Ray Projection Research Articles

Sensory Deviations Subsequent to Senile Cataract

To evaluate the effect of extracapsular cataract extraction with posterior chamber intraocular lens (IOL) implantation in patients with sensory deviations subsequent to senile cataract. Twenty patients with dense cataract and associated sensory deviations underwent follow-up between April 1996 and April 1998 after extracapsular cataract extraction with posterior chamber IOL implantation in the deviating eye. All patients underwent follow-up for a minimum period of 6 months. Preoperatively, all patients had a visual acuity of PL positive (perception of light present) and PR (projection of rays) accurate in the deviating eye. Two patients had an esodeviation, and 18 patients had an exodeviation. Postoperatively, all patients had a corrected visual acuity of 20/40 or better in the operated eye at 12 weeks. Nineteen patients had ocular alignment within +/-8 prism diopters of orthophoria at 12 weeks. Sensory deviations subsequent to senile cataract usually resolve spontaneously after cataract surgery if visual gains are 20/40 or better. The prognosis for binocular vision is good.

Calculation of temporal, angular, and intensity characteristics of the sound field in a coastal area with an arbitrary bottom relief and a constant sound speed in the medium

Computational algorithms and some computed data are presented for the total sound field in a waveguide whose depth arbitrarily depends on two horizontal coordinates. The sound speed is supposed to be constant, and the bottom slopes are considered as small. The algorithm involves three steps. First, horizontal rays, i.e., horizontal projections of the real rays multiply bottom-and surface-reflected, are calculated. Second, the horizontal rays are set up to a point. Third, the real rays are set up to a point. The computational accuracy is analyzed for a homogeneous wedge lying on a halfspace. Calculations are carried out for a coastal region of the ocean.

Backscattering enhancements of ultrasound by tilted solid plastic cylinders in water due to the caustic merging transition: High angular resolution scans

Bulk shear and longitudinal waves can make important contributions to the scattering of ultrasound by tilted finite plastic and rubber cylinders in water when the phase velocity of the wave is less than the speed of sound of the surrounding fluid. At a certain critical tilt angle, a backscattering enhancement is observed as a result of merging rainbow caustics associated with bulk transmitted rays internally reflected off the cylinder truncation [F. J. Blonigen and P. L. Marston, J. Acoust. Soc. Am. 107 (2000)]. The backscattering away from this angle is otherwise weak. The critical angle is calculated using the Bravais effective refractive index for the projections of rays on the base plane of the cylinder. New ultrasonic observations are reported for a polystyrene cylinder over a wide range of tilt angles at high angular resolution. The backscattering amplitude angle scan takes on the shape of a Pearcey function with the peak amplitude offset from the critical angle. Backscattering amplitudes at the critical angle are also compared with a ray theory prediction as a function of frequency for both the polystyrene and a silicone rubber cylinder. [Work supported by ONR.]

Ultrasound transmission tomography image distortions caused by the refraction effect

This paper presents the influence of ultrasonic beam ray refraction effect on the internal object structure imaging using the ultrasound transmission tomography method (UTT), in parallel ray projection geometry, for ultrasonic pulse run-time measurements. Simulation calculations carried out using specially elaborated software were verified experimentally by means of real measurements on a research set-up for UTT. Simple ways to minimize image distortions caused by the refraction effect were also suggested.

Backscattering enhancements for tilted solid plastic cylinders in water due to the caustic merging transition: observations and theory

Bulk shear and longitudinal waves give rise to important contributions to the scattering of ultrasound by tilted finite plastic and rubber cylinders in water. This occurs in situations where either the shear or longitudinal speed is less than the speed of sound in the surrounding water. At a certain critical tilt angle, large backscattering enhancements are observed for finite cylinders, where the wave vector can reverse direction upon reflection from the cylinder truncation. The scattering process is analogous to the enhancement produced by the merging of rainbow caustics of primary rainbow rays in the scattering of light by long dielectric cylinders, also known as the caustic merging transition [C. M. Mount, D. B. Thiessen, and P. L. Marston, Appl. Opt. 37, 1534-1539 (1998)]. A ray theory was developed to model the backscattering mechanism at the critical tilt angle. It employs the idea of the Bravais effective refractive index, convenient for constructing ray diagrams for the projections of rays in the base plane of the cylinder. There is general agreement between the theory and the experiment down to relatively low ultrasonic frequencies (ka as small as 10). The enhancement is the most significant backscattering contribution for a wide range of tilt angles.

