X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-08-25
2001-01-30
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S098800, C378S901000, C382S131000
Reexamination Certificate
active
06181766
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to computerized tomography (CT) systems, and more particularly to communication of high data rate signal images across the CT rotating interface.
As known, CT systems are used to obtain non-invasive sectional images of test objects. The most common use is to provide internal images of human patients for medical analysis and treatment. In operation, the object or patient is positioned on a table within a central aperture of a rotating frame, or gantry, which is supported within a stationary frame. The gantry includes an x-ray source and a detector array positioned on opposite sides of the aperture, within the system's imaging plane, and each rotate with the gantry around the object being imaged. At each of several angular positions along the rotational path the x-ray source emits a collimated beam which passes through the object and is received by the detector array. Sensors within the detector array produce electrical signal indications of the x-ray intensity incident at their surface, and these signals are collated by circuitry within the rotating frame into a set of image data at each angle. Each image data set is referred to as a view, and the plurality of views taken in each revolution, referred to as a scan, are processed by a stationary side computer into a cross sectional image of the object.
It is known to transfer detector data across the rotating gantry interface to the stationary side computer using a non-contact, electromagnetic coupling referred to as an RF (radio frequency) slipring. The data transfer occurs during scanning. There are nominally 1000 views in a full (360°) scan, and a typical maximum gantry slew rate of 360° per second. For a CT system with 752 detector channels, each channel providing a data signal with 16 bit image resolution, the data signal bit speed=(752×1000×16)/1.0=12.03 Mbps. The bit cell time is 83 nano seconds. This is a comparatively slow bit rate, with a corresponding long interval bit cell time, which minimizes the affects of ambient noise on the signal integrity. In these systems the data is amplitude modulated with an RF carrier signal and transmitted through the RF slipring to the stationary side.
In newer CT systems, for reasons related to patient comfort and efficiency, there is an emphasis on reducing the time spent in performing CT scans. This has led to CT designs capable of producing multiple slice images within a single rotation. One such proposed CT system produces four slices per revolution and a gantry slew rate of 720° per second, or 0.5 seconds per revolution. With the same 16 bit element signal resolution and 1000 images per slice per revolution, the resulting data rate is: (752×4×1000×16)/0.5=96.26 Mbps. With the addition of overhead bits the signal bit rate approaches 110 Mbps with a bit cell time of 9.2 nano seconds. This is nearly an order of magnitude increase in required throughput across the rotating interface.
While RF amplitude modulation is cost effective compared with alternative modulation methods, it is noise susceptible. As the data signal bit speed increases, ambient noise has an increasingly greater effect due to the smaller bit cell times. This reduced cell time causes the data bits to be increasingly susceptible to induced noise, including the loss of or displacement of the data bits, so as to lose synchronization and cause “jitter” in the data stream. It is currently known to use forward error correction (FEC) of the data stream to reduce this noise and jitter, however, FEC is expensive and complex to implement.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide apparatus and method for coupling high bit speed digital signal data across a rotating interface with lower cost and comparable accuracy to that provided with prior art methods. Another object of the present invention is to provide improved CT apparatus capable of higher image scan rates than that available in the prior art.
According to a first aspect of the present invention, a rotating side serial data signal comprising sequential digital signal bits propagating at a selected bit speed, each bit occurring in an associated data bit interval and each representing, alternatively, a first logic state and a second logic state, is electromagnetically coupled to a stationary side of the rotating interface by modulating each first logic state bit with a digital radio frequency (RF) carrier signal, the coupled data signal being demodulated on the stationary side to restore each such modulated bit to its first side first logic state. In further accord with this aspect of the invention the first side RF modulated signal is electromagnetically coupled to the second side through an RF slipring. In still further accord with this aspect of the invention the digital RF carrier signal digitally encodes each rotating side first logic state of the data signal in an RF digital signal pattern, and the stationary side received data signal is decoded in accordance with a rules based algorithm capable of distinguishing the appearance of a first logic state from the appearance of noise in the received pattern.
In yet still further accord with this aspect of the present invention the RF digital signal pattern comprises N serial pulses at a frequency which is substantially equal to N times the selected bit speed of the data signal. In yet still further accord with this aspect of the invention the N serial pulses are provided on the rotating frame at a selected minimum duty cycle, and the rules based algorithm on the stationary frame decodes the appearance of more than half of the N pulses in a data bit cell time as a first logic state and the appearance of all other numbers of pulses as a second logic state. In yet still further accord with this aspect of the invention the first logic state bits are encoded with a four pulse, fifty percent duty cycle pattern on the rotating frame side, and the stationary frame side algorithm decodes each appearance of three of four and four of four received pulses in a data bit interval as a first logic state, and decodes each appearance of two or less received pulses in a data bit interval as a second logic state.
According to a second aspect of the present invention the RF digital signal pattern is synchronized with the serial data signal on the first side of the rotating interface, thereby minimizing mis-registration of the decoded second side data bits from their associated data bit interval. In further accord with this second aspect of the invention, synchronization is achieved by phase locking the RF digital signal pattern to the serial data signal on both sides of the rotating interface.
According to a third aspect of the present invention, transmitter circuitry on the first side of the rotating surface digitally encodes the serial data signal with an RF digital signal pattern and provides the encoded signal as plural differential signals, each substantially identical and each presented to an associated one of plural transmission lines disposed in cascade over a 360° arc on the rotating side, each such transmission line being arrayed to provide electromagnetic coupling of the RF digital encoded signal therein to a coupler element on the second side of the interface, the coupler presenting the coupled signal to receiver circuitry which decodes and restores the serial data signal to its original state. In further accord with this aspect of the invention, the transmitter circuitry and receiver circuitry each comprise emitter coupled logic (ECL) circuit elements. In still further accord with this third aspect of the invention the ECL elements of the transmitter and receiver circuitry comprise positive ECL (PECL) circuit elements.
The present invention provides for high integrity transmission of high bit speed data signals across a rotating interface. The transmission occurs through digital encoding of the serial bit data signal with an RF digital signal pattern, which crosses the interface on an
Omick James K.
Pearson, Jr. Phil E.
Armstrong Teasdale
Cabou Christian G.
Dunn Drew A.
General Electric Company
Porta David P.
LandOfFree
Digital encoding of RF computerized tomography data does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital encoding of RF computerized tomography data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital encoding of RF computerized tomography data will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467187