Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to a hybrid collimator for x-rays and a method of making same.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a post patient x-ray collimator for collimating x-ray beams received at the detector, a scintillator adjacent to the collimator for converting x-rays to light energy, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
The post patient x-ray collimator used in CT detection is a device mainly made of a highly absorbing material such as Tungsten or Molybdenum plates aligned to a focal spot on the x-ray tube. The main function of the collimator is to select x-rays along a particular direction (primary beam from focal spot) and to reject scattered radiation from other directions (patient scattered radiation). For this purpose, collimating plates are placed in front of the scintillator pixels to eliminate scattered radiation from the patient. In one example, a collimator includes tungsten plates placed in front of the interfaces of the detector cells (detector septa), requiring high precision manufacturing and alignment/precision features within the individual parts for alignment purpose. The dimension in the Y-axis (x-ray path/direction) is determined by the amount of the scatter-to-primary ratio (SPR) desired. Obviously, the higher the dimension in Y-axis, the lower is the SPR. Since the advent of multi-slice detectors, the coverage in Z-axis keeps increasing and leading to higher SPR. The high SPR has a significant impact in image quality in general and in low signal applications/Low Contrast Detectability Application (LCD) in particular.
Therefore, it would be desirable to design a collimator that reduces the scatter in two dimensions such that SPR is decreased.
According to an aspect of the invention, an x-ray collimator comprises a first plurality of x-ray attenuation plates having a width and a length, the length extending along a first direction, wherein the plates of the first plurality of x-ray attenuation plates are spaced apart from one another along a second direction. The collimator further comprises a second plurality of x-ray attenuation plates having a width and a length, the length extending along the second direction, wherein the plates of the second plurality of x-ray attenuation plates are spaced apart from one another along the first direction and wherein the plates of the second plurality of x-ray attenuation plates extend through the plates of the first plurality of x-ray attenuation plates. The first and second directions are orthogonal, and the width of the plates of the first plurality of x-ray attenuation plates is greater than the width of the plates of the second plurality of x-ray attenuation plates.
According to another aspect of the invention, a CT system comprises a rotatable gantry having an opening to receive an object to be scanned, an x-ray projection source positioned on the rotatable gantry and configured to project a beam of x-rays from a focal spot of the x-ray projection source toward the object, and a detector module positioned on the rotatable gantry. The detector comprises a two-dimensional array of detector cells configured to receive x-rays attenuated by the object, wherein a space between neighboring detector cells forms a two-dimensional grid of septa having a first plurality of septa aligned in parallel along a first dimension and a second plurality of septa aligned in parallel along a second dimension orthogonal to the first dimension and a collimator positioned on the rotatable gantry adjacently to the detector module. The collimator is configured to collimate x-rays impinging thereon and comprises a first plurality of plates aligned with the first plurality of septa and a second plurality of plates aligned with the second plurality of septa; the second plurality of plates having a portion thereof extending through the first plurality of plates. A width of the second plurality of plates along a third dimension orthogonal to the first and second dimensions is less that a width of the first plurality of plates along a third dimension.
According to yet another aspect of the invention, a method of making an x-ray collimator comprises forming a plurality of slots along a length of a first plurality of x-ray attenuation plates, each slot extending along a width of a respective x-ray attenuation plate and aligning the lengths of the first plurality of x-ray attenuation plates along a first direction such that a each slot in one of the first plurality of x-ray attenuation plates is aligned with a corresponding slot in each of the other first plurality of x-ray attenuation plates along a second direction orthogonal to the first direction to form a plurality of aligned slots. The method also comprises inserting each x-ray attenuation plate of a second plurality of x-ray attenuation plates through a respective aligned slot of the plurality of aligned slots such that a length of the each x-ray attenuation plate is aligned along the second direction and wherein a width of the x-ray attenuation plates of the second plurality of x-ray attenuation plates is less than the width of the x-ray attenuation plates of the first plurality of x-ray attenuation plates.
Various other features and advantages will be made apparent from the following detailed description and the drawings.
The drawings illustrate preferred embodiments presently contemplated for carrying out the invention.
In the drawings:
The operating environment of the invention is described with respect to a 256-slice computed tomography (CT) system. However, it will be appreciated by those skilled in the art that the invention is equally applicable for use with other multi-slice configurations. Moreover, the invention will be described with respect to the detection and conversion of x-rays. However, one skilled in the art will further appreciate that the invention is equally applicable for the detection and conversion of other high frequency electromagnetic energy. The invention will be described with respect to a “third generation” CT scanner, but is equally applicable with other CT systems.
Referring to
Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 30 of CT system 10. Control mechanism 30 includes an x-ray controller 32 that provides power and timing signals to an x-ray source 14 and a gantry motor controller 34 that controls the rotational speed and position of gantry 12. An image reconstructor 36 receives sampled and digitized x-ray data from DAS 22 and performs high speed reconstruction. The reconstructed image is applied as an input to a computer 38 which stores the image in a mass storage device 40.
