A teaching eye model for ophthalmoscopy.
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Eye↗
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Musculoskeletal injection skills competency in physical medicine and rehabilitation residents: a method for development and assessment.
An educational module was developed in attempt to satisfy two main objectives: to develop and implement a methodology for instruction of generally encountered injection techniques in the practice of physical medicine and rehabilitation and to implement an objective assessment format to measure attainment of these skills. Guidelines for this module were developed in consideration of Accreditation Council for Graduate Medical Education (ACGME) physical medicine and rehabilitation residency program requirements and ACGME Outcome Project. Eleven physical medicine and rehabilitation residents participated in a 1-day didactic/laboratory workshop covering injection education and techniques, followed by a supervised 2-wk practice session. Knowledge acquisition and skill attainment were measured via before and after multiple-choice written examination and simulated patient encounters utilizing anatomic models. An increase in knowledge was observed on the multiple-choice examination from pretest to posttest (pretest, 59.3%; posttest, 90.6%). Before instruction, 0 of 11 residents were able to perform any of the injection techniques (14 injection techniques and one sterile technique). At completion of the module, 7 of 11 residents (64%) competently performed 15 of 15 techniques (100%), 3 of 11 (26%) competently performed 14 of 15 techniques (93%), and 1 of 11 (9%) competently performed 11 of 15 techniques (73%). Participation in this module resulted in substantial acquisition of knowledge and skills regarding musculoskeletal injections for physical medicine and rehabilitation residents. This workshop provided a framework for the definition of baseline competency in this clinical skill area.
Attitude of Health Personnel↗
Mechanisms of orbital floor fractures: a clinical, experimental, and theoretical study.
PURPOSE: The purpose of this study was to investigate the two accepted mechanisms of the orbital blowout fracture (the hydraulic and the buckling theories) from a clinical, experimental, and theoretical standpoint. METHODS: Clinical cases in which blowout fractures resulted from both a pure hydraulic mechanism and a pure buckling mechanism are presented. Twenty-one intact orbital floors were obtained from human cadavers. A metal rod was dropped, experimentally, onto each specimen until a fracture was produced, and the energy required in each instance was calculated. A biomathematical model of the human bony orbit, depicted as a thin-walled truncated conical shell, was devised. Two previously published (by the National Aeronautics and Space Administration) theoretical structural engineering formulas for the fracture of thin-walled truncated conical shells were used to predict the energy required to fracture the bone of the orbital floor via the hydraulic and buckling mechanisms. RESULTS: Experimentally, the mean energy required to fracture the bone of the human cadaver orbital floor directly was 78 millijoules (mJ) (range, 29-127 mJ). Using the engineering formula for the hydraulic theory, the predicted theoretical energy is 71 mJ (range, 38-120 mJ); for the buckling theory, the predicted theoretical energy is 68 mJ (range, 40-106 mJ). CONCLUSION: Through this study, we have experimentally determined the amount of energy required to fracture the bone of the human orbital floor directly and have provided support for each mechanism of the orbital blowout fracture from a clinical and theoretical basis.
Adult↗
Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws.
The bone-screw interface is critical in the use of spinal instrumentation. The purpose of these experiments described here was twofold. First, to determine whether a correlation existed between torque generated during screw insertion and the pullout strength. Second, to determine how differing surgical methods of screw hole preparation influenced torque of insertion and screw pullout strength. A series of experiments were carried out in which screws were inserted into synthetic bone (experiment 1) and into calf vertebrae (experiment 2). The method of screw hole preparation (i.e., diameter of entrance hole and pilot hole) was varied while the resulting torque of insertion and the pullout strength of the screw was measured in each case. A torque screwdriver was used to measure the torque of insertion of the screws. Screw pullout strength was measured using a materials testing machine. Two important results emerged from these experiments. First, a higher torque of insertion correlated with a higher screw pullout force. This correlation may be useful intraoperatively in evaluating fixation. Second, torque of insertion and pullout force were more influenced by cortex over-drill diameter than pilot hole diameter. These experiments show the importance of the dorsal cortex in pedicle screw fixation.
Animals↗
Aerosol deposition in the nose as a function of body size.
