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Biomedical subjects

S Vinitski

Publications and source records attributed to S Vinitski.

At least 55 records · Page 3Linked to original sources
PubMed1987

Effect of the sampling rate on magnetic resonance imaging.

Effects of the sampling rate on spatial resolution and the signal-to-noise ratio in spin-echo MR imaging were calculated. The theoretical results suggest that as T2* decreases, due to either static magnetic field inhomogeneities or shortened T2 relaxation times, the calculated optimum sampling rate increases accordingly. Since biological tissues exhibit wide variations in their magnetic susceptibilities and T2 relaxation times for various isotopes but modern magnets are characterized by good magnetic field homogeneity, the optimum sampling rate should exhibit an observable dependence on the tissue type. Proton and sodium imaging experiments confirm this conclusion.

Animals↗
PubMed1987

The biophysical basis of tissue contrast in extracranial MR imaging.

So that radiologists can understand better the differences between tissues that determine MR image contrast, the biophysical basis of proton-MR tissue contrast is reviewed. Differences in the molecular sizes of water, fat, and protein macromolecules affect the rate of molecular motion, which in turn influences relaxation times. Differences in the physical state of water within tissues determine the extent to which the motion of water is restricted by binding to hydrophilic macromolecules (e.g., protein), which in turn causes variable amounts of T1 and T2 shortening. Understanding these concepts and knowing the location in the body of free water, cellular tissues, fat, collagen, bone, and tissue iron improve the radiologist's ability to extract useful information from MR images.

Adipose Tissue↗
PubMed1986

Correlates of brain-stem oculomotor disorders in multiple sclerosis. Magnetic resonance imaging.

Three patients with focal brain-stem oculomotor disturbances (nuclear sixth nerve syndrome, sixth nerve palsy, bilateral internuclear ophthalmoplegia) as a consequence of multiple sclerosis have been studied with high-volume delayed computed tomography and high-field magnetic resonance imaging. In all of them, high-volume delayed computed tomography was inconclusive in the brain stem, but magnetic resonance imaging showed an area of prolonged T1 and/or T2 in the region appropriate to the oculomotor findings. Magnetic resonance imaging is the imaging technique of choice of small plaques in the brain stem. It can considerably aid clinicotopographic correlation in multiple sclerosis.

Adult↗
PubMed1986

Differentiation of parenchymal lung disorders with in vitro proton nuclear magnetic resonance.

We investigated in vitro NMR properties of bleomycin-induced alveolitis and pulmonary fibrosis in 18 Lewis rats (6 controls). When alveolitis or fibrosis had developed, animal lungs were excised and examined histologically and gravimetrically and their T1 and T2 were determined by a NMR spectrometer at 10.7 MHz and 37 degrees C. Clinical diagnosis was confirmed histologically in each case. The NMR signal intensities were significantly elevated in both disease states (P less than 0.001). Both T1 and T2 values of alveolitic lungs were about the same as in controls, but were significantly decreased in fibrotic lungs (P less than 0.01). Changes in T1 and T2 correlated well (P less than 0.001) with changes in water content of diseased lungs.

Animals↗
PubMed1985

Radioaerosol ventilation imaging in ventilator-dependent patients. Technical considerations.

The differentiation of pulmonary embolism (PE) from regional ventilatory abnormalities accompanied by reduced perfusion requires contemporary perfusion and ventilation studies. Distinguishing these conditions in ventilator-dependent patients is aided by administering a Tc-99m aerosol to characterize regional ventilation, and by performing a conventional Tc-99m MAA perfusion study. The technique uses a simple "in-house" constructed apparatus. Simple photographic techniques suffice, but computer subtraction of perfusion from the combined perfusion-ventilation image renders interpretation easier if aerosol administration follows perfusion imaging. Multiple defects can be examined in a single study. Excluding normal or near-normal perfusion studies, PE was thought to be present in eight of 16 patients after perfusion imaging alone, but in only one of eight after added aerosol imaging. Angiography confirmed the diagnosis in that patient. Of the eight patients who had abnormal perfusion but were thought unlikely to have PE from the perfusion study alone, two had normal ventilation, and subsequently were shown to have PE by angiography. Because angiography was only performed on patients who were thought to have a high probability of PE on sequential perfusion-ventilation imaging, the true incidence of PE may have been higher. Aerosol ventilation imaging is a useful adjunct to perfusion imaging in patients on ventilators. It requires an efficient delivery system, particularly if aerosol administration follows perfusion imaging, as it does in this study. The major disadvantage of aerosol imaging compared to a gas in intubated patients is the significant bronchial deposition due to retained mucus secretions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1985

