Integration of dental models in a three-dimensional replica.
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Facial Bones↗
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Results for “Models, Anatomic”
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A new three-dimensional treatment algorithm for complex surfaces: applications in surgery.
PURPOSE: Recent advances in computer technology enable automatic reconstruction of surface models using digitized contour lines and three-dimensional (3D) representation on a graphic terminal. This work was aimed at obtaining 3D reconstructions of facial bones to help guide oral surgery and complex dental implantology procedures. MATERIAL AND METHODS: The starting point was a computed tomographic examination. The limits of the cortical bone were automatically outlined and then digitized using a special computer program. The resulting data were then compiled for computer-aided design (CAD) purposes, and a virtual 3D model of the bone was mathematically computed. This model was next transferred to a computer program that piloted a CAD/computer-aided manufacture (CAM) machine that guided a laser stereolithography process. RESULTS: The early results of the use of 3D images, as well as solid models, for clinical and surgical purposes, indicate a high degree of reliability in morphologic diagnosis, determining the surgical procedure, and establishing the subsequent prognosis.
Algorithms↗
A phantom for imaging biological fluids by ultrasound and CT scanning.
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Acoustics↗
Quantitative contrast measurements in B-mode images comparison between experiment and theory.
Quantitative measurements of image contrast were carried out for B-mode images of anechoic spheres (cysts) embedded in a random scattering medium. Four transducer geometries were used: (a) f/5.7 spherical transducer in pulse echo mode, (b) f/2.4 spherical transducer in pulse echo mode, (c) f/2.4, 30 degrees cone (hybrid transducer), (d) f/5.7, 30 degrees cone (hybrid transducer). The image contrast was also calculated via two methods; (i) a three-dimensional computer simulation and (ii) a relatively simple numerical convolution which relates the image of a small point-like scatterer [point spread function (PSF)] to image contrast. Generally, good agreement was found between the experimental measurements and the values calculated via both theoretical methods. The results indicate that image contrast is not determined solely by the full width at half maximum (FWHM) of the PSF. In particular, the results demonstrate the importance of far off-axis contributions of the ultrasound beam to the significant degradation of contrast in images obtained with high resolution (low f-number) axicons.
Computers↗
Correction of phase aberrations for sectored annular array ultrasound transducers.
Two methods for correction of unknown phase aberrations induced by inhomogeneous acoustic velocities in tissues are explored for the two dimensional geometry of a sectored annular array system. The methods employed are adaptations of a cross correlation technique and a speckle brightness maximization technique. The methods correct phase distortions via the introduction of phase shifts in the timing sequence at the beamformer stage of a sectored annular array transducer. The techniques are investigated employing software models and a computer controlled automated scanning system. A 65-element sectored annular array is modelled via a rotating 5 element transducer. Tissue equivalent materials were moulded into a double layer aberrating medium to simulate phase distortions encountered in the rectus abdominis muscle in vivo. A comparison of the effectiveness of the two correction methods is presented. Contrast of an anechoic region is increased from 0.34 +/- 0.08 to 0.48 +/- 0.06 for the cross correlation technique, and up to 0.62 +/- 0.05 for the speckle brightness maximization method. The performance of these correction techniques on target phantoms suggests that considerable improvements in image quality should be possible for clinical systems.
Models, Anatomic↗
Comparison of diastolic filling models and their fit to transmitral Doppler contours.
Anatomic/physiologic and kinematic mathematical models of diastolic filling which employ (lumped) parameters of diastolic function have been used to predict or characterize transmitral flow. The ability to determine model parameters from clinical transmitral flow, the Doppler velocity profile (DVP), is equivalent to solving the "inverse problem" of diastole. Systematic model-to-model and model-to-data comparison has never been carried out, in part due to the requirement that DVPs be digitized by hand. We developed, tested and verified a computerized method of DVP acquisition and reproduction, and carried out numerical determination of model-to-model and model-to-data goodness-of-fit. The transmitral flow velocity of two anatomic/physiologic models and one kinematic model were compared. Each model's ability to fit computer-acquired and reproduced transmitral DVPs was assessed. Results indicate that transmitral flow velocities generated by the three models are 'graphically indistinguishable and are able to fit the E-wave of clinical DVPs with comparable mean-square errors. Nonunique invertibility of the anatomic/physiologic models was verified, i.e., multiple sets of model parameters could be found that fit a single DVP with comparable mean-square error. The kinematic formulation permitted automated, unique, model-parameter determination, solving the "inverse problem" for the Doppler E-wave. We conclude that automated, quantitative characterization of clinical Doppler E-wave contours using this method is feasible. The relation of kinematic parameters to physiologic variables is a subject of current investigation.
