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PubMed2000

Neuroanatomically based approaches to obsessive-compulsive disorder. Neurosurgery and transcranial magnetic stimulation.

Obsessive-compulsive disorder is a severe condition. Unfortunately, current medication and behavior therapies fail to adequately benefit some patients most severely affected. Advancing knowledge of brain circuit involvement has potential treatment implications. The neurosurgical techniques most often used in the United States for crippling, treatment-refractory obsessive-compulsive disorder are reviewed in the context of anatomic models of the illness. The use of transcranial magnetic stimulation to probe possible neuroanatomic and neurophysiologic substrates of this disorder is considered, and how the knowledge gained from such studies might advance treatment is presented.

Brain↗
PubMed1997

Current controversies and future directions in basal ganglia research. Integrating basic neuroscience and clinical investigation.

This article discusses current controversies and future directions in basal ganglia research, detailing behavioral aspects, anatomic models, neurochemistry, pharmacology, and diagnostic methods as well as surgical techniques. A neuroethologic perspective is highlighted. Furthermore, the relevant literature pertaining to contemporary molecular approaches such as brain microinjections of embryonic or genetically modified cells, for therapeutic purposes and the use of transgenic and knockout animals.

Animals↗
PubMed2001

Modelling the response of the spinal system to whole-body vibration and repeated shock.

Back problems are very common and contribute to discomfort and days off work. Some back disorders are attributed to inappropriate loading of the spine that can be combined with other influential factors such a body posture, whole-body vibration and shock. Many models have been developed to predict the forces in the spine associated with vibration and shock. However, the problem is complex due to the incompletely understood dynamic responses of the body, the influence of many variables and the effect of muscle forces. This paper summarises the current state of knowledge relevant to the prediction of forces in the spine associated with whole-body vibration and shock. The paper also introduces presentations at a workshop on the modelling of spinal loads associated with vibration and shock held in Berlin in October 1999. RelevanceBiodynamic models may be used to estimate risks of injury or disease and optimise environments so as to minimise risks. However, the development of useful models requires an understanding of the complex interaction between mechanical forces and the living body. The application of models requires knowledge of their accuracy and limitations.

Humans↗
PubMed1999

A new technique for determining 3-D joint angles: the tilt/twist method.

OBJECTIVE: To develop a new method of representing 3-D joint angles that is both physically meaningful and mathematically stable. DESIGN: The two halves of a joint are modeled as overlapping cylinders. This simple physical model is easily understood and yields mathematically stable angle equations. BACKGROUND: Two currently-used methods are the Euler/Cardan (joint coordinate system) method and the projection angle method. Both of these methods approach a singularity at 90 degrees that limits their use. The helical angle (attitude vector) method is mathematically stable but has limited physical meaning and is difficult to communicate. METHODS: Calculation of the tilt/twist angles is described. Tilt/twist angles are compared to Euler/Cardan, projection, and helical angles in terms of behavior and stability. RESULTS: Through a small range of angulation, tilt/twist angles match the specific projection and Euler/Cardan angles previously found to be appropriate for describing spinal motion. Through larger ranges, tilt/twist angles do not match the other angles studied. Although not as stable as helical angles, tilt/twist angles are twice as stable as Euler/Cardan and projection angles, reaching a singularity only at 180 degrees. CONCLUSIONS: Because of their mathematical stability and simple physical interpretation, tilt/twist angles are recommended as a standard in describing angular joint motion.

Biomechanical Phenomena↗
PubMed2003

Issues of exploration: human health and wellbeing during a mission to Mars.

Today, the tools are in our hands to enable us to travel away from our home planet and become citizens of the solar system. Even now, we are seriously beginning to develop the robust infrastructure that will make the 21st century the Century of Space Travel. But this bold step must be taken with due concern for the health, safety and wellbeing of future space explorers. Our long experience with space biomedical research convinces us that, if we are to deal effectively with the medical and biomedical issues of exploration, then dramatic and bold steps are also necessary in this field. We can no longer treat the human body as if it were composed of muscles, bones, heart and brain acting independently. Instead, we must lead the effort to develop a fully integrated view of the body, with all parts connected and fully interacting in a realistic way. This paper will present the status of current (2000) plans by the National Space Biomedical Research Institute to initiate research in this area of integrative physiology and medicine. Specifically, three example projects are discussed as potential stepping stones towards the ultimate goal of producing a digital human. These projects relate to developing a functional model of the human musculoskeletal system and the heart.

