Robert C. Stadalnik

Benign causes of 18-FDG uptake on whole body imaging

C OST-EFFECTIVENESS and high accuracy of whole body 1 8-Fluorodeoxyglucose positron emission tomography (18-FDG-PET) have been established for several malignancies. 2,3 However, pitfalls have been encountered due to variable degrees of 18-FDG uptake by benign pathology. 4-66 In the majority of the cases visual interpretation (slight uptake, irregular or diffuse pattern) and quantitative analysis with different cut-off values, along with the physical examination and radiological correlation, will clarify the underlying causes. The physiological and artifactual accumulation 4,67 in 18-FDG whole body scans, and the technical and biological factors causing false-positive results 15 have been reviewed recently. We report seven cases of 1 8-FDG uptake related to lactation (Fig 1), muscle artifact at the insertion of the Latissmus Dorsi (Fig 2), esophagitis (Fig 3), a tracheostomy tube (Fig 4), ectopic pelvic kidney (Fig 5), hydatid cyst (Fig 6), and chronic nonspecific lymphadenitis (sinus histiocytosis) (Fig 7). The following are the reported benign causes of 1 8-FDG uptake that should be considered in interpreting whole body scans to decrease the rate of false-positive results in oncologic patients.

Identifiability Analysis of an In Vivo Receptor-Binding Radiopharmacokinetic System

A five-state, nonlinear model describing the pharmacokinetics of a receptor-binding radiopharmaceutical is presented. Local parameter identifiability analysis was performed preexperimentally to investigate the chemical and observational conditions required for adequate estimates of hepatic blood flow, receptor-ligand affinity, and receptor population. The ability to estimate the above parameters from externally observed kinetic data depended upon receptor-ligand affinity, the molar dose of the radiopharmaceutical, the number and coupling of the observers, and independent knowledge of the coupling coefficients or ligand-receptor affinity.

Scintigraphy in the diagnosis of osteonecrosis.

Scintigraphy, using 99mTc diphosphonate, has the potential for diagnosing osteonecrosis before irreversible changes are visible in routine roentgenograms. If obtained within weeks of an avascular insult, a cold area will appear on scintiscan. However, months later, the revascularization and reparative processes of the dead bone produce a hot area on scintiscan.

A molecular receptor-binding contrast agent for magnetic resonance imaging of the liver.

RATIONALE AND OBJECTIVES A gadolinium complex of polydiethylenetriamine pentaacetic acid polyneogalactosyl polylysine (Gd-DTPA-gal-PL) was developed and tested as a paramagnetic contrast agent for magnetic resonance (MR) imaging of the liver. The agent was designed for receptor-mediated uptake by the asialoglycoprotein receptor (ASGP-R), which is unique to hepatocytes and exhibits high specificity for galactose-terminated glycoconjugates. METHODS Polylysine was alkylated with a mixed anhydride of diethylenetriamine pentaacetic acid. This product was complexed with gadolinium and N-alkylated with 3-oxopropyl-1-thio-beta-D-galactopyranoside. With this reaction sequence, we prepared a gadolinium complex consisting of 2284 galactose groups and 858 chelators per polylysine having 2136 amino groups. Hepatic enhancement was tested by MR imaging of nine rats with liver-implanted mammary adenocarcinoma before and after injection of 20 x 10(-9) mol/kg Gd-DTPA858-gal2284-PL2136. The conjugate was labeled with technetium-99m and tested (1.5 x 10(-10) mol/kg) for hepatic specificity via nuclear imaging. RESULTS Mean hepatic enhancement was 86% within 10 min and remained constant for 25 min. Hepatic relative intensity exceeded preinjection intensities by at least four times the standard deviation of the preinjection values (p < .01). The tumors, which are devoid of ASGP-R, did not exhibit significant enhancement (p > .1). The liver accumulated 90% of the technetium-99m-labeled conjugate. CONCLUSION A molecular paramagnetic ligand to the asialoglycoprotein receptor has been developed for hepatocyte-specific MR contrast enhancement.

A musculoskeletal radiologist's view of nuclear medicine

The introduction of cross-sectional and multiplanar imaging techniques has not diminished the value of radionuclide bone scanning. Skeletal scintigraphy remains an extremely effective and relatively inexpensive tool for diagnosis of many disorders of bones and joints. The sensitivity of scintigraphy in detecting stress fractures approaches 100%, although it is less specific than plain film radiography. However, radionuclide bone scanning can reveal subtle early changes in bone metabolism. For evaluation of infections, particularly in patients with diabetic foot neuropathy, scintigraphy is the modality of choice, although a combination of imaging techniques may be necessary in previously damaged bone. Radionuclide bone scanning has retained its place in the evaluation of primary bone tumors and metastases, and in screening of patients with metabolic bone disease. The radiologist should be aware that although this modality is generally used as an ancillary technique in conjunction with plain radiography, conventional tomography, computed tomography (CT), and magnetic resonance imaging (MRI), at times it can be used as the primary modality not only for the identification of skeletal lesions but also to provide important information required to make a definite diagnosis.

