeding should be
stopped for
24 hours
The most frequent indication for three-
phase imaging is to
assess possible
osteomyelitis
Three-Phase Skeletal Scintigraphy
FLOW PHASE
BLOOD POOL AND TISSUE PHASE
SKELETAL PHASE
• If dynamic three-phase scanning is to be performed, a _____ is injected intravenously with the area in question under the camera.
bolus of Tc-99m MDP
- Serial 2- to 5-second dynamic images acquired for 60 seconds.
First phase
- Images are obtained of the region and secondary areas of interest, such as in patients with arthritis or multiple stress
injuries
Blood pool or soft tissue second-phase
- Done alone for routine studies, such as the assessment of metastatic disease.
Delayed images (third phase)
Delay of 2 hours
- May yield images of sufficient quality in ____
younger patients
- Often necessary in the elderly and in those with poor renal function.
3 or 4 hours after injection
- May be needed to clear soft tissue activity in the most severe
c a s e s .
24 hours (Fourth phase)
• Allows rapid, seamless coverage as the camera moves over the
patient at a predetermined rate.
Whole-body scan
• Can provide greater detail because of higher resolution and can better define pathological conditions by using different camera positions
Spot views
- Commonly used in cases of osteonecrosis of the hips and trauma to the carpal bones.
Magnified pinhole collimator views
- May be needed in children to better visualize the joints.
Pinhole images
Magnified pinhole collimator views.
- Commonly used in cases of ____ of the hips and trauma to the carpal bones.
osteonecrosis
allows for high- contrast images that can be formatted in transaxial, sagittal, and coronal planes.
Three-dimensional assessment of
the bones with SPECT
The ___ is a common site of benign uptake and is an unlikely location for solitary metastasis.
costochondral junction
are routinely seen and usually identified by classic locations.
Osteoarthritic changes
is frequently bilateral and occurs on both sides of the joint.
Arthritis
may result in insufficiency
vertebral compression fractures
Osteoporosis
