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Biomedical subjects

F D Thomas

Publications and source records attributed to F D Thomas.

At least 55 records · Page 3Linked to original sources
PubMed1984

N,N'-bis(S-benzoylmercaptoacetamido) ethylenediamine and propylenediamine ligands as renal function imaging agents. I. Alternate synthetic methods.

A new method was developed to synthesize tetradentate ligands containing the N,N'-bis(S- benzoylmercaptoacetyl ) ethylenediamine and propylenediamine moieties (DADS compounds). Methods are also represented with which to synthesize some of the positional isomers of the above compounds. These isomers represent a new class of compounds. A total of 21 different compounds were prepared. These will be used in an effort to establish a relationship between structure and renal imaging properties.

Alanine↗
PubMed1983

New diphosphonate compounds for skeletal imaging: comparison with methylene diphosphonate.

Three-hour biodistribution of Tc-99m complexes of six diphosphonates was compared in rabbits with tibial lesions to determine which was best for detection of focal bone lesions. Sr-85 was used as a standard. N,N-dimethylaminomethylene diphosphonate (DMAD) was the only agent with a higher lesion/normal bone ratio than methylene diphosphonate (MDP), attributable to lower concentration in normal bone. Hydroxymethane diphosphonate (HDP) and 2,3-dicarboxypropane-1, 1-diphosphonate (DPD) demonstrated higher concentration than MDP in normal bone without improving lesion contrast. They also exhibited much higher uptake in the liver and kidney, as well as muscle and red marrow in the case of DPD. None was superior to MDP as an all-purpose skeletal agent, though others may be better for specific applications.

Animals↗
PubMed1983

The influence of pulmonary insufficiency on ventricular function following repair of tetralogy of Fallot. Evaluation using radionuclide ventriculography.

Long-standing pulmonary insufficiency after repair of tetralogy of Fallot may adversely affect ventricular function. We evaluated 20 patients at a mean of 9 years after repair by radionuclide ventriculography, 24 hour Holter monitoring, and M-mode echocardiography. The mean age at complete repair was 7.1 +/- 2.6 years. Patients were divided into groups as follows: Group I (eight patients), no clinical pulmonary insufficiency; Group II (12 patients), moderate to severe pulmonary insufficiency. Group II was further divided: Group IIa, transannular patch (six patients); Group IIb, no transannular patch (six patients). There was no difference between groups for age at operation, duration of follow-up, right ventricular pressure, or right ventricular-pulmonary arterial gradient. No patient had a residual shunt and all were in New York Heart Association Class I. Serious ventricular dysrhythmias occurred in 38% of Group I patients and 50% of Group II (p = NS). The echocardiographic ratio of right to left ventricular end-diastolic dimension was greater in patients with pulmonary insufficiency than in those without pulmonary insufficiency: 0.83 +/- 0.17 versus 0.55 +/- 0.15, p less than 0.01. Right ventricular ejection fraction was 0.39 +/- 0.08 in Group I and 0.27 +/- 0.07 in Group II, p less than 0.01. Left ventricular ejection fraction was 0.64 +/- 0.12 in Group I and 0.53 +/- 0.07 in Group II, p less than 0.02. Radionuclide angiography is a useful means of identifying right ventricular dysfunction following repair of tetralogy of Fallot. The dysfunction appears significantly worse in patients with pulmonary insufficiency.

Adolescent↗
PubMed1982

A new formulation of Tc-99m minimicroaggregated albumin for marrow imaging: comparison with other colloids, In-111 and Fe-59.

The biodistributions of five Tc-99m colloids were compared with the 24-hr distributions of Fe-59 and In-111 in dogs by direct radioassay 1 hr after intravenous injection. One formulation of Tc-99m minmicroaggregated albumin (particle size 30-100 mn), produced the highest marrow concentration, approximately six times that of Tc-99m sulfur colloid, with similar blood, and liver concentrations and a lower splenic uptake. Nevertheless, the best colloid marrow uptake was lower than the 24-hr value for In-11 and much lower than that for Fe-59. The marrow concentration of minimicroaggregated albumin was also higher than that of sulfur colloid in rats at 30 min after injection. The principal disadvantage of Tc-99m antimony sulfide colloid was its slow blood clearance. Clinical evaluation of Tc-99m minimicroaggregated albumin for marrow imaging appears warranted, although its hepatic activity will obscure overlying and immediately adjacent marrow.

