Intravenous angiography using scanned projection radiography: preliminary investigation of a new method

The use of digital subtraction techniques combined with fluoroscopy has rekindled interest in arteriography using intranvenous injections of contrast media. A new method is proposed for intravenous angiography in which an x-ray source and xenon detector array from a computed tomographic (CT) scanner are used to scan a region of interest to produce projection image. In order to provide adequate visualization of small concentrations of iodine in blood vessels, a subtraction scheme is used to remove the contribution from overlapping soft tissue and bone. Initial experiments with a temporal subtraction algorithm on phantoms have demonstrated the ability to image simulated blood vessels of 1.7-mm diameter containing dilute diatrizoate with an iodine concentration of 3.7 mg/cc, at an exposure of less than 100 mR. Vascular structures 5-8 mm in diameter have been imaged in dogs with iodine concentrations of less than 37 mg/cc using temporal subtraction. Principal advantages of the method over other film or fluoroscopic subtraction techniques are: 1) wide dynamic range an low noise of the (CT) detectors, providing excellent iodine sensitivity; 2) high scatter rejection; and 3) efficient utilization of x-ray dose.     

A detector for scanned projection radiography

A solid-state electronic x-ray detector, the multilinear array (MLA), was developed for general-purpose digital overhead radiography (DOR). The image sensor of the MLA consists of an x-ray phosphor affixed to approximately 29,000 photodiodes. The image sensor is rectangular (35.2 cm X 1.05 cm) and is designed for scanned projection imaging with a 1.05-cm-thick fan beam. The MLA incorporates charge-coupled device circuitry that performs time-delay integration of the photocharge. The MLA is installed in a prototype DOR system that generates a 35.2-cm X 35.8-cm image with a 2,014 X 2,048 12-bit image matrix and 0.175-mm pixels. The scan time per image is 7 seconds, and the exposure time of any given point of a patient is 0.21 seconds. Operational principles of the MLA are described, performance measurements presented, and images acquired with the prototype DOR system shown. The MLA has an exposure latitude of 333:1 10% modulation transfer function response at 1.8 cycles per millimeter, 15% detector detective quantum efficiency (DQE) at 60 keV, and 78% scatter DQE under high-scatter imaging conditions. DOR images of a contrast-detail phantom are superior to those produced by conventional medium-speed screen-film radiography.     

Dual-energy scanned projection radiography of osseous metastatic disease

Dual-energy scanned projection radiography was used to evaluate eight patients with both lytic and blastic metastatic disease in the axial skeleton. The ability to selectively cancel obscuring soft-tissue structures from images resulted in improved conspicuity of involved sites, compared with conventional radiographic studies, despite greater quantum noise and lower inherent spatial resolution. Other desirable features of the technique include a projected format, image enhancement by contrast and brightness optimization, rapid data acquisition, convenient image storage and retrieval, and low radiation dose. Since the majority of osseous metastases involve axial sites, dual-energy scanned projection radiography may be a useful adjunctive modality in the management of oncology patients.     

Digital scanned projection radiography: optimization of image characteristics

Fast interactive programs for the investigation of the effects of different processing methods were developed in an attempt to optimize the diagnostic value of digital scanned projection radiography (SPR) data. Filters from two classes of functions with varied frequency characteristics were evaluated. Arbitrary combinations of filtered and unfiltered images were generated. Speed was achieved by implementing the filtering as a convolution operation with standard computed tomography hardware (20 sec/image). The criteria for the choice of the reconstruction parameters are discussed. The clinical results show that suppressing the low-frequency content of the image, as in smoothing, low-pass filtering, and subtracting the background from the original image, optimizes the diagnostic value of SPR images.     

A method for increasing the resolution of scanned projection radiography and other digital X-ray systems

A method for increasing the sampling frequency of digital X-ray systems is described. The method employs discrete, stepwise magnetic deflection of the focal spot and the recombination of the resulting displaced images. The technique was applied to a GE CT/T 8800 scanner operating in "Scout View" mode. The hardware and software modifications were minor. The transverse resolution was shown to improve from 0.63 to 0.9 line pairs per mm, using a test phantom. The effect of the improvement in resolution is also illustrated in the human. The possibility of further improving the resolution of the system is discussed.     

