Note: Descriptions are shown in the official language in which they were submitted.
-
Descr~tion
11~95~4
Technical Field
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- Th~ invention relates to an improved apparatus
for supplying electrical power to orbital elements
of a computed tomography scanning unit.
sBackground Art
The art of computed tomography (CT) scanning
; has greatly improved a physician's ability to acurately
diagnose the internal structure of a patient. The
process of CT scanning involves the sending of X
radiation through a patient from a variety oE different
locations, and determining the intensity oE the
transmitted radiation with one or more X-ray detectors.
Intensity data is sent to imaging electronics for
image reconstruction. In many studies, the image
viewed by the doctor presents greater detail than
conventional X-ray techniques and therefore can be
better used to diagnose the patient's condition.
; In a typical computed tomography scanning environ-
; m~nt, an X-ray source is orbited about a patient
20while the patient is irradiated. The detector or
d~tectors either orbit with tbe source or form a
non orbiting array of detecting units. In either
configuration a substantial amount of X-ray emitting
and shaping apparatus rotates with the X-ray source.
25This apparatus as well as the X-ray source must be
powered by electrical energy supplied from a source
- exterior to the rotating CT apparatus.
One particular computed tomography scanning
unit includes an orbiting source of X radiation which
30emits an X-ray beam in a spread configuration. The
detector units are stationary relative to the X-ray
source and form an annular ring of detectors about
the patient. The X radiation source is positioned
to transmit X-rays through the patient along a series
35Of beam paths as it is orbited. Since a variety
of beam generating, shaping and transmitting functions
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must be performed on the orbiting apparatus as orbiting
occurs, a num~er of electricaI signals must be supplied
to tbis apparatus.
- To create X-~adiation, a large potential diEference
5 on the order of 150 kilovolts must be provided.
This voltage is used to accelerate electrons from
an X-ray tube cathode to an anode for X radiation
generation. Typically a filament voltage and an
X-ray focusing cup control are required so that a
10 number of high voltage inputs are necessary. Providing
these high voltage potential differences to the
X radiation source creates design problems which
have in the past required sophisticated cabling and
input techniques.
A number of low voltage control and energization
signals must also be transmitted to the orbiting
apparatus. It is known that the X-ray tube tends
to heat up due to the collisions of the accelerated
electrons with the X-ray anode and to dissipate the
20 heat build up some CT units require tbat the X-ray
anode be continuously rotated. A motor, which typically
requires at least two and possibly three leads,
provides this rotational cooling.
In order that the beam produced by the X radiation
25 tube occupies the proper dimensions, it is necessary
that the X radiation be collimated. A collimator
is therefore mounted to orbit with the x-ray tube.
The collimator includes an adjustment motor which
is powered by an external source of energy.
Control solenoids and a laser source to aid
in patient positioning also orbit the patient and
receive power from a stationary power source. Actuation
of the solenoids is achieved via command signals
which are also transmitted to the orbiting apparatus.
35 Since these various functions must be coordinated
to produce the proper X-ray transmission and shaping,
a clocking signal must also be sent to the orbiting
apparatus.
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~ lt'hb~h most of the detectors on the descr,ibed CT
apparatus are stationary, one orbitinq de'cector is in-
cIuded which is u~ed to calibrate the X radiation and
provide a reference signal. This orbiting detector
5 requires ener~i~ation from a stationary source ~nd pro-
vides an O~ltput signal which musc also pass through
cabling ~hich leads from the orbiting appara-tus to non-
rotating'elements, namely imaging elec-tronics.
Present state of the art CT scanning units provide
, 10 the requisite ~abling inputs to the rotating portions
i of the CT unit through rather sophisticated cable takeup
mechanisms. Although such cable takeup mechanism have
been used successfully they are limited in applicability
by certain design disadvantages.
One such cable takeup mechanism includes a flex-
ible cable of finite length which is woLlnd and unwouncl
from a mandrel as the CT unit causes the X-ray tube to
orbit. A CT unit employing such a mechanism can only
be rotated a finite amount before its direction of rota-
' 20 tion must be reversed. Such a reversal in direction
introduces a complexity in controlling the rotation of
the CT unit. Moreover, at leas~c one proposed diagnostic
procedure has not been generally adopted by clinicians
because of this limitation. That procedure would syn-
2~ chronise CT X-ray tube energization during a heart study
with heart movement through con-'crol signals generated
; by an EI~G machine. The problem has been the cyclical
rever~al of orbital mo~tion is too apt to occur when the
X-ray tube should be energized.
