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.     

Digital subtraction angiography: technology, equipment, and techniques

The equipment used in digital subtraction angiography is a combination of x-ray equipment and high-speed image-processing equipment. In this article, the components of a DSA system are described, including the x-ray generator, x-ray tube, image intensifier, television system, analog-to-digital (A-D) convertor, image processor, and image acquisition console, as well as available commercial equipment. Techniques for DSA examination are also discussed.     

The AAPM/RSNA physics tutorial for residents: digital fluoroscopy.

A digital fluoroscopy system is most commonly configured as a conventional fluoroscopy system (tube, table, image intensifier, video system) in which the analog video signal is converted to and stored as digital data. Other methods of acquiring the digital data (eg, digital or charge-coupled device video and flat-panel detectors) will become more prevalent in the future. Fundamental concepts related to digital imaging in general include binary numbers, pixels, and gray levels. Digital image data allow the convenient use of several image processing techniques including last image hold, gray-scale processing, temporal frame averaging, and edge enhancement. Real-time subtraction of digital fluoroscopic images after injection of contrast material has led to widespread use of digital subtraction angiography (DSA). Additional image processing techniques used with DSA include road mapping, image fade, mask pixel shift, frame summation, and vessel size measurement. Peripheral angiography performed with an automatic moving table allows imaging of the peripheral vasculature with a single contrast material injection.     

Threshold contrast detail detectability curves for fluoroscopy and digital acquisition using modern image intensifier systems

Threshold contrast detail detectability (TCDD) test objects are a commonly used tool to assess image quality of imaging systems. FAXIL (The Facility for the Assessment of X-ray imaging, Leeds) produced updated standard TCDD curves, for fluoroscopy systems in good adjustment, in 1992. Fluoroscopy curves can be corrected to account for the effect of image intensifier input air kerma rate and field size. This paper presents updated TCDD curves for fluoroscopy and new curves for digital acquisition. The results for digital acquisition suggest that the TCDD curves should not be corrected for input air kerma, as the quantum noise is not dominant and system noise is significant. These curves will prove useful for accepting new equipment, to give an indication of the expected image quality for a new image intensifier system.     

Dynamic digital subtraction evaluation of regional pulmonary ventilation with nonradioactive xenon

A method of evaluating pulmonary ventilation with a 57-cm image intensifier/television (II/TV) digital chest system is reported. With this method, the patient inhales a mixture of xenon and oxygen gases while dynamic imaging of the chest is done. Images of the airways and ventilated portions of the lungs are obtained by subtraction of images acquired before and after the xenon-oxygen mixture is administered. The feasibility of the method was evaluated by studies with xenon-filled tubes, an airway phantom, and a ventilation phantom. The results indicate that tubes larger than 3.2 mm in diameter are detectable at a xenon concentration of 41%, and that gas flow and flow distribution can be examined after image subtraction. If background subtraction is incomplete because of motion, the visibility of small airways is reduced greatly, although unventilated regions can still be delineated. The initial evaluation of this technique included imaging a healthy volunteer during xenon inhalation.     

Digital imaging of the chest

During the past several years, image acquisition in nuclear medicine, computed tomography, ultrasonography, subtraction angiography, and magnetic resonance has been by digitization. Despite these advances, research in the development of digital imaging in conventional radiography has lagged behind. Although studies with a variety of digital techniques have been carried out on several fronts, we still do not possess a method that has captured the imagination of the majority of radiologists and other physicians to a point where it could replace conventional screen-film imaging. This article reviews the current status and general principles of the technology, focusing on the four digital radiographic techniques that have shown the greatest promise - film digitization, an image intensifier - based system, photostimulable phosphor plates, and a scanned projection system. The physical aspects of each of the four systems and the clinical results that have been reported to date, as well as the advantages and disadvantages of each system, are presented.     

Effects of optimization and image processing in digital chest radiography: an ROC study with an anthropomorphic phantom.

A digital system for chest radiography based on a large image intensifier was compared to a conventional film-screen system. The digital system was optimized with regard to spatial and contrast resolution and dose. The images were digitally processed for contrast and edge enhancement. A simulated pneumothorax and two simulated nodules were positioned over the lungs and the mediastinum of an anthropomorphic phantom. Observer performance was evaluated with ROC analysis. Five observers assessed the processed digital images and the conventional full-size radiographs. The time spent viewing the full-size radiographs and the digital images was recorded. For the simulated pneumothorax, the results showed perfect performance for the full-size radiographs and detectability was high also for the processed digital images. No significant difference in the detectability of the simulated nodules was seen between the two imaging systems. The results for the digital images showed a significantly improved detectability for the nodules in the mediastinum as compared to a previous ROC study where no optimization and image processing was available. No significant difference in detectability was seen between the former and the present ROC study for small nodules in the lung. No difference was seen in the time spent assessing the conventional full-size radiographs and the digital images. The study indicates that processed digital images produced by a large image intensifier are equal in image quality to conventional full-size radiographs for low-contrast objects such as nodules.     