Virtual 3D Sculpting

This paper presents a virtual sculpting method for interactive 3D object deformation. The method is based on the use of an electronic glove. A parametric control hand surface defined by an open-uniform B-spline tensor product surface is first created to model the hand gesture. The geometric attributes of the object in the Euclidean 3D space are then mapped to the parametric domain of the control hand surface through a ray projection method. By maintaining the distances between the mapped pairs, change of hand gesture can be efficiently transferred to control the deformation of the object. Copyright © 2000 John Wiley & Sons, Ltd.

Improvement of X-ray CT image quality by use of prior information

Most objects processed by industrial CT contain materials having a large ray-absorption coefficient (e.g., metal). In such cases, streak artifacts (SA) occur due to excessive X-ray attenuation. If a region having a large absorption coefficient is in a section to be examined, this affects the whole measurement. However, since the size, shape, material, and structure of an industrial object are known from its design information, this region can be treated separately. This paper describes an algorithm to reconstruct such a special region by using a sequential approximation. Since previously known ray-absorption coefficients are given to the rest of the region in the object, the influence of SA can be reduced. Computer simulations with several phantoms were carried out, and the proposed method was demonstrated to have a very significant effect. If the abnormal part is large, the effect of the method is degraded. However, it has been found that this degradation is suppressed by increasing the directions of ray projections. If regions of high absorption and low absorption are in a single region, the effect of image improving by the method is also degraded, but a solution of this problem has been found. © 1999 Scripta Technica, Syst Comp Jpn, 30(11): 67–76, 1999

Patient Dosimetry in Arteriography of the Lower Limbs. Part I: Quantification of Exposure

The purpose of this study was to quantify patient exposure to X rays in arteriography of the lower limbs and to derive hitherto unavailable characteristics of common projections. In a study of 455 patients three types of arteriography have been monitored: Seldinger catherisation for arteriography of both legs, percutaneous needle puncture arteriography of one leg and intravenous digital subtraction arteriography of peripheral vessels. Using a microcomputer-controlled automatic data acquisition system, information was obtained on fluoroscopy time, focus-to-patient distance, position and direction of the X ray beam, field size, X ray tube voltage, dose-area product (DAP), digital subtraction arteriography (DSA) runs, DSA frames, conventional cut film runs and cut films. Exposure parameters needed for the definition of X ray projections in peripheral arteriography have been derived, as well as associated DAP values and entrance dose estimates.

Patient Dosimetry in Arteriography of the Lower Limbs. Part II: Dose Conversion Coefficients, Organ Doses and Effective Dose

X ray projection data (see Part I) and GSF phantoms ADAM and EVA were used as input for the GSF Monte Carlo transport code to calculate hitherto unavailable dose conversion coefficients (DCCs) for common projections in arteriography of the lower limbs. These DCCs served to estimate organ equivalent doses and effective dose in a study of 455 patients. The effective dose caused by percutaneous needle puncture arteriography of one leg was on average I mSv, by Seldinger catherisation for arteriography of both legs 4 mSv, and by intravenous digital subtraction arteriography (DSA) 5 mSv, For needle puncture and Seldinger arteriography the effective dose attributable to fluoroscopy was about 50% for male and 60% for female patients. The contribution of DSA was between 15 and 35%, that of cut films between 17 to 28%, depending on gender and procedure. The effective dose in intravenous arteriography was mainly due to DSA (91-93%).

