Biomedical subjects

R A Kruger

Publications and source records attributed to R A Kruger.

71 records · Page 4Linked to original sources

PubMedDate not supplied

Estimation of the diameter of and iodine concentration within blood vessels using digital radiography devices.

A variety of digital radiographic and fluoroscopic devices have been developed which can isolate small concentrations of iodine within the cardiovascular system. Using these devices, time dependent subtraction images have been formed which only display opacified vasculature. Theory is presented and simple methods have been developed for determining vessel diameters and iodine concentration from such subtraction images. The methods have been verified using plexiglass and aluminum vessel phantoms imaged with a computerized radiography device. Using this device the diameter of a 5 mm diameter vessel could be determined to within 6% (0.28 mm) even though the pixel width in the digitized image corresponded to 1.34 mm. In the same vessel, it is estimated that an iodine concentration of 46 mg/cm3 could be determined with 10% accuracy.

Angiography↗

PubMedDate not supplied

Blood flow measurement using digital angiography and parametric imaging.

A method of blood flow measurement is described that determines flow through a particular artery in absolute units or as a fraction of the cardiac output. For measuring flow as a percentage of cardiac output, no assumption about the vessel's cross-sectional shape is necessary. If one assumes that the vessel's cross section is circular, then absolute flow determination is possible. All methods would require only a single intravenous injection of contrast material. Details of the theory of these methods are presented and alternative data analysis options are developed and discussed.

Angiography↗

PubMedDate not supplied

Selective plane removal in limited angle tomographic imaging.

A method of improving a planar image in limited angle tomography by removing blurred image information from selected out-of-focus planes is discussed. Focused tomosynthesized images rather than individual projections are used. The necessary equations for removing the information from either two or four adjacent planes, produced with a symmetrical, but otherwise arbitrary blurring function, are developed and specialized to the geometry of circular tomography. Results of a phantom experiment illustrating the technique are presented.

Humans↗

PubMedDate not supplied

A signal processing model of diagnostic x-ray scatter.

A model of scatter is developed from a signal processing approach. The scattering process is viewed as a nonlinear filter (NLF), which transforms a two-dimensional signal representing phantom thickness into a two-dimensional signal of scattered radiation. The NLF point spread function (PSF) is derived from a single scattering model, using the principles of Compton scattering and x-ray attenuation. The PSF is characterized by three approximations: a constant geometric shape, a volume that depends on the phantom thickness, and a width that depends on the phantom-to-detector distance. This leads to a closed form expression for the scatter-to-primary ratio as a function of phantom thickness, field size, photon energy, source-to-phantom distance, and phantom-to-detector distance. The NLF model is compared with previously reported measurements using constant thickness phantoms, and discrepancies are discussed. The good agreement found between the NLF model and measured data shows that the functional dependence of scatter on the above parameters, previously only explained in terms of empirical models or Monte Carlo simulations, can be incorporated into a signal processing model.

Humans↗

PubMedDate not supplied

Scatter rejection by electronic collimation.

An electronic scanning-slit technology is under development which involves replacing paired fore and aft slits for scatter rejection with only one fore slit. As the slit scans across the portion of the patient to be imaged, pulsed x-ray exposures produce images of the slit in successive positions, which are digitized and stored in computer memory. Software techniques are used for tracking the slit image, and discriminating against scatter and veiling glare lying outside the slit image. Such "electronic collimation" does not require synchronization between the slit-scanning and detector readout, which makes it much simpler than alternative methods and potentially adaptable to any digital fluorography system. The performance characteristics of a prototype unit are described and images of a low-contrast phantom are presented.

Angiography↗

PubMedDate not supplied

Reconstruction of blood vessels from x-ray subtraction projections: limited angle geometry.

Several algorithms have been investigated for reconstructing blood vessels from a limited number of x-ray subtraction projections, distributed over a limited range of angles. Both computer simulations and an in vivo animal study were carried out. The best reconstruction performance was achieved using an algorithm that folded in two pieces of a priori knowledge of the vascular density distributions: (1) the object is dilute, consisting mainly of a void; and (2) the density distribution in the reconstructions is most likely to be non-negative. Both the signal-to-noise ratio (SNR) and the signal to out-of-focus blur were quantitated. Compared to tomosynthetic reconstruction (backprojection), the amount of residual blur from out-of-focus planes was significantly reduced with only a small penalty in diminished SNR. The combined effect resulted in significant qualitative image improvement for real arterial distributions as demonstrated in a canine arterial imaging example.

