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Biomedical subjects

J J Kaufman

Publications and source records attributed to J J Kaufman.

At least 19 recordsLinked to original sources
PubMed2001

Structures and electron attachment properties of halomethanes (CX(n)Y(m), X=H, F; Y=Cl, Br, I; n=0,4; m=4-n).

Theoretical studies of structures of neutral molecules and their anions as well as dissociative electron attachment properties are presented for the halomethanes of general formula CX(n) Y(m); X=H, F; Y=Cl, Br, I; n=0,4; m=4-n. The dissociative electron attachment seems to be the primary process resulting in toxicity of these species. The halomethane anions containing hydrogens are formed as radical-anion adducts. When H is replaced by F, these species become true sigma* radicals. The electron affinities are computed using a variety of computational techniques including the four-order Møller-Plesset (MP4) technique that included 250 basis functions. It is challenging to compare the computed results with experiment due to dearth of experimental data and uncertainties in the existing experimental data. Thus in certain cases larger differences are found between the computed and experimental values.

Anions↗
PubMed2000

Zeeman-Stark modeling of the RF EMF interaction with ligand binding.

The influence of radiofrequency electromagnetic exposure on ligand binding to hydrophobic receptor proteins is a plausible early event of the interaction mechanism. A comprehensive quantum Zeeman-Stark model has been developed which takes into account the energy losses of the ligand ion due to its collisions inside the receptor crevice, the attracting nonlinear endogenous force due to the potential energy of the ion in the binding site, the out of equilibrium state of the ligand-receptor system due to the basal cell metabolism, and the thermal noise. The biophysical "output" is the change of the ligand binding probability that, in some instances, may be affected by a suitable low intensity exogenous electromagnetic "input" exposure, e.g., if the depth of the potential energy well of a putative receptor protein matches the energy of the radiofrequency photon. These results point toward both the possibility of the electromagnetic control of biochemical processes and the need for a new database of safety standards.

Algorithms↗
PubMed1999

Relationship between plain radiographic patterns and three- dimensional trabecular architecture in the human calcaneus.

The purpose of this study was to determine the relationship between three-dimensional (3D) trabecular structure and two-dimensional plain radiographic patterns. An in vitro cylinder of human calcaneal trabecular bone was three-dimensionally imaged by micro-CT using synchrotron radiation, at 33.4 micrometer resolution. The original 3D image was processed using 14 distinct sequences of morphologic operations, i.e., of dilations and erosions, to obtain a total of 15 3D models or images of calcaneal trabecular bone. These 15 models had distinct densities (volume fractions) and architectures. The 3D structure of each calcaneal model was assessed using mean intercept length (fabric), by averaging individual fabric measurements associated with each medial-lateral image slice, and determining the relative anisotropy, R(3D), of the structure. A summated pattern or plain radiograph was also computed from the 3D image data for each calcaneal model. Each summated pattern was then locally thresholded, and the resulting two-dimensional (2D) binary image analyzed using the same fabric analysis as used for the 3D data. The anisotropy of the 2D summated pattern was denoted by R(x-ray). The volume fractions of the 15 models ranged from 0.08 to 0.19 with a mean of 0. 14. The medial-lateral anisotropies, R(3D), ranged from 1.38 to 2.54 with a mean of 1.88. The anisotropy of the 2D summated patterns, R(x-ray), ranged from 1.35 to 2.18 with a mean of 1.71. The linear correlation of the 3D trabecular architecture, R(3D), with the radiographic trabecular architecture, R(x-ray), was 0.99 (p<0.0001). This study shows that the plain radiograph contains architectural information directly related to the underlying 3D structure. A well-controlled sequential reproducible plain radiograph may prove useful for monitoring changes in trabecular architecture in vivo and in identifying those individuals at increased risk of osteoporotic fracture.

Anisotropy↗
PubMed1999

Computational methods for ultrasonic bone assessment.

