With the advent of computerized tomography (CT), an increasing number of patients with only minimal neurological symptoms and no signs of brain herniation are found to harbor subacute or chronic extradural hematomas (EH's). The authors present the cases of 11 symptomatic but neurologically normal children with medium to large EH's managed by close observation. These EH's were discovered 4 hours to 6 days after injury; three were in the posterior fossa, seven over the frontoparietal convexity, and one in the temporal fossa. These clots were followed by serial CT scans. Nine children recovered without surgery from 4 to 18 days after injury, and all had evidence on CT of spontaneous clot resorption. Of these nine EH's, five clots displayed volume expansion from 5 to 16 days after injury before final resorption occurred. Expansion correlated with persistence or increase in symptoms, whereas resorption correlated with improvement. Two patients showed gradual uncal herniation on Days 6 and 8, respectively, presumably during the "expansile phase" of their clots. Both had emergency craniotomy and recovered without morbidity. It is hypothesized that the resorption dynamics of the subacute or chronic EH are similar to that of the chronic subdural hematoma, with predictable volume changes, and the outcome of each lesion depends on the interplay between the patient's intracranial pressure buffering capacity and the rate of volume change. If subtle signs of brain dysfunction are adopted to signal the failure of conservative treatment and the need for craniotomy, these patients may be safely, and many successfully, managed without surgery. Factors that influence outcome of medical treatment include the size, location, configuration, and the rapidity of accumulation of the clot, the presence of associated intradural lesions, the extracranial decompression of blood through skull diastases, and the age of the patient. These factors, the criteria for patient selection, and the indications for immediate operative intervention are discussed.
At a resolution of 400-microm pixels or higher across the field of view and a luminance of 260 cd/m(2) or more, primary diagnosis with posteroanterior chest radiographs is not likely to be affected by the quality of display.
It has been shown that dual-screen image acquisition technique can be used to improve the image signal-to-noise ratio (SNR) in computed radiography (CR) imaging. In chest imaging situations, acquisition with a high resolution (HR) screen and a standard resolution (ST) screen can also be used to improve the modulation transfer function. Unlike in conventional radiography using two screens, the front and back images in dual-screen CR imaging can be separately read out and superimposed with the weighting factors selected to optimize a specific image quality descriptor. The purpose of this paper is to determine the weighting method which would optimize the frequency dependent detective quantum efficiency (DQE) in dual-screen CR imaging with an HR and a ST screen. A theoretical model is derived to relate the DQE in the superimposed image to those in the front and back images and to determine the optimal weighting factors and the maximum DQE that can be achieved. Using this model and DQEs measured for the HR and ST screens, we could estimate optimal weighting factors and maximum DQEs as a function of frequency. Various screen combinations were studied and compared for the maximum DQE that can be achieved. We have shown that for maximum DQE, the front and back images should be weighted in such a way that their magnitudes are proportional to the DQE divided by the MTF. The maximum DQE in the optimally superimposed image is equal to the sum of the DQEs of the front and back images.
A simple, easy to use, quality assurance and performance test phantom was developed for the xenon/computed tomography (CT) cerebral blood flow method. The phantom combines an inhalation system which allows for the simulation of xenon buildup or washout in the arterial blood as well as a multisection translatable cylinder in which several sections can be scanned during a preselected protocol to simulate the CT enhancement in brain tissue during a study. The phantom and scanning protocol are described and their use is demonstrated. The results compare favorably to the theoretically expected fast, intermediate, and slow "flow" values designed into the phantom.
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