Method and apparatus of radiographic imaging with an energy beam tailored for a subject to be scanned

Patent Center

The Netherlands

<img file="NL1027338C2_D0001.tif" />

© 1027338 © C PATENT²⁰

<td>© Patent application: 1027338</td><td>© lnt.CI.⁸</td>

<td>© Submitted: 26.10.2004</td><td>A61B6 / 03</td>

<td>© Priority:</td><td>© Patent holder (s):</td>

<td>27.10.2003 US 10/605789</td><td>GE Medical Systems Global Technology</td>

<td>@ Signed up:</td><td>Company, LLC of Waukesha, Wisconsin, United States of America (US).</td>

<td>28.04.2005 IE 2005/07 @ Date:</td><td>© Inventor (s): Thomas L. Toth of Brookfield, Wisconsin (US)</td>

<td> 30.11.2005</td><td>Eric J. Tkaczyk of Delanson, New York (US)</td>

<td>© Published: 01.02.2006 IE 2006/02</td><td>Jiang Hsieh of Brookfield, Wisconsin (US) © Authorized representative:</td>

<td> •</td><td>Ir. A. van Westenbrugge et al. At 2502 LS The Hague.</td>

© Method and apparatus for radiographic imaging with an energy beam adapted to an object to be scanned.

A method and apparatus for tuning the profile (92) of an X-ray beam (90) for radiographic imaging for a specific object (22, 134) is disclosed. The invention includes a filter assembly (94) having a pair of filters (96, 98), each of which can be dynamically controlled by a motor assembly (112, 114) during data acquisition. The filters (96, 98) can be positioned in the X-ray beam (90) to form the intensity profile (92) of the X-ray beam (90) of the X-ray beam (90). In one exemplary embodiment, the filters (96, 98) are dynamically positioned during CT data acquisition based on the shape of the object (22,

134). A method of determining the shape of the object (22, 134) prior to CT data acquisition is also disclosed.

NL C 1027338

<img file="NL1027338C2_D0002.tif" />

The contents of this patent correspond to the original filed description with claim (s) and any drawings.

The Netherlands Patent Office is the Office for Industrial Property, an agency of the Ministry of Economic Affairs

METHOD AND APPARATUS FOR RADIOGRAPHIC IMAGING WITH AN ENERGY BUNDLE TAILORED FOR AN OBJECT TO BE SCANNED!

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:! 5 Background of the invention&gt; I

The present invention relates generally to diagnostic imaging and, more particularly, to a method and apparatus for dynamic filtering of radiation emitted to an object during radiographic imaging in a manner adapted to the shape and / or position of an object to be displayed.

Typically, in radiographic imaging systems, an X-ray source emits X-rays to a person or object, such as a patient or piece of luggage. After this, the terms "person" and "object" can be used interchangeably to describe anything to which imaging can be applied. After being muted by the person, the beam falls on an array of radiation detectors. The intensity of the damped beam radiation received on the detector array typically depends on the attenuation of the X-rays. Each detector element of the detector array produces a tone electrical signal characteristic of the damped beam received by each detector element. The electrical signals are transferred to a data processing system for analysis that eventually produces an image,

In CT (computed tomography) imaging systems, the X-ray source and detector array are rotated around a scaffold within an imaging plane and around the object. X-ray sources typically include X-ray tubes, which emit the X-rays as a beam at a focus. X-ray detectors typically include a collimator for collimating X-ray beams received at the detector, a scintillator for converting X-rays into light energy adjacent to the collimator, and a photodiode for receiving the light energy from an adjacent scintillator and producing electric signals therefrom Typically, each scintillator of a scintillator array converts x-rays into light energy. Each photodiode detects the light energy and generates a corresponding electrical signal. The execution of the

/.7338 2 photodiodes are then transferred to the image reconstruction data processing system.