The effect of body size on nasal doses from inhaled aerosols has not been measured directly in people. Two basic types of computational models are used to calculate inhaled particle deposition in adults. One type uses an impaction parameter that incorporates particle aerodynamic diameter and the average airflow rate. The second type uses the nasal pressure drop and particle aerodynamic diameter. Although both types of models have been adjusted to give reasonably accurate deposition efficiencies for adults, they predict very different deposition efficiencies when they are applied to young children. This is not surprising because the airflow-type model has no body-size-dependent parameters, unlike the pressure-drop-type model. The objective of our studies was to test these two types of computational models using idealized hollow nasal models of two sizes, representing the adult and young child. The results indicate that a pressure-drop relationship fits the aerosol deposition data very well. When the properly scaled physiological air flows and minute ventilations are used in a nasal dose calculation, the young child is seen to have potentially larger nasal doses than those of an adult.
Adult↗
The gender-specific chest wall thickness prediction equations for routine measurements of 239Pu and 241Am within the lungs using HPGe detectors.
The current chest wall thickness prediction equation is not applicable to use in routine lung counting measurements for detection of low energy photons (17--60 keV) within the lungs of male and female subjects. The current chest wall thickness prediction equation was derived for the NaI-CsI "phoswich" detection system, which is not the routine detection system in use; the subject position was supine, which is not the routine position; the equation did not account for the intercostal tissue thicknesses of muscle and adipose which significantly attenuate low energy photons (17--60keV); it was derived from male subjects only and is used to predict the chest wall thickness of female subjects for whom it is not applicable. The current chest wall thickness prediction equation yields unacceptable percent errors in the HPGe detection efficiency calibration for 239Pu and 241Am (17- and 59.5-keV photons, respectively) relative to the gender-specific HPGe chest wall thickness prediction equations of this paper (+284% to --73% for 239Pu; (+)42% to --39% for 241Am). As a result, use of the current chest wall thickness prediction equation yields unacceptable percent errors (proportional in magnitude to the percent errors in the detection efficiency calibration) in the calculation of the minimum detectable activity (Bq) or in an initial assessment of a radioactive contamination exposure detected by a routine lung count measurement.
Adult↗
Deposition of monodisperse particles in hollow models representing adult and child-size tracheobronchial airways.
A series of experiments was performed to determine deposition efficiencies of four sizes of radiolabeled monodisperse particles in custom-made hollow tracheobronchial models. The particles had geometric diameters of about 1, 5, 10, and 15 microm. The tracheobronchial models, consisting of a trachea and two or more additional generations, had dimensions representative of a typical adult, a 7-y-old child, and a 4-y-old child; the child-size models were appropriately scaled-down replicas of the adult-size model. Each deposition experiment was conducted using a steady inspiratory airflow representative of low physical activity for the appropriate age of individual: 20 L min(-1) for the adult; 9 L min(-1) for the 7-y-old; 5.5 L min(-1) for the 4-y-old. The results indicate that deposition efficiency of the particles increased substantially (up to 35 times) in all three models as particle diameter increased from 1-15 microm, undoubtedly as a result of particle impaction and sedimentation-related phenomena. An analysis of variance demonstrated the occurrence of statistically-significant (p < 0.05) main effects of hollow model size and particle size; the interaction between the two parameters was also significant. In general, deposition efficiencies of the various sizes of particles were greater in the child-size models than in the adult-size model; this effect may have risk assessment implications. In addition, the results obtained experimentally agreed more closely with those predicted using a radiation-protection mathematical particle deposition formulation as the particle size increased for each of the sizes of models.
Adult↗
New approach for dose reconstruction: application to one case of localized irradiation with radiological burns.
When localized accidental irradiation occurs, it is necessary to determine the extent to which tissues and vital organs have been damaged, mainly in the vicinity of the source. At present, biological markers cannot be used to estimate the heterogeneity of the dose distribution. An alternative is to map the absorbed dose in the different regions of the body. Using a Monte Carlo calculation code, it is possible to simulate the accident while taking into account the specific morphology of the irradiated individual and his environment, as well as the source characteristics. The calculated values are matched to the clinical signs of the lesion, particularly around the rim of the radiation-induced necrosis. This technique was applied successfully on two patients who presented very severe lesions due to acute localized irradiation after an accident that occurred at Lilo (Georgia) in 1996-1997; only the most demonstrative case is presented here.
