Correlation of bioscintigraphy, contrast venography, and iodine-125 fibrinogen uptake test.

In 40 patients believed to have deep venous thrombosis, bioscintigrams performed with I-123 fibrinogen were available for comparison with either contrast venograms or I-125 fibrinogen uptake tests. If either contrast venography or the fibrinogen uptake test was accepted as a standard for comparison, the accuracy of bioscintigraphic imaging was 90%. Most discrepancies between the procedures could be interpreted as due to heparin treatment, although bioscintigrams often were positive in patients treated with heparin for a short interval of time. Additionally, bioscintigrams provided information to distinguish venous thrombosis from other sources for local accumulation of radioactivity. Bioscintigraphy seems to be a promising noninvasive method for the detection of deep venous thrombosis of the lower extremities.

Work in progress. Gastrointestinal ulcerations: detection using a technetium-99m-labeled ulcer-avid agent.

Technetium-99m-labeled sucralfate, an ulcer-avid material, was shown in preliminary animal and human studies to be stable in vivo with good sensitivity. Eight experimentally produced discrete gastric ulcers in three rabbits were visualized using this material. Of seven human studies, four studies were true-positive and three were true-negative. It is suggested that Tc-99m-labeled sucralfate may prove to have significant clinical advantages for the evaluation of gastrointestinal ulcer disease and other diseases that are associated with loss of mucosal integrity. The method for labeling sucralfate with Tc-99m was developed by the authors.

Clinical experience with 99mTc-disofenin as a cholescintigraphic agent.

99mTc-disofenin, a derivative of iminodiacetic acid, was used for cholescintigraphy in 6 volunteers (in addition to assessment of blood and urine clearance) and in 82 patients referred for evaluation of hepatobiliary tract disease. This radionuclide was cleared rapidly from the blood by the hepatocytes, which permitted satisfactory to excellent images of the hepatobiliary system; interference by renal activity was seen in only 9/82 patients (11%). Acute cholecystitis was correctly diagnosed in 20 patients, although 9 (45%) had jaundice; bilirubin levels ranged from 1.2 to 7.6 mg/dl. The biliary tract was normal in 16 of the 27 patients with jaundice (60%).

Renal clearance and extraction parameters of ortho-iodohippurate (I-123) compared with OIH(I-131) and PAH.

o-[131I] iodohippurate [OIH(I-131)] has been used for many years in the estimation of effective renal plasma flow. This compound suffers from low photon yield and poor images when the quantity used is limited to stay within a reasonable radiation dose. To test the validity of substituting I-123 for I-131, a series of experiments was performed in a surgically prepared dog model. The extraction ratios and clearance values OIH(I-123) prepared from radionuclidically pure I-123 were compared with those of commercial OIH(I-131) and PAH. The extraction ratios for OIH(I-123) and OIH(I-131) were 0.65 and 0.67, representing 0.86 and 0.88 that of PAH, respectively. The clearance values (cc/min/kg) for the I123 and I-123) can be used to estimate effective renal plasma flow; moreover, because of the high yield within an acceptable radiation dose range, images of good quality can be produced.

Catabolism and protein binding of Tc-99m pyridoxylideneglutamate.

Various Tc-99m-labeled compounds have been suggested as replacements for [I-131] rose bengal for imaging of the hepatobiliary system. Among such compounds are Schiff's bases, which are tin-free Tc-chelates easily prepared by 30-min autoclaving of an equimolar mixture of pyridoxal and an amino acid at pH 8.5. We have compared the properties of several Schiff's bases, including Tc-99m pyridoxylideneglutamate (Tc PyG) with [I-131] rose bengal. Under conditions described, Tc-PyG can be prepared free of Tc-pyridoxal and with less than 2% TcO4- radiochemical impurity. Blood clearance and biliary excretion were studied in three animal models, and in normal human volunteers. In all animal models, Tc-PyG initially cleared from the blood more rapidly than rose bengal, but a significant amount of Tc-PyG was excreted in the urine, this in contrast to [I-131] rose bengal which was almost completely excreted through the biliary system. Species differences were observed in the degree of urinary versus biliary clearance of Tc-PyG, with significantly greater urinary excretion in dogs than in monkeys and rabbits. Replacing glutamate with other amino acids did not significantly increase the blood clearance rate or decrease urinary excretion, so that Tc-PyG appears to be at least as good as any of the others studied. Tc-PyG was only 20% bound to plasma proteins, and electrophoretic and chromatographic studies did not reveal any in vivo changes of Tc-PyG before excretion in urine or bile.

Assessment of conventional criteria for the early diagnosis of thrombophlebitis with the 125I-fibrinogen uptake test.

Analysis of 55 positive tests of a total of 300 tests by conventional criteria revealed that 125I-fibrinogen provides useful information early enough for clinical management. Of the tests which were ultimately interpreted as positive by conventional criteria, at least one was positive at 3-4 hours in 67% of the tests and 98% of the tests were positive at 24 hours after the administration of 125I-fibrinogen. A 20% difference between contralateral identical locations of the legs and a 20% difference between adjacent locations of the ipsilateral leg were found with almost equal frequency in the positive tests, whereas a 20% increase at the same location was less sensitive. The 125I-fibrogen uptake test is a simple and accurate technique for early diagnosis of active thrombophlebitis.

Technetium-99m pyridoxylideneglutamate (P.G.) cholescintigraphy.

Technetium-99m P.G. cholescintigraphy was performed in 27 human volunteers and 81 patients referred for hepatobiliary tract disease. The gallbladder, biliary system, and gastrointestinal tract were well visualized in the normal patients and volunteers. The gallbladder was not visualized in 22 patients with histologically proved cholecystitis with cystic duct obstruction. Nine patients with complet extrahepatic obstruction of the common bile duct were correctly diagnosed. Hepatocellular disease and incomplete obstruction, with and without jaundice, were diagnosed with this technique. Oral cholecystography is superior to this method for the detection of cholelithiasis in nonjaundiced patients.

Production and characteristics of 125Xe: a new noble gas for in vivo studies.

Radionuclides of the noble gases are extensively used to assess ventilation and blood flow in clinical and investigative studies. Xenon-133 is most commonly used but is not optimal for these in vivo studies. Xenon-125 has better physical characteristics and can be produced with a cyclotron by a 127I(p,3n)125Xe reaction; this reaction results in a maximum of 25 mCi/gm/cm2/muA-hr for 31-MeV protons. Under actual production conditions, 11 mCi/muA-hr were collected. Xenon-125 decays by electron capture with a 17.2-hr half-life and contributes less radiation per dose of radioactivity than 133Xe. The radiation dose to the lungs from 133Xe and 125Xe is 5.0 and 1.8 mrads/mCi-min, respectively. The radiation dose per usable photon for 125Xe is only 0.3 of 133Xe. The principal photons of 125Xe, 188 keV (55%) and 243 keV (29%), are more intense and are in an energy range that is more advantageous for imaging than the 81 keV (35%) of 133Xe. These physical properties of 125Xe result in better spatial resolution at the same information density and with less radioactivity administered to the patient. Phantom studies showed that 12.7-, 9.5-, and 6.4-mm lead bars were resolved with 125Xe using a 410- keV diverging collimator wheras only the 12.7- and 9.k-mm lead bars were resolved using 133Xe and either a 410-keV or 140keV diverging collimator.