Nukes Flashcards
Whole body scan > bones > spleen > hot spleen >
in-WBC
Whole body scan > bones > spleen > liver = spleen
sulfur colloid
Whole body scan > bones > spleen > light spleen
gallium
Whole body scan > no bones > heart > kidneys
MIBI
Whole body scan > no bones > heart > no kidneys
MIBG
Whole body scan > no bones > no heart > liver
MIBG
Whole body scan > no bones > no heart > no liver
iodine
MIBG with 1-123 is more likely to have heart than
I-131
Whole body scan > bones > liver > spleen > more photons
Tc99m sulfur colloid
Whole body scan > bones > (liver > spleen) > less photons
gallium
Whole body scan > (spleen > liver)
In - WBC
Whole body scan > no bones > liver and spleen > (liver > spleen)
I-131 MIBG
Whole body scan > no bones > liver and spleen > (liver > spleen) + intense renal
octreotide
Whole body scan > no bones > no liver or spleen
I123 or I131
Bones > lacrimal glands
with free TC
bones will be weak
Bones > lacrimal glands
with gallium
no spleen
bones > no lacrimal glands
sulfure colloid
liver=spleen
bones > no lacrimal glands
In 111 WBC
hot spleen
MIBG overview
I’ll talk about this more later in the chapter, but MIBG can be labeled with either 1-123 or 1-131.
The energy of the 1-123 (159 keV) is better for imaging, you can give a higher dose, and the
results are typically available within 24 hours (1-131 usually requires delated to optimize target to
background noise). Having said that 1-131 labeled MIBG is still used all over the place, especially
with adults. 1-131 may also be better for estimation of tumor uptake, for planning related to
MIBG therapy. The point of me rambling here is that you have two different MIBGs - so telling
which scan is which requires a little finesse.
MIBG
Cardiac
It has variable cardiac uptake, so it finds itself on multiple branch points. Cardiac activity is more
often seen on an 1-123 MIBG scan (as opposed to 1-131 MIBG). Another thing that helps me
remember this stuff: when you do a MIBG you are often looking for neuroblastoma. If the kidney
was also hot it would be hard to tell a mass near the kidney from the kidney - so part of the
reason the study works is that the kidney does NOT take up MIBG.
MIBG
adrenal glands
Normal adrenal glands are not seen. However, you can have faint uptake in the
adrenals in about 15% of 1-131 patients, and around 75% of 1-123 patients. So, if you see
adrenals and you are sure they are normal (faint and symmetric) it’s more likely to be 1-123.
DARK SPLEEN +
DARK KIDNEYS
knee jerk
octreotide
DARK SPLEEN +
DARK KIDNEYS
count study
This is a high count study, so the
images should be clearer (relative to
the normal “un-clear medicine.”
no bones + liver + dark spleen + dark kidneys
octreotide
Tc WBC vs In WBC
labeled
Just like MIBG can be labeled with either 1-123 or 1-131
you can label WBCs with Tc or Indium.
Tc WBC vs In WBC
Both will have hot spleens. Additionally,
Tc is a higher count study and
will typically look cleaner.
Tc WBC
The trick here can be imaging at 4 hours vs imaging at 24 hours. At 4 hours you can see lung uptake. At 24 hours the lungs are clearing up, but you start to get some bowel uptake. Just like an In-WBC the spleen is still darker than the Liver.
Tc WBC quick
Renal, GI
In WBC quick
no renal, no GI
18F - Sodium Fluoride vs Tc-MDP
You can do bone scans with several different tracers, the main two are 18F Sodium Fluoride and
Tc-MDP. If you were trying to differentiate the two, the primary take home point is F-18 PET is
way way way better than Tc-M DP. By “better” I mean that the image quality and sensitivity of F18
is multiple orders of magnitude better than Tc-MDP. It also has a shorter examination time. So,
why do you never see l8F? Because it costs more, and insurances won’t pay etc… Politics and
Finance are the reasons. Another potentially testable factoid would be which organ gets the
highest dose? The organ receiving the highest dose is Bone with MDP, and Bladder with ,8F
(overall l8F > Tc-MDP) — probably… honestly y o u ’ll read different things in different sources.
18F - Sodium Fluoride vs Tc-MDP
scan on scan on scan
This is a common trick, popular in case books & case conferences - asking you to distinguish F-18
bone scan vs Tc-MDP bone scan vs PET-FDG with marrow stimulation.
This is how you do it:
* Tc-MDP will have bone and kidney uptake. It will be a blurry fuzzy piece of crap.
* ,8F will be beautiful, super high resolution, and look like a MIP PET.
* FDG -PET with bone stimulation - will look similar to the F-l 8, but will have brain
uptake. Also, this can show increased uptake in the spleen.
the workhorse of
skeletal imaging is
methylene diphosphonate (MDP) tagged with
Tc-99m. This is prepared from a kit which has MDP and stannous
ion. You add free pertechnetate and the stannous ion reduces it so
it will bind to the MDP. If you don’t have enough stannous ion
(or you get air into the vial or syringe - that can cause oxidation)
you might get free Tc (salivary gland, thyroid, stomach uptake).
After you inject the tracer ( 15-25mCi) you wait 2-4 hours to let
the tracer clear from the soft tissues (so you can see them bones).
skeletal imaging mechanism
Phosphonate binding to bone (ehemisorption).
Distribution is based on blood flow and osteoblastic activity.
skeletal imaging gamesmanship
MDP and HDP are both bone agents so don’t get confused if they say HDP to
purposefully confuse you.
skeletal imaging what factors will affect tracer uptake
OsteoBLASTIC activity (why pure lytic lesions can be cold)
Blood Flow
skeletal imaging where is tracer uptake normal
Bone (dull), but also the Epiphyses in kids
Kidney (not seen *or very faint = Super Scan), Bladder
Breasts (especially in young women)
Soft tissues - low levels
skeletal imaging
abnormal distribution
Increased focal uptake is very nonspecific, and basically is just showing you bone turn over.