Animals↗
PubMed1981

Detection of experimentally produced acute pulmonary arterial occlusion by methyl iodide-131 inhalation imaging.

Methyl iodide-131 (CH3I-131) is described as an agent for detection of acute experimentally produced pulmonary arterial occlusion in dogs. When gaseous CH3I-131 is inhaled, radioactivity passes instantaneously from the alveoli to the lung capillary bed. Where pulmonary blood flow exists, activity is washed out into the systemic circulation, but in areas of blood stasis, a transient pulmonary "hot spot" remains. CH3I-131 is easily produced and inexpensive, but administration is awkward and strict radiation safety precautions are mandatory.

Animals↗
PubMed1981

Comparison of renal extraction efficiencies for radioactive agents in the normal dog.

The renal extraction efficiencies for various radioactive agents were measured in normal anesthetized dogs during 1 hr after a single intravenous injection. Radioassays were made on serial blood samples drawn simultaneously from the aorta upstream from the renal arteries and from one renal vein. As a reference substance [131I]o-iodohippurate was injected concurrently in all experiments. Blood clearances from serial venous samples and urinary excretion also were measured. Extraction efficiency from whole blood was calculated as (A-V) divided by A, where A = aortic concentration and V = renal venous concentration. This ratio for commercial [131I]o-iodohippurate fell steadily from 88% at 30 sec to 50% at 1 hr. For "purified" [131I]o-iodohippurate the fall was less marked, to 61% at 1 hr. The EE ratios for all other agents were stable after the first minute. The Tc-99m complexes of DTPA, glucoheptonate, and acetylcysteine had ratios averaging 27-29%. The ratios of Tc-99m DMS and Hg-197 chlormerodrin had much lower average values of 8 and 14%, respectively. None of the newer agents approached the extraction efficiency of [131I]o-iodohippurate.

Animals↗
PubMed1980

LeVeen shunt patency studies: clarification of scinigraphic findings.

In an experimental model we have demonstrated that visualization of the target organ is the only dependable criterion for the scintigraphic evaluation of LeVeen shunt patency or nonpatency. The lungs are best suited as the target, because the presence or absence of pulmonary uptake can be easily seen without interference from radiolabeled peritoneal fluid. Proof of shunt patency should not rely upon direct visualization of shunt tubing, because very high or low flow rates are both associated with poor visualization. Maximum accumulation of activity in the shunt tubing occurs with intermediate flow rates (approximately 60 cc/hr).

Ascites↗
PubMed1980

Density patterns in the normal lung as determined by computed tomography.

Lung density patterns in a group of randomly selected, normal individuals were determined by computed tomography, using two methods: one measuring the density of the peripheral lung (parenchyma), and the other determining the density of the whole lung field. The effects of body position and respiratory phase, as well as patient age were assessed. The potential use for this information in clinical settings and in physiological investigation is suggested.

Age Factors↗
PubMed1980

Distribution of leukocytes labeled with In-111 oxine in dogs with acute inflammatory lesions.

The biodistributions of In-111 oxine (with and without leukocyte labeling) of Ga-67 citrate and of In-111 chloride were compared in 30 dogs with chemical and bacterial abscesses and acute joint inflammation. Serial blood samples were taken and tissues radioassayed at 24 hr. The concentration of In-111-oxine leukocytes in all three types of inflammatory lesion was invariably much higher than that of Ga-67 injected simultaneously. For bacterial abscesses, the mean abscess-to-muscle concentration ratio was 3,000 for labeled leukocytes and 72 for Ga-67. Aqueous buffered In-111 oxine sulfate solution appeared better for labeling leukocytes than In-111 oxine in ethanol. When In-111 oxine was not incubated with leukocytes before injection, or if the cells were poorly labeled or damaged, the abscess localization was often inferior to that of gallium. Localization of In-111 chloride also appeared inferior to that of gallium. No significant difference in distribution in the major organs or inflammatory lesions was demonstrable between labeled suspensions of "pure"neutrophils harvested by elutriation and "mixed"cell suspensions of leukocytes after erythrocyte sedimentation with hydroxyethyl starch. For both types of leukocyte suspension labeled with In-111 oxine, the average recovery of cell-bound activity in the circulating blood at 4 hr was 32% of the administered activity, inferior to that of DFP-32. It is concluded, therefore, that In-111 oxine is a more effective agent than Ga-67 for the detection of acute focal inflammatory lesions if leukocytes are properly labeled, but current techniques are unsatisfactory for the study of neutrophil kinetics.