Algorithms↗
Pigment color patterns of molluscs as an autonomous process generated by asynchronous automata.
Pigment color patterns of molluscs are studied from the viewpoint of autonomy. Brownian algebra developed by Spencer-Brown (1969) is extensively used for the expression of cellular-automaton rules. When asynchronous updating is introduced for the transition of cellular automata, various kinds of patterns such as traveling waves, kinks, oscillatory local patterns etc. are generated from the same transitional rule. The type of patterns depends more sensitively on the asynchronous updating relationship rather than the transitional rule itself. Therefore, pattern changes in ontogeny can be explained without any changes in transitional rules or reaction processes. It is proposed that asynchronousness is intrinsic to living systems and that recognition of the intrinsic time is essential in understanding living systems.
Animals↗
The origin and evolution of vertebrate pattern and form--a theory of vertebrate development by preformation based on the genetic molecular shape.
A new hypothesis is presented to explain the origin of vertebrate form and the guiding mechanism by which embryological development occurs. The hypothesis is based on the observation which is demonstrated, that both vertebrate form and embryological development follow a pattern which correlates with the shapes formed by a spiral as it unfolds. The fact that the DNA molecule which carries the genetic information for embryological development, also has a helical structure, has suggested the hypothesis, that vertebrate form and its development are related to the molecular shape of the genetic material. A theoretical vertebrate genetic molecular structure is proposed and it is demonstrated how this structure by "unfolding", as growth occurs, (the mechanism for which is suggested) provides an accurate prepattern and a template for vertebrate embryological development and vertebrate form. Evolutionary implications follow, which question the Neo-Darwinian synthesis. These are firstly, that the vertebrate pattern is not the result of random genetic variations and natural selection, but owes its origin to a spiral pattern, possibly that of DNA. Secondly, that progressive changes occurring in the shape of the genetic molecule provide an explanation and a mechanism for the evolution of species; a concept which is demonstrated.
Animals↗
A three-dimensional finite-difference thermoregulatory model of a squirrel monkey.
A three-dimensional thermoregulatory model of a squirrel monkey, whose shape is approximated by 742 rectangular blocks of varying sizes, has been developed. The inhomogeneous model has four layers: a core, a composite layer of muscle and fat, skin, and fur. The model simulates the flow of heat into and out of the body, including internal heat generation (metabolism) by the body, cooling and distribution of heat by blood, thermal conduction throughout the body, evaporative heat loss from sweating, and radiation and convection from the outer surface of the body. It also simulates dynamic thermoregulatory behavior such as peripheral vasomotor responses (skin vasodilation and vasoconstriction) and variable sweating rates. Computed results are compared with available experimental data; the agreement is good, especially for ambient temperatures above 26 degrees C.
Animals↗
Portal dose images. I: Quantitative treatment plan verification.
The comparison of a predicted portal dose image, calculated during treatment planning, with the measured image obtained during treatment is proposed as an approach to verify the correct implementation of a patient treatment plan. The comparison inherently verifies both the geometric alignment and the dose delivered. Feasibility studies were conducted with 60Co irradiation of a modular plastic phantom, an anthropomorphic phantom and a patient with lung cancer. Calculations were made with the 3-dimensional scatter ray-trace Delta Volume method. Calculated distributions and/or selected points of transmitted dose correction factors were compared with measurements made with TLD, scanning ionization chamber and film. For the two phantom studies, excellent agreement, usually to within 3%, was achieved when positioning of the phantoms were accurate. The patient study showed that selected point comparisons were inadequate in identifying the cause of errors when disagreement occurred. Simple subtraction of the calculated and measured images showed a 4 mm translational misalignment. The results are encouraging and demonstrate that portal dose images can be used to detect large geometric and dosimetric discrepancies between treatment plan calculations and measurements. The results also show that perfect verification is virtually impossible in the clinical situation. More work is required to use the verification information for improving the estimation of dose to the patient.
Cobalt Radioisotopes↗
On-line radiotherapy imaging with an array of fiber-optic image reducers.
