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Biomedical subjects

M A Foster

Publications and source records attributed to M A Foster.

At least 55 records · Page 3Linked to original sources
PubMed1990

CT of the extrahepatic bile ducts: wall thickness and contrast enhancement in normal and abnormal ducts.

Recent reports have described thickening and enhancement of the extrahepatic bile duct wall on CT scans obtained after administration of IV contrast material. We undertook this study to establish parameters for the normal thickness and enhancement of the bile duct wall on CT, and to develop a differential diagnosis for thickening of the duct wall. Routine CT examinations of 100 patients without biliary disease were evaluated prospectively. The common hepatic duct and common bile duct could be visualized in 66% and 82% of cases, respectively; the walls of these ducts could be separately discerned in 59% and 52%. The mean thickness of the duct wall was 1 mm, with a maximal thickness of 1.5 mm. Wall enhancement was similar to (51%), slightly greater than (44%), or markedly greater than (5%) the enhancement of adjacent pancreatic parenchyma. A review of records covering a 5-year period identified 52 patients in whom CT showed thickening of the bile duct wall (greater than or equal to 2 mm). These patients could be categorized by seven underlying diseases, and analysis of the CT scans revealed four general patterns of thickening. Focal, concentric wall thickening in the distal common bile duct was associated with pancreatitis, pancreatic cancer, and common bile duct stones; focal, eccentric thickening tended to occur with cholangiocarcinoma and sclerosing cholangitis. Diffuse, concentric thickening was seen with acute cholangitis; diffuse, eccentric thickening was associated with oriental cholangiohepatitis and sclerosing cholangitis. Thickening of greater than 5 mm was seen only with cholangiocarcinoma. Enhancement of the duct wall in these groups varied and was of no predictive value. In summary, the extrahepatic bile ducts can be visualized in the majority of patients, and the normal duct wall should be 1.5 mm or less in thickness. Contrast enhancement of the duct wall occurs in patients without biliary tract disease and alone is predictive not predictive of pathology. Pancreatitis, pancreatic cancer, common bile duct stones, cholangiocarcinoma, sclerosing cholangitis, acute cholangitis, and oriental cholangiohepatitis are associated with thickening of the duct wall.

Acute Disease↗
PubMed1989

Stimulation of Isopentenyl Pyrophosphate Incorporation into Polyisoprene in Extracts from Guayule Plants (Parthenium argentatum Gray) by Low Temperature and 2-(3,4-Dichlorophenoxy) Triethylamine.

Rubber particles isolated from guayule (Parthenium argentatum Gray) stem homogenates contain a polyprenyl transferase which catalyzes the polymerization of isopentenyl pyrophosphate into polyisoprene. The polymerization reaction is stimulated with the addition of an allylic pyrophosphate initiator and forms a polymer of polyisoprene with a molecular weight distribution from 10(3) to 10(7). The polymerization reaction in crude stem homogenates is not affected by the addition of an initiator probably due to the high activity of isopentenyl pyrophosphate isomerase furnishing saturating levels of dimethylallyl pyrophosphate. Polyisoprene formation in stems of guayule plants exposed to cold winter temperatures increased from 15.4 milligrams per gram dry weight in October to 24.5 milligrams per gram dry weight in January and increased from 16.2 to 38.1 milligrams per gram dry weight in the same period by additionally treating the plants with 5000 ppm of 2-(3,4-dichlorophenoxy)triethylamine. The rate of polymerization of isopentenyl pyrophosphate into polyisoprene in stem homogenates of the cold treated plants increased from 12.1 nanomoles per hour per gram fresh weight in October to 144.3 nanomoles per hour per gram fresh weight in January and increased from 17.7 to 446.8 nanomoles per hour per gram fresh weight in the same period by additionally treating the plants with 5000 ppm of 2-(3,4-dichlorophenoxy)triethylamine. These results show that the increase in polyprenyl transferase activity partially accounts for the increase in polyisoprene synthesis in guayule plants exposed to low temperature and treated with 2-(3,4-dichlorophenoxy)triethylamine.

Journal Article↗
PubMed1989

Effects of ethanol on the NMR characteristics of rat brain. Acute administration, dependency, and long-term effects.