Ultrasound has been proposed as a means to noninvasively assess bone and, particularly, bone strength and fracture risk. Although there has been some success in this application, there is still much that is unknown regarding the propagation of ultrasound through bone. Because strength and fracture risk are a function of both bone mineral density and architectural structure, this study was carried out to examine how architecture and density interact in ultrasound propagation. Due to the difficulties inherent in obtaining fresh bone specimens and associated architectural and density features, simulation methods were used to explore the interactions of ultrasound with bone. A sample of calcaneal trabecular bone was scanned with micro-CT and subjected to morphological image processing (erosions and dilations) operations to obtain a total of 15 three-dimensional (3-D) data sets. Fifteen two-dimensional (2-D) slices obtained from the 3-D data sets were then analyzed to evaluate their respective architectures and densities. The architecture was characterized through the fabric feature, and the density was represented in terms of the bone volume fraction. Computer simulations of ultrasonic propagation through each of the 15 2-D bone slices were carried out, and the ultrasonic velocity and mean frequency of the received waveforms were evaluated. Results demonstrate that ultrasound propagation is affected by both density and architecture, although there was not a simple linear correlation between the relative degree of structural anisotropy with the ultrasound measurements. This study elucidates further aspects of propagation of ultrasound through bone, and demonstrates as well as the power of computational methods for ultrasound research in general and tissue and bone characterization in particular.

Biophysical Phenomena↗
PubMed1996

Influence of marrow on ultrasonic velocity and attenuation in bovine trabecular bone.

Measurements of ultrasonic velocity and specific differential attenuation (SDA) were obtained on 24 bovine trabecular bone specimens from the femoral condyles. The measurements were obtained using two pairs of ultrasonic transducers, one with a low nominal center frequency (500 kHz) and the other pair with a high nominal center frequency (1 MHz). The ultrasonic velocity and specific differential attenuation associated with the bone samples were determined both with and without marrow, i.e., replacing the marrow with water in the pores of the trabecular bone. Significant increases (2.1% and 2.9%) in the velocity of ultrasound were observed after removal of the marrow, for the low and high frequency transducer pairs, respectively. In contrast, significant decreases (-6.5% and -8.8%) in SDA were observed after removal of the marrow, for the low and high frequency transducer pairs, respectively. The bone densities (BD) of the samples were also determined using single photon absorptiometry (SPA). Correlations between ultrasonic parameters and bone densities for samples both with and without marrow were found to be similar. For example, for the 1 MHz transducer pair, the correlation between BD and velocity was r = 0. 86 with marrow, and r = 0.89 without marrow. This study also compared the results obtained using a contact (no water bath) technique and an insertion (with a water bath) technique of ultrasonic measurements. For the high frequency transducer pair, the correlation coefficients between the two methods were r = 0.99 and r = 0.93, for the velocity and specific differential attenuation, respectively. Similar results were found for the low frequency transducer pair as well. In addition, approximately equal correlations between BD and ultrasonic velocity and SDA were also found, indicating that contact and insertion measurements provide essentially equivalent information.

Absorptiometry, Photon↗
PubMed1996

Dynamic relationships of trabecular bone density, architecture, and strength in a computational model of osteopenia.

A computational model was developed to study the effects of short- and long-term periods of disuse osteopenia and repair to elucidate the interrelationships between bone mass, architecture, and strength. The model is one in which the sequence of structural change events is followed in time. This temporal feature contrasts with studies of real trabecular tissue which are necessarily cross-sectional in nature and do not lend themselves to insights into the dynamic nature of the structural changes with time. In the model it was assumed that the stimulus for bone adaptation to mechanical load is the local mechanical strain rate, according to which the trabecular surfaces are differentially formed and resorbed. The effects of mechanical loading and unloading (disuse) on the cancelous bone properties were studied. The bone mass, architecture, and elastic stiffness were shown to be strongly dependent upon the period of the unloading phase, as well as the period of the reloading phase. Mechanical stiffness is demonstrated computationally to be a multivalued function of bone mass, if architecture is not accounted for. The model shows how the same value of trabecular bone mass can be associated with two or more distinct values of biomechanical stiffness. This result is the first explicit demonstration of how bone mass, architecture, and strength are related under dynamical load-bearing conditions. The results explain the empirical observation that bone mass can account for about 65% of the observed variation in bone strength, but that by incorporating measures of bony architecture into the analysis, the predictability is increased to 94%. The computational model may be used to explore the effects of different loading regimes on mass, architecture, and strength, and potentially for assistance in designing both animal and clinical bone loss studies.

