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Biomedical subjects

R M Donati

Publications and source records attributed to R M Donati.

At least 19 recordsLinked to original sources
PubMed1986

Two-point T1 measurement: wide-coverage optimizations by stochastic simulations.

Stochastic reliability of T1 measurement from image signal ratios is examined in the ideal case by stochastic simulations in the context of wide-coverage optimizations. Precise measurements prove to be accurate, and accurate ones precise. Sign-preserved inversion-recovery (IR)/non-IR techniques are the best ratio method, reciprocal non-IR/IR ones being equivalent, but inconvenient. Wide-coverage optima are relatively unsharp. Suggested guidelines for covering the 150- to 1500-ms T1 band are minimal relevant TE; TI about 400 ms; effective repetition times about in the ratio, TR2(IR)/TR1 (non-IR) = 2.5-3.0, and in a sum as long as possible up to about TR1 + TR2 = 3.5-4.0 s; signal-averaging after and only after TR1 + TR2 has been lengthened to the said region. Also suggested are different guidelines for covering T1 bands, 120-1200 and 200-1800 ms. Typically, precisions and accuracies improve linearly or faster with increasing S/N and (S/N)2, respectively. Unnecessarily high pixel resolutions or thin slicings exact great penalties in accuracies. Progressively shortening TR1 eventually transforms a wide coverage into a sharp targeting with small potential gains in a narrow T1 locality and large compromises almost everywhere else. The simulations yield an insight into applicabilities of standard error propagation analyses in two-point T1 measurement.

Biometry↗
PubMed1986

Numerical T1 computation from NMR intensity ratios.

Two-point measurement of tissue T1 from NMR intensity ratios consists of forming an a priori ratio function describing a T1 dependence of the ratio R(T1) and computing T1 from an observed ratio Q by numerically solving R(T1)-Q = 0 or an equivalent equation. Impact of R(T1) designs on the numerical computation and dependence of relative speeds of three numerical methods on desired computational precisions q and on other factors are examined. All three methods begin with computing a table of R(T1) entries in uniform T1 steps (delta T1). In two iterative methods, a step containing the T1 root is looked up, and the precise T1 location within the step is pinpointed to within a q value by either linear-interpolative (LI) or Newton-Raphson (NR) iteration. The third method simply consists of computing a large table of delta T1 = q for a mere "look-up" with no iterative search. All three methods require a monotonous R(T1) for uniformly effective computation over wide T1 ranges. Speeds of either iterative method for computing T1 images are expected to vary with delta T1 and q with unsharp speed maxima at delta T1 near 20, 6, and 2 ms for q = 10(-1), 10(-2), and 10(-3) ms, respectively. Either iterative method is suitable for both low- and high-precision computations, the LI method being generally faster. The simple look-up is the fastest of the three for T1 image computation to low precisions of q greater than or equal to 1 ms, is likely the slowest for that to q = 0.1 ms, and is impractical for that to q less than or equal to 0.01 ms.

Algorithms↗
PubMed1983

Renal allograft accumulation of Tc-99m sulfur colloid: temporal quantitation and scintigraphic assessment.

Renal allograft accumulation of Tc-99m sulfur colloid (TSC) was studied using visual assessment of scintigraphic displays and a quantitative temporal model in 210 examinations of 56 transplant recipients. The quantitative temporal model related the immediate pool of the radioagent in the transplant to the fixed allograft accumulation of TSC at 20 minutes after administration. Examinations performed less than 3 days after grafting or steroid pulse therapy were excluded. Rejection was established by clinical and biochemical evaluation in all 84 examinations that showed acute or chronic allograft rejection. Rejection was accurately diagnosed by visual scintigraphic assessment in 82% of the established cases; this improved to 99% with relative temporal quantitation analysis. Sensitivity improved from 78% by visual examination to 95% with temporal quantitation and specificity improved from 83% to 100%.

Graft Rejection↗
PubMed1981

Local colloid trapping in the liver in the inferior vena cava syndrome.