In rats, neither acute administration of ethanol nor the establishment of ethanol dependence by chronic administration for 28 days produced significant 1H-NMR relaxation changes. However, chronic ethanol intake for six months produced a transient rise in T1, with no change in T2 or water content. The significance of these results for study in man is discussed and a hypothesis is proposed to explain discrepant differences between T1, T2 and water content. It is suggested that T1 change with long-term ethanol exposure is related to altered free/bound water state secondary to cell membrane changes.

Alcoholic Intoxication↗
PubMed1987

Meconium peritonitis: prenatal sonographic findings and their clinical significance.

Ultrasonographic (US) findings were correlated with clinical outcome in seven cases of meconium peritonitis detected with prenatal US during a 2-year period. Nineteen previously reported cases were also reviewed. US findings included intraabdominal calcifications (n = six cases), fetal ascites (n = 3), echogenic ascites without calcifications (n = 1), bowel dilatation (n = 2), and polyhydramnios (n = 5). Following delivery, six infants were still alive after a mean follow-up of 13 months (range, 6-26 months); the seventh died of hydrocephalus. Of the six, four required surgical correction of a small-bowel perforation and two did not. All six are thriving, and none has yet been found to have cystic fibrosis. In the 19 previously reported cases, there were only two cases of cystic fibrosis, neither with intraabdominal calcifications. The presence of calcifications was significantly associated with causes other than cystic fibrosis. Prenatally diagnosed cases of meconium peritonitis are associated with cystic fibrosis less frequently than previous studies suggest.

Ascites↗
PubMed1987

Hydration, volume changes and nuclear magnetic resonance proton relaxation times of HeLa S-3 cells in M-phase and the subsequent cell cycle.

Most mitotic HeLa cells divided into two daughter cells with half the volume of the parent; no additional reduction in volume was detectable during late telophase or the early part of G1. Synchronous growth throughout the next generation cycle was exponential, without an additional and sudden rise in volume being detectable as cells entered M-phase. Since the wet weight/dry weight ratio and the protein per unit mass of cells remained constant throughout the cycle, measurements based on volume changes accurately reflected growth parameters and cell water content. Nuclear magnetic resonance (n.m.r.) t1 (spin-lattice) proton relaxation times for intracellular water for M-phase cells measured at both 32 MHz (25 degrees C) and 80 MHz (37 degrees C) in a Bruker spectrometer had the same values as normal interphase cells. Furthermore, cells arrested in metaphase by nitrous oxide or alkaloids gave the same t1 values. Artificial manipulation of cell hydration by adjustment of the tonicity of the external medium led to t1 values that correlated well with the level of intracellular water. On this basis, a 40% increase in hydration raised t1 values by a factor of 1.29 at 32 MHz and 1.5 at 80 MHz. This is considerably less than the increase by a factor of 1.9 in t1 time reported with the 40% rise in cell water accompanying mitosis, measured at 30 MHz and 25 degrees C under isotonic conditions by others. The protein-synthesizing ability of hydrated cells was reduced to only half the normal level after a doubling of intracellular water. The data from these several different analyses, taken together, strongly indicate that the water content of mitotic cells is very similar to that of interphase cells, and that certain features unique to the mitotic phase of the cell cycle cannot be ascribed to an elevated (free) water content.

Cell Cycle↗
PubMed1986

Measurement of total lung water from nuclear magnetic resonance images.

An accurate, non-invasive means of measuring pulmonary water is desirable, for both clinical and research use. Nuclear magnetic resonance imaging is theoretically very suitable for this purpose. Nuclear magnetic resonance (NMR) spectroscopy was used to show that the water content of lung tissue could be predicted accurately from the intensity of signal resulting from a 90 degree saturation recovery sequence. The water contained in an image section may, therefore, be calculated by reference to a 100% water standard. Lung water was obtained by imaging the lung in continuous sections and summing the water contents of the component sections. The method performed well when applied to a sponge phantom, but underestimated by up to 30% in excised sheep lung. The total (vascular and extravascular) pulmonary water measured by NMR in six healthy volunteers was 292 g (SD 58 g) or 4.6 g/kg body weight, less than predicted by some other indirect methods and post-mortem values. A briefer examination comprising two axial sections at standardised levels was also devised. In 15 healthy volunteers the mean water content of a 1.6 cm-thick axial section through the right lung was 17.8 g at the sternal angle, and 23.3 g 5 cm caudally. In the left lung, the values were 16.4 g and 16.3 g, respectively.

