Search PubMed⌕ Search

Biomedical subjects

R C Brasch

Publications and source records attributed to R C Brasch.

At least 145 records · Page 8Linked to original sources
PubMed1985

Magnetic field dependence of spin-lattice relaxation enhancement using piperidinyl nitroxyl spin-labels.

We examined the magnetic resonance properties of 12 paramagnetic piperidinyl nitroxyls in water and plasma solutions. Paramagnetic contributions to proton relaxation times were measured using 10.7 and 100 MHz spectrometers. Proton relaxation enhancement from nitroxyls increased with ascending molecular weight, in plasma solutions versus equimolar aqueous solutions, and with measurements at 10.7 MHz compared to 100 MHz. Relaxation rates were observed to approximately double at 10.7 MHz compared to 100 MHz and from water to plasma solutions. The data indicate that proton spin-lattice relaxation enhancement is magnetic field-dependent, and increases using nitroxyls of large molecular weight and with chemical substitutents that increase the microviscosity of solvent water molecules. The development of nitroxyls for diagnostic MRI will be aided by understanding these in vitro physical characteristics and trends.

Contrast Media↗
PubMed1985

Factors affecting nitroxide reduction in ascorbate solution and tissue homogenates.

Because of their paramagnetic properties, nitroxides are potentially useful as contrast agents in magnetic resonance imaging (MRI). They are reduced in vivo to their corresponding hydroxylamines which are nonparamagnetic and have no contrast enhancing property. Nitroxides with high resistance to reduction would be advantageous as pharmaceutical contrast enhancing agents. We show that in the presence of ascorbic acid and in tissue homogenates, the reduction is faster for piperidine than for pyrrolidine nitroxides and for positively-charged than for negatively-charged derivatives. The data also suggest that nitroxide reduction in tissue homogenates is mainly due to sulfhydryl groups on proteins and that endogenous ascorbic acid plays a relatively minor role.

Animals↗
PubMed1985

Enhanced MRI of tumors utilizing a new nitroxyl spin label contrast agent.

Nitroxyl spin labels have been shown to be effective in vivo contrast agents for magnetic resonance imaging (MRI) of the central nervous system, myocardium, and urinary tract. A new pyrrolidine nitroxyl contrast agent (PCA) with better resistance to in vivo metabolic inactivation than previously tested agents was studied for its potential to enhance subcutaneous neoplasms in an animal model. Twenty-two contrast enhancement trials were performed on a total of 15 animals 4-6 weeks after implantation with human renal adenocarcinoma. Spin echo imaging was performed using a .35 T animal imager before and after intravenous administration of PCA in doses ranging from 0.5 to 3mM/kg. The intensity of tumor tissue in the images increased an average of 35% in animals receiving a dose of 3 mM/kg. The average enhancement with smaller doses was proportionately less. Tumor intensity reached a maximum within 15 min of injection. The average intensity difference between tumor and adjacent skeletal muscle more than doubled following administration of 3 mM/kg of PCA. Well-perfused tumor tissue was more intensely enhanced than adjacent poorly perfused and necrotic tissue.

Animals↗
PubMed1985

AUR memorial Award. Induced alignment of flowing sickle erythrocytes in a magnetic field. A preliminary report.

Deoxygenated sickle erythrocytes in static suspension align perpendicular to a magnetic field. To assess the importance of this observation to MRI of sickle-cell disease, an in vitro flow apparatus was devised and the orientation of sickle erythrocytes flowing through a 0.38 T magnetic field was investigated. We showed a significant perpendicular alignment of fully deoxygenated sickle erythrocytes flowing at 3 to 4 mm/minute (P less than .001). These results suggest that deoxygenated erythrocytes in a sickle-cell patient could orient perpendicular to a magnetic field, and therefore that MRI of such patients could possibly result in worsening of vaso-occlusive complications. Further studies are needed to assess the possible hazards of MRI of sickle-cell disease, especially at high field strengths.

Anemia, Sickle Cell↗
PubMed1985

Assessment of severity of experimental pulmonary edema with magnetic resonance imaging. Effect of relaxation enhancement by Gd-DTPA.

