Apparatus for the disintegration of calculi

An apparatus for disintegrating calculi situated in the body of a life form has a shock wave generator and an examination apparatus for locating the calculi within the body. The examination apparatus includes at least one image memory in which an image of a portion of the body, including the calculi to be disintegrated, is stored. A comparator compares the stored image with an image chronologically following the store image to determine any movement of the calculi which may have occurred between the generation of the compared images. The position of a shock wave generator relative to the calculi is set based on the stored image, and the shock wave generator is energized to disintegrate the calculi upon the recognition of a subsequent image most closely corresponding to the stored image.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an apparatus for disintegrating 
calculi situated in the body of a life form, and in particular to such an 
apparatus having a shock wave generator and an examination apparatus for 
locating the position of the calculi within the body for accurately 
positioning the shock wave generator. 
2. Description of the Prior Art 
An apparatus for disintegrating urinary and renal calculi, gallstones, or 
the like is disclosed in German OS No. 31 22 056. In this apparatus, a 
focussing chamber is used as a shock wave generator, in which a shock wave 
is generated by, for example, spark discharge. The shock wave is 
concentrated within the focussing chamber onto the calculus, and 
disintegrates the calculus. In order to make an exact determination as to 
whether the calculus is situated at the focal point of the focussing 
chamber, a locating apparatus is connected to an x-ray examination 
apparatus. In a transillumination mode, individual images of a stereo 
image pair are entered in an image memory in the video chain, being 
entered either individually or integrated over a plurality of images. A 
problem in accurately locating the position of such calculi arises, 
particularly when treating kidney stones, due to movement of such calculi 
during respiration. Thus the calculi may not be in the same position at 
the time the shock wave generator is energized to disintegrate the calculi 
as the calculi were at the time when the locating of the shock wave 
generator was initially set. The same problem can occur in the use of 
ultrasound examination devices. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provided an apparatus for 
disintegrating calculi making use of a shock wave generator and an 
apparatus for locating the calculi, wherein an extremely precise 
identification of the location of the calculi can be made at the point in 
time at which the shock waves are initiated, so that a reliable 
disintegration of the calculi is achieved, with minimum damage to healthy 
surrounding tissue. 
The above object is achieved in accordance with the principles of the 
present invention in an apparatus for disintegrating calculi having an 
image memory in which an image containing the calculi is stored at the 
time the position of the shock wave generator is set relative to the 
calculi, and a comparison means for comparing the stored image with a 
chronologically following image. The comparison means determines when a 
chronologically following image most closely resembles the stored image, 
thus indicating, if movement has occurred due to, for example, 
respiration, between the images, the calculi has substantially returned to 
its initial position and the shock wave generator is then triggered. The 
shock waves can be triggered upon the occurrence of substantial equality 
the stored image with a current x-ray image or a current ultrasound image. 
Equality is only established, however, when the examination subject is at 
substantially the same position in a respiration cycle or a heartbeat 
cycle compared to the point in time at which the first image was stored. A 
precise coincidence of the localized point of the calculi with the focal 
point of the shock wave generator is thus achieved, so that the total 
energy expended can be utilized for comminuting the calculus and damage to 
healthy surrounding tissue is minimized. 
Precise coincidence of the position of the calculi with the focal point of 
the shock wave generator can be even further improved by comparing images 
of only a small region of interest of the patient. This permits slight 
movements outside of the field of interest, and which would not 
significantly disturb the calculi disintegration, to be ignored. This can 
be accomplished, for example, by the use of an evaluation circuit which 
counts the number of equal or unequal picture elements in the compared 
images. Such an evaluation circuit may be connected to a threshold circuit 
which enables triggering of the shock waves only when the output of the 
evaluation circuit is above (if counting equal picture elements) or below 
(if counting unequal picture elements) a defined, adjustable threshold. 
Triggering of a plurality of shock waves in one motion phase is enabled by 
the use of a detector for a phase of minimal movement of the calculi, with 
the output signal of such a detector controlling the storing procedure of 
the image memory.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The apparatus constructed in accordance with the principles of the present 
invention shown in the drawing includes an x-ray examination apparatus 
having two x-ray sources 1 and 2 which generate respective x-ray beams in 
which an examination subject 4, having a calculus therein is disposed. The 
examination subject 4 is supported on a patient support 3. The x-ray 
attenuated by the examination subject 4 are incident on respective input 
luminescent screens of respective x-ray image intensifier 6 5 and 6. The 
x-ray source 1 and the x-ray image intensifier 6 may, for example, be 
arranged such that the central ray of the x-ray beam from the x-ray source 
1 is perpendicular with respect to the examination subject 4 (a.p. 
projection). The x-ray source 2 and the x-ray image intensifier 5 may be 
obliquely arranged such that the central ray of the x-ray source 2 
intersects the central ray of the x-ray source 1 at an angle of, for 
example, 45.degree. at a target area inside the examination subject 4 
(c.c. projection). As a result, transillumination images from two 
different projection directions are obtained, so that the examination 
subject 4 can be displaced using the patient support 3 so that the calculi 
are situated inthe target area of an apparatus for disintegrating the 
calculi, described below. 