Adult↗
PubMed1985

Particulate oral NMR contrast agents.

Insoluble paramagnetic compounds in suspension can be used to achieve visualization of the gastrointestinal system on magnetic resonance imaging (NMR). Particulate preparations of these agents decrease the T1 and T2 of solutions to which they are added. Gadolinium oxalate, a prototype of these particulate agents, was evaluated in vitro and in vivo (in rabbits) by NMR imaging. The effect of this compound upon T1 and T2 in vitro was also quantitated by NMR spectroscopy. Opacification of the upper gastrointestinal tract was achieved with gadolinium oxalate following oral administration. The colon was visualized following rectal administration.

Administration, Oral↗
PubMed1985

Pulsed magnetic field exposure during pregnancy and implications for NMR foetal imaging: a study with mice.

Following the recent progress in NMR imaging of the foetus in utero an investigation has been made of the effect of exposure to strong pulsed magnetic fields on the pregnancy of mice and the post natal development of their litters. 23 pregnant mice received exposures ranging from 3.5-12kT/s with pulse periods in the range 0.33-0.56ms at various times during gestation. A similar number of pregnant mice served as controls. No adverse effect was observed on the pregnancy. There was no significant difference between the litter numbers and growth rates of the exposed litters compared with controls. The implications of these results are discussed with regard to the safety of NMR imaging during pregnancy.

Animals↗
PubMed1984

Nuclear magnetic resonance pulse sequence and discrimination of high- and low-fat tissues.

Signal size compared to independently measured T1 is described for various pulse sequences on the Aberdeen Mk II nuclear magnetic resonance imager. The ability of these sequences to discriminate between certain tissue types, and in particular between adipose tissue and muscle, is discussed. Inversion recovery, with a t interval of 200 ms, gives the best discrimination for this purpose, with a contrast ratio of 6 between fat and muscle. Other image types, and especially T1, give better contrast for low-lipid soft tissue such as liver and spleen.

Adipose Tissue↗
PubMed1984

Thresholds for biological effects of time-varying magnetic fields.

Investigations of the biological effects of time-varying magnetic fields in the extremely low frequency range have been carried out with particular reference to NMR imaging. One effect encountered is the stimulation of nerves and muscles by induced eddy currents. The nature of this effect has been studied in rats exposed to whole body homogeneous fields and in the human forearm with local exposures. Electromyography was used to provide quantitative measurements of thresholds and responses for human exposures. The field exposures required to produce a detectable response are dependent upon the pulse period, pulse waveform and the current path in tissue. For the rat experiments the lowest threshold occurred for a damped sinusoidal pulse of period 0.33 ms with a maximum rate of change of field of 2400 T s-1. The lowest threshold for sensation in the human experiments was 2100 T s-1 for a similar type of field. Simple theory for conduction is considered and current densities induced are estimated as 5 A m-2.

Animals↗
PubMed1984

Contrast enhancement of magnetic resonance images by chromium EDTA: an experimental study.

Chromium EDTA was evaluated as an intravenous contrast agent for magnetic resonance (MR) imaging in vitro and in vivo in rabbits and rats. The effect of Cr EDTA on T1 and T2 values in vitro was first quantitated by spectroscopy at 2.5 MHz, followed by animal trials in which the effects of intravenous injection of Cr EDTA on calculated T1 MR images (obtained by the spin- warp technique at 1.7 MHz) were determined. Following administration of chromium EDTA, differences in T1 values between normal and abnormal kidneys were noted, renal hydronephrosis and renal ischemia were readily identified by the pattern of change in T1, and changes were observed in the normal rabbit brain and in tumors implanted in rats. It is concluded that the use of stable paramagnetic metal ion chelates, such as Cr EDTA, as intravenous contrast agents in MR imaging is feasible and that such agents would make possible the observation of tissue vascularity, breakdown of the blood-brain barrier, and renal function.

Animals↗
PubMed1983

Fetal imaging by nuclear magnetic resonance: a study in goats. Work in progress.

Nuclear magnetic resonance proton imaging was used to obtain images of goat fetuses in utero. The long T1 relaxation time of amniotic fluid makes it appear black on proton density images when examined using the Aberdeen imager, and so allows very good discrimination of the position and structure of the fetus. Some fetal internal tissues can be seen on T1 images. These findings suggest that NMR imaging has great potential in pregnancy studies.

Animals↗