Clinical experience with combined videofluorography and pulsed fluoroscopy.
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Fluoroscopy↗
Biomedical subjects
J A Rowlands
Publications and source records attributed to J A Rowlands.
Absorption and noise in cesium iodide x-ray image intensifiers.
The measured and theoretically predicted values of detective quantum efficiency (DQE) for a CsI x-ray image intensifier are compared for nine monoenergetic beams of x rays. The agreement between measurement and theory of better than +/- 5% indicates that we have a sound understanding of the physical parameters controlling the DQE. It is shown that the fraction of K-fluorescent x rays escaping from the input phosphor is independent of incident energy. The number of electrons released within the x-ray image intensifier (XRII) by an incident x ray has been measured. The mechanism for energy broadening within the XRII is shown to be predominantly the limited number of electrons and not light absorption.
Cesium↗
Videofluorography: the role of temporal averaging.
Videofluorography is the technique of obtaining radiographic images by photographing with a multiformat camera the television images produced during x-ray image intensified fluoroscopy. This technique of producing images has received considerable clinical use, but the radiation exposure used has been in doubt. Experiments were performed to evaluate this radiation exposure. It was found that the imaging chain was reducing mottle by temporal integration. These results were tested by comparing the image quality of videofluorographs with that of photofluorographs . The blurring effect of motion on images was also evaluated as this is a factor which must be balanced against the improvement of mottle due to temporal integration. It was found that exposures used for videofluorography were of the order of 10 microR (2.58 X 10(-9) C kg-1) to the input of the x-ray image intensifier.
Fluoroscopy↗
Detective quantum efficiency of x-ray image intensifiers: comparison of scintillation spectrum and rms methods.
For monoenergetic x rays, the detective quantum efficiency (DQE) of an x-ray image intensifier (XRII) obtained by measuring the ratio of signal to root-mean-square (rms) noise is compared with the DQE obtained by the scintillation spectrum method. To obtain agreement between the two methods, the rms noise must be measured at a very low frequency because of the temporal response RXRII (f) of the XRII. This takes a long time and the measurement of the DQE from the scintillation spectrum is much quicker. Measurement of RXRII (f) shows that it is dependent on x-ray flux rate. RXRII (f) measured at the same flux rate as DQE permits correction of DQE measurements to zero frequency. In order to estimate DQE for polyenergetic beams, we need to know as a function of energy not only the DQE but the amount of energy deposited per absorbed x ray. The latter is also obtained from the rms measurement.
Methods↗
Noise in stenosis measurement using digital subtraction angiography.
This paper examines statistical errors in the measurement of arterial stenoses by digital videodensitometry. Images of vessel phantoms were acquired using digital subtraction angiographic techniques with low concentrations of an iodine contrast medium and low levels of x-ray exposure. Effects of the spatial and temporal averaging of image information on signal-to-noise ratios in the stenosis measurement were of primary interest. The influences of iodine concentration, x-ray scatter, veiling glare, x-ray energy spectrum, x-ray exposure, and detective quantum efficiency of the system were also included in the theoretical analysis. The agreement between theoretical calculation and experimental measurement of a simulated vessel was verified using measured values of the imaging system parameters. With a 14.2 mg/ml iodine concentration, using 20 mR per image at the entrance to a 13-cm water phantom, and averaging over a 6-mm length of a vessel 6.2 mm in diameter, the standard deviation in a measurement of a vessel's relative cross-sectional area was about 0.05. The extension of these results to practical applications in vivo is discussed.
Angiography↗
Optical factors affecting the detective quantum efficiency of radiographic screens.