There is an increasing need to reduce the dose of radiation received by a patient during an imaging session. It is well known that significant dose reduction can be achieved by using a “bowtie” filter to shape the intensity profile of an X-ray beam. Surface dose reductions can be up to 50% when using a bowtie filter. It is also well known that different anatomical regions of a patient advantageously prescribe differently shaped bowtie filters to reduce radiation dose. For example, scanning the head or small area of ​​a patient may require that a bowtie filter is shaped differently than a filter used during a large body scan session. It is therefore desirable to have an imaging system with a large number of bowtie filter shapes available to best suit each patient. However, modeling an imaging system with an adequate number of bowtie filters to record the idiosyncrasies encountered during scanning of numerous patients can be problematic in that each individual patient cannot be taken into account. Furthermore, fabrication of an imaging system with a plurality of bowtie filters can increase the overall manufacturing cost of the imaging system.

Furthermore, for optimal dose efficiency, i.e. best image quality at the lowest possible dose, the attenuation profile generated by the bowtie filter should be patient specific. That is, it is desirable and preferred that when a pre-patient filter is selected, the size, shape and relative position of the patient are taken into account. By taking into account the size, shape and position of the patient, radiation exposure can be tailored to the specific patient. Furthermore, it is well known that CT systems for photon counting (PT) and energy discrimination (ED) are not possible today, mainly because the large dynamic range of photon flux velocities exceeds the counting rate capabilities of current PT and ED detectors. Tuning the pre-patient filter to the object to be scanned also allows to adjust the filter to minimize photon flux rates in an area suitable to allow continuous development of PT and ED-CT systems. As indicated above, the differences in patients in the potential object pool are significant

10273383 large and equipping a CT system with a pre-patient filter for every possible patient profile is more than priceless; it is simply not practical.

Therefore, it would be desirable to design an apparatus and method for dynamically filtering the radiation emitted to the object for data acquisition in a manner tailored to specific physical characteristics of the object. It would further be desirable to have a system that tunes the radiation emitted to the object during data acquisition based on an exploration scan of the object.

Brief description of the invention

The present invention is a directed method and device for defining a tuned attenuation profile of a pre-object beam shaping filter that overcomes the above-mentioned drawbacks. A filter assembly is provided and has a pair of filters, each of which can be dynamically controlled by a motor assembly during data acquisition. The filters can be positioned in the X-ray beam to form the profile of the X-ray beam. In one exemplary embodiment, the filters are dynamically positioned during CT data acquisition based on the shape of the object. A method of determining the shape of the object prior to CT data acquisition is also disclosed.

Therefore, in accordance with one aspect of the present invention, a beamforming filter assembly is provided. The filter assembly includes a first movable filter that has a non-uniform thickness and a second movable filter that is independent of the first movable filter and has a non-uniform thickness. Each filter is configured to be placed in a high-frequency electromagnetic energy beam to attenuate the beam for radiographic data acquisition.

In accordance with another aspect, a CT system is disclosed that includes a rotatable rack that has an opening for receiving an object to be scanned and a high-frequency electromagnetic energy projection source configured to project a high-frequency electromagnetic energy beam to the object. Also provided are a pre-object filter assembly comprising a pair of filters and a scintillator array having a plurality of scintillator cells, each cell configured to detect high-frequency electromagnetic energy passing through the object. The CT system also includes a photodiode array which is optically coupled to the scintillator airay and which includes a plurality of photodiodes configured to detect light output from a corresponding scintillator cell and a ¹ I data acquisition system (DAS) connected to the photodiode array and configured to receive the photodiode outputs. An image reconstructor is provided and connected to the DAS and is configured to reconstruct an image of the object from the photodiode outputs received by the DAS. The CT system further includes a control unit configured to independently position each filter of the pair of filters in the high-frequency electromagnetic energy beam to modulate the beam so as to have a profile substantially corresponding to at least an approximate shape of the object .

In accordance with another aspect, the present invention includes an X-ray filter assembly having a first filter and a second filter. A first motor assembly is connected to the first filter and a second motor assembly is connected to the second filter. The first and second motor assemblies are configured to independently position a respective filter in an X-ray path to define a damping profile that substantially approximates a target shape

Various other features, objects, and advantages of the present invention will become apparent from the following detailed description and drawings.

Brief description of the drawings

The drawings illustrate one preferred embodiment which is now contemplated for performing the method.

Figure 1 is an image representation of a CT imaging system.

Figure 2 is a block diagram of the system illustrated in Figure 1.

Figure 3 is a plan view of a representative X-ray system.