So a metastatic deposit can do that (and this is the classic indication). But, you can also see
it with arthritis (classically shoulder) and healing fractures (most commonly shown with
segmental ribs).
skeletal imaging Abnormal Distribution
skull sutures
It’s normal to see some persistent visualization of the skull
sutures, BUT when this is marked you may be thinking about renal
osteodystrophy.
skeletal imaging Abnormal Distribution
breast uptake
Some mild diffuse breast uptake is normal (especially in
younger women), BUT focal uptake can be cancer.
skeletal imaging Abnormal Distribution
renal cortex activity
You are supposed to have renal activity (not
seeing kidneys can make you think super scan), BUT when the renal
cortex is hotter than the adjacent lumber spine you should think
about hemochromatosis.
skeletal imaging Abnormal Distribution
diffuse renal uptake
This often occurs in the setting of chemotherapy
(especially if the study is looking for bone mets). This also can be seen
with urinary obstruction.
skeletal imaging Abnormal Distribution
liver uptake
This can be several things, but the main ones to think about arc (1) Too Much Al+3 contamination in the Tc, (2) Cancereither primary hepatoma or mets, (3) Amyloidosis, (4) Liver Necrosis
skeletal imaging Abnormal Distribution
spleen uptake
This is a common trick to show an auto-infarcted
spleen - common in sickle cell patients. These same patients are going
to have scattered hot and cold areas from multiple bone infarcts.
skeletal imaging Abnormal Distribution
lung uptake
In most cases this is some type of heterotopic calcification (dystrophic or mets).
The classic MDP hot lung met would be an osteosarcoma. Ultimately, it’s not specific and can be
seen in a ton of other random situations (fibrothorax, primarily tung tumors, radiation changes,
sarcoid, berylliosis, alveolar microlithiasis, Wegener’s, etc…).
skeletal imaging Abnormal Distribution
the single lesion
When you see a single hot lesion, the false positive rate for attributing the
finding to a met is high. Only about 15% to 20% of patients with proven mets have a single
lesion (most commonly in the spine). In other words, 80% of the time it’s benign. A classic
exception is a single sternal lesion in a patient with breast cancer. This is due to breast CA
80% of the time.
skeletal imaging Abnormal Distribution
sacral insufficiency fracture
This is a hot geographic area,
confined to the sacrum, often with a characteristic butterfly or “H”
shaped (Honda sign). Osteoporosis is the most common cause, but
it can also occur in a patient who has had radiation.
skeletal imaging Abnormal Distribution
diffusely decreased skeletal uptake
This can be seen with
(1) free Tc, or (2) Bisphosphonate therapy.
skeletal imaging Abnormal Distribution
fractures in the elderly (including abuse)
In older populations, bone scans may be negative for several days. A bone
scan obtained at 1 week will exclude a fracture.
skeletal imaging Abnormal Distribution
vertebral body fx (benign vs malignant)
A horizontal linear pattern of tracer uptake is the
classic look for an osteoporotic fracture (especially if they are multiple and of varying intensity).
If the tracer extends from the vertebral body into the posterior elements or just involves the
pedicles then you should think cancer. Lastly, followup of the osteoporotic fracture should show
tracer activity decreasing (cancer isn’t gonna do that).
skeletal imaging Abnormal Distribution
muscle
MDP is for bones, but it will also localize to injured skeletal muscle. The classic
way to show this is very hot quads, calfs, shoulders in a marathon runner (or military recruit) - as
a way to show rhabdomyolysis.
“Honda Sign”
sacral insufficiency fx
“Honda Sign”
sacral insufficiency fx
Hypertrophic Osteoarthopathy
This is a “Tramline” along the periosteum of long bones,
which is associated with conditions o f chronic hypoxia (CF,
Cyanotic Heart Disease, Mesothelioma, Pneumoconiosis).
However, when you see this - you need to think lung cancer.
Apparently it’s actually seen in 10% o f patients with lung cancer.
Next Step? CXR, Chest CT e tc …
Heterotopic ossification
the pattern is typically outside to
in, with the eventual development o f mature cortical bone. In some cases this abnormal
bone proliferation can reduce joint motility and cause pain. Therefore, in some cases
surgical resection is performed to preserve the function o f the joint.
Enter the MDP Bone Scan.
The main reason you image this is to see if it’s “mature.” Serial exams are used to
evaluate if the process is active or not (not = “mature”). If it’s still active it has a higher
rate o f recurrence after it’s resected. The idea is you can follow it with imaging until
it’s mature (cold), then you can hack it out (if someone bothers to do that).
AVN
Avascular Necrosis (AVN) as discussed in the MSK chapter, this can occur from a
variety of causes (EtOH, Steroids, Trauma, Sickle Cell, Gauchers).
The trick on bone scan is the timing.
• Early and late AVN is cold.
• Middle (repairing) will be hot.
PAgets
Seen primarily in older patients (8% at 80), it’s classically shown five ways
- Super Hot Enlarged Femur
- Super Hot Enlarged Pelvis,
- Super hot skull,
- Expanded hot “entire” vertebral body
- Metabolic Superscan - from widespread Pagets. Although, as a point of gamesmanship if they show you a metabolic superscan the answer is probably hyper PTH.
PAgets spine
Classically involves BOTH the vertebral body and posterior elements.
Primary Bone Tumors:
overview
Both Osteosarcoma and Ewings will be hot. Primary utility o f the bone scan is to see extent
of disease. With regard to benign bone tumors the only ones worth knowing are the HOT
ones and the COLD ones. Osteoid Osteoma is worth knowing a few extra things about
(because they lend themselves easily to multiple choice questions).
Osteoid osteoma
The lesion will be focal and three phase hot. A central hot nidus is often seen
(double density or hotter spot
within hot area). A normal bone
scan excludes this entity.
Fibrous Dysplasia
Be aware that in case books / case conference this is sometimes shown as a super hot mandible. Could also be shown as a leg that looks similar to Paget.
Specific Cancers - Specific Trivia
- Prostate Cancer Loves Bone Mets (85% of dying patients have it)
- Prostate Cancer bone mets are uncommon with a PSA less than 10 mg/ml
- Lung Cancer bone mets tend to be in the appendicular skeleton
- Lung Cancer can have hypertrophic osteoarthropathy (10%)
- Breast Cancer bone mets are most common to the spine, but the solitary sternal lesion is more specific
- Neuroblastoma frequently mets to the bones (metaphysis of long bones)
- 1-123 and 131 M1BG are superior for detection of neuroblastoma bone mets
Any bone uptake on
MIBG, 1-131, or Octreotide is abnormal, & concerning for mets.