Local radioactive areas in the liver were observed as a result of superficial cavoportal shunting of radiocolloids in two patients with the inferior vena cava syndrome. In one patient a paraumbilical and/or a recanalized umbilical vein was apparently involved in the hepatopetal shunting. In the other patient a superficial anastomosis other than the paraumbilical vein shunted colloid to the liver. Relatively discrete areas of increased radioactivity, single or multiple, were seen in the left lobe. Virtually all reported instances of hepatopetal shunting of radioparticles in a superior or an inferior vena cava syndrome have demonstrated similar findings. Various hepatopetal collateral pathways in infrarenal caval obstruction are considered, and factors that could affect liver scan findings in the infrarenal obstruction are discussed.

Collateral Circulation↗
PubMed1979

Radionuclide venography and lung scanning: Concise communication.

In 102 patients suspected of pulmonary embolism, we have assessed the ability of a radionuclide (emission) venogram to complement the pulmonary perfusion scintigram in establishing a diagnosis. The efficacy was compared using decision analysis and Bayes's theorem. Two criteria for a positive test were compared: Criterion 1--the test is positive if the lung scan a) indicates a high probability of pulmonary embolus, or b) is abnormal but indeterminate for pulmonary embolus; Criterion 2--the test is positive a) if the lung scan indicates a high probability of pulmonary embolus, or b) if the emission venogram is positive in a patient with a lung scan considered abnormal but indeterminate for pulmonary embolus. The use of Criterion 2 decreased the sensitivity from 100% to 95% and increased the specificity from 74% to 93%. We conclude that a simultaneous emission venogram assists in improving the specificity, accuracy, and the predictive value of a standard pulmonary perfusion study in the diagnosis of pulmonary embolus.

Foot↗
PubMed1979

Xenon-133 retention in hepatic steatosis-correlation with liver biopsy in 45 patients: concise communication.

This study presents the results of comparison of hepatic fat content with hepatic xenon retention in 45 patients. The degree of hepatic Xe-133 retention was measured during pulmonary ventilation studies. The amount of hepatic steatosis was graded 0 to 4+ on histologic liver sections obtained by needle or surgical biopsy. There was agreement between the amount of hepatic xenon retention determined scintigraphically and the degree of steatosis determined histologically. These results suggest that Xe-133 retention in the liver provides a simple means of evaluating fatty infiltration of the liver. The potential of this technique as a noninvasive means of investigating hepatic fatty infiltration is discussed.

Adult↗
PubMed1978

Iron transport in NRK cells synchronized in G(1) by picolinic acid.

NRK cells treated with picolinic acid are arrested in G(1)(G0). After removal of the agent a wave of transferrin-dependent iron uptake was observed only in early G(1). Therefore, iron transport is a primary event in the reinitiation of cell growth and may be connected with subsequent metabolic steps leading to initiation of DNA synthesis.

Animals↗
PubMed1978

Diagnosis of coronary artery disease with 201Tl. Computer analysis of myocardial perfusion images.

The diagnostic sensitivity of visually interpreted and computer-analyzed 201Tl myocardial perfusion images was compared to that of exercise electrocardiograms in 8 angiographically normal subjects and 24 patients with significant coronary artery disease. Visual interpretation was not significantly better than exercise ECGs. An index of perfusion homogeneity, derived from computer analysis of the 201Tl images, was more sensitive than visual interpretation (79% vs. 58%) and much more sensitive (p less than 0.05) than the exercise ECG (79% VS. 46%). The best overall sensitivity (88%) and specificity (75%) were achieved by combining computer analysis with exercise electrocardiography. The computer also permits enhanced detection of subtle perfusion changes which may not seem significant to the eye.

Computers↗
PubMed1976

Comparative evaluation of renal transplant rejection with radioiodinated fibrinogen 99mTc-sulfur collid, and 67Ga-citrate.