Bone and Bones↗
Age-specific uncertainty in particulate deposition for 1 microm AMAD particles using the ICRP 66 lung model.
The ICRP 66 lung model may be used to determine age-specific dose estimates for members of the public via the inhalation pathway. A significant source of uncertainty in internal dosimetric modeling is due to particulate deposition in regions of the respiratory tract. Uncertainties in estimates of particulate deposition are present because of the inherent variability in the deposition model and its various input parameters. An improved understanding of the uncertainty in particulate deposition will further guide research efforts and improve our ability to quantify internal dose estimates. The ICRP 66 lung deposition model is most sensitive to breathing rate when 1 microm AMAD particles are inhaled by members of the public. Uncertainties in deposition fractions are shown to span an order of magnitude with their distributions varying by age and sex for a particular lung region. Age-specific uncertainties of deposition fraction demonstrate increased estimates of extrathoracic deposition in younger age groups due to the decreased size of the respiratory tract airways. This age-specific trend becomes more pronounced for very young children and infants. The largest fractional deposition occurs in the alveolar and extrathoracic regions, regardless of age and sex.
Adolescent↗
Models to facilitate the learning of fiberoptic technique.
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Bronchoscopy↗
A breast phantom method for evaluating mammography technique.
A new breast phantom has been designed for use in evaluating mammographic system performance. This phantom incorporates simulated calcifications and fibrillar objects in fat, of graded size, to permit measurements of detail visibility. A special methodology has been developed for measuring visible object size to achieve reproducible and clinically relevant results. Materials and construction of the phantom also permit carrying out dosimetry with an appropriate ionization chamber. Dosage and detail visibility measurements are reported for the Xerox 125, Min-R and Xonics systems. In addition to providing information regarding technique and image receptors, these results demonstrate the usefulness of the basic phantom design, and suggest possible improvements.
Breast Neoplasms↗
Effects of turbulence on signal intensity in gradient echo images.
Although the appearance of laminar vascular flow in magnetic resonance (MR) images has been characterized, there is no general agreement about the effect of turbulent flow on MR signal intensity. This study uses a fast scan gradient echo pulse sequence to evaluate nonpulsatile turbulent flow in two different models. The first model simulated flow in normal vascular structure. It generated nonpulsatile, laminar and turbulent flow in straight, smooth-walled Plexiglas tubes. The second model simulated flow through a vascular stenosis. It generated nonpulsatile, laminar, and turbulent flow through an orifice. Velocities and flow rates ranged from low physiologic to well above the physiologic range (velocity = .3 to 280 cm/second, flow rate from .15 to 40 L/minute). Transition from laminar to turbulent flow was observed with dye streams. Turbulent flow in straight, smooth-walled vessels was not associated with a decrease in MR signal intensity even at the highest velocities and flow rates studied. The transition from laminar to turbulent flow through an orifice is not associated with a decrease in gradient echo signal intensity. As the intensity of the turbulent flow increases, however, there is a threshold above which signal intensity decreases linearly as turbulence increases (r = .97). This study suggests that flow in normal vascular structures should not be associated with decreased signal intensity in gradient echo images. Turbulent flow through areas such as valves, valvular lesions or vascular stenoses, may be associated with a decrease in gradient echo signal intensity.
Blood Flow Velocity↗
Mixing problems of low flow hepatic artery infusion. Improvement with small caliber double lumen balloon catheters.
