Showing papers on "Image resolution published in 1972"

A Multi-Crystal Positron Camera

Abstract: A multicrystal positron camera designed for use with radionuclides produced with a medical cyclotron is described. The camera uses coincidence techniques for collimation by detecting the positron annihilation radiation. Typical radionuclides are 11C, 13N, 15O with half lives of 20, 10, and 2 minutes, respectively. The principal object of the design is to achieve a data rate capacity to 5 × 104 coincidence events per second, as well as high sensitivity and resolution. This will allow time sequential images of fractional second duration. Each of the camera's two identical detectors consist of a planar array of 127 small NaI(Tl) crystals viewed by an array of 72 phototubes. Timing signals are derived from the phototubes and are subsequently used to identify 2549 crystal pairs. The coincidence data is stored in a magnetic-core memory and used for a local data display; alternatively data may be transferred under program control to a PDP-9 computer. The sensitive field area is 27 cm × 30 cm and the spatial resolution is less than 1 cm at the midplane. The camera is currently being used for a number of clinical applications.

Proportional Counter Photon Camera

Abstract: A gas-filled proportional counter camera that images photon emitting sources was built and tested. This camera measures and displays the impact location of individual photons in an energy range between 1 and 150 keV and permits pulse shape and energy discrimination for background reduction. Possible fields of applications for this camera include nuclear medicine, nuclear physics, x-ray diffraction, and related areas. The signal processing of the camera is based on further improvements and simplifications of the risetime method as applied to multiwire position-sensitive counters. Materials inside the counter were selected so that the camera can be used over long periods of time without purification of the counter gas. The sensitive area of the camera is 200 × 200 mm2, and the size of each picture element is 1 × 1 mm2; thus 40,000 picture elements are resolved. Counting rates of up to 20,000 photons/s do not appreciably affect the spatial resolution. The camera has been tested only with low energy photons ( 10 atm) Xe counter gas, a useful detection efficiency (>30%) and good spatial resolution are expected for 150-keV photons.

A Liquid Xenon Radioisotope Camera

Abstract: The increasing availability of short lived gamma and positron emitting isotopes, coupled with the importance of dynamical studies and better imaging, has generated the need for an improved ?-ray camera. We discuss a new type of ?-ray camera which makes use of electron avalanches in liquid xenon. A configuration currently under development is shown in Fig. 1. The successful operation of a liquid xenon proportional counter was recently reported. The liquid xenon camera promises better spatial resolution and higher counting rate than the existing NaI (Tl) scintillation camera. The spatial resolution for ? rays is in principle limited only by the range of photoelectrons in liquid xenon, which is < 0. 2 mm for energies < 1 MeV. A counting rate of 106 C/s or more appears possible. As a result of the better resolution and high counting rate capability, the definition of the picture is improved. In addition, the high counting rate capability makes possible dynamic studies which were previously unfeasible. Although we expect the energy resolution with liquid xenon to be superior to that of NaI (see next section), our preliminary measurements show 17% FWHM for 279 keV ?'s. Improvements are expected by using better geometry and smoother wire.

X-Ray and gamma-Ray Imaging with Multiple-Pinhole Cameras Using a posteriori Image Synthesis.

Abstract: In 1968, Dicke had suggested that multiple-pinhole camera systems would have significant advantages concerning the SNR in X-ray and gamma-ray astronomy if the multiple images could be somehow synthesized into a single image. The practical development of an image-synthesis method based on these suggestions is discussed. A formulation of the SNR gain theory which is particularly suited for dealing with the proposal by Dicke is considered. It is found that the SNR gain is by no means uniform in all X-ray astronomy applications.

Fresnel zone plate imaging in radiology and nuclear medicine

Abstract: X-ray tubes and gamma ray cameras have traditionally involved trade-offs between spatial resolution and radiation flux. Recently we have shown that the use of a Fresnel zone plate as a spatially-coded source or aperture can avoid this trade-off. In radiology, this technique can eliminate the need for a rotating anode and give higher resolution, while in nuclear medicine it can be used either to decrease patient dose or exposure time, or to increase resolution and greatly simplify the apparatus. With a coded source or aperture, the image is also coded, like a hologram and can be reconstructed optically. The system is tomographic with information about all planes contained in a single film.© (1972) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Scintillation camera with improved resolution

Abstract: An Anger-type scintillation camera system fitted with a gamma ray filter between the object under study and the detector and an output signal filter of the signal funneling type which employs a non-linear array of signal filter windows to compensate for inherent non-linear spatial response characteristics in the camera system.

Holography and Medicine

Abstract: Holography has emerged from the laboratory and is slowly becoming a useful tool in a variety of engineering and scientific areas. The potential exists for holography to serve as such a tool in medical and biological research. Holography can be used to form three-dimensional images. Three dimensionality is a consequence of the recording of phase information in the hologram. The presence of phase information in holographic images makes them extremely versatile and amenable to such a posteriori techniques as interferometry and dark-field imagery. Holography can also be used to analyze images, that is, to enhance image contrast and resolution, or to perform such functions as correlation analyses and pattern recognition. Moreover, the versatility of holography extends beyond the visible portion of the electromagnetic spectrum; holograms made with infrared, ultraviolet, microwave, or ultrasonic illumination, or ``synthetic'' holograms made using a computer can be used to produce visible images or to analyze nonvisible images. The manner in which holography's potential can be used in biomedical applications is discussed.

