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Biomedical subjects

C T Burt

Publications and source records attributed to C T Burt.

At least 37 records · Page 2Linked to original sources
PubMed1984

The fluorinated anesthetic halothane as a potential NMR biologic probe.

Fluorinated anesthetics such as halothane preferentially partition into hydrophobic environments such as cell membranes. The 19F-NMR spectrum of halothane in a rat adenocarcinoma (with known altered lipid metabolism and membrane composition) shows an altered chemical shift pattern compared to the anesthetic in normal tissue. In eight tumor samples examined, the 19F-NMR spectra exhibit two distinct resonances, compared to a single resonance observed in normal tissues. This is explained by an enhanced or altered hydrophobic component in the tumor tissue giving rise to two discrete halothane environments. Another fluorinated anesthetic, isoflurane, shows similar behavior in distinguishing normal from diseased tissue. Given the large chemical shift range of fluorine and the inherent sensitivity of this nucleus, 19F-NMR spectra of fluorinated anesthetics can also be used to follow anesthetic degradation by the liver. The ability of fluorinated anesthetics to discriminate tissues and to monitor metabolic processes is potentially useful for in vivo 19F-NMR surface coil and imaging studies.

Adenocarcinoma↗
PubMed1984

Nuclear magnetic resonance imaging of the vitreous body.

Imaging with proton nuclear magnetic resonance is a valuable new tool for studying the vitreous body of the eye. It is particularly suited for the detection of vitreal liquefaction and intraocular hemorrhage because of the dependence of the signal on the physical environment of water. Conversely, the vitreous body provides a new model for studying changes in proton relaxation times of protein solutions in biological systems.

Animals↗
PubMed1984

Principles of imaging by nuclear magnetic resonance.

Imaging by nuclear magnetic resonance (NMR) is a new modality for obtaining anatomic data. Magnetic field gradients are used to obtain spatial information. The advantages of NMR imaging include the ability to obtain images in multiple orientations (coronal, sagittal, and transverse), absence of ionizing radiation, and the potential to obtain chemical information. NMR images of the central nervous system have been equal to those of TCT, and in some cases superior. The utility of NMR imaging is yet to be determined, although preliminary findings are encouraging.

Humans↗
PubMed1984

Contrast agents and spectroscopic probes in NMR.

The demand for higher diagnostic specificity has led to the increased use of "foreign" agents to increase tissue contrast and/or spectroscopic sensitivity in NMR studies. The primary agents used to enhance tissue contrast in NMR imaging are paramagnetic. They cause a decrease in the proton T1 of H2O leading to enhanced signal intensity. This effect depends on the large gyromagnetic ratio of the electron, the number of unpaired electrons, the concentration of paramagnetic ions, the number of coordinated water molecules, and the rate of exchange of water. Spectroscopic enhancement has relied primarily on attempt at isotopic enrichment (usually C-13), which causes a direct increase in signal.

Carbon Isotopes↗
PubMed1984

Principles of nuclear magnetic resonance.

The basic principles of nuclear magnetic resonance (NMR) are discussed. The concepts presented include a qualitative quantum-mechanical approach to NMR spectroscopy and a classical-mechanical approach to time-dependent NMR phenomena (relaxation effects). The spectroscopic concepts discussed include absorption of radiation by matter, spin and energy quantization , chemical shift, and spin-spin splitting. The time-dependent phenomena include the concepts of T1 and T2, the spin-lattice and spin-spin relaxation time, and Fourier-transform NMR spectroscopy.

Electromagnetic Phenomena↗
PubMed1984

Multinuclear NMR studies of naturally occurring nuclei.

The ability to obtain nuclear magnetic resonance spectra from spatially localized regions of living animals and patients has led to the possibility of measuring biochemical processes in vivo. Localization is generally achieved through the use of surface coils. Using this technique, intracellular pH, and concentrations of high-energy phosphates and "abnormal" marker compounds have been measured in animal organs (both in vitro and in vivo) and in human brain and muscle (in vivo). The majority of studies have used the P-31 nucleus, but carbon (C-13) and hydrogen (H-1) have also been studied. However, both C-13 and H-1 experiments have technical difficulties. Carbon-13 has a low natural abundance, and H-1-containing metabolites may have their signals obscured by the large water peak. The phosphorus studies have been largely preclinical, but diagnostic possibilities are appearing from the many research problems now under investigation.

Animals↗
PubMed1984

Intracellular pH of the urinary bladder and red blood cells of the fresh water turtle.

Intracellular pH is thought to play an important role in several aspects of cell function including urinary acidification. The turtle urinary bladder is capable of urinary acidification in vitro and it is considered an analogue of the mammalian distal nephron. In the present study we measured intracellular pH in the epithelial layer of the turtle urinary bladder utilizing phosphorus nuclear magnetic resonance. In 14 experiments, the intracellular pH of the stripped turtle bladder epithelium bubbled with compressed air was 6.91 +/- 0.02; in turtle red blood cells the mean intracellular pH was 6.97 +/- 0.05 (n = 20), a value not significantly different from the pH value obtained in the turtle bladder. Gassing the turtle bladder with 95% air and 5% CO2 while maintaining the extracellular pH constant resulted in a rapid decrease in intracellular pH. Lowering of extracellular pH with HCl also resulted in a decrease in intracellular pH. The results demonstrate that phosphorus nuclear magnetic resonance allows rapid, noninvasive measurement and frequent monitoring of intracellular pH in the turtle bladder.

Animals↗
PubMed1983

Multiple environments of fluorinated anesthetics in intact tissues observed with 19F NMR spectroscopy.

