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Biomedical subjects

M L Johns

Publications and source records attributed to M L Johns.

At least 19 recordsLinked to original sources
PubMed2005

Droplet migration in emulsion systems measured using MR methods.

The migration of emulsion droplets under shear flow remains a largely unexplored area of study, despite the existence of an extensive literature on the analogous problem of solid particle migration. A novel methodology is presented to track the shear-induced migration of emulsion droplets based on magnetic resonance imaging (MRI). The work is in three parts: first, single droplets of one Newtonian fluid are suspended in a second Newtonian fluid (water in silicone oil (PDMS)) and are tracked as they migrate within a Couette cell; second, the migration of emulsion droplets in Poiseuille flow is considered; third, water-in-silicone oil emulsions are sheared in a Couette cell. The effect of (a) rotational speed of the Couette, (b) the continuous phase viscosity, and (c) the droplet phase concentration are considered. The equilibrium extent of migration and rate of migration increase with rotational speed for two different emulsion systems and increased continuous phase viscosity, leads to a greater equilibrium extent of migration. The relationship between the droplet phase concentration and migration is however complex. These results for semi-concentrated emulsion systems and wide-gap Couette cells are not well described by existing models of emulsion droplet migration.

Journal Article↗
PubMed2005

Spatially resolved emulsion droplet sizing using inverse Abel transforms.

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) is well established as a tool for determining emulsion droplet-size distributions via measurement of restricted self-diffusion. Most measurements made to date have not been spatially resolved, but have measured an average size distribution for a certain volume of emulsion. This paper demonstrates a rapid method of performing spatially resolved, restricted diffusion measurements, which enables emulsion droplet sizing to be spatially resolved as a function of radius in cylindrical geometries or pipes. This is achieved by the use of an Abel transform. The technique is demonstrated in various annular systems containing two emulsions, with different droplet-size distributions, and/or a pure fluid. It is also shown that by modifying the pulse sequence by the inclusion of flow-compensating magnetic field gradients, the technique can measure spatially resolved droplet-size distributions in flowing emulsions, with potential applications in spatially resolved on-line droplet-size analysis.

Journal Article↗
PubMed2004

An NMR study of the freezing of emulsion-containing drops.

Various nuclear magnetic resonance (NMR) techniques were used to monitor the freezing behaviour of suspended 2-mm-diameter drops. The drops were composed of hydrocarbon oils emulsified in either water or water/sucrose mixtures. As such they were good model systems for the study of spray freezing, sharing structural similarities with potential products such as ice cream. In particular, simple 1H NMR spectroscopy was used to monitor and individually quantify the freezing or solidification behaviour of the various constituent species of the drops. In addition, the effect of freezing on the emulsion droplet size distribution (and hence emulsion stability) was also measured based on NMR self-diffusion measurements. The effect of freeze/thaw cycling was also similarly studied. The nucleation temperature of the emulsion droplets was found to depend on the emulsion droplet size distribution: the smaller the droplets, the lower the nucleation temperature. Emulsion droplet sizing indicated that oil-in-sucrose-solution emulsions were more stable, showing minimal coalescence, whereas oil-in-water emulsions showed significant coalescence during freezing and freeze/thaw cycling.

Journal Article↗
PubMed2004

Fast emulsion droplet sizing using NMR self-diffusion measurements.

Emulsion droplet sizing using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) is a well-established technique. Traditionally these measurements require total acquisition times of typically 5-20 min per sample, which severely limits our ability to use this method to study dynamic processes. Here we present the application and verification of an NMR pulse sequence, Difftrain, which enables emulsion droplet size distributions to be measured in 3-10 s. We have previously introduced applications of Difftrain (C. Buckley, K.G. Hollingsworth, A.J. Sederman, D.J. Holland, M.L. Johns, L.F. Gladden, J. Magn. Reson. 161 (2003) 112-117), including the droplet sizing of a single unimodal emulsion sample. In this paper, several model emulsions containing different oils are measured and the results compared directly with sizing provided by laser scattering. In this manner, the Difftrain method is verified and its possibilities and limitations are explored. Guidelines are proposed for the range of droplet sizes for which accurate results can be produced. The Difftrain technique opens up the possibility of studying non-equilibrium emulsions; a study of the in situ emulsification of a 21% v/v water-in-silicone oil emulsion is presented.

Journal Article↗
PubMed2004

Development and application of rotationally compensated RARE.

In this paper we describe a new extension to the RARE rapid imaging technique--ROTACOR--which compensates for constant sample rotational motion by rotating the direction of the gradient coordinate system (read and phase directions) between each refocusing RF pulse and therefore between each acquisition of a line of k-space in the read direction. In the laboratory frame this corresponds to an irregularly sampled k-space raster; for a sample rotating at the predefined rotation rate this will correspond to the sampling of a rectilinear k-space raster. This technique is applied to two rotating systems. First, to demonstrate the technique, a rotating mixing paddle in water is imaged using conventional RARE and then using the ROTACOR sequence, demonstrating the improvement of image quality produced by ROTACOR. Second, ROTACOR is used to image the deformation of water droplets in silicone oil, being sheared in a wide-gap Couette cell. Accurate imaging of the droplet shape as a function of shear rate, permits determination of the interfacial tension between the two fluids concerned; the results compare favourably with reported literature values.

Journal Article↗
PubMed2003

Measurement of emulsion droplet sizes using PFG NMR and regularization methods.