The problem of inhomogeneous mixing encountered during hepatic artery (HA) chemotherapy infusion was assessed and a practical solution examined. A glass model of the human HA distribution was used to determine mixing homogeneity of low flow (1.4 mL/minute) dye infusion into pulsatile flow (280-300 mL/minute) of a fluid isoviscous to blood. Dye concentration in each of 16 HA branches was determined by photospectrometry. Dye infusion was carried out through 2-2.5F double lumen end hole or proximal side hole balloon catheters without balloon inflation, with balloon inflation maintaining full HA flow, and with the balloon inflated so that HA flow was reduced by 50%. The measurements taken without balloon inflation showed gross inhomogeneity of dye concentration in various branches. The inhomogeneity was not improved during balloon inflation as long as full HA flow was maintained. After balloon inflation reduced HA flow by 50%, dye mixing was improved significantly, with infusion through side hole catheters (alpha = .002) but not significantly (alpha = .2) with infusion through end hold catheters. This investigation suggests that the proposed technique might be useful for clinical application and deserves further evaluation in an in vivo system.
Antineoplastic Agents↗
Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging.
Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.
Brain↗
Defining epileptogenic foci: past, present, future.
There is a direct relationship between the geometry (location, area, and orientation) of cortex-generating epileptiform discharges and resultant spike or seizure voltage fields at the scalp. Epileptogenic foci have been localized traditionally with EEG by identifying the negative field maximum (e.g., a phase reversal between adjacent bipolar channels). However, it is the shape of the entire voltage field over the head, including both negative and positive maxima, which provides information necessary to characterize the focus properly. Source location and orientation can be inferred from spike or seizure voltage topography, however, three-dimensional visualization can be obtained from mathematical source models, such as an equivalent dipole. Recent investigations have shown that dipole models can identify the location of epileptogenic foci with sub-lobar precision. Accuracy is enhanced by using additional electrodes, particularly on the lower half of the head, and by measuring their location. Realistic head models obtained from three-dimensional reconstructions of MR images can overcome errors introduced by simple spherical models of the cranium. Co-registering EEG voltage topography and source models with a patient's own cerebral anatomy will make EEG an unparalleled functional imaging technique for defining epileptogenic foci.
Brain↗
Functional imaging of postmovement beta event-related synchronization.
The linear estimation (LE) and spline surface Laplacian (SL) method were applied to single-trial EEG data. EEG was recorded in three subjects during voluntary, self-paced movements of the index finger. The EEG data were bandpass-filtered in the lower beta frequency range and showed short-lasting bursts of oscillations after termination of movement. These oscillations are termed postmovement beta synchronization. The realistic head geometry and the digitized positions of the electrodes were taken into account for accurate modeling of the anatomy. Regularization of the LE method was achieved by the truncated singular value decomposition. The LE and SL distribution of the postmovement beta synchronization showed similar spatial and temporal patterns. A clear increase of the LE source activity was found over the primary motor area. These results indicate that the postmovement beta synchronization is generated over the anterior bank of the central sulcus.
Brain↗
The geometry of slipped capital femoral epiphysis: implications for movement, impingement, and corrective osteotomy.
Metaphyseal impingement limits motion in high-grade slipped capital femoral epiphysis (SCFE). A three-dimensional volume/surface computer model was used to study the geometry of impingement, which may take the form of impaction, which causes levering or requires compensatory alteration in motion, or inclusion that occurs after remodeling and may lead to acetabular cartilage damage. The majority of deformities seen clinically can be reproduced with posterior epiphyseal displacement in the plane of the physis. By using the 3-D movements of normal walking, this model predicts little anterior metaphyseal impingement in the normal hip. As posterior slip angle increases to 25 degrees , minor impingement can be eliminated with as little as 20 degrees of external rotation. High-grade posterior slips (75 degrees ) require external rotation of 50-60 degrees during walking to minimize impaction. Sitting increases impingement for all slip geometries, requiring proportionately greater external rotation. As remodeling restores a more normal arc of motion, an increasing proportion of the femoral head is composed of the remodeled, included metaphyseal prominence. This study explores the potential role of contact between the acetabulum and the metaphysis in the production of abnormal range of motion after SCFE, and simulation estimates the correction needed by osteotomy to allow normal walking and sitting. The inclusion of significant metaphyseal surfaces in the remodeled hip may be one factor in subsequent degenerative changes associated with SCFE.
Acetabulum↗
Demonstration of beam hardening correction in computed tomography of the head.
The efficacy of a method of removing artifacts due to beam hardening in computed tomography of the human head is demonstrated on a realistic, mathematically described phantom. An efficient implementation is discussed.
Head↗