X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-11-07
2003-12-30
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S098800
Reexamination Certificate
active
06671345
ABSTRACT:
BACKGROUND
The present invention relates to the field of medical imaging and has particular applicability to computed tomography (CT). The invention also finds application in the fields of x-ray detection and imaging, including industrial inspection systems, non-destructive testing, baggage inspection, and the like.
Early CT scanners had only a single pencil beam x-ray source for transmitting x-rays through an examination region and a single detector for receiving attenuated x-rays after they had passed through a patient in the examination region. The source and detector were repeatedly rotated and translated about the examination region to obtain an image of the patient. The process of obtaining images with these scanners was slow and resulted in low resolution images.
Subsequent developments in CT technology have been made to decrease scanning time, increase patient throughput, and increase spatial resolution of images. These goals have been accomplished by, among other things, increasing the size of the beam radiation generated by the x-ray source and by increasing the number of detectors in a scanner.
As with the early scanners, second generation scanners used a rotation-translation system, but improved on the data acquisition speed of the earlier scanners through the use of an array of detectors and a small fan-beam x-ray source.
Third generation CT scanners also used a fan-beam x-ray source and an array of detectors that rotated simultaneously about the subject. However, the fan-beam of the third generation scanner was wide enough to cover the cross-section of a region of interest of the patient. Therefore, there was no need to translate the source-detector assembly.
Like the third generation scanners, fourth generation CT scanners used a fan-beam x-ray source that rotated about the examination region. However, the detectors were distributed around the examination region and did not rotate with the x-ray source.
Regardless of the configuration, CT scanners included at least one discrete radiation detector which converted x-ray radiation which traversed the patient examination area into electronic signals. Each radiation detector included a x-ray sensitive face, such as a scintillation crystal, which converted the received radiation into a corresponding quantity of light. A solid state photodiode was provided to convert the light emitted by the scintillation crystal into analog electrical signals indicative of the intensity of the crystal emitted light, hence the intensity of the received radiation.
In the case of multi-slice imaging, a two-dimensional array of radiation detectors was used. The radiation detectors were separately arranged on a circuit board. Each circuit board supported an array of photodiodes and attached scintillation crystals. In addition, a preamplifier was operatively connected to the circuit board and connected to each photodiode output to convert the photodiode current to an appropriate voltage within the dynamic range of the analog-to-digital conversion system.
The analog signals from the circuit board were carried to a separate processing area where they were converted from their analog state into a corresponding digital signal. The processing area was typically located some distance from the detectors. The analog signals were carried to the processing area via a relatively long bus system which extended from the photodiode to the analog-to-digital converter.
One problem with such a system relates to degradation of the analog signals as they travel over the long bus system between the radiation detectors and the processing area.
CT scanners operate in an environment of extraneous radio frequency electromagnetic signals, the frequencies of which vary over a wide band. Sources of extraneous signals include nearby operating electrical components, equipment, signals from other detectors, and the like. The long bus systems include long lead wires which inadvertently act as antennas in picking up extraneous electromagnetic signals and converting them into analog signals. The extraneous analog signals are superimposed on and mix with the analog signals from the detectors. The superimposed extraneous signals appear as noise and fictitious data when reconstructed into images. The resulting images are degraded by noise, ghosting, and other artifacts.
Another problem relates to the complexity of the electronic circuitry associated with the detectors as the number of detectors increased.
Each detector normally required a separate channel with all of the front end electronics and hardware to support the detector. As the number of detectors increased, the circuitry and associated electrical connections required to process and transfer the signals generated by the detectors increased as well. Therefore, implementing a large numbers of detectors has been a difficult task.
SUMMARY
Those skilled in the art will, upon reading and understanding the appended description, appreciate that aspects of the present invention address the above and other matters.
In accordance with one aspect of the present invention, a computerized tomographic imaging system is provided. The system includes a stationary gantry portion defining an examination region and a rotating gantry portion for rotation about the examination region. An x-ray source is disposed on the rotating gantry portion for projecting x-rays through the examination region and a plurality of modular radiation detector units are disposed across the examination region from the x-ray source. Each radiation detector unit includes an array of x-ray sensitive cells for receiving radiation from the x-ray source after it has passed through the examination region and for generating an analog signal indicative of the radiation received thereby. Each radiation detector unit also includes a plurality of integrated circuits connected to the x-ray sensitive cells with each integrated circuit including a plurality of channels. Each channel receives the analog signal from an x-ray sensitive cell and generates digital data indicative of the value of the analog signal.
In accordance with a more limited aspect of the present invention, each modular radiation detector unit also includes a circuit board and the plurality of x-ray sensitive cells and plurality of integrated circuits are disposed on the circuit board.
In accordance with a more limited aspect of the present invention, the integrated circuits are disposed on the circuit board so that the variability of the distances from the x-ray sensitive cells to their respective integrated circuits is minimized.
In accordance with a more limited aspect of the present invention, each integrated circuit includes at least thirty-two channels.
In accordance with a more limited aspect of the present invention, each channel includes a ratiometric current to frequency converter which generates a number of electrical pulses during a time period, the number of pulses being proportional to the magnitude of the analog signal.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, each channel comprises a parallel to serial converter, the parallel to serial converter including means for interconnecting the channels so that the digital data from a plurality of the channels are combined to form a single output stream of digital data.
In accordance with a more limited aspect of the present invention, the array of x-ray sensitive cells is an array having M rows and N columns, M and N being integers greater than or equal to two.
In accordance with a more limited aspect of the present invention, each row of the array of x-ray sensitive cells corresponds to a single slice of image data.
In accordance with a more limited aspect of the present inventio
Chappo Marc A.
Krecic Anthony F.
Vrettos Chris J.
Dunn Drew A.
Koninklijke Philips Electronics , N.V.
Lundin, Esq. Thomas M.
Thomas Courtney
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