SP13:Infection Scintigraphy Flashcards
Which of the following is true of 67Ga citrate- and 111In-labeled leukocytes?
(a)Both require the use of a medium-energy collimator.
(b) Both can be used to effectively image neoplasms and infections.
(c) Both have three gamma peaks available for imaging.
(d) All of the above.
(e) (a) and (b) only.
(a) 67Ga emits gamma rays of 93, 184, 269, and 394 keV. 111In emits gamma rays of 172 and 247 keV, so choice c is not true. Labeled leukocytes are used for infection imaging rather than neoplasms. Medium-energy collimation is used for both.
In general, the best radiopharmaceutical to use for a suspected abdominal abscess is:
(a)67Ga citrate
(b) 111In-labeled leukocytes
(c) 111In satumomab pendetide
(d) 111In octreotide
(b) It is best to use a radiopharmaceutical with less gastrointestinal excretion; therefore, 67Ga should be excluded. Octreotide is used for tumors with somatostatin receptors, and satumomab pendetide is a monoclonal antibody used mainly for colorectal and ovarian cancers, so these are not helpful. 111In-labeled leukocytes would be useful; GI activity will not be present when disease is absent.
For imaging of inflammation or infection, leukocytes may be labeled with:
(a)111In oxine
(b) 99mTc exametazime
(c) 67Ga citrate
(d) All of the above
(e) (a) and (b) only
(e) Leukocytes are labeled with 111In and 99mTc for infection imaging, but 67Ga-labeled leukocytes are not used clinically.
The images in Fig. 1 were obtained 24 h following the injection of radiopharmaceutical to visualize infection in the right leg. The radiopharmaceutical used was: (high activity in liver and spleen)(no activity in bowel and nasopharyngeal)
(a)99mTc sulfur colloid
(b) 111In-labeled WBCs
(c) 67Ga citrate
(d) 99mTc exametazime
(b) It can be assumed, because of the high activity present at 24 h, that the image was not obtained using a 99mTc radiopharmaceutical. One would expect to see bowel and nasopharyngeal activity if 67Ga were used.
If platelets are inadvertently labeled along with leukocytes during labeling with 111In oxine for imaging infection, the resulting scan may be:
(a)False negative
(b)False positive
(b) Inadvertently labeled platelets may show thrombosis.
The collection of whole blood for leukocyte labeling should be performed:
(a)With a small-bore needle
(b) Through an existing IV line
(c) Using a heparinized syringe
(d) With a shielded syringe
(c) To prevent clotting, either heparin, ACD solution, or other anticoagulant should be used in the collecting syringe. Heparin is less desirable as some patients display hypersensitivity. Small-bore needles may damage cells, and, as there is not yet activity present, no syringe shield is needed.
To screen for infection in a severely leukopenic patient, the best choice of radiopharmaceutical would be:
(a)99mTc-labeled WBCs
(b) 67Ga citrate
(c) 111In-labeled WBCs
(d) 99mTc sulfur colloid
(b) Patients who are leukopenic have too few white blood cells, so labeling their leukocytes may not be feasible, ruling out choices a and c (although donor cells could possibly be used). 99mTc sulfur colloid would not be useful for infection screening, so 67Ga citrate is the correct choice.
Gravity sedimentation involves the settling of cells:
(a)After centrifugation
(b) After time has passed
(c) After the syringe or test tube is inverted
(d) After the sample has been placed over a magnet
(b) Gravity sedimentation is the settling of solids to the bottom of a liquid based on weight and does not require centrifugation or magnets. It may be used for separation of erythrocytes and is often facilitated by the addition of hetastarch to increase the attraction of erythrocytes to one another.
The most appropriate dose to inject for imaging inflammation with 111In-labeled leukocytes is:
(a)0.5-1.0 mCi
(b) 2.0-4.0 mCi
(c) 5-10 mCi
(d) 6-8 mCi
(a) Five hundred uCi to 1.0 mCi of 111In oxine-labeled leukocytes is a common dose range for imaging infection. Using 99mTc exametazime allows more activity to be administered and offers a shorter injection to imaging time.
67Ga is often used with three-phase bone scans to detect:
(a)Arthritis
(b) Lung metastases
(c) Osteomyelitis
(d) Avascular necrosis
(e) Rib fractures
(c) The immediate and blood pool phases of bone scans can be used to differentiate cellulitis and osteomyelitis; 67Ga citrate is a helpful addition in cases of complicated osteomyelitis.
On planar abdominal images obtained with 67Ga citrate, suspicious activity is noticed. Which technique would be the first choice for further investigation of that activity?
(a)Sequential SPECT scanning to observer change in the activity.
(b) Subtract images obtained with 99mTc sulfure colloid.
(c) Hydrate the patient and encourage voiding before reimaging.
(d) Perform another exam with 111In leukocytes.
(a) If scanning for infection, the 111In leukocyte exam could be used, but the radiation dose to the patient might be avoided by obtaining further images over time to confirm whether the activity is changing as gallium is excreted through bowel. Hydration and voiding are not helpful in ruling out bowel excretion of gallium, neither are subtracted liver/spleen images. Laxatives or enemas may also be of help.
A patient has suspected osteomyelitis of lumbar spine. Which of the following study is best indicated?
(a)Triple-phase bone scan
(b) 111In-WBC scan
(c) 99mTc-WBC scan
(d) 67Ga citrate scan
(d) 67Ga provides high sensitivity for the diagnosis of vertebral osteomyelitis.
A patient has suspected abdominal infection. Which of the following study is best indicated?
(a)Triple-phase bone scan
(b) 111In-WBC scan
(c) 99mTc-WBC scan
(d) 67Ga citrate scan
(b) 111In-WBC scan is the best choice. 99mTc-WBC scan and 67Ga citrate scan both have physiologic activity in the abdomen and thus complicate the study. Bone scan has no role here.
To evaluate suspected infection in pediatric patients, _____ is preferred because of _____:
(a)111In-WBC scan, better image quality
(b) 111In-WBC scan, lower dose
(c) 99mTc-WBC scan, better image quality
(d) 99mTc-WBC scan, lower radiation
(d) 99mTc-WBC scan is preferred in pediatric patients, due to lower radiation.
When 111In-WBC scan is used to evaluate osteomyelitis, 99mTc sulfur colloid imaging is commonly included because 99mTc sulfur colloid imaging may:
(a)Increase the sensitivity of 111In-WBC scan
(b) Increase the specificity of 111In-WBC scan
(c) Decrease nonspecific uptake of 111In-WBC imaging
(d) Increase specific uptake of 111In-WBC imaging
(b) 99mTc sulfur colloid imaging help to determine if increased 111In-WBC activity is due to excess of bone marrow tissue, thus increase the specificity of 111In-WBC scan.
