Nuclear: What Scan Is It?

Question 1

What are the major options for a whole body scan that shows bone uptake?

Answer 1

• 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.

Question 2

What scan?

Answer 2

In-WBC

Note: Bones uptake AND spleen is hotter than liver.

Question 3

What scan?

Answer 3

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.

Question 4

What scan?

Answer 4

Tc99m Sulfur colloid

Note: Bone uptake AND spleen <= liver (also very high photon counts, very black liver/spleen).

Question 5

What scan?

Answer 5

Tc99m-MIBI

Note: No bone uptake and BOTH heart and kidneys are visible.

Question 6

What scan?

Answer 6

I-123 or I-131 (s/p thyroidectomy)

Note: No bones, no heart, no liver, no spleen.

Question 7

What scan?

Answer 7

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).

Question 8

What scan?

Answer 8

In-111 Octreotide

Note: No bones, VERY hot spleen and kidneys.

Question 9

Is there normally cardiac uptake on MIBG scans?

Answer 9

There can be

Note: I-123 MIBG is more likely to have cardiac uptake than I-131 MIBG.

Question 10

What are the major options for a whole body scan that does not show bone uptake?

Answer 10

• Tc99m-MIBI
• Iodine-MIBG
• Iodine (I-123/I-131)
• In-111 Octreotide

Question 11

Differential for a whole body scan that shows lacrimal gland uptake

Answer 11

• Gallium
• MIBG (no bones)
• Artifact from free technetium (no/very faint bones)

Note: WBC and sulfur colloid scans will NOT have lacrimal gland uptake.

Question 12

Whole body scan with avid bone and lacrimal gland uptake…

Answer 12

Gallium scan

Question 13

Whole body scan with lacrimal gland uptake and faint bone uptake…

Answer 13

Think artifact from free technetium

Question 14

Whole body scan with bone uptake and no lacrimal gland uptake…

Answer 14

In-111 WBC (hot spleen) OR sulfur colloid (liver = spleen)

Question 15

MIBG scans are often used to look for ____ because ____

Answer 15

Neuroblastoma

Note: MIBG has no kidney uptake (allowing adrenal neuroblastomas to be identified more easily).

Question 16

What factors should make you think that an MIBG scan was done using I-123 rather than I-131?

Answer 16

• Cardiac uptake
• Faint, symmetric “normal appearing” adrenal uptake

Question 17

What is the main benefit of using I-123 to label MIBG (rather than I-131)

Answer 17

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.

Question 18

What scan?

Answer 18

In-111 Octreotide

Note: VERY hot kidneys and VERY hot spleen (high count study).

Question 19

What are white blood cells usually labeled with for WMC scans?

Answer 19

• Technetium
• Indium

Question 20

How can you differentiate Tc-labeled WBC scan from an In-labeled WBC scan?

Answer 20

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).

Question 21

What scan?

Answer 21

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.

Question 22

Localization mechanism of Tc-99m Medronate (MDP)

Answer 22

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.

Question 23

Localization mechanism of F18-FDG

Answer 23

Facilitated diffusion and secondary active transport

Note: FDG is a glucose analog and gets trapped inside metabolically active cells via phosphorylation.

Question 24

Localization mechanism of Iodine-123/131

Answer 24

Transported into thyroid cells by the Na/I symporter and incorporated into thyroid hormone

Note: It is an iodine analog.

Question 25

Localization mechanism of Tc-99m pertechnetate

Answer 25

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.

Question 26

Localization mechanism of Thallium 201

Answer 26

Active transport (transported into the cell via Na/K ATPase pump)

Note: Thallium is a potassium analog.

Question 27

Localization mechanism of Indium 111

Answer 27

WBC chemotaxis (when tagged to neutrophils)

Note: Indium oxide is lipophilic and passively diffuses into WBCs during the labeling process.

Question 28

Localization mechanism of Tc-99m HMPAO

Answer 28

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.

Question 29

Localization mechanism of Tc-99m ECD

Answer 29

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.

Question 30

Localization mechanism of Tc-99m Sestamibi

Answer 30

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.

Question 31

Localization mechanism of MIBG

Answer 31

Active uptake via norepinephrine transporters where it is stores in neurosecretory granules

Note: MIBG is a norepinephrine analog.

Question 32

Localization mechanism of Indium 111 pentetreotide

Answer 32

Binds to somatostatin receptors (types 2, 3, and 5)

Note: Pentreotide is a somatostatin analog.

Question 33

Localization mechanism of gallium 67

Answer 33

Binds to transferrin and lactoferrin receptors

Note: Gallium is an iron analog (acts as an acute phase reactant).

Question 34

Where is the Na/I symporter located?

Answer 34

The basolateral membrane of thyroid follicular cells