GALLIUM
IMAGING
Clinical indication
1. Whole
body survey to localize source of fever in patient with Fever of Unknown
Origin.
2. Diagnosing
osteomyelitis and / or disk space infection. Ga – 67 is preferred over labeled
leukocytes for disk space infection.
3. Detection
of pulmonary and mediastinal inflammation / infection especially in
immunocompromised patients (AIDS, transplant patients).
4. Evaluation
and follow up of active lymphocytic or granulomatous inflammatory process such
as sarcoidosis or tuberculosis
5. Evaluation
and follow up of drug induced pulmonary toxicity.
Clinical procedure
1. 2–10
mCi Ga–67 citrate is the typical dose administered.
2. Imaging
is performed 6–72 hours after.
a. Earlier
imaging times are favored for abscess detection.
b. Later
imaging is preferred for neoplastic disease.
3. Ga–67
citrate has physical half–life of 78 hours with photopeaks at
a. 93
keV –
40%
b. 184
keV –
24%
c. 296
keV –
22%
d. 388
keV –
7%
4. The
largest organ absorbed radiation dose (about 750 mrems/mCi) is the lower large
intestine
5. For
whole body scintigraphy, anterior and posterior views are obtained at a rate of
6–8 cm/minute or 25–35 minutes or 1.5–2.5 million counts whichever comes first.
6. For
spot views, 250,000 to 1,000,000 counts should be obtained.
7. Increase
gallium biodistribution may result from blood transfusion, chemotherapy or iron
therapy and recent trauma.
8. Decreased
gallium localization is seen in patients with gadolinium within 24 hours.
INDIUM–111
LEUKOCYTE IMAGING
Clinical indication
1. To
detect site of infection / inflammation in patients with granulocytosis and
fever of unknown origin
2. To
localize an unknown source of sepsis and to detect additional sites of
infection in patients with persistent or recurrent fever and a known infection
site.
3. To
survey for sites of abscess or infection in a febrile post–op patients without
localizing signs or symptoms.
4. To
detect sites and extent of inflammatory bowel disease.
5. To
detect osteomyelitis of different etiology.
6. To
detect mycotic aneurysm, vascular graft and shunt infection.
Radiopharmaceutical used
1. Leukocytes
are harvested from 40–80 ml venous blood for adult and 10–15 ml for pediatrics
with granulocyte of 1–3 x 103 cells/ml in ACD or heparin
anticoagulant. Leukocytes are labeled with In–111 oxine with methylene blue
used as stabilizer.
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here for full discussion on Blood Component Separation
2. Radiolabeled
leukocytes should be administered within 1–2 hours of cell labeling. Dextrose
in water solutions should not be used, as these can cause clumping of labeled
cells.
3. 70oF
temperature increase cell damage thus should be avoided.
4. Dosage
for adult is 0.3 – 0.5 mCi while for pediatrics is 0.25 – 0.5 MBq/kg.
5. In
adults, the injected Tc99m sulfur colloid dose is in the range of 8–10 mCi and
20–25 mCi for MDP.
6. Aspirin
and antibiotics will exhibit lower labeling efficiencies.
7. If
platelets are tagged along with leukocytes, a false positive image may result
because platelet concentrates in sites of thrombosis rather than areas of
infection.
Acquisition parameters
1. Imaging
is performed at 4 and 24 hours after labeled leukocytes are administered to the
patient. If the infection site is unknown, anterior and posterior views of the
head, abdomen, pelvis and chest should be obtained.
2. Indium–111
emits energy at 173 and 247 keV, both centered at 15–20% window.
3. Whole
body scan are acquired at a rate of 5–6 cm/minute which can last for 25 –35
minutes
4. Tc99m
sulfur colloid imaging is usually done after In–111 leukocyte imaging if there
is question concerning bone marrow distribution.
5. A
normal image demonstrates tracer activity in the spleen, liver and bone marrow.
Other Indium–111 labeled
radiopharmaceuticals
1. Oncoscint
a. 5–6
mCi Indium–111 chloride is mixed with buffing solution
b. The
buffered solution is then added to the antibody
c. The
mixture is incubated for 30 minutes
d. Since
the antibody is a protein that can form particles, the preparation is filtered
before intravenous administration
Oncoscint is a
monoclonal antibody to the tumor antigen TAG–72 that is associated with ovarian
and colorectal cancer. Because OncoScint is a human anti–murine antibody
(HAMA), it has to be tested for allergic reaction. Imaging maybe performed as
early as 2 days or as late as 5 days.
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here for full discussion on Tumor Markers
Click
here for full discussion on Hypersensitivity
2. Octreoscan
a. 3.3
mCi Indium–111 chloride is mixed with pentetriotide and incubated for 30
minutes at 25oC.
Octreoscan is
used in localizing metastatic tumors of neuroendocrine origin. This includes
pituitary and endocrine tumors, paraganglioma, medullary thyroid carcinoma,
carcinoids and small lung cancer. Octreoscan is an analog of octreotide, an
analog hormone, somatostatin and bind on somatostatin receptor on surface of
cells, concentrating in tumors with a high density for receptor sites.
Click
here for full discussion on Somatostatin (Gastrointestinal Gland)
Tc99m–LEUKOCYTE
IMAGING
Clinical indication
1. To
detect suspected sites of acute inflammation/infection in febrile patient with
or without localizing signs and symptoms.
2. To
detect and determine the extent of inflammatory or ischemic bowel disease.
3. To
detect and follow up musculoskeletal infection such as septic arthritis and
osteomyelitis
Radiopharmaceutical used
1. Leukocytes
are harvested from 20 – 40 ml venous blood for adult mixed with ACD
anticoagulant with minimum granulocytes of 2 x 109 cells/liter.