This study was done to demonstrate the capability of magnetic resonance imaging (MRI), using a spin-echo technique to detect permeability pulmonary edema in vivo, to correlate the signal intensity to the water content of the lung, and to assess the influence of administration of gadolinium-DTPA upon this relationship. Pulmonary edema was induced in 28 rats by intravenous injection of oleic acid (0.05-0.1 cc/kg). This was detected in all animals on images obtained with a repetition time (TR) of 2.0 seconds and echo times (TE) of 28 or 56 msec as increased signal intensity. Compared with control animals, the intensity was increased primarily in the dependent and peripheral portions of the lung. There was a significant linear relationship between the mean signal intensity, obtained from the area of both lungs within one slice, and the water content of both lungs (r = .94). Intravenous administration of gadolinium (Gd)-DTPA, 5 minutes prior to imaging, produced an easily observable increase in signal intensity on images of short TR (0.5 second) in the edematous lung tissue. However, these values did not exceed the intensities obtained without Gd-DTPA, if a long TR (2.0 seconds) was used for imaging. Thus, MRI has the capability for quantitating the severity of oleic acid-induced pulmonary edema. Gd-DTPA distributes rapidly into permeability pulmonary edema. It allows improved sensitivity at shorter pulse sequence repetition times and thus may diminish imaging time.

Animals↗
PubMed1985

Inherent contrast in magnetic resonance imaging and the potential for contrast enhancement. The 1984 L. Henry Garland lecture.

Magnetic resonance (MR) imaging is emerging as a powerful new diagnostic tool valued for its apparent lack of adverse effects. The excellent inherent contrast between biologic tissues and fluids afforded by MR imaging is one of the foremost characteristics of this technique and depends on physicochemical properties such as hydrogen density and T1 and T2 relaxation rates, on magnetic field strength and on operator-chosen factors for acquiring the MR imaging signal. Pharmaceutical contrast-enhancing agents shorten the MR imaging process and improve sensitivity and diagnostic accuracy.

Animals↗
PubMed1985

Magnetic resonance imaging of acute myocardial infarction using a nitroxyl spin label (PCA).

The effects of an intravenously administered nitroxyl spin label (PCA) on the magnetic resonance imaging (MRI) appearance and relaxation times of acute canine myocardial infarctions were studied. Twenty-four hours after ligation of the left anterior descending coronary artery (LAD), animals were either sacrificed immediately (three dogs) or injected with 3.0 mmol/kg of PCA prior to sacrifice (six dogs). The PCA group dogs were sacrificed at either 5 minutes postinjection (three dogs) or 15 minutes postinjection (three dogs). Magnetic resonance imaging (0.35 T) using spin-echo techniques demonstrated high signal intensity in the infarct relative to normal myocardium in all three groups. In the control group, the T1 and T2 relaxation times were longer in infarcted compared with normal myocardium, but only the measure in T2 reached statistical significance (P less than .05). PCA produced infarct-avid T1 shortening in the six dogs that received it. Contrast in the group sacrificed at 15 minutes postcontrast administration was greater than that in the control group due to T1 shortening in the infarct. Thus, PCA produces differential effects on normal and infarcted myocardium. Between 5 and 15 minutes after IV administration, it causes greater changes in the infarct due to prolonged retention in this region.

Animals↗
PubMed1984

Radiographic assessment of venous catheter position in children: value of the lateral view.

Frontal chest radiographs can be misleading in the evaluation of central venous catheter placement. Lateral chest radiographs were obtained, in addition to the standard frontal radiographs, in 25 young children. In five (20%) of the children, the catheters were found to be malpositioned, and the frontal radiograph showed evidence of the abnormality in all five. The lateral radiographs also showed evidence of the abnormality in all five children; however, in three of the five, the lateral radiographs provided additional, more specific, diagnostic information. The lateral chest radiographs also demonstrated satisfactory catheter positioning in three other children in whom the frontal radiographs suggested abnormal positioning. Accurate assessment of catheter position was possible in all patients using both frontal and lateral chest radiographs. Injection of contrast material was not necessary to locate malpositioned catheters. Lateral radiographs are recommended whenever an abnormal catheter position is suspected clinically or from findings on the routine frontal radiograph.

Catheterization↗
PubMed1984

Magnetic resonance imaging in cystic fibrosis.

