The values for energy imparted at CT in pediatric patients were generally lower than in adults. The smaller mass of children, however, caused the corresponding effective doses to be higher than those in adults undergoing similar CT examinations.
Most clinical quantitative computed tomographic (CT) determinations of bone mineral content are hampered by inability to properly account for the various substances contained within the spongiosa (spongy bone). In general, the presence of adipose tissue lowers the CT numbers (Hounsfield units) and leads to underestimation of bone mineral content. Collagen matrix has the opposite effect. A new approach to obtaining data from postreconstruction dual-energy CT scans accounts for five principal constituents of the spongiosa. In addition to bone mineral values, the method also provides the adipose tissue concentration, calcium content, and density of the total trabecular space. Since calcium values are provided, the measurements can be compared with prereconstruction dual-energy data that are acquired simultaneously. A new solid-plastic calibration phantom was utilized in this study, and data were obtained from 26 subjects. Dual-energy data were correlated with single-energy measurements (r greater than .96), and calcium measurements were correlated with the bone mineral determinations (r = .97) in these 26 cases. All measurements of the various vertebral constituents agreed with published values.
The influence of focal spot intensity distribution and geometry upon mammographic image quality were evaluated. The modulation transfer functions (MTF's) for eight different intensity distributions were determined and plotted in a manner to eliminate the effects of magnification and focal spot dimension. The results indicated that the total cross-sectional area is important for focal spots with uniform intensity distributions and equivalent diameters. For equivalent focal spot dimensions, intensity distributions with edge bands were shown to have less spatial resolution than uniform intensity distributions. Focal spots with greater intensities towards their centers provided better resolution than either uniform intensity distributions or distributions with edge bands for equivalent sizes. The type of intensity distribution was also shown to affect the accuracy of star pattern measurements of focal spot size; this method of measurement is only precise for a uniform square intensity distribution. Errors obtained with several other intensity distributions were tabulated. The variations of the effective focal spot size with position along the anode-cathode axis were shown to be of a factor of approximately two to three. The combined effects of geometric blur and film/screen blur were present for various heights above the cassette tray on several different mammographic systems.
The radiation risk to patients undergoing computed tomography (CT) examinations may be characterized by using the dose descriptors of effective dose equivalent (HE) and effective dose (E). Values of HE and E, however, are much more difficult to obtain than the total energy imparted (epsilon) to the patient. In this study, representative values of the ratios HE/epsilon and E/epsilon were obtained using published Monte Carlo organ dose computations for typical CT x-ray spectra. Values of patient dose per unit energy imparted can be combined with independent estimates of energy imparted to quantify the dose to a patient undergoing any type of CT examination.
The largest series of patients (n = 10) with dissecting intramural haematoma of the oesophagus is described. The typical features, chest pain with odynophagia or dysphagia and minor haematemesis are usually present but not always elicited at presentation. If elicited, these symptoms should suggest the diagnosis and avoid mistaken attribution to a cardiac origin for the pain. Precipitating factors such as a forced Valsalva manoeuvre cannot be identified in at least half the cases. Early endoscopy is safe, and confirms the diagnosis when an haematoma within the oesophageal wall or the later appearances of a longitudinal ulcer are seen. Dissecting intramural haematoma of the oesophagus has an excellent prognosis when managed conservatively.
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