Apparatus for transmitting signals

In the exemplary embodiments, a ring made of light-conductive material curved around the center of rotation is provided, onto the surface of which a light source radiates, which emits light signals corresponding to the signals to be transmitted. The light-conductive ring is formed in such a manner that it passes on the incident light over its entire periphery and has at least one point of interruption on which a light receiver is arranged. The invention is particularly suited for use in a computer-tomograph, in which an x-ray source and a detector for scanning the radiography subject at different projections rotate around the radiography subject, and data processing equipment determine an image of the examined transverse layer of the radiography subject from the detector signals. In this case the light-conductive ring can transmit the detector signals to the stationary part.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for transmitting signals between a 
rotating and a stationary part. 
An apparatus of this kind is desirable for example in an x-ray examination 
device in which case the patient is scanned by means of a measuring 
arrangement consisting of an x-ray tube and a radiation detector at 
different projections and the attenuation coefficients of the examined 
layer of the patient are determined from the output signals of the 
detector. In a computer-tomograph of this kind, the examination time is 
determined essentially by the scanning time of the measuring arrangement. 
It is known to revolve the measuring arrangement by an angle of 
360.degree. around the patient for a scanning procedure and subsequently 
to return it to its starting position for the next scanning procedure. In 
this case the detector can be connected to the electronics which process 
the measured values by way of cables. However the times required for 
accelerating the measuring arrangement limit the scanning time. It would 
be possible to shorten the scanning time if the measuring arrangement were 
to rotate continuously. In this case cables would no longer have to be 
used for the x-ray tube or the detector for the purpose of supplying 
current or removing signals respectively. The supply to the x-ray tube can 
take place for example by way of slip rings. However in this case neither 
slip rings nor inductive transformers can be considered for detecting the 
signals of the detector because of the high data rate and the requisite 
freedom from interference. In order to economize on the expensive 
temporary memory on the rotating part, the data transmission must take 
place at least exactly as quickly as the data collection. Hence very high 
speeds of approximately one to thirty megabits per second (1 to 30 
mbit/sec) are suitable. 
SUMMARY OF THE INVENTION 
The object of the invention is to produce an apparatus of the type 
mentioned in the introduction which allows data to be transmitted in an 
extremely short time in an interference- and contact-free manner. 
This object is achieved according to the invention by means of a ring made 
of light-conductive material curved around the center of rotation, onto 
the surface of which a light source radiates, which emits corresponding 
light signals to the signals to be transmitted, said ring being formed in 
such a manner that it passes on the incident light over its entire 
periphery and has at least one coupling point at which a light receiver is 
arranged. An object can be inserted thereby into the ring without 
disturbing the data transmission. Therefore the apparatus is particularly 
suited to data transmission in a computer-tomograph of the type mentioned 
in the introduction, in which case the ring encloses the patient. It can 
remain stationary thereby while the data from the detector is transmitted 
by way of the light source in the form of light pulses. The reverse case 
is also possible, i.e. a stationary light source and a rotating ring with 
rotating light receiver for transmitting data to a rotating part, i.e. to 
the rotating x-ray tube of a computer-tomograph. 
Details of the invention are to be found in the subclaims. 
The invention is explained in greater detail as follows in conjunction with 
some exemplary embodiments represented in the drawings; and other objects, 
features and advantages will be apparent from this detailed disclosure and 
from the appended claims.

DETAILED DESCRIPTION 
FIG. 1 shows an x-ray diagnostic unit for producing transverse layer images 
of a patient 1, a so-called computer-tomograph. The apparatus has a 
rotatable support 3 in a frame 2, said support being rotatable about an 
axis 5 running perpendicular to the plane of the drawing by means of a 
motor 4. An x-ray tube 7 and a detector 8 for x-ray radiation are provided 
for scanning the patient 1 lying on a support 6. The x-ray tube 7 emits a 
fan-shaped x-ray radiation beam 9, the extent of which is chosen so that 
the entire transverse layer of the patient 1 which is to be examined is 
penetrated by x-ray radiation. The thickness of the x-ray radiation beam 9 
perpendicular to the plane of the layer is equal to the thickness of the 
layer, i.e. a few millimeters. 
In order to scan the patient 1, the measuring arrangement, consisting of 
x-ray tube 7 and detector 8 is rotated about the patient 1 by an angle of 
approximately 360.degree. and at predetermined projections, e.g. at each 
angular degree a set of output signals of the detector 8 is read. The 
detector 8 consists of a series of single detectors, e.g. 256 single 
detectors, so that for example 256 signals of the detector 8 are read per 
projection and for example 360.times.256 signals are available for 
processing per scanning procedure. The signals are transmitted in the 
manner described in greater detail hereinafter to a stationary data 
processing device 10 which determines from these the attenuation values of 
predetermined points in the examined transverse layer of the patient 1 in 
the form of a matrix and effects the image reproduction on a monitor 11. 