High-Resolution Video Display of X-Ray Topographs with the Divergent Laue Method

Abstract: An X-ray imaging device utilizing a high sensitivity image orthicon tube has been incorporated in the divergent Laue method of diffraction topography using a point source. An X-ray optical magnification of diffraction images has made it possible to obtain a spatial resolution better than that of the imaging device. Preliminary experiments have demonstrated that individual dislocations in silicon crystals can be displayed with a resolution of better than 25 µm.

Image resolution in infrared thermography

Abstract: The rise of apparent temperature in the thermograph as the detector is scanned across a temperature discontinuity is shown to be approximately exponential and to depend on the time constant of the circuit, the rate of scanning and the field size. The implication for clinical thermography is that the rise in temperature over a narrow region will be underestimated and such a region may not then be 'resolved' from the surrounding body surface. The effective response is estimated from measurements of the apparent temperature of the sources at the same black body temperature but of different width, and curves indicating the limits of resolution are derived. The relevance of the number of lines scanned in a frame and the definition of the image are also considered.

Positron mode of the Total Organ Kinetic Imaging Monitor: system design and applications

Abstract: The TOKIM system consists of two Anger-type scintillation camera detectors operated in coincidence to obtain three-dimensional resolution for positron emitting radionuclides. An IBM 1800 computer is used for data acquisition and analysis. Several different types of display are available in this system, including alpha-numeric print-out, dot density and isometric read-outs on a storage oscilloscope. The maximum coincidence input data rate for the TOKIM is limited by electronic pile-up to about 3000 c.p.s. The spatial resolution depends on the distance of separation of the detectors, but for a practical case is 1.25 cm (FWHM) in lateral planes and 3.0 cm (FWMH) in axial planes for a point source measured in air. There is very little change in spatial resolution for sources in scattering media.

Novel Method for Measuring Transient Surface Temperatures with High Spatial and Temporal Resolution

Abstract: Rapid temperature fluctuations occurring at the surfaces of solids over areas as small as a few wavelengths in diameter can be measured by a new technique. The sample is coated with a semiconductor film which exhibits a suitable shift of its absorption edge with temperature. It is shown that changes in the transmission of an incident monochromatic beam can be used to measure the thermal transients of the underlying surface with a spatial resolution as high as ∼1λ and a temporal resolution as high as 1 nsec.

X-ray image enhancement by least-mean-square estimation.

Abstract: The x-ray penumbra effect, caused by the finite focal spot of an x-ray tube, and inherent sources of random noise are the primary limiting factors regarding radiographic image quality. An attempt has been made to devise an optimum spatial filter, which, when realized in binary form, provides substantive image improvement.

Detection of weak optical images with photon counting techniques

Abstract: A technique has been developed to record very weak images with the use of photon counting techniques. It is shown that the photon counting method is about 2 orders of magnitude more sensitive than a photographic emulsion of comparable signal-to-noise ratio.

A solid-state infrared image converter

Abstract: A photoconductor-electroluminescent type infrared image converter panel has been studied through the application of doped CdSe photoconductive powder layers of different thickness to the earlier type of image converter and through temperature operation. The spectral sensitivity extended from 0.7 to 1.2 µm with sensitivity peak at 0.9 µm and the minimum detectable input power density reached approximately 2×10-10W/cm2for 0.9 µm at 0°C. Projected infrared images are converted to visible electroluminescent images with a resolution of 3 to 8 TV lines/mm and a response time of an order of 1 to 10-2s, depending upon the photoconductor thickness and the operating temperature. The converter panel may be used as a night vision panel with an additional infrared source. This paper describes a preparation of doped CdSe photoconductor suitable for a photoconductor-electroluminescent device, some of its properties, and the effect of the photoconductor thickness and of the operating temperature on the performance of the solid-state infrared image converter. Converted visible images using experimental panels are also shown.

Image quality in telescopes with image motion compensation by secondary mirror control.

Abstract: Image motion compensation by servocontrolled tilt of the secondary mirror is applied in a 40-cm diam f/7.5 Cassegrainian balloon-borne telescope. A tilted-aplanatic configuration is used, i.e., the mirrors are aspherized to render the stabilized image free of third-order coma. A spatial resolution of 2 sec of arc is maintained in the presence of pointing errors up to 10 min of arc. The most important remaining aberrations are third-order astigmatism and fifth-order spherical aberration. For the latter, a general expression is presented that can also be applied to other two-mirror telescopes.

Optical design of an imaging spectral radiometer for earth resources applications.

