Abstract:
A multislice detector module producing an alterable quantity of slices and slice resolutions. In one embodiment, the detector module includes a plurality of photodiodes arranged in an array of rows and columns, a switch apparatus electrically coupled to photodiode output signals, and a decoder. The decoder is configured to enable or prevent each photodiode from being transmitted through the switch apparatus. The configuration of the decoder determines how many slices of data are transmitted and the resolution of each slice.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to computed tomograph (CT) imaging and, more particularly, to detector modules utilized in connection with CT systems. 
     BACKGROUND OF THE INVENTION 
     In at least some computed tomograph (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile. 
     In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector. A scintillator is located adjacent the collimator, and photodiodes are positioned adjacent the scintillator. 
     Multislice CT systems are used to obtain data for an increased number of slices during a scan. Known multislice systems typically include detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of detector elements form separate channels arranged in columns and rows. Each row of detectors forms a separate slice. For example, a two slice detector has two rows of detector elements, and a four slice detector has four rows of detector elements. During a multislice scan, multiple rows of detector cells are simultaneously impinged by the x-ray beam, and therefore data for several slices is obtained. 
     Multislice detectors generate much more data than single slice detectors. This increased data generation capability is not, however, always required or desired. For example, a variety of tests performed by a CT system do not require high slice quantity or high slice resolution. Also, with such large amounts of data being collected, the time required to perform a scan may increase, resulting in higher costs and lower throughput. 
     Accordingly, it would be desirable to provide a detector module that allows data to transmitted from an alterable number of slices to accommodate the specific needs of a test. In addition, it is desirable to provide a detector module having an alterable slice resolution. 
     SUMMARY OF THE INVENTION 
     These and other objects may be attained by a detector module which, in one embodiment, enables modification of the quantity of slices and slice resolution, or slice thickness. The detector module includes a photodiode array optically coupled to a scintillator array. The photodiode array includes a plurality of photodiodes arranged in rows and columns. A collimator array is aligned and positioned adjacent to the scintillator array to collimate the x-ray beams. 
     The detector module further includes a switch apparatus and a decoder. The switch apparatus is electrically coupled between the photodiode output lines and a CT system data acquisition system (DAS). The switch apparatus, in one embodiment, is an array of FETs and alters the number of slices and the thickness of each slice by allowing each photodiode output line to be enabled, disabled, or combined with other photodiode output lines. 
     More specifically, after an operator has determined the desired number of slices and slice thickness, the appropriate switch apparatus configuration is electrically transmitted from the CT system computer to the decoder, e.g., via a flexible cable. The appropriate decoder output lines are then connected to the switch apparatus control lines so that data is transmitted from the photodiodes output lines in the selected configuration. 
     In one embodiment, the detector module is fabricated by depositing, or forming, the photodiode array, the switch apparatus, and the decoder on a substrate. Each photodiode output line is electrically connected to the switch apparatus inputs, and each switch apparatus output and each decoder control line are then electrically coupled to the first end of a flex cable. After installing the detector modules into the detector array, the second end of the flex cable is electrically connected to the CT system data acquisition system (DAS). 
     The above described detector module enables selection of the number of slices of data to be electrically transmitted for each rotation of the CT system. In addition, the detector module allows the slice thickness to be selected to produce various slice resolutions. As a result, the configuration of the detector module can be altered to accommodate the specific needs and requirements of the test. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of a CT imaging system. 
     FIG. 2 is a block schematic diagram of the system illustrated in FIG.  1 . 
     FIG. 3 is a perspective view of a detector array in accordance with the present invention. 
     FIG. 4 is a perspective view of a detector module in accordance with the present invention. 
     FIG. 5 is various configurations of the detector module in FIG. 4 in a four slice mode. 
