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Biomedical subjects

H Roehrig

Publications and source records attributed to H Roehrig.

16 recordsLinked to original sources
PubMed1995

Image quality control for digital mammographic systems: initial experience and outlook.

This report presents (1) a broad topical review and a tutorial of the possibilities for image quality control (IQC) with digital systems, and (2) results and initial experience for IQC with two commercial digital imaging systems, but with limited discussion on any particular method. Digital imaging systems used for mammographically guided digital stereotactic breast biopsy were evaluated extensively at the University of Arizona. Measurements were made of linearity, sensitivity, signal-to-noise ratio, and square-wave modulation. Images of phantoms such as the American College of Radiology Accreditation Phantom and the contrast detail mammography Phantom were evaluated as well as images of the x-ray source's focal spot. The evaluation also included the cathode ray tubes for the imaging systems. The data collected show that digital imaging systems have an important advantage over film-screen systems because they provide a digital signal as output that can be used for quantitative analysis. As a result, IQC can become a much more quantitative discipline than presently practiced, providing more information on the imaging systems under evaluation, and providing better control over their properties during actual operation.

Computer Terminals↗
PubMed1992

Performance characteristics and image fidelity of gray-scale monitors.

Gray-scale monitors are an essential element of electronic radiology, and their ability to provide images that are perceived to be identical to those available on conventional or laser-printed film is crucial to success of electronic radiology. Image fidelity is measured in physical characteristics (luminance, dynamic range, distortion, resolution, and noise) and with psychophysical techniques, including receiver operator characteristics analysis with clinical images and testing with contrast-detail patterns to determine threshold contrast. Currently, laser-printed images facilitate greater information transfer than does a gray-scale monitor because of their higher absolute luminance (500 ft-L vs 60 ft-L), greater perceived dynamic range, and better spatial resolution. In the near future, the developments of gray-scale monitors with 150-200 ft-L luminance, a display standard based on just noticeable differences, and algorithms to improve similarities between gray-scale display images and laser-printed images will help increase the acceptability of monitors as a means to make primary diagnoses.

Computer Peripherals↗
PubMed1990

Performance tests and quality control of cathode ray tube displays.

Spatial resolution, noise, characteristic curve, and absolute luminance are the essential parameters that describe physical image quality of a display. This paper presents simple procedures for assessing the performance of a cathode ray tube (CRT) in terms of these parameters as well as easy set up techniques. The procedures can be used in the environment where the CRT is used. The procedures are based on a digital representation of the Society of Motion Pictures and Television Engineers pattern plus a few simple other digital patterns. Additionally, measurement techniques are discussed for estimating brightness uniformity, veiling glare, and distortion. Apart from the absolute luminance, all performance features can be assessed with an uncalibrated photodetector and the eyes of a human observer. The measurement techniques especially enable the user to perform comparisons of different display systems.

Data Display↗
PubMed1990

Computer-simulated lung nodules in digital chest radiographs for detection studies.

Computer simulations of lung nodules overcome many shortcomings of creating radiographs using anthropomorphic nodule phantoms for lung nodule detection studies, but these algorithms can be cumbersome and involved. A simple, fast, and flexible computer program to simulate lung nodules in digital chest radiographs for detection studies is reported. To verify the realism of the simulated nodules, a psychophysical study and a statistical study were conducted. In the psychophysical study, six radiologists and four nonradiologists were asked to distinguish between 17 real lung nodules and 17 computer-simulated lung nodules shown in eight radiographs. The results show that the computer-simulated lung nodules are indistinguishable visually from real lung nodules. Using parameters from the Rose model of vision, results show that the simulated and real nodules are the same statistically. Thus, besides visual validity, statistical analysis in confirming the validity of the simulated lung nodules is included.

Computer Simulation↗
PubMed1989

Intraoperative arteriography: comparison of conventional screen-film with photostimulable imaging plate radiographs.

This prospective study compared images obtained with a photostimulable imaging plate with matched images obtained with a conventional screen-film combination in 26 patients undergoing intraoperative arteriography. Diagnostic accuracy of the two techniques was assessed objectively, and image quality was assessed subjectively. In 16 patients (62%), the radiation exposure was reduced by 50% for the imaging plate technique by decreasing the mAs level generally used for the screen-film combination. Because of the dynamic range of the imaging plate system, no repeat examinations were necessary, while 12% of the screen-film studies had to be repeated because of over- or under-penetration. Imaging plate studies required 6% more time for processing than screen-film studies. Receiver-operating-characteristic analysis indicated no difference in diagnostic accuracy between the two imaging techniques. Subjective evaluation also revealed no difference in observer preference for imaging plate or screen-film studies. The imaging plate technique is an excellent alternative to screen-film studies in the operating room.

Angiography↗
PubMed1987

Finite-length line-spread function.

In this paper we derive a formula for calculating the point-spread function (PSF) of a rotationally symmetric imaging system from measurements along a line through the image of an arbitrary separable input object. An important special case of this formula is when the input object is a finite-length slit. The set of measurements in this case is called the finite-length line-spread function (FLSF). The FLSF differs from the infinite-length line-spread function (LSF) only in the assumed finite length of the line that is input into the system. This difference between the FLSF and the LSF becomes important for imaging systems for which the PSF is large in extent and in which the isoplanatic patch is relatively small. The usual LSF-to-PSF conversion formulas cannot be applied accurately to such systems.

Fourier Analysis↗
PubMed1985

The digital radiology department of the future.

The boom in microelectronics, including cost-effectiveness, has now allowed us to consider the use of these objects to store digital images. There remains much research, development, and clinical evaluation to be done in receptor technology. Further improvements in image processing, optical laser disk storage, and optical transmission and further commercial development of display technology must take place. All of these developments are occurring simultaneously. Within 5 to 10 years, radiology departments will most likely be totally electronic, probably cost-effective, and, it is hoped, more diagnostically accurate.

