Surgery – Endoscope – With camera or solid state imager
Reexamination Certificate
1998-05-26
2001-02-20
Leubecker, John P. (Department: 3739)
Surgery
Endoscope
With camera or solid state imager
C600S921000, C348S065000, C348S188000
Reexamination Certificate
active
06190308
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an endoscopic video system for correct a video image of an object to be studied, as well as to a process for calibrating such a video system. Endoscopic video systems of this type are employed for various applications in the technical as well as in the medical field.
BACKGROUND OF THE INVENTION
Endoscopic video systems are known, by way of illustration, from DE-A-32 04 316. The endoscopic video system described in this printed publication is provided with an illumination fiber bundle and an imaging fiber bundle. The illumination fiber bundle guides the light of an illumination device to a light exit aperture at the distal end of the endoscope. An endoscope lens disposed at the distal end of the endoscope images the object field illuminated by the illumination device. This image of the object field is transmitted by the imaging fiber bundle to an electronic image recorder which is disposed proximally and can be, by way of illustration, a vidicon tube or a charge-coupled device such as a CCD chip.
Hitherto fiber bundles which are “ordered” and respectively “coherent” have been employed as imaging fiber bundles in endoscopes. What is meant thereby is that the light entry surface and the light exit surface of each optical fiber of the fiber bundle is located, always in relation to the same position, on the lens plane (i.e., image plane of the endoscope lens) and the image plane (i.e., lens plane of the image recorder).
However, the production of ordered fiber bundles is complicated and therefore expensive. In particular, waste is quite high because, on the one hand the individual fibers break or are otherwise damaged during production, and on the other hand sorting the individual fibers is not always optimal.
In the endoscopic video system known from DE-A-32 04 316, the imaging fiber bundle is an incoherent bundle. What is meant thereby is that the entry-side end and the exit-side end of each fiber are not disposed at the same relative position in the image plane of the endoscope lens and in the lens plane of the image recorder so that the transmitted image in the lens plane of the image recorder is “mixed up”. With regard to this, reference is made to page 7, lines 7 to 14 of DE-A-32 04 316.
A decoder, or an image processing unit, corrects the “incoherent” image signal from the image recorder in such a manner that the image is “coherently” represented, by way of illustration, on a monitor.
In the generic endoscopic video system known from DE-A-32 04 316, the relative orientation of the lens-side ends of the incoherent fiber bundles with respect to the image-side ends prior to inserting the fiber bundle into the endoscope is fixed permanently, or “once and for all”. (cf. page 8, lines 26f of DE-A-32 04 316).
BRIEF SUMMARY OF THE INVENTION
The present invention is based on an understanding that a video system is needed which permits not only correction of possible incoherencies of the imaging fiber bundles, but also a wide elimination of other typical imaging errors of generic endoscopic video systems. The present invention is based in particular on an understanding that a substantial source of image falsifications, or variances, is the illumination of the object field by the illumination device and the downstream illumination fiber bundle.
Thus, it is an object of the present invention is to improve a generic endoscopic video system in such a manner that other typical image falsifications, or typical variances, of the endoscope are eliminated.
An element of the present invention is that detection and storage of the necessary corrections of the image of the video system does not occur prior to assembling the endoscope, but rather during operation of the endoscope video system using all the components required therefore, and preferably using the illumination device which is to be subsequently employed for recording the endoscope images.
Therefore, an image processing unit is provided with a “learning mode” and a “recording mode”. In the learning mode, the image of at least one known test object is recorded, which preferably is illuminated by the illumination unit. The image processing unit compares, in the learning mode, the output signal of each element of the image from the image recorder with a predetermined desired output signal from the test object. The image processing unit determines therefrom, for each image element, the change in intensity and color of the recorded image relative to that of the test object resulting from the variances in illumination due to the lens edge cut-off, transmission errors of the image transmitter, and variances in the sensitivity of the image recorder, and determines therefrom a correction value assigned to the respective image element. In the recording mode, the image processing unit corrects the respective output signal from each image element by means of the correction value assigned to that image element.
Therefore, the invented endoscopic video system permits the correction of errors of the entire system and not only of single components of the system, such as by way of illustration, is the case in the system known from DE-A-32 04 316, which corrects only disorder in the imaging fiber bundle.
A special advantage of the invented endoscopic video system is that the brightness of the image can be evened over the entire object field in use conditions. Nearly all endoscopic images have a center-emphasizing basic brightness distribution which usually diminishes with the radius and which can, furthermore, be inhomogenous. This has a number of possible causes, some of which are as follows:
(1) Due to the focusing of the lamp helix, the non-uniform arrangement and design of the optical fibers in the optical cable between the illumination device and the endoscope, the non-uniform arrangement and design of the optical fibers in the endoscope, and the arrangement of distal light exit apertures, the object field of the endoscope lens is illuminated with a radial distribution of light which is superimposed by random variances. Although a variety of patent applications describe that a more homogeneous distribution of light can be obtained by means of an improved distal-side optical fiber arrangement, and that illumination can be made more homogeneous thereby, uniform illumination using these arrangements is unachievable.
(2) Most endoscope lenses have an “edge cut-off” in the transmission function which usually is larger than the radial decrease of the transmission function which is inversely proportional to the fourth power of the distance from the optical axis (i.e., the “r
4
cut-off”).
(3) The image transmission system also has an edge cut-off if relay lens systems or gradient lenses are employed. If imaging fiber bundles are used, the result is additional variances caused by broken fibers, or fibers with reduced overall transmission or different spectral transmission compared to most of the fibers.
(4) The individual image elements of the image recorder may have different sensitivity.
According to the present invention the following is undertaken to correct the non-uniform basic image brightness as well as other imaging errors.
In the learning mode, one test object or a multiplicity of test objects are placed in succession in the object field of the endoscope. These test objects may be a matt (e.g., white) glass which is illuminated from the rear, a homogeneous gray or white chart, homogeneous color charts, preferably with pure prime colors, and/or charts which permit detection of distortion of the whole system comprising a lens, an image transmitter and an image recorder. These charts are disposed in such a manner that they stand perpendicular to the viewing direction of the endoscope and are spaced in a certain manner.
In order to meet these conditions, a test cavity is preferably provided into which, in the learning mode, the distal end of the endoscope is inserted and in which the test object(s) (i.e. test charts) are disposed such that they are in the object field of the endoscope lens.
If
Chatenever David
Faust Uwe
Irion Klaus
Strobl Karl-Heinz
Karl Storz GmbH & Co. KG
Leubecker John P.
St. Onge Stewart Johnston & Reens LLC
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