Cold bone lesions
- Radiation Therapy (usually segmental)
- Early Osteonecrosis
- Infarction (very early or late)
- Anaplastic Tumor (Renal, Thyroid, Neuroblastoma, Myeloma)
- Artifact from prosthesis, pacemaker, spine stimulator, etc….
- Hemangioma ** this is variable
- Bone Cyst (without fracture)
Bone Island vs
Prostate Met:
• Both are sclerotic on plain film / CT • The Prostate Met should be very HOT on Bone Scan • The Bone Island should be cold, or faintly warm • Osteopoikilosis should be cold
Skeletal tumors
hot lesions
• Fibrous Dysplasia • Giant Cell Tumor • Osteoblastoma • Osteoid Osteoma • Aneurysmal Bone Cyst *donut sign (centrally cold)
Bone Scan vs Skeletal Survey (Trivia)
- Bone Scan is way better (more sensitive) than skeletal survey for blastic mets
- Skeletal Survey is superior (more sensitive) for lvtic mets
- Skeletal survey is the preferred evaluation for osseous involvement in myeloma
Equivocal Lesion N e x t S tep ?
If a bone scan “equivocal lesion” is found the next step is a plain film. If the plain film shows no corresponding lesion this is MORE suspicious for mets. Next step at that point would be a MRI.
Super Scans
overview
This is a common trick, where the scan shows no abnormal focal uptake, but you can’t see
the kidneys. The trick is that everything is hot.
Super Scans
types
diffuse mets
metabolic
Super Scans
duffuse mets
Diffuse skeletal
metastatic activity (breast and
prostate are the common culprits).
Super Scans
metabolic
From metabolic bone pathology; including hyperparathyroid, renal ® osteodystrophy, Pagets, or severe thyrotoxicosis.
Super Scans
how can you tell them apart
- The Skull will be asymmetrically hot on the metabolic super scan.
super scans
gamesmanship
A common sneaky move is to show you a bone scan, with no renals. But it’s
because there is a horseshoe kidney in the pelvis. Could be phrased as a next step question, with
the answer being look at prior CT to confirm normal anatomy.
Flair Phenomenon
This is a sneaky situation shown on bone scan, where a good response to therapy will mimic
a bad response. What happens is you have increased radiotracer uptake (both in number and
size of lesions) seen 2 weeks to 3 months after treatment.
So how can you tell it’s fla ir and not actually cancer getting worse?
- On plain film lesions should get more sclerotic
• After 3 months they should improve.
The Three Phase Scan
Bone scans can be done in a single delayed phase, or in 3 phases (flow, pool, and delayed). A
lot o f things can be “3 phase hot”, including osteomyelitis, fracture, tumor, osteoid osteoma,
charcot joint, and even reflex sympathetic dystrophy.
The Three Phase Scan
Cellulitis vs Osteomyelitis
The benefit of using 3 phases is to distinguish between cellulitis (which will be hot on flow
and pool, but not delays), and osteomyelitis (which is 3 phase hot). In children, a whole body
bone scan is often performed to evaluate extent. Additionally, because o f subperiosteal pus/
edema you can actually have decreased vascularity to the infected area (cold on initial phases)
but clearly hot on delayed phases.
In the spine, gallium (combined with bone scan) or MRI are the preferred imaging modalities
Three phase scan repsonse
You can also use a bone scan to evaluate response to treatment. Blood flow and blood pool
tend to stay abnormal for about 2 months, with delayed activity persisting for up to 2 years.
This is especially true when dealing with load bearing bones. Gallium67 and Indium111 WBC
are superior for monitoring response to therapy.
Three phase scan
Reflex Sympathetic Dystrophy (RSD):
Sometimes called “complex regional pain syndrome,” it can be seen after a stroke, trauma, or
acute illness. The classic description is increased uptake on flow and blood pool, with
periarticular uptake on delayed phase. The uptake often involves the entire extremity.
About one third o f adult patients with documented RSD do not show increased perfusion and
uptake (which probably means they are faking it, and need a rheumatology consult fo r
fibromyalgia). In children, sometimes you actually see decreased uptake.
Sulfur Colloid Bone Scan & WBC Imaging
Tc can be tagged to sulfur colloid with the idea o f getting a normal localization to the bone
marrow. You can actually perform Tc sulfur colloid studies to map the bone marrow in
patients with sickle cell (with the idea to demonstrate marrow expansion and bone infarct).
However, the major utility is to use it in combination with tagged WBC or Gallium.
Both Tc Sulfur Colloid and WBCs will accumulate in normal bone marrow, in a spatially
congruent way (they overlap). The principal is that infected bone marrow will become
photopenic on Tc-Sulfur Colloid. Now, this takes about a week after the onset of infection, so
you have to be careful in the acute setting. WBC, on the other hand, will obviously still
accumulate in an area o f infection.
Combined Tc-Sulfur Colloid and WBC study is positive fo r infection i f there
is activity on WBC image, without corresponding Tc S u lfu r Colloid activity on the bone marrow image
Tc sulfur colloid in infected bone
less uptake
In-WBc in infected bone
more uptake
Sulfur Colloid Bone Scan & WBC Imaging
the spine
When imaging the spine, WBC frequently fails to migrate showing a photopenic area
(WBC = False Negative in the Spinel. This is why gallium is preferred for osteomyelitis of
the spine.
gallium in infected bone
more uptake
ln-wbc less uptake in infected bone
false negative
Prosthesis Evaluation
Differentiating infection from aseptic loosening is challenging and the most common reason a
nuclear medicine doctor would get involved in the situation. Bone scan findings o f
periprosthetic activity is very nonspecific, because you can see increased tracer activity in a
hip up to 1 year after placement (even longer in cementless arthroplasty). Typically, there
would be diffusely increased activity on imaging with Tc-MDP in the case of infection (more
focal along the stem and lesser trochanter with loosening) - but this isn’t specific either.
Combined Tc-Sulfur Colloid and WBC imaging is needed to tell the difference.
Prosthesis evaluation is helful when negative
A negative bone scan excludes loosening or infection
Neuropathic Foot
Most commonly seen in the tarsal and tarsal-metatarsal joints (60%), in diabetics. When the
question is infection (which diabetics also get), it’s difficult to distinguish arthritis changes vs
infection with Tc-MDP. Again, combined marrow + WBC study is the way to go.