2. The
usual dose for adult is 5–10 mCi
3. Exametazime
(HMPAO) is a lipophilic complex which penetrates the leukocyte cell membrane
and is retained within the cells.
Acquisition parameters
1. The
pulse height analyzer is centered at 140 keV using a 15 – 20% window.
2. Early
imaging of the pelvis and abdomen is essential (bowel activity is seen in
20–30% of children by 1 hour and 2–6% of adults by 3–4 hours post– injection).
3. Spot
views should be at 800,000 counts/large field of view or 5–10 minutes.
4. Images
of limbs should be acquired for 10 minutes/view at 4 – 8 hours and at least 15
minutes/view at 16 – 24 hours.
BONE IMAGING
Indications
1. Staging
of malignant disease, screening of patients with primary tumors (e.g. breast,
lung, prostate carcinoma) known to metastasize readily to bone, evaluation of
response to therapy, localization of biopsy sites.
2. Evaluation
of primary bone neoplasms (e.g. Ewing’s sarcoma, osteogenic sarcoma); detection
of sites in other bones; detection of soft tissue metastases.
3. Diagnosis
of skeletal inflammatory disease (e.g. osteomyelitis)
4. Evaluation
of skeletal pain of unknown cause
5. Evaluation
of elevated serum alkaline phosphatase level of unknown origin
6. Determination
of bone viability when blood supply to the area is in question
7. Evaluation
of painful joint prostheses
8. Detection
of occult fractures (e.g. sports injury) not demonstrated radiographically
Procedure of the test:
1. Explain
to the patient the reason for the delay between tracer administration and
imaging.
2. Administer
15–20 mCi Tc99m MDP intravenously. If a flow study is requested, position
patient under the scintillation camera prior to tracer administration.
3. Unless
contraindicated, encourage the patient to drink four to six 8–oz glasses of
liquid and to void frequently during the delay before imaging. Hydration of the
patient helps clear the tracer from the body. Frequent voiding decreases the
bladder’s exposure to radiation.
4. Patient
should void immediately before imaging. A large amount of radioactive urine in
the bladder can obscure bony structures of the pelvis.
5. Imaging
can begin 3 hours after tracer administration.
6. Ascertain
patient has voided before proceeding with imaging.
7. Use
the spot image technique, whole body table technique or SPECT imaging technique
to acquire data.
Image findings:
1.
Normal tracer
distribution
a. The
radiopharmaceutical is normally taken up symmetrically throughout the skeleton.
Areas of normally increased activity include sacroiliac joints, anterior iliac
crests, sternum, nasopharyngeal area, shoulder joints and spine.
2.
Abnormal
tracer distribution
a. Abnormal
tracer distribution can include areas of increased tracer accumulation within
the skeleton itself or outside in soft tissue.
b. Extraosseus
activity is sometimes seen in the following sites: renal abnormalities, soft
tissue inflammation, neoplastic masses, female breast, acute MI.
c. Photopenic
areas (areas of decreased tracer accumulation) are usually related to diminish
blood flow to the area or to complete destruction or replacement of normal bone
tissue.
Three phase / Four–phase Bone
Imaging
1. When
an inflammatory process, such as osteomyelitis is suspected, dynamic or
multiple phase bone imaging may be helpful to the physician in making a
differential diagnosis.
2. In
this technique, the patient is first positioned under the gamma camera with the
affected area in the field of view. The standard tracer dose is administered as
a bolus injection while dynamic images are acquired beginning at the time of
injection and continuing for about 1 minute.
3. Immediate
static images are then acquired, followed by delayed images at 2– 4 hours. The
fourth phase consists of 24–hour delayed images.
4. Both
cellulitis and osteomyelitis demonstrate increased activity on the early
images. With osteomyelitis, however, the tracer concentration persists
throughout the delayed images.
Technical consideration:
1. Extravasation
of the tracer at the injection site may be construed as pathology or obscure
bony pathology underlying the area of infiltration.
2. There
may appear to be overall decreased activity concentration in the bones if a
significant amount of tracer is not administered intravenously. Imaging time
may need to be extended in this instance to achieve adequate counting
statistics.
3. Since
the tracer is excreted from the body throughout the urinary tract, radioactive
urine contamination is possible with young children or older incontinent
patients. Equipment should be protected and the patient should be checked for
contaminated garments or linens before imaging begins.
4. It
is important that patients void immediately prior to imaging the pelvis. Excess
activity in the bladder can obscure pelvic structures. Images of the pelvis
should be obtained first, if the spot view technique is being used. Separate
spot images of the pelvis may be necessary when whole body imaging is
performed.
5. Any
attenuating materials such as jewelry, belt knuckles, removable prostheses,
pocket contents or ECG leads, could cause a photopenic area on the image. Such
materials should be removed from the patient prior to imaging.
6. Contralateral
sides of bony structures must be positioned at the same angle and at the same
distance from the detector. Failure to do so may cause one side to appear to
have a greater tracer concentration than the other. Asymmetry of contralateral
sides may be falsely interpreted as an abnormality. It is equally important to
include all areas of interest on the bone images a problem sometimes arises
when certain parts of the skeleton, usually the arms, cannot be positioned
within the field of view during whole body imaging.
7. An
unexpected pattern of tracer distribution may indicate improper preparation of
the radiopharmaceutical and can degrade the quality of bone images. Excess free
pertechnetate appears as tracer concentration in the thyroid, salivary glands
and stomach. Liver uptake or increased soft tissue and kidney uptake can also
be indicators of radiopharmaceutical problem.
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