NUCLEAR RADIOLOGY
CHAPTER22
RADIONUCLIDES
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RADIONUCLIDE = RADIOISOTOPE
ISOTOPES- chemical elements with the same
atomic number (# of protons) but different
mass (# of neutrons). Because of this
difference in mass, the nuclei of isotopes are
unstable and they spontaneously decay,
emitting radiation in the process.
See http://en.wikipedia.org/wiki/Isotope
RADIONUCLIDES
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Some occur naturally, others are
produced by bombarding the nucleus with
subatomic fragments in a cyclotron to
make them unstable.
Radionuclides can be used both for
therapeutic and diagnostic purposes
(I131).
Here we will look only at their diagnostic
uses.
RADIATION HAZARD
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“SLIGHT” – low dose, brief duration.
However, cells that are dividing rapidly are
more susceptible to effects of radiation.
As such, radionuclides are not used in
pregnancy or childhood if other diagnostic
measures suffice.
Pregnant women should void frequently postexposure to minimize exposure to the fetus.
In breast-feeding women, breast milk should be
discarded post-exposure until radionuclide is
eliminated.
RADIONUCLIDES USED IN
DIAGNOSTIC TESTING
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I131.
Technetium. (Tc-99m)
Gallium.
Indium.
Thallium.
Sodium chromate (Cr-51).
Cobalt (Co-57).
TECHNETIUM
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Tc-99m- very unstable, has a short half-life of 6
hrs. Commonly used for numerous types of
scans.
Can be combined w/ various biologically-active
substances (“tagged”) that transport Tc-99m to
target organs.
Bone Scans- Tc-99m combined with
pyrophosphate.
Lung Scans- Tc-99m combined with albumin.
Other- RBC’s, thyroid, brain, hepatobiliary.
BONE SCANS
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Tc-99m-labelled pyrophosphate
incorporated into bone.
Entire body is scanned.
Detects areas of increased bone activity,
osteolytic and osteoblastic.
Used to detect metastases, fractures.
Metastases show up on bone scan 6
months or so before they show on a plain
radiograph.
Bone Scan – Metastatic Prostate
Cancer
PLAIN FILM- 21 YOM W/ LEFT KNEE PAIN
BONE SCAN – OSTEOSARCOMA
NO METASTASES
BONE SCAN – PAGET’S DISEASE
BRAIN SCANS
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1) EVALUATION FOR DISRUPTION OF THE
BLOOD-BRAIN BARRIER.
2) PERFUSION SCAN.
BRAIN SCANS
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EVALUATION FOR DISRUPTION OF THE
BLOOD-BRAIN BARRIER
Blood-brain barrier is a “complex system
of membranes and fluid spaces that keeps
substances in the blood from diffusing
into the brain tissue.” Tc-99m given IV →
localizes in areas where the blood-brain
barrier is disrupted, by stroke, trauma,
neoplasms, etc.
BRAIN SCANS
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PERFUSION SCAN
Lipid-soluble radiopharmaceuticals that
can cross the blood-brain barrier used to
evaluate perfusion of certain areas of the
brain.
BRAIN SCAN (PET) - ALZHEIMERS
PET SCAN – ALZHEIMERS
GALLIUM SCAN
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Gallium (Ga-67) localizes in areas of
inflammation and in some neoplasms.
Used to detect areas of inflammation such
as osteomyelitis, abscesses, and to look
for occult metastases.
Highly sensitive and specific for detecting
Hodgkin’s Disease, for staging and for
post-treatment evaluation to assess
response to therapy.
GALLIUM SCAN- LYMPHOMA
GALLIUM SCAN- 2 MOS POST-OP BUNIONECTOMY W/
CONTINUED PAIN
OSTEOMYELITIS
INDIUM SCAN
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INDIUM – In-111-labelled leukocytes go
to areas of acute infection, not as much
for chronic infection which is better
evaluated by Gallium.
Indium is not taken up by neoplastic
tissue.
Can also be used to tag RBC’s and
paltelets.
Patients blood is drawn, tagged w/
Indium, and reinjected. Scan is done
GALL BLADDER SCAN
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HIDA SCAN- used to evaluate for
cholecystitis.
Tc-99m-labeled HIDA is excreted
into the bile the same as bilirubin →
fills the hepatobiliary tree.
In cholecystitis the gall bladder
does not visualize.
Highly specific and highly sensitive.
HIDA SCAN- NON-VIS GALL BLADDER- ACUTE
CHOLEYCYSTITIS
GASTROINTESTINAL SCANS
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Variety of scans used to evaluate:
1) GI Motility- gastric and esophageal emptying, reflux,
etc.
2) GI Bleeding.
