Method and system for automatically determining regions in a scanned object

The present invention relates generally to imaging methods and systems, and more specifically to methods and systems for automatically determining an area within an object to be scanned using a medical imaging system in particular. is there.

Imaging systems are typically used to scan an object and are often used to identify areas of interest within the object. For example, one known computed tomography (CT) imaging system emits an X-ray beam from an X-ray source through an object of interest. The beam after being attenuated by the object is incident on the radiation detector array. The intensity of the radiation of the attenuated beam received by the detector array depends on the degree of attenuation of the X-ray beam by the object. Each detector element in the array generates a separate electrical signal that is a measurement of beam attenuation at its detector position. These attenuation measurements from the detectors are collected separately for each detector element to form a comprehensive projection data set or transmission distribution.

The X-ray source and detector array can be rotated around the object to be imaged on the gantry in the imaging plane so that the angle at which the X-ray beam crosses the object is constantly changing. A group of X-ray attenuation measurements (eg, a projection data set) from a detector array at a gantry angle is called a "view". An object "scan" consists of a set of views acquired at various gantry angles or view angles (shooting angles) during one revolution of the X-ray source and detector. The projection data set is processed to compose an image corresponding to the 2D slices taken through the object at various angles. An exemplary method of reconstructing an image from a projection data set is called filter-corrected backprojection.

Obtaining an optimal scan, eg, an optimal CT scan at the lowest possible dose, is based on patient-dependent information. X-ray flux management systems are known to obtain patient-dependent information to determine various scanning operating parameters such as proper tube currents, bowtie filters and patient centering. Other information, such as where to scan the patient, must be determined by the technician and manually entered into the system in some way. Generally, this manual operation is performed by using a graphic Rx display device to mark a position on the scout image with a mouse and a cursor. A scout image is a radiation projection image of an object acquired while translating the object in the Z-axis direction using an X-ray tube in a fixed stationary position. Marking a position on a scout image can be a very time consuming and complex process that depends on the experience of the technician. Not only does this reduce scanning throughput, but it can also increase errors, for example, based on technician misjudgment.

In addition, many potential dose management features can be cumbersome and time consuming for the user as they are currently impractical or require identification of the required anatomical information. For example, reductions in radiation dose for organs that are sensitive to radiation dose are not currently available with CT scanners. One reason is that the technician must identify and mark the location of sensitive organs such as the chest, thyroid, eyes, and uterus on the graphic Rx display. An averaged Scout projection over the torso (from the top of the lungs to the buttocks) is used to ideally determine the size-adjusted noise figure and patient center alignment. These results can occur when averaging includes neck or leg parts that can occur using known manual marking methods (this can occur using known manual marking methods). May be adversely affected. In addition, radiologists may want to use different scan parameters for different regions of the helical scan. For example, in the chest-abdominal protocol, a relatively high noise figure may be desirable because nodular lesions have greater contrast than lesions in the liver. When different areas (such as the lungs) are manually identified by the technician on the graphic Rx display, they result in more anatomical structures than required for areas of clinical interest. This may increase patient irradiation dose and tube load.

In addition, in some areas of the anatomy, special compute intensive Type image reconstruction pre-processing correction step may be required. For example, the head requires corrections to compensate for beam hardening due to bone and detector spectral errors that can cause artifacts due to the presence of the skull. This correction is very computationally intensive as it requires an iterative approach to the computation. If this correction were applied to all individual images, the image reconstruction time would be too long. In some hospitals, traumatic disorders are scanned in a single pass that includes both the head and torso. In this case, the area is not properly identified due to a technician's error in the manual identification process, so corrections may be made for data that does not require correction. Effective dose is also a common metric that allows estimation of biological hazards and comparison of different imaging modality and dose. There are many known methods for calculating the effective dose, but all of them require knowing the organs exposed to X-rays so that the appropriate organ dose can be determined. There is. A lengthy Monte Carlo simulation is needed to obtain accurate organ exposures. To speed up the calculation, organ doses can be characterized by anthropomorphic phantoms and deterministic equations developed to convert exposures of a given human region into organ dose estimates. However, manual organ determination and identification again adds extra time to this process.<patcit num="1"><text>U.S. Pat. No. 7031425</text></patcit>