The output signals of video cameras 7 and 8 respectively coupled to the 
x-ray image intensifiers 5 and 6 are entered in two image memories 11 and 
12 through respective analog-to-digital converters 9 and 10. The output 
signals from the image memories 11 and 12 can be viewed on respective 
monitors 15 and 16 through respective digital-to-analog converters 13 and 
14. When the calculi are situated in the target area, the calculi appear 
in the center of the picture screens of the monitors 15 and 16. 
A shock wave generator 17 is provided for comminuting the calculi situated 
in the target area. The shock wave generator is schematically shown in the 
drawing. The shock wave generator 17 generates shock waves in a known 
manner, resulting in disintegration of the calculi. Most effective results 
are obtained when the calculi are situated in the focal point of the shock 
wave generator 17. The examination apparatus and the shock wave generator 
17 are permanently connected to each other such that the shock waves are 
focussed at the target area of the x-ray examination apparatus. The shock 
wave generator 17 is operated by a drive circuit 18. A control unit 19 is 
connected to a high voltage supply 20 for supplying the x-ray sources 1 
and 2. The control unit 19 is also connected to the image memories 11 and 
12, and to the drive circuit 18 for the shock wave generator 17. 
The output signal of the analog-to-digital converter 10 is supplied to a 
further image memory 21, having a control input connected to the control 
unit 19 through a detector 22. The detector 22 detects miminal motion of 
the calculi resulting from patient movement, such as by respiration or 
heart activity. The detector 22 is also supplied with the current video 
signal from the analog-to-digital converter 10, and with the stored video 
signal from the image memory 21. The outputs of the image memory 21 and 
the analog-to-digital converter 10 are connected to a comparator 24 
through a selection circuit 23. The output signal of the comparator 24 
supplies a signal to the control unit through an evaluation circuit 25 and 
a threshold circuit 26. 
At the beginning of an examination, the x-ray sources 1 and 2 are 
energized, so that x-ray images of the examination subject 4 are produced, 
and are entered in the image memories 11 and 12. The x-ray images are 
viewed on the monitors 15 and 16. By appropriately shifting the patient 
support 3, the examination subject 4 is aligned such that the calculi to 
be disintegrated are situated in the target area. This position of the 
examination subject 4 can be identified when the calculi are located in 
the center of the picture screens of the monitors 15 and 16. This 
alignment is undertaken in the transillumination mode. 
After patient alignment has been completed, storage of an x-ray image into 
the further image memory 21 can be initiated, for example by actuation of 
a knob 27 on the control unit 19. The control unit 19 then enables the 
detector 22. The detector 22 enables entry of successive x-ray images, 
into the further image memory 21. By comparing the stored and current 
video signals, the phase having the least movement of the calculi is 
identified by, the detector 22, and the image entry procedure is 
terminated. The result is storage of an x-ray image corresponding to the 
phase of least movement of the calculi in the further image memory 21. 
The detector 22 then provides an answerback signal to the control unit 19. 
The control unit 19 then drives the selection unit 23, enabling the 
selected picture elements corresponding to an area of interest to be 
transmitted to the comparator 24. Such selection can be undertaken in a 
known manner, for example, by a light cursor (not shown) on the monitor 
16. It is also possible, because the calculi will always be situated in 
the center of the x-ray image displayed on the monitor 16, to transfer a 
predetermined prescribed central region of the image. It is also possible, 
instead of a selected area, to supply complete x-ray images to the 
comparator 24. 
The comparator 24 compares the stored and the current video signals picture 
element-by-picture element, and generates an output signal corresponding 
to the number of identical and/or non-identical picture elements in those 
images. The comparator 24 may alternatively be a subtraction stage, which 
generates a difference signal for those picture elements which deviate 
from one another. 
An evaluation circuit 25 is connected to the output of the comparator 24, 
and may consist, for example, of one or more adders which total the number 
of identical and/or non-identical picture elements. If the counter reading 
corresponding to the number of identical picture elements exceeds a 
threshold set by an adjustment means 28 of the threshold circuit 26, the 
threshold circuit 26 generates an enabling signal for the shock wave 
generator 17, supplied thereto through the control unit 19 and the drive 
circuit 18. The number of non-identical picture elements may also be 
evaluated, in which case the threshold circuit 26 generates an enabling 
signal when the output of the evaluation circuit 25 is below a threshold 
set by the adjustment means 28. 
Shock waves are thus triggered only when the calculi in the examination 
subject 4 are disposed in their phase of least movement. 
If the x-ray examination apparatus is to be operated only in the 
transillumination mode, the image memories 11 and 12 can be omitted. It is 
alternatively possible to omit only the image memory 12, if the output 
signal of the image memory 11 is supplied to both the digital-to-analog 
converters 13 and 14, and thus to both monitors 15 and 16. In a further 
embodiment, the calculi movement in various directions can be monitored by 
connecting the same circuit elements 21 through 28 to the output of the 
analog-to-digital converter 9, which supplies an image of the second x-ray 
projection. 
Instead of coupling the video signal from the x-ray examination apparatus 
for use in triggering the shock waves, the trigger pulses may be acquired 
from the picture signal, of an ultrasound examination apparatus. The 
radiation dose applied to the patient is thus eliminated. It is also 
possible, instead of using a separate ultrasound examination apparatus, to 
use the mechanical energy of the shock wave reflected by the calculus for 
generating the image used for comparison. The costs for the overall 
installation can be thereby reduced. 
Although modifications and changes may be suggested by those skilled in the 
art it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.