Organ Dose Calculation in Medical X Ray Examinations by the Program PCXMC

PCXMC is a PC-based Monte Carlo program for calculating patients' organ doses and the effective dose in medical X ray examinations. It uses mathematical phantom models, and can be used to compute the doses in 25 organs of patients of different ages and sizes in freely adjustable X ray projections and other examination conditions of projection radiography and fluoroscopy. The organ doses calculated with PCXMC agree well with the doses calculated by the National Radiological Protection Board for common X ray examinations and with the doses calculated by Stern et al for cineangiographic examinations of coronary arteries.

Characterization of a cold neutron beam from a curved guide

A supermirror guide that includes both straight sections and curved channels has been installed at a cold neutron source facility. A description of the beam line and the beam characteristics are given. The transmitted neutron wavelength spectrum and the beam current density have been measured. Factors that affect the spectrum are discussed. Though the final straight guide section improves the spatial uniformity of the beam intensity at the guide exit, the spatial-angular correlations caused by the curved channels persist. These correlations are observed in the beam divergence measurements at various positions along the beam line using neutron imaging plate technology, and are explained by ray projections. The divergence of the transmitted beam is determined both by the critical angle of the guide and the collimation beyond the guide.

Main error sources in ultrasound transmission tomography imaging

Ultrasound transmission tomography (UTT) consists in the usage of information included in ultrasonic pulses penetrating through an object in order to reconstruct sectional images of its inner structure. The contrast in the images corresponds to the distribution of local values of the acoustic parameter measured in projections. The measurement errors usually distort the tomographic image of the inner object structure. How different measurement errors are manifested and how big the changes they bring about in the reconstructed tomographic image can be fundamental for the determination of the ultrasound transmission tomography application range. The main sources of errors in ultrasound transmission tomography are the measurement accuracy and geometry, the ultrasonic refraction, the changing of measurement conditions, the measurement method, the reconstruction algorithm, and the disappearance of the receiving signal. Some different tomographic measurement errors (caused by the above-mentioned sources) were computer simulated and compared with the real ones. The influence of these errors on the ultrasonic tomographic imaging was shown. All of these errors refer to the run-time measurements in the parallel ray projection geometry using the convolution and backprojection algorithm for the image reconstructions.

Bravais effective refractive index for tilted plastic cylinders and the caustic-merging transition in the meridional plane: Demonstration of an optical analogy

Some solid scatterers in water such as plastic cylinders do not support leaky Rayleigh waves because the shear wave velocity of the solid is less than the speed of sound in water. The high-frequency scattering from such objects is generally weak. In that case the ray diagram for transmitted shear waves is analogous to the refraction of light by an object in air. For a tilted cylindrical object, the projection of rays on a base plane may be determined by ignoring the tilt by replacing the true refractive index n by the Bravais value (n2−sin2γ)1/2/cosγ where γ is the tilt. For a circular cylinder, when the Bravais value reaches 2, the rainbow caustics merge in the meridional plane defined by the incident wave vector and the cylinder’s axis [C. M. Mount and P. L. Marston, in Light and Color in the Open Air (OSA, Washington, DC, 1997), pp. 14–16]. The merged caustics greatly enhance the scattering because of the far-field focusing of a cusp point. The analysis is also relevant to light scattering by icicles and to the scattering of sound by certain liquid-filled cylinders. [Work supported by the Office of Naval Research.]

Volumetric (helical/spiral) CT (VCT) of the airways.

Volumetric computed tomography (VCT) represents an important improvement over conventional CT for assessing most airway abnormalities. Elimination of misregistration due to variations in respiration coupled with decreased motion artifact and the ability to obtain routine overlapping sections allow a more confident estimation of the presence and extent of disease. Recently, attention has focused on newer reconstruction techniques including: multiplanar reconstructions (MPRs), including curved multiplanar reformations; multiplanar volume reconstructions (MPVRs) using ray projection techniques, such as maximum and minimum projection imaging; external rendering, or 3D-shaded surface displays; and, most recently, internal rendering or so-called "virtual bronchoscopy". Given the often redundant nature of many of these methodologies determining indications for their use remains to be established, especially by comparison to axial imaging. The purpose of this article is to review these various reconstruction techniques and, based on current knowledge, place them in an appropriate clinical context.