<p num="0007"> Therefore, known methods for identifying regions within an object to be scanned are often time consuming and often result in human error. Moreover, this manual identification also increases the time and complexity of the process of using the manual identification information.</p>

<p num="0008"> In one embodiment, a method for controlling an imaging system is provided. The method includes performing a scout scan of the object and automatically determining a region within the object based on attenuation information from the scout scan.</p><p num="0009"> In another embodiment, a method is provided for locating an area in the human body scanned by a medical imaging system. The method includes performing a scout scan of the human body with a medical imaging system and automatically locating anatomical structures within the human body using the scout scan.</p><p num="0010"> Yet another embodiment provides a medical imaging system. The system includes a scanner configured to perform a scout scan and an anatomical structure elucidator configured to automatically determine an anatomical position in the human body based on the scout scan. Including.</p>

FIG. 1 is a perspective view of an exemplary imaging system 10. FIG. 2 is a schematic block diagram of the imaging system 10 (shown in FIG. 1). In an exemplary embodiment, the imaging system 10 is a single modality imaging system, such as a computed tomography (CT) system. However, it should be understood that various embodiments can be implemented in the context of an imaging system with more than one imaging modality (ie, a multi-modality imaging system). Also, various embodiments can be described in connection with a particular imaging modality, such as CT imaging, but different imaging modality for medical and non-medical purposes, such as positron emission tomography (PET), and general. Any type of X-ray or nuclear imaging can be used.

Explaining FIGS. 1 and 2 in detail here, a computed tomography (CT) imaging system 10 is shown as including a gantry 12 for a CT scanner. The gantry 12 contains an X-ray source 14, which projects an X-ray beam 16 toward a detector array 18 on the opposite side of the gantry. The detector array 18 is formed by a plurality of detector elements 20 (for example, a plurality of detector rows), and these detector elements 20 together transmit projected X-rays that have passed through an object 22 (for example, a patient). Detect. The detector array 18 can be manufactured in a single slice or multi-slice configuration. Each detector element 20 generates an electrical signal that represents the intensity of the X-ray beam incident on it, and thus the degree of attenuation of the X-ray beam as it passes through the object 22. During a scan to collect X-ray projection data, the gantry 12 and its mounted components rotate around a center of rotation 24. The center of rotation 24 can define the inspection axis.

The rotation of the gantry 12 and the operation of the X-ray source 14 are controlled by the control mechanism 26 of the imaging system 10. In one embodiment, the control mechanism 26 includes an X-ray control device 28 that supplies electric power and timing signals to the X-ray source 14, and a gantry motor control device 30 that controls the rotation speed and position of the gantry 12. The data acquisition system (DAS) 32 in the control mechanism 26 samples the data (eg, analog data) from the detector element 20 and converts (or conditions) the data into a digital signal for further processing. .. The DAS32 outputs, for example, a projection data set containing attenuation measurements obtained from a scout scan at a particular gantry rotation angle. A set of projected data sets forms a complete scan of object 22. The image reconstruction module 34 receives the X-ray data sampled and digitized from the DAS 32 and performs image reconstruction as described below. The reconstruction data set output by the reconstruction module 34 is supplied as an input to the computer 36 or as an input to another processing device that stores the reconstruction data set in the memory 38. The reconstructed data set can represent a volume data set and / or an image slice passing through object 22. The computer 36 also receives commands and scanning parameters from the operator via an operator console 40 that can include one or more input to use, eg, a keyboard (not shown). An attached display device, such as a cathode ray tube display device 42, allows the operator to observe the reconstructed image and other data from the computer 36. Further, the computer 36 supplies the control signals and information to the DAS 32, the X-ray control device 28 and the gantry motor control device 30 by using the commands and parameters supplied by the operator. Moreover, the computer 36 operates a table motor controller 44 that controls the electric table 46 to position the object 22 within the gantry 12. Ingredients

In one embodiment, the computer 36 reads instructions and / or data from a computer-readable medium such as a flexible disk, CD-ROM, DVD, or from another digital source (such as a network or the Internet). Includes a read / write device (not shown), eg, a flexible disk drive, a CD-ROM drive, a DVD drive, a magneto-optical disk (MOD) device, or a network connection device such as an Ethernet device. Includes other digital devices, as well as digital means to be developed. In another embodiment, the computer 36 executes an instruction stored in firmware (not shown). The computer 36 is programmed to perform the functions described in this document, and the term "computer" used in this document is not limited to integrated circuits called computers in the art, but in a broad sense, computers. , Processors, microcontrollers, microcontrollers, programmable logic controllers, application-specific integrated circuits, and other programmable circuits, these terms are used interchangeably herein.