Neuropathic foot
next step
the need for a fourth phase
in diabetic feet. As these patient’s tend to have reduced peripheral blood flow, the addition of
a 4th phase at 24 hours may help you distinguish between bone and delayed soft tissue clearance.
When would you consider Tc99 HMPAO instead o f In-WBC for infection ? Two main reasons
(1) Kids - Tc99 will have a lower absorbed dose & shorter imaging time
(2) Small Parts - Tc99 does better in hands and feet
Why not use Tc99 HMPAO all the time ? The downsides to Tc99 HMPAO are:
(1) It has a shorter half life -6 hrs- which limits delayed imaging, and
(2) It has normal GI and gallbladder activity which obscures activity in those areas.
In-WBC Chem and Pharm
• The vast majority (like 90%) o f the labeled cells are Neutrophils. This allows you to
“trace” anything that triggers neutrophil migration (inflammation / infection).
• The radiation dose that the Indium deposits on the neutrophil doesn’t mess with its
function (supposedly). Lymphocytes on the other hand, tend to be killed by the radiation
(they don’t turn into cancer).
• In the normal situation the critical organ is the spleen.
• If the cells become fragmented - the Indium binds with transferrin and you see more
uptake in the liver and bone marrow.
If 1940 calls and wants to rule out a PE
you’ll want to get the angiography room ready. In 2014,
textbooks and papers still frequently lead with the following statement “Pulmonary’ angiography is
the definitive diagnostic modality and reference standard in the diagnosis o f acute PE. “ In reality,
pulmonary angiography is almost never done, and CTPA is the new diagnostic test of choice. V/Q
scan is usually only done if the patient is allergic to contrast or has a very low GFR. The primary
reason V/Q isn’t done is that it’s often intennediate probability, and the running joke is that if you
don’t know how to read one, just say it’s intermediate and you’ll probably be right.
The idea behind the test is that you give two tracers: one for ventilation and one for perfusion. If you
have areas of ventilated lung that are not being perfused, that may be due to PE. Normally
Ventilation and Perfusion are matched, with a normal gradient (less perfusion to the apex - when
standing).
Tracers
perfusion
For perfusion, Tc-99m macroaggregated albumin (Tc-99m MAA) is the most common
tracer used. MAA is prepared by heat denaturation of human serum albumin, with the size of the
particles commercially controlled. You give it IV and the tracer should stay in the pulmonary
circulation (vein-> SVC-> right heart -> pulmonary artery -> lung *STOP). The tracer should light up
the entire lung. A nonnal perfusion study excludes PE. Areas of perfusion abnormality can be from
PE or other things (more on this later). The biologic half life is around 4 hours (they eventually fall
apart, becoming small enough to enter the systemic circulation to eventually be eaten by the
reticuloendothelial system).
tracers
ventilation
There are two ways to do the ventilation; you can use a radioactive gas (Xenon-133) or a radioactive aerosol (Tc-99m DTPA).
xenon 133
The physical half-life is 5.3 days, the biologic half-life is 30 seconds (you breath it out). Because it has low energy (81 keV) it is essential to do this part of the test first (more on this in the physics chapter). Additionally, because the biologic half life is so short, you only can
do one view (usually posterior) with a single detector (dual detector can do anterior and posterior). There are 3 phases to the study: (1) wash in (single max inspiration and breath hold), (2) equilibrium (breathing room air and xenon mix), and (3) wash out (breathing normal air).
Tc99m DTPA
This one requires patient cooperation because they have to breath through a
mouth guard with a nose clamp for several minutes. It is also essential to do this part of the test first.
Quantitative Perfusion
overview
You can do quantitative studies typically to evaluate prior to lung resection, or prior to transplant.
You want to make sure that one lung can hold its own if you are going to take the other one out.
Quantitative Perfusion
testable trivia
Quantification is NOT possible if you use Tc-99 DTPA aerosol. You can do it with a
combined Xe + Tc MAA because the Xe will not interfere with the Tc.
Trivia Questions about Tc99m MAA
They show tracer in the brain
This is a classic way o f showing you a shunt (it got into the systemic circulation somehow, maybe an ASD, VSD, or Pulmonary AVM).
Trivia Questions about Tc99m MAA
How big are the particles?
A capillary is about 10 micrometers. You need your particles to stay in the lung, so they can’t be smaller than that. You don’t want them to be so big they block arterioles (150 micrometers). So the answer is 10-100 micrometers.
Trivia Questions about Tc99m MAA
When do you reduce the particle amount?
few situations. You don’t want to
block more than about 0.1% o f the capillaries, so anyone who has fewer
capillaries (children, people with one lung). Also you don’t want to block
capillaries in the brain, so anyone with a right to left shunt. Lastly anyone with
pulmonary hypertension (or who is pregnant).
Trivia Questions about Tc99m MAA
Is reduced particle the same as reduced dose?
Nope. The normal dose of Tc can be added to fewer particles.
Trivia Questions about Tc99m MAA
They show you multiple focal scattered hot spots
This is the classic way of showing “clumped MAA” , which happens if the tech draws blood into the syringe prior to injection.
Classic Trivia Questions for Xenon 133:
They show you persistent pulmonary activity during washout’.
This indicates Air Trapping (COPD)
Classic Trivia Questions for Xenon 133:
They show you accumulation o f tracer over the RUQ
This is fatty infiltration of the liver (xenon is fat soluble).
Classic Trivia Questions forTc-99m DTPA
Xenon
Quick Wash Out only one or two views
Activity homogenous in the lungs
Classic Trivia Questions forTc-99m DTPA
TC-99m DTPA
Slower Wash Out - multiple projections
“Clumping” common in the mouth,
central airways, and stomach (from
swallowing).
VQ scan
What i f you see tracer in the thyroid or stomach on VQ Scan??
You should think 2 things: (1) Free Tc, or (2) Right - to - Left Shunt
VQ scan
What do you need to call a Right - to - Left Shunt ?
tracer in the brain
VQ scan
I f you suspect a shunt (or the shunt is known) how do you alter the scan?
You reduce the number o f particles. If the normal amount o f particles is around 500K., you would reduce it to around 100K.
