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RADIOPHARMACY
Diagnostic Nuclear Medicine 4
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BRAIN IMAGING
Cerebral perfusion brain- imaging agents.
Radiopharmaceuticals for evaluating brain perfusion must possess
a lipophilic partition coefficient sufficient to diffuse passively
across the blood-brain barrier (BBB) almost completely within one
pass of the cerebral circulation, as well as being sufficiently
retained to permit data collection.
The regional uptake of these agents is proportional to cerebral
blood flow. This class of radiopharmaceuticals is useful in the
diagnosis of altered regional blood perfusion as in stroke.
Tc-99m HMBAO hexamethylpropyleneamine oxine
Tc-99m HMBAO is a neutral , lipid-soluble complex that freely
crosses the BBB. This is a relatively unstable complex, which
rapidly converts to a secondary, less lipophilic complex incapable
of penetrating into the brain.
The in vitro addition of a methylene blue/phosphate buffer
stabilizing solution after preparing the Tc-99m HMBAO will
stabilize the lipid-soluble complex for 4 hr .
Administration and dosage. IV, 20 mCi (740 MBq)
INFECTION AND INFLAMMATION.
Evaluation of sites of infection include the use of agents that can
associate with components of the natural defence mechanisms
and can accumulate where they localize.
Gallium (Ga-67) citrate
It is supplied as a sterile, pyrogen-free radiopharmaceutcal with preservatives.
The mechanism of localization depends on the format ion of a gallium transferrin
complex in the blood and on binding to transferrin receptors associated
with infection and inflammation.
It accumulates in areas of white blood cell (WBC) localization.
Biodistribution
After administration, the highest concentration of Ga-67 citrate, other than at the
site of infection, is in the liver and spleen, renal cortex and bone.
Physical half - life: 78 hr
Decay emissions: 185 kev γ photons
Administration and dosage. IV, 3 mCi (111 MBq) .
A daily laxative or an enema should be used by the patient after the injection and
before the images to cleanse the bowel of radioactivity that may interfere with the
images and possibly lead to a false positive result.
WBC labelling agents
Radiolabeled WBCs are used in the detect ion of a wide variety of
infectious and inflammatory processes.
Current use includes the diagnosis of intra-abdominal abscesses,
inflammatory bowel disease, appendicitis, fever of unknown
origin, and osteomyelitis.
WBCs can be radiolabeled with In-111 oxine or Tc-HMPAO.
Tc-99mHMPAO
Tc-99m HMPAO is used to radiolabel leukocytes after reconstitution with
sodium pertechnetate.
Tc-99m HMPAO is a neutral , lipid-soluble complex that is able to penetrate the
WBC membrane. This lipophilic complex is relatively unstable and rapidly
converts to a secondary complex incapable of penetrating (leaving) the WBCs.
The methylene blue/phosphate buffer stabilized solution is not able to radiolabel
cells and should not be used.
Biodistribution
(1) After IV injection, the radiolabeled cells localize in the lungs, liver , spleen,
blood pool , bone marrow, and bladder as well as the sites of WBC accumulation.
(2) Elimination is primarily via the liver .
Administration and dosage. IV, for infection, 20 mCi (740 MBq)
The Relative Effectiveness of Imaging with 111In-WBC, 99mTcHMPAO-WBC, and 67Ga-Citrate
TUMOR IMAGING
The usefulness of radiopharmaceuticals in the detection of tumours varies in
sensitivity and specificity, with differences in tumour location and type.
Ga-67
The mechanism of localization is thought to depend on the formation of a
gallium transferrin complex or binding to transferrin receptors on tumour cells.
It accumulates in primary metastatic tumour sites and may detect the presence
of Hodgkin disease, lymphoma, and bronchogenic carcinoma.
Tl-201
This agent has utility as a tumour- imaging agent because of its accumulation
in the rapidly metabolizing cells of certain tumours in accordance with its
mechanism of localization.
Tc-99m MIBI
Tc-99m MIBI is used for both tumour and cardiac imaging.
Tc-99mMIBI is indicated for imaging as a second line of evaluating breast
lesions in patients with an abnormal mammogram or a palpable breast mass.
NB. Tumour imaging agent are not used to screen breast cancer,
to confirm the presence or absence of malignancy, or to replace a
biopsy.
99mTC-sestamibi
studies of a breast cancer patient before and
after chemotherapy treatment
I-131 MIBG (meta-iodobenzylguanidine)
It is supplied as a sterile, pyrogen- free radiopharmaceut ical for use as an
adjunctive diagnostic agent for the localization of primary and metastatic
pheochromocytomas and neuroblastomas.
MIBG (meta-iodobenzylguanidine) labeled with I-131 acts as a physiological
analog of norepinephrine and is transported and accumulated in the adrenal
medulla.
This allows for the detection of neuroendocrine tumours via the specific
uptake of labeled MIBG.
Because of its physiological similarities to norepinephrine, many classes of
drugs that interfere with catecholamine transport and function may affect the
uptake and localization of labeled MIBG .
Biodistribution
(1) After IV injection, there is rapid uptake in the liver , with lesser amounts
accumulating in the lungs, heart , and spleen.
(2) Normal adrenal gland uptake is low; but for tumours such as
pheochromocytomas and neuroblastomas, the uptake is relatively higher .
(3) Elimination is renal ; most of the drug is excreted mainly unchanged.
(4) Administration of potassium iodide 1 day before and for 10 days after
administration is suggested to reduce thyroid uptake of potential radioiodide
contaminants.
Physical data. See I-131
Administration and dosage. IV, 1 mCi ( 37 MBq )
Right Adrenal Pheochromocytoma - MIBG Scan
I-131 MIBG scan demonstrated a large focus of tracer
accumulation that corresponds to ganglioneuroblastoma
Thank you and Good Luck
Prof. Dr. Omar Shebl Zahra