Quantitation of lung water by nuclear magnetic resonance imaging. A preliminary study.

Pulmonary edema was produced in four anesthetized dogs by saline lavage. The animals were maintained by assisted ventilation with O2/halothane and examined by a nuclear magnetic resonance (NMR) 0.15T resistive-magnet imager. The distribution of edematous fluid was clearly observed. Image contrast increased with prolongation of the cycle time (TR). Tomographic maps of spin-lattice relaxation times (T1) of the lungs were calculated from the NMR images. Comparison of T1 values with gravimetric measurements of water content of lung samples showed significant correlation (r = .7, P less than .02, n = 12) suggesting a potential for in vivo lung water quantitation by NMR imaging. This in vivo correlation is qualitatively similar to the in vitro correlation. Accurate in vivo determinations of pulmonary T2 values may require respiratory gating.

Animals↗
PubMed1985

Aminophylline and mucociliary clearance in patients with irreversible airflow limitation.

Were aminophylline to improve mucociliary function, it might prove useful in the management of irreversible airflow limitation. Eight subjects with irreversible airflow limitation due to emphysema inhaled an aerosol of 99mTc sulphur-colloid particles on each of 2 days. On day 1 aminophylline was administered intravenously, while on the other nothing was given. Particle clearance was measured by recording posterior gamma-camera images sequentially over a 24 h period. No significant differences were recorded between aminophylline and control studies, but there were marked variations in clearance between study days and between individuals. These differences were compatible with the known effects of airways obstruction and breathing pattern on the sites of particle deposition within the bronchial tree. The latter factors appeared to exert a far greater influence on the observed mucociliary clearance than did aminophylline.

Aminophylline↗
PubMed1985

Regional deposition of particles in the lung during cigarette smoking in humans.

Studies were carried out on 11 habitual cigarette smokers to ascertain whether there was a difference in the regional deposition of particles during cigarette smoking compared with tidal breathing and also to investigate whether the ventilatory maneuvers associated with smoking influence the deposition site. A cigarette holder was constructed that permitted cigarette smoke to mix with a radioaerosol. An added resistance simulated the airflow resistance present in a filter-tipped cigarette. Respiratory patterns for the control period of tidal breathing and during smoking were monitored with a respiratory inductance plethysmograph. Smoking resulted in greater apical and central deposition than expected from the distribution of resting ventilation. The changes in the site of deposition during smoking are probably influenced mainly by the properties of the particles concerned, namely, its size, reactivity, and hygroscopicity. Changes in respiratory patterns that occur during inhalation of cigarette smoke may also have an effect but are difficult to quantify and show marked intersubject variation. In selected subjects smoking caused apical deposition to exceed that of the lower zones.

Adult↗
PubMed1984

The effect of exercise on the deposition of an inhaled aerosol.

We investigated the regional deposition in the lungs, of an inhaled submicron aerosol at rest and during exercise in 13 normal volunteers of whom 5 were cigarette smokers. The degree of exercise (VO2 approximately 2 L/min) was chosen to simulate moderately heavy physical labour. Tracheobronchial and alveolar components of deposition were measured by comparing images immediately after inhalation of aerosol and 24 h later when mucociliary clearance was complete. At rest almost all deposition was alveolar (97%). The increase in total deposition on exercise was of similar order to the increase in ventilation. On exercise regional alveolar deposition became more even, although basal still exceeded apical deposition. Tracheobronchial deposition on exercise was increased in all zones but particularly in the upper zones, thereby contrasting with the base to apex gradient of parenchymal deposition. These changes were exaggerated in the smokers. The increased upper zone tracheobronchial deposition may have implications in regard to the pathogenesis of diseases caused by the inhalation of dusts and fumes.