VQ scan
What i f the patient has pulmonary> hypertension?
reduce the particles
VQ scan
Particle reduction is the same as dose reduction?
Nope. You keep the dose the same - otherwise the study is non-diagnostic.
VQ scan
What about a neonate ? Do you do anything different?
What about a neonate ? Do you do anything different?
A: Yes - major particle reduction. Down to 10K- 50K particles (depending on who you
ask). The reason is that kids have less capillaries than adults. An adult number of
particles (500K) could functionally cause a PE - by blocking the majority of the
capillaries.
VQ scan
What i f you see a unilateral perfusion defect (o f the whole lung), but no ventilation defect ?
Get a CT or MRI. DDx is gonna be a mass, fibrosing mediastinitis, or Central PE.
O f those which is the MOST COMMON?
A: Most sources will say “central obstructing mass” i.e. “bronchogenic carcinoma”
VQ scan
How do you grade this unilateral perfusion defect (o f the whole lung), but no ventilation defect ?
te hnically low probability
Gallium 67 Scan
overview
The body handles Ga+3 the same way it would Fe+3 - which as you may remember from
step 1 gets bound (via lactoferrin) and concentrated in areas of inflammation, infection,
and rapid cell division. Therefore it’s a very non-specific way to look for infection or
tumor. Back in the stone ages this was the gold-standard for cancer staging (now we use
FDG-PET). 1 should point out that Gallium can also bind to neutrophil membranes even
after the cells are dead, which gives it some advantages over Indium WBC - especially in
the setting o f chronic infection.
Gallium 67 Scan
creation
Gallium is produced in a cyclotron via the bombardment
of Zn68, at which point it’s complexed with citric acid to
make Gallium Citrate. The half life is around 3 days
(78hours). It decays via electron capture, emitting gamma
rays at 4 photopeaks
Gallium 67 Scan
4 photopeaks
93 keV - 40%
184 k eV -2 0%
300 keV - 17%
393 keV - 5%
Gallium 67 Scan
imaging
Images are not typically done sooner than 24 hours -
because background is too high. The critical organ is the
colon. Remember “critical organ” = the first organ to be
subjected to radiation in excess o f the maximum allowable
amount.
Gallium 67 Scan
normal localization
Liver (which is the highest uptake), bone marrow ( “Poor Mans s
hone sca n”), spleen, salivary glands, lacrimal glands, breasts (especially if lactating, or
pregnancy). Kidneys and bladder can be seen in the first 24 (faintly up to 72 hours). Faint
uptake in the lungs can be seen in < 24 hours. After 24 hours you will see some bowel. In
children the growth plates and thymus.
Gallium 67 Scan
poor mans bone scan
Uptake is in both cortex (like regular bone scan) and marrow. Degenerative change, fractures, growth plates, all are hot - just like bone scan.
Gallium uptake is nonspecific and can be seen with a variety o f things
infection,
but also CHF, atelectasis, and ARDS.
Sarcoidosis
overview
The utility o f Gallium in Sarcoidosis patients is to help look for active disease. Increased
uptake in the lungs is 90% sensitive for active disease (scans are negative in inactive
disease). Additionally, Gallium can be used to help guide biopsy and lavage - if looking to
prove the diagnosis. The degree o f uptake is graded relative to surrounding tissue (greater
than lung is positive, less than soft tissue is negative).
Sarcoidosis
classic signs
- Lambda Sign - The nuke equivalent to the “ 1 -2-3 Sign” on Chest x-ray. You have
increased uptake in the bilateral hila, and right paratracheal lymph node. - Panda Sign - Prominent uptake in the nasopharyngeal region, parotid salivary gland,
and lacrimal glands. This can also been seen in Sjogrens and Treated Lymphoma.
Other Noninfectious Things
- Gallium can be used to show early drug reaction from chemotherapy (Bleomycin) or
other drugs (Amiodarone). - Gallium is elevated in IPF (idiopathic pulmonary fibrosis) and can be used to monitor
response to therapy.
PCP
Gallium Hot, Characteristic Gallium Pattern is Diffuse Bilateral Pulmonary Uptake
Kaposi Sarcoma
Gallium Negative, Thallium Positive
Galium 67 - Pneumonia
- Lung Uptake at 72 Hours
Bacterial Pneumonia
gallium?
Intense lobar configuration without parotid or nodal uptake.
Misc Infections That Gallium Can Pick Up:
• Abdominal and Pelvic Infections - In-111 WBC is superior to Gallium
(Gallium has some normal GI uptake).
• Malignant Otitis Media - Will be both Gallium and Bone Scan (Temporal Bone) Hot.
• Spinal Osteomyelitis - Gallium is superior to Indium WBC for spinal infections.
Thyroid overview
The thyroid likes to drink Iodine (it’s sort o f its job). Imaging takes advantage of this with
Iodine analogs. The distinction between “trapping” and “organification” is a common
question.
Thyroid
trapping
Analog is transported into gland. I23I, l3lI, and 99mTc all do this.
Thyroid tracer
I-131
The major advantage here is that it’s cheap as dirt. The disadvantage is that it has a
long half life (8 days), and that it’s a high energy (364 keV) beta emitter. The high energy
makes a crappy image with a ‘A inch crystal. It’s ideal for therapy, not for routine imaging.
It’s contraindicated in kids and pregnant women.
Thyroid tracer
Tc 99m
Remember that this guy is trapped but not organified. Background levels are higher
because only 1-5% o f the tracer is taken up by the thyroid gland. A common scenario to
choose Tc over Iodine is when they’ve had a recent thyroid blocker on board (iodinated
contrast is the sneaky one).
Thyroid
trivia
Thyroid formation takes place in fetus at 8-12 weeks
Thyroid tracer
I-123
This guy has a shorter half life (13 hours) and ideal energy (159 keV). It decays via
electron capture and all around makes a prettier image. The problem is that it costs more.
Thyroid
organification
Analog is oxidized by thyroid peroxidase and bound to tyrosyl
moiety. I23I and l3ll do this. 99mTc does NOT do this. Instead 99mTc slowly washes
out o f the gland.
Random Trivia on Breastfeeding
- Tc-99m: You can resume breast feeding in 12-24 hours
- 1-123: You can resume breast feeding in 2-3 days
- 1-131: You should not breast feed - pump and dump.
