Method and device for mammographic stereotactic punction of pathological lesions in the female breast

Method and apparatus for stereotactic localization of cancer suspect lesions of the female breast in connection with X-ray mammography. The object is imaged in two directions, and the position of the lesions is calculated from the parallax displacement between the two images. The X-ray tube and the film are held stationary, and the parallax displacement is effected by moving the object laterally.

Mammography is a radiographic method for early detection of breast cancer. 
It is not always possible to decide whether the detected lesions are 
benign or malignant. One way to decide this is punction with a thin 
cannula in order to extract cells for microscopic diagnosis. In order to 
succeed it is necessary to hit the lesions with the cannula. The 
suspicious lesions are often so small that they can not be palpated (felt 
with the fingers) and therefore some technique for mammographic 
localization is necessary. 
Mammographic apparatus at present available comprises special versions for 
the said purpose with stereotactic localization facilities. These imply an 
extensive modification of the apparatus and raise the price with about 
250,000 Swedish crowns. The stereotactic principle (tomography) 
traditionally used in radiology is based on the object being stationary 
and the X-ray tube (radiation source) and film cassette (image medium) 
moving synchronously. Two exposures are made and with the aid of simple 
geometry it is possible to calculate the position within the object. Such 
equipment is technically complicated and therefor expensive, especially 
since it is usually combined with relatively sophisticated 
computerization. 
The present invention suggests a principle that is the reverse of the above 
and not previously used in radiological technique, i.e. to allow the X-ray 
tube and the image to remain stationary and to move the object. As a 
consequence, the X-ray unit need not be modified. The geometry in this 
case is also simple, being based on similar triangles. There is, however, 
requested an apparatus having a movable holder adapted to hold the 
object--the female breast--during the movement between the two positions 
of exposure. The invention can be adapted to all existing mammography 
units without having to modify these.

CONVENTIONAL MAMMOGRAPHY 
The principle for a conventional mammography unit without stereographic 
means is shown in FIGS. 1a and b. The X-ray tube 10 is mounted on a stand 
11 which is immovable in relation to the film cassette holder 12. The 
outer limits of the radiation field from the X-ray tube are schematically 
shown by the continuous lines 13. The primary diaphragm 14 of the X-ray 
tube and the radiation window 15 decide the size of the radiation field. 
FIG. 1b shows the object 16, a female breast, with the suspicious lesion 
17. The object is fixed by a compression plate 18 on top of the film 
cassette, also fixed. The X-ray beam passing through the lesion is shown 
by a broken line 19. 
TOMOGRAPHY 
FIGS. 2a to c show a conventional X-ray unit with stereographic means for 
tomography. The X-ray tube is mounted on a stand which is movable around 
an axis 21. The movement limits of the X-ray tube are delineated by line 
22. The stand is mechanically fixed to the film cassette holder 23, which 
will move accordingly in a direction opposite to the X-ray tube. FIGS. 2b 
and c show exposures in the two extreme positions. As mentioned the unit 
is technically advanced and thus expensive. 
MOVEMENT OF THE OBJECT 
The method and device according to the present invention are presented in 
the following descriptions and figures of principle. The device may be 
used on presently existing mammography units without modification of the 
latter. The device consists of four main components, i.e. base, object 
holder, compression plate and needle director. 
BASE 
FIG. 3 shows a base 30 which is attached in connection with the cassette 
holder of an existing mammography unit. The base has two functions: 
1. It allows for magnification of the image by increasing the object-film 
distance. 
2. It acts as a slide track for lateral movements of the object holder 40 
(see FIG. 4). 
OBJECT HOLDER 
FIG. 4 shows the object holder 40 mounted on the base. The object holder 
has a base plate 41 on which the object (the breast) rests. The object 
holder has also a stand 42, allowing for vertical movement of the 
compression plate 50 (see FIG. 5). The object holder can be moved 
laterally in relation to the base between two fixed extreme positions. The 
length of the lateral movement is known and constant. 
COMPRESSION PLATE 
The compression plate 50 is mounted on the object holder. The compression 
plate is movable in the vertical direction as shown in FIGS. 5a and b. The 
object is held in a locked position between the compression plate and the 
base plate 41. 
FIG. 5c shows the compression plate as viewed from above. In the fore 
middle part of the compression plate there is a hold 51 which is 5 cm by 5 
cm and allows the passage of X-radiation for film exposure and later is 
used for punction. 
The rest of the plate is covered by a thin iron sheet, the function of 
which is to: 
1. serve as a secondary diaphragm, reducing the size of the irradiated 
field of the breast and the patient to only 25 cm.sup.2. 
2. serve as a receptor for the needle director 60 which is provided with a 
magnet (see FIG. 6). 
Around the hole 51 there are markings 52. They are cut out in the iron 
sheet and let thus through the X-rays which accordingly are visible on the 
exposed X-ray film. The markings are used for deciding the x and y 
coordinates when performing the punction (see below). 
