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Biomedical subjects

D E Bohning

Publications and source records attributed to D E Bohning.

34 records · Page 2Linked to original sources
PubMed1997

Mapping transcranial magnetic stimulation (TMS) fields in vivo with MRI.

Transcranial magnetic stimulation (TMS) is a non-invasive technique for investigating brain function that uses pulsed magnetic fields created by special coils to induce localized neuronal depolarization. Despite the technique's expanding application, the exact magnetic field produced by TMS coils have never been directly measured in human subjects. Using a standard 1.5T MR scanner and TMS coils constructed from non magnetic materials, we have obtained 3D maps of the magnetic field created by TMS coils in human volunteers. Further, we mapped the combined field of two coils and demonstrated that combinations of coils might be used to focus the magnetic field to achieve improved stimulation patterns and, perhaps, reach areas out of reach of single coils.

Brain↗
PubMed1997

Multi-modality mapping of motor cortex: comparing echoplanar BOLD fMRI and transcranial magnetic stimulation. Short communication.

Multiple non-invasive methods of imaging brain function are now available for presurgical planning and neurobiological research. As these new methods become available, it is important to understand their relative advantages and liabilities, as well as how the information gained compares across different methods. A current and future trend in neurobiological studies as well as presurgical planning is to combine information from different imaging techniques. Multi-modal integration may perhaps give more powerful information than each modality alone, especially when one of the methods is transcranial magnetic stimulation (TMS), with its ability to non-invasively activate the brain. As an initial venture in cross comparing new imaging methods, we performed the following 2 studies, locating motor cortex with echoplanar BOLD fMRI and TMS. The two methods can be readily integrated, with concurring results, although each have important limitations.

Adult↗
PubMed1997

Histological correlates to pig gastrointestinal wall layers imaged in vitro with the magnetic resonance endoscope.

BACKGROUND & AIMS: The magnetic resonance endoscope consists of a nonferromagnetic endoscope with a receiver coil incorporated into its tip. The aim of this study was to define the anatomic correlates of the gastrointestinal wall layers imaged in vitro with the magnetic resonance endoscope. METHODS: Twenty-two tissue specimens from various segments of the porcine gastrointestinal tract were imaged with the magnetic resonance endoscope using up to four different scanning sequences. Cyanoacrylate, serving as a marker, was randomly injected into the tissue strips before imaging. Histological sections were then compared with the magnetic resonance images. RESULTS: T1-weighted spin echo sequences yielded the highest image quality and typically showed three wall layers that corresponded to distinct histological layers. The mucosa showed high signal intensity, the submucosa low signal intensity, and the muscularis propria an intermediate signal intensity. In the esophagus and rectum, the muscularis propria could be visualized as separate circular and longitudinal layers. CONCLUSIONS: In vitro imaging with the magnetic resonance endoscope shows three to five wall layers of the porcine gastrointestinal tract depending on the segment scanned. This degree of gut wall resolution suggests that endoscopic magnetic resonance imaging may have potential for local staging of gastrointestinal tumors.

Animals↗
PubMed1997

MR endoscopy: preliminary experience in human trials.

The authors performed local staging of esophageal and rectal cancer (without pathologic correlation) with use of a nonferromagnetic magnetic resonance (MR) endoscope with a 3-cm-long receive-only coil embedded in its tip in 16 patients (eight with esophageal cancer and eight with anorectal cancer). Results with spin-echo sequences were optimal in all cases [corrected].

Anal Canal↗
PubMed1996

In vivo phosphorus spectroscopy of human skin.