Iodine Uptake Test:
You give either 5 micro Ci o f 131 or 10-20 micro Ci o f 123. This is conventionally reported
at 4-6 hours, and 24 hours. Normals are 5-15% (4-6 hours), and 10-35% at 24 hours. A
correction for background is done on measurements prior to 24 hours (using the neck counts
- thigh counts).
Iodine Uptake Test:
factors affecting the test
Renal Function (increases stable iodine pool, reduces numbers)
Dietary Iodine - variable and controversial
Medications - thyroid blockers, Nitrates,
IV Contrast, Amiodarone
Iodine Uptake Test
increased uptake
graves
Early hashimoto
Rebound after Abrupt withdrawal of antithyroid medication
Dietary Iodine Deficiency
Iodine Uptake Test
decreased uptake
Primary or secondary causes of Hypothyroidism
Renal failure
Medications (thyroid blockers, Nitrates, IV Contrast, Amiodarone)
Dietary iodine overload
Graves disease
overview
About 75% of the time, if you have hyperthyroidism the
cause is going to be graves. Graves is an autoimmune
disease where an antibody to the thyrotropin receptor
stimulates the thyroid to produce hormone. TSH will be
very low, where T3 and T4 will be high. The classic
clinical scenario is a middle aged women with a protracted
course, pre-tibial edema, and exophthalmos. Scintigraphy
is going to give you a homogeneously increased gland,
with uptakes increased at both 4 hours and 24 hours.
Sometimes the 24 hour uptake is lower than the 4 hours (or
even at a normal range) - this is from rapid thyroid
hormone production.
Graves disease
visualization of the pyramidal lobe
The pyramidal lobe is seen in about 10%
o f normal thyroids. In patients with Graves disease it is seen as much as 45% of the time. Therefore, it’s suggestive when you see it.
Graves disease
quick
Diffuse homogenous uptake
Multi-nodular Toxic Goiter (Plummer Disease):
The classic scenario is an
elderly women with weight loss, anxiety, insomnia, and tachycardia. The gland is typically
heterogeneous, with uptake that is only moderately elevated. The nodules will be hot on the
background o f a cold gland.
Toxic Multi-nodular Goiter vs Non-Toxic Multi-nodular goiter
The toxic goiter will have hot nodules on a background o f cold thyroid. The Non-toxic one will have warm/hot nodules on a normal background of the thyroid.
Graves quick
Uptake High : 70s (typically > 50%)
homogenous
Toxic Multi-Nodular Goiter
quick
Uptake Medium High: 40s (typically <50%)
heterogenous
Hashimotos
The most common cause of goitrous hypothyroidism (in the US). It is an autoimmune
disease that causes hyper first then hypothyroidism second (as the gland bums out later). It’s
usually hypo - when it’s seen. It has an increased risk of primary thyroid lymphoma.
Step 1 trivia; associated with autoantibodies to thyroid peroxidase (TPO) and antithyroglobulin.
The appearance o f the hypothyroid gland is typically an inhomogeneous gland
with focal cold areas. The hyperthyroid (acute) gland looks very much like Graves with
diffusely increased tracer.
Subacute Thyroiditis
If you have a viral prodrome followed by hyperthyroidism, and then thyroid uptake scan
shows a DECREASED % RAIU you have de Quervains (Granulomatous thyroiditis).
During this acute phase, the disease can mimic Graves with a low TSH, high T3 and high T4
The difference is the uptake scan. After the gland bums out, it may stay hypothyroid or
recover. If they ask you about this, it’s most likely going to try and fool you into saying
Graves based on the labs, but have a low % RAIU.
Solitary Nodules
thyroid
20-40% Cold Nodules = Cancer
< 1% Warm Nodules = Cancer
Hot Nodule vs Cold Nodule
Most thyroid nodules are actually cold, and therefore most are benign (colloid, cysts, etc..).
In fact, cold nodules in a multi-nodular goiter are even less likely to be cancer compared to a
single cold nodule. Having said that, cold nodules are much more likely to be cancer when
compared to a functional (warm) nodule.
Discordant Nodule
This is a nodule that is HOT on Tc” but COLD on I123. Because some
cancers can maintain their ability to trap, but lose the ability to organify a hot nodule on Tc, it
shouldn’t be considered benign until you show that it’s also hot on I 123.
Gamesmanship: Iodine vs tc
A classic move is to show you a thyroid that will take up Tc, but NOT Iodine on 24 hour
imaging. This can be from a couple o f things: (1) congenital enzyme deficiency that
inhibits organification, (2) a drug like propylthiouracil that blocks organification.
Now if they just show you an Iodine Thyroid with low uptake on 24 hours, this is de Quervains, or a burned out Hashimotos.
I131 can be used to treat
both malignant and non-malignant thyroid disease.
Thyroid Cancer
overview
Papillary is the most common subtype (papillary is popular), and it does well with surgery + 1-131.
Medullary thyroid CA (the one the MENs get), does NOT drink the 1-131 and therefore
doesn’t respond well to radiotherapy. Prior treatment can also make you more resistant to
treatment, and re-treatment dosing is typically 50% more than the original dose.
Thyroid Cancer
things taht make you tratment resistan
- Medullary Subtype CA (will not drink the tracer)
- History of prior 1-131 (“easy gland has been killed o ff ’)
- History o f Methimazole treatment (even if years ago)
Thyroid Cancer
medullary subtype CA
Neuroendocrine in origin, so can occasionally (around 10%) have uptake on MIBG or Octreotide. They will be cold on thyroid scan and don’t drink the treatment 1-131. If forced to pick - I’d go with Octreoscan for medullary CA. Associated with MEN 2a and 2b
Thyroid Cancer
tratment timeline
So, normally the patient gets diagnosed and then they go for surgery. After surgery they will
come to nuclear medicine. You expect that they will have some residual thyroid (it’s really
hard to get it all out). Prior to actually treating them you will give them a tiny dose o f 1-131 to
see how much thyroid they have left. If the uptake is less than 5% this is ideal. Uptake more
than 5% will result in a painful ablation (may need steroids on top of the NSAIDs) and may
need to go back to the OR. Next, you will treat them. You want their TSH really ramped up.
The higher the TSH the thirstier the cancer /residual thyroid tissue. An ideal TSH is like 50
(30 would be a minimum).