Adaptation, Physiological↗
PubMed1996

Ultrasonic assessment of human and bovine trabecular bone: a comparison study.

A comparison study is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and ultrasonic attenuation were evaluated through a transmission insertion technique and correlated with bone mineral density as determined with single photon absorptiometry. For a 1-MHz ultrasonic transducer pair and the human cancellous bone samples the correlations were 0.91 and 0.89 between density and velocity and attenuation, respectively. For a 500-kHz ultrasonic transducer pair the correlations were 0.89 and 0.81 between density and velocity and attenuation, respectively. For the bovine bone samples, the correlations were 0.90 and -0.31 for the velocity and attenuation, respectively, for the 1 MHz transducer pair. For the 500-kHz transducers, the correlations were 0.85 and -0.17 for the velocity and attenuation, respectively. By combining both velocity and attenuation in a multivariate regression, an improvement was achieved in the estimation of bone density in the human samples for both the 500-kHz and 1-MHz transducer pairs. No significant improvement was achieved in the multivariate regressions for the bovine bone samples. In conclusion, the results indicate that ultrasonic measurements are in general highly correlated with bone mineral density in trabecular bone samples. This correlation is more consistent and strong in relatively low density human samples compared with the higher density bovine samples.

Adult↗
PubMed1996

Acoustic assessment of fracture healing. Capabilities and limitations of "a lost art".

The ability of bone to conduct sound was applied clinically over 50 years ago to identify the presence of fresh fractures, although the technique has become a relatively "a lost art" as more sophisticated X-ray and other imaging techniques have been developed. The objective of this report is to challenge clinical orthopaedic surgeons unfamiliar with the technique to explore this simple beside method in the clinical management of fractures. A portable computer-based vibrational analysis device was employed and experiments conducted to objectively evaluate the capabilities of auscultatory percussion techniques. Auscultatory percussion can, with certain limitations, detect the presence of fractures, assess qualitatively the progress of healing, detect delayed or nonunions, and indicate when sufficiently firm continuity has occurred to permit early mobilization or loadbearing. Vibrational assessment is, however, subject to systematic and random errors, and thus cannot always discriminate between the stages of healing in a fractured bone; in addition, various artifacts can lead to significant uncertainty in the diagnosis. Nevertheless, auscultatory percussion is a useful tool in clinical fracture management, and particularly where roentgenographic facilities are inadequate or not available. Computerized vibrational analysis can be used in place of classical percussion/stethoscope methods by those with poor tonal capabilities,or when more objective record keeping is desired.

Auscultation↗
PubMed1994

Usefulness of one electron properties in the study of the nitromethane-to-methyl nitrite rearrangement.

Large-scale multiple reference configuration interaction calculations for a unimolecular rearrangement reaction of nitromethane to methyl nitrite are presented. The complicated structure of potential energy curves is explained in terms of interactions between ground and excited states. An explanation for an extremely long C--N and C--O bond distances in the transition state is also given. The study of corresponding dipole moments and electrostatic molecular potentials enhances the overall understanding of the reaction.

Computer Graphics↗
PubMed1993

Diffraction correction methods for insertion ultrasound attenuation estimation.

We describe diffraction effects in acoustic ultrasound attenuation coefficient estimation using an insertion technique. We characterize the estimation error produced by diffraction as a function of distance and nominal attenuation values. Two new methods for correcting for the diffraction effect are presented. They are termed the Theoretical Diffraction Correction (TDC) and Experimental Diffraction Correction (EDC) techniques, respectively. Experimental validation of the two techniques is also presented, using two different sets of ultrasound measurements obtained with 1 MHz and 500 kHz transducer pairs, respectively. Significant improvement in the accuracy of the acoustic attenuation coefficient is demonstrated using both techniques.

Computer Simulation↗
PubMed1990

Non-invasive low-intensity pulsed ultrasound accelerates bone healing in the rabbit.