Adaptation, Physiological↗
PubMed2003

Model surgery with a passive robot arm for orthognathic surgery planning.

PURPOSE: The aims of the study were to assess the degree of accuracy of model surgery performed manually using the Eastman technique and to compare it with model surgery performed with the aid of a robot arm. PATIENTS AND METHODS: Twenty-one patients undergoing orthognathic surgery gave consent for this study. They were divided into 2 groups based on the model surgery technique used. Group A (52%) had model surgery performed manually, whereas group B (48%) had their model surgery performed using the robot arm. Patients' maxillary casts were measured before and after model surgery, and results were compared with those for the original treatment plan in horizontal (x-axis), vertical (y-axis), and transverse (z-axis) planes. RESULTS: Statistical analysis using Mann-Whitney U test for x- and y-axis and independent sample t test for z-axis have shown significant differences between both groups in x-axis (P =.024) and y-axis (P =.01) but not in z-axis (P =.776). CONCLUSIONS: Model surgery performed with the aid of a robot arm is significantly more accurate in anteroposterior and vertical planes than is manual model surgery. Robot arm has an important role to play in orthognathic surgery planning and in determining the biometrics of orthognathic surgical change at the model surgery stage.

Cephalometry↗
PubMed1977

A simplified model for teaching minor oral surgery.

A teaching model, specially constructed for the purpose of training senior dental students in the use of surgical instruments, is described. The advantages of this model are inexpensiveness and reproducible simulated surgical situations securing a uniform teaching objective.

Education, Dental↗
PubMed1979

Photoelastic experiments on the implantation of a bone graft into the mandible with stable compression osteosynthesis.

The implantation of a bone graft into the mandible was simulated in photoelastic model tests. Problems posed by the lingual and alveolar areas untouched by the plate are discussed. The tests showed that in both problem areas enough interfragmentary pressure can be built up using a five-hold DC (dynamic compression) plate with a short implant and two four-hole DC plates with a long implant, whenever the metal plates have dynamic compression holes (DC), are prebent and the screws are in converging position. This is a prerequisite for a rapid revascularization of the implanted bone graft and primary bone healing. These tests and our clinical experience showed that with small implants using a five-hold plate and with long implants using two four-hole plates, and physiologically stressing the bone implant, the principles of stable compression osteosynthesis without intermaxillary immobilization have proved themselves.

Biomechanical Phenomena↗
PubMed2001

Construction and geometric stability of physiological flow rate wall-less stenosis phantoms.

Wall-less flow phantoms are preferred for ultrasound (US) because tissue-mimicking material (TMM) with good acoustical properties can be made and cast to form anatomical models. The construction and geometrical stability of wall-less TMM flow phantoms is described using a novel method of sealing to prevent leakage of the blood-mimicking fluid (BMF). Wall-less stenosis flow models were constructed using a robust agar-based TMM and sealed using reticulated foam at the inlet and outlet tubes. There was no BMF leakage at the highest flow rate of 2.8 L/min in 0%, 35% and 57% diameter reduction stenoses models. Failure of the 75% stenosis model, due to TMM fracture, occurred at maximum flow rate of 2 L/min (mean velocity 10 m/s within the stenosis). No change of stenosis geometry was measured over 4 days. The construction is simple and effective and extends the possibility for high flow rate studies using robust TMM wall-less phantoms.

Acoustics↗
PubMedDate not supplied

Morphometric modeling of olfactory circuits in the insect antennal lobe: I. Simulations of spiking local interneurons.

