Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-10-28
2001-07-17
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C378S098000, C378S021000, C378S062000, C345S428000, C345S426000, C382S103000, C382S132000, C382S131000, C324S307000, C128S922000
Reexamination Certificate
active
06263231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diagnostic imaging apparatus for acquiring image information representing at least one region of an examination subject, which generates image signals that correspond to the acquired image information, of the type having a signal processor, to which the image signals are fed, which subjects the image signals to spatial-frequency filtering with a bandpass characteristic, and which feeds the thus-acquired signals to a display for image representation.
2. Description of the Prior Art
Diagnostic imaging systems of this type are known, for instance which have an X-ray source and an X-ray receiver cooperating therewith that emits image signals corresponding to the received X-rays.
In many applications of such diagnostic imaging systems, for instance in the localization of kidney stones in lithotripsy, it is a problem to reliably distinguish the kidney stones from the background noise. Specifically in adipose patients, the kidney stones are displayed in very poor contrast in the fluoroscopy mode, so that the useful signal, that is, the signal components representing the kidney stone, are significantly below the noise level. This problem is intensified by the fact that the treatment in recidivist cases ensues at an ever earlier time, that is, at a time at which the size of the stones is still very small.
If an unambiguous localization of the kidney stone is not possible, treatment can be very difficult or in certain circumstances impossible.
It may be attempted to improve the signal
oise interval by conventional methods, for instance by integrating several images and subsequently windowing the resultant image. In any case, due to the motion of the stone caused by the patient's breathing, it is not possible to select high integration times, since otherwise the kidney stone would be displayed blurred, or would not be displayed at all because of poor contrast. In addition, windowing is only suitable in cases where homogenous structures are imaged, which is usually not the case in the localization of kidney stones.
The known measure of edge highlighting, which uses spatial-frequency filtering with a high-pass characteristic, usually only makes the signal
oise ratio worse.
Of course, in the case of radiographic diagnostic systems, the image quality can be improved by increasing the X-ray dose; however, this is possible only to a limited degree in view of the radiation load on the patient.
The text “Lexikon der Computergrafik und Bildverarbeitung” (Vieweg Verlagsgesellschaft, 1994, pages 141,142,340 and 341) teaches performing a spatial filtering with a bandpass characteristic, with the result that noise components beyond the upper limit frequency of the bandpass characteristic are suppressed, and subjects of a size exceeding the lower limit frequency of the bandpass characteristic and not visibly displayed or are displayed only in an attenuated manner. Thus, an improvement of the signal
oise ratio is achieved, while an enhancement of the contrast in the display of preferred subjects is achieved as well.
The application of bandpass filters in image processing is also described in German Patent Specification 38 26 285, PCT Application WO 86/01 920, German Patent Specification 195 00 338 and German Patent Specification 41 09 159.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a diagnostic imaging apparatus of the type described above with which it is possible to display the respective subjects clearly even under unfavorable conditions, for instance in cases where the image signals have a very low signal
oise ratio.
This object is inventively achieved in a diagnostic imaging apparatus for acquiring image information representing at least one region of an examination subject, which generates image signals from the acquired image information, having a signal processor, to which the image signals are fed, which subjects the image signals to spatial-frequency filtering with an adjustable bandpass characteristic, and which feeds the thus-acquired signals to a display for image representation, wherein the bandpass characteristics are set by at least one of the following types of units: (a) a unit for entering the minimum dimension of a subject that is to be displayed, which adjusts the upper limit frequency of the bandpass characteristic such that it has at least the value required in order to display subjects of the entered minimum dimension; (b) a unit for entering the maximum dimension of a subject that is to be displayed, which adjusts the lower limit frequency of the bandpass characteristic such that it does not fall below the value required in order to display subjects of the entered maximum dimension; (c) a unit for calculating the spectral characteristics of the noise that is superimposed on the image signals, which adjusts the upper limit frequency of the bandpass characteristic dependent on the calculated spectral characteristics of the noise; and (d) a unit for entering the contour of a subject that is to be displayed which has a pattern detector, which examines the image signals for the presence of a subject having the entered contour, and which adjusts the upper and lower limit frequencies of the bandpass characteristic dependent on the smallest dimension and the largest dimension of the detected subject, given the presence of such a subject in the image signals.
Because the unit for calculating the spectral characteristics of the noise that is superimposed on the image signals adjust the upper limit frequency of the bandpass characteristic dependent on the calculated spectral characteristics of the noise, the upper limit frequency of the bandpass characteristic is adjusted such that the spectral section that has the lowest frequency and that exceeds a specific amplitude, and the spectral sections having a higher frequency than this, are suppressed. Because the unit for entering the minimum dimensions of a subject that is to be displayed sets the upper limit frequency of the bandpass characteristic such that this has at least the value required in order to display subjects of the entered minimum dimension, it is guaranteed that useful information is not suppressed at the same time. Because the unit for entering the maximum dimension of a subject that is to be displayed sets the lower limit frequency of the bandpass characteristic such that it does not fall below the value required in order to display subjects of the entered maximum dimension, it is guaranteed that signal components which do not originate from the subject that is to be displayed, but rather relate to larger objects, are suppressed or attenuated, as needed, in the interest of improving contrast. Because the unit for entering the contour of a subject that is to be displayed, which has a pattern recognition stage, examines the image signals for the presence of a subject of the entered contour and adjusts the filter parameters of the bandpass characteristic accordingly, an additional contrast enhancement (signal
oise ratio) of the detected subjects is effectuated, so that, by employing pattern recognition, which is known, it is possible to improve the recognizability of specific subjects and possibly to capture their movement.
By means of the invention, it is possible to suppress, in the image representation, movements of a subject which are caused by a patient's respiratory activity, namely by generating a series of images of the subject, and, of the generated images, only a section that surrounds the subject is displayed on the monitor. If the aforementioned unit for entering the contour of the subject with a pattern recognition stage is used, the image signals are analyzed dependent on the entered contour to identify the position of the subject in the individual images of the series, and the signal processor selects the sections that are to be displayed of the individual images of the series. This results in the subject to be displayed always being displayed at substantially the same location
Lateef Marvin M.
Mantis Mercader Eleni
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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