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PubMed2001

Radial keyhole sequences for low field projection reconstruction interventional MRI.

Interventional magnetic resonance imaging (IMRI) is a rapidly emerging application for MRI in which diagnostic and therapeutic procedures are performed with MR image guidance. Real-time or near-real-time image acquisition and relative insensitivity to motion are essential for most intraoperative, therapeutic, and diagnostic procedures performed under MR guidance. The purpose of this work was to demonstrate the development and utility of two alternative rapid acquisition strategies during IMRI that are analogous to computed tomography fluoroscopy or keyhole MRI in a radial rather than rectilinear coordinate frame. The two strategies discussed here, interleaved projection reconstruction and continuous projection reconstruction, are compared and the feasibility of their application in experimental interventional applications is studied. J. Magn. Reson. Imaging 2001;13:142-151.

Animals↗
PubMed1976

Aerobic microbial growth in semisolid matrices: heat and mass transfer limitation.

A conceptual model of aerobic microbial growth in semisolid matrices were developed as a first step in the prediction of the rate of breakdown in semisolid cellulosic material. The conceptual model was described by a series of equations simplified by the assumption of steady-state microbial activity, and heat and mass transfer limitation. Temperature and oxygen distribution in compost piles were measured experimentally at the Butler County Mushroom Farm, Butler County, Pennsylvania, to test the validity of these assumptions. The compost piles consisted of ground corn husks, straw, and race horse manure. The data fit with the model was excellent with deviation between model predictions (as solved by an anglog computer) and actual temperature measurements never exceeding 3 degrees C. The effects of compost pile geometry, external temperature, compost density, external oxygen concentration, and insulation at the bottom of the pile were then predicted using a digital computer to solve the model. The predicitions show that the maximum breakdown rate occurs for an optimum height (which depends upon the system), insulating the base increases the breakdown rate, increasing the external temperature increases the initial breakdown rate but decreases the pseudo-steady-state breakdown rate and the uniformity and any increase in the external oxygen concentration increases the breakdown rate but decreases the uniformity.

Aerobiosis↗
PubMed1983

A comparison of conventional contrast ventriculography and digital subtraction ventriculography.

We studied 46 patients with a history of transmural myocardial infarction or angiographic evidence of coronary artery stenosis with both conventional contrast ventriculography and digital subtraction ventriculography from May to September 1982. Urografin 76, 30 ml, was administered at a flow rate of 18 ml/s, by means of a catheter in the superior vena cava during digital subtraction ventriculography (DSV). Results of the latter were compared with conventional contrast ventriculograms. The correlation coefficient was r =0.938 (p less than 0.001) for determination of ejection fraction with both methods. The data in individual cases suggest that DSV is more sensitive than conventional contrast ventriculography in determination of severely reduced ejection fractions. The methods are practically identical in qualitative evaluation of disorders of regional wall motion in the anterolateral region, while DSV is more sensitive than conventional ventriculography in evaluating the apical region. Sensitivity was 85.7% when the two methods were compared in evaluation of the inferior region of the left ventricle. Both methods are identical in demonstration of severely deformed ventricles. Digital subtraction ventriculography may replace conventional contrast ventriculography in some of the situations discussed above.

Adult↗
PubMed1978

Kinetics of acetaminophen absorption and gastric emptying in man.

Eight healthy male volunteers ingested an aqueous solution containing acetaminophen (20 mg/kg) and a nonabsorbable isotopic marker. The concentrations of unconjugated acetaminophen in samples of blood plasma taken at frequent intervals were measured by gas-liquid chromatography. The data points followed a smooth curve in most cases and were fitted to the classical two-compartment pharmacokinetic model to obtain KA, the apparent first-order rate constant for absorption from the gastrointestinal tract. Gastric emptying was measured simultaneously from serial scintiscans of the subject's abdomen. The subjects were also studied after intramuscular injection of meperidine (150 mg) and pentazocine (60 mg) with and without naloxone (1.2 mg). The acetaminophen absorption curves and gastric emptying patterns were consistent with negligible absorption from the stomach. A new model is proposed in which the conventional single compartment used to represent the gastrointestinal tract is replaced by two compartments: one represents the stomach and the other the small intestine, from which absorption occurs rapidly. Pharmacokinetic analysis using this model showed good agreement in all cases, and provided an estimate of KA, the first-order rate constant for drug transfer from the intestinal lumen into the systemic circulation. The mean half-time for transfer was 6.8 +/- 0.9 min. As expected, KA was greater than KG (the first-order rate constant for gastric emptying), showing that gastric emptying was rate-limiting in the absorption of acetaminophen. The value of KA was greater than KA and the two were not related. The value of KA was not equal to KG in most studies because gastric emptying was not a single exponential process.

Acetaminophen↗
PubMed1975

Maturation of membrane function: the permeability of the rat erythroblastic leukemic cell to water and to non-electrolytes.

The erythroblastic leukemia produced in Long-Evans rats by the administration of 7, 8, 12 trimethylbenz (a) anthracene has been used as a model of the most immature form of the erythrocyte series. In conjunction with studies of the maturation of several other membrane functions, the permeability of this cell to water and to certain definitive non-electrolytes was measured with osmotic methods. The hydraulic conductivity, L-p was 6.2 micro (minute)-1, (atm)-1 at 25 degrees C, quite high and characteristic of mature erythrocytes, but different from values of 0.65 for immature myeloid cells. The effect of temperature provided an energy of activation of 4.4 kCal/mole, also typical of mature mammalian erythrocytes but again different from 13 to 18 kCal/mole for immature myeloid cells. Urea was compared to thiourea. The permeability coefficient for urea was 76.7 micra (minute)-1 plus or minus 13.8 (S. E.); the value for thiourea was 1.55 micra (minute)-1 plus or minus 0.18 (S. E.). Phloretin at 0.25 mM inhibited urea permeability by 90% with 50% inhibition occurring at 0.05 mM. Inhibition was reversible. Permeability to the glycols was also compatible with mature erythrocytes. We infer from these findings that the structure which underlies these basic, passive membrane functions is laid down early and persists after loss of nucleus and subsequent maturation.

Animals↗
PubMed1978

[Multiphasic growth of microorganisms: modeling and computer simulation of linear growth phases].

A phenomenological and a more causal model are developed for the multiphasic discontinuous growth. The first model distinguished between the lag-phase, the exponential phase, the transient phase from the exponential to the linear phase, the linear phase, the transient phase from the linear to the stationary phase, and the stationary phase. The parameters are rate constants, critical values of biomass, and time constants. The parameters are estimated for experimental data of growth of Candida lipolytica under limitation of thiamine (Müller et al. 1978). These data are fitted also by a more causal model. This second model is in agreement with Monod's idea that a linear growth phase may be due to an enzyme or enzyme system which has a constant activity. In the analysed case of limitation of thiamine the constancy of the dehydrogenase activity is caused by a constant level of the coenzymethiaminepyrophosphate. Thus, when such a thiamine requiring enzymatic step becomes to the "bottle-neck", bacterial culture switches over from exponential to linear growth. The end of linear phase is discussed more hypothetically by the high cooperativity of activity of dehydrogenases and the existence of a mimimal specific growth rate. The results of modeling and parameter estimation are compared with experimental data of C. lipolytica. These two models are able to interpret the growth kinetic of these multiphasic growth.

Candida↗