Inhibitory local interneurons (LNs) play a critical role in shaping the output of olfactory glomeruli in both the olfactory bulb of vertebrates and the antennal lobe of insects and other invertebrates. In order to examine how the complex geometry of LNs may affect signaling in the antennal lobe, we constructed detailed multi-compartmental models of single LNs from the sphinx moth, Manduca sexta, using morphometric data from confocal-microscopic images. Simulations clearly revealed a directionality in LNs that impeded the propagation of injected currents from the sub-micron-diameter glomerular dendrites toward the much larger-diameter integrating segment (IS) in the coarse neuropil. Furthermore, the addition of randomly-firing synapses distributed across the LN dendrites (simulating the noisy baseline activity of afferent input recorded from LNs in the odor-free state) led to a significant depolarization of the LN. Thus the background activity typically recorded from LNs in vivo could influence synaptic integration and spike transformation in LNs through voltage-dependent mechanisms. Other model manipulations showed that active currents inserted into the IS can help synchronize the activation of inhibitory synapses in glomeruli across the antennal lobe. These data, therefore, support experimental findings suggesting that spiking inhibitory LNs can operate as multifunctional units under different ambient odor conditions. At low odor intensities, (i.e. subthreshold for IS spiking), they participate in local, mostly intra-glomerular processing. When activated by elevated odor concentrations, however, the same neurons will fire overshooting action potentials, resulting in the spread of inhibition more globally across the antennal lobe. Modulation of the passive and active properties of LNs may, therefore, be a deciding factor in defining the multi-glomerular representations of odors in the brain.

Animals↗
PubMed1999

Computational modeling of an early evolutionary stage of the nervous system.

The object of this work is to create a computational model that examines the early evolution of the nervous system in relation to adaptive behavior. The main questions are: how did the nervous system and the most primitive forms of intelligence came into being, how a system can be organized during evolution that is able to ensure the adaptive behavior of a being, what are the basic rules of construction that are sufficient to create a workable nervous system without specifying the details of the construction. The biological bases of the model are the phyla Cnidaria and Porifera as they stand at the beginning of the genesis of nervous organization. We found in our model that in a network of homogenous epithelial-like cells, which is considered the starting point of the genesis of the nervous system, the changes that have positive influence on the behavior are those that make the spreading of the electric potential more efficient. It can cause the increase of the effectiveness of the behavior by itself without creating new specific cell-types. There are some alternatives to increasing the effectiveness of spreading of stimuli, for example increasing the value of biophysical parameters of the cells, or increasing the density of nerve cells and the number of synapses. If during the evolution a sort of cell comes into being that is able to conduct electrical stimuli--even in a rudimentary way--it can increase the adaptivity of behavior by itself without the need for specific information of how to organize the construction of this system.

Adaptation, Physiological↗
PubMed2003

Aqueous humor dynamics and the iris.

Solutes concentration in the aqueous humor of the eye is highest near the ciliary processes in the posterior chamber (p.c.) and lowest near the trabecular meshwork in the anterior chamber (a.c.). The high osmotic gradient across the semipermeable iris causes it to easily move forward at this location and occasionally occlude the iridocorneal angle. Vector analysis of the forces generated by miosis helps explain on osmotic grounds why it reduces the intraocular pressure, while at the same time the analysis elucidates the reason for the higher frequency of angle closure glaucoma when the anterior chamber is shallow.

Aqueous Humor↗
PubMed2002

Ultrasonography and fluoroscopic fusion for prostate brachytherapy dosimetry.

PURPOSE: To investigate the feasibility of performing postimplant and intraoperative dosimetry for prostate brachytherapy by fusing transrectal ultrasound (TRUS) and fluoroscopic data. METHODS AND MATERIALS: Registration of ultrasound (prostate boundary) and fluoroscopic (seed) data requires spatial markers that are detectable by both imaging modalities. In this study, the needle tips were considered as such fiducials. Prostate phantoms were implanted with the seeds, and four localization needles were inserted. In the TRUS frame of reference, the longitudinal coordinate of the needle tip was determined by advancing the needle until the echo from its tip just registered at a known probe depth. The tip's transverse coordinates were determined from the associated TRUS slice. The three-dimensional needle tip positions were also calculated in the fluoroscopic coordinate system using a seed reconstruction method. The transformation between the TRUS and fluoroscopy coordinate systems was established by the least-squares solution using the singular value decomposition. RESULTS: With three of four needle tips as fiducials and the one remaining needle as a test target, the mean fiducial registration error was 0.8 mm and the test target registration error was 2.5 mm. When all four points were used for registration, the errors decreased to 1.1 mm. A comparison between the proposed method and CT-based dosimetry yielded a percentage of prostate volume receiving 100% and 150% of the prescribed minimal peripheral dose and minimal dose received by 90% of the prostate gland that agreed within 0.4%, 2.7%, and 4.2%, respectively. CONCLUSION: The combination of TRUS and fluoroscopy is a feasible alternative to the currently used CT-based postimplant dosimetry. Furthermore, because of online imaging capability, the method lends itself to real-time intraoperative applications.