Figure 4 is a cross-sectional view of a portion of the X-ray system shown in Figure 1.

Figure 5 is a schematic view of one embodiment of a pre-object beam-forming filter assembly according to the present invention.

10273385

Figure 6 is a schematic view of another embodiment of a pre-object beamforming filter according to the present invention.

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Figure 7 is a schematic view of another embodiment of a filter assembly in accordance with the present invention.

Figure 8 is an image view of a CT system for use with a non-invasive package inspection system.

Detailed description of the preferred embodiment

The present invention has been described with respect to a radiographic imaging system such as the CT system shown in Figures 1-2 and 8 and the X-ray system shown in Figures 3-4. However, it will be apparent to those skilled in the art that the present invention may equally well be used for use with other radiographic imaging systems. Furthermore, the present invention will be described with respect to the emission and detection of X-rays. However, it will be clear to a person skilled in the art that the present invention can equally be applied for the emission and detection of other high-frequency electromagnetic energy.

With reference to Figs. 1 and 2, a CT "third generation" imaging system 10 is shown, comprising a rack 12. However, the present invention can be applied with other CT systems. The rack 12 has an X-ray source 14 which projects a beam of X-rays 16 through filter assembly 15 to a detector array 18 on the opposite side of the rack 12. Detector array 18 is constituted by a plurality of detectors 20 which together detect the projected X-rays that can pass through a medical patient 22. Each detector 20 produces an electrical signal representing the intensity of a conspicuous X-ray beam and thus the damped beam as it passes through the patient 22. During a scan to acquire X-ray projection data, the scaffold 12 and the components mounted thereon rotate about a center of rotation 24.

Rotation of the scaffold 12 and operation of X-ray source 14 are controlled by a control mechanism 26 of the CT system 10. The control mechanism 26 includes an X-ray control unit 28 which provides power and timing signals to an X-ray source 14, a scaffold motor control unit.

6 controlling the rotational speed and position of the scaffold 12, and filter assembly controller 33 controlling the filter assembly 15. A data acquisition system (DAS) 32 in the control mechanism 26 samples analog data from detectors 20 and converts the data into digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized X-ray data from DAS 32 and performs high speed reconstruction. The reconstructed image is supplied as an input to a computer 36 which stores the image in a mass memory device 38.

The computer 36 also receives commands and scan parameters from an operator through console 40 which has a keyboard. An associated cathode ray tube display screen 42 allows the operator to observe the reconstructed image and other data from computer 36. The commands and parameters provided by the operator are used by computer 36 to transmit control signals and information to DAS 32, X-ray control unit

28, and provide actuating motor control unit 30. In addition, computer 36 operates a table motor control unit 44 that controls a motorized table 46 to position patient 22 and rack 12. In particular, the table 46 moves parts of the patient 22 through a scaffold opening 48.

Referring now to Figures 3-4, an X-ray system 50 embodying the present invention is shown. The X-ray system 50 includes an oil pump 52, an anode end 54, and a cathode end 56. A central sheath 58 is provided and positioned between the anode end 54 and the cathode end 56. Housed within the central sheath 58 is a X-ray generating device or X-ray tube 60. A fluid chamber 62 is provided and housed within a lead-lined housing 64. Fluid chamber 62 is typically filled with coolant 66 which will be used to divert heat within the X-ray generator 60. Coolant 66 is typically a dielectric oil, but other coolants including air can be implemented. Oil pump 52 circulates the coolant through the X-ray system 50 around the X-ray generator

60 to cool and to isolate the housing 64 from high electrical charges found within vacuum vessel 68. To cool the refrigerant to suitable temperatures, a radiator 70 is provided and positioned on one side of the central enclosure 58. Furthermore, fans 72, 74 are mounted near the

0273 38 Ί radiator 70 to provide a cooling air flow over the radiator 70 as the dielectric oil circulates through it. Electrical connections are provided in anode receptacle 76 and cathode receptacle 78 that allow electrons 79 to flow through the X-ray system 50.