Dual-energy projection radiography using condenser x-ray generator and digital radiography apparatus

The authors describe a system for dual-energy projection radiography using a modified condenser-type x-ray generator and a digital radiography unit. High- and low-energy images are obtained within a practical exposure interval. This method provides better visualization of soft tissues that are otherwise obscured by skeletal structures and also allows better visualization of bone and calcifications (e.g., calcified nodules in the lung) without interference by overlying soft tissue.     

Digital projection radiography

Several hundred storage phosphor digital projection radiography (DR) systems are in operation in many parts of the world in experimental and clinical settings. They are used clinically for almost all projection radiographic studies except mammography. An overview is given of the experimental and clinical results achieved so far. Image post-processing has yet to meet the initial expectations. The average image quality will certainly improve with automatic brightness control. Edge enhancement should be performed in selected applications only. A true increase in diagnostic information probably cannot be expected except with dual energy techniques. Dose reductions are possible only in those studies in which the specific imaging task permits a decrease in signal-to-noise ratio.     

Breast imaging: dual-energy projection radiography with digital radiography

Dual-energy projection radiography was applied to breast examinations. To perform the dual-energy subtraction radiography with use of a digital radiography unit, high- and low-energy projections were made at an appropriate time interval under differing x-ray exposure conditions. Dual-energy projection radiography appears to offer clear, detailed images and may be a useful supplement to standard mammography.     

Image quality and dose comparison among screen-film, computed, and CT scanned projection radiography: applications to CT urography.

PURPOSE: To evaluate image quality and dose for abdominal imaging techniques that could be used as part of a computed tomographic (CT) urographic examination: screen-film (S-F) radiography or computed radiography (CR), performed with moving and stationary grids, and CT scanned projection radiography (CT SPR). MATERIALS AND METHODS: An image quality phantom underwent imaging with moving and stationary grids with both a clinical S-F combination and CR plate. CT SPR was performed with six CT scanners at various milliampere second and kilovolt peak settings. Entrance skin exposure (ESE); spatial, contrast, and temporal resolutions; geometric accuracy; and artifacts were assessed. RESULTS: S-F or CR images, with either grid, provided image quality equivalent to that with the clinical standard, S-F with a moving grid. ESE values for both S-F and CR were 435 mR (112.2 microC/kg [1 mR = 0.258 microC/kg]) with a moving grid and 226 mR (58.3 microC/kg) with a stationary grid. All CT SPR images provided inferior spatial resolution compared with S-F or CR images. High-contrast objects generated substantial artifacts on CT SPR images. Compared with S-F, CR and CT SPR provided improved resolution of small low-contrast objects. The contrast between iodine and soft-tissue-mimicking structures on CT SPR images acquired at 80 kVp was twice that at 120 kVp. CT SPR images with acceptable noise levels required a midline ESE value of approximately 300 mR (77.4 microC/kg) at 80 kVp. CONCLUSION: S-F and CR provided better spatial resolution than did CT SPR. However, CT SPR provided improved low-contrast resolution compared with S-F, at exposures comparable to those used for S-F or CR.     

Digital projection radiography of the chest

Direct and film-based radiographic systems are undergoing evaluation by observer performance studies for use in digital imaging of the chest. Many issues intrinsic to digital imaging are not settled, including the minimal pixel size necessary for images of accurate diagnostic quality, the characteristics of the display console, and the usefulness of digital imaging processing techniques. The chest is a particularly difficult anatomic region for examination by digital radiography because of the broad spectrum of disease findings encountered. These issues are discussed in reference to four reports that use observer performance tests for evaluating various facets of chest diagnosis using digital radiography.     