Brachytherapy↗
PubMed2002

Towards integrating functional imaging in the treatment of prostate cancer with radiation: the registration of the MR spectroscopy imaging to ultrasound/CT images and its implementation in treatment planning.

PURPOSE: Dose-escalation to intraprostatic tumor deposits detected by magnetic resonance spectroscopy (MRS) is an example of tumor-targeted radiation therapy. Because treatment planning for prostate brachytherapy is performed based on ultrasound (US)/computed tomography (CT) images, a sine qua non of this technique is the ability to map MRS-positive volumes (obtained in a gland deformed by the endorectal balloon coil) to the US/CT images. An empirical algorithm designed to perform this function, and its validation, are described. METHODS AND MATERIALS: Mathematically, the problem of mapping points between the MR and US/CT domains comes to: (a) ascertaining that the position of any point in the interior of the prostate is uniquely determined by the shape of the gland, and (b) finding an algorithm that describes this relationship. The image registration algorithm described here is based on the assumption that points within the gland maintain the same relative position with respect to both the axial contours of the prostate and the center of the prostate along the superior-inferior direction. Relative positions of MRS-positive voxels are calculated with this method in both MR and US/CT space. For a particular voxel in the MR space, one obtains first the z coordinate in the US/CT space, that is, along the superior-inferior direction. This determines the axial slice in the US/CT frame of reference where the other two coordinates (x, y) will be calculated. The validity of this algorithm was examined with the aid of a pelvic phantom built to simulate realistically the prostate and its surrounding bony and tissue structures and with CT scans of implanted patients obtained, at several weeks' intervals, as part of an edema-resolution study. Seventy-five "dummy" seeds were placed in the phantom, within the simulated prostate gland, in a quasi-regular pattern. The coordinates of these seeds were determined and thus served as markers of prostate deformation when an inflated rectal probe was introduced in the phantom. CT images of this phantom were taken for different volumes of the MR rectal probe and in each case the prostate outlines were contoured and seed coordinates calculated. Using these data, the predictions of the mapping algorithm could be directly verified. RESULTS: Absolute values of the 3D-positional errors in this algorithm were 2.2 mm +/- 1.2 mm (average +/- SD). Only 6 of 75 seeds had positional displacement of 4 mm or more. Similar results were obtained in the patient analysis. CONCLUSIONS: In comparison to the MRS voxel size (6.25 x 6.25 x 3.0 mm3), the present algorithm achieves the desired clinical accuracy. As well, with this 3D algorithm seed positions are reconstructed with an uncertainty that, along the z direction, is less than half the thickness of the typical US slice (0.5 cm).

Algorithms↗
PubMed1999

Dose-wall histograms and normalized dose-surface histograms for the rectum: a new method to analyze the dose distribution over the rectum in conformal radiotherapy.