A certain amount of power is expended in moving
the cable during CT unit rocation. This adcl-~d power
expenditu-e limits scanning speed and may add a non-
uniformi~y oE rotation dllring an X~ray exposure.
~laintenancA of the cables i5 perhaps the most
35 disadvant~geous feature of the cable takeup energiza-
tion method. Constant f:lexing of the cable even
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with the tak~-up mechanism previously described may
~entu~lly cause it to crack or break so that it
must perlo~icc~lly be replaced.
To overco~.e some disadvantages noted with regarcls
5 to the ca~le take~up mechanisms, a slip ring t~pe of
power transferral has been suggested. The suggest~d
s:lip ring arrangement, however, has not completely
solved the problems inherent with prior mechanisms
and may n~t ade~uately ins~late -the hiyh voltage
10 poten~ia~s required for CT scanning. The arrangement
disclos.es only one slip ring for prov;ding power
while from the above it is appar-ent that a number
of high power inputs are necessary.
More CT sc2nning in~ormation is available if
1~ the plane in which the pa.ient lies can be tilte~
wi.h res~ect to the X-ray bea~ plane. Due to the
siæe and configuration of prior art CT slip rings~
tlle e~amination oE the patient and the orbital axis
could not be changed relatively. Thus, additional
2~ information was available only i~ the patient were
shifted laterally with respect to the X-ray beam
plane. It is there~ore apparent tha-t suggested slip
ring power arrangements have inadequacely dealt with
the power transmittal problems in prior art cable
25 take-up mechanisms
Disclosure of Invention
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The present invention provides a unified, compact,
slip-ring arrangement for transmitting electrical
energ~ to orbiting components in a CT scanning unit.
30 The slip-ring arran~ement is completely immersed
in an insulating fluid ade~uately to insulate the
high X-ray generating voltages ~rom the est o~ the
unit. A plurality of ~otll high and low voltage slip
rings are provided to genera-te, calibrate and shape
35 the X radiation.
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One embodiment of the invention includes a station-
ary gantry apparatus to which an orbiting assembly
is mounted for orbital rotation about a scanning
axis coincident with a patient axis. An X-ray source
5 powered by a high voltage input is attached to the
: assembly and irradiates a patient for reconstruction
imaging. The source generates X radiation which
is collimated into beams beLore traversing the patient.
The radiation impinges upon an array of X-ray detectors
10 ~hich can either be non orbital or movable with the
source.
Both high and low electrical potential is provided
to the rotating assembly by the present design.
A high voltage input receptacle is mounted to the
15 gantry for receiving a high electrical input. The
high ~lectrical input is transmitted to the orbitally
rota~ing portion of the assembly by means of a connec-
tion technique which includes spring loaded brushes
i attached to the orbitally stationary gantry and a
number of annularly shaped slip-rings attached to
the rotating assembly. The brushes are maintained
in contact with the slip rings to insure there exists
a low resistance path from the input receptacle to
the rotating assembly. Attached to the slip ring
is a transmission line for coupling the hi~h input
potential to the X-ray source. By means of this
arrangement, a high electrical potential is transmitted
to the orbiting ,Y-ray source without the use of a
complex cable takeup arrangement.
In the preferred embodiment o~ the invention,
a number o~ high voltage rotating slip rings are
electrically coupled via brushes to stationary high
voltage input receptacles. Multiple focus X-ray
tubes with grid potential control require multiple
high potential voltage inputs so that apparatus
embodying the invention utilizes four orbitally
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rotating hig~ voltage slip rings. The apparatus
further includes a plurality of low input 51ip rings
for transmitting -low input voltages from the stationary
gantry to the orhiting assembly. This configuration
5 provides the CT user significant design flexibilit~
in sending power and control signals to the orbiting
assembly.
