Gamma camera with an improved patient carrier bed

A gamma camera equipped with at least two radiation detectors inclined in relation to each other and a patient-carrier bed including a platform which includes a window that is more transparent to radiation than the rest of the platform. The platform includes two parts defining the window therebetween and connected to each other by a lateral arch.

Gamma camera with an improved patient-carrier bed. The subject of the 
present invention is a gamma camera with an improved patient-carrier bed. 
This invention can be used for nuclear medicine especially for 
cardiography and mammography examinations. 
Gamma cameras are radiography devices on which gamma radiations emitted by 
a patient or possibly X-rays emitted by a source and passing through the 
patient are measured. There are many types of devices very different from 
each other. We know of the existence of gamma cameras by patent U.S. Pat. 
No. 3,011,057. Gamma cameras can be of the multi-detector type. An example 
of two detectors can be found in patent EP-B-0 517 600. 
Conventional patient-carrier beds made of wood or composite materials (for 
example carbon fibre) and metal frames, used in known devices, are not 
completely transparent to gamma- or X-radiation. The disturbances 
generated by the bed platform during measurements may hinder certain 
examinations such as cardiac tomographies. Also, certain examinations such 
as mammographies require that the breasts of the patient be compressed as 
least as possible requiring the patient to lie on her back when it would 
be preferable to let the breasts hang. 
The aim of the invention is to overcome the above mentioned disadvantages 
with a solution in which a same patient-carrier bed platform will be used 
for the specific above mentioned examinations. 
With these objectives in mind, the subject of the invention is a gamma 
camera equipped with at least two radiation detectors inclined in relation 
to each other and a patient-carrier bed including a platform which 
includes a window more transparent to radiation than the rest of the 
platform. So that the window offers an examination field as large as 
possible, the platform of the bed includes two parts, connected by a 
lateral arch and defining between them the window. 
The device according to the invention is a gamma camera of known type, 
possessing several detectors, with a patient-carrier bed the platform of 
which has been subjected to certain modifications. The idea on which the 
invention is based was to remove a part of the hindering material from the 
patient-carrier bed platform to obtain a clearer image during a cardiac 
tomography where at least two images are taken simultaneously. Moreover, 
it is also very interesting to be able to let the breasts of the patient 
hang during a mammography. The bed could also be used for other types of 
examinations. 
In order not to hinder the patient or the movements of the gamma camera 
detectors, the arch is preferably curved, as will be explained later. 
Indeed, using two detectors simultaneously means that the position of each 
of the detectors must be simultaneously taken into account. No benefits 
are gained in having two detectors if one of them cannot be used or if it 
hinders the movements of the other detector. We will use an arch with a 
change in curvature in relation to a curvature of the platform at a 
certain distance from the lateral edge of the platform. 
Patients may have certain particularities, especially organs symmetrically 
inversed when compared with the majority of the population. An improvement 
consisting in making the arch removable so that it can be placed 
indifferently on either side of the platform makes the use of the patient 
carrier bed symmetrical. 
Examinations using gamma cameras are fairly long, some of them around 
thirty minutes, and the patients must remain completely still in order not 
to disturb the examination. Lack of support in the patient-carrier bed 
platform window area may therefore be a hindrance to the patient. The 
patient, not being at ease, may move therefore during the examination. 
Preferably, to reduce hindrance to the patient as far as possible, a sheet 
of material very transparent to radiation is added to the bed window. 
Other improvements concern the attachment method of the above mentioned 
sheet. 
For mammographies, it may be interesting to have a separate image of the 
two breasts of the patient. To this end, the bed can be equipped with a 
removable image separator. 
To stiffen the patient-carrier bed when installing the patient, to avoid 
distortions to the platform, it can be equipped with a removable 
reinforcement. 
The platform of the patient-carrier bed, according to the invention, does 
not however permit all types of examinations which are possible with a 
gamma camera. Rather than using two different beds, a removable bed 
platform system allows the platform to be easily changed keeping the same 
base and therefore allows costs and the size of the equipment to be 
limited.

FIG. 1 represents a gamma camera 1 including two detectors 2 and 3 which 
operate with a certain inclination in relation to each other. Detectors 2 
and 3 are carried by a stand 4 which turns around a patient-carrier bed 5. 
This patient-carrier bed 5, that can be seen in more detail on FIG. 2, 
includes a base 10 and a platform 11. 