A device for determining a specific region of the object 22 is communicatively coupled to the computer 36, which in one exemplary embodiment is an anatomical structure determination device 21. Although the anatomical structure determination device 21 is shown as a separate means, it is of course possible to incorporate the functions performed by the anatomical structure determination device 21 into, for example, the functions performed by the computer 36. Is. Therefore, the anatomical structure determination device 21 can be embodied in a software code segment executed by a multifunctional processor, or can be embodied in a combination of hardware and software.

Further, although described in relation to the medical environment, embodiments of the present invention are for industrial use, such as a CT system for baggage scanning typically used in a traffic center such as an airport or train station. It is considered that it can be put into practical use in connection with other imaging systems including an imaging system.

Various embodiments make automatic determination of the area of the object based on a preliminary scan. Various thresholds determined by the projection area or oval ratio are used to determine the location of at least one landmark within an object, and from that location to other areas. Identify. FIG. 3 is a flow diagram illustrating an exemplary method 60 performed by the anatomical structure detector 21 to automatically determine an anatomical region or landmark in the human body. Here, method 60 can be modified and used in connection with scanning of a non-human object by an imaging system other than a medical imaging system.

More specifically, Method 60 presents an automatic anatomical structure determination process for use in connection with medical imaging systems, especially CT imaging systems. Specifically, at step 62, a scout scan, which may be either a lateral or anteroposterior (A / P) scout scan, is performed as known to create a scout image. To do. The scout image is essentially an attenuation image. The projected area (PA) and ellipticity (OR) of the Scout scan are then used to identify anatomical regions or landmarks within the human body. Note that in an exemplary embodiment, the cross section of the human body 100 as shown in FIG. 4 can be considered as an ellipse 102 with an elliptical cross section of dimensions x and y. The patient's projection is formed by a set of individual detector channel measurements. The channel measurement represents the X-ray transmission value along the line passing through the patient. The transmission value is processed to represent the effective μ of the object along the transmission path and the number of attenuation units related to the length. The sum of the individual channel measurements is PA106. The set of highest measurements in the projection is called the projection measure (PM) 104. The ellipticity is the x / y ratio of the effective ellipse. The x-dimension for ellipticity is determined using the equation for the area of the ellipse. Here, PA106 is the area of the ellipse, and PM104 is the y-axis of the ellipse. In essence, each slice from a scout scan performed by a CT scanner in an imaging system is a projection. A set of projections produces a scout image.

Once the attenuation PA for each projection or sample along the entire scan is determined, for example, for each slice along the scan, at step 64, the attenuation PA for the first PA at the start of the scan is first. It is determined whether or not it is smaller than the threshold value of, or is larger than the first threshold value and smaller than the second threshold value. For example, in the case of a CT scan, step 64 determines if the degree of attenuation for the first PA is less than 160 or between 160 and 400. It should be noted here that values including weakness values for the different thresholds presented herein can be modified or modified as desired or as needed (eg, based on the object to be scanned). If the degree of attenuation is less than 160, at step 66, the scan start position is identified as the CT scanner head cage, or more specifically, the scan bed head cage to support the human head. Will be done. This discrimination is made, for example, based on the distribution of the average projected area of the head cage. The beginning of the head is then located by finding a circular object, eg, a point where the ellipticity is equal to 1. If the ellipticity is not 1, the object is not circular and is not identified as the beginning of the head. The ellipticity is the ratio of the length to the width of the object to be scanned, for example the ratio of the x and y dimensions as shown in FIG.