In this embodiment the orbiting and nonrotating
portions of the CT scanning unit are configured to
10 define a cavity surrounding the high voltage input
slip rings. This cavity is filled with an insulating
dielectric fluid which completely surrounds the high
volcage slip ring and brush arrangement to effectively
insulate the high potential passing through the slip
15 ring from the rest of the CT unit. In this way
arcing from the high poten-tial slip ring to electrical
ground does not occur. Seals are provided to prevent
- leakage o~ the dielectric fluid from the CT unit
thereby maintaining the insulating fluid in contact
20 with the entire slip ring. Only the high potential
slip ring arrangements are insulated since the low
potential slip rings carry low power current and
present no arcing danger.
The length along the axial dimension of the
25 CT unit embodying the improved high voltage slip-
ring arrangement is short. This compact design
allows the unit to be tilted about an axis transverse
to the scanning axis by approximately 20 and allows
the patient to be scanned in planes other than a
30 vertical cross section.
From the above, it is apparent that one feature
and object of the present invention is to provide
a simplified~ compact and safely insulated brush
and slip-ring arrangement for providing both high
35 and low power to orbiting components of a CT scanning
unit. A second advantage of the invention is to
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provide a number of slip-rings thereby providing
CT unit design flexibility. The compact nature of
the apparatus allows the slip-ring arrangement to
he tilted so the orbiting X-ray tube can transmit
S radiation across non-vertical sross sections.
These and other features and advantages oE the
invention will become more apparent as the invention
- becomes better understood from the detailed description
that follows, when considered in conjunction with
10 the accompanying drawings.
Brief_Description of the Drawings
FIGURE 1 shows schematically the elements com-
prising a CT scanning arrangement.
j FIGURE 2 schematically shows a source of X-rays
15 positioned to irradiate a patient cross section.
FI~URE 3A shows a front elevational view of
elements of a CT scanner.
FIGURE 3B shows a partially sectioned view of
the CT scanner shown in Figure 3A.
FIGURE 4 is an enlarged cross sectional view
of a portion of the scanner shown in Figure 3B.
FIGURE 4A shows a further enlarged part of the
cross sectional portion shown in Figure 4.
FIGURES 5A-5C sho~ wiring schematics for high
25 voltage energization of a CT X-ray tube.
Best Mode for Carrying Out the Invention
Referring now to the drawings and Figure 1 in
particular, a computed tomography system 10 designed
for examining the internal structure of a patient
30 is shown. The system comprises a scanning unit 12,
a couch 16, a signal processor ~0, and imager 22.
The scanning unit includes a housing 13 which covers
the X-ray apparatus and provides an attractive appear-
ance to the unit. Before a CT scan the couch 16
35 and a patient lying on the couch are moved into an
aperture 14 in the housing 13. An X-ray tube within
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the unit is energized and transmits X radiation,
thereby irradiating the patien~.
The scanning unit 12 can be tilted about an
axis 24 parallel to the floor. This movement provides
5 a flexibility in scanning without repositioning of
the patient. Two support columns 23 mount the unit
12 for rotation about the axis 24. Rotational motion
is applied by an AC motor 25, a right angle drive
;; 2~, and a pivot arm 27.
A series of X-ray detectors detect X-ray intensity
af.er it passes through the patient and produce
electrical signals in response to the radiation.
These electronic signals representing patient densities
are sent from the scanning unit to the signal processor
15 20 by an electrical connection 15. The signal processor
receives these signals and utlliæes known CT processing
; techniques to produce signals representing the varia-
~ tions in patient density across a patient cross
; section. The signal processor then sends signals
20 to an imager 22 which provides an image o~ the patient.
Figure 2 schematically illustrates a CT X-ray
source 30 and array of detectors 32 positioned about
the patient aperture 14. The source 30 emits a
spread of X radiation which passes through a collimator
25 34 which shapes the X radiation into a number of
individual beams. One X-ray beam 33 is shown as
it passes through the patient aperture and impinges
upon a detector in the circular array 32 of X radiation
detectors. The illustrated detectors are shown
30 positioned on the side of the patient aperture opposed
from the source 30 and therefore certain of them
detect radiation intensity a~ter that radiation has
passed through the patient.
