Nuclear: What Scan Is It? Flashcards
What are the major options for a whole body scan that shows bone uptake?
- In-WBC (spleen > liver)
- Tc-99m Sulfur colloid (liver > spleen, more photon counts)
- Gallium (Liver > spleen, less photon counts)
Note: Look at the spleen to differentiate these.
What scan?
In-WBC
Note: Bones uptake AND spleen is hotter than liver.
What scan?
Gallium
Note: Bone uptake AND spleen is faint compared to liver. Image shows variability in uptake on normal Gallium scans, but these two things are still true.
What scan?
Tc99m Sulfur colloid
Note: Bone uptake AND spleen <= liver (also very high photon counts, very black liver/spleen).
What scan?
Tc99m-MIBI
Note: No bone uptake and BOTH heart and kidneys are visible.
What scan?
I-123 or I-131 (s/p thyroidectomy)
Note: No bones, no heart, no liver, no spleen.
What scan?
I-123 MIBG
Note: No bone uptake AND no kidneys +/- heart uptake (I-123 MIBG is more likely to have heart uptake Thant I-131 MIBG).
What scan?
In-111 Octreotide
Note: No bones, VERY hot spleen and kidneys.
Is there normally cardiac uptake on MIBG scans?
There can be
Note: I-123 MIBG is more likely to have cardiac uptake than I-131 MIBG.
What are the major options for a whole body scan that does not show bone uptake?
- Tc99m-MIBI
- Iodine-MIBG
- Iodine (I-123/I-131)
- In-111 Octreotide
Differential for a whole body scan that shows lacrimal gland uptake
- Gallium
- MIBG (no bones)
- Artifact from free technetium (no/very faint bones)
Note: WBC and sulfur colloid scans will NOT have lacrimal gland uptake.
Whole body scan with avid bone and lacrimal gland uptake…
Gallium scan
Whole body scan with lacrimal gland uptake and faint bone uptake…
Think artifact from free technetium
Whole body scan with bone uptake and no lacrimal gland uptake…
In-111 WBC (hot spleen) OR sulfur colloid (liver = spleen)
MIBG scans are often used to look for ____ because ____
Neuroblastoma
Note: MIBG has no kidney uptake (allowing adrenal neuroblastomas to be identified more easily).
What factors should make you think that an MIBG scan was done using I-123 rather than I-131?
- Cardiac uptake
- Faint, symmetric “normal appearing” adrenal uptake
What is the main benefit of using I-123 to label MIBG (rather than I-131)
Faster imaging, usually within 24 hours (I-123 has a higher energy and can be given in a higher dose)
Note: Using I-131 is better to estimate tumor uptake and planning for MIBG therapy.
What scan?
In-111 Octreotide
Note: VERY hot kidneys and VERY hot spleen (high count study).
What are white blood cells usually labeled with for WMC scans?
- Technetium
- Indium
How can you differentiate Tc-labeled WBC scan from an In-labeled WBC scan?
Look for renal/GI uptake (which is present with Tc and not with In)
Note: Tc will also have a higher resolution (due to it being a higher count study than In).
What scan?
Tc-99m WBC scan
Note: Pulmonary uptake is seen at 4 hours that mostly washes out by 24 hours. Spleen is darker than liver. GI uptake.
Localization mechanism of Tc-99m Medronate (MDP)
Chemisorption (binds with hydroxyapatite on the bone surface)
Note: MDP is a phosphate analog and there will be more uptake in regions of osteoblastic bone activity.
Localization mechanism of F18-FDG
Facilitated diffusion and secondary active transport
Note: FDG is a glucose analog and gets trapped inside metabolically active cells via phosphorylation.
Localization mechanism of Iodine-123/131
Transported into thyroid cells by the Na/I symporter and incorporated into thyroid hormone
Note: It is an iodine analog.
Localization mechanism of Tc-99m pertechnetate
Transported into thyroid cells by the Na/I symporter (but is NOT incorporated into thyroid hormone like I-123/I-131)
Note: Acts as an iodine analog.
Localization mechanism of Thallium 201
Active transport (transported into the cell via Na/K ATPase pump)
Note: Thallium is a potassium analog.
Localization mechanism of Indium 111
WBC chemotaxis (when tagged to neutrophils)
Note: Indium oxide is lipophilic and passively diffuses into WBCs during the labeling process.
Localization mechanism of Tc-99m HMPAO
Passive diffusion into brain cells on first pass (proportional to blood flow) because it is initially lipophilic and can cross the blood-brain barrier
Note: It gets trapped in the brain because its metabolized to a hydrophilic form that can’t diffuse back out across the blood-brain barrier.
Localization mechanism of Tc-99m ECD
Passive diffusion into brain cells on first pass (proportional to blood flow) because it is initially lipophilic and can cross the blood-brain barrier
Note: This is the same as for HMPAO, but ECD is cleared more rapidly from the blood pool.
Localization mechanism of Tc-99m Sestamibi
Passive diffusion into cells where it latches onto negatively charged mitochondrial membranes (active transport into mitochondria)
Note: Sestamibi is a lipophilic cation that localizes to metabolically active cells with more mitochondria.
Localization mechanism of MIBG
Active uptake via norepinephrine transporters where it is stores in neurosecretory granules
Note: MIBG is a norepinephrine analog.
Localization mechanism of Indium 111 pentetreotide
Binds to somatostatin receptors (types 2, 3, and 5)
Note: Pentreotide is a somatostatin analog.
Localization mechanism of gallium 67
Binds to transferrin and lactoferrin receptors
Note: Gallium is an iron analog (acts as an acute phase reactant).
Where is the Na/I symporter located?
The basolateral membrane of thyroid follicular cells