The housing 64 is typically formed from an aluminum-based material and is coated with lead to prevent parasitic X-ray emissions. A stator 70 is also provided adjacent to vacuum vessel 68 and within the housing 64. A window 82 is provided which allows X-ray emissions created within the system 50 to exit the system and project in the direction of an object, such as a medical patient, for diagnostic imaging. Typically, window 82 is formed in housing 64. Housing 64 is designed such that most of the generated X-rays 84 are blocked from emission except through window 82. X-ray system 50 includes a pre-object filter assembly 86 designed to provide an attenuation profile of X-rays 84. control.

Referring now to Figure 5, an X-ray generating and filtering assembly according to the present invention has been schematically shown which can be used at least with the CT systems and X-ray systems described above. Assembly 87 includes an X-ray source 88 that projects a beam of X-rays 90, or other high-frequency electromagnetic energy beam, to an object (not shown). As will be described, beam 90 has a profile 92 adapted to at least approximate physical characteristics, e.g. shape, of the object. Attenuation of the X-ray beam 90 prior to attenuation by the object to define the profile 92 occurs through a pre-object 25 beam-forming filter assembly 94.

Filter assembly 94 includes a pair of filters or filter components 96 and 98 that generally reflect each other in shape and orientation. In this regard, each filter 96, 98 makes up roughly half of the filter assembly. As will be described below, in a preferred embodiment, the filters are not equivalent in dimension. Despite the size differences, each filter is defined by a base 100, 102, a tail 104, 106, and a curved or curved portion 108, 110. In this regard, X-ray attenuation by each filter is non-uniform across the filter body. That is, since the base of each filter is thicker than the tail of each filter, the

10273388 bases of each filter have more x-rays than the tails of each filter. In one embodiment, the base of each filter has a thickness of 30 mm and each tail has a thickness of 0.25 ram. The degree of attenuation is a function of the attenuation material used to fabricate the filter and the relative thickness of each filter portion.

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Each filter 96, 98 is operatively connected to a motor assembly 112 and 114, respectively. Each motor assembly receives control signals from a control unit and / or computer of the imaging system, which, when received, causes each motor assembly to position a respective filter in the X-ray beam or pad 90. In one embodiment, each motor assembly includes a step 10 pen motor, but it is contemplated that other types of motors can be used to position the filters. The motor assemblies 112,114 are also designed to independently reposition the filters during data acquisition. In this regard, each filter can be individually or dynamically controlled or positioned to achieve a specific attenuation profile 92 during data acquisition. In addition, it is preferable that both filters are connected and controlled by a respective motor assembly. Furthermore, one filter could be fixed and remain stationary with respect to the other filter. It is further contemplated that more than two filters can be used.

In an exemplary embodiment, the distal end (with respect to the X-ray source) of filter 96 is 117 mm from the X-ray source 88. The distal end of filter 98 in this exemplary embodiment is located 148 mm from the X-ray source. Furthermore, in this exemplary embodiment, the base of the filter 96 has a length along the x-axis of 45 mm, the tail has a length of 135 mm, and the connecting curved part has a length of 24.9 mm. In contrast, the base of the filter 98 has a length in the x direction of 53 mm, the tail has a length of 168 mm, and the connected curved part has a length of 34.2 mm. The dimensions of each curved part are set out in the table below. Those skilled in the art will easily understand that the above dimensions are illustrative of only one embodiment of a number of possible embodiments.

10273389

Bend-X-. Y coordinate dimensions

<td></td><td>¹ Filter 96 X</td><td>Filter 96 Y</td><td>Filter 98 X</td><td>Filter 98 Y</td>

<td></td><td> 0.00000</td><td> 0.140964</td><td> 0.00000</td><td> 0.140964</td>

<td> 5</td><td> 1.52658</td><td> 0.277455</td><td> 1.92109</td><td> 0.277455</td>