Parameters related to the detective quantum efficiency (DQE) of several representative screens of different thicknesses, phosphor grain sizes, and optical properties were measured by the scintillation spectrum method, using monoenergetic x rays produced from x-ray fluorescence. The experimental results, including those for spectral shape and average light energies (EA) emitted, are compared with conventional theories of the operation of screens. It was hoped that this would vindicate the theory of the effect of optical properties and so permit the simple calculation of all parameters related to DQE from standard x-ray attenuation tables. Rather more substantial energy-dependent deviations of EA are found than was previously realized, which preliminary analysis suggests are due to both optical effects and photoelectron escape. We conclude that although DQE for a single energy can be calculated by simplified methods to within +/- 10%, the effective DQE when polyenergetic beams are used is much less accurately estimated and requires a fuller theoretical treatment.
Filtration↗
Optimization of readout rate of television cameras in pulsed digital radiography.
Adaptation of existing fluoroscopic television rooms to permit radiographs to be recorded directly by the television system would be a very practical way to introduce digital radiography into general use if the image quality was adequate. The main limitation of current systems is spatial resolution. Although a digital system can change the spatial frequency response by application of spatial frequency enhancement, the amount of enhancement which can be usefully applied is a function both of the spatial frequency response of the whole system and image noise. Slow scan television systems have been proposed as a way to reduce noise; and hence, as a way to potentially improve limiting resolution. We examine all the consequences of changing readout scan rate, both theoretically and with measurements on a commercial camera with a lead oxide image tube. It is found that recent improvements in camera tube design, specifically the increase in current capability of the electron gun, have reduced the advantages theoretically available with slow scan. However, an order of magnitude increase in useful dynamic range is still possible.
Humans↗
Measurement of the spatial Wiener spectrum of nonstorage imaging devices.
All previous methods for measuring image noise spectra require a noise realization, a static image, typified as a photograph which can be scanned to create the Wiener spectrum. We wished to analyze the spatial noise power spectrum at the output phosphor of a continuously irradiated imaging device, an x-ray image intensifier (XRII), which is incapable of image storage and thus the image is continually changing as a function of both time and space. Our new method utilizes a pair of slits to measure the relative Wiener spectrum of the temporally changing components of the image (i.e., x-ray quantum and XRII gain noises). By measuring the modulation transfer function and the Wiener spectrum of the same XRII on the same apparatus it was possible to demonstrate the spatial frequency dependence of the detective quantum efficiency. Adaptations of the method should permit the measurement of Wiener spectra of fluoroscopic television systems directly from the TV monitor.
Fourier Analysis↗
System for digital acquisition of gastrointestinal images.
Previous theoretical work and clinical experience with digital acquisition of fluoroscopic images have identified several problems which needed to be solved. These are: image resolution; blurring due to patient motion, combined with long exposure times; and excessive x-ray quantum mottle levels. We will show that application of pulsed progressive readout (PPR) methods to the TV camera solves these problems. By permitting a high-intensity x-ray pulse to be delivered, all motion is stopped and quantum mottle is reduced to acceptable levels. It will be shown that 1024 x 1024 digital matrices provide adequate resolution and 8-bit digitization is sufficient to permit the same quality as is used in conventional 100-mm photofluorography. User acceptance can be made easier by incorporation of existing photofluorographic controls (with which the radiologist is already familiar) to acquire the digital images. It is possible to interface PPR video systems using existing 100-mm exposure circuits without much modification and the resulting system can be regarded as a digital 100-mm camera.
Digestive System↗
A study of motion in gastrointestinal x-ray fluoroscopy.
Studying motion in the gastrointestinal (G.I.) tract is the first step towards our goal of designing a digital algorithm for real-time noise and motion blurring reduction by temporal and spatial averaging in x-ray fluoroscopy. The present work concerns the types of motion relevant to G.I. fluoroscopy (e.g., motion of the walls of the oesophagus, the stomach, the small intestine, and the colon), and measurement of the range of velocities in different parts of the G.I. tract from tape recorded fluoroscopic sequences. The relationship between image contrast and velocity, the effects of motion on system response, and in particular the influence of these parameters on the evaluation of velocities will also be discussed.
Adolescent↗
A light source for testing radiological television cameras.