Radioiodine Therapy
How do you get the TSH up?
o (1) is to stop the thyroid hormone (post op they are obviously hypothyroid),
o (2) is to give recombinant TSH “Thyrogen.”
Radioiodine Therapy
How do you decide on dosing?
Dosing is dependent on the stage of the disease; 100 for thyroid only, 150 for thyroid
+ nodes, 200 for distal. They are told about the precautions etc… Then you give them
the dose. Before you let them go home, you test them to see if they need to go to the
hospital.
Radioiodine Therapy
So when do patients need to he admitted to the hospital?
NRC limit is 7mR/h measured at 1 meter from the patient’s chest (some agreement
states use 5 mR/h). The number to remember is 33 mCi of residual activity (or 30
mCi in some strict agreement states).
Radioiodine Therapy
Possible Side Effects o f Treatment:
- Can cause pulmonary fibrosis if given to patient with lung mets. This is really only the case of macro-nodular disease (as opposed to micronodular disease). That isn’t necessarily a contraindication
- Sjogrens have a greater risk of salivary gland damage
- Salivary gland damage is dose related - so cancer treatment patients have a greater risk
Radioiodine Therapy
What routes does the body use to eliminate I, i l?
Urine is the main way it is eliminated but sweat, tears, saliva, and breast milk are other
routes.
Radioiodine Therapy
I f they don’t need to be admitted to the hospital, what precautions should they take?
There is a whole bunch of crap they are asked to do. Drink lots of water (increase renal excretion). Suck on hard candy (keep radiotracer from jacking your salivary glands). Patients are encouraged to stay away from people (distance principal). Sleep alone for 3 days (no sex, no kissing - keep that dirty dick in your pants!). Good bathroom hygiene (flush twice, and sit down if you are a guy). Use disposable utensils and plates. Clothes and linens should be washed separately. Most of these things are done for 3 days.
Radioiodine Therapy
Is it ok to breast feed? Is it ok to try> and get pregnant?
- No breast feeding. If you take I131 your breast feeding days are over (at least this time
around) . - No getting pregnant for at least 6-12 months after therapy
Radioiodine Therapy
other trivia
- If you participated in the therapy, you need your thyroid
checked 24 hours later. - If the patient got admitted to the hospital the RSO needs to
inspect the room after discharge before the janitor can
clean it or the next patient can move in. - Thyroglobulin is a lab test to monitor for recurrence.
Anything over zero - after thyroidectomy, is technically
abnormal, although the trend is more important (going up
is bad)
‘ Severe uncontrolled thyrotoxicosis and pregnancy are
absolute contraindications.
Radioiodine Therapy
gamesmanship for iodine post treatment
If you see an Iodine Scan,
and you see uptake in the
liver , this is ALWAYS a post
treatment scan.
Radioiodine Therapy
pt is on dialysis and needs I131 rx
Give I131 immediately following dialysis to maximize the time the I131 is on board. Decrease
dose as there is limited (essentially no) excretion until next dialysis. Dialysate can go down
sewer. Dialysis tubing needs to stay in storage.
Hyperthyroidism
treatment
I131 can also be used to treat hyperthyroidism. Dosing depends
on the etiology; 15 mCi for Graves (more vascular), 30 mCi
for multi nodular (harder to treat the capsule). Again the TSH
must be high for the therapy to be effective. By 3-4 months,
there should be clinical evidence of resolution of signs and
symptoms of hyperthyroidism, if 1-131 therapy was
successful.
Hyperthyroidism
emergent treatment
As an aside, there is no such thing as an “emergent
hyperthyroid treatment.” You can always use meds to cool it
down. The standard medication is Methimazole. However, if
there is an allergy to Methimazole, the patient is having WBC
issues (side effect is neutropenia) or the patient is pregnant
-use propylthiouracil (PTU). PTU is recommended during
pregnancy.
Hyperthyroidism
thyroid eye disease
It’s controversial, but some people believe that thyroid eye
disease will worsen after 1-131 treatment. If you are prompted, I would just have optho look at
their eyes, bad outcome is likely severity related. *You might not want to treat a bug-eyed dude
(depends on who you ask).
Hyperthyroidism
wolff-chaikoff effect
Since we are talking about hyperthyroid treatment, there is no better time than
to discuss the W.C. effect. Essentially, this is a reduction in thyroid hormone levels caused by ingestion
of a large amount of iodine. The Wolff-Chaikoff effect lasts several days (around 10 days), after which
it is followed by an “escape phenomenon.” The W.C. effect can be used as a treatment principle
against hyperthyroidism (especially thyroid storm) by infusion of a large amount of iodine to suppress
the thyroid gland. The physiology of the W.C. effect also explains why hypothyroidism is sometimes
produced in patients taking several iodine-containing drugs, including amiodarone.
What Causes Hyperparathyroidism ?
- Most common cause is a hyperfunctional adenoma (85%).
- Second most common cause is multiple gland hyperplasia (12%).
- Third most common cause is cancer (3%).
Parathyroid
Nuclear medicine can offer two techniques to localize these lesions;
dual phase and dual tracer
Dual Phase Technique
In dual phase technique, a single tracer (Tc”-Sestamibi) is administered, and both early (10
mins) and delayed (3 hours) imaging is performed. The idea is that sestamibi likes things with
lots of blood flow, and lots of mitochondria. Parathyroid pathology tends to have both of
these things, so the tracer will be more avid early, and stick around longer (after the tracer
washes out of normal tissue). SPECT can give you more precise localization.
Dual Phase Technique
initial phase
both thyroid and parathryroid
Dual Phase Technique
delayed phase
uptake remains in abnormal parathyroid (hyperplasia in this case)
Dual Phase Technique
trivia
Sestamibi parathyroid imaging depends on mitochondrial density and blood flow
Dual Phase Technique
false positives
Caused by things other than parathyroid pathology that like to drink Sestamibi.
• Thyroid Nodules
• Head and Neck Cancers
• Lymphadenopathy
Dual Tracer Technique
overview
In dual tracer technique two different agents are used and then subtraction is done. The first
agent is chosen because it goes to both thyroid and parathyroid (options are either Tc99-
Sestamibi or 201- Thallium Chloride). The second agent is chosen because it only goes to the
thyroid (options are either 1-123 or Pertechnetate). When subtraction is done, anything left hot
could be a parathyroid adenoma.