     FIG. 6 is a side view of the detector module shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system  10  is shown as including a gantry  12  representative of a “third generation” CT scanner. Gantry  12  has an x-ray source  14  that projects a beam of x-rays  16  toward a detector array  18  on the opposite side of gantry  12 . Detector array  18  is formed by detector modules  20  which together sense the projected x-rays that pass through a medical patient  22 . Each detector module  20  produces electrical signals that represent the intensity of impinging x-ray beams and hence the attenuation of the beams as they pass through patient  22 . During a scan to acquire x-ray projection data, gantry  12  and the components mounted thereon rotate about a center of rotation  24 . 
     Rotation of gantry  12  and the operation of x-ray source  14  are governed by a control mechanism  26  of CT system  10 . Control mechanism  26  includes an x-ray controller  28  that provides power and timing signals to x-ray source  14  and a gantry motor controller  30  that controls the rotational speed and position of gantry  12 . A data acquisition system (DAS)  32  in control mechanism  26  samples analog data from detector modules  20  and converts the data to digital signals for subsequent processing. An image reconstructor  34  receives sampled and digitized x-ray data from DAS  32  and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer  36  which stores the image in a mass storage device  38 . 
     Computer  36  also receives commands and scanning parameters from an operator via console  40  that has a keyboard. An associated cathode ray tube display  42  allows the operator to observe the reconstructed image and other data from computer  36 . The operator supplied commands and parameters are used by computer  36  to provide control signals and information to DAS  32 , x-ray controller  28  and gantry motor controller  30 . In addition, computer  36  operates a table motor controller  44  which controls a motorized table  46  to position patient  22  in gantry  12 . Particularly, table  46  moves portions of patient  22  through a gantry opening  48 . 
     As shown in FIGS. 3 and 4, detector array  18  includes a plurality of detector modules  20 . Each detector module  20  includes a multidimensional photodiode array  52  and a multidimensional scintillator array  56  positioned above and adjacent to photodiode array  52 . A collimator (not shown) is positioned above and adjacent scintillator array  56  to collimate x-ray beams  16  before such beams impinge upon scintillator array  56 . Photodiode array  52  includes a plurality of photodiodes  60  which are optically coupled to scintillator array  56 , and photodiodes  60  generate electrical output signals  64  representative of the light output by each scintillator of scintillator array  56 . 
     In one embodiment, as shown in FIG. 3, detector array  18  includes fifty-seven detector modules  20 . Each detector module  20  includes a photodiode array  52  and scintillator array  56 , each having an array size of 16×16. As a result, array  18  has 16 rows and 912 columns (16×57 modules) allowing 16 simultaneous slices of data to be collected with each rotation of gantry  12 . 
     Detector module  20  also includes a switch apparatus  68  electrically coupled to a decoder  72 . Switch apparatus  68  is a multidimensional semiconductor switch array of similar size as photodiode array  52 . In one embodiment, switch apparatus  68  includes an array of field effect transistors (not shown) with each field effect transistor (FET) having an input, an output, and a control line (not shown). Switch apparatus  68  is coupled between photodiode array  52  and DAS  32 . Particularly, each switch apparatus FET input is electrically connected to a photodiode array output  64  and each switch apparatus FET output is electrically connected to DAS  32 , for example, using flexible electrical cables  74  and  76 . Cables  74  and  76  are secured to detector module  20  with mounting blocks  80 A and  80 B. 
     Decoder  72  controls the operation of switch apparatus  68  to enable, disable, or combine photodiode outputs  64  in accordance with a desired number of slices and slice resolutions for each slice. Decoder  72 , in one embodiment, is a decoder chip or a FET controller as known in the art. Decoder  72  includes a plurality of output and control lines coupled to switch apparatus and computer  36 . Particularly, the decoder outputs are electrically connected to the switch apparatus control lines to enable switch apparatus  68  to transmit the proper data from the switch apparatus inputs to the switch apparatus outputs. The decoder control lines are electrically connected to the switch apparatus control lines and determine which of the decoder outputs will be enabled. Utilizing decoder  72 , specific FETs within switch apparatus  68  are enabled, disable, or combined so that specific photodiode outputs  64  are electrically connected to CT system DAS  32 . In one embodiment defined as a 16 slice mode, decoder  72  enables switch apparatus  68  so that all rows of photodiode array  52  are connected to DAS  32 , resulting in 16 simultaneous slices of data are electrically connected to DAS  32 . Of course, many other slice combinations are possible. 