In the optical approach for on-line radiotherapy imaging, a large metal sheet-fluorescent screen combination is used to convert the radiation intensity distribution into a visible light image. Data are then captured via a mirror with a camera located out of the beam. Although usable portal images can be acquired, presence of the large mirror renders the system impractical in many treatment geometries. We have overcome this limitation by replacing the mirror with an array of 16 by 16 bundles of plastic fiber-optic image reducers. Each bundle, in turn, is made up of 16 by 16 individual optical fibers. The total of 256 by 256 fibers spans an input area of 40 cm by 40 cm with each individual fiber viewing an area of 1.6 mm by 1.6 mm. Within a height of 12 cm, each fiber is reduced to an area of 0.1 mm by 0.1 mm. The reduced portal image is then turned and "piped" to a final 3.0 cm by 3.0 cm output area. For data acquisition and digitization, the fiber output is directly coupled to the sensor of a TV camera interfaced to a small computer via a 512 by 512 frame grabber. In this initial evaluation, the imaging system has been characterized in terms of its line spread function, noise and resistance to radiation damage. Adequate phantom and patient images are presented.
Fiber Optic Technology↗
Custom beam profiles in computer-controlled radiation therapy.
A computer-controlled radiation therapy technique is demonstrated which uses multiple concurrent boost fields to modify the beam profile of a conventional treatment beam. A principal field, identical to that of a corresponding conventional treatment plan, delivers the major component of the prescribed dose. Dose increments given from boost fields placed within this principal field compensate for variations in patient anatomy, for variations in target volume shape, and/or for imperfect beam characteristics, such as excessive off-axis dose or inadequate beam wedge angle. This concurrent boost field technique is demonstrated for several treatment sites. It produces significant improvement in uniformity of dose delivered to the target compared to conventional treatment. Implementation of these treatments requires a computer-controlled linear accelerator with independently-movable collimator jaws, an automatic beam set-up procedure, and a patient prescription database. Since all fields are delivered under computer control, concurrent boost technique treatment times are not much longer than those of conventional treatments.
Feasibility Studies↗
The effect of the number of computed tomographic slices on dose distributions and evaluation of treatment planning systems for radiation therapy of intact breast.
PURPOSE: This study was undertaken to answer the following questions in breast irradiation: (a) How many calculation planes are sufficient for three-dimensional (3-D) treatment planning? (b) Is pseudo-3-D planning system sufficiently accurate for 3-D treatment planning of a breast? METHODS AND MATERIALS: We carried out dose calculations and differential dose-volume analysis on three representative patients covering the range of breast size encountered in a clinic. The breast volumes were reconstructed from computed tomography (CT) scans using three slices, five slices and the full CT scan respectively. An established 3-D dose algorithm and two pseudo-3-D commercial systems were used in the calculations. Comparison of isodose distributions were made between the central axis plane, a cephalic and a caudal plane 6 cm above or below the central axis respectively. RESULTS: When comparing isodose distributions generated with conventional two-dimensional treatment planning with 3-D dose calculations, the former underestimated the size and magnitude of the hot spots in the medial and the lateral subcutaneous (SC) regions. When comparing the three-slice with the full CT model, while the three-slice model was found to be adequate for the "small" and the "medium" size patients, the full CT model provided a more accurate representation of dose distributions for the "large" patient. Comparison of a true 3-D algorithm with pseudo-3-D algorithms showed that while the latter systems were adequate for the "small" and the "medium" patients, significant differences were noted between the true 3-D and the pseudo-3-D algorithms for the "large" patient. CONCLUSION: For patients whose breast contours vary slowly within the tangential fields, a three-slice CT scan as well as a pseudo-3-D approach appears to be adequate for clinical decision. However, for patients with large variation of contours within the tangential fields, a full scale CT scan with a true 3-D dose algorithm is more accurate than either the three-slice or the five-slice model.
Breast↗
Transmission dosimetry with a liquid-filled electronic portal imaging device.