NEEDLE DIRECTOR 
FIGS. 6a and b are drawn at twice the scale of the previous figures. FIG. 
6a shows the principle for the needle director 60 as viewed from above, 
while FIG. 6b shows a view from the side. The needle director is made of 
clear plastic and is held in position on the compression plate by magnets 
61 at the rear end of the needle director which thus can be moved along 
the upper surface of the compression plate. On the upper side of the 
needle director are two marking 62 lines at right angles. These marking 
lines 62 will cast a shadow when lighted by a common light-bulb. The 
markings form a hair-line cross and an origin 63 with a steering hole 64 
for the punction cannula. 
Before punction the origin 63 is adjusted to the determined xy-coordinate 
with the aid of the light diaphragm 81 (see FIG. 8). Concerning punction 
see below under "Operation". 
FIG. 7 shows that the needle director is constructed to enable the origin 
63 to be set to all xy-coordinates within the hole 51. 
On one of the corners of the needle director there is attached a very thin 
lead (Pb) indicator 65. On exposures this indicator is positioned within 
the radiation beam, limited by the hole 51. By this procedure the 
displacement of the position of the indicator 65 on the X-ray film can be 
measured directly, which substantially facilitates the calculation of the 
level of the lesion. 
FIG. 8 is taken from a leaflet from Siemens on X-ray light diaphragms. The 
X-ray radiation source, the anode 82, emits the X-ray beam marked with the 
dashed lines 83. The X-rays pass without deviation through a mirror 84. In 
connection with the X-ray tube there is also a light bulb, a so called 
light diaphragm 81, the beam of which will be directionally identical to 
the X-ray beam. 
FUNCTION 
FIGS. 9a and b show the lateral movement of the object holder 40. The 
movement is between two fixed extreme positions and the movement distance 
91 is thus known. The X-ray beam is shadowed in the figure and as the 
figures show the radiation is allowed to pass only through the hole 51 of 
5.times.5 cm.sup.2 size in the compression plate 50. By this procedure 
only half of the film medium will be used per exposure, while the other 
half is screened from radiation. The two images will be exposed on the 
same film. 
FIGS. 9a and 9b are drawn with the compression plate in its bottom 
position. 
FIG. 9c shows the X-ray film 92 after one exposure with the object holder 
in the right extreme position according to FIG. 9b. As shown in FIG. 9c, 
only the right half of the film will be exposed. Without changing film the 
object holder can now be moved to the left extreme position, as is shown 
in FIG. 9a, and the second exposure is made, thus allowing the left half 
of the film to be used for this exposure. FIG. 9c also shows how the 
millimeter markings 52 on the compression plate are seen at 93 on the 
exposed X-ray film. 
FIG. 10a shows the apparatus in the same position as in FIG. 9a, however 
the difference being that the compression plate is moved vertically to its 
top position (in reality 8 cm). Otherwise the conditions are the same as 
in FIG. 9a. FIG. 10b shows the X-ray film after an exposure with a setting 
as in FIG. 10a. As shown in FIG. 10b only the left half of the film is 
exposed. On comparing with FIG. 9c the exposed part of the film is larger. 
Exposing as in FIG. 10a results in exposing the left half of the film from 
the middle line to the outer edge. 
OPERATION 
With the aid of a previously made complete mammographic examination the 
suspicious lesion area 17 in the breast 16 is positioned within the image 
field, which is limited by the square hole 51 in the compression plate 50. 
In the image field is placed also the lead (Pb) indicator 65. 
In FIG. 11a the compression plate is transparent for didactic reasons. FIG. 
11a is viewed from above. The object (the breast) 16 is compressed by the 
compression plate 50. In the hole 51 the suspicious lesion 17 is placed. 
The needle director 60 is placed so that the indicator 65 lies within the 
image field. FIG. 11b shows the same as 11a with the difference that the 
compression plate is X-ray opaque. 
FIG. 11c shows the same situation as viewed from the front. The object 
holder is in the right extreme position. The X-ray beams passing through 
the indicator 65 and the lesion 17 are marked with lines 112 and 111 
respectively. The X-ray field is shaded as in FIG. 9b. FIG. 11d shows the 
exposed film in accordance with FIG. 11c. On the film the images of the 
lesion 113 and the indicator 114 are shown. 
FIGS. 12a and 12b show the practical operation. After placing the 
suspicious lesion 17 and the indicator 65 within the image field, as shown 
in FIG. 11, the first exposure is made in one extreme position. The object 
holder is then moved to the opposite extreme position while retaining the 
fixation of the breast, and a second exposure is made on the same film. 
The lateral movement 91 (referred to below as D.sub.F) is in reality only 
8 centimeters, and clinical tests have shown that the lateral movement can 
be performed without problems and without disturbing the fixation of the 
breast. 