A light source for testing and setting up radiological television systems has been designed and built using green light emitting diodes and an optical integrating sphere. It is shown to have an optical spectrum similar to the green output phosphors used in x-ray image intensifiers (XRII's). It can be made uniform in intensity across the output port and does not show the small scale granularity characteristic of phosphors. It has a Lambertian angular distribution which, by the addition of neutral density filters, can be made to mimic the angular distribution at the output of an XRII. It can easily and accurately be modulated or switched and a luminance comparable to that of an XRII output phosphor can be achieved.
Lighting↗
Origins of flare in x-ray image intensifiers.
The disk spread function of flare of an x-ray image intensifier (XRII) was measured using monoenergetic x rays. The signal-to-noise ratio at the center of the disks and the pulse height spectrum of the flare are also measured. These measurements are correlated with the physical construction of the XRII. A simple model of the XRII is developed which is used to identify the various sources of flare.
Models, Theoretical↗
Wiener noise power spectra of radiological television systems using a digital oscilloscope.
Measurement of spatial noise power spectra from television based radiographic and fluoroscopic systems is essential to the understanding of their operation and optimization. However, conventional methods require acquisition and processing of large numbers of complete images, thus confining such measurements to special applications where accessible frame buffers already exist or elaborately equipped laboratories. We have developed a method which only requires storage of single TV lines or point scans. A digital oscilloscope captures these point scans and a laboratory microcomputer facilitates manipulation of the data to separate out different components of the noise power spectra. The x-ray dependent component of the noise power spectrum so produced is not the ordinary Wiener spectrum. However, it is shown that reconstruction of the full Wiener spectrum from this is possible subject only to the requirement that the x-ray noise spectrum at the output of the imaging system is circularly symmetric.
Fluoroscopy↗
X-ray imaging using amorphous selenium: a photoinduced discharge readout method for digital mammography.
A new digital image readout method for electrostatic charge images on photoconductive plates is described. The method can be used to read out images on selenium plates similar to those used in xeromammography. The readout method, called the air-gap photoinduced discharge method (PID), discharges the latent image pixel by pixel and measures the charge. The PID readout method, like electrometer methods, is linear. However, the PID method permits much better resolution than scanning electrometers while maintaining quantum limited performance at high radiation exposure levels. Thus the air-gap PID method appears to be uniquely superior for high-resolution digital imaging tasks such as mammography.
Female↗
X-ray imaging using amorphous selenium: determination of x-ray sensitivity by pulse height spectroscopy.
There is a renewed interest in the application of photoconductors especially amorphous selenium (a-Se) to x-ray imaging. A new method for evaluating W +/-, the energy absorption necessary to release an electron-hole pair in a-Se is described. All previous methods used for the evaluation of the x-ray sensitivity of a-Se measure a change in surface potential on a charged plate due to irradiation by x rays. This results in a measurement of W +/- and other factors in combination. These factors include the energy absorbed from the spectrum of irradiating x rays and the a-Se layer capacitance. Such indirect methods are prone to error. A direct method for the evaluation of W +/-, which is based on the pulse height spectra resulting from the absorption of individual monoenergetic x-ray photons in a-Se, has been developed.
Humans↗
Flat-panel digital radiology with amorphous selenium and active-matrix readout.
Future imaging techniques will be capable of high image quality, fast acquisition, compactness, and versatile operation. A flat-panel imager that is expected to achieve these goals is under development. It consists of a thin layer of amorphous selenium that converts x rays directly to an electric charge and a thin-film electronic circuit, or active matrix, to read out the electronic signal directly to a computer host. The advantages of amorphous selenium include high resolution and low noise without loss of signal strength. The advantages of the active matrix are real-time readout, flexible design parameters, and compactness of the readout structures. A prototype of this imager has been built and operated, and initial images (of an x-ray test bar pattern and a hand phantom) have been acquired. Although the prototype was built to test scientific principles and many possibilities for optimization remain, the images already possess the quality necessary for many radiographic procedures. A large range of current and new applications exist for this imager.
Hand↗