The diagnostic accuracy, ease, and technical feasibility of imaging with 131I-or 125 I-fibrinogen, 99mTc-sulfur colloid, and 67 Ga-citrate in renal transplant rejection are compared. Radiofibrinogen data resulted from literature review, radiocolloid data from 125 studies in 52 transplant patients, and gallium citrate data from 24 examinations in seven renal transplant patients performed simultaneously with the radiocolloid studied. Specificity of graft labeling during rejection appears to be similar with radiofibrinogen, 99mTc-sulfur colloid, and 67Ga-citrate. For routine clinical use 99mTc-sulfur colloid surpasses radiofibrinogen and radiogallium because of its better imaging qualities with a permissible radiation dose, leading to better separation of positive and negative results. The 99mTc-sulfur colloid accumulates in areas of intravascular fibrin thrombosis in acute and chronic rejecting renal transplants. Hence, the mechanisms for accumulation of 99mTc-sulfur colloid and labeled fibrinogen in rejecting transplants would seem to be similar. Such physiologic properties as rapid blood clearance and such physical properties as short physical half-life combine to produce reliable graft visualization with adequate definition, thus favoring 99mTc-sulfur colloid as the single agent of choice for clinical evaluation of renal transplant rejection at this time.

Animals↗
PubMed1975

Brain scans, dexamethasone therapy, and brain tumors.

Eight men with primary or metastatic brain tumors were examined with brain scans before and after the administration of dexamethasone. All patients demonstrated some improvement in their clinical neurologic status during therapy, and two patients had a dramatic response. Seven of the eight patients examined showed a decrease in the apparent size of the original lesion on recent brain scan while receiving dexamethasone. Comparison of immediate scans obtained 15 to 20 minutes following the administration of sodium pertechnetate Tc 99m with those obtained two or three hours later suggests that the change in apparent size of the original lesion results from decrease in peritumor edema.

Adult↗
PubMed1975

Further evaluation of 99m-Tc sulfur colloid accumulation in rejecting renal transplants in man and a canine model.

Renal transplant accumulation of 99m-Tc sulfur colloid was evaluated in 41 patients. Ninety-five examinations were performed comparing transplant with bone marrow activity and clinical or pathological diagnosis. 99m-Tc sulfur colloid accumulated in acute or chronic rejection as long as the vascular supply of the grafted kidney was not severely impaired. Accumulation was marked in chronic rejection, slight in acute rejection and absent in normally functioning transplants or in those with acute tubular necrosis. In the 10 dog models, no accumulation was seen in autografted transplants and early accumulation was demonstrated within the hyperacutely rejecting kidneys of allografted dogs.

Angiography↗
PubMed1975

67Ga citrate distribution following whole-body irradiation or chemotherapy.

Whole-body retention, organ distribution, excretion, and serum binding of 67Ga were evaluated in rats under normal conditions and following whole-body gamma irradiation, vincristine sulfate, or mechlorethamine. The results suggest that both irradiation and chemotherapy lead to reduced whole-body retention of injected radiogallium, explained in part by an alteration in the serum binding of gallium. Recognition of these findings should be considered in interpreting decreased tumor concentration of gallium in patients following radiotherapy or chemotherapy.

Animals↗
PubMed1975

67Ga citrate in renal allograft rejection.

Eight renal allograft recipients were examined on 31 occasions following administration of 99mTc sulfur colloid and 67Ga citrate. Transplant accumulation of each agent was compared and collated with the clinical diagnosis. The procedures matched in 25 instances (81%). Gallium accumulated in the graft producing a false positive result in 2 instances of acute tubular necrosis with anuria, and failed to accumulate within the graft in one case of chronic rejection and in 2 instances of acute rejection. Both radioagents failed to accumulate in 3 patients with acute rejection following heparin therapy. These data indicate that 99mTc sulfur colloid is superior to 67Ga citrate in establishing the diagnosis of transplant rejection and also provides more timely information.

Gallium Radioisotopes↗
PubMed1975

Liver scanning and the intrahepatic gallbladder: Case report.

Hepatic focal defects identified with 99mTc-sulfur colloid imaging procedures are nonspecific. This report describes a case of an ectopic gallbladder localized by cholecystography and 131I-rose bengal studies in a patient with cirrhosis and suspected intrahepatic neoplasm.

Colloids↗