Base 10 is telescopic and is equipped with means for movement. This 
provides platform 11 with complete freedom of movement in translation on 
the three axes X, Y and Z in space. Base 10 is also equipped with slaved 
motors controlled by the gamma camera 1. During the examination, the 
position of the platform is completely stable and controlled by gamma 
camera 1. 
Platform 11 includes a window 12 between a first part 13 and a second part 
14. An arch 15 connects first part 13 to second part 14. Second part 14 is 
designed to accommodate the upper part of the patient's trunk, shoulders 
and head, it can even include a rest for the arms when the patient is 
lying on his/her stomach. First part 13 supports the pelvis and the legs 
of the patient when stretched out. 
Platform 11 must be sufficiently stiff to support the weight of any person 
undergoing examinations, its dimensions are, for example, a total length 
of 2 m, a width of 0.4 m and a thickness of 0.04 m. For this purpose, the 
two parts 13 and 14 include high-strength metal frames 6 and 7, for 
example, rectangular section extrusions measuring 20 mm.times.50 mm placed 
longitudinally along the sides of the platform are suitable. These frames 
are embedded in a composite material shell, for example carbon fibre. 
First part 13 is 1.35 m long. Second part 14 is 0.3 m long. 
Connecting arch 15 extends beyond the lateral edge of patient-carrier bed 
5; this means, on the one hand, that there will no hindrance for the 
patient and, on the other hand, that an examination angle of more than 
270.degree. will be available around the patient's thorax. 
In order to obtain more freedom of movement for detectors 2 and 3 of gamma 
camera 1, arch 15 should be placed as near as possible to the patient. A 
trade-off imposes a certain curvature for arch 15 in relation to the plane 
of the bed to skirt round the patient as close as possible. For 
manufacturing reasons, an approximation of the curvature by multiple 
angles has been retained, this being represented on the section on FIG. 3. 
FIG. 3 shows a preferred dual angle with, in dotted lines, positions A, B 
and C taken by the detector during the possible movements. 
As the arch is submitted to high torsional stresses, it preferably consists 
of two bars 16 and 17, for example of rectangular section, measuring 
20.times.50 mm, which are attached together by one end to a first arm 26 
and by the other end to a second arm 27, by mechanical welding. The first 
arm 26 is securely attached to first part 13. The second arm 27 is 
securely attached to second part 14. 
Certain persons have the particularity of having their heart on the right 
whereas most persons have them on the left. This is why the possibility of 
having a removable arch 15 which can be installed both on the right and 
the left of the platform is provided to reduce imaging hindrance to a 
minimum. For this, the two arms 26 and 27 can slide in two slides 36 and 
37. The first slide 36 is attached by mechanical welding to first part 13. 
The second slide 37 is attached by mechanical welding to second part 14. 
The fits between the two arms 26 and 27 and the two slides 36 and 37 are 
especially accurate to allow easy installation and retention in a stable 
position. A safety pin, not shown, holds the arch in position. 
Window 12 is more transparent to gamma radiation than the rest of the 
platform. In one example, there is only air in the radiation trajectory 
between the patient and the detector. But, for cardiac tomographies, 
examination times are fairly long. It is advisable to support the patient 
to avoid fatigue, discomfort and therefore movement. To this end, we place 
a sheet 20 made of a material very transparent to gamma- and X-radiation, 
preferably tensioned, in this window. We can, for example, use a sheet of 
polyester film marketed under the trademark Mylar. 
The weight of the patients and the installation-removal of this sheet may 
cause it to distort. To remedy this, a tensioning system compensates for 
sheet distortion. 
For example, the tensioning system represented on FIG. 4a includes an 
attaching item 18, attaching first part 13 and a straight L-shaped bar 19. 
This L-shaped bar 19, perpendicular to the longitudinal direction of 
patient-carrier bed 5, is used to attach, by overlapping and clamping, 
sheet 20 on one of its sides to first part 13. The other side of sheet 20 
is attached to second part 14, by clamping, using a straight U-shaped bar 
21. This U-shaped bar 21 sliding longitudinally to patient-carrier bed 5 
on second part 14 includes a hole 28 to accommodate screw 22 which passes 
through second part 14. The end of screw 22 which protrudes from second 
part 14 is screwed into a wheel 23 to tighten and tension sheet 20. 
