Biomedical subjects
Publications and source records attributed to T P Mitchell.
The treatment of soft-tissue sarcomas has undergone significant changes over the past several decades. Previously, patients were often treated with surgery alone, which frequently necessitated amputation of the affected extremity. Less extensive, limb-sparing operations combined with adjuvant irradiation are now feasible for most patients without compromising the likelihood of cure.
A QA test tool is designed to quantitatively measure the HDR source positioning error, and to facilitate quick and dependable HDR timer linearity test and daily output constancy check. The test tool consists of two concentric disks. The lower disk has a cutout for inserting an HDR catheter, and the upper disk accepts a diode or miniature ionization chamber and can rotate relative to the lower disk. Ionization readings from the source (transferred to the center of the disks) are obtained at two rotational positions of the upper disk which houses the detector. The ratio of the readings is used to determine the source-positioning error of the HDR unit relative to the nominal source position by a simple triangulation principle. Experimental measurements confirm that the QA test tool is sensitive to approximately 0.2 mm variance in source positioning errors. In addition, the QA test tool is suitable for other common HDR QA tests such as the source travel step size test, the daily HDR unit output constancy check, and the timer linearity test. Its simple and robust design permits routine clinical use and provides a high confidence level in the accurate operation of HDR units.
Virtual simulation departs from normal practice by replacing conventional treatment simulation with 3-dimensional image data and computer software. Implementation of virtual simulation requires the ability to transfer the planned treatment geometry from the computer to the treatment room in a way which is accurate, reproducible, and efficient enough for routine use. We have separated this process into: (a) immobilization of the patient; (b) establishment and alignment of a practical coordinate system for the patient/couch system; and (c) setup of the patient/couch been addressed by the use of hemi- or full-body foam casts, the second by use of an alignment jig on the treatment couch, and the third with the aid of a patient coordinate system referenced to easily located landmarks. Phantom studies and clinical practice have shown these techniques to be practical and effective within reasonable clinical bounds.
Relationships between the out-of-body experience and personality adjustment were studied. A total of 445 college students, including 65 reporting out-of-body experiences, completed self-report measures of death orientation, defensive style, narcissism, paranormal beliefs, self-concept, and social desirability. No significant differences were found between respondents reporting out-of-body experiences and nonreporters on any of the instruments, except for the Paranormal Belief Scale. Reporters of out-of-body experiences showed significantly greater belief in precognition, psi, spiritualism, and witchcraft than did nonreporters. Findings indicate considerable similarity between reporters and nonreporters in personality adjustment. It is clear that, on these personality adjustment measures, the out-of-body experience was associated with neither less effective nor more effective adjustment.
Analyses of erythrocyte deformation commonly assume the discocytic shape to be unstressed and hence to be without strain energy. This assumption is based on micropipet experiments and a theoretical disparity between observed and requisite curvature rigidity. The polynomial description of Evans and Fung and strain energy expressions introduced by Zarda et al. have been used to explore the dependence of erythrocyte strain energy on unstressed surface curvature and elastic moduli. As unstressed membrane curvature is varied from flatness to curvatures greater than that of the sphered erythrocyte, the strain energy is found to fall to a value about two-thirds that of the sphered cell. This value occurs for a cell with a thickness, surface area and volume comparable to those of observed erythrocytes assuming a curvature elastic modulus of 1.5 X 10(-11) ergs and an extensional elastic modulus of 6.6 X 10(-3) ergs cm-1. The erythrocyte so characterized has a slightly smaller diameter than that of the measured erythrocyte as does a cell similar in thickness to the expanded cell studied by Evans and Fung. A cup-shaped erythrocyte with similar surface area and volume has a slightly greater strain energy than the standard discocyte when its unstressed curvature is that of a sphered cell. Its strain energy falls below that of the discocyte as its unstressed curvature approaches flatness. Curvature strain energy was found to be concentrated in the dimple of the erythrocyte, the effect being more striking when unstressed curvature was greater. Extensional strain energy, lower in density, was concentrated at the equator. The basis for current emphasis on the unstressed discocyte is reviewed. While no clear conclusion can be reached, the alternative model presented here is attractive in explaining cup-shaped erythrocyte formation but requires a rather high resistance to curvature deformation. Until conclusive evidence is developed both the unstressed and the present discocyte models should be evaluated in examining erythrocyte deformation and adhesive behavior.
Erythrocyte deformation involves both viscous dissipation in the cell interior and viscoelastic motion of the cell membrane. Reports that describe reduced filterability of diabetic erythrocytes, altered response to oscillatory motion in a capillary-sized pipet, and impaired packing during centrifugation indicate a disturbance of red cell rheology in diabetes. We have selected conditions that minimize the macromolecule-mediated energy of attraction between erythrocytes and studied erythrocyte motion during doublet formation. Under such conditions, doublet formation frequency is strikingly reduced in diabetes. For nondiabetic erythrocytes the formation rate is 0.73 doublets per minute, whereas for diabetic erythrocytes the rate is 0.23 doublets per minute. In addition, mean velocity of doublet formation was found to be decreased to half of normal in diabetes. Completeness of doublet formation, regularly diminished when cell size of the two component cells was similar, was the same for diabetic and nondiabetic erythrocytes. Observation of several features of doublet formation gave a picture of the mechanical process. The initial cell making contact with the glass microscope slide was observed to remain fixed in position. The late arriving cell's ability to form a doublet was seen to decrease rapidly, apparently because it came to adhere to the glass surface. The attractive force between the cells overcomes the force of gravity, but cell deformation resistance slows doublet formation by balancing the tendency for cell-cell contact area to increase. An integral equation combining strain energy and viscous dissipation was applied to the doublet formation process. Slowing of doublet formation in diabetes appears to be produced by a doubling of resistance to rate of change of curvature of diabetic erythrocytes.
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A small stainless steel bar was machined to accept radium needles. The stainless steel bar will hold a rack of two, three, four, or five radium needles in a single plane. The crossing needle may be affixed to the bar so that textbook-like geometry is possible. The stainless steel bar remains in place during the entire implant. Spacing between needles is close to perfect. The time required to insers the implant is reduced compared to free-hand insertions, and less variation in dose is seen on computer-assisted calculations. Two years' experience in the use and development of the radium needle holder will be reviewed.