Abstract: Description of the optics, thermal compensation measures, and calibration procedures for a scanning imaging spectroradiometer to be used in earth resources sensing applications. The spectral range covered extends from 4000 to 8500 A. Two possible modes of operation include (1) a high-spatial-resolution terrestrial survey mode with moderate spectral resolution, and (2) a high-spectral-resolution ocean survey mode with decreased spatial resolution. Two high-aperture f/1.4 objective lenses (providing fields of view of 10 and 25 deg) are interchangeable to give added flexibility in planning experiments with this instrument. A diffraction grating disperses the spectrum which is then scanned by the image sensor.

Acoustic Holographic Scanning Techniques For Imaging Flaws In Thick Metal Sections

Abstract: This paper discusses the application of various scanning configurations used in acoustic holography for imaging internal flaws or voids in thick metal sections; i.e., 10 to 25 cm. The following source-receiving scanning configurations were employed: 1. Simultaneous (inclined plane-wave) source and point receiver scan-ning; 2. Simultaneous (focused) source-receiver scanning employing a simulated acoustic off-axis reference; 3. Simultaneous point source-receiver scanning employing a simulated acoustic off-axis reference; and 4. Stationary (plane-wave) source and point receiver scanning employing a simulated acoustic off-axis reference. All of the above mentioned configurations impose a linear diffraction grating on the hologram and provide the necessary conditions for imaging flaws directly in the projected aperture and separation of the reconstruct-ed images. The flaw images appear two-dimensional as a result of the large difference between the construction and reconstruction wavelengths. Longitudinal magnification is much greater than the lateral magnification and the images appear stretched in depth. However, the hologram does contain the complete depth information of the flaws and this is easily observed by focusing on different planes in the metal sections parallel to the hologram plane (i.e., different depths within the metal section are viewed simply bymanipulation of the optical imaging lens in the reconstruction The images of the internal flaws are viewed by adjusting the lens until the image is in focus. The lateral and longitudinal dimensions of the flaws are then calculated using the conventional image location and magnification equations.

Optical system for color television cameras

Abstract: An optical system for a color television camera comprises a beam-splitting arrangement for separating an incident light beam from a main objective lens into three partial beams corresponding respectively to three different parts of the visible spectrum, the three partial beams being supplied to the photoelectric cathodes of respective camera tubes. One of the partial beams is supplied to the respective photoelectric cathode by way of an intermediate lens, so that the size of the image on the photoelectric cathode is different from the size of the images on the other two photoelectric cathodes. A deflector is added to allow placement of the reduced image size camera tube perpendicular to the main objective lens.

High Resolution Solar Imaging at 1.65 micro with a 64-Element Array.

Abstract: An imaging system using a 64-element array of PbS detectors has been successfully tested at Kitt Peak. The first images of the low contrast solar granulation at 1.65 μ have been obtained with a signal-to-noise ratio better than 200 and a resolution of the order of 1 see of arc. The problem of imaging systems for low contrast objects in the infrared is discussed.

Improved image position sensor for high resolution optical tracking.

Abstract: The narrow beamwidth of a laser source can provide advantages, relative to a microwave source, in applications such as short range, high angular resolution trackers. In such applications, an image position sensor (IPS) is used which senses the angle of arrival of the optical radiation from the target. It is shown analytically and empirically that, in the case of a rotating mirror IPS, cross coupling between azimuthal and elevation channels as well as nonlinear and saturation effects result when the image displacements on the rotating mirror are large compared to the image size. The performance of the rotating mirror IPS and consequently that of the tracker has been greatly enhanced by incorporating a computer generated variable density spatial filter (VDSF) in front of the rotating mirror.

Spherical Aberration in Long Wavelength Holography

Abstract: Images reconstructed from long wavelength holograms have aberrations as a result of large construction to reconstruction wavelength ratios. For many practical recording geometries, these aberrations of which spherical aberration is often the largest may seriously degrade image resolution.

The Application of Channel Image Intensifiers to Low Light-level Television

Abstract: Publisher Summary This chapter discusses the application of channel image intensifiers to low light-level television. The performance of a low light-level television system can in general be characterized with the aid of acuity curves, which indicate the size of the smallest object detectable with the system for a given contrast in the scene, as a function of the illumination level. As in the case of image intensifiers for direct viewing, the two factors of photon noise and modulation transfer normally limit the maximum resolution of the camera chain for stationary objects. In television systems, however, two important additional problems can be created by the translation of the optical image into a video signal by means of a scanning electron beam. The number of bars that can just be resolved per picture width on the photosensitive surface of the camera tube can be related to the signal-to-noise ratio in the video signal. Any reduction in picture resolution, due to the decrease in modulation depth per amplification stage, will be accompanied by a corresponding reduction in the perceptibility of that part of the noise, which was present before the amplification. It is found that the measured square-wave response agreed well with that computed from the component parts.

Application of the Spatial Spectral Power Density to the Calculation of Resolution Limits

Abstract: Resolution as a function of aperture length in the presence of phase errors is investigated with the aid of the spatial power spectral density Numerical calculations are made for power spectra thought to be appropriate for phase errors due to atmospheric turbulence Both Gaussian and uniform illumination are considered, and the results obtained here are compared with those reported by Brown and Riordan [2]