Biopsy arc means and the use of the same

The invention relates to a biopsy arc intended to be the support of examination needles in connection with computer tomography. The arc is removably secured to the patient's table and angularly adjustable to be adapted to the direction of the respective section image plane. The arc has a plurality of apertures directed towards the area enclosed by the arc for guiding the examination needles. The arc is made of a material which has an attenuation with respect to X-ray radiation which lies at or below the value exhibited by organic tissue, whereby the arc as well as organs can be brought to appear and stand out together on the section picture in order that a suitable aperture and direction of examination can be selected without risk of disturbing artefacts.

TECHNICAL FIELD 
In connection with computed tomographic examinations nowadays often so 
called biopsy arcs are used, that is, guiding instruments for inserting 
properly and safely examination means, such as sampling needles and the 
like, into the patient body concerned. Usually such biopsy arcs are 
provided with complicated adjustment means for directing the needles, and 
they require that the operating personnel be thoroughly trained in order 
that said means be used in an appropriate manner. Furthermore there are 
very often a risk of so called disturbing artefacts caused by the 
structure of the devices when these come into the vicinity of the section 
image. In examinations of the said kind it is thus very important that the 
occurring section images of the patient body concerned are not disturbed 
by structural material attenuating the radiation, as the contents of the 
images can easily be misinterpreted in such cases. 
PRIOR ART 
In this technical field there are a plurality of known designs, as can be 
seen from the patent literature. As an example the German Publication DE 
32 05 915 can be mentioned. The device shown in this paper includes an arc 
which encloses substantially 270.degree. of a circle and is secured to a 
patient's table. On the arc, which is provided with indicia, there is a 
slider to be slidably pushed along the arc. The slider includes a needle 
carrier which is movable about an axis and thus able to be turned in the 
plane of the arc. After a section image of a body under examination has 
been studied and the organ to be examined or punctured has been localized, 
the approximate insert angle of the needle is determined, also the depth 
of insertion, after which the needle carrier is set on the arc in the 
estimated position and approximately directed. Then the needle is inserted 
into the patient and loosened from the arc in order that a check picture 
be taken and the needle position obtained evaluated. Should positioning 
not be carried out exactly as intended the needle has to be pulled out, a 
new directing operation be carried out and the needle be inserted again. 
This is of course not satisfactory neither with respect to the examination 
nor to the patient. 
The German Patent Specification DE 33 39 259 discloses an arc arrangement 
provided with some radial apertures through which guide means can be 
inserted for, in this case, drilling. The arrangement has no direct 
bearing on computed tomography but still it is mentioned as representing 
prior art guiding instruments. 
As an example of usually occurring biopsy arc arrangements reference is 
made to the U.S. Pat. Nos. 4,350,159 and 4,463,758. These arrangements 
both include advanced structures for adjusting needles when carrying out 
examinations of the said type in connection with computed tomography. As 
can be clearly seen from the structure of these arrangements very 
disturbing artefacts can arise in the tomographic pictures if parts of the 
structures concerned should enter into the respective section picture. 
Thus there is a need of a simple and safe method of determining the 
position as well as the penetration depth of an examination needle without 
it being necessary to resort to either intricate trigonometric 
calculations or complicated apparatus adjustments. 
SUMMARY OF THE INVENTION 
The present invention solves the problem mentioned above in a very simple 
and appropriate manner. A biopsy arc according to the invention, in 
particular for computed tomography, is provided with a plurality of 
apertures directed towards the area within the arc, the arc being mounted 
in such a way that it can be angularly set for adjustment of the plane of 
the arc to a plane of image section in the computed tomographic apparatus. 
Furthermore, the arc should be such as to exhibit such an attenuation of 
the radiation concerned which is equal to or less than that exhibited by 
organic issue. The arc will then form part of the related section image, 
whereby the directions of the apertures will be identifiable. Hereby it is 
possible, in order to select to suitable path for inserting an examination 
means, to select a suitably directed aperture through which said means can 
be inserted. Expediently the apertures have such a diameter that they can 
receive guiding sleeves for the examination means concerned, such as a 
needle or the like. Thanks to the fact that the arc has apertures of a 
comparatively large size these apertures will be clearly depicted in the 
section image as channels of given directions. Hence, it is comparatively 
simple to select an aperture for inserting an examination means if, in the 
image, the direction of the aperture agrees with the desired path of 
insertion. Contrary to what is occurring in known techniques the biopsy 
arc is allowed to remain in the path of the X-ray beam creating the image 
section, in order to render it possible to utilize the arc configuration 
in the section image in connection with the examination contemplated. 
The characterizing features of the present invention appear from the patent 
claims following the specification. 
The invention will be described in greater detail with reference to the 
accompanying drawings which illustrate embodiments of the invention.