PURPOSE: To assess the accuracy of transmission dose rate measurements for various phantom-detector geometries, performed with an electronic portal imaging device (EPID) and to compare these transmission dose rate values with exit dose rate data. METHODS AND MATERIALS: Transmission dose rate values on the central beam axis and beam profiles were measured with an EPID consisting of a matrix of liquid-filled ionization chambers. These data were compared with transmission and exit dose rate values, obtained using air-filled ionization chambers for a number of field sizes, phantom thickness, and phantom-detector distances. Various homogeneous and inhomogeneous phantoms were applied. RESULTS: The increase in dose rate with field size is larger for the EPID than in air, due to the larger amount of side scatter in the EPID. The difference has been taken into account by a deconvolution of the EPID images. An additional build-up layer on top of the commercial device is needed to reach dose maximum at the liquid ionization chambers for photon beam energies higher than about 4 MV. The transmission off-axis ratios (OAR) determined with the EPID and in air agreed within 2% for all tested cases, after deconvolution of the EPID signal. The agreement between the EPID-and exit-OAR decreased with increasing phantom-detector distance and the presence of inhomogeneities. For a phantom-detector distance of about 10 cm, the EPID- and exit-OARs agree within 2.5%. The difference could be up to 8% for an air inhomogeneity and a phantom-detector distance of 30 cm. CONCLUSIONS: The difference between EPID measurements and measurements in air can be explained by side scatter effects in the EPID and lack of adequate buildup, and can easily be taken into account. The loss of scatter compared with the situation at the exit side of the phantom explains the difference between transmission and exit dose values. At short phantom-detector distances, good agreement exists between transmission and exit dose rate. This implies that at this distance, the EPID can be used for simple comparison with exit dose calculations during patient treatments. At larger distances, more sophisticated conversion methods are required.
Models, Anatomic↗
Measurements of the partial volume phenomenon.
The partial volume phenomenon can produce subtle changes in the reconstructed value of the linear attenuation coefficient which may in turn make the detection of an object more difficult. A model for studying the effects of the partial volume phenomenon is presented along with measurements made on the General Electric CT/T whole body scanner. The results of these measurements indicate that small differences in the linear attenuation coefficient may go unnoticed when the video display format is used exclusively to evaluate the CT image. It is suggested that this display format incorporate profiles of the CT numbers to assist the viewer in the evaluation of the CT scans.
Data Display↗
The tectorial membrane of mammals.
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Animals↗
A possibility of sharp tuning in a linear transversally inhomogeneous cochlear model.
Considerable sharpening of basilar membrane frequency selectivity and simultaneous decreasing of phase lag can be obtained in a linear ('passive') hydromechanical three-dimensional cochlear model, if the transverse geometry of the cochlea is taken into account. Both the tuning qualities, Q10, and the phase angles at CF of some transversally inhomogeneous linear models can be set into the range of experimental data [Sellick et al. (1983) Hear. Res. 10, 93-108; Robles et al. (1986) J. Acoust. Soc. Am. 80, 1364-1379.] The calculations are developed on the base of WKB-approximation. The integral coefficients of eiconal equation are the transversally averaged means of basilar membrane surface mass density and stiffness: (formula; see text) where eta(y) is the major eigenfunction of basilar membrane cross-sectional vibrations. The classical Ritz's method is used for calculation of the cross-sectional eigenfunctions. The size and the form of cochlear cross-section are found also to alter the tuning. The rapid increase of the model response towards the peak is due to that damping remains negligible up to the peak position, where the imaginery part of the wave-number begins to increase sharply.
Acoustic Stimulation↗
Analysis and classification of delay-sensitive cortical neurons based on response to temporal parameters in echolocation signals.
Echolocating bats generate an acoustic image of their target by processing target-reflected echoes of their emitted biosonar pulses. Efforts in building computational models of auditory processing in the bat auditory system, using extensive neurophysiological data from cortical studies are challenged by the intrinsic complexity and the significant variability in neural response to stimuli. In this paper, we use a computerized method for the analysis and classification of delay-sensitive neurons to classify neurons from the auditory cortex of Myotis lucifugus, a species that echolocates with FM signals. The coefficients of the bi-linear fit to the best delay response surfaces (mean R2 = 0.01) were used in classifying the neurons. Six classes were derived that corresponded to the four previously characterized neurophysiologically. The first class corresponded to delay-tuned neurons which exhibited a constant best delay at different pulse repetition rates and pulse durations. Three other classes corresponded to the different subtypes of tracking neurons which changed their best delay to one or both of these stimulus temporal parameters. Two additional classes were differentiated although their best-delay response were similar to either the delay-tuned or the duration and pulse-repetition rate sensitive class. Artificial delay-sensitive neurons built from the parameters of the centroid of each class, will serve a key role in the FM bat auditory system model that we are building.
Acoustic Stimulation↗