Surgery – Endoscope – Having imaging and illumination means
Reexamination Certificate
2001-07-13
2003-06-24
Mulcahy, John (Department: 3739)
Surgery
Endoscope
Having imaging and illumination means
C600S168000, C359S379000, C359S380000, C359S656000
Reexamination Certificate
active
06582362
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an endoscope system that is provided with a photographing optical system using a solid-state image sensor.
2) Description of Related Art
In recent years, electronic endoscopes using solid-state image sensors such as compact CCDs have become popular. Since such an endoscope allows a plurality of persons to observe lesion in a body cavity via a TV monitor, examination and diagnosis can be made by a plurality of medical doctors. Also, it is greatly advantageous to patients also in that they can view their own lesion while being informed of doctor's diagnosis. Of such endoscopes, so-called “magnifying endoscope”, which is used for near observation of lesion to facilitate examination of its minute structure for the purpose of determining the degree of infiltration of the minute lesion or the regional extent to be subjected to incision, has drawn particular attention most recently.
Some of optical systems for the magnifying endoscopes are disclosed, for example, in Japanese Patent Publication (KOKOKU) No. Sho 61-44283 and Japanese Patent Application Preliminary Publication (KOKAI) No. 4-218012. Each of these optical systems are three- or four-unit-type optical systems and are able to provide high magnification, while involving a problem in that the entire length of the optical system is considerably long, to cause bulkiness of the insertion section of the endoscope and thus to impose a great burden on a patient.
Also, such a magnifying endoscope of prior example has a drawback in that it has an extremely narrow depth of field and thus has poor operability.
Here, brief explanation is made of the definition of depth of field.
FIG. 16
is a sectional view of an endoscope optical system taken along the optical axis. As shown in the drawing, placing a CCD at a position where an image I of an object O is formed makes it possible to obtain an in-focus image. If the object O is moved toward the endoscope to the position O′, the image I is shifted to be formed at a position I′. On the other hand, if the object O is moved away from the endoscope to a position O″, the image I is shifted to be formed at a position I″. Where the position of the CCD is fixed, the image I′ or the image I″ at the position of the CCD becomes a circle of confusion with a diameter &dgr;, to cause an out-of-focus image. However, if the resolution of the CCD is greater than the diameter &dgr; of the circle of confusion, image quality is determined by the resolution of the CCD and, accordingly, the object-position range from O′ to O″ seems to be in focus. This range is called “depth of field”, where a distance X
n
from the optical system to the point O′ is defined as the nearest distance in the range of the depth of field, while a distance X
f
from the optical system to the point O″ is defined as the farthest distance in the range of the depth of field.
In this case, the following equation is true:
|1
/X
n
−1
/X
f
|=2
&dgr;F
no
/f
L
2
(1)
where the effective aperture ratio (F number) is represented by F
no
and the focal length of the optical system is represented by f
L
2
.
Here, the depth of field D is given by:
D=X
f
−X
n
(2)
If we regard X
n
, X
f
as two values of the variable X of the function 1/X=Y, we can view a value of the operation on the left of Equation (1) in the form of a difference in Y direction between two points that lie on the curve of 1/X=Y shown in FIG.
17
. If the value of 2&dgr;F
no
/f
L
2
is constant, a smaller value of X
n
, or the near observation condition yields a smaller depth of field D
1
.
To be specific, the depth of field of a magnifying endoscope in the magnifying mode is as narrow as 2 mm or 3 mm. Such a specification would require, for example, an operator to perform subtle manipulation on the order of 1 mm while the endoscope being inserted into the large intestine over lm deep. In short, it requires a lot of skill to manipulate the endoscope (Problem 1).
Also, in the conventional magnifying endoscope system, the same image processing is performed in the normal observation mode and in the magnifying observation mode. In general, when a tissue is magnified, minute lesion in it also is observed as magnified and thus the image provided for observation would contain a large amount of low-frequency components. In contrast, since an endoscopic image in the normal observation mode shows a web pattern of fine blood vessels at a low magnification, the image provided for observation would contain a large amount of high-frequency components. Therefore, if the image processing that is optimized for the magnifying observation mode is employed in the normal observation mode, the image of the blood vessels collapses to be hardly observable (Problem 2).
Furthermore, according to the conventional magnifying endoscope, a part of the optical system located 1 m or more away is driven via a wire for switching between the normal observation mode and the magnifying observation mode. No medical doctor but the operator can know the magnification currently selected and thus there may be difference in recognition regarding the size of the lesion among them. Resultantly, it is difficult for them to make a discussion (Problem 3).
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above-mentioned problems involved in the conventional art. An object of the present invention is to provide an endoscope system which is made compact so as to impose less burden on a patient, is provided with a wide depth of field so as to allow even a person without considerable skills to easily manipulate the system in the magnifying observation mode, is able to improve accuracy of diagnosis information by enhancing seeming resolution regarding the magnified information, and is able to improve accuracy of diagnosis by facilitating discussion among a plurality of medical doctors.
In order to attain the above-mentioned object, the endoscope system according to the present invention is configured to photograph an image obtained in the normal observation mode and an image obtained in the near observation mode on a solid-state image sensor by controlling a focus adjustment means which changes the focal length and the working distance and to display the image on a display unit, wherein the following conditions are satisfied:
WD
wide
>WD
tele
(3)
f
wide
≧f
tele
(4)
where f
wide
is a focal length in the normal observation mode, WD
wide
is a working distance in the normal observation mode, f
tele
is a focal length in the near observation mode, and WD
tele
is a working distance in the near observation mode.
In general, where f
L
is a focal length of an optical system, f
F
is a front-side focal length of the optical system and z is a distance from the surface of the optical system to an object, magnification &bgr; of the optical system is given by:
&bgr;=−f
L
/(
f
F
+z
) (5)
Accordingly, for the purpose of securing as large a magnification &bgr; as possible, it is necessary to set the distance z as short as possible or to set the focal length f
L
as long as possible.
On the other hand, as explained above regarding Problem 1, if the distance z from the surface of the optical system to the object is set short or the focal length f
L
is set long, the depth of field becomes narrow, to make the system less operable. Condition (3) is specified, according to the present invention, so that the requirement for the magnification and the requirement for the depth of field are compatibly satisfied. This is a minimum necessary condition for securing a sufficiently high magnification. In performing magnifying observation, a medical doctor would spread coloring over lesion so that the lesion is viewed in high contrast. However, this treatment would attenuate light reflected back from the object, sometimes to make the visual field
Mulcahy John
Olympus Optical Co,. Ltd.
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