DISCLOSURE OF EMBODIMENTS 
The biopsy arc 1 shown in FIG. 1 is connected, by a detachable support 
member 2, with guide rails 3 or either side of a patient's table 4. The 
biopsy arc is provided with a plurality of apertures 5. Patient's table 4 
is insertable in a computed tomography installation 6, in a manner not to 
be described in detail. 
As seen from FIG. 2 there are, on one half of the biopsy arc, a number of 
radially extending apertures 7 which are directed towards a central target 
point 8. On the opposite side of the arc 1 there are a number of apertures 
9 parallel with each other and chordally directed. 
As can be clearly seen in FIGS. 2 and 3 the support member 2 of the biopsy 
arc 1 is provided with a slide 10 intended to run along the respective 
side rail 3 and to be locked to the rail in desired positions by means of 
set screws 11. The biopsy arc 1 itself can be clamped by its legs or 
shanks against the respective slide 10 by means of a plate 12 having slits 
13, 14 through which retaining screws 15, 16 are inserted. By the slit 
arrangement 13, 14 the biopsy arc 1 can be adjusted in various angular 
positions in relation to the patient's table 4, as indicated by the double 
arrow 17. To this end indicia 18 are provided on the side of each plate 
12. The disengageable clamping of the biopsy arc shanks by means of the 
plates 12 and the retaining screws 15, 16 brings with it that a certain 
adjustment of height can be performed in order to adjust to the body of 
the patient concerned, as indicated by the double arrow 19. On the biopsy 
arc 1 itself indicia 20 are provided on each shank. 
To make it possible to guide and secure an examination needle in the 
desired position in any of the apertures 5 a sleeve 21 having a flange 22 
is provided. The sleeve is made with a central through hole, through which 
a needle 23 can be inserted, as shown in FIG. 4. Suitable a socket 24 is 
pushed onto the needle, to be secured to the needle by a set screw. Hereby 
an insertion stop is provided, whose position is adjusted in accord with 
the required length to which the needle is to be inserted into the 
patient's body. The device shown in FIG. 4 has the advantage that only the 
needle 23 and the sleeve 21, 22 need be sterilized between various 
examinations of a patient, thus not the arc proper. 
The biopsy arc 1 is made of a material having a density and properties in 
relationship to the X-ray radiation concerned which can be ranked in the 
same category as organic tissue density, that is, the density of tissue 
occurring in a patient's body. The density of tissue generally lies 
between 40 and 150 Hounsfield units, abbreviated H-units. To clarify the 
meaning of H-units the following may be pointed out. As it is not 
practical to work with .mu.-values in computed tomographic scanning a new 
scale of values related to the linear attenuation coefficient have been 
defined by Hounsfield. The unit in this new scale is abbreviated H 
(meaning Hounsfield). 
The scanning device used by Hounsfield operated at 120 kV with an aluminium 
filter of thickness 4.5 mm and a water container 27 cm thick. Under these 
particular conditions it was found that the .mu.-value of water was 0.19 
cm.sup.-1 (i.e. 0.19 per cm), which is equivalent to the .mu.-value of 
water measured by a monocromatic beam of 73 keV. In consequence herewith a 
Houndsfield unit for a substance `x` is defined by the following equation 
##EQU1## 
or H=5263 .mu.x-1000 
It is important to know that the above equation is based on the 
prerequisite that 10 H-units correspond to a change of 1% of .mu.x, in 
relation to the .mu.-value of water. 
From the above formula it can be calculated that H of water is 0 while the 
value of air is -1000 and that the value of dense bone tissue can raise up 
to +3095 H . A scanning system can thus handle 4096 different H-values for 
each image element. H-values of some anatomic substances and synthetic 
materials are shown in the table below. 
______________________________________ 
Dense bone tissue up to 3095 
Bone 200-1000 
Teflon 950 
Delrin 365 
Bakelite 264 
Perspex 125 
Lexan 105 
Nylon 89 
Dense tumour tissue 50-90 
Coagulated blood 55-75 
Brain tissue (grey) 36-46 
Brain tissue (white) 22-32 
Blood 12 
Water 0 
Polystyrene -28 
Fat -100 
Air -1000 
______________________________________ 
Thus the material density of the biopsy arc must not exceed such values 
that artefact disturbances can arise in the image concerned. Preferably 
the material should have a value below 200 H. 
Polyamide plastics, having a H-value about 80, is satisfactory for most 
practical purposes. What is essential is the feature that the arc stands 
out in the section image so that the respective aperture and its direction 
can be identified. 
USE AND FUNCTION OF THE ARRANGEMENT 
Examination of a patient while using the biopsy arc according to the 
invention is conducted in the following way: 
In modern computed tomographic installations there are laser light beams 
for positioning so that the section plane of the scanning unit can be 
projected on the patient's body, after which pencil markings can be made. 