Adult↗
PubMed1983

Factors influencing the regional deposition of inhaled particles in man.

1. Although ventilation in normal human lungs has been shown to decrease from apex to base, comparable observations are lacking in regard to particle deposition. 2. We compared regional ventilation and particle deposition in normal subjects by using radioactive xenon and a radioactive aerosol while sitting, lying, and while breathing at an increased rate. Both smokers and non-smokers were studied. 3. Particle deposition and ventilation were closely related, and the greater the ventilation the greater the deposition of particles, a situation which prevailed irrespective of position and breathing rate. While supine, the apex to base gradient for both ventilation and particle deposition decreased but did not entirely disappear. At higher respiratory rates, central deposition of particles, especially in smokers, increased. 4. We concluded that there are regional differences in the deposition of particles and that such differences are closely related to regional ventilation.

Adult↗
PubMed1983

Histamine bronchial challenge: effect on regional ventilation and aerosol deposition.

We studied regional changes in ventilation and aerosol deposition after histamine challenge in six patients with asthma and two with rhinitis and a history of wheezing. All were known to have bronchial hyperreactivity and all showed an increased response to histamine. Ventilation and aerosol deposition studies, using xenon-133 and an aerosol of sulphur colloid tagged with technetium 99m, were performed while they were sitting. Before administration of histamine radioaerosol scintiscans were abnormal in five of six patients; after histamine challenge all were abnormal and central deposition was significantly greater in all of them. The decrease in aerosol penetration correlated with the percentage decrease in FEV1, indicating that the efficiency of aerodynamic filtration depends on the degree of airway narrowing. In six of the eight subjects the distribution of ventilation changed from predominantly basal to predominantly apical after histamine, which suggests the airways response was greater, at least initially, in the better ventilated regions. This indicates a close relationship between regional ventilation and the site of histamine deposition and has implications for the delivery of aerosolised agents in general.

Adult↗
PubMed1983

Radiation dose calculations for inhalation of Tc-99m sulfur colloid radioaerosol.

The radiation dose to the lung from the administration of Tc-99m sulfur colloid aerosol (for ventilation investigations) has been calculated. The dose to the ciliated airway epithelium varies between 0.34 to 2.5 rads, compared with 0.31 rads to the lung parenchyma. The calculation was normalized to a total of 1 mCi of Tc-99m deposited in the lung.

Aerosols↗
PubMedDate not supplied

MR image contrast at high field strength.

The T1 of soft tissues increases with magnetic field strength. Some tissue contrast may be diminished on high-field-strength magnetic resonance (MR) images when conventional TRs are used, because of altered T1 effects on the MR signals. This necessitates longer TRs in techniques that use long TRs, which prolongs the examination excessively. Behavior of macroscopic magnetization is governed by the Bloch equations. Therefore, T1 contributions to the MR signal can be modulated by means of both timing intervals and radio-frequency pulses. The analytic solution to the Block equations allowed calculation of white matter/gray matter and gray matter/cerebrospinal fluid contrast in both spin-echo and inversion-recovery (IR) imaging. Rabbit brains (normal and tumor-containing) were then imaged in vivo at 1.5 and 4.7 T. In addition, MR images of a human head were obtained at 4.0 T. Experimental results supported the theoretical predictions that brain contrast on long TR spin-echo or IR images increases with field strength. However, varying the excitation flip angle allowed optimization of the T1 contribution to the MR signals, improving image contrast and/or reducing examination time. Thus, the dependence of T1 on field strength determines the optimum choice of imaging techniques and parameters in a predictable fashion.

Animals↗