Dual Tracer Technique
problems
- Mo Tracers, Mo Problems
- Motion: subtraction imaging can’t tolerate much motion
- Stuff Messing with the Thyroid Tracers: recent iodinated contrast, etc…
Parathyroid
implantatio
The parathyroid gland can be surgically implanted into the forearm - typically done with hyperplasia surgery where they carve out 3 1/2 glands.
Parathyroid
what is considered successful treatment
Successful surgical treatment of hyperparathyroidism is often defined as intra-operative reduction of
PTH by 50%.
Parathyroid
false positive
Thyroid adenoma (most common), thyroid cancer, parathyroid cancer.
Parathyroid
false negative
Small sized adenoma (most common), 4 gland hyperplasia. A negative study in the setting of abnormal / suspicious labs should raise concern for these things (multiple gland
hyperplasia or a small adenoma).
Gamesmanship - MIBI - Lymph Nodes
On any study, parathyroid or a heart, if the tracer is MIBI than you should NOT see lymph
nodes. If you see lymph nodes they are suspicious (maybe cancer). Next step would be
ultrasound to further evaluate them.
Oh, and don’t forget about focal breast uptake (also cancer), - Breast Specific Gamma Imaging (BSGI) uses MIBI for a reason.
planar imaging is used for
brain death
planar imaig uses and is proportional to
lipophilic perfusion agents
proportional to blood flow
Spect imaging uses and is proportional to
lipophilic perfusion agents
proportional to blood flow
PET imagingis proportional to
metabolism
CNS Nukes agents
extracted
Can be used for Parenchymal Imaging)
HMPAO
ECD
CNS Nukes agents
not extracted
(Not used for Parenchymal Imaging - i.e. no SPECT)
DTPA
THIS vs THAT -HMPAOand ECD
Tc HMPAO (hexamethylpropyleneamine oxime) and Tc ECD (ethyl cysteinate dimer).
HMPAO and ECD can be used in both dementia imaging and for seizure focus localization.
These studies are typically performed with SPECT. The idea behind brain SPECT is that you
can look at brain blood flow, which should mimic metabolism. These two agents are neutral
and lipophilic, which lets them cross the blood brain barrier and accumulate in the brain.
Where and how much they accumulate should follow flow (and metabolism).
HMPAO overview
Neutral and Lipophilic
Accumulate in the cortex proportional to blood flow (Gray Matter > White Matter)
washout is fast
Uptake favors the frontal lobe, thalamus, and cerebellum
ECD Overview
Neutral and Lipophilic
Accumulate in the cortex proportional to blood flow (Gray Matter > White Matter)
Washout is slow (more rapid clearance
from blood p o o l)
Uptake favors the parietal and occipital lobes
* Makes comparison between HMPAO and
ECD difficult
HMPAO and ECD
Key points
Both agents pass blood brain barrier and stick to gray matter proportional to CBF
HMPAO washes out faster
ECD washout is slower, has better background clearance, and does not demonstrate intracerebral redistribution.
Tc- DTPA
overview
Unlike HMPAO or ECD, this agent is lipoPHOBIC - and is best thought o f as an “angiographic tracer” because it stays in the blood (or CSF if you put it there).
Tc- DTPA
key points
DTPA does NOT cross the blood brain barrier and therefore cannot be used for brain parenchymal imaging. *You can NOT do SPECT
Has the advantage over HMPAO and ECD in that it can be repeated without delay
DTPAs main utility is for shunt studies. NPH, and Brain Death.
Seizure Focus
The idea is that a seizure focus will be hot (hypermetabolic and hyperperfusion) during the seizure “ictal.” Then cold between seizures “interictal.” You need to inject tracer (HMPAO or ECD) within 30 seconds o f the seizure to get a good study. PET can be used, but is less practical.
Thallium 201
overview
Thallium is produced in a cyclotron, decays via electron capture, and has a half life of
around 3 days (73 hours). The major emissions are via the characteristic x-rays o f its
daughter product Mercury 201 - at 69 keV and 81 keV. The tracer is normally given as a
chloride and will therefore rapidly be removed from the blood
Thallium 201
behaves
Thallium behaves like potassium, crossing the cell membrane by active transport (Na+/
K pump). Tumors and inflammatory conditions will increase the uptake o f this tracer.
The higher the grade tumor, the more uptake you get. As Thallium requires active
transport, it can be thought o f as a viability marker - you need a living cell to transport it.
Thallium 201
normal distribution
Thyroid, salivary glands, lungs, heart, skeletal muscle, liver, spleen,
bowel, kidneys, and bladder. Any muscle twitching will turn hot.
Thallium 201
using with gallium
If you are going to use it with Gallium, you must use the Thallium first as the Gallium
will scatter all over the Thallium peaks.
Thallium 201
high yield
Toxoplasma Infection is Thallium Negative
Lymphoma is Thallium Positive
Kaposi Sarcoma is Thallium Positive (Gallium Negative)
Tumor is Thallium Positive
Necrosis is Thallium Negative
CNS
Tumor vs Necrosis
The tracers used for SPECT tumor studies are different than
those used for dementia or seizures. The tumor tracers are
20ITI (more common) and 99mTc Sestamibi (less common).
20ITI is a potassium analog, that enters the cell via the Na/K
pump. Inflammatory conditions will increase the uptake o f this
tracer, but not as much as tumors. The higher the tumor grade,
the more intense the uptake. Thallium can be thought o f as a
marker o f viability, as it will localize in living tumor cells, and
not necrosis. The control is the scalp (abnormalities will have
greater uptake than the scalp). You can use Thallium in
combination with perfusion tracers (HMPAO).
CNS tumor
Thallium Hot,
HMPAO Cold
CNS NEcrosis
Thallium Cold,
HMPAO Cold
CNS Lymphoma vs Toxoplasmosis:
As discussed in the neuro chapter CNS lymphoma
vs CNS Toxoplasmosis can be a diagnostic
dilemma. Thallium has a role in helping to distinguish the two (Toxo Cold, Lymphoma Hot).
Typically CNS lymphoma, toxoplasmosis,
bacterial abscess, cryptococcus infection,
and tuberculosis are all positive on
Ga-67 scintigraphy.
