Nouria Salehi

In vitro evaluation of canine leukocytes radiolabeled in whole blood with 99mTc stannous colloid

INTRODUCTION Technetium-99m stannous colloid ((99m)TcSnC)-labeled leukocytes are used to investigate a variety of inflammatory diseases in human medicine. The present study investigates the in vitro behavior of canine leukocytes labeled in whole blood with (99m)TcSnC. METHODS Blood samples from 10 healthy dogs were labeled with (99m)TcSnC using a standard procedure. The distribution of radioactivity among blood components (plasma, leukocyte layers and erythrocytes) was measured following separation of the radiolabeled samples across Histopaque density gradients. Phagocytic function of labeled and unlabeled leukocytes was estimated using zymosan particles. Labeling retention by leukocytes was determined at 1, 3, 4 and 7 h postlabeling. RESULTS The mean+/-standard error percentage of radioactivity associated with plasma, erythrocyte and leukocyte fractions was 2.0+/-0.21%, 55.5+/-0.60% and 42.5+/-0.54%, respectively (the last comprising 70.2+/-0.83% in polymorphonuclear leukocytes and 29.8+/-0.83% in mononuclear leukocytes). Labeled canine leukocytes had a phagocytic activity of 91.3+/-0.28% (control, 91.7+/-0.26%). The radiolabeled canine leukocytes retained 94.1+/-0.30% of radioactivity at 7 h postlabeling. CONCLUSIONS Radiolabeling of canine leukocytes in whole blood with (99m)TcSnC has minor adverse effect on their phagocytic function. The radiolabeled canine leukocytes retained a large percentage of radioactivity for at least 7 h postlabeling.

Conversion of an old gamma camera to a bone mineral densitometer.

A 1974-vintage 25 cm field of view gamma camera was converted to a bone mineral densitometer using a purpose-built converging collimator with attached C-arm holding a 250 mCi gadolinium (Gd) 153 source. After addition of a second pulse-height analyser, increasing the high voltage gain and connecting to a digital computer, spinal and hip bone mineral density measurements were made. Accuracy of 2% and long-term reproducibility of 2.7% were obtained using an anthropomorphic bone phantom. For lumbar spine measurements in normal volunteers, long-term reproducibility was 3.2% and for osteoporotic (spinal fracture) patients (mean density 831 mg cm-2) reproducibility was 3.7%.

Tailoring 99mTc Macroaggregated Albumin administration to optimize patient dose reduction

In the ever-changing field of nuclear medicine, best-practice considerations cannot simply go unchallenged for months and years, with the need to minimize radiation exposure to patients highlighted in “as low as reasonably achievable” principles. The Australian Radiation Protection and Nuclear Safety Agency reports that the dose for 99mTc-macroaggregated albumin (99mTc-MAA) administered should be 180–200 MBq. An objective of imaging in pulmonary embolism, or indeed any diagnostic procedure involving radiation, is to minimize radiation exposure without sacrificing image quality and diagnostic accuracy. The amount of radiation involved must be considered together with imaging protocols. Our aim was to reduce the amount of 99mTc-MAA administered without compromising the diagnostic quality of the scan. Methods: To achieve a ventilation-to-perfusion ratio of 1:4, we ventilated the patient as per standard protocol and then placed intravenous access into the patient. For the perfusion component, 180–200 MBq were prepared in a 2-mL injection. Aliquots of 0.5 mL of 99mTc-MAA were administered every 30 s followed by a 5-mL saline flush until the required ventilation-to-perfusion ratio was achieved. Results: With this protocol, the average administered dose was 105 ± 20.7 MBq (vs. 180 ± 5.3 MBq, P < 0.0001). Conclusion: By individually tailoring the administered dose, diagnostic quality is maintained while achieving a significant dose reduction.

Biodistribution of canine leucocytes labelled with technetium-99m stannous fluoride colloid in whole blood and their ability to localise to sites of induced inflammation.

This study assessed the biodistribution of autologous leucocytes radiolabelled with technetium-99m stannous fluoride colloid (99mTcSnC) for detection of foci of induced inflammation in dogs. Venous blood was collected from seven healthy dogs and incubated with 99mTcSnC for 1h at room temperature. Radiolabelled samples were injected intravenously (IV) and the dogs were scanned using a gamma camera. Another seven healthy dogs were injected intradermally with tumour necrosis factor alpha and then IV with 99mTcSnC radiolabelled autologous blood 3h later before being scanned. The radiolabelled leucocytes localised to sites of inflammation by 30 min post-injection. IV injection of autologous leucocytes radiolabelled with 99mTcSnC appears to be a sensitive method for localisation of induced foci of inflammation in dogs.

Tc-99m MIBI scan in atypical chest pain. Exclusion of myocardial ischemia and acute cholecystitis.

A 33-year-old woman with known cholelithiasis had fever and right upper quadrant pain. A clinical diagnosis of acute cholecystitis was made. Before cholecystectomy, she complained of atypical chest pain. To exclude the possibility of myocardial ischemia, the patient was injected with Tc-99m sestamibi at the time of chest pain. SPECT images were performed 1 hour after injection. These showed normal myocardial perfusion and therefore ischemia was excluded. On planar images the gall bladder was visualized confirming a patent cystic duct; thus, the diagnosis of acute cholecystitis was also discounted. Surgery was deferred, and elective cholecystectomy 1 month later confirmed chronic cholecystitis. In this case, Tc-99m sestamibi not only excluded myocardial ischemia, but also excluded acute cholecystitis.