1257 results about "Attenuation coefficient" patented technology

The present invention pertains to a method and an apparatus to generate a density image of an object using fan or cone beams of radiation and collimated detectors on one side of the object. The method consists of irradiating an object with a plurality of pairs of non-parallel radiation beams wherein the beams in each pair intersect a same segment along the axis of the detector. Compton-scattering radiation from the beams are then measured, and corrected attenuation coefficients along each beam are obtained. This latter step is effected by taking a first ratio of detector measurements for the beams in each pair; comparing the first ratio with a second ratio of corresponding calculated detector measurements and balancing discrepancies between the first and second ratios in a forward-inverse numerical analysis algorithm. Taking ratios of attenuation coefficients along related incident beams eliminates non-linearity problems whereby the aforesaid algorithm can be solved.

Imaging apparatus, is provided, comprising a first device, for obtaining a first image, by a first modality, selected from the group consisting of SPECT, PET, CT, an extracorporeal gamma scan, an extracorporeal beta scan, x-rays, an intracorporeal gamma scan, an intracorporeal beta scan, an intravascular gamma scan, an intravascular beta scan, and a combination thereof, and a second device, for obtaining a second, structural image, by a second modality, selected from the group consisting of a three-dimensional ultrasound, an MRI operative by an internal magnetic field, an extracorporeal ultrasound, an extracorporeal MRI operative by an external magnetic field, an intracorporeal ultrasound, an intracorporeal MRI operative by an external magnetic field, an intravascular ultrasound, and a combination thereof, and wherein the apparatus further includes a computerized system, configured to construct an attenuation map, for the first image, based on the second, structural image. Additionally, the computerized system is configured to display an attenuation-corrected first image as well as a superposition of the attenuation-corrected first image and the second, structural image. Furthermore, the apparatus is operative to guide an in-vivo instrument based on the superposition.

Cone beam volume CT breast imaging is performed with a gantry frame on which a cone-beam radiation source and a digital area detector are mounted. The patient rests on an ergonomically designed table with a hole or two holes to allow one breast or two breasts to extend through the table such that the gantry frame surrounds that breast. The breast hole is surrounded by a bowl so that the entire breast can be exposed to the cone beam. Spectral and compensation filters are used to improve the characteristics of the beam. A materials library is used to provide x-ray linear attenuation coefficients for various breast tissues and lesions.

An apparatus and method for measuring coefficients of retroreflectance of retroreflective surfaces such as road signs involves use of a modified light based range finder. The apparatus includes a power attenuation factor data base which relates pulse width of received pulses to power attenuation of the transmitted pulses. The range finder calculates target range based on time of flight of light pulses. The apparatus automatically calculates the absolute coefficient of retroreflectance for an unknown reflective surface being measured by comparison of the measurement to a reading with the same instrument of a known reflectance standard. The method involves either recalling a stored standard reference reflectance factor or determining a reflectance factor via the range finder for a sample of retroreflective material with a predetermined coefficient of retroreflectance, and then measuring the distance to an unknown target, determining a power attenuation factor from the received pulse width from the unknown target and then calculating the absolute coefficient of retroreflectance based upon these determined values of power attenuation factor, distance and the reference reflectance factor.

A digital filter is provided with a plurality of selectors. Switchover from one selector to another switches the digital filter operation between a separation filter function and a synthesis filter function. When the digital filter functions as either separation filter or synthesis filter, it switches over between the functions of multiplying data by a filter coefficient and multiplying data by an attenuation coefficient. The entire digital filter circuit size can thus be reduced.

A method is provided for conducting an electromagnetic induction survey of a geological formation penetrated by a borehole lined with a conductive casing. The method includes positioning a transmitter in the borehole, whereby the transmitter generates a transmitter magnetic moment, and positioning a distant receiver external of the borehole to detect a magnetic field induced by the transmitter, whereby the distant receiver is disposed across part of the formation from the borehole. Furthermore, an auxiliary receiver is positioned in the borehole proximate the transmitter to detect a magnetic field induced by the transmitter and attenuated by the conductive casing. Subsequently, a first casing attenuation factor that is applicable to the magnetic field measured by the auxiliary receiver is determined from a ratio of the measured magnetic field at the auxiliary receiver and the transmitter magnetic moment. A second casing attenuation factor applicable to the measurement of the magnetic field at the distant receiver is determined from a non-linear relationship (e.g., a power law relationship) between the first casing attenuation factor and the second attenuation factor, wherein the second attenuation factor is less than the first attenuation factor. Then, a formation attenuation factor applicable to the measured magnetic field at the distant receiver is determined from a relationship between the magnetic moment of the transmitter, the second casing attenuation factor, and the measured magnetic field at the distant receiver. Finally, the method correlates the determined value of the formation attenuation factor to a resistivity characteristic of the formation between the distant receiver and the transmitter.

Aspects of this invention include a downhole tool having first and second radially offset ultrasonic standoff sensors and a controller including instructions to determine at least one of a drilling fluid acoustic velocity and a drilling fluid attenuation coefficient from the reflected waveforms received at the standoff sensors. The drilling fluid acoustic velocity may be determined via processing the time delay between arrivals of a predetermined wellbore reflection component at the first and second sensors. The drilling fluid attenuation coefficient may be determined via processing amplitudes of the predetermined wellbore reflection coefficients. The invention advantageously enables the acoustic velocity and attenuation coefficient of drilling fluid in the borehole annulus to be determined in substantially real-time.

A system and method for tomographic image reconstruction using truncated limited-angle projection data that allows exact interior reconstruction (interior tomography) of a region of interest (ROI) based on the linear attenuation coefficient distribution of a subregion within the ROI, thereby improving image quality while reducing radiation dosage. In addition, the method includes parallel interior tomography using multiple sources beamed at multiple angles through an ROI and that enables higher temporal resolution.

A photographic flash unit comprises a direct flash unit and a bounce flash unit rotatably connected to the direct flash unit. Status and control lines coupled between a hot shoe and each flash unit enable independent triggering and control of each flash unit. The direct and bounce flash units may be a part of a digital camera adapted to make a first test exposure using direct flash illumination and second test exposure using bounce flash illumination, then computing an attenuation factor for compensating a selected flash exposure parameter by dividing the selected parameter by the attenuation factor. Steps in a method embodiment include making a first test image, making a second test image, selecting regions in the first and second test images, computing an attenuation factor from luminosity values for the first and second test images, and compensating settings for a final bounce flash image by the attenuation factor.