A clinical dilemma in patients with cystic fibrosis is the determination of the nature of linear areas of decreased aeration in the lungs. It is difficult using chest roentgenograms or even computed tomography to differentiate atelectasis, mucoid impacted bronchi, or peribronchial inflammatory disease from normal pulmonary vascularity. Magnetic resonance imaging is a noninvasive sensitive means that provides the distinction. Pulmonary vessels are easily identified, because with the spin-echo sequence that we use, the rapidly flowing blood within the vessels has no signal intensity. In contradistinction, mucoid-impacted bronchi appear as high-intensity linear branching structures. Peribronchial inflammatory disease appears as curvilinear areas of high intensity, representing inflammatory edema, around central lucencies representing bronchi.

Adolescent↗
PubMed1984

Nuclear magnetic resonance imaging of the brain in children.

Nuclear magnetic resonance imaging of the hydrogen nucleus provides a unique noninvasive display of proton dynamics in biologic tissues and fluids as well as internal anatomy in a sectional imaging format. No ionizing radiation is utilized. Our experience with NMR imaging of the brain in 14 pediatric patients is presented and compared with computed tomography. The major advantages of NMR over CT include its greater sensitivity to blood flow, edema, hemorrhage, and myelinization and its lack of beam-hardening artifacts. In addition, the potential for tissue characterization exists by determination of T1 and T2 relaxation times and of mobile proton density. Disadvantages of NMR over CT include its failure to demonstrate calcification and bone detail and longer data acquisition times.

Adolescent↗
PubMed1984

Incidence and significance of a widened esophageal hiatus at CT scan.

We studied the anatomy of the esophageal hiatus using axial CT scans in 320 patients. Normally, the diaphragmatic crura are tightly opposed and closely related to the esophagus. Widening of the esophageal hiatus is readily demonstrated by CT as a separation of the diaphragmatic crura and an increased distance between the crura and esophageal wall. The incidence of widening increases with age, lending support to the hypothesis that the abnormality is acquired. In 100 patients who also had barium studies of the upper gastrointestinal tract, a sliding hiatus hernia was found in 37/43 (86.4%) patients who had a widened esophageal hiatus shown by CT. In 26 of 37 (70.2%) patients, the hernia was demonstrated on CT as a pseudomass usually filled with contrast material lying within and/or above the esophageal hiatus. Small hiatus hernias were shown without a widened esophageal hiatus in only two patients.

Adolescent↗
PubMed1984

Magnetic resonance imaging of the thorax in childhood. Work in progress.

Magnetic resonance (MR) imaging was performed in 10 children with intrathoracic disease. Entities imaged included mediastinal lymphoma and neuroblastoma, pulmonary metastases from hepatoblastoma and osteogenic sarcoma, hemorrhagic pleural effusion, and nonmalignant disease such as abscess, cystic fibrosis, and bronchogenic cyst. MR imaging was particularly valuable in delineating mediastinal and parenchymal masses from adjacent vascular structures without the need for contrast material enhancement. However, MR was insensitive to lesion calcification. Since pulmonary vessels give very low signal, differentiation of high-intensity pulmonary nodules from vessels is readily apparent. For similar reasons, MR was excellent in distinguishing endobronchial mucus plugs from peripheral pulmonary vessels.

Adolescent↗
PubMed1984

Magnetic resonance imaging of transfusional hemosiderosis complicating thalassemia major.

Tissue deposits of hemosiderin, a paramagnetic iron-protein complex, resulted in marked abnormalities of magnetic resonance (MR) spin-echo signal intensity within the viscera of three children with transfusional hemosiderosis and thalassemia major. In all patients the liver and bone marrow demonstrated abnormally low spin-echo intensities and the kidneys and muscles had abnormally high intensities. These observations correlate with in vitro MR observations of ferric (Fe+3) solutions, in which concentrations of ferric salts greater than 20 mmol yielded a low MR intensity signal and ferric concentrations less than 15 mmol yielded higher intensities than did water alone. MR imaging is sensitive to the tissue deposition of hemosiderin, and MR intensity appears to provide a rough measure of the amount of iron deposited.

Adolescent↗
PubMed1984

Orbital tumors in children. Characterization by computed tomography.

CT characteristics of orbital masses in 39 children were reviewed. Histological types and their relative frequencies differed considerably from reported adult cases. Analysis of seven separate CT characteristics for each type of mass indicated certain trends which may aid in the differential diagnosis.

Adolescent↗
PubMed1984

Hydropneumothorax: detection on supine radiographs.

Hydropneumothorax may be diagnosed on a supine radiograph by recognition of a pleural line with increased density lateral to it in the pleural space. Recognition of this condition may have implications for therapeutic chest tube placement.

Adolescent↗