It is also possible to replace this tensioning system by a movable frame 
system 30, represented on FIG. 4b, that a man of the trade could define 
himself in a material as transparent to gamma radiation as the sheet which 
covers the window. This removable frame 30 consists of a rectangular frame 
with dimensions same as the window and bears on the platform on each side 
of the window. A sheet 20 is attached to the upper face of the frame by 
means of suitable fasteners. The use of such a frame makes utilisation 
easier as it can be held simply by gravity or be installed on slides 
between first part 13 and second part 14. A frame tensioning system can 
also be considered for the above mentioned reasons. 
If one wishes to conduct a mammography with the breasts hanging, the image 
of one breast may show interference caused by the other breast. To improve 
the possibilities of the system, a separator 24, represented on FIG. 5, 
can be added perpendicularly to the platform plane. This mammary image 
separator 24 isolates the radiation of each of the breasts. This separator 
24 is attached between first part 13 and second part 14 using the same 
attaching means as that of sheet 20. For the sheet 20 tensioning system, 
we will use the tensioner to hold separator 24 in position. For attachment 
of sheet 20 by removable frame 30, another frame must be provided to carry 
this separator 24 that will be used for mammographies. This other frame 
can be made from any material provided that it has a hole on each side of 
separator 24 allowing the patient's breasts to pass. This separator 24 
consists of a plate of a material very opaque to gamma rays; lead, 
tungsten or gold are suitable. This separator 24 must not protrude beyond 
the upper part of platform 11 in order not to injure the patient's body. 
For hygiene and cleanliness reasons, separator 24 will be padded and even 
covered by a hypoallergenic material. 
When the patient is being installed on the patient-carrier bed, kinetic 
distortions may damage arch 15 which is normally designed to support 
static distortions. This is why a removable reinforcement 25 is placed on 
the side opposite arch 15 between first part 13 and second part 14 to 
stiffen platform 11 during the installation of the patient. The 
attachments of this removable reinforcement 25 are of same type as those 
of removable arch 15. It uses the same slides 36 and 37 and a safety 
position retention safety device by a pin same as that of arch 15. Thus, 
irrespective of the choice made concerning position of arch 15 in relation 
to platform 11, removable reinforcement 25 can be used on the edge 
opposite platform 11. The removable reinforcement 25 is removed to conduct 
the examinations in order not to disturb the detectors. 
Other examinations require patient-carrier beds with other features. The 
complete patient-carrier bed 5 is relatively costly and large, it is 
therefore beneficial to be able to conserve the same base and use a 
removable platform 11. Removability of platform 11 must be ensured in a 
safe and rapid manner. The inventor has therefore imagined the slide 
system represented on FIGS. 6, 7, 8, 9. 
FIG. 6 shows a top view of patient-carrier bed 5. We can see platform 11 
attached to base 10 by means of an attaching lug 40 and a pin 41. FIG. 7 
shows the platform detached from the base. An attaching rail 43 is added 
to this attaching lug 40. This attaching rail 43 includes a first shoulder 
44, located around one quarter of the way along the length of attaching 
rail 43, a first hole 42, and a tab 45. Tab 45 is located on the side 
opposite platform 11 and extends upwards. The first shoulder 44 causes on 
an end of attaching rail 43 a thickness lower than the rest of the 
attaching rail 43. 
Base 10 includes a third slide 46 with a profile reflecting attaching rail 
43 as can be seen on FIGS. 8 and 9. This third slide 46 includes a second 
shoulder 47, a slot 48 at the bottom of the third slide 46, and a second 
hole 49 which aligns with the first hole 42 when attaching rail 43 is 
positioned in the third slide 46. 
To assemble platform 11 and base 10, we slide attaching rail 43 in the 
third slide 46. The first shoulder 44 and the second shoulder 47 define a 
press fit area. When platform 11 is installed, three quarters of attaching 
rail 43 are easily inserted into the third slide 46, the last quarter 
requires higher thrust, for example 10 kg of thrust, this ensures 
retention of platform 11 in position by friction. When shoulders 44 and 47 
bear on each other, the platform is in utilisation position. Tab 45 which 
fits into groove 48 prevents platform 11 from being torn out by the weight 
of the patient. Pin 41 which fits into the first hole 42 and the second 
hole 49 is a safety device preventing attaching rail 43 from sliding in 
the third slide 46 throughout the examination.