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P Milgram

Publications and source records attributed to P Milgram.

7 recordsLinked to original sources
PubMed2000

Virtual tape measure for the operating microscope: system specifications and performance evaluation.

OBJECTIVE: The Virtual Tape Measure for the Operating Microscope (VTMOM) was created to assist surgeons in making accurate 3D measurements of anatomical structures seen in the surgical field under the operating microscope. The VTMOM employs augmented reality techniques by combining stereoscopic video images with stereoscopic computer graphics, and functions by relying on an operator's ability to align a 3D graphic pointer, which serves as the end-point of the virtual tape measure, with designated locations on the anatomical structure being measured. The VTMOM was evaluated for its baseline and application performances as well as its application efficacy. METHODS: Baseline performance was determined by measuring the mean error (bias) and standard deviation of error (imprecision) in measurements of non-anatomical objects. Application performance was determined by comparing the error in measuring the dimensions of aneurysm models with and without the VTMOM. Application efficacy was determined by comparing the error in selecting the appropriate aneurysm clip size with and without the VTMOM. RESULTS: Baseline performance indicated a bias of 0.3 mm and an imprecision of 0.6 mm. Application bias was 3.8 mm and imprecision was 2.8 mm for aneurysm diameter. The VTMOM did not improve aneurysm clip size selection accuracy. DISCUSSION AND CONCLUSION: The VTMOM is a potentially accurate tool for use under the operating microscope. However, its performance when measuring anatomical objects is highly dependent on complex visual features of the object surfaces.

Aneurysm↗
PubMed1997

Chelation and mobilization of cellular iron by different classes of chelators.

Iron chelators belonging to three distinct chemical families were assessed in terms of their physicochemical properties and the kinetics of iron chelation in solution and in two biological systems. Several hydroxypyridinones, reversed siderophores, and desferrioxamine derivatives were selected to cover agents with different iron-binding stoichiometry and geometry and a wide range of lipophilicity, as determined by the octanol-water partition coefficients. The selection also included highly lipophilic chelators with potentially cell-cleavable ester groups that can serve as precursors of hydrophilic and membrane-impermeant chelators. Iron binding was determined by the chelator capacity for restoring the fluorescence of iron-quenched calcein (CA), a dynamic fluorescent metallosensor. The iron-scavenging properties of the chelators were assessed under three different conditions: (a) in solution, by mixing iron salts with free CA; (b) in resealed red cell ghosts, by encapsulation of CA followed by loading with iron; and (c) in human erythroleukemia K562 cells, by loading with the permeant CA-acetomethoxy ester, in situ formation of free CA, and binding of cytosolic labile iron. The time-dependent recovery of fluorescence in the presence of a given chelator provided a continuous measure for the capacity of the chelator to access the iron/CA-containing compartment. The resulting rate constants of fluorescence recovery indicated that chelation in solution was comparable for the members of each family of chelators, whereas chelation in either biological system was largely dictated by the lipophilicity of the free chelator. For example, desferrioxamine was among the fastest and most efficient iron scavengers in solution but was essentially ineffective in either biological system when used at < or = 200 microM over a 2-hr period at 37 degrees. On the other hand, the highly lipophilic and potentially cell-cleavable hydroxypyridinones and reversed siderophores were highly efficient in all biological systems tested. It is implied that in K562 cells, hydrolysis of these chelators is relatively slower than their ingress and binding of intracellular iron. The chelator-mediated translocation of iron from cells to medium was assessed in 55Fe-transferrin-loaded K562 cells. The speed of iron mobilization by members of the three families of chelators correlated with the lipophilicity of the free ligand or the iron-complexed chelator. The acquired information is of relevance for the design of chelators with improved biological performance.

Fluorescent Dyes↗
PubMed1997

Combining time and intensity effects in assessing operator information-processing load.

A quantitative description of the human information processor is required for predicting operator workload and performance from the simulated task time line data generated by task network models and related methods. Although many models of workload exist, few appear to be well founded in theory or to provide a satisfactory basis for a quantitative representation of operator load. Adherents of both time- and intensity-based models of operator load individually claim success for their methods, which might suggest that both factors are operating in determining operator workload and performance. This paper describes a study that explicitly investigates the relationship between a time-based factor and an intensity-based factor (amount of information to be processed) within a simulated air traffic control environment. A model is developed that posits that the load on the human information-processing system results directly from the ratio of the time necessary to process the required information to the time allowable for making a decision. This ratio, which can be identified with time pressure, determines subjective estimates of workload as well as operator performance. The model is tested against the data from the air traffic control simulation.

Adult↗
PubMed1996

A fluorescence assay for assessing chelation of intracellular iron in a membrane model system and in mammalian cells.

Iron chelators are important tools in biochemical studies of iron metabolism and in the therapy of iron overload diseases. Their mode of action is comprised of entry into cells and scavenging intracellular metal, which includes complexation and egress of the complex. Iron is a metal which appears in the cells in various chemical forms and in different compartments. The form of the metal directly affected by the chelators is the most labile, low-molecular-weight type, which is present in the cytosol and is known as the "chelatable iron." This form is thought to be in dynamic equilibrium with several sequestered forms present in the cell, including the iron-responsive proteins. We recently introduced a fluorescent method for assessing the chelatable iron pool of cells, based on the quenching of the fluorescent calcein by metal ions (Breuer et al., J. Biol. Chem., 1995, 270, 24209-24215). In this work we adapted the method for dynamic assessment of chelator efficacy in scavenging iron from cells. In assay 1, red blood cells ghosts are used as a cell membrane model. The free-acid (impermeant) form of calcein is loaded into ghosts by encapsulation (lysis and resealing) and its fluorescence is quenched by addition of permeant iron(II). Chelators added to ghosts lead to iron removal from calcein and hence to recovery of fluorescence, commensurate with their permeation into ghosts and iron binding affinity. In assay 2, human K562 erythroleukemia cells are loaded with calcein via its permeating and cleavable acetoxymethyl form. A fraction of the intracellular calcein fluorescence is quenched in situ by endogenous cellular iron. The rate of dequenching which is obtained after addition of a chelator provides a measure for the scavenging of the intracellular metal, a process which, as in assay 1, depends on chelator permeation and binding affinity for iron. The two methods provide convenient means for assessing the efficacy of candidate chelator structures in depleting cell iron pools. They are also potentially applicable to chelation of other metals such as Co(II), Ni(II), and Cu(II) and to any cellular system or membrane vesicles.

Erythrocyte Membrane↗
PubMed1993

Effects of stereoscopic and rotational displays in a three-dimensional path-tracing task.

A series of three experiments investigated the effectiveness of stereoscopic and rotational display techniques for the purpose of establishing human factors guidelines for the design of three-dimensional (3D) displays. In the described experiments, depth perception was evaluated by examining accuracy in a 3D path-tracing task, with stimulus displays resembling the structure of cerebral angiograms. The first experiment allowed subjects to control rotation in dynamic displays. The results indicated that performance improved using either technique relative to viewing two-dimensional (2D) displays. However, rotational displays were superior to stereoscopic displays, and performance was best when both techniques were combined. The second experiment compared subject-controlled rotation with observation of continuously rotating displays at different rates of rotation. Performance declined at faster rotation rates; however, there were no advantages of subject-controlled rotation. In the third experiment, performance in rotational displays was no better than that in stereoscopic displays enhanced with multiple static viewing angles. However, performance was always best when both 3D techniques were jointly implemented. The results are discussed in terms of the visual information available using either 3D display technique and are related to the weighted additive model of depth perception.

Adult↗