<td></td><td> 3.02431</td><td> 0.736801</td><td> 3.81409</td><td> 0.736801</td>

<td></td><td> 4.48315</td><td> 1.49686</td><td> 5.66911</td><td> 1.49686</td>

<td> 10</td><td> 5.89467</td><td> 2.53118</td><td> 7.47786</td><td> 2.53118</td>

<td></td><td> 7.25198</td><td> 3.81159</td><td> 9.23358</td><td> 3.81159</td>

<td></td><td> 8.54973</td><td> 5.30908</td><td> 10.9311</td><td> 5.30908</td>

<td> 15</td><td> 9.78406</td><td> 6.99454</td><td> 12.5666</td><td> 6.99454</td>

<td></td><td> 10.9524</td><td> 8.83954</td><td> 14.1378</td><td> 8.83954</td>

<td></td><td> 12.0536</td><td> 10.8169</td><td> 15.6436</td><td> 10.8169</td>

<td> 20</td><td> 13.0874</td><td> 12.9009</td><td> 17.0839</td><td> 12.9009</td>

<td></td><td> 14.0545</td><td> 15.0681</td><td> 18.4596</td><td> 15.0681</td>

<td></td><td> 14.9562</td><td> 17.2971</td><td> 19.7722</td><td> 17.2971</td>

<td> 25</td><td> 15.7946</td><td> 19.5688</td><td> 21.0238</td><td> 19.5688</td>

<td></td><td> 16.5720</td><td> 21.8668</td><td> 22.2169</td><td> 21.8668</td>

<td></td><td> 17.2910</td><td> 24.1766</td><td> 23.3544</td><td> 24.1766</td>

<td> 30</td><td> 17.9543</td><td> 26.4862</td><td> 24.4391</td><td> 26.4862</td>

<td></td><td> 18.8075</td><td> 27.9529</td><td> 25.7168</td><td> 27.9529</td>

<td></td><td> 19.8335</td><td> 28.7495</td><td> 27.1705</td><td> 28.7495</td>

027338 10

<td> 20.9281</td><td> 29.2923</td><td> 28.6963</td><td> 29.2923</td>

<td> 22.0739</td><td> 29.6668</td><td> 30.2769</td><td> 29.6668</td>

<td> 23.2688</td><td> 29.9013</td><td> 31.9104</td><td> 29.9013</td>

<td> 24.5186</td><td> 29.9983</td><td> 33.6029</td><td> 29.9983</td>

Motor assemblies 112, 114 position filters 96 and 100 respectively axially and independently along the x direction in the x-ray path so that the joint attenuation of the filters defines a target attenuation profile. In one embodiment, each engine positions a respective filter by pulling out and retracting respective piston assemblies 113 and 115. Those skilled in the art will easily understand that other assemblies could be used to retract and retract the filters in and out of the X-ray path. Based on the positioning of the filters, the damping effected by the filter 96 is added to the damping effected by the filter 98. Since each filter has a contour that defines a multiple thickness, the combined contours together define a plurality of possible beam profiles. A specific beam profile can therefore be selected from the plurality of possible beam profiles so that the resulting beam profile is tailored to the specific patient or object. That is, filters 96, 98 may be positioned relative to each other by their respective motor assemblies 112,114 to define a beam profile that substantially matches an approximate shape of the patient. Filters 96 and 98 are also shown to at least partially overlap. However, it is considered that the filters are positioned so that no overlap occurs.

Shown in Figure 6 is another embodiment of the present invention. To limit size limitations on the CT or X-ray system, filters 96 and 98, as shown in Figure 6, are oriented relative to each other such that tail 104 of filter 96 is positioned close to base 102 of filter 98. Similar to the orientation of Figure 5, a desired damping profile can be formed by positioning the filters 96 and 98 independently of one another. Furthermore, the volume occupied by the orientation shown in Figure 6 is effectively half of the volume required by the orientation of i. , figure 5. It should be noted that in the orientation shown in Figure 6, it is preferable that the filter 98 has a shape different from the shape of the II filter 96, so that the X-ray path lengths are identical for both filters. Determining the appropriate shape can be accomplished by determining the path length for each fan angle on filter 96 and then locating (determining) the location of the filter boundary on filter 98 with the same fan angle.

Referring now to Figure 7, another embodiment of a filter assembly according to the present invention is shown schematically. In this embodiment, filters 96 and 98 are constructed without tail portions 104 and 106, respectively. In this regard, each filter 96 and 98 has a base 100, 102 and a curved portion 108,110. The replacement of the tail sections is a retractable or stationary, and relatively thin, damping plate 116. In the illustrated embodiment, plate 116 is fixed, but it is contemplated that plate 116 can be connected to a motor assembly that controls the position of plate 116 in the X-ray path. Plate 116 also functions to provide a minimum, non-zero degree of attenuation if filters 96 and 98 are separated from each other, i.e. there is no filter overlap.