3) Presence of specific tissue types in abnormal
locations- Ex Meckel’s Diverticulum – a congenital
malformation of the terminal ileum in which a
diverticulum is present and contains gastric or
pancreatic tissue- associated w/ GI bleeding mostly in
children- “currant jelly stools.”
MECKEL’S DIVERTICULUM
Tc-99-TAGGED RBC’S
BLEEDING FROM JEJUNUM/J-TUBE
LIVER-SPLEEN SCANS
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Tc-99m used to asses hepatic function and
biliary function.
Tc-99m taken up by the reticuloendothelial
system so can be used to image both the liver
and the spleen.
Used to look for: changes of cirrhosis, areas of
hypo- or hyperfunction, presence of metastases
or an abscess, and to assess liver damage in
trauma → leakage of bile into the abdomen
around the liver.
NORMAL Tc-99 LIVER-SPLEEN SCAN
Tc-99 LIVER SCAN
FOCAL NODULAR HYPERPLASIA
3 WEEKS POST-OP REPAIR OF
LIVER LACERATION
BILOMA
LUNG SCANS
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VENTILATION / PERFUSION SCANS
Done to R/O pulmonary embolus.
Ventilation scan- inhaled Xenon-123,
exhaled. Scan looks for uniformity (or
lack of) in the lungs, looking for areas
that are not being ventilated, due to
collapse, atelectasis, pneumothorax, etc
Perfusion scan- Tc-99m-labeled albumin
injected, scan looks for uniformity (or lack
of) in perfusion.
LUNG SCANS
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VENTILATION / PERFUSION SCANS
Comparison is done of the ventilation and
the perfusion scans looking for a
“mismatch” of perfusion in 2 or more
lungs field.
Results are given as high, intermediate,
or low probability, and used along w/
clinical suspicion to assess for likelihood
of pulmonary embolus.
Need to compare to chest X-Ray to be
sure symptoms are not due to other
pathology.
V / Q SCAN – P.E.
VENTILATION
SCAN:
NORMAL
V / Q SCAN – P.E.
VENTILATION
SCAN:
NORMAL
V / Q SCAN – P.E.
PERFUSION
STUDY
ABNORMAL:
2 AREAS OF
“MISMATCH”
(COMPARED
TO
VENTILATION)
ANGIOGRAM – P.E.
CARDIAC SCANS
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PERFUSION SCANS
Thallium is a physiologic analog of
potassium.
Taken up by normally-perfused areas of
myocardium.
Low uptake can indicate poor coronary
perfusion vs. old infarction.
Often combined with a stress / treadmill
test, aka “thallium treadmill.”
CARDIAC SCANS
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MUGA SCAN
Multiple gated acquisition scan.
Measures ventricular wall motion and
ejection fraction.
Used in the evaluation of cardiac function
in patients with cardiomyopathy, heart
failure, ventricular aneurysms.
RENAL SCANS
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Used to assess renal perfusion, structure,
and/or excretory ability. When all 3 are
measured, referred to as a triple renal
study.
Tc-99m or iodine-tagged substance give
IV, dynamic images taken to assess
perfusion, static images taken to assess
structure.
Can be used as an alternative to IVP if
patients are allergic to iodinated-IVP dye.
THYROID SCANS
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I-123
Used for evaluation of thyroid nodules.
I-123 given PO or IV.
“Cold” Nodules = do not take up the
iodine. Associated w/ malignant nodules.
“Hot”Nodules = take up the iodine.
Associated w/ benign nodules.
Still need to prove benign or malnigant w/
biopsy.
THYROID SCANS
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I-131
Used to detect metastases from thyroid
malignancy.
RAIU
Radioactive iodine uptake.
Uptake of iodine is a representation of its
function.
Hypothyroidism – decreased uptake.
Hyperthyroidism – increased uptake.
THYROID SCAN – GRAVE’S
DISEASE- I131 + Tc-99
Tc-99 THYROID SCANAUTONOMOUSLY FX NODULE
RBC TESTS
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RBC SURVIVAL TEST
Sodium chromate (Cr-51) binds w/
hemoglobin.
RBC’s can be tagged to evaluate RBC
survival, to assess for hemolysis.
RED CELL VOLUME
Cr-51 tagged onto RBC’s, other isotopes
used to tag plasma.
Used in the evaluation of polycythemia
vera.
SCHILLING TEST
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Used to evaluate intestinal absorption of
Vitamin B-12 in patients w/ macrocytic
anemia.
B-12 tagged with Co-57.
Test measures how much Co-57 is
eliminated in the urine.
Given with and without intrinsic factor to
evaluate for pernicious anemia vs.
malabsorption.
WHOLE BODY BONE SCAN SCAN –
Tc-99m
54 YOF W/ BREAST
CANCER,
BONE SCAN TO R/O
METASTASES
SAME PATIENT
RENAL AGENESIS