PURPOSE: To develop an accurate method to generate a dose-volume histogram (DVH) of the rectum wall, solely based on the outer contours of the rectum wall. METHODS AND MATERIALS: A mathematical model for the rectum wall is developed, incorporating the stretching of the rectum wall due to variable rectal filling and neighboring structures. The model is based on the assumption that the amount of intersected rectum wall tissue normal to the central axis of the rectum is constant. The main objective of the model is to determine the thickness of the rectum wall in each wall element. Two approaches are described, each yielding a DVH of the rectum wall, based only on the delineated outer contours of the rectum. In the first approach, the model is used to create a set of inner contours out of the axial outer contours. Both sets of contours are used to derive a dose-wall histogram (DWH) of the rectum. In the second approach, the model is used to generate a normalized 2D sampling space, which is subsequently binned into a normalized dose-surface histogram (NDSH). The model is verified using 20 sets of CT data (5 patients x 4 scans) in which both outer and inner contours of the rectum are carefully delineated. The DWHs and NDSHs are compared with DVHs of the rectum wall, which require contouring of the outer and inner surfaces of the rectum wall, and with DVHs of the total rectum (including rectal filling). The variation between DWHs, NDSHs, and DVHs is investigated using normal tissue complication probability (NTCP) calculations. RESULTS: The local wall thickness of the rectum as outlined on CT data was in conformity with the described rectum model. The amount of rectum wall tissue per unit length rectum varied considerably between patients (27%, 1 SD). In all analyzed patients, the DWHs and NDSHs corresponded well to the DVHs of the rectum wall. Much more discrepancies were observed between the DVHs of the total rectum and the DVHs of the rectum wall. CONCLUSION: The applied methods yield accurate dose distributions of the rectum wall, without delineating the inner surface of the rectum. This reduces both the workload and variations due to inaccurate delineation of the rectum wall. The DWH and NDSH are effective tools to evaluate 3D dose distributions of the rectum wall and to estimate the complication probability of the rectum in high-dose conformal radiotherapy.

Humans↗
PubMed2001

A model of the electrically excited human cochlear neuron. II. Influence of the three-dimensional cochlear structure on neural excitability.

A simplified spiraled model of the human cochlea is developed from a cross sectional photograph. The potential distribution within this model cochlea is calculated with the finite element technique for an active scala tympani implant. The method in the companion article [Rattay et al., 2001] allows for simulation of the excitation process of selected elements of the cochlear nerve. The bony boundary has an insulating influence along every nerve fiber which shifts the stimulation condition from that of a homogeneous extracellular medium towards constant field stimulation: for a target neuron which is stimulated by a ring electrode positioned just below the peripheral end of the fiber the extracellular voltage profile is rather linear. About half of the cochlear neurons of a completely innervated cochlea are excited with monopolar stimulation at three-fold threshold intensity, whereas bipolar and especially quadrupolar stimulation focuses the excited region even for stronger stimuli. In contrast to single fiber experiments with cats, the long peripheral processes in human cochlear neurons cause first excitation in the periphery and, consequently, neurons with lost dendrite need higher stimuli.

Animals↗
PubMed2002

Descending projections to the inferior colliculus from the posterior thalamus and the auditory cortex in rat, cat, and monkey.

Projections from the posterior thalamus and medial geniculate body were labeled retrogradely with wheat germ agglutinin conjugated to horseradish peroxidase injected into the rat, cat, and squirrel monkey inferior colliculus. Neurons were found ipsilaterally in the (1) medial division of the medial geniculate body, (2) central gray, (3) posterior limitans nucleus, and the (4) reticular part of the substantia nigra. Bilateral projections involved the (5) peripeduncular/suprapeduncular nucleus, (6) subparafascicular and posterior intralaminar nuclei, (7) nucleus of the brachium of the inferior colliculus, (8) lateral tegmental/lateral mesencephalic areas, and (9) deep layers of the superior colliculus. The medial geniculate projection was concentrated in the caudal one-third of the thalamus; in contrast, the labeling in the subparafascicular nucleus, substantia nigra, and central gray continued much further rostrally. Robust anterograde labeling corresponded to known patterns of tectothalamic projection. Biotinylated dextran amine deposits in the rat inferior colliculus revealed that (1) many thalamotectal cells were elongated multipolar neurons with long, sparsely branched dendrites, resembling neurons in the posterior intralaminar system, and that other labeled cells were more typical of thalamic relay neurons; (2) some cells have reciprocal projections. Similar results were seen in the cat and squirrel monkey. The widespread origins of descending thalamic influences on the inferior colliculus may represent a phylogenetically ancient feedback system onto the acoustic tectum, one that predates the corticocollicular system and modulates nonauditory centers and brainstem autonomic nuclei. Besides their role in normal hearing such pathways may influence behaviors ranging from the startle reflex to the genesis of sound-induced seizures.

Animals↗