5297551 Weighted ray projection imaging for MR angiography

5297551 Weighted ray projection imaging for MR angiography

An Automated Measurement System for Characterisation of Patient Exposure During Angiography

Angiographic investigations and interventions rely on fluoroscopy, digital subtraction angiography (DSA) and series of large area photographic images (serial cut films). X ray projections are applied in a number of different directions. Fluoroscopy and images may encompass a small part of the body up to approximately 70%. In order to be able to estimate radiation dose to the patient under such varying exposure conditions a real-time monitoring system has been developed. This system records automatically a number of system parameters, such as tube high voltage, beam diaphragm settings, tube current, mA.s, beam entrance position, beam direction, fluoroscopy time, number of DSA frames and number of serial cut films. Measurements of the quantity dose-area product (DAP) are also performed continuously, providing DAP data for fluoroscopy, and DSA and cut film separately for each stage of the angiographic procedure. Selected data on patient exposure conditions will be used as input data for Monte Carlo organ dose calculations. Features of the real-time monitoring system are described and some results of clinical applications are presented.

Fast Three-Dimensional Measurement Technique Using a Reference Table. Measurement of a Human Head.

This paper describes a system which enables fast 3-dimensional measurementof a human head by means of a slit ray projection method. The system developed here consists of a laser slit ray projector, two CCD TV cameras, a real-time video signal processor and a 32-bit computer. Due to the employment of this real-time video signal processor and a fast data-processing technique using a reference table, a 3-dimensional measurement of the human head can be Accomplished in 4.3 seconds, and all the image data are converted to 3-dimensional data in one second. Experimental data reveal the applicability of our system.

Gadolinium-enhanced MR angiography.

Experience in three patients (one each with meningioma, pineal tumor, and prominent jugular bulb) illustrates that magnetic resonance (MR) angiography can benefit from the administration of gadolinium diethylenetriaminepentaacetic acid. Data were acquired with a three-dimensional velocity-compensated (fast imaging with steady-state precession) sequence. MR angiograms were obtained with a ray projection algorithm by using maximum intensity values. Portions of the vascular anatomy--particularly venous structures and smaller arteries--were better portrayed on the postcontrast than on the precontrast angiograms. Enhancing lesions were also seen on the projection images. Enhancement of dura and extracranial tissues (sinus and nasal mucosa) can obscure vascular detail.

Possibility of the appearance of an anomalous mode in the propagation of short radio waves in the low-latitude ionosphere

The possibility of the appearance of an anomalous mechanism of propagation of short radio waves in the low-latitude ionosphere, in which a particular family of ray trajectories trapped between crests of the equatorial anomaly arises, is discussed within the framework of geometrical optics. A numerical analysis of such trajectories is made. An analytic procedure, connected with the calculation of horizontal projections of rays, is proposed for quantitative estimates of this propagation mechanism. A series of time, angle, and energy estimates is given.

Three-dimensional reconstruction from projections with incomplete and noisy data by object estimation

An estimation approach to three-dimensional reconstruction from parallel ray projections, with incomplete and very noisy data, is described. Using a stochastic dynamic model for an object of interest in a probed domain of known background density, the reconstruction problem is reformulated as a n onlinear state estimation problem. An approximate minimum mean square error globally optimal algorithm for the solution of this problem is presented. The algorithm, which is recursive in a hybrid frequency-space domain, operates directly on the Fourier transformed projection data, eliminating altogether the attempt to invert the projection integral equation. The simulation example considered in this paper demonstrates that good object estimates may be obtained with as few as five views in a limited sector of 90° and at a signal-to-noise ratio as low as 0 dB.