     For example, decoder  72  may also select from other multiple slice modes, including one, two, and four slice modes. As shown in FIG. 5, by transmitting the appropriate decoder control lines, switch apparatus  68  can be configured in the four slice mode so that data is collected from four slices of one or more rows of photodiode array  52 . Depending upon the specific configuration of switch apparatus  68  as defined by decoder control lines, various combinations of photodiode outputs  64  can be enabled, disabled, or combined so that the slice thickness may be 1.25 mm, 2.5 mm, 3.75 mm, or 5 mm. Additional examples include, a single slice mode including one slice with slices ranging from 1.25 mm thick to 20 mm thick; and a two slice mode including two slices with slices ranging from 1.25 mm thick to 10 mm thick. Additional modes beyond those described are possible. 
     In one embodiment and referring to FIG. 6, switch apparatus  68  and decoder  72  are combined into a FET array  104 . FET array  104  includes a plurality of field effect transistors (FET) (not shown) arranged as a multidimensional array. In one embodiment, two semiconductor devices  106  and  108  are utilized so that one-half of photodiode output lines  64  are connected to device  106  and one-half of photodiode output lines  64  are connected to device  108 . FET arrays  106  and  108  each include respective input lines  110  and  112 , output lines  114  and  116 , and control lines (not shown). Internal to device  106 , input lines  110  are electrically connected to the switch apparatus input lines, output lines  114  are electrically connected to the switch apparatus output lines, and decoder output lines are electrically connected to FET control lines. Switch  108  is internally configured identical to switch  106 . 
     In fabrication of detector module  20 , photodiode array  52  including scintillator array  56  and FET arrays  106  and  108  are deposited, or formed, on substrate  200  in a manner known in the art so that photodiode outputs  64  are adjacent arrays  106  and  108 . Photodiode outputs  64  are then connected to inputs  110  and  112  of respective FET arrays  106  and  108 . Particularly, one-half of photodiode outputs  64  are wire bonded to FET array inputs  110  and one-half of photodiode outputs  64  are wire bonded to respective PET array inputs  112  so that each output  64  is electrically connected to a FET input line. Photodiode outputs are wire bonded to FET input lines using various wire bonding techniques, including, for example, aluminum wire wedge bonding and gold wire ball bonding as known in the art. First ends of flexible electrical cables  74  and  76  are then electrically connected and secured to FET arrays  106  and  108 . FET array output and control lines are electrically connected to cables  74  and  76 . Particularly, each FET array output line  114  and  116  is wire bonded to a wire of respective cables  74  and  76 . Detector module  20  is completed by securing first ends of cables  74  and  76  with mounting blocks  80 A and  80 B. 
     After fabricating detector modules  20  as described above, detector modules  20  are mechanically mounted into array  18 . Second ends of cables  74  and  76  of each detector module  20  are then electrically connected to CT system DAS  32 . The collimator is then aligned and secured adjacent to scintillator arrays  56 . 
     In operation, the operator determines the number of slices and thickness of each slice. The appropriate configuration information is transmitted to the array control lines to configure switch apparatus  68  using decoder  72 . As X-ray beams  16  impinge upon detector modules  20 , data for the selected configuration is transmitted to DAS  32 . 
     The above described detector module enables selection of the number of slices of data to be electrically transmitted for each rotation of the CT system. In addition, the detector module allows the slice thickness to be selected to produce various slice resolutions. As a result, the configuration of the detector module can be altered to accommodate the specific needs and requirements of the test. 
     From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.