As described, filters 96 and 98 may be positioned in the X-ray path through respective motor assemblies. The positioning of filters 96 and 98 can be adjusted prior to the start of a scan and can remain fixed during data acquisition, or filters 96 and 98 can be dynamically and automatically repositioned during the data acquisition process to achieve a desired attenuation profile or target attenuation profile. In either case, it is preferable to perform an exploration scan for the object to determine an optimal beam profile for that specific object. The exploration scan preferably collects information regarding the shape and size of the object. Those of ordinary skill in the art will easily understand that other characteristics can be taken into account when determining a suitable damping profile. From this reconnaissance scan, a computer in the imaging system provides control signals to the respective motor assemblies which, when executed, cause the mo102733812 torsion assemblies to position the filters relative to each other in a specified position and, if applicable, reposition the filters during data acquisition. In this regard, the intensity of the X-ray beam at specific anatomical locations can be accurately controlled.

Referring now to Figure 8, the package / baggage inspection system 118 includes a rotatable rack 120 that has an opening 122 therein through which packages or pieces of baggage can pass. The rotatable rack 120 houses a high-frequency electromagnetic energy source 124 as well as a detector assembly 126. A conveyor system 128 is also provided and includes a conveyor belt 130 which is supported by structure 132 to automatically and continuously pass packages or items of baggage 134 through opening 102 for scanning. Objects 134 are fed through opening 122 through conveyor 130, imaging data is then acquired, and conveyor 130 removes packets 134 from opening 122 in a controlled and continuous manner. As a result, postal inspectors, baggage processors, and other security personnel can non-invasively inspect the contents of packages 134 for explosives, knives, weapons, contraband, and so on.

The present invention is directed to a radiographic imaging scanner filter assembly that allows the x-ray profile to be adjusted along a continuum tailored to the features of the object to control a dynamic range of x-ray flux and to achieve optimal dose efficiency. Furthermore, the X-ray beam can be controlled during data acquisition to account for an eccentric object. In addition, image artifacts are reduced because the filters are absent discontinuous edges or mechanical interfaces. Furthermore, fabricability of the filters is not very complex and implementation of the filters does not require extensive changes in the existing design of a radiographic imaging system.

Therefore, according to one embodiment of the present invention, a beamforming filter assembly is provided. The filter assembly includes a first movable filter that has a non-uniform thickness and a second movable filter independent of the first movable filter, which has a non-uniform thickness. Each filter is configured to be placed in a high-frequency electromagnetic energy beam to attenuate the beam for radiographic data acquisition.

027338 13

In accordance with another embodiment, a CT system is disclosed that includes a rotatable rack that has an opening to receive an object to be scanned and a high-frequency electromagnetic energy projection source configured to project a high-frequency electromagnetic energy beam to the object. A pre-subject filter assembly comprising a pair of filters and a scintillator array having a plurality of scintillator cells, each cell configured to detect high-frequency electromagnetic energy passing through the object are also provided. The CT system also includes a photodiode array which is optically coupled to the scintillator array and includes a plurality of photodiodes configured to detect light output from a corresponding scintillator cell and a data acquisition system (DAS) connected to the photodiode array and is configured to receive the photodiode outputs. An image reconstructor is provided and connected to the DAS and is configured to reconstruct an image of the object from the photodiode outputs received by the DAS. The CT system further includes a control unit configured to independently position each filter of the pair of filters in the high-frequency electromagnetic energy beam to modulate the beam so as to have a profile substantially corresponding to at least an approximate shape of the object .

In accordance with another embodiment, the present invention includes an X-ray filter assembly having a first filter and a second filter. A first motor assembly is connected to the first filter and a second motor assembly is connected to the second filter. The first and second motor assemblies are configured to independently position a respective filter in an X-ray path to define an attenuation profile that substantially approximates a target shape.

The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, in addition to those expressly stated, are possible and are within the scope of the appended claims.

102733814