Abscess↗
PubMed1980

Left ventricular function following aortic valve replacement: assessment by radionuclide ventriculography.

Left ventricular function following aortic valve replacement has been evaluated in 15 consecutive patients. Cold potassium cardioplegia was utilized for myocardial preservation. Left ventricular function was assessed by radionuclide ventriculography performed preoperatively and 3 months postoperatively. The predominant lesion was aortic insufficiency in 10 patients and aortic stenosis in five patients. All patients demonstrated improved ejection fractions at 3 months. The mean increases of ejection fraction in the aortic insufficiency group were 20% from the anterior (Ant.) position and 12.5% from the left anterior oblique (LAO) position; in the aortic stenosis group they were 15.2% (Ant.) and 14.8% (LAO). It is our contention that cold potassium cardioplegia is an effective means of myocardial preservation and that it showed no measurable deleterious effect on left heart function in this group of patients.

Adult↗
PubMed1980

An adjustable zoom-made gain control for computerized gamma-camera systems.

Many nuclear medicine departments use a digital computer to process scintillation-camera images. For optimal use of the computer, there should be a means to amplify the position signals of each scintillation event by an appropriate amount before their conversion to digital form. What is needed is a series of calibrated gains from which the best value may be chosen. Many systems now in use do not provide such a selection. The circuitry described here provides an inexpensive solution to this problem. It may be inserted between the camera and the computer's analog-to-digital converters to provide the desired amplification. No internal modification of the computer or the camera is required.

Computers↗
PubMed1979

Radionuclide assessment of peritoneo-venous shunt patency.

LeVeen shunt patency can be easily assessed by sequential scintigraphy with a gamma camera after an intraperitoneal injection of Tc-99m-macroaggregated albumin (Tc-99m-MAA). If the shunt is patent, the particles of MAA reach the pulmonary capillary bed and the lungs are visualized. The activity in the lungs is easily discerned without any interference from radioactivity in the peritoneal cavity. The study is semiquantitative since the intensity of lung activity is directly proportional to the shunt patency and flow rate across shunt tubing.

Ascites↗
PubMed1979

Transmission computed tomographic diagnosis of experimentally produced acute pulmonary vascular occlusion in the dog.

Acute experimental pulmonary arterial occlusions were produced in 5 dogs. The chest was subsequently imaged with computed tomography (CT), 99mTc-MAA scintigraphy, and plain radiography. Gamma images revealed all 6 lesions, and plain radiographs were uniformly negative. Enhanced CT scans demonstrated 3 of 5 lesions, and unenhanced scans revealed 1 of 6. CT findings were variable.

Animals↗
PubMed1979

Transmission computed tomography, Tc-99m MAA scintigraphy, and plain chest radiography after experimentally produced acute pulmonary arterial occulusion in the dog.

We have occluded segmental and subsegmental pulmonary arteries in the dog with Swan-Ganz balloon catheters or i.v. injection of autologous clot, and have studied the chest with transmission computed tomography (TCT), Tc-99m-MAA gamma imaging, and plain radiographs. The arterial occlusions were between 1 and 5 hr old at the time of imaging. Radiographs revealed no lesions. Tc-99m MAA scanns revealed ten of 11 lesions. When a TCT image was made before i.v. injection of Renografin-60, two of 11 lesions were identified; after Renografin the score was four out of ten. The appearance of lesions on TCT was highly variable. Tc-99m-MAA gamma imaging, therefore, is far more accurate than TCT in the identification of small experimentally produced acute pulmonary arterial occlusions in the dog, and our study fails to suggest a secure place for TCT in the diagnosis of small, acute human pulmonary emboli. The commonly-held assumption that postembolic lung is oligemic is questioned.

Animals↗
PubMed1978

Effect of signaled versus unsignaled stress of rat myocardium.

Foot-shock stress resulted in a threefold increase in myocardial uptake of technetium-99m-methylene diphosphonate (Tc-99m-MDP) in rats compared to unstressed controls. The introduction of a 4-sec signal prior to each shock resulted in a two-thirds reduction in this stress-induced Tc-99m-MDP myocardial uptake, suggesting that most of the stress-induced myocardial damage was psychologically mediated.

Animals↗