Although the Figure 2 -illustration shows a finite
35 num~er of detectors, so-called "stationary detector"
CT designs provide an array of detectors which com-
pletely surround the patient aperture. Thus, it
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is possible for the~X radiation detectors to remai
stationary while the X radiation source 30 orbits
about the patient~ aperture irradiating the patient
from a number of different positions. The detec~ors
5 are of a known design and convert X radiation into
an electrical signal whose outputs can be sen-t to
the signal processor 20 ~or CT image formation.
All CT reconstruction algorithims require that
the X radiation impinge upon the patient cross section
10 from a number of different positions so that intensity
data from radiation originating ~rom various positions
is obtained. By obtaining this multi-position intensity
data it is possible to reconstruct a mapping or image
of the density variations within the patient cross
15 section. To achieve this mul-ti~position irradiation
the present invention includes a rotating assembly
which supports the X-ray source 30 and is movable
relative to the X-ray detector array 3~.
Movement of the X-ray source in a circular path
20 causes electrical energization problems which are
compounded by the high voltage potential differences
coupled to the X-ray tube.
Figures 3A and 3B illustrate a new and improved
CT apparatus which facilitates the sending of potential
25 differences to the X-ray source for X-ray generation.
The CT apparatus shown includes a stationary gantry
arrangement 40, a rotating assembly 42 and an X-ray
tube housing 44. During operation a belt drive 48
causes the rotating assembly 42 to rotate within
30 the stationary gantry 40 thereby irradiating a patient
cross section of interest from a number of different
positions. The rotating assembly comprises a frame
50 attached to an annular portion of the assembly
by eight connectors 43 (See Figure 3A) spaced evenly
35 about the patient aperture 14. The frame 50 carries
the X-ray housing 44 Eor orbital rotation about the
patient aperture 14.
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One aspect of the invention is ~he provision
of high potential differences ~o the ca~hode and
anode of the X-ray tube. In one embodiment of the
invention the potential difference between cathode
5 and anode is on the order of 150,000 volts. This
potential difference is provided by a positive and
negative input each on the order of 75,000 volts
removed from ground. To transmit electrical energy
to the X-ray tube the stationary gantry 40 includes
1~ both a positive 46 and negative 47 high voltage
electrical receptacle or connector. The positive
voltage receptacle 46 shown ~n Figure 3B receives
a voltage input of plus 75,000 volts from an external
voltage source. The negative high voltage receptacle
~not shown in Figure 3B) receives an input voltage
of approximately 75 t 000 negative volts.
The assembly further comprises a positive 56
and negative 58 slip ring portion which receive these
high voltage inputs and transmit a high voltage
20 differential from the stationary gantry portion 40
to the rotating assembly 42 for transmittal to the
X-ray tu~e. The first positive portion 56 includes
only one slip ring which is coupled to the positive
receptacle 46. The second negative portion 58 includes
25 four slip rings and is designed to receive more than
one negative high voltage inputO The purpose of
- this multiplicity in high voltage slip ring configura- -
t~on is to allow control of the X radiation generation
by utilization of either multiple focus or grid
30 potential voltage inputs.
After the high voltage potential is transmitted
to the rotating assembly 42 it is further transmitted
along cabling (shown in Fiyure 4 as reference numeral
120) to two high voltage receptacles 60, 62 mounted
35 to the frame 50. A first receptacle 60 receives
the positive voltage and a second receptacle 62 receives
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the ne~ati~e high vQl~age potentia7 inputs. Frcm
these receptacles the high voltage is transmitted
to the anode (positive) and cathode (negative) of
the rotating X-ray tube.
The gantry is attached to a support 52 radially
removed from the patient aperture by means oE suitable
connectors 54 such as a nut and bolt arrangement.
This mounting serves to maintain the stationary
gantry 40 in position while allowing the support
10 52 to be tilted about an axis perpendicular to the
axis of CT scanning 36. If the support 52 is tilted
while the patient maintained in a horizontal position
the X radiation will traverse the patient aperture
at a non vertical angle and thereby provide flexibility
. 15 in CT scanning. If, for example, the support 52
is tilted 20 about an axis perpendicular to the
scan axis 36 the cross section of patient irradiation '
will also be tilted 2~ to the vertical.