Bone mineral density in the femoral neck: quantitative assessment using dual-energy projection radiography

Two different dual-energy projection radiography techniques were used to quantitate bone mineral density in the femoral neck. A heterogeneous population of normal aging individuals of both genders was studied. Using a dual-energy scanned projection method, femoral neck mineralization was shown to decline with age in men and women with normal endocrine status, and to correlate positively with serum calcium level in women and both genders combined. No significant relation to incidence and severity of vertebral body compression fractures, the Singh trabecular index, glomerular filtration rate, urinary calcium excretion, plasma levels of vitamin D, parathyroid hormone, or alkaline phosphatase was demonstrated. According to both methods, femoral neck density tended to be higher in taller and heavier subjects. Although it may not be possible to predict accurately the occurrence of femoral neck fracture in a given individual, dual-energy scanned projection radiography appears to be useful in determining mineral status of the site at risk.     

Intravenous radionuclide total body arteriography: a new technique

We have developed a technique using a blood pool agent Tc-99m labeled red blood cells and a detector head set moving at a high speed to obtain total body arterial and blood pool images with only a single intravenous injection. Previously with an intravenous radiotracer injection, only regional arterial images could be obtained. Now, with this simple, non-invasive technique, we can evaluate the major arterial system, organs, and soft tissues in the whole body, as well as cardiac function. On reviewing 500 cases, more than 90% of the first-pass arterial phase images clearly demonstrated the aorta, ilio-femoral arteries, and, to a lesser extent, the more distal arteries in the lower extremities. The second-pass blood pool images revealed the anatomical and morphological status of the solid organs, as well as perfusion changes in various organs and soft tissues.     

An evaluation of paediatric projection radiography in Ireland

PurposeThis study investigated common paediatric radiography examinations in Ireland and analysed any potential for improvement by considering compliance with requirements for justification, the range of doses delivered and potential Diagnostic Reference Levels, and technique approaches that enhance optimisation.MethodReferral information, Dose Area Product (DAP) dose, technique details and patient data were gathered from 568 paediatric examinations performed across several hospitals. The examinations were mobile infant chest (n = 66), chest (n = 266), abdomen (n = 96), lumbar spine (n = 14), full spine (n = 5), pelvis (n = 151) and skull (n = 28). Data were analysed to allow comment on the adequacy of justification, the range of doses being delivered and possible Diagnostic Reference Levels (DRLs), and the potential for optimisation of radiographic technique.Results/conclusionsResults indicate that the principle of justification is generally applied well in paediatric practice.Dose results indicate that age-related doses are generally comparable to published data, although dose variations exist within and between hospitals. Although differences between minimum and maximum DAP values were substantial, differences between the first and third quartile values were rarely greater than a factor of three. With regard to DRLs, age-related, 75th centile DAP values are presented for five paediatric X-ray examinations. While DAP DRLs stated as a function of age are a pragmatic approach to preliminary DRL values, size related DRLs are acknowledged as a better approach and the necessity of objective paediatric patient size measurement is emphasised.With regard to potential for optimisation, small samples limited analysis of factorial influences on DAP. However, trends indicate that objective consideration of kVp and mAs, careful collimation, and matching of exposure to baby weight in neonates and to measured patient depth in children could all contribute to better optimisation. These factors are all within the radiographer's control, thus highlighting the pivotal role of the radiographer in ensuring that the principle of optimisation is attained.     

Axillary projection in radiography of the nontraumatized shoulder

A series of 239 consecutive radiographic examinations of the shoulder performed on patients without acute trauma was analyzed prospectively. Each examination included anteroposterior projections with external and internal rotation of the humerous and an axillary projection. The abnormalities that could be identified on each view were listed separately. There were 109 normal examinations and 130 abnormal examinations. The anteroposterior view with external rotation identified 14 abnormalities not seen on the other views. The axillary projection identified 15 abnormalities not seen on other views. If only these two views had been obtained, 99.3% of the abnormalities would have been identified. The implications for altering routine film series are discussed.