Biomedical subjects

D L Rubin

Publications and source records attributed to D L Rubin.

43 records · Page 3Linked to original sources

PubMedDate not supplied

Intraluminal contrast enhancement and MR visualization of the bowel wall: efficacy of PFOB.

Efforts to develop satisfactory intraluminal gastrointestinal contrast agents for magnetic resonance (MR) imaging have focused on depicting only the bowel lumen to exclude possible involvement by a pathologic process. To determine whether the bowel wall can be adequately imaged with use of the contrast agent and whether bowel wall visualization is a better index of the utility of the contrast agent for MR imaging, perfluoroocytlbromide (PFOB) was studied in human subjects. Twenty consecutive patients referred for abdominal or pelvic MR imaging were selected. All patients were given 400-1,000 mL of PFOB orally. MR imaging was performed at 0.38 and 1.5 T with T1- and T2-weighted spin-echo pulse sequences before and after administration of PFOB. The images were graded independently by three blinded readers. All readers reported significantly superior conspicuity of the bowel lumen and wall after PFOB than before PFOB administration (P less than .002). Among the post-PFOB studies, those with superior bowel wall visualization demonstrated superior overall image quality. In three patients, lesions were optimally demonstrated because the relationship of the process to the bowel wall, rather than just to the lumen, was identified. In two patients, masses arising within the bowel wall could be identified prospectively only when the bowel wall was adequately imaged. The authors conclude that while lumen identification is improved with PFOB, its greatest clinical utility may be in facilitating intestinal wall visualization.

Administration, Oral↗

PubMedDate not supplied

Liquid oral magnetic particles as a gastrointestinal contrast agent for MR imaging: efficacy in vivo.

Recent in vitro studies suggested there is an optimal range of concentration and viscosity for a liquid formulation of oral magnetic particles (WIN 39996) for magnetic resonance (MR) imaging of the gastrointestinal (GI) tract. To determine whether this formulation is also effective in vivo and whether differing viscosity and administration regimen affect GI distribution of the contrast agent, a range of concentrations of iron (75, 150, and 200 micrograms/mL) and viscosities (1, 150, and 600 cp) were imaged in dogs at 1.5 T with conventional spin-echo and fat-saturation pulse sequences. The effects of dose regimen (single vs divided dose) and subject position (supine vs right lateral decubitus) were also studied. The 75 and 200 micrograms/mL concentrations were unacceptable for MR imaging, while 150 micrograms/mL was effective. The GI distribution of the contrast agent was affected jointly by viscosity, subject position, and dose regimen. The 150 micrograms/mL formulation produced excellent GI contrast enhancement in vivo for both 150- and 600-cp viscosities. The choice of optimal viscosity may depend on the preferred administration regimen.

Animals↗

PubMedDate not supplied

Dynamics of tumor imaging with Gd-DTPA-polyethylene glycol polymers: dependence on molecular weight.

Macromolecular contrast media offer potential advantages over freely diffusible agents in magnetic resonance (MR) imaging outside the central nervous system. To identify an optimum molecular weight for macromolecular contrast media, the authors studied a novel macromolecular contrast agent, gadolinium diethylenetriaminepentaacetic acid polyethylene glycol (DTPA-PEG), synthesized in seven polymer (average) molecular weights ranging from 10 to 83 kd. Twenty-eight rabbits bearing V2 carcinoma in thighs underwent T1-weighted spin-echo imaging before injection and 5-60 minutes and 24 hours after injection of the Gd-DTPA-PEG polymers or Gd-DTPA at a gadolinium dose of 0.1 mmol/kg. Tumor region-of-interest measurements were obtained at each time point to determine contrast enhancement dynamics. Blood-pool enhancement dynamics were observed for the Gd-DTPA-PEG polymers larger than 20 kd. Polymers smaller than 20 kd displayed dynamics similar to those of the freely diffusible agent Gd-DTPA. Above the 20 kd threshold, tumor enhancement was more rapid for smaller polymers. The authors conclude that the 21.9-kd Gd-DTPA-PEG polymer is best suited for clinical MR imaging.

Animals↗

PubMedDate not supplied

A multicenter clinical trial of Gadolite Oral Suspension as a contrast agent for MRI.

