technetium-tc-99m-lidofenin and iminodiacetic-acid

Tests for liver function have by and large centered around clinical laboratory diagnostic procedures for a number of years. Besides these, radiographic imaging procedures, including oral cholecystography and intravenous cholangiography, serve a very useful purpose, but several of them are invasive and involve a certain degree of risk from the administered contrast media as well as discomfort to the patient. The cholescintigraphic procedures, though noninvasive, have not played a significant role in the evaluation of hepatobiliary disorders prior to the introduction of the currently available. 99mTc-labeled IDAs. These new hepatobiliary agents offer many advantages over the previously utilized radiopharmaceuticals (131I-rose bengal in particular) in terms of the high degree of specificity for localization in the gallbladder with rapid extraction rates by the polygonal cells of the liver and very low excretion via the GU tract. A detailed understanding of the structure distribution relationship of the various groups in the complex enable the design of agents with an improvement in hepatobiliary specificity and other desirable characteristics. In many clinical situations, even in patients with high bilirubin levels, the 99m-Fc-labeled IDAs offer far superior clinical information over the alternative diagnostic imaging modalities. Further, the absorbed radiation dose imparted to the critical organs is far lower than with the older agents. Thus, the introduction of the cholescintigraphic procedures with the 99mTc-labeled IDAs have ushered in a new phase in the diagnostic workup of patients with impaired hepatocellular function and other biliary disorders.

Topics: Biliary Tract; Humans; Imino Acids; Iodine Radioisotopes; Liver; Organotechnetium Compounds; Pyridoxine; Radiation Dosage; Radioisotopes; Radionuclide Imaging; Sodium Pertechnetate Tc 99m; Technetium; Technetium Tc 99m Disofenin; Technetium Tc 99m Lidofenin

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.

Topics: History, 20th Century; Imino Acids; Nuclear Medicine; Sarcosine; Technetium; Technetium Tc 99m Lidofenin