The geometrical configuration of the frame 50
20 and X-ray housing 44 is such that the rotating assembly
42 is well balanced about the scan axis 36. The
frame 50 is much wider at a side 51 opposed from
the X-ray housing and this width counterbalances
the weight of the X-ray housing and enclosed tube
25 and provides a symmetrical mass distribution about
; the axis 36.
The stationary gantry 40 supports the rotating
assembly 42 along an annular bearing connection 64,
Figure 4 which allows free orbital rotation of the
30 assembly a~ about the axis 36. rhe compact design
of the apparatus allows one bearing to provide sufficient
support to the rotating assembly~
It is important in CT scanning that the position
of the X-ray tube be precisely known during all times
35 of an X-ray exposure. For this reason, an encoder
66 in the form of an annular ring is a-~tachecl to
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the rotating-assemblg ~. rrhis encoder 66 insludes
- a number of marks equally spaced about the ring which
indicate the angular orientation of the encoder.
As the annular ring moves a~out the center axls an
5 optical encoder 67 determines the posi~ion of the
ring relative to the stationary gantry 40. In this
way the precise position of ~the X~ray source can
be de~ermined at all times cluring irradiation of
the patient. Th;s position data is correlated with
lO intensity readings from the X-ray detector array
and utilized in reconstruction algorithms ~nown
within the art.
Figures 5A-C illustrate three di~ferent X-ray
tube input configurations for energization of an
15 X-ray tube. Each con~iyuration shows an anode 70
and a cathode 72 coupled to energi2ation inputs.
A series of these high voltage energiza~ion inpu~s
74 are shown transmitting potential differences to
the tu~e.
In a single focus X-ray tube (See Figure 5A)
three high voltage inputs are needed. A first input
76 is the positive input to th~ X-ray anode and in
the preferred embodiment of the invention is input
through a first positive p~rtion 56 of the slip ring
25 arrangement. Two negative inputs 78, 80 are used
.o energize the cathode 72 and in the preferred
embodiment are transmitted via the secon~ portion
58 of the slip ring arrangement. A transformer 82
supplies a filament current which causes electrons
30 84 to be emitted thermionically from the cathode
for acceleration towards the high potential anode
70.
Figure 5B illustrates a double focus X-ray tube.
Three negative high voltage inputs 86-88 are transmitted
35 to the X-ray tube cathocle 7~. Through control of
the voltages appearing on a primary oE the transformer
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82, i-t i8 pos~:Lble~ to con~rol the high voltage inputs
86-B8 and pLo-vide a measure of x radiation control
unavailable on the single focus tube.
An X-ray tube which includes a grid con~rol
5 is illustrated in Figure 5C. This tube includes
a high voltage positive input 76 and three high
voltage negative inputs 90-92. Two inputs 30, 91
transmit a voltage appearing across the secondary
of the transformer 82. A third input 92 ser~es to
10 maintain a control voltage on a grid 94 within the
X-ray tube. Through adjustment oE grid tube potential
a means oE control over electron transmittal to the
anode unavailable in the single focus tube is provide~.
From the illustrations in Figures 5A-5C it is
15 apparent that a plurality of high voltage negative
inputs must be available if single focus, double
focus and grid X-ray tube control is to be achieved.
The second negative portion 58 of the 51ip ring
arrangement (See Figure 3B) includes a plurality
20 f 51ip rings for t~is purpose. In the preferr~d
embodiment four slip rings are included to provide
flexibility in CT scanner design. The volta~e inputs
to these slip rings are ~t many thousands of volts
below ground but are each separated by relatively
25 low voltag~s. In a single focus X-ray tube configura-
tion, for example, the voltage separation between
the two inputs 78, 80 need only be l~rge enough to
cause a filament current to flow in the X-ray tube
cathode.
Fisure 4 shows a more detailed cross sectional
view of the slip ring arrangement shown in Figure
3B. That figure illustrates the X-ray tube housing
44, the rotating assembly 42 mounted by the bearing
64 inside the stationary gantry 40. The cross section
35 depicted shows the frame 50 and one of its eight
mountiny connectors 43.
