Bone scintigraphy is a sensitive and commonly used tool for localization of obscure or multifocal sources of bone-related lameness in horses.1–3 Unlike other traditional diagnostic imaging techniques, scintigraphy can readily be used to survey multiple areas of the equine skeleton in a single diagnostic procedure. It can also be used to identify subtle abnormalities or those in their early stages of development as well as lesions that cannot be evaluated via radiography or ultrasonography3–5
In contrast, scintigraphy is used infrequently for the diagnosis of soft tissue inflammation in horses because of the limitations of other available radiophar-maceuticals. Bone agents such as 99mTc-HDP and 99mTc-methylene diphosphonate have been used for imaging of soft tissue inflammation. However, the time interval during which images can be acquired (imaging window) associated with either agent is limited (approx 10 to 15 minutes) because each is rapidly cleared from soft tissues and are taken up by bones.5–9 In addition, image interpretation is made difficult by concurrent isotope uptake in bones. Sodium pertechnetate also has a short imaging window, and it does not persist in inflamed soft tissues.10 The use of indium In Ill-labeled leukocytes exposes patients and personnel to high levels of radiation11; because of its half-life of 2.8 days, its use results in prolonged hospitalization of treated animals before radioactivity decays to safe levels. Technetium Tc 99m-labeled leukocytes also require ex vivo labeling of cells, which can be expensive.10 Although other advanced imaging techniques, such as computed tomography and magnetic resonance imaging, are capable of detecting soft tissue inflammation, their application is too often limited in equine practice by patient size or the need for general anesthesia.
A need therefore exists for an alternative method of detecting subtle or occult soft tissue inflammatory lesions. The radiopharmaceutical 99mTc-EBla offers several potential advantages. This 99mTc-based agent is readily available and inexpensive and has a short half-life of 6 hours. In addition, it provides good tissue penetration and, compared with other radionuclides,2,7 the radiation dose to patients and attending personnel is low. This radiopharmaceutical also contains biotin, a natural component of the B vitamin complex; the EDTA moiety chelates the 99mTc.
For localization of soft tissue infection, inflammation, and neoplasia in humans, radiolabeled biotin has been used extensively as part of a 2- or 3-step targeting system with either avidin or streptavidin.12–16,b,c However, to our knowledge, there have been no previously published reports of the use of radiolabeled biotin in horses. The purpose of the study reported here was to evaluate the use of 99mTc-EBl as a scintigraphic imaging agent for soft tissue inflammatory lesions in horses. The objectives of phase 1 were to determine the safety and blood-tissue clearance of 99mTc-EBl and to establish an appropriate imaging protocol for its use in horses. The objectives of phase 2 were to determine whether 99mTc-EBl could be used to detect experimentally induced soft tissue inflammation and to compare images generated after administration of 99mTc-EBl with soft tissue-phase images generated after administration of 99mTc-HDP. We hypothesized that 99mTc-EBl could be used safely in horses and that it would have prolonged uptake in focal areas of soft tissue inflammation, compared with uptake of 99mTc-HDP.
TechnetiumTc 99m-labeled hydroxymethylene diphosphonate
TechnetiumTc 99m-labeled EDTA-biotin monomer
Instant thin-layer chromatography
Region of interest
Provided by M. Rusckowski, University of Massachusetts. Worcester, Mass.
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Instant thin-layer chromatography paper, Pall Corp, East Hills, NY.
Acetone HPLC grade, Lab Safety Supply, Hanover, Pa.
Whatman chromatography paper, Whatman International, Maidstone, Kent, England.
Large field-of-view planar scintillation camera, IS2 Research Corp, Ottawa, ON, Canada.
Mirage processing application, Segami Corp, Columbia, Md.
Dormosedan, Pfizer Animal Health, Exton, Pa.
Abbocath-T, Abbott Ireland, Sligo, Ireland.
Foley catheter, Cardinal Health, McGaw Park, I11.
Oxidronate, Technescan-HDP, Mallinckrodt Medical, North Attleboro, Mass.
Carbocaine-V, Pfizer Inc, New York, NY.
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