ABSTRACT
A study of mammography systems with green-emitting screens was conducted to determine how the image quality parameters (apart from dose requirement), such as modulation transfer function (MTF) and Wiener spectrum (WS), depend on the dye content of the compound and coating weight of the screen. In addition, the contribution to total noise of the individual components, i.e., film, screen, and quantum noise, was studied. The quantities derived from MTF and WS, namely detective quantum efficiency (DQE) and noise equivalent quanta (NEQ), were also investigated in regard to their dose dependency. It can be demonstrated that the MTF of the screens becomes more favorable when the dye content is increased, while noise is not significantly affected. This suggests the use of a mammography screen capable of greater detail recognition, requiring at least double the dose of today's conventional systems with approximately 80 microGy system dose. On the other hand, the manufacture of a screen with about 60% of the dose of the conventional system is possible with very little loss in image quality. For the systems in common use today (80 microGy), quantum noise represents a considerable share of the total noise at low spatial frequencies, whereas in high spatial frequencies, the graininess of the film dominates quantum noise and screen structure.
Subject(s)
Mammography/instrumentation , X-Ray Intensifying Screens/standards , Evaluation Studies as Topic , Female , Humans , Quality Assurance, Health CareABSTRACT
Phototiming over the lung fields frequently compromises the signal-to-noise ratio available in the mediastinal and diaphragmatic regions of the chest. A moderate dose increase would be justified if a significant improvement in diagnostic performance could be achieved. We compared the impact of mediastinal phototiming (150 kVp, 150 cm FFD, 1.0 mm focus, 12:1 grid [higher kVp chosen to minimize dose increase]) to standard lungfield phototiming (125 kVp, 150 cm FFD, 1.0 mm focus, 12:1 grid) on the detectability of simulated pulmonary nodules (wax, 0.5-2.5 cm in diameter) superimposed on human volunteers in storage phosphor radiographs (1744 x 2144 pixels, 10 bit). ROC analysis of 1920 observations by 8 readers showed a significantly higher (p less than 0.03) detectability of simulated pulmonary nodules with mediastinal phototiming (ROC area = 0.89) than standard lungfield phototiming (ROC area = 0.84).
Subject(s)
Radiographic Image Enhancement/methods , Radiography, Thoracic/methods , Solitary Pulmonary Nodule/diagnostic imaging , Humans , Models, Structural , ROC Curve , Radiographic Image Enhancement/instrumentation , Radiography, Thoracic/instrumentationSubject(s)
Dentifrices/therapeutic use , Dentin Sensitivity/drug therapy , Fluorides/therapeutic use , Toothpastes/therapeutic use , Adult , Dental Cementum/drug effects , Dental Enamel/drug effects , Dentin Sensitivity/physiopathology , Fluorides/administration & dosage , Fluorides/pharmacology , HumansABSTRACT
By means of the biocybernetically conceived step and impulse loads on the forearm the motor postural regulation of healthy test persons and neurological patients with rigor, spasticity and flaccid pareses of slight degree, respectively, were examined. The analysis of the forms of the transient processes rendered possible a significant differentiation of the groups of test persons and patients. With the help of the mathematical mode the response curves of healthy test persons as well as of patients could be simulated with sufficient exactness. Apart from the step and impulse loads psendorandom binary series of test signals are particularly suitable for the analysis of the motor postural regulation.