FIG. 12a shows the exposure with the object holder in the left position 
with only significant rays being marked in the figure, i.e. the one 
through the lesion 121 and through the indicator 122. FIG. 12b shows the 
corresponding situation in the right position, with X-rays 111 through the 
lesion and 112 through the indicator. 
FIG. 13a shows the significant rays at exposures according to FIGS. 12a and 
12b (compare also FIGS. 14 to 19). FIG. 13b shows the X-ray film after the 
two exposures. 
The patient remains sitting with the breast under fixation, while the film 
cassette is removed and the film processed. The distances 131 (D.sub.T) 
and 132 (D.sub.I) are measured directly on the film. The penetration depth 
S from the steering hole 64 of the cannula director to the lesion can 
thereafter be directly read from a table which is based on the 
calculations below (FIG. 13c). The penetration depth is marked on the 
punction cannula with a sterile plastic tube of the correct length. By 
means of the last image exposed the x-y-coordinates are determined. (In 
this case the righthand picture, corresponding to FIG. 12b). 
The apparatus remains in the same position as for the last exposure, and 
the breast is still fixed. With the aid of the mm-markings 52 on the 
compression plate the hairline cross 62 on the cannula director is set to 
the correct x-y-coordinate in the light of the light diaphragm 81. The 
punction is then performed through the steering hole 64 in the direction 
of the light from the diaphragm to the correct depth, which thus is marked 
on the cannula. 
The whole procedure inclusive film developing, measuring and setting the 
penetration depth, measuring and setting x-y-coordinates etc takes only a 
few minutes, and the patient has no problem remaining seated with her 
breast fixed in the object holder during this time. 
MATHEMATICAL BACKGROUND 
In FIGS. 14a and 14b the aspects of FIGS. 12 and 13 have been combined and 
completed with symbols. The factual positions (marked x) of the lesion 17 
have been called Ta and Tb respectively, while the factual positions of 
the indicator have been called Ia and Ib respectively. Rays are marked as 
in the previous figures. 
FIG. 14b shows the X-ray film after both exposures as described in FIG. 12. 
In FIG. 12b the circumstances are identical with FIG. 11d, and on the film 
the lesion 113 and indicator 114 are imaged as in the right part of FIG. 
14b. In analogy, the images of the lesion and the indicator in the left 
part of FIG. 14b are called 123 and 124 respectively. The distance between 
the images of the lesion is called 131 (in the equations below D.sub.T) 
and the distance between the images of the indicator is called 132 (in the 
equations below D.sub.I). These distances 131 and 132 are measured 
directly on the film. 
FIG. 15 is similar to FIG. 14a, however magnified to twice the size, and 
the designations are as in the previous figures. The basis for 
calculations is the geometry of similar triangles. The following symbols 
are used in the equations and calculations: 
H.sub.T =level of focus over the lesion 
H.sub.I =level of focus over the indicator 
D.sub.T =distance between the images of the lesion (above called 131) 
D.sub.I =factual movement of the holder (above called 91). As the lesion 
and the indicator are moved together with the holder, also their factual 
movement=D.sub.F 
FFD=film-focus distance. 
FIG. 16 shows the triangle, also found in FIG. 15, with the corners 10, 113 
and 123. According to the law of similar triangles is obtained: 
##EQU1## 
FIG. 17 shows the triangle, also found in FIG. 15, with the corners 10, 114 
and 124. In analogy with FIG. 16 is obtained: 
##EQU2## 
The important distance is the one between the levels of indicator and 
lesion, which below is called S. It follows from FIG. 18 that 
EQU S=H.sub.T -H.sub.I 
in which equation the above obtained expressions for H.sub.T and H.sub.I 
are substituted: 
##EQU3## 
FFD is a known figure for any X-ray unit. D.sub.F is also known. These two 
figures can thus be combined to a constant K, specific for the apparatus. 
##EQU4## 
It can be noted that the punction is not made perpendicularly to the 
compression plate but in the direction of the beam from the light 
diaphragm. The punction channel is the hypotenuse in a 90 degree triangle 
in which the altitude is S. There is thus a slight discrepancy between the 
calculated S and the factual punction depth. FIG. 19 shows a lesion 17 and 
the 90 degree triangle in which the direction of the beam through the 
lesion is the hypotenuse 191 and the altitude S is the calculated punction 
depth. 
The circumstances for punction in FIG. 19 are at maximum disadvantage, due 
to a maximum distance between the compression plate and the base plate 
combined with a lesion situated near the base plate and near the edge of 
the image field. In such a case the difference between S and the punction 
channel (hypotenuse) will be &lt;2 millimeters. 
This extreme example can easily be avoided by compressing the breast in 
another direction. 
In normal circumstances the difference between S and the hypotenuse is not 
measurable, and thus clinically insignificant.