George A. Wilson

Kinetics and Imaging Characteristics of 99mTc-Labeled Complexes Used for Bone Imaging1

Activity levels of 99TC-labeled compounds, 18F, and 85Sr were obtained at 1, 3, and 5 hr. postinjection in normal and healing fractured bone and in soft-tissue rat specimens. Serial diagnostic bone images and blood and urine kinetics were obtained in patients with each of the TC-labeled compounds. Computer-processed images were used to evaluate in vivo kinetics. 99mTC pyrophosphate provides the best overall characteristics for bone imaging. Improved quality and bioassay procedures are required, however, before any one agent can be designated the radiopharmaceutical of choice for diagnostic bone imaging.

99mTc Pyrophosphate for Diagnostic Bone Imaging

The kinetics and imaging characteristics of 99mTc-labeled stannous pyrophosphate were evaluated in 30 patients. Blood chemistries, urinalyses, serial blood activity measurements and 24-hour fractionated urine activity assays were obtained in selected patient studies. Digital gamma camera images were recorded on magnetic disk and quantitatively analyzed. Total body rectilinear scans were also recorded. Results indicate that 99mTc pyrophosphate is useful for bone imaging. Preparations yielded reproducibly high binding efficiencies; soft tissue clearance was rapid; no pharmacologic effects were observed; and count levels and contrast between lesion-involved bone and normal bone were adequate. Image quality was acceptable between 1 and 6 hours after administration. Abnormal areas were detected at all imaging times; however, the best image quality was usually observed in the delayed views.

The usefulness of the dynamic phase in pertechnetate thyroid imaging for solitary hypofunctioning nodules.

One hundred patients, each with a solitary thyroid nodule detected by clinical palpation, underwent three-phase Tc-99m pertechnetate thyroid imaging. The degree of perfusion of the thyroid nodule was classified as hypoperfused, euperfused, or hyperperfused compared to the remainder of the gland by a consensus of three nuclear medicine physicians. The nodules were subsequently biopsied, and the degree of perfusion of the nodules was correlated with their histologic diagnosis. Twenty-two nodules were classified as hyperperfused, 64 as euperfused, and 14 as hypoperfused. Malignancy rates of the hyperperfused, euperfused, and hypoperfused nodules were 36%, 31% and 0%, respectively. This seems to indicate that malignant thyroid nodules demonstrate a degree of perfusion at least equal to or greater than the rest of the thyroid gland. Conversely, none of the hypoperfused nodules was found to be malignant. The perfusion phase of thyroid imaging may provide useful clinical information regarding possible malignancy of a thyroid nodule.

Technetium Tc 99m plasmin in the diagnosis of inflammatory disease

The localization characteristics of technetium Tc 99m plasmin were studied in experimental animals to investigate the use of99mTc-plasmin for imaging inflammatory processes. At various times after abscess induction using turpentine in rats, the in vivo distribution properties of99mTc-plasmin, gallium citrate Ga 67,125I-fibrinogen, and99mTc-human serum albumin (HSA) were studied by gamma-camera imaging. The in vivo binding of each radiopharmaceutical was also tested in rat and human plasma clots. Region-of-interest analyses of gamma-camera images showed relatively poor99mTc-plasmin localization at sites of abscess formation. The ratio of abscess-to-control activity of this radiopharmaceutical did not exceed that of67Ga,125I-fibrinogen, or99mTc-HSA. In vitro assays of each of the radiopharmaceuticals in plasma clots showed99mTc-phasmin and125I-fibrinogen to have the best localization characteristics.

The interactions of99mTc phosphorus radiopharmaceuticals and human serum proteins

Dialysis and precipitation methods have been used to study the binding affinity of selected technetium-99m phosphorus radiopharmaceuticals to human serum proteins. The binding affinities of three different99mTc bone imaging agents were found to be inversely related to their respective clearance rates from blood in vivo. The binding order showed99mTcPPi>99mTcHEDP>99mTcMDP. The99mTc phosphorus radiopharmaceuticals were bound primarily to alpha globulins. The results suggest that the binding of99mTc phosphorus radiopharmaceuticals to human serum proteins in blood is largely determined by their affinities to the alpha globulins.