99mTechnetium labelled Escherichia coli.

Samples of a culture of unlabeled Escherichia coli were incubated with different concentrations of stannous chloride for various time periods. 99mTc (26.0 MBq) was added to each preparation and the results showed a labelling yield of 98% for E. coli. Since the bacterial viability of 99mTc-E. coli and E. coli did not show any statistical differences, these results demonstrate that labelling of E. coli with 99mTc does not modify the bacterial viability, and the radiolabelled bacteria may be a good model to study bacterial translocation.     

External radiation exposure of personnel working with 99mTechnetium

Radiation from ^99mTc was measured at typical locations in those areas of a nuclear medicine department where approximately 50 Ci ^99mTc is used per year. In addition, measurements of shielded and unshielded syringes containing ^99mTc-labelled radiopharmaceuticals were carried out. From these data radiation exposure of hands and of the whole body of personnel was calculated, taking into consideration the mean working times in the areas and the times of direct and indirect handling of ^99mTc. They were compared with the mean values obtained by personnel dosimetry through quartz fibre pocket dosimeters and TLD finger ring dosimeters. The whole body radiation calculated from local measurements for technicians (163±15 mR/year) (mean±SE) and for physicians (260±15 mR/year) was very low judged by the maximum permissible dose of 5,000 mrem/year and correlated well with those of personnel dosimetry (165±15 R and 265±15 R/year respectively). Although local radiation was rather high during generator elution and while preparing radiopharmaceuticals (13±1.2 mR/h) the radiation exposure to the hands of the radiochemists measured by the TLD finger ring dosimeter was low (2.6±0.2 R/year). This was attained by consistently using long distance tools in order to avoid direct contact with ^99mTc-containing vials and syringes. The most critical point of radiation exposure in our investigation were the finger tips during injection of ^99mTc, when syringe shielding was not used (80–130 mR/injection of 10 mCi). Under our conditions this amounts to 330–560 R/year when a total of 40 Ci is injected by the same physician. This by far exceeds the maximum permissible dose of 60 rem/year. The dose can be reduced extensively to only 2–3 R/year when tungsten shielding of the syringe is consistently used.     

Mechanism of hepatic extraction of gelatinized 99mTechnetium sulfur colloid

Hepatic extraction, cellular and subcellular localization of gelatin stabilized Tc-99m sulfur colloid was studied in the rat model with time sequenced microautoradiography from 15 min to 24 h following I.V. administration of the tracer. Hepatic lobular and cellular distribution, quality and quantity of focal grain pattern, grain clusters, remained essentially constant for the period of study. Grain clusters were associated predominantly with Kupffer cells lining the peripheral segment of hepatic lobular sinusoids. Subcellular localization of gelatinized Tc sulfur colloid, stained prior to the I.V. administration with osmium tetroxide, was demonstrated with a transmission electron microscope in unosmicated liver tissue. Extracted Tc sulfur colloid particles were attached in groups to cytoplasmatic membranous intrasinusoidal projections of activated Kupffer cells. Intracytoplasmatic phagocytosis was not demonstrated. The kinetic arrest and en groupe extraction of Tc sulfur colloid particles at the Kupffer cell membrane suggests a specific membrane receptor site and specific Tc sulfur colloid particle-plasma protein interaction at the time of extraction. Hepatic extraction of gelatinized Tc sulfur colloid thus reflects primarily extra and intra hepatic hemodynamics and does not serve as an indicator of phagocytic hepatic reticuloendothelial system function.Medical Research Information System (MRIS) #3080     

A quantitative clinical comparison of three 99mTechnetium labeled brain imaging radiopharmaceuticals

In a comparison study of three commonly employed 99mTc brain imaging pharmaceuticals, 16 patients with proven brain lesions had imaging performed with DTPA, glucoheptonate, and pertechnetate over a short interval of time. Lesion detectability was assessed by a data processing system which evaluated average lesion-to-background activity ratios for each patient examination. Statistical analysis of the resultant data demonstrated a significant improvement (20%) in lesion-to-background ratio in favor of one hour delayed DTPA images versus two hour delayed pertechnetate images. Comparison of one hour delayed DTPA images with one hour delayed glucoheptonate images did not reveal a significant difference in lesion-to-background ratio. The authors conclude that both Tc-DTPA and Tc-glucoheptonate are superior alternatives to pertechnetate when employed in the manner described.     

Aspects of 99mTechnetium binding from an ethane-1-hydroxy-1,1-diphosphonate-99mTc complex to bone

In vivo and in vitro experiments were under-taken to study factors influencing ^99mTc binding from an EHDP complex to bone. In vivo ^99mTc (IV) complexes of EHDP, ATP, citrate and ascorbate were injected into rats. The effects of pretreatment of rats with EHDP on EHDP- and ATP-Tc (IV) injection were examined. Citrate and ascorbate gave no bone scintigram, ATP gave a bone scintigram inferior to EHDP-Tc (IV). EHDP pretreatment deteriorated EHDP- and ATP-Tc (IV) scintigrams. Micro-autoradiography showed that Tc-activity is only found in the bone matrix of 15-day-old rats and that EHDP-pretreatment diminishes this labelling. In vitro experiments showed that EHDP also diminishes labelling of hydroxyapatite by EHDP-Tc (IV), but that an excess of Ca can augment this labelling. It is suggested that Tc (IV) binds to bone because EHDP binds to bone, permitting released Tc (IV) to bind to bone separately.     

Kinetics of 99mTc-labeled pyrophosphate and polyphosphate in man.

Thekinetic of 99mTc-labeled pyrophosphate were compared with those of polyphosphate in ten patients in a combined study. Both agents cleared from the blood in a biexpoential fashion. The clearance half-time of Exponent I was the same for both and was shorter than the clearance half-time of Exponent ii. Urinary excretion of both agents was the same during the first hour but during the next 3 hr Tc-pyrophosphate cleared at a slightly more rapid rate, resulting in lower blood background radioactivity. Both agents were bound loosely to plasma proteins, mainly to globulin fractions. The sensitivity of lesion detection was similar for both. Excellent bone images were obtained with both agents. The images with Tc-pyrophosphatewere consistently superior owing to the low blood background and they took less time to accumulate an identical number of counts from identical regions. With the amount of 99mTc-complex used, no hyocalcemia or tetany was noted, nor was there any significant effect on 1-hr serum levels of inorganic phosphours and alkaline phosphatase. Four hours after injection, 9.5% of the dose of Tc-pyrophosphate was circulating in blood, 31.7% was excreted in urine, and the remaining 58.8% was taken up by bone and other tissues. The corresponding values with Tc-polyphosphate were 12.5% in blood, 29.0% in urine, and 58.5% in bone and other tissues. Among the soft tissues, the genitourinary system is most consistently visualized. It is concluded that both Tc-pyroposphate and Tc-polyphosphate are excellent skeletal-imaging agents and that Tc-pyrophosphate appears slightly superior to Tc-polyphosphate.     

Cranial cholesteatoma: unusual 99mTc-Sn polyphosphate and 99mTc-pertechnetate scintiphotos.

Results of the brain and bone scintigraphy in a case of cranial cholesteatoma are described and the differential diagnosis is discussed. With both techniques, the lesion is characterized by diminished central and increased peripheral activity.