The droplet size distributions of emulsions have been measured using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) for many years. This technique finds particular application with emulsions that are concentrated and/or opaque, since such emulsion systems are difficult to characterize by other methods. Most studies employing PFG techniques assume a lognormal form when extracting the droplet size distribution from the experimental data. It is clearly desirable to retrieve a droplet size distribution from the experimental data without assuming such a functional form. This is achieved for the first time using regularization techniques. Regularization based on the distribution area and on its second derivative are compared and assessed along with the following techniques for selecting the optimal regularization parameter: the L-curve method, generalized cross validation (GCV), and the discrepancy principle. Regularization is applied to both simulated data sets and experimental data. It is found that when the experimental error can be estimated accurately, the discrepancy principle with area regularization is the best approach. When the error is not known the GCV method, with second derivative regularization and allowing only nonnegative values, is most effective.

Journal Article↗
PubMed2003

Applications of fast diffusion measurement using Difftrain.

Novel applications of fast self-diffusion measurement are presented. Difftrain (Diffusion train), which uses successive stimulated echoes from a single excitation pulse where a portion of the available magnetisation is recovered for each echo, is used to measure self-diffusion by varying the observation time. It is applied to produce the droplet size distribution of an oil-in-water emulsion in less than 4s. This is verified by comparison with the droplet size distribution produced by a standard pulsed field gradient (PFG) technique. Difftrain is also extended to enable the application of incremental gradients, in addition to varying the observation time. This is used to produce propagators or displacement probabilities of water flowing through a packed bed for a range of 16 observation times in under 10 min. Again verification is provided by acquisition of the same propagators using a conventional PFG technique.

Journal Article↗
PubMed2002

Sizing of emulsion droplets under flow using flow-compensating NMR-PFG techniques.

Using the nuclear magnetic resonance (NMR) pulsed field gradient (PFG) technique, it is possible to determine the size distribution of emulsion droplets. This method is extended so that the same measurements can be performed in the presence of flow. The resultant flow-compensating NMR-PFG technique is used to determine the oil droplet-size distribution of an oil-in-water emulsion flowing in a narrow tube at various flow rates. Comparison with the nonflowing oil droplet-size distribution enables the effect of velocity shear on the oil droplet-size distribution to be quantified.

Emulsions↗
PubMed2001

Application of a hybrid analysis method for a Web-enabled information system: a case study.

A successful developmental effort frequently is defined as one that produces a deliverable that is satisfactory to the client, on time, within budget, and has had no adverse impact on ongoing business operations. This article describes through a case study approach the activities that one project used to ensure a successful development effort. The author advocates a hybrid methodological approach to systems analysis and design that is tailored for the specific project. The article also describes the project and people management practices used to support the developmental effort.

Institutional Management Teams↗
PubMed1995

Issuing the challenge: creating leadership for health information management.

Fundamental and profound changes are occurring within the health care industry that directly affect and change the roles and functions of health information managers. To meet and survive these changes, the health information management profession must exercise leadership and transform itself. A model of leadership consisting of systems thinking, personal mastery, mental models, shared vision, and team learning to accomplish this transformation is described.

Hospital Administrators↗
PubMed1995

An Internet health care information resources server as a component of a statewide medical information network.

A health care information server utilizing Internet resource discovery technology is presented as a component of a statewide medical information network. The development of an information server, including the development process and its design and operation, is presented. Menu design and implementation, which involved providing access to information resources in support of the tasks that make up the health care delivery process, are described. The potential impact of this technology on the health care delivery process is explored, and ways in which access to information can be facilitated and matched with the information needs of the various health care delivery tasks are identified. Issues associated with the use of public domain information resources are discussed, including control over Internet resources, access to information resources, network operational delays, client connection and software availability, information quality, and menu navigation. This project has demonstrated that Internet information resources exist that match the information needs of the tasks that make up the health care delivery process. Positive response has been received from physicians after initial utilization of the server in a stand-alone context. In the future, more applications will integrate the vast information resources on the Internet with traditional computing systems.

Alabama↗
PubMed1994

Providing access to healthcare information resources using Internet Gopher technology as a part of a state-wide medical information network.

An Internet healthcare information resources Gopher server is described as a part of a state-wide medical information network. The development of the server and its design and operation are presented. The potential impact of this technology on the healthcare delivery process and issues associated with the use of public domain information resources are discussed.

Computer Communication Networks↗
PubMed1994

The development of a graduate program in health information management.

The development of a graduate program in Health Information Management is described. The purpose of the program is to prepare individuals to assume executive level roles in a variety of health-care enterprises in health information resources management. The curriculum is based on empirical findings of a role delineation study of chief information officers (CIOs) in the USA. A model of professional practice of the CIO was developed from study findings which describes the role of the CIO from the standpoint of functional areas of entrepreneur, resource allocator, negotiator, information disseminator, information monitor, leader, and operations manager.

Education, Graduate↗
PubMed1990

The effects of positive incentive programs on physician chart completion.

It seems evident that both concurrent review programs and positive incentive programs have been implemented by a number of facilities in which little, if any, monitoring has occurred. Only half of the hospitals performing concurrent analysis provided statistics concerning the percentage of daily discharges arriving in the medical record department complete. Only one fourth of the hospitals provided information concerning the number of incomplete and delinquent medical records before and after the implementation of concurrent review. These data underscore the need for medical record administrators to evaluate the effectiveness of various strategies used to improve completion of medical records. Likewise, only a few of the hospitals that have implemented an incentive program for chart completion were able to provide all of the requested statistics concerning their chart status prior to and following the implementation of their programs. The results of the study indicate that numerous innovative procedures have been implemented in hospitals, with varying degrees of impact on the number of incomplete and delinquent medical records. The use of positive incentive programs in conjunction with punitive action is effective in helping to reduce the number of incomplete medical records.

Concurrent Review↗