Algorithms↗

PubMedDate not supplied

Dual-energy electronic scanning-slit fluorography for the determination of vertebral bone mineral content.

A technique for performing accurate bone mineral content (BMC) determination, using dual-energy scanning-slit fluorography, has been developed. X-ray scatter and veiling glare are suppressed using a multiple scanning-slit device interfaced to a conventional digital subtraction angiography system. The technique employs a pair of calibration step wedges, one tissue and one bone equivalent. The proper use of the step wedges obviates the need for accurate kVp calibration or absolute calibration of the system's response to BMC. Phantom studies intended to simulate vertebral BMC measurement indicate that the technique is capable of measuring BMC with less than 30 mg/cm2 inaccuracy over a wide range of BMC.

Fluoroscopy↗

PubMedDate not supplied

Electronic scanning-slit fluorography: design and performance of a prototype unit.

Electronic scanning-slit fluorography involves replacing paired fore and aft slits for scatter rejection with only one beam-defining tantalum fore aperture. Since the video signal within the projection of the aperture on the image intensifier is much more intense than behind the tantalum, one can discriminate electronically between these two signals and thus eliminate the unwanted x-ray scatter and veiling glare. The general features of a prototype unit are described along with the rationale for the choice of design factors employed. Imaging time of 1-2 s has been achieved using multiple scanning slits. Small focal-spot size and large number of pixels are favored for higher dose utilization, shorter imaging time, and lower x-ray tube loading, as well as for better spatial resolution. Images of a chest phantom show better visibility of low-contrast details, especially in poorly penetrated areas, when compared with the image obtained and displayed under the same conditions, but using a conventional grid to reject scattered radiation.

Biophysical Phenomena↗

PubMedDate not supplied

Scatter estimation for a digital radiographic system using convolution filtering.

The use of a convolution-filtering method to estimate the scatter distribution in images acquired with a digital subtraction angiography (DSA) imaging system has been studied. Investigation of more than 175 convolution kernels applied to images of anthropomorphic head, chest, and pelvic phantoms using 15-, 25-, and 36-cm fields of view (digitized onto a 512 X 512 pixel image matrix) showed that two-dimensional exponential kernels with a full width at half maximum (FWHM) of 50-150 pixels best reproduced the scatter fields within these images with a root-mean-square percentage error from 4% to 8%. A two-dimensional exponential kernal with a FWHM of 75 pixels in each dimension applied to ten different anatomic presentations and fields of view, resulted in an average root-mean-square percentage error of 6.6% for the ten cases studied. The method should be implementable using an array of small lead beam stops placed in the field of only a single mask image and the above described convolution kernel applied to both mask and postopacification images. The mask beam-stop data are used to scale both mask and postopacification convolution-filtered images. This scaled, convolution-filtered image is then subtracted from the original image to produce a largely scatter-corrected image.

Humans↗

PubMedDate not supplied

Computer simulation of image intensifier-based computed tomography detector: vascular application.

This present study reports the results of a computer simulation whose aim was to predict the low-contrast imaging performance of which a conventional x-ray image intensifier with charge coupled device (CCD) camera would be capable if incorporated into a computed tomography (CT) volume imager. A vascular imaging task was modeled in our simulation. The effects of detector noise, x-ray exposure levels, analog-to-digital conversion (ADC) precision and residual levels of detected x-ray scatter were considered. The results of this simulation indicate that the low-contrast imaging performance of an image intensifier-based CT system was most limited by the CCD detector readout noise. Given this limitation the detection of greater than about 100,000 detected photons/pixel/projection gave marginal improvement in low-contrast resolution. At these exposures 12 bit ADC precision resulted in little additional image noise. The effects of detecting scattered x rays are twofold; decreasing the signal-to-noise ratio associated with our modeled artery and introducing a cupping artifact. Based on the results from the simulation, it appears that an image intensifier-based CT system is a feasible concept from a noise viewpoint, if the anticipated imaging task is intravenous angiography.