The biopsy arc is then secured to the patient's table 4 and angularly 
adjusted in accordance with the markings drawn so that the plane of the 
arc will coincide with the plane of the image section of the computed 
tomograph. When the patient's table 4 is again introduced into the 
tomograph 6 and the requested section pictures are taken, the arc with its 
apertured channels will be outline in each picture together with the 
organic tissues occurring in the image section, in a way as illustrated in 
FIG. 5. It is assumed that in FIG. 5 a vertebra 25 with ribs 26 belonging 
thereto are outlined in the picture. Within the area designated 27 the 
image of swollen organ stands out which, for example, is to be punctured. 
Now, the question is to insert the puncturing needle to this organ in such 
a way that no adjacent organs are damaged. So in this case one of the 
apertures 7 is selected which as to its direction seems to be the suitable 
one for reaching the said organ 27, as indicated by the dashed line. 
However, in order to make it possible to determine the path and depth of 
needle penetration a reference grid 28 having a center line 29 is applied 
on the monitor image obtained, as seen in FIG. 6, said center line passing 
in this case through the spinal cord portion 30 of the vertebra 25. The 
reference grid is used to find the point 8 towards which the radially 
directed channels converge, in doing which there is marked on the center 
line 29, which coincides with the radial direction of the central aperture 
of the arc, the point which forms the target point of all radial apertures 
7, that is, point 8 in FIG. 2. Starting from said point lines can then be 
drawn towards apertures 7 in order to select a suitable path of insertion 
and the associated needle. This reference grid is divided into such 
measuring units that they are directly, or by computer, convertable to the 
penetration depth of the puncturing needle concerned. In practice it is 
advisable to design the software of the computer such that measures of the 
depth of penetration and also of the needle socket length can be readily 
read by cursor control. As have been previously pointed out in connection 
with FIG. 4, the length of insertion is set by means of the socket 24 
which abuts the flange 22 of the sleeve 21 when the proper length of the 
needle has been inserted. 
Thus when the position of an organ 27 has been established a suitable 
aperture in the arc is selected in accordance with the above, i.e. an 
aperture having the correct direction towards the organ. The needle length 
is adjusted as described, after which the patient's table 4 with the 
patient is pulled out from the computed tomograph, and with the arc in its 
set position the aperture 7 concerned is used for inserting of the sleeve 
21 and said needle 23. The needle is inserted to the depth aimed at and 
the patient can now be introduced again with the table 4 into the computed 
tomograph so that a picture for checking can be taken. It should be noted 
that it is not necessary to remove the arc when checking the position of 
the needle, as the arc, the needle, as well as the guide sleeve 21 can be 
allowed to appear in the section image, and this without any disturbing 
artefacts arising. The result of the organ puncture can also be checked in 
this manner with all settings unchanged. 
If, in viewing the section image, it is seen that the radial apertures 7 
cannot be used for the necessary measure, the biopsy arc can readily be 
turned by its shanks being pulled out from their engagement with the 
respective support member 2 and turned 180.degree. so that the chordially 
directed apertures 9 are now located on the side where the organ 27 is 
situated. A suitable aperture having the requested position and direction 
can now be selected for the examination intended. In this case lines 
parallel with the line 29 of the reference grid 28 will now be essentially 
parallel with the direction of needle introduction, rendering it easy to 
read the depth of penetration. As can be seen the use of a biopsy arc 
according to the invention involves only a small number of manipulation 
steps and calculations as compared with known designs. Thanks to the 
feature that the arc can be allowed to form part of the examination image 
without creating disturbing obstacles and that it is possible to determine 
in a simple way from this image apertures and positions for inserting the 
needle, contribution is given to a perspicuity which is very valuable in 
the practical work involved in computed tomographic examinations. In view 
of its simple structure and the perspicuous way the arc is used its 
handling will be very easy to learn. 
In some connections it could be advisable to use arcs which e.g. have 
cordally directed apertures only. Such a structure is shown in FIG. 7. 
Likewise it could be advisable sometimes to use an arc which has throughout 
radial apertures directed towards a central target point. Such a structure 
can be seen in FIG. 8. 
As a matter of course a plurality of designs can be contemplated within the 
scope of the invention where, for instance, several different types of 
apertures 5 can occur. For example, such structures can be conceived 
wherein differently directed apertures are located adjacent one another or 
in the interspace between apertures. Thus e.g. every second aperture can 
be radially directed, such as apertures 7, and every second chordally 
directed, as apertures 9. In a manner suitable for certain purposes groups 
of apertures can be distributed along the arc and have various directions. 
Of course also arrays of apertures adjacent each other can be provided, 
differently directed. Such solutions can be valuable if it is desirable to 
select an aperture having a very specific direction, in doing which the 
biopsy arc can be angularly tilted through the plane of the image section 
according to arrow 17 in order to determine the desired aperture. 
The biopsy arc can also be secured to another base member than the 
patient's table shown. For example, a separate base slab can be used which 
can be placed on the patient's table and retained thereon by the patient 
resting on the slab by his own weight.