X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-08-18
2001-07-10
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S901000
Reexamination Certificate
active
06259761
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
FIELD OF THE INVENTION
The present invention relates to methods of efficiently transferring digital data over a band-limited channel, and more particularly, to efficiently transferring data from a CT detector array to an image reconstruction computer via an existing data channel.
BACKGROUND OF THE INVENTION
It is well known to use electromechanical slip rings, to enable the transfer of data to and from a rotating device, such as the drum that is rotatably mounted in the gantry of a computer tomography (CT) scanner so that the X-ray equipment supported by the drum can be rotated about a patient during a tomographic scan. It is equally well known to employ a radio frequency (RF) link to enable such a data transfer. For example, U.S. Pat. No. 5,577,026, entitled “Apparatus for Transferring Data to and from a Moving Device,” illustrates the use of an RF link to transfer data in a CT scanner.
U.S. Pat. Nos. 4,928,283 and RE 34,379 briefly describe a CT scan system employing a “two-way communication link” between “an electronics package” secured to the rotating disk of the system and a “computer used for image processing and control”. No further detail is provided.
In a CT scanning system, the two-way communication link (hereinafter data link) typically has a maximum throughput rate that is not easily increased due to physical limitations of the components used to implement the data link. Thus, the number of views of raw data per rotation of the CT scanner is limited by the data transfer rate over the data link. However, the quality of the reconstructed image can be improved by using more views of data. For example, an existing CT system can collect and transfer up to 960 views per rotation. It has been shown that using 1440 to 1920 views per rotation significantly improves the reconstructed image, for example by reducing blurriness around the edges of the image. Increasing the number of views to be processed in existing systems is often difficult or impossible due to limitations of the data link throughput. One method of increasing the effective throughput rate of the data link without modifying the existing hardware components and configurations used to implement the data link is to utilize data compression techniques prior to transferring the raw data. However, conventional data compression techniques are generally not suitable for compressing raw CT data. First, the compression rate of a conventional compression algorithm is generally dependent upon the redundancy of the bit pattern in the data being compressed, i.e., the more repetition of the constituent bit patterns, the more the data will compress without the subsequent loss of data. Raw CT data tends to be highly random in the bit pattern, so the compression rate necessarily has to be low in order to preserve the data. As a result the available compression rate using conventional compression techniques are typically inadequate for CT applications. Second, the compression rates provided by conventional compression techniques are data dependent, and thus variable, which makes the transfer protocol more complex and the error checking more difficult in a CT application. Third, rare but relatively large loss in the compressed data can possibly cause destructive damage to the reconstructed CT image. Many conventional compression techniques were designed for applications that do not require that a constant data compression rate be maintained, or for applications that can tolerate an occasional large loss of data.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art, and to provide a data compression technique suitable for raw CT data.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by the invention which in one aspect comprises an apparatus for transferring an ordered sequence of data elements from a first location to a second location via a communication channel. The apparatus includes a multiplexor for selecting at least two primary data elements occurring at predetermined intervals within the series, and for selecting at least one intermediate data element occurring within the predetermined intervals between the primary data elements. The apparatus further includes an estimator for determining, for each of the intermediate data elements, an estimated value corresponding to the intermediate data element. Each of the estimated values is a predetermined function of an immediately preceding primary data element and an immediately subsequent primary data element in the ordered sequence. The apparatus also includes a processor for calculating a difference value for each of the intermediate data elements. The difference value is a representative of a mathematical difference between the intermediate element and the corresponding estimated value. The apparatus further includes a transmitter for transmitting each of the primary data elements and the difference elements along the communication channel.
In another embodiment of the invention, the communication channel is band-limited, so as to define a maximum data throughput capability of the channel.
In another embodiment of the invention, the sequence of data elements is ordered corresponding to a plurality of angular positions of a rotatable device, relative to an associated stationary support structure, such that the predetermined intervals include an integral number of angular position increments.
In another embodiment of the invention, the predetermined interval is two angular position increments, such that one intermediate data element occurs between two consecutive primary data elements.
In another embodiment of the invention, the predetermined interval is four angular position increments, such that three intermediate data elements occur between two consecutive primary data elements.
In another embodiment of the invention, the sequence of data elements is ordered corresponding to a plurality of detectors from a detector array, corresponding to at least one angular position of a rotatable device. In this embodiment, the predetermined intervals include an integral number of detectors.
In another embodiment of the invention, the predetermined function includes a linear interpolation of two consecutive primary elements. When the interval between the two primary elements is two, the linear interpolation includes a mathematical average of two consecutive primary elements. When the interval between the two primary elements is three or more, the linear interpolation includes a weighted averaging, with linearly varying weights, of the two consecutive primary elements.
In another embodiment of the invention, the mathematical difference includes a limiting function, such that the difference value is limited to a maximum value when the calculated difference value exceeds the maximum value, and the difference value is limited to a minimum value when the calculated difference value exceeds the minimum value.
In another embodiment of the invention, the apparatus is used by a CT scanning system having a drum being rotatably mounted in a gantry support structure to transfer an ordered sequence of data elements from the drum to the gantry support structure via a communication channel.
REFERENCES:
patent: 4691233 (1987-09-01), Acampora
patent: 4794455 (1988-12-01), Ericsson
patent: 5577026 (1996-11-01), Gordon et al.
Analogic Corporation
Bruce David V.
McDermott & Will & Emery
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