Data Display↗
PubMed1983

Digital nephropyelography following intravenous renal digital subtraction angiography.

A 14-inch image intensifier designed for digital radiography has made feasible adjunctive evaluation of the renal parenchyma and collecting structures following intravenous digital subtraction angiography (DSA). Initial experiments with rabbits showed digital nephrography to be superior to film-based nephrotomography in terms of renal conspicuity and imaging flexibility. Preliminary experience with 30 patients undergoing DSA reaffirms the suitability of this method for the evaluation of renal anatomy and function. Only about half the amount of contrast material needed for conventional excretory urography is required.

Angiography↗
PubMed1982

Digital subtraction angiography of peripheral vascular bypass procedures.

Without premedication or special preparation, digital video subtraction angiography, also known as photoelectronic intravenous angiography, was effectively used for evaluating patients who had undergone peripheral vascular reconstructive procedures. Thirty-eight studies in 20 patients were performed using computer contrast enhancement after an intravenous injection. Patency of arterial grafts was thereby evaluated, thus obviating further routine angiography. Graft patency, even of small complex graft sites, was easily recognized. Occlusions were also readily identified. Patient acceptance was excellent since the procedure is almost painless and can be done on an outpatient basis. The technique is fast, safe, and less expensive than routine angiography.

Angiography↗
PubMed1981

Digital video subtraction angiography of renal vascular abnormalities.

A digital subtraction system for performing intravenous angiography has been developed and applied to the diagnosis of renal vascular abnormalities. A total of 35 patients underwent 39 intravenous angiographic examinations for a variety of renal-related clinical indications. Satisfactory examinations were achieved in 36 cases (92%) with a high degree of diagnostic accuracy. Digital video subtraction angiography is an outpatient procedure that is accurate, safe, and inexpensive to perform.

Adult↗
PubMed1980

Intravenous angiography using digital video subtraction: x-ray imaging system.

An x-ray imaging system, using digital subtraction techniques, has been developed. The system requires: (1) high output generation equipment; (2) an image intensifier capable of receiving high output exposures, 1 mR (2.58 X 10(-7) C/kg) at the face of the intensifier, without loss of either contrast or resolution; (3) a precision digital video camera; (4) processing computer with sufficient storage capacity; and (5) digital image storage. With this system it is possible to visualize the major arteries after intravenous contrast injection. The system, angiography technique, and early results are described.

Angiography↗
PubMed1980

Intravenous angiography using digital video subtraction: intravenous cervicocerebrovascular angiography.

The clinical application of intravenous angiography to study the cervicocerebrovascular system using the digital video subtraction system described in a companion article is reported. About 0.75 ml/kg of a standard 76% iodine contrast solution is injected into an antecubital vein using a power injector. Then 15-20 exposures of the head and neck region at a 1/sec rate are made on the image intensifier. The images are recorded by a high performance video system and the output signal is digitized for subsequent computer manipulation. The subtraction images of these vessels produced by the computer show the vessels clearly, even though they contain very low concentrations of contrast media. Standard exposure factors of 75-80 kVp, 9-10 msec at 800-1,000 mA are used. Clinically pertinent features of the data alteration and flow through the system and the step-by-step computer procedures used to achieve and analyze the various forms of subtracted images are described. Five experimental and clinical cases demonstrate appropriate applications to cervicocerebrovascular disease: (1) evaluating the effects of surgical and medical therapy on atherosclerosis; (2) providing a screening angiographic test for patients with asymptomatic bruits and/or positive noninvasive studies; (3) evaluating patients who have significant generalized vascular disease either precluding or presenting hazardous contraindications to transarterial catheterization; (4) evaluating significantly aged patients in whom standard angiography has higher risk; and (5) evaluating currently asymptomatic patients who are medically at higher risk for developing atherosclerotic lesions. Numerous examples of the various types of image manipulations are presented: (1) linear subtraction; (2) logarithmic subtraction; (3) alterations of electronic contrast enhancement (map slope); (4) the usefulness of a series of angiographic images; and (5) the importance of multiple projections with this technique.

Aged↗
PubMedDate not supplied

A computerized method for the measurement of conspicuity. Comparison of film and digital nephrograms.

We have designed a computer program appropriate for comparing the conspicuity of an object of interest portrayed on film-based and photoelectronic images. To test this program, we evaluated nephrograms generated by exposing matched film tomograms and digital images of rabbit kidneys following contrast administration. We then evaluated their conspicuity--a measure of how well an object can be distinguished from its surround--by a computer program which automatically traced a concentric and equal area of surrounding background around operator-defined nephrograms. Computerized evaluation of these areas provides the formula elements (mean object and background density and variance values and the number of pixels) from which conspicuity is automatically calculated. Nephrogram conspicuity was greatest for digital subtraction images. This approach is useful for comparing film and digital techniques.

Analog-Digital Conversion↗
PubMedDate not supplied

Use of storage phosphor imaging plates in portal imaging and high-energy radiography: the intensifying effect of metallic screens on the sensitivity.

The sensitivity of storage phosphor imaging plates (SPIP) at megavolt photon energies (60Co, 6-, 10-, and 18-MV radiotherapy beams) is studied both experimentally and by Monte Carlo radiation transport calculations. In addition, the same techniques are used to investigate the intensifying effect of metal screens on the sensitivity of the SPIP. The results provide evidence that the sensitivity of the SPIPs is proportional to the absorbed energy in the phosphor layer per cGy. The spectral sensitivity is calculated for photon energies between 10 keV and 20 MeV for various SPIP-screen combinations.

Aluminum↗