Computer 38 also receives commands and scanning parameters from an operator via console 42 that has some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus. An associated display 44 allows the operator to observe the reconstructed image and other data from computer 38. The operator supplied commands and parameters are used by computer 38 to provide control signals and information to DAS 22, x-ray controller 32 and gantry motor controller 34. In addition, computer 38 operates a table motor controller 46 which controls a motorized table 48 to position patient 26 and gantry 12. Particularly, table 48 moves patients 26 through a gantry opening 50 of
A width 66 of plates 54 and a width 68 of plates 60 generally extend along a third axis 70 orthogonal to both the first and second axes 56, 62. In one embodiment, plates 54, 60 may not all be parallel with each other when a focusing arrangement of plates 54 and/or plates 60 toward an x-ray source, such as x-ray source 14, is desired as discussed below with respect to
As shown and discussed below, plates 60 are coupled to plates 54 via a plurality of slots 72 formed in each plate 54. Referring to
Collimator 52 includes a pair of mounting members 80, 82 configured to couple collimator 52 to a plurality of rails (not shown) of a detector assembly (not shown). In this manner, a plurality of collimators 52 may be positioned adjacently to one another to create a collimator assembly having, for example, 256 rows and 912 columns.
Widths 66, 68 of plates 54, 60 are designed to allow primary x-rays 84 from an x-ray source, such as x-ray source 14, to pass through collimating passageways 74 to impinge on detector cells 76 and to fully attenuate or absorb scattered x-rays 86 such that scattered x-rays 86 are prevented from impinging on detector cells 76. Plates 54 are constructed of an x-ray attenuation material such as tungsten, molybdenum, tantalum, high z-material alloys, or the like. Plates 60 are also constructed of an x-ray attenuation material such as tungsten, molybdenum, tantalum, high z-material alloys, or the like but need not be constructed of the same material as plates 54.
According to another embodiment of the invention, the number of collimating passageways 74 in collimator 52 is less than the number of detector cells 76. For example, each collimating passageway 74 may correspond with two detector cells 76 such that a plate 60 is positioned in collimator 52 to correspond with every other detector cells 76. Depending on the scatter-to-primary ratio (SPR) desired, plates 60 may be positioned such that each collimating passageway 74 corresponds with two, three, or more detector cells 76. In addition, plates 54 may also be positioned such that collimating passageways 74 correspond with one- or two-dimensional groups of detector cells 76.
As illustrated in
A plurality of plates 54 is shown in phantom to illustrate an engagement of plates 54 with plates 60. A first end 94 of plate 60 may be formed to have one or more tabs 96, 98 to help prevent first end 94 of plate 60 from passing through plates 54 for manufacturability purpose.
Referring now to
A collimator according to embodiments of the invention allows for high scatter rejection (e.g., an SPR less than 10% may be achieved) for 160 mm X-ray coverage at ISO (corresponding to a size of imaging an organ such as the heart) and includes a high stiffness up to high G-loads. Accordingly, speed calibrations become more simplified. In addition, a hybrid 1D-2D collimator as described herein has an exterior envelope that is interchangeable with existing 1D collimators and allows for the upgrade of such 1D collimators.
Therefore, according to an embodiment of the invention, an x-ray collimator comprises a first plurality of x-ray attenuation plates having a width and a length, the length extending along a first direction, wherein the plates of the first plurality of x-ray attenuation plates are spaced apart from one another along a second direction. The collimator further comprises a second plurality of x-ray attenuation plates having a width and a length, the length extending along the second direction, wherein the plates of the second plurality of x-ray attenuation plates are spaced apart from one another along the first direction and wherein the plates of the second plurality of x-ray attenuation plates extend through the plates of the first plurality of x-ray attenuation plates. The first and second directions are orthogonal, and the width of the plates of the first plurality of x-ray attenuation plates is greater than the width of the plates of the second plurality of x-ray attenuation plates.
According to another embodiment of the invention, a CT system comprises a rotatable gantry having an opening to receive an object to be scanned, an x-ray projection source positioned on the rotatable gantry and configured to project a beam of x-rays from a focal spot of the x-ray projection source toward the object, and a detector module positioned on the rotatable gantry. The detector comprises a two-dimensional array of detector cells configured to receive x-rays attenuated by the object, wherein a space between neighboring detector cells forms a two-dimensional grid of septa having a first plurality of septa aligned in parallel along a first dimension and a second plurality of septa aligned in parallel along a second dimension orthogonal to the first dimension and a collimator positioned on the rotatable gantry adjacently to the detector module. The collimator is configured to collimate x-rays impinging thereon and comprises a first plurality of plates aligned with the first plurality of septa and a second plurality of plates aligned with the second plurality of septa; the second plurality of plates having a portion thereof extending through the first plurality of plates. A width of the second plurality of plates along a third dimension orthogonal to the first and second dimensions is less that a width of the first plurality of plates along a third dimension.
According to yet another embodiment of the invention, a method of making an x-ray collimator comprises forming a plurality of slots along a length of a first plurality of x-ray attenuation plates, each slot extending along a width of a respective x-ray attenuation plate and aligning the lengths of the first plurality of x-ray attenuation plates along a first direction such that a each slot in one of the first plurality of x-ray attenuation plates is aligned with a corresponding slot in each of the other first plurality of x-ray attenuation plates along a second direction orthogonal to the first direction to form a plurality of aligned slots. The method also comprises inserting each x-ray attenuation plate of a second plurality of x-ray attenuation plates through a respective aligned slot of the plurality of aligned slots such that a length of the each x-ray attenuation plate is aligned along the second direction and wherein a width of the x-ray attenuation plates of the second plurality of x-ray attenuation plates is less than the width of the x-ray attenuation plates of the first plurality of x-ray attenuation plates.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.