The incorporation of two fluorine-containing general anesthetic agents, halothane and methoxyflurane, into erythrocytes (from three different species), rabbit muscle and rabbit nerve, was followed with 19F NMR spectroscopy. Two major findings emerged from these studies: (1) multiple environments indicative of domain structure in the membrane can be observed depending on the anesthetic and the tissue type; and (2) the 19F chemical shifts of a given anesthetic were characteristic for the tissue examined. Halothane showed a single resonance in erythrocytes and multiple resonances in muscle and nerve, while methoxyflurane showed multiple resonances in both muscle and erythrocytes. The range of the 19F chemical shifts for the multiple peaks was as great as 6 ppm.

Animals↗
PubMed1983

Nuclear magnetic resonance imaging in central nervous system disease.

From the preliminary work of many investigators, it appears that proton nuclear magnetic resonance (NMR) imaging will have wide application in the diagnostic assessment (and potential management) of patients with vascular, neoplastic, and demyelinating diseases of the central nervous system (CNS). Findings in isolated cases and small series suggest that NMR imaging may play a role in the evaluation of patients with other CNS conditions including hydrocephalus, malformations, infections, developmental and metabolic disorders, and degenerative processes. Because of the dynamic nature of disease processes involving the CNS, the precise meaning of NMR image parameters (rho, T1, and T2) remains unclear. A comprehensive study correlating NMR images in neurologic disease with precise neuropathologic examination is required. In the future, with accurate quantitative measurements of these NMR parameters, in vivo imaging may provide insight into the dynamic nature of neurologic disease.

Central Nervous System Diseases↗
PubMed1983

Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic resonance imaging.

The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region.

Aneurysm↗
PubMed1983

Acid-base metabolism, intracellular pH and water transport by the toad bladder.

A decrease in extracellular pH is well known to inhibit vasopressin stimulated water flow in the toad bladder. It remains unclear whether this inhibition is the result of the effect of extracellular pH per se or the consequence of altered intracellular pH. In the present study we evaluated the effect of several maneuvers capable of altering intracellular pH on vasopressin or cyclic AMP stimulated water flow in the toad bladder in the absence of alterations of extracellular pH. In the presence of a normal extracellular pH, bladders subjected to a high partial pressure of CO2 or bladders from acidotic toads had a significant decrease in vasopressin or cyclic AMP stimulated water flow as compared to controls. We also examined the effect of maneuvers capable of increasing intracellular pH on vasopressin and cyclic AMP stimulated water flow. Intracellular alkalosis was induced by exposing the bladders in vitro to NH4Cl at pH 8 or to acetazolamide. Both maneuvers resulted in a significant decrease in vasopressin, but not in cyclic AMP stimulated water flow. Bladders removed from alkalotic toads, incubated in a normal extracellular pH also showed a decrease in AVP stimulated water flow. Intracellular muscle pH assessed with phosphorus nuclear magnetic resonance, was not different among bladders from control, acidotic and alkalotic toads. It is concluded that alterations of intracellular pH, in the absence of alterations of extracellular pH, are important in regulation of water transport in the toad bladder in response to vasopressin or cyclic AMP. In addition, metabolic acidosis or alkalosis alters AVP or cyclic AMP stimulated water flow by a mechanism independent of the intracellular pH.

Acetazolamide↗
PubMed1982

31P nuclear magnetic resonance of phosphonic acid analogues of adenosine nucleotides as functions of pH and magnesium ion concentration.

The 31P NMR proton-decoupled spectra of alpha, beta-methylene-ATP [Ap(CH2)pp], beta, gamma-methylene-ATP [App(CH2)p], and alpha, beta-methylene-ADP [Ap(CH2)p] were measured as functions of pH and Mg2+ concentration. Each ATP analogue yielded three resonances: two doublets and one doublet-of-a-doublet. Assignments of resonances were based upon spin-coupling multiplets, their coupling constant magnitudes (24-27 Hz for -P-O-P- and 4-10 Hz for -P-CH2-P-), and the magnitude of the chemical shift movement during proton titration or its direction of movement. All phosphonyl resonances are substantially downfield compared to phosphoryl resonances. The chemical shifts of terminal phosphonyl units moved upfield with increasing pH or rising Mg2+ concentration. The chemical shifts of phosphonyl and phosphoryl anhydride plus ester units usually either moved downfield during proton titration and addition of Mg2+ or remained constant. Accurate pKa' values were readily determined from chemical shift movements as a function of pH: 3.05 +/- 0.04 and 8.80 +/- 0.05 for App(CH2)p, 7.34 +/- 0.06 for Ap(CH2)pp, and 8.29 +/- 0.02 for Ap(CH2)p. Addition of Mg2+ or Tris produced an acidic shift of the alkaline pKa' values. Addition of Mg2+ at pH 7.0 to the nucleotides caused large movements in the chemical shifts of their terminal two phosphorus atoms.

Adenine Nucleotides↗
PubMed1982

Proton nuclear magnetic resonance imaging of regionally ischemic canine hearts: effect of paramagnetic proton signal enhancement.

In a study to evaluate the potential of proton nuclear magnetic resonance (NMR) imaging with and without manganese contrast with and without manganese contrast enhancement for detecting acute myocardial infarction, 12 dogs underwent 90-minute occlusion of the left circumflex coronary artery. Transverse-section NMR images of the excised, nonbeating heart were obtained at 1-cm intervals using the steady-state-free-precession (SSFP) technique. All NMR images revealed detailed structure of the heart. The three hearts without manganese showed no difference in intensity between the normal and the ischemic posterior regions, whereas those with manganese demonstrated a clearly demarcated zone of reduced signal intensity consistent with the ischemic zone. It is concluded that high-resolution tomograms of the excised canine myocardium can be obtained using proton NMR imaging. With the SSFP imaging technique, proton signal enhancement with manganese infusion is necessary to differentiate between ischemic and nonischemic myocardium after 90 minutes of coronary occlusion.

Animals↗