NON-SKELETAL DISTRIBUTION OF BONE-SEEKING RADIOPHARMACEUTICALS

Focal skeletal muscle uptake of 99mTechnetium-hydroxymethylene diphosphonate following peroneal nerve blocks in horses

We have observed focal skeletal muscle uptake of 99mTechnetium-hydroxymethylene diphosphonate (Tc-HDP), which could mimic a tibial lesion, in horses following peroneal nerve blocks. To characterize this observation further, 45 bone phase scintigrams were performed in 12 horses undergoing peroneal nerve blocks. Scans were performed before, and 1, 3, 7, and 14 days postblock. The superficial and deep branches of the peroneal nerve were blocked by injecting 10 ml of 2% mepivacaine in one limb and 20 ml in the other. Images were evaluated for uptake at the block site and uptake likely to mimic a tibial lesion. Regions of interest were placed over the block site and distal tibia. Count density ratios were used to estimate change in uptake intensity over time. The overall proportion affected was 0.52 (95% confidence interval [CI], 0.36-0.68; P < 0.001) 1 day postblock and 0.24 (95% CI, 0.13-0.40; P = 0.005) 3 days postblock. The overall proportion likely to mimic a tibial lesion was 0.19 (95% CI, 0.09-0.33; P < 0.001) 1 day postblock and 0.21 (95% CI, 0.09-0.40; P = 0.005) 3 days postblock. Focal skeletal muscle uptake was seen in only one horse 7 days postblock. Increased uptake intensity was associated with higher local anesthetic dose (P = 0.042). Peroneal nerve blocks cause focal skeletal muscle uptake of 99mTc-HDP on bone phase scintigraphy. This occurs in approximately 50% of blocked limbs and can mimic a tibial lesion on the lateral view in approximately 20% of blocked limbs.

Evaluation of technetium Tc 99m-labeled biotin for scintigraphic detection of soft tissue inflammation in horses

OBJECTIVE

To evaluate the use of technetium Tc 99m-labeled EDTA-biotin monomer ((99m)Tc-EB1) as a scintigraphic imaging agent for soft tissue inflammatory lesions in horses.

ANIMALS

6 healthy adult horses.

PROCEDURES

First (phase 1), the agent's safety and blood-tissue clearance and an appropriate imaging protocol were determined in 6 horses. Each horse was injected with (99m)Tc-EB1 (1.1 GBq, IV, once); images were acquired at intervals during the following 24-hour period. Subsequently (phase 2), inflammation was induced via injection of 200 mg (10 mL) of mepivacaine (0.4 mg/kg) into the right neck musculature and perineurally in the proximal palmar metacarpal region of the right forelimb of 2 horses. Six hours after mepivacaine injection, (99m)Tc-EB1 (2.2 GBq, IV, once) was administered; 8 hours after injection, comparative soft tissue images were acquired after administration of technetium (99m)Tc-hydroxymethylene diphosphonate ((99m)Tc-HDP; 7.4 GBq, IV, once).

RESULTS

After injections of (99m)Tc-EB1, physical examinations, CBCs, and serum biochemical analyses revealed no abnormalities in any horse. Blood clearance of (99m)Tc-EB1 was rapid (A phase, 2.2 minutes; beta phase, 58 minutes). Soft tissue uptake of (99m)Tc-EB1 was immediate and persisted for as long as 4 hours after injection. At 6 hours after IM and perineural mepivacaine injections, mepivacaine-induced inflammation was detectable by use of (99m)Tc-EB1.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that (99m)Tc-EB1 is safe for use in horses and can identify soft tissue inflammation without concurrent uptake in bone. Compared with (99m)Tc-HDP administration, use of (99m)Tc-EB1 extended the duration of soft tissue scintigraphic image acquisition.

Non-skeletal scintigraphy of the horse: indications and validity

Gamma scintigraphy is an established imaging modality in the horse and is principally utilised to investigate skeletal disease using bone-seeking radiopharmaceuticals. However, depending on the radiopharmaceutical and imaging sequence, scintigraphy can be used to investigate disease in virtually any organ system. In this article the indications and validity of scintigraphy as a clinical diagnostic tool to investigate non-skeletal disease in the horse are reviewed. These indications include: investigation of dental disease, identification of inflammatory foci, vascular lesions, muscle and tendon pathology, assessment of physiological function of the lungs, gastrointestinal tract and other organs. Some of the techniques described for use in the horse have not been validated fully and as a result non-skeletal scintigraphy requires further investigation and validation using well-designed prospective studies. Such information can be used by clinicians to make informed decisions regarding the clinical and economic issues associated with a specific scintigraphic technique and may help when interpreting the results.

Bone scintigraphy in the investigation of occult lameness in the dog

99mTechnetium methylene diphosphonate (99mTc-MDP) scintigraphy was performed in 14 dogs of different breeds after clinical lameness examination, radiography and synovial fluid analysis failed to localise lameness to a specific area of pain. The scintigraphic protocol included an intravenous injection of 17 MBq 99mTc-MDP/kg bodyweight and vascular, soft tissue and bone phase scans in standardised positions with a low-energy all-purpose collimator. Confirmation of diagnosis was achieved in nine dogs by arthroscopy, repeated lesion-orientated radiography, computed tomography and response to treatment. In seven cases, bone phase scans showed single elbow uptakes, in two cases unilateral limb uptake, and in one case each a single shoulder and tibia uptake; in three cases there was no increased uptake. Vascular and soft tissue phase images did not reveal additional information. Diagnosis of humeral condyle fissures, a fragmented medial coronoid process, panosteitis and arthropathy was possible in nine cases. Skeletal pathology was ruled out in three normal scintigrams. In two dogs with unilateral uptake of multiple joints, no diagnostic benefit was gained from scintigraphy. The highly sensitive and relatively specific uptake allowed localisation and characterisation or exclusion of skeletal lesions in most dogs.