Digital angiography in pulmonary embolism

Pulmonary digital subtraction angiography was diagnostic in 98.3 per cent of patients with possible acute pulmonary embolism. The procedure was well tolerated even in severely ill patients. A large image intensifier made simultaneous imaging of both lungs possible, reducing the number of contrast injections necessary. Small volumes of low iso-osmolar concentration of modern contrast media were used. There was no need for catheterization of the pulmonary artery. Theoretical considerations and our limited experience indicate that this will reduce the number of complications compared with conventional pulmonary angiography. The procedure is rapidly performed and the diagnostic accuracy high. This makes digital subtraction angiography cost effective. Digital pulmonary angiography can be recommended as the primary diagnostic method in most patients with possible pulmonary embolism.     

Gastrointestinal radiology from the time of Walter B. Cannon to the 21st century

From its very inception, gastrointestinal radiology was at the forefront of radiology, combining physiologic and anatomic information. From evaluation of esophageal motility to the first depiction of gastric ulcers and carcinomas of the alimentary tube, gastrointestinal radiology became indispensable to physicians and surgeons. Improvements in fluoroscopic and radiographic equipment, the tilting table, the image intensifier with the television train, the introduction of selective visceral angiography with safer contrast media and, more recently, digital subtraction angiography, digital ultrasound (US), color Doppler US, computed tomography, and magnetic resonance (MR) imaging--all of these advances have made imaging diagnosis more precise and specific. A new modality--localized tissue MR spectroscopy--should offer an insight into metabolism and suggest optimal modes of treatment and follow-up. The gastrointestinal radiologist of the future will have to be multimodality trained. A new generation of alimentary tract interventional radiologists will further the trend toward less invasive surgical therapy. No end of advances is in sight.     

The design and imaging characteristics of dynamic, solid-state, flat-panel x-ray image detectors for digital fluoroscopy and fluorography

Dynamic, flat-panel, solid-state, x-ray image detectors for use in digital fluoroscopy and fluorography emerged at the turn of the millennium. This new generation of dynamic detectors utilize a thin layer of x-ray absorptive material superimposed upon an electronic active matrix array fabricated in a film of hydrogenated amorphous silicon (a-Si:H). Dynamic solid-state detectors come in two basic designs, the indirect-conversion (x-ray scintillator based) and the direct-conversion (x-ray photoconductor based). This review explains the underlying principles and enabling technologies associated with these detector designs, and evaluates their physical imaging characteristics, comparing their performance against the long established x-ray image intensifier television (TV) system. Solid-state detectors afford a number of physical imaging benefits compared with the latter. These include zero geometrical distortion and vignetting, immunity from blooming at exposure highlights and negligible contrast loss (due to internal scatter). They also exhibit a wider dynamic range and maintain higher spatial resolution when imaging over larger fields of view. The detective quantum efficiency of indirect-conversion, dynamic, solid-state detectors is superior to that of both x-ray image intensifier TV systems and direct-conversion detectors. Dynamic solid-state detectors are playing a burgeoning role in fluoroscopy-guided diagnosis and intervention, leading to the displacement of x-ray image intensifier TV-based systems. Future trends in dynamic, solid-state, digital fluoroscopy detectors are also briefly considered. These include the growth in associated three-dimensional (3D) visualization techniques and potential improvements in dynamic detector design.     

Real-time digital angiocardiography using a temporal high-pass filter

A temporal high-pass filtration technique for digital subtraction angiocardiography was studied, using real-time digital studies performed simultaneously with routine cineangiocardiography (cine) for qualitative image comparison. The digital studies showed increased contrast and suppression of background anatomy and also enhanced detection of wall motion abnormalities when compared with cine. This digital technique is compatible with panning the image intensifier during an injection. The digital images are comparable with, and in some cases better than, cine images. Clinical efficacy of this digital technique is currently being evaluated. Real-time display, as well as potential reductions in radiation and contrast material doses, may make digital angiocardiography an attractive technique.     

Evaluation of the processing functions of a digital subtraction angiography image processor

A large number of imaging systems for digital subtraction angiography (DSA) are now commercially available. Numerous evaluations of the performance of these systems have been reported in the literature. However systematic evaluations of the processing functions of DSA image processors have not been widely reported. Such an evaluation for one commercial system is presented in this paper. Functions evaluated include linear transformation, logarithmic transformation, integration, subtraction and temporal filtration. The observations indicate that image processing results are frequently achieved by indirect routes which compromise the fidelity of the image data.     