A stationary ring 12 made of light-conductive material, e.g. synthetic 
glass, curved around the axis of rotation 5, is provided for transmitting 
the detector signals, onto the surface of which a light source 13 radiates 
by way of optics 14. The light source 13 is connected to a modulation 
stage 15, which converts the detector signals into sequential 
light-producing signals. A pulse spacing coding can be used thereby for 
example. The ring 12 is formed in such a manner that the light from the 
light source 13 is passed on over its entire periphery. It has a gap 16 
and a light receiver 17, which converts the light signals into electrical 
signals again, is arranged on one of the faces bordering the gap. These 
signals are demodulated in a demodulator stage 18 and are supplied to the 
data processing device 10. The signal transmission takes place thereby 
during a projection in a consecutive manner, this means the detector 
signals of the single detectors are transmitted consecutively by means of 
the described apparatus. The light source 13 can for example be a 
luminescence or a laser diode working in the infrared area. The modulated 
stage 15, the light source 13 and the optics 14 rotate with the measuring 
arrangement 7, 8 while the patient is being scanned, whereas the 
structural elements 12, 17, 18, 10, 11 are stationary during the scanning 
procedure. Consequently a contact-free signal transmission takes place 
from a rotating part to a stationary part and the speed of rotation of the 
rotating part, i.e. of the rotatable support 3, can be selected to be at a 
very high level. In particular it is possible to allow the rotatable 
support 3 to rotate continuously with a great number of rotations per 
minute and to make a radiograph when required during an angle of rotation 
of approximately 360.degree.. 
In FIG. 2 the system for optical signal transmission is clearly delineated 
again in two views which are taken perpendicular to each other. It may be 
seen from FIG. 2A that the ring 12 is provided on its inside with steps 19 
which extend over its entire periphery and cause a reflection of light so 
that the light of the light source 1 disperses uniformly over the entire 
periphery of the ring 12. Data transmission from the stationary part to 
the rotating part can also be realized with an apparatus according to FIG. 
2. This transmission can be important for example for the triggering of 
the x-ray tube 7 which is supplied from a generator 20, the changing of 
collimators for the x-ray tube 7, the control of the measuring 
electronics, etc. In this case the ring 12 is arranged with the receiver 
17 on the rotating part, and the light source 13 with the optics 14 is 
arranged in a stationary manner. 
In the described computer-tomograph the x-ray tube 7 rotates, so that it 
cannot be connected directly to the generator 20 by cable. Rotating 
transmission means, e.g. slip rings, must be provided in this case. 
The ring 12 is almost closed. Data transmission cannot take place only in 
the area in which the light receiver 17 is accommodated. It must be 
ensured with electronic means that the transmission discontinues in this 
place and that the measured value is not lost. 
The optics 14 needs to concentrate the light only in a plane which passes 
through the axis 5. Therefore they can be formed from a cylindrical lens. 
FIG. 3 shows a ring 21 which is formed in a slightly spiral manner, so that 
the two ring ends lie at the point of interruption on different radii but 
in a common plane. The light receiver 17 is arranged on the face of a ring 
end in this case also. The two ring ends overlap a little, so that the 
complete range of 360.degree. can be utilized for the detection and 
transmission of measured values. 
In the example according to FIG. 4 the ring is formed from two halves 22, 
23 which are radially displaced relative to each other approximately by 
the width of the ring. A light receiver 17a, 17b is coupled respectively 
on one end in each case of a ring half on the face. A demodulator 18a, 18b 
is allocated respectively to each light receiver 17a, 17b. The ends of the 
ring halves overlap slightly in this case also. FIG. 4 is based on the 
concept that the rate of data to be transmitted by means of the pulse 
expansion of the light signals during the transmission is limited by the 
length of the light-conductive ring or ring part respectively. Therefore 
this length determines the rate of data which can be transmitted. 
Consequently the ring must be divided into two or even more parts for very 
high rates of data. Accordingly many receivers are provided. Any loss of 
data is prevented here also in that the parts of the ring are alternately 
radially displaced and arranged so that they overlap. 
In the exemplary embodiment according to FIG. 5 the point of interruption 
of a ring 24 forms a gap 25 penetrating the ring 24 obliquely at an angle 
different from 90.degree.. The face 26 provides for a deflection of the 
light and optics 27 supply the deflected light to the light receiver 17. 
Any loss of data is prevented here also because of the oblique arrangement 
of the gap 25. 
In a modification of the exemplary embodiments a light-conductive cable, 
which for example may be flexible, can also be coupled to the respective 
faces of the light-conductive ring, said cable transmitting the light from 
the light-conductive ring to the receiver. 
In the exemplary embodiments the steps 19 of course extend over the entire 
inner surface of the ring. They are shown in the drawing only over a part 
of this inner surface for the sake of simplicity. 
In the case that the signal transmission takes place from a stationary part 
to the x-ray tube 7 for its control, the detector 8 of course rotates with 
the x-ray tube 7. The light source 13 is controlled thereby not by the 
signals of the detector but by a control stage for the x-ray tube 7. The 
light receiver corotating with the ring and the measuring arrangement 
controls the x-ray tube by way of control circuit stages. 
It will be apparent that many modifications and variations may be effected 
without departing from the scope of the novel concepts and teachings of 
the present invention.