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The Fi~ure -,4 cross section shows the first
positive 56 and second negative 58 slip riny portions
noted with regard to Fiyure 3B. The first portion
~sends a positive high voltage signal to the X-ray
`;5 tube and the second portion includes 4 individual
sllp rings to provide the controlled energization
'of the cathode as mentioned above. Both the ~ir,s~
56 and second 58 portions of the slip ring arrangement
are immersed in an oil bath in a cavity 11~. This
10 oil prevents arciny between high voltage portions
of the slip ring arrangement and other portions oE
the CT apparatus which could damage both the control
circuitry and the X-ray tube in prior art systems.
The portion o~ the stationary gantry 40 bordering
15 on this cavity 112 is prefera~ly of aluminum construction
and the portion of the rotating assembly which borders
the cavity is o~ a plastic construction. These light
weight materials allow the apparatus to be readily
tilted and the plastic rotating portions allow the
20 system to be more easily rotated by the belt drive.
Four elastomeric seals 114-117 maintain a dielectric
fluid such as oil in the cavity. These seals are
mounted to the nonrotating gantry 40 and are biased
against the rotating assembly by means of spring
25 biasing members 118. As the assembly rotates with
respect to the stationary gantry, these sprin~s
maintain the seals in contact with the rotating
portions and threby prevent leakaye o~ the insulating
fluid from the cavity 112.
The transmission path o~ the positive high voltage
signal is clearly illustrated in Figure 4. The high
voltage signal (typically 75,000 volts) is input
into the high voltage receptacle 46 transmitted to
the ~irst slip ring portion 56 then through hlgh
35 voltage cabling to a second high voltage receptacle
60 attachecl to the rotating assembly for transmittal
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to the anode portion of the X-ray tube. The hiyh
voltage passes through a brush which is biased towards
the slip ring by a spring to insure contact b~tween
the brush and rotating slip ring. One type o cabling
5 used to transmi L the high voltages between the slip
ring and the X-ray tube is Federal cabling which
is known in the ark of X-ray CT scanning. The cabling
120 passes through a bore machined into the plastic
portion of the rotating assembly.
The second portion 58 of the slip ring assembly
includes four rotating slip rings 1~2-125 which
transmit four separate negative high voltage signals
to the X-ray tube. A more detailed schematic oE
this second 58 portion o the slip ring arrangement
15 is shown in Figure 4A. As seen in that figure each
rotating slip ring is contac~ed by a biased brush
127 which in turn i5 connected to an electrical
contact in a housing 126. In the embodiment illustrated
a single focus tube has been utilized and therefore
20 only two nega-tive high potential inputs 128, 129
are required with two spares available should other
tubes be used.
At a location removed from the high voltage
slip ring arrangement are a number of low voltage
25 slip rings 130-135 for transmitting low voltage
electrical signals from the stationary gantry to
the rotating assembly. Since these slip rings transmit
low voltages they need not be immersed in an oil
bath to insure electrical isolation. Although only
30 six slip rings are shown in the figure for clarity~
16 low voltage slip are utili2ed in a preferred
embodiment of one commercial CT unit. Three of the
low voltage inputs are utili~ed to provide power
to a motor located in the rotating assembly 42 which
35 cools the anode of the X-ray tube by rotating it.
Three more of the low voltage slip rings are used
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as common or ground potential. Four other low voltage
slip rings are utilized as general alternating current
power inputs. These inpu~s are used to operate a
number of solenoids mounted ~o the assembly 42 which
5 must be powered by AC signals.
Five remaining slip rings are used to monitor
and contxol the condition of three switches mounted
to the rotating assembly which operate a shutter,
a filter, and the collimator. The functioning of
10 these three components must be coordinated with X-
ray generation in the CT imaging process. One of
these five remaining inputs transmits a frequency
proportional to a re~erence intensity from the rotating
; assembly 42 to the stationary imaging electronics
15 20. Two of the remaining four inputs are used to
provide synchroni2ation and clock signals. The
remaining two slip rings operate to send and receive
digital data from a multiplexing board which both
controls and monitors the condition of the three
20 switches.
Since there are 16 rotating slip rings and the
function of only 15 inputs have been described one
of these 16 slip rings has no function in the present
design but is available for future design modification.
While the embodiment described above has been
characteri2ed with some particularity, it should
be appreciated to those skilled in the art that
certain modification and changes could be insorporated
without departing from the spirit or scope of the
30 invention as detailed in the appended claims.
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