If in step 64 it is determined that the initial PA attenuation is between 160 and 400 (and the attenuation is substantially smooth or flat over that region), then in step 68 the scan start position. Is identified as a CT scanner table, and the onset of the head is determined by locating in a scout scan that the PA attenuation is greater than the third threshold, in this example the PA attenuation is greater than 420. To. Table identification can be done, for example, based on the distribution of the average projected area of the scanner table. It should be noted here that substantially flatness is identified, for example, when the standard deviation occurs at a given number, eg, at the first 10 data points measured in a Scout scan. I want to.

If the initial PA attenuation is neither less than the first threshold nor between the first and second thresholds, the scan start position is identified as a point within the object, and then at step 70, It is determined whether the first PA attenuation is less than the fourth threshold within a predetermined distance (eg, length) along the object to be scanned. In this example, at step 70, a determination is made as to whether the first PA attenuation is less than 850 at any point within about 300 millimeters from the first scan point. If the first PA attenuation is not less than the fourth threshold at a point along a given distance, then in step 72, the scan start position is identified as starting within the body of the object. If the first PA attenuation is less than the fourth threshold at a point along a given distance, then in step 74, the scan start position is identified as the head of the object.

In essence, if at stage 64 it was determined that the Scout scan was initiated in an unoccupied portion of the table, a determination would be made for the first significant increase in PA attenuation, eg, where 400 or more would occur. The location is identified as the beginning of the head. If the head cage is identified as the starting point for scout scanning, the first point where the ellipticity is substantially greater than or equal to 1 is determined and identified as the beginning of the skull. If it is determined that the Scout scan started at a point along the object, there is a substantial reduction in the magnitude of the attenuation at the start of the Scout scan, and such a magnitude level is the neck of the object. By determining if it is low enough to be identified as, a determination is made as to whether the scan started at the head or part of the torso.

After determining or identifying the location of the starting point of the scout scan in the torso, in an exemplary embodiment, a determination is made to identify the diaphragm of the torso. The diaphragm region is generally characterized by a sharp increase in attenuation in the projected area. For example, once the position of the maximum PA attenuation is determined, for example, a determination is made as to whether the distance is appropriate based on the distance from the beginning of the fuselage for which the maximum PA attenuation has been determined. If the head is identified, the maximum PA attenuation, or more specifically, this distance to identify the maximum tilt is limited to a given distance from the apex of the head, otherwise the distance. Is limited to shorter distances. Specifically, with reference to FIG. 3, if the beginning of the head is located at stage 66 or 68, or if it is determined at stage 74 that the scout scan started at the head, then at stage 76, A point at a predetermined distance from the apex of the head where the maximum tilt of PA attenuation has occurred is identified. In this example, at stage 76, a determination is made as to whether the point with the greatest PA attenuation tilt is within about 400 mm to about 600 mm from the identified apex of the head, and if so, this point is the diaphragm. Identified as the location of. If it is determined at stage 72 that the scout scan has been initiated within the fuselage, then at step 78 another predetermined distance point from the beginning of the fuselage where the maximum tilt of PA attenuation occurs is identified. In this example, at stage 78, it is determined whether the point with the greatest PA attenuation tilt is within about 400 mm from the identified starting point of the torso, and if so, this point is the position of the diaphragm. Be identified.

Also, a determination is made regarding the width of each projection at the position of the diaphragm. For example, a width threshold can be used to ensure that the projection does not include the arm or shoulder of the part that may have been involved in determining the maximum tilt.