Digital chest radiography with a large image intensifier. An ROC study with an anthropomorphic phantom

The diagnostic performance of two systems for chest radiography was studied. One system was based on a large image intensifier, the other was a conventional film-screen system. The images from the image intensifier were studied either on a digital TV screen or on 100 mm photofluorograms. Receiver operating characteristic curve analysis was performed on images of an anthropomorphic chest phantom. Low-contrast MMAP (methyl methacrylate polymer) nodules and simulated vessels were positioned over the parenchymal and the mediastinal region of the phantom. Five observers assessed the digital monitor images, photofluorograms, and conventional full-size radiograms. The results showed a significantly superior detectability for the full-size radiograms over the digital monitor images both in the parenchyma and in the mediastinum. No significant difference was found between photofluorograms and digital images.     

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.     

Tomosynthesis applied to digital subtraction angiography

This extension of our previous work on tomographic digital subtraction angiography (DSA) describes the theory of tomosynthetic DSA image reconstruction techniques. In addition to developing the resolution limits resulting from x-ray exposure length and image intensifier field curvature, we describe one method of image formation and show tomosynthetic DSA images of animal and human anatomy. Methods for improving the present technique are discussed.     

New chest imaging techniques: a comparison of five analogue and digital methods

In recent years new analogue and digital techniques have become available for chest imaging. This study compares conventional film/screen, asymmetric film/screen (InSight), equalization (Amber), storage phosphor and digital image intensifier techniques by phantom exposures and patient examinations. The quality of chest images of 43 patients was classified by seven observers in four different hospitals. According to the results of phantom measurements and a previous study, digital image intensifier radiography was excluded from the patient examinations because of its low image quality. The Amber system had the best image quality. Images of the storage phosphor system were of good quality in both mediastinal and peripheral fields of the chest. Compared to conventional film/screen, the asymmetric film/screen (InSight) was graded higher in the mediastinal field, but lower in the peripheral field. Correspondence to: H. P. Busch     

Comparison of digital subtraction arteriography and conventional film screen subtraction arteriography for neuroradiology

Summary Sixty-nine patients with 91 separate abnormal findings were studied by both intra-arterial digital subtraction arteriography (ADSA) and conventional film screen subtraction arteriography (CFSA) in the same projection, with the same magnification. Digital subtraction arteriography has distinct advantages over CFSA in the form of reduced contrast utilization, better patient tolerance of arteriography because of reduced contrast concentration, superior contrast resolution, and rapid, on-line visualization of the abnormalities. Digital subtraction arteriography is limited by its availability in only a single plane, by decreased spatial resolution which affected the image quality for intracranial blood vessels at an image intensifier (I.I.) field of 12 inches, and by relatively limited field of view both intracranially and extracranially for I. I. fields of 6 and 9 inches.     

A high frame-rate digital subtraction angiography imaging technique for evaluation of aortofemoral runoff

Intravenous digital subtraction angiography was used to obtain a complete aortofemoral runoff examination of high diagnostic quality in a single patient session in eight patients. Using a 9-inch (22.9-cm) image intensifier, oblique and posteroanterior projections were obtained from the level of the aortic bifurcation to the tibial artery trifurcation. This technique is based upon the administration of one-half of the usual dose of contrast agent combined with a high frame-rate imaging technique and postacquisition integration to increase the signal-to-noise ratio. It is easily performed on an outpatient basis, lowers patient risk, and allows a significant savings of time, film, and cost compared with the conventional intra-arterial aortofemoral runoff examination.     

Clinical study with angiography system using a flat panel detecter

We have been using an X-ray angiography system that incorporates a flat panel detector (FPD) since December 2001. This system is equipped with the scintillator-type FPD PaxScan 4030A from Varian Medical Systems, and for objective comparison of the image intensifier (I.I.) and FPD, the system is constructed so that these detectors can be used alternatively. Using this system and other X-ray angiography systems, visual studies have been conducted on the digital subtraction angiography (DSA) images acquired by FPD and I.I. We have found from the clinical images that the FPD is superior to the I.I. in depiction of fine blood vessels as well as of physical characteristics. Fluoroscopy images acquired by the FPD were not entirely satisfactory, however the improvement made in its performance now permits equal use of the FPD and I.I. systems.     

Digital subtraction angiography using a temporal bandpass filter: initial clinical results

A dual digital memory recursive filtering system provides an effective alternative to digital subtraction imaging by using routine fluoroscopic equipment operated with slightly elevated fluoroscopic technical factors. This is accomplished with relatively inexpensive portable electronic equipment that can be connected to the video output of most modern fluoroscopic systems. Initial clinical experimental studies suggest that the system can produce diagnostic images comparable with pulsed fluoroscopic digital systems. The temporal filtering approach offers a real-time vascular imaging technique that requires no postprocessing and can be used either with arterial or intravenous injections of contrast materials.