Skin 31P MRS measurements might detect metabolic damage from irradiation, chemotherapy, or ischemia. Although rat and cadaver data have demonstrated this potential (C.D. Cuono, et al., Plast. Reconstr. Surg. 81, 1-11 (1988), H.W. Klein, et al., Ann. Plast. Surg. 20, 547-551 (1988)), few studies of in vivo phosphorus human skin spectra have been published (A. Zemtsov, et al., J. Dermatol. Surg. Oncol. 15, 1207-1211 (1989), A Zemtsov, et al., J. Am. Acad. Dermatol. 30, 959-965 (1994)), and those likely reflect underlying muscle as much as skin. To separate 31P skin and muscle spectra, we have developed a unique two-layer "flotation" phantom for mapping coil sensitivity and an associated semiempirical two-power RF depth-resolved technique. Phantom and method have been applied in a study of 17 normal volunteers to obtain human in vivo 31P skin spectra uncompromised by muscle contamination and to quantitate ratios of major phosphometabolites. Skin results consistently showed low ratios of phosphocreatine (PCr) to adenosine triphosphate (ATP), high levels of phosphomonoester (PME), P(i), and phosphodiester (PDE) relative to PCr, and demonstrated a shift in pH toward greater alkalinity, compared to that with simultaneous muscle results.

Adenosine Triphosphate↗
PubMed1990

PC-based system for retrospective cardiac and respiratory gating of NMR data.

A method and a means for retrospectively clustering NMR k-space measurement profiles with respect to both cardiac and respiratory phases were developed to explore strategies for (1) reducing cardiovascular and respiratory flow/motion image artifacts and (2) improving T1 and T2 characterization of the heart. The image data are collected at a uniform rate so that echo (TE) and repetition (TR) times are independent of the varying cardiac cycle R-R interval and/or respiratory motions. Cardiac (C) time, respiratory (R) time or diaphragm position, and NMR data acquisition (A) cycle time are collected by microcomputer in parallel with free running (untriggered) image collection on a standard magnetic resonance imager. After the raw data equivalent of multiple images are collected, the C-A-R phase timing data are uploaded from the microcomputer to the scanner's minicomputer for use in a normalized C-R phase plane clustering of the image raw data. Each profile's position in the C-R phase plane is determined and then clustered into a new set of data, one image being equivalent for each desired C-R phase combination. These raw data are then zero-filled and (optionally) filtered to compensate for the nonuniform k-space sampling and, finally, reconstructed. Cardiac "cines" made from these retrospectively gated images are comparable to similarly phased triggered images. When high time resolution is required, retrospective gating can be expected to show improvements over triggering, especially toward the critical latter part of the cardiac cycle, where coronary artery filling occurs. The system described can readily be assembled from generally available components.

Electrocardiography↗
PubMed1976

Effect of adrenergic agents and their mode of action on mucociliary clearance in man.

The aerosolized adrenergic (ADR) agent, isoproterenol (ISO), was found markedly to accelerate mucus clearance within the human tracheobronchial tree. Mucus transport was measured by external gamma counting of aerosolized Fe2O3 particles deposited on the mucous membrane during inhalation. Aerosolized epinephrine (EPI), despite its alpha-ADR bronchial vasoconstrictor activity, increased mucus clearance to the same degree as did aerosolized ISO, with its beta-ADR bronchial vasodilator activity. The vehicle used for delivery of the ADR agents, i.e., a H2O aerosol by intermittent positive-pressure breathing (IPPB), itself increased mucus clearance slightly, but did not elicit the enormous increases produced by the ADR agents. Parenteral ISO caused increases in clearances similar to aerosolized ISO and EPI (consistent with different tissue drug levels achieved). Oral atropine delayed clearance, but atropine prior to an ADR aerosol did not alter the mucus transport effect of the ADR agent. ISO and atropine, despite opposite effects on mucus clearance, caused equal bronchodilation. Thus, increased clearance following aerosolized ISO was not dependent on bronchial vasodilation, aqueous aerosol droplets, reflex parasympathetic activation, or bronchodilation, and seems best attributable to increased ciliary beat rate.

Adult↗
PubMed1976

Effect of pretest temperature on aerosol penetration and clearance in donkeys.