After the point of maximum slope of PA attenuation is identified in either step 76 or 78, step 80 determines if the ellipticity is greater than a given value, 0.55 in this example (lower ellipse). The rate generally identifies a person's neck). If the ellipticity is 0.55 or less, in step 82 it is determined that the shoulder or neck has been identified, and the point where the maximum slope of PA attenuation occurs is again the given additional distance, about 200 mm in this example ~ Judgment is also made over about 300 mm. After that, or if the ellipticity is 0. If greater than 55, at step 84 a determination is made as to whether the position of maximum tilt occurred at a point known to be within the range of the Scout scan, eg, based on the known length of the Scout scan. .. If at step 84 it is determined that the point that identifies the position of the diaphragm is within the scope of the scout scan, then at step 86, for example, the buttocks and other areas of interest, based on this position and the degree of attenuation at this point. The position of other parts of the fuselage, including, can be identified. Moreover, estimating the size of the patient's body by the PA attenuation value, for example, using the mean PA attenuation value for patients of different sizes in the diaphragm as determined by clinical evaluation or research. Can be done. In essence, PA attenuation is associated with a person's height and with an intermediate distance, such as the distance from the diaphragm to the buttocks. It should be noted here that individual linear fitting functions can be used to estimate from the diaphragm to other areas of interest, such as other organs of interest. In addition, the area from the diaphragm to the buttocks can be used to calculate the center alignment error, and a typical relative distance measurement to the diaphragm, which can be determined, for example, based on age and gender. Based on, a bowtie-shaped selection filter can be used to identify the location of other areas in the human body. Information such as the above can be determined by clinical measurements or, for example, using known charts / tables described in the literature below. Those references are "The Measure of Man &amp; Woman", Henry Dreyfuss, 2002, or "IGRP Publication 70: Basic Anatomical &amp; Physiological Data for Use in Radiologic Protection", published by Pergamon, 1996, both of which. Incorporate the whole into this book by citation.

If in step 84 it is determined that the point is not within the scout scan, then in step 88 whether this point is on the scout scan and is the beginning of the identified head as previously mentioned. Judgment is made. If that position is identified as the beginning of the head, at stage 90, for example, of other parts of the human body, including the eyes, shoulders and other areas of interest based on PA attenuation as previously mentioned. The position can be identified. If step 88 determines that this point is not on the scout scan and / or is not the beginning of the head, then step 92 identifies any landmarks for use in locating other areas of the human body. It is judged that it cannot be done. There, an error display (eg, visual or audible) can be provided.

Therefore, using tables or measurements of the size, rate of change (inclination) and symmetry of the X-ray data, and the expected anatomical structure of the human body (compared to age, gender, size, etc.) , Various embodiments of the present invention provide automatic determination of regions within the human body to be scanned. For example, the anatomical position in the human body can be determined automatically using scout scanning. In addition, a priori protocols and patient information can be used to improve prediction accuracy.

Automatic positioning of areas within an object, or more specifically, automatic positioning of areas within the human body, can be used in connection with other procedures. For example, various embodiments can be used in connection with CT dose reduction for organs that are sensitive to radiation dose. Once the location of the sensitive organ is identified, the system can reduce and increase mA respectively when in front of and behind the area of the automatically identified sensitive organ. Automatic identification can reduce or eliminate the need to mark various locations on the graphic Rx display. In addition, automatic identification of the human body can provide more consistently assisted patient centering and size adjusted noise figure performance. Also, different areas (eg, lungs) can be automatically identified on the graphic Rx display to minimize the need for manual identification of the area to be scanned. Accurate automatic identification of the scan area can minimize the extra scan range and save patient dose and tube load.

In addition, areas of the anatomical structure that may require special computationally intensive image reconstruction pre-processing correction steps can be automatically identified. In addition, the effective CT irradiation dose can be calculated by automatically determining the organs exposed to X-rays. Automatically identified location information, such as patient-dependent anatomical location and landmarks, can be used to automatically adjust the start or marker position, as well as the loaded or unloaded position of the medical imaging scanner. it can. This information can also be used to center the human body in an imaging scanner based on landmark positions or anatomical structures.

Having described the invention in various specific embodiments, those skilled in the art will appreciate that the invention can be modified and practiced within the spirit and scope of the claims.

<figref num="1">FIG. 3 is a perspective view of an exemplary imaging system operated according to an embodiment of the present invention.</figref><figref num="2">It is a block diagram of the imaging system shown in FIG.</figref><figref num="3">FIG. 5 is a flow chart of a method for automatically determining a region in an object to be scanned according to an embodiment of the present invention.</figref><figref num="4">It is a schematic diagram which illustrates the projected area determined according to one Embodiment of this invention.</figref>

Code description

003210 Imaging system 12 Gantry 14 X-ray source 16 X-ray beam 18 detector array 20 Detector element 22 Object 24 center of rotation 26 Control mechanism 32 Data collection system 42 Cathode ray tube display device 48 gantry opening 60 exemplary method 100 human body 102 ellipse 104 Projection Measure (PM) 106 Projected area (PA)