The purpose of this study was to assess the effectiveness and safety of Gadolite Oral Suspension as a gastrointestinal (GI) contrast agent for MRI in a phase II and two phase III multicenter clinical trials. Gadolite was administered to 306 patients with known or suspected abdominal and/or pelvic disease. MRI with T1- and T2-weighted sequences was performed before and after ingestion. Efficacy was evaluated by having two masked readers rate the certainty of their MR diagnosis (0 = uncertain, 1 = probable, 2 = definite) on randomly presented pre- and post-Gadolite Oral Suspension enhanced images. Principal investigators also evaluated the images and established the final diagnosis. Vital signs, clinical chemistries, and adverse events were documented. Blood and urine samples were analyzed for gadolinium content to determine whether Gadolite Oral Suspension was absorbed systemically. Certainty in MR diagnosis increased significantly (P < .001) for both blinded readers between pre- and post-Gadolite images (.49-1.18 for reader 1: .46-1.53 for reader 2). Sensitivity, specificity, and accuracy also increased for both masked readers. No gadolinium was detected in blood or urine samples. There were no serious adverse events and no apparent drug-related trends in mean vital signs or laboratory values. Gadolite is a highly effective, safe, and well tolerated contrast agent for clinical use with MRI.

Administration, Oral↗

PubMedDate not supplied

Polymeric gadolinium chelate magnetic resonance imaging contrast agents: design, synthesis, and properties.

We have synthesized and evaluated five series of polymeric gadolinium chelates which are of interest as potential MRI blood pool contrast agents. The polymers were designed so that important physical properties including molecular weight, relaxivity, metal content, viscosity, and chelate stability could be varied. We have shown that, by selecting polymers of the appropriate MW, extended blood pool retention can be achieved. In addition, relaxivity can be manipulated by changing the polymer rigidity, metal content affected by monomer selection, viscosity by polymer shape, and chelate stability by chelator selection.

Animals↗

PubMedDate not supplied

The harmful effects of aqueous contrast agents on the gastrointestinal tract: a study of mechanism and means of counteraction.

The effect of mildly and strongly hypertonic solutions on intestinal tone and motility was tested with aqueous contrast solutions and with mannitol as a control in 15 dogs. These experiments were repeated in animals premedicated with atropine sulfate and/or methysergide maleate. Intestinal motility was recorded on serial x-ray films. Tone and motility were estimated by variations of intestinal caliber and rate of transit of contrast solution, respectively. The results obtained contradict the currently accepted mechanism of action of iodinated contrast media on the intestinal tract, which assumes that the effect is osmotic like that of a saline laxative. Solutions of different osmolarity produce hyperperistalsis of the same magnitude. This effect begins rapidly after the onset of gastric emptying and much sooner than a significant osmotic fluid shift occurs. Atropine sulfate and methysergide maleate (serotonin blocker), when given individually, are incapable of completely inhibiting hyperperistalsis induced by hypertonic solutions. However, when these agents are given in combination, motility is completely inhibited. The evidence supports a serotonin role in the hyperperistalsis induced by hypertonic solutions, partly by direct action of serotonin on the smooth muscle cells and partly by indirect action on the intramural cholinergic ganglion cells. This concept offers a possible means of eliminating one of the adverse effects of aqueous contrast media on the gastrointestinal tract.

Animals↗

PubMedDate not supplied

An experimental evaluation of central vs. peripheral injection for intravenous digital subtraction angiography (IV-DSA).

At a given radiation dosage and field of view, five variables are under meaningful control for intravenous digital subtraction angiography (IV-DSA): concentration and quantity of contrast media injected, volume of injectate, rate of injection, and site of injection. Some controversy exists regarding the selection of a central vs. a peripheral injection site for IV-DSA. This study determined the influence of the site of injection on the peak and width of the arterial time-concentration curve produced by contrast media. Using a noninvasive, in vivo, quantitative x-ray measurement method, 36 separate injections (10 ml of ioxaglate at 8 ml/sec) were administered into the cephalic vein, subclavian vein, and main pulmonary artery in dogs. Injection sites were varied using a Latin-square experimental design. Cardiac output, central blood volume and the peak and width of the contrast media time-concentration curves were measured. The average peak enhancement was greatest for the pulmonary artery injection site. Normalizing peak and width values to make the pulmonary artery values 100%, the average peak values for injections into the subclavian vein and cephalic vein were 93% and 56%, and the average widths were 141% and 163%, respectively. These data support the use of a more central injection site for optimizing IV-DSA examinations.

Angiography↗