Hepatobiliary scintigraphy with technetium-99m disofenin in the evaluation of neonatal cholestasis.

To assess the reliability of technetium-99m disofenin scanning in evaluating neonatal cholestasis, 33 neonates (less than 3 months of age) with direct hyperbilirubinemia were evaluated prospectively by cholescintigraphy. Results of this test were compared to those of standard serum tests of liver function, ultrasonography, and liver biopsy. The diagnosis of biliary atresia was suggested by a serum gamma-glutamyl transpeptidase (gamma-GTP) greater than 300 units/L, absence of the gallbladder on ultrasonography, and a lack of detectable radioisotope in the gastrointestinal and/or extrahepatic biliary tract on cholescintigraphy. Each of these tests lacked sensitivity and/or specificity when compared to liver biopsy. Of the nine neonates with biliary atresia, three had gallbladders identified by ultrasonography and two had gamma-GTP less than 300 units/L. Of the 24 neonates without biliary atresia, eight had cholescintigraphy without detectable radioisotope excretion, four had ultrasonography that failed to visualize the gallbladder, and nine had gamma-GTP greater than 300 units/L. Cholescintigraphy excluded the diagnosis of biliary atresia when gut and/or extrahepatic biliary excretion of isotope was seen. However, cholescintigraphy required more time, 6-8 days, and was less specific than ultrasonography and liver biopsy. We recommend that cholescintigraphy should not be routinely used in evaluating neonatal cholestasis, especially if it delays surgical intervention.

The Validity of 99mTc-Pyridoxylideneglutamate (P.G.) Cholescintigraphy as a Diagnostic Test for Cholecystitis

The purpose of this investigation was to determine the diagnostic value (validity) of technetium-99mpyridoxylideneglutamate cholescintigraphy (99mTc- PGC) in patients with and without cholecystitis and to compare its validity to those of oral cholecystography (OC) and ultrasonography (US). 99mTc-PGC was applied to 50 patients with acute, subacute, and/or chronic cholecystitis with cystic duct obstruction proven histologically and operatively, and also to 27 non-diseased volunteers and 43 patients with right upper quadrant abdominal pain who subsequently were proven free of gallbladder disease. In addition, 38 patients had OC, and 31 had US performed. The results shows that the sensitivity and specificity of 99mTc-PGC were 100%. Whereas for OC the sensitivity was 87%, specificity was 100%. For US the sensitivity was 70%, and specificity was 93%. The repeatability of 99mTc-PGC, OC, and US were 100%, 94% and 81% respectively. These data show that 99mTc-pyridoxylideneglutamate cholescintigraphy is a valid diagnostic tool in the evaluation of patients with cholecystitis, and is also safe and simple.

Negative bone scintigraphy with diffuse osteoblastic breast carcinoma metastases.

A patient with diffuse osteoblastic metastases from invasive lobular carcinoma of the breast is presented in whom radionuclldo bone scan was negative for skeletal lesions. Skeletal metastases were documented by plain radiography, CT, MRI, and bone marrow biopsy. This case report points to the value of plain-film, CT, and MRI findings in situations of high clinical suspicion of metastatic disease despite a normal scintigraphy.

Vascularity of the Femoral Head: 18Fluorine Scintigraphy Validated with Tetracycline Labeling

Blood flow to the femoral head was assessed by 18F positron scintigraphy and tetracycline fluorescent labeling in 17 patients undergoing replacement of the femoral head with an endoprosthesis. Radioactivity was absent in the femoral head of 10 patients, normal in 5, and increased in 2. Normal or increased radioactivity indicated presence of blood flow to the femoral head; decreased or absent radioactivity indicated absence of blood flow. Results of 18F scintigraphy correlated with those of tetracycline labeling.

Goodness-of-fit and local identifiability of a receptor-binding radio-pharmacokinetic system

A four-state nonlinear model describing a radiopharmacokinetic system for a hepatic receptor-binding radiopharmaceutical, (/sup 99m/Tc)-galactosyl-neoglycoalbumin, (TcNGA), was tested for goodness-of-fit and local identifiability using scanning data from nine healthy subjects and seven patients with severe liver disease. Based on standard deviations of liver and heart imaging data at equilibria as a measure of observational error, the reduced chi-square ranged from 0.5 to 2.6. Values above 1.2 occurred when the subject moved during the 30 min study. Relative standard errors for each parameter were determined. The highest standard errors occurred when the amount of TcNGA injected exceeded the total amount of receptor. Therefore, when TcNGA functional imaging was performed without excess patient motion and receptor saturation, the kinetic model provided data fits of low systematic error and yielded high precision estimates of receptor concentration and forward binding rate constant.<<ETX>>