The effect of ultrasound (US) on the rate of fibula osteotomy healing in 139 mature New Zealand white rabbits was assessed in this study. Bilateral midshaft fibular osteotomies were made using a 1-mm Gigli saw. US was noninvasively applied to one limb for 20 minutes daily, while the contralateral limb served as a control. A 2.5-cm PZT transducer was applied to both limbs, with the treated limb receiving a 200-microseconds burst of 1.5-MHz sine waves repeated at 1.0 kHz. The incident intensity was approximately 30 mW/cm2. Animals were killed at intervals between 14 and 28 days. Maximum strength increases (significant to p less than or equal to 0.01) ranged from 40 to 85% from postoperative day 14 to 23. On day 28, no significant difference in ultimate strength was noted. From day 17 through day 28, all US-treated fractures were as strong as intact bones (p less than or equal to 0.005). On the other hand, the ultimate strength of the control osteotomies attained intact values only by day 28. These results indicate that biomechanical healing is accelerated by a factor of nearly 1.7. This occurs with an overall acceleration of the healing curve in this fresh fracture model. If noninvasive low-intensity pulsed sine wave ultrasound can significantly accelerate bone repair in clinical application with an in-home treatment of 20 minutes daily, then US may be a useful adjunct for fracture care with a concomitant impact on patient morbidity.

Animals↗
PubMed1989

Successful use of transureteroureterostomy to salvage ureterosigmoidostomy after anastomotic failure.

Four cases are presented of patients who had undergone ureterosigmoidostomy and in whom a unilateral ureteral anastomotic complication developed that was salvaged subsequently by a transureteroureterostomy. Although other forms of urinary diversion are now being utilized routinely in many centers, the ureterosigmoidostomy is still being employed worldwide, and urologic surgeons need to be versed in its potential problems and how to correct them.

Adult↗
PubMed1989

Unique urinary-fecal calculus after cystectomy and ureterosigmoidostomy.

A 36-year-old m an had stage B1 bladder cancer-treated by cystectomy and ureterosigmoidostomy. Postoperatively, a urinary leak was managed successfully by transureteroureterostomy and temporary colostomy. In succeeding years a large calculus developed in the region where the bladder had been and it also involved the sigmoid colon. The huge stone was removed successfully. A nonabsorbable suture was found in the center of the stone. This is a unique complication of ureterosigmoidostomy.

Adult↗
PubMed1987

Urethral gap in complete disruption of membranous urethra.

In patients with complete disruption of the membranous urethra treated initially with placement of a suprapubic cystostomy, delayed synchronous retrograde and voiding cystourethrograms failed to demonstrate accurately the distance between the two urethral ends. Radiographic exposure obtained during synchronous instrumentation of the anterior and posterior urethra in the anesthetized patient was the most precise method of defining the extent of the urethral gap. Any surgical decision should be based on this type of investigation. In most cases of pelvic crush injuries, the severed membranous urethra probably remains attached in close proximity to the distal segment, thus directing the redescent of the prostate and bladder base in the presence of a contracting pelvic hematoma.

Adult↗
PubMed1987

The effect of verapamil in reducing the severity of acute tubular necrosis in canine renal autotransplants.

Calcium channel blockade has been shown to prevent warm renal ischemic damage. The ability of verapamil to decrease the severity of acute tubular necrosis (ATN) after 24-hr cold storage and autotransplantation was studied in a randomized paired study of 12 dogs. Experimental animals pretreated with intraarterial verapamil and flushing of the harvested kidney with cold intracellular solution containing verapamil demonstrated significantly (P less than .05) greater renal function preservation over their matched controls. A subsequent nonpaired study of 6 dogs treated only with flushing of the harvested kidney with perfusate containing verapamil demonstrated no significant preservation advantage over controls. We conclude that verapamil, administered prior to the ischemic event, can enhance the protective effect of hypothermia and decrease the severity of ATN in ischemically injured kidneys.

Acute Kidney Injury↗
PubMed1986

Nephrocolic fistula: a complication of percutaneous nephrostolithotomy.

Percutaneous nephrostolithotomy has proved to be a safe and effective approach to the management of upper tract calculi, which is associated with a low rate of significant complications. Bowel perforation is an unusual complication of this technique. We report a case of a nephrocolic fistula following percutaneous nephrostolithotomy, and discuss the diagnosis and management of this rare complication.

Adult↗