Pretest temperature and humidity were correlated with tracheobronchial particle penetration and clearance data from donkeys housed in unheated outdoor facilities and tested after spending 1-2 h in a temperature- and humidity-controlled laboratory. The animals inhaled an inert insoluble radioisotope-labeled monodisperse aerosol for several minutes. Its retention was monitored continuously for 3 h by external gamma detection. Aerosol deposition pattern and bronchial clearance were linearly correlated with pretest outdoor temperature which ranged from -10 to 30 degrees C. The fraction depositing in the unciliated regions of the lung decreased 0.6% per degrees C drop in outdoor temperature. Overall bronchial transport decreased at least 1.5% per degrees C decrease. Multiple linear regression analysis and correction for the positive correlation between temperature and humidity left no significant residual humidity dependence. Acclimatization of the animals in the laboratory for 6 h before testing significantly reduced these effects.

Aerosols↗
PubMed1975

Tracheobronchial particle deposition and clearance. A study of the effects of cigarette smoking in monozygotic twins.

Particle deposition and tracheobronchial clearance were measured in six pairs of male monozygotic twins, four of which were discordant for cigarette smoking. The fraction of an inhaled aerosol that deposited on the ciliated airways showed variations within twin pairs comparable with variations in repeated tests on a single subject, and significantly smaller (P less than .001) than among tests on different subjects. Variations that did occur were consistent with differences in forced expiratory volume (FEV1.0) values. The proximal shift of aerosol deposition and reduced FEV1.0 values in smokers indicated that they had some degree of bronchoconstriction. Mucociliary clearance characteristics are qualitatively and quantitatively similar for nonsmoking and smoking concordant monozygotic twins, ie, comparable with repeated tests on a single individual, reflecting their constitutional similarity. With one exception, clearance curves for twin pairs discordant with respect to smoking were also qualitatively indistinguishable. Nonsmokers, however, had greater upper bronchial clearance rates than their smoking twins.

Aerosols↗
PubMed1975

Factors affecting tracheobronchial mucociliary transport.

In vivo mucus transport rates were studied in humans and donkeys by external measurement of the rate of clearance of insoluble monodisperse gamma-tagged aerosols. The influence of temperature, environmental toxicants and drugs which affect the autonomic nervous system were studied by determining the changes in clearance produced by them in individual subjects. In donkeys, increased pretest ambient temperature accelerated clearance by greater than 1.7%/ degrees C. Smoking 2-7 cigarettes reduced the duration of bronchial clearance by approximately 50% in both humans and donkeys. Donkeys were exposed to higher doses; with progressive slowing of tracheal and bronchial clearance for greater than 10 cigarettes. HCN, at concentrations up to 1230 ppm, produced only a mild transient slowing of clearance. In man, atropine slowed clearance, while the adrenergic stimulating drugs, isoproterenol and epinephrine, both accelerated it by greater than or equal to 4 times, as did isoproterenol when given subsequent to atropine. The cholinergic stimulating drug methacholine increased mucociliary transport in the the donkey. Administration of a tap water aerosol for 10-15 min in humans increased bronchial clearance rates by approximately 25%.

Aerosols↗
PubMedDate not supplied

Effects of acceleration on the accuracy of MR phase velocity measurements.

Acceleration in blood flow can affect the accuracy of phase velocity measurements. Convective acceleration is due to changes in flow geometry and is independent of the time-varying acceleration caused by flow pulsatility. To analyze the effects of convective acceleration on flow velocity measurements, phase velocity measurements were obtained in steady laminar flow in the convergent segment of a 90%, hourglass-shaped stenosis phantom at a Reynolds number of 1,500. Measurements at the stenosis indicated that convective acceleration caused the measured values of average cross-sectional velocity to deviate as much as 37% from the theoretical values. The magnitude of the error could be accounted for by including the convective acceleration term in the phase shift equation. Convective acceleration effects should not be ignored in flow velocity measurements through stenoses, even when time-dependent acceleration due to flow pulsatility can be neglected.

Acceleration↗