摘要:
It is known that perturbations caused by scattered-radiation in an x-ray image can be partially avoided by employing a scattered-radiation grid. A device for further improvement of an x-ray image, in that real-time correction of scattered-radiation effects is achieved, is provided according to the invention. Behind x-ray absorbing parts of the scattered-radiation grid only scattered-radiation appears, whereas both scattered-radiation and primary radiation appear behind transparent channels of the scattered-radiation grid. The scattered-radiation grid gives rise to a high-frequency intensity modulation in the x-ray image. From the high-frequency component of the corresponding video signal produced by the x-ray detector, selection signals are generated by a double pulse generator for distinguishing signal amplitudes of the video signal, corresponding to intensities behind absorbing parts and transparent parts, respectively, of the scattered-radiation grid. The selection signals are supplied to a synchronous detector to split the video signal from the x-ray detector into separated video signals corresponding to scattered-radiation and primary radiation and to scattered-radiation only, respectively. A video signal corresponding to a corrected image is obtained by subtraction of the separated video signals.
摘要:
A quadrature mode rf coil system in a magnetic resonance apparatus includes a pair of orthogonal rf coils which, for excitation and/or detection are coupled to an rf source or receiver by an electronic switching circuit built up from inductances and capacities. The switching circuit includes preferably frequency adjustable 90.degree. first delay lines feeding each coil which transforms the 50.OMEGA. coil impedance of each coil to 100.OMEGA. so that the parallel combination of transformed impedances is 50.OMEGA.. A second 90.degree. delay line is cascaded with the first delay line feeding one of the coils to establish a 90.degree. phase difference between the coils.
摘要:
An X-ray television pick-up and display system which is suitable for continuous and short-duration pick-up operation and continuous display. In continuous pick-up operation, in display on a display device an interlaced television picture is composed of two line scanning rasters in a standard manner. In short-duration pick-up operation a synchronizing pulse generator is changed over so that a single line-scanning raster comprising an integral number of lines is obtained for information pick-up, which information is stored in a signal store which for repeated signal supply is connected to the display device. As a result, the picture displayed does not show motional unsharpness and is free from flicker effects.
摘要:
The circuit has an input terminal (1) for supplying a picture signal (CS) formed line and field-sequentially with line and field or frame periods (TV) and an output terminal (2) for supplying a processed picture signal (CS') to be applied to a picture display device (5) comprising a picture display tube operating by way of electron beam scanning (e) of a display screen (8). In the circuit the input terminal (1) is coupled to a filter circuit (10) which has a first output (11) and a second output (12) for supplying a low-frequency (CS.sub.L) or high-frequency (CS.sub.H) picture signal component, respectively. The first output (11) is coupled via an amplifier circuit (16) to a first input (21) of a time-division multiplex circuit (20) having a second input (22) to which the first output (11) and the second output (12) of the filter circuit (10) are coupled each via an amplifier circuit (17, 18) and an adder circuit (19). The time-division multiplex circuit (20) has a switching input (23) which is coupled to an output (29) of a switching signal generator (28) for supplying a periodical switching signal (VS) of the double field or frame period (2TV). An output (24) of the time-division multiplex circuit (20) is coupled to the output terminal (2) of the picture signal processing circuit. The resultant spatial time-division multiplex display yields the improved high-frequency picture resolution.
摘要:
In an apparatus for performing magnetic resonance measurements by means of an orthogonal system of excitation detection coils there is provided a switching circuit for powering and reading the coil system which includes a 1/4 .lambda. coaxial conductor as a connection between the two coil assemblies and a 1/4 .lambda. coaxial conductor with a 90.degree. phase delay as a connection between the first 1/4 .lambda. conductor and the second coil assembly and a detection device. By suitable tuning of the relevant circuit components and the coils, preferably based on 50 Ohms, a simple switching circuit with appropriate matching and phase correction is thus achieved. Specifically, the r.f. power source can be connected to the circuit via an n .lambda. conductor. In the open condition during detection, the n .lambda. conductor represents an infinite impedance for the switching circuit.
摘要:
A phosphor screen in a display device is scanned by separate electron beams in order to generate images of different frequency content in one color in substantially the same part of the phosphor screen. The different images can be perceived as a composite image for some time. The individual electron beams can be modulated by means of a cathode modulator on the basis of a high frequency and a low frequency component of an electronic image signal or on the basis of an image component and a text component of an electronic image signal. The modulations of the individual electron beams may be slightly delayed relative to one another in order to avoid overloading of the phosphor material.
摘要:
An X-ray apparatus is provided with a filter (12) for limiting the dynamic range of an X-ray image formed on an X-ray detector (4) by exposure of an object (3), for example a patient to be examined, to X-rays (2). The filter (12) has filter elements (13) including one or more capillary tubes (13), one end of which communicates with a reservoir with an X-ray absorbing liquid. The adhesion of the X-ray absorbing liquid to the inner side of the capillary tubes can be adjusted by means of an electric voltage applied to an electrically conductive layer provided on the inner side of the capillary tubes (13). The degree of filling of the capillary tubes (13) with the X-ray absorbing liquid is adjusted by way of the electric voltage value. The X-ray absorption profile is adjusted within a very short period of time, for example within one second, by adjustment of the electric voltages applied to the capillary tubes (13).
摘要:
Disclosed is a magnetic resonance imaging apparatus, with an r.f. coil which is designed on the basis of the sinusoidal current distribution across a circular-cylindrical surface about a central coil axis and which is, subject to a generally applicable looping-through condition z.sub.1 =-K z.sub.2, when K is a positive constant which depends on the number of bars and geometrical deviations, z.sub.1 is the impedance of the bar conductors, and z.sub.2 is the impedance of ring conductor elements between each two pair of bar conductors. The coil based on the above condition is particularly adapted to parasitic capacitances of the bar conductors and to the general shape of objects to be examined.
摘要:
For increasing the sensitivity of an MR apparatus when measuring comparatively high frequencies, the radio frequency excitation measurement coil (10, 30) is divided into two individual symmetrically drivable and readable coil halves (32, 34), respectively. The mutual connection of central connections of the coil halves can be realized by means of a balun (54) but for this purpose any other symmetrical form of coupling, for example using a strip-line transformer (70) or suitably dimensioned coaxial cables (60, 62) may alternatively be used.
摘要:
The transmitter/measurement coil of a nuclear magnetic resonance tomography apparatus for medical diagnosis in which comparatively high Larmor frequencies are used, is divided into a number of parallel-connected subcoils. The self resonance frequency of the coil can thus be made substantially higher than the Larmor frequency, with the result that the coil will have a suitably improved quality factor at higher frequencies, and measurements can be performed with an acceptable signal-to-noise ratio.