X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2001-11-21
2004-11-23
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S062000, C382S130000
Reexamination Certificate
active
06823044
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to x-ray imaging and more particularly to an x-ray system for producing three-dimensional images.
BACKGROUND ART
Substantial development has been made in the field of x-ray imaging since the discovery of the penetrating capability of x-ray radiation. In many applications, radiography is still utilized to produce a simple two-dimensional projected image, but developments have been made to add modalities to this framework. Although developed in the 1930's, mathematical algorithms for tomography (i.e., the reconstruction of a three-dimensional image of an object from a set of cross-sectional two-dimensional detections) have only recently been exploited, with the evolution of computer-aided tomography (CAT) technology.
In the medical field a CAT system is used for detecting images representing internal parts of a patient's body, such as a heart or stomach, for subsequent diagnosis and treatment. A typical medical CAT system synchronously rotates a radiation source and a corresponding singular large array detector to “scan” a set of radiographs and then compute slices of planar cross-sectional views of the interior of a human body utilizing reconstruction algorithms.
In the electronics part fabrication field, a CAT system may be used during a quality control phase to monitor the state of soldered joints for electrical components, such as printed circuit boards (PCBs). Without requiring physical, visual or electrical access, defects such as shorts, opens, insufficient/excess solder, misaligned and missing components, and reversed polarized capacitors, can be detected. Other products commonly subjected to x-ray inspection include cellular and wireless phones, notebook computers, routers, switches, and PC motherboards. A typical electronic CAT system includes a fixed x-ray source for projecting imaging radiation onto a movable object. A fixed continuous detector array located on a side of the object opposite to the x-ray source captures the sampled radiation that has passed through the object. In a case where the area of the sampled object to be imaged is larger than a field of view of the imaging system, the object and/or the source must be moved in order to obtain multiple views. A disadvantage with this approach is that there is a time delay associated with the repetitive start-and-stop motion, since data relating to the sampled radiation cannot be continuously taken.
In the field of tomography, an important process parameter in collecting data for assembling three-dimensional information is to obtain a wide range of angular projections of the radiation that has passed through the sampled object. The tomographic angle is defined for each arbitrarily small region of the sampled object as the angular range of the projected views that have been collected through this region. For example, two rays through a point inclined oppositely 30 degrees from the normal to the sampled object would create a data set having a tomographic angle of 60 degrees. Accordingly, a large number of two-dimensional views captured by an x-ray detector at different angular projections is required in order to build a sufficient data set. Mathematical algorithms reconstruct the three-dimensional image by computationally combining the two-dimensional views captured at the various angles. This computational combination can be either tomographic or tomosynthetic. In tomographic reconstruction, non-linear reconstruction algorithms converge a hypothetical three-dimensional description to the available data set. In tomosynthetic reconstruction, reasonably simple arithmetic and linear operations calculate a three-dimensional description from the available data set.
One conventional x-ray detection technique utilizes photosensitive film for capturing an image. However, the drawbacks of utilizing film include the use of chemicals for film development and the requirement of a time-consuming development process. Recent advances have eliminated the need of film. In one available system, a scintillator converts x-ray radiation that has propagated through the sampled object of interest into visible light, and a charged coupled device (CCD) converts the light into electrical signals for processing in the digital domain. Other filmless systems employ complementary metal oxide semiconductor (CMOS) pixel sensors.
Notwithstanding the advances made in x-ray detection techniques, an array of sensor elements for capturing a contiguous image is commonly used. Several disadvantages and problems are associated with a continuous array of sensor elements. First, if any detecting element (e.g., one pixel sensor) of the array become defective, replacement of the entire array may be required. Second, if the image captured by the continuous array includes regions of the sampled object not required for diagnosis, the data acquisition rate is unnecessarily extended. Third, since it is critical in collecting images for use in computing three dimensional information to obtain the largest possible tomographic angle in the data set, the requirement of a single contiguous detector can either limit the tomographic angle for a given active area of detector or increase the cost unnecessarily.
Consequently, what is needed is an x-ray imaging system having a detecting arrangement that allows for reliability, efficiency, and manufacturing and operational cost savings.
SUMMARY OF THE INVENTION
The invention is an x-ray imaging system that utilizes multiple detecting modules distributed in a sparse configuration for detecting sub-image data sets with a large tomographic angle of regions of a three-dimensional object. The x-ray imaging system comprises: (1) an x-ray source for projecting pulses of imaging radiation onto a sampled object, (2) a support member on which the sampled object is placed, and (3) a detector assembly having multiple detecting modules sparsely distributed for detecting imaging radiation that has passed through the object. A sparse configuration is herein defined as an arrangement of detecting modules in which each detecting module is spaced apart from an adjacent detecting module by an intermediate distance. In one embodiment, the intermediate distance is greater than the pixel spacing within the module. A projected pulse of radiation is directed at the object from a single addressable point at the x-ray source for a clearly defined period of time. The x-ray source and the detector assembly are on opposite sides of the support member. For each area-wide pulse of radiation that is projected onto the object at various angles, a data sample of sub-images of non-overlapping regions is captured. Moreover, by manipulating the relative position of the object with respect to the imaging radiation projected from the source and by illuminating the object with pulses of radiation at selected intervals, a time series of successive sub-images corresponding to overlapping regions of the object are captured by each detecting module. Variations of existing mathematical algorithms reconstruct the captured sub-images to form a composite tomographic or tomosynthetic image. In one application, the sampled object is a printed circuit board (PCB).
The detector assembly also includes a supporting structure for the placement of the sparsely distributed detecting modules. The modules may be identical, but each module is coupled to a dedicated readout channel for data transmissions that are electrically isolated from each neighboring module. Thus, if a module becomes non-functional, the sparse configuration of modules enables part replacement to be limited to the defective module, rather than the entire detecting array.
In the sparse configuration, each module is strategically located on the supporting structure and is spaced apart by an intermediate distance from a neighboring module. The distance between each neighboring module may be determined on the basis of various factors, such as the specific application, economics (e.g., cost savings), and the desired throughput rate. The distance between module
Agilent Technologie,s Inc.
Bruce David V.
Kiknadze Irakli
LandOfFree
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