Angiography↗

PubMedDate not supplied

Comparison of dual and single exposure techniques in dual-energy chest radiography.

Conventional chest radiography is the most effective tool for lung cancer detection and diagnosis; nevertheless, a high percentage of lung cancer tumors are missed because of the overlap of lung nodule image contrast with bone image contrast in a chest radiograph. Two different energy subtraction strategies, dual exposure and single exposure techniques, were studied for decomposing a radiograph into bone-free and soft tissue-free images to address this problem. For comparing the efficiency of these two techniques in lung nodule detection, the performances of the techniques were evaluated on the basis of residual tissue contrast, energy separation, and signal-to-noise ratio. The evaluation was based on both computer simulation and experimental verification. The dual exposure technique was found to be better than the single exposure technique because of its higher signal-to-noise ratio and greater residual tissue contrast. However, x-ray tube loading and patient motion are problems.

Computer Simulation↗

PubMedDate not supplied

Transillumination imaging performance: a time-of-flight imaging system.

A series of Monte Carlo simulations have been performed in order to investigate the feasibility of constructing a time-of-flight transillumination imaging system that could be used as an effective tool for screening for breast disease. The conceptual design of such a system is described, and simulated images are presented that demonstrate its likely performance. It is found that, whereas the spatial resolution achievable with such a system is only dependent upon its temporal resolution, the scattering characteristics of the tissue being imaged will strongly affect the ultimate imaging performance of such a system.

Breast Neoplasms↗

PubMedDate not supplied

Transillumination imaging performance: spatial resolution simulation studies.

Monte Carlo calculations were used to simulate the propagation of visible and near-infrared light through homogenous tissue in order to quantitate the potential spatial resolution performance for transillumination imaging. Specifically, the relative effectiveness of coaxial collimation and time of flight (TOF) detection for improving spatial resolution was investigated. The results demonstrate that significant improvements in spatial resolution can be achieved through these techniques, with TOF methods offering superior performance for a given level of detected signal intensity.

Computer Simulation↗

PubMedDate not supplied

Light equalization radiography.

An electro-optical, photographic dodging technique, called light equalization radiography (LER), has been developed. The use of LER extends the dynamic range of radiographic film by enhancing the film contrast in the "toe" region of a radiographic film. Contrast recorded above some predetermined optical density is unaffected. The use of LER permits high-contrast films to be used in radiographic exams where low-contrast, "latitude" film types have been used traditionally, e.g., in chest radiography.

Humans↗

PubMedDate not supplied

Real-time digital subtraction angiography for therapeutic neuroradiologic procedures.

Procedural control during therapeutic neuroradiologic procedures is generally based on repeated angiograms to assess the degree to which embolization has reduced abnormal blood flow. Due to the complex craniofacial skeletal anatomy that is superimposed over lesions in this area, subtraction studies are usually required to see the vessels and visualize a tumor stain satisfactorily. We have used a device incorporating continuous recursive digital video filtration, which allows the operator to view a subtracted fluoroscopic image of each control angiographic sequence in real time. The advantages of this technique for therapeutic procedures are described.

Adult↗

PubMedDate not supplied

Tomographic DSA using temporal filtration: initial neurovascular application.

A preliminary study showed that encouraging laboratory results reported previously using tomographic digital subtraction angiography (DSA) can be transferred to clinical application for neurovascular imaging. Tomography may show cervical carotid disease more clearly than standard DSA images, and it eliminates the interference caused by overlapping vessels. Production of multiple tomographic image planes from a single set of projection data, tomosynthesis, must be incorporated into this imaging system before tomographic DSA becomes clinically useful. This is a practical reality with the present equipment; clinical evaluation of this new capability is underway.

Carotid Arteries↗

PubMedDate not supplied

Intravenous video arteriography of the intracranial vasculature: early experience.

A computerized fluoroscopic apparatus developed by members of the University of Wisconsin Medical Physics Section was used for 12 months to perform intravenous video arteriography. In previous papers, the apparatus was described and its use was illustrated for performing time subtraction intravenous video arteriography of the extracranial carotid arteries, the arteries of the abdomen and extremities, as well as angiocardiography. In this report, the use and current limitations of this technique for evaluation of the intracranial vasculature are described and illustrated.

Aged↗