Contact avoidance apparatus and medical apparatus

A CT apparatus comprises; a sensor section outputting distance data for determining a distance between the sensor section and at least part of a subject to be examined laid on a cradle; contour-data generating means for generating contour data representing a contour of the at least part of the subject based on the distance data obtained from the sensor section; and deciding means for deciding whether or not there is a risk for said subject to come into contact with said gantry while said gantry or said table is moving based on data representing a limit of a range up to which said subject can come close to the gantry and on said contour data.

FIELD OF THE INVENTION

The present invention relates to a contact avoidance apparatus for avoiding contact of a subject to be examined laid on a cradle of a table with a gantry, a medical apparatus having the contact avoidance apparatus, and a program applied to the contact avoidance apparatus.

BACKGROUND OF THE INVENTION

Medical apparatuses, such as a CT (Computed Tomography) apparatus and an MRI (Magnetic Resonance Imaging) apparatus, are known as apparatuses for acquiring an image of the inside of a subject to be examined. Since the CT and MRI apparatuses are capable of non-invasively imaging the subject, they are used as apparatuses indispensable in diagnosing the subject's health.

On the other hand, in imaging the subject with the CT apparatus and MRI apparatus, a radiographer has to carry out various tasks for preparing a scan, which poses a problem that radiographers experience a lot of work stress. Accordingly, to mitigate the radiographers' work stress, there is disclosed a technique of automatically operating a table of a CT apparatus (see PTL 1).

According to Japanese Patent Application Publication No. 2014-161392, a table can be automatically operated, which makes it possible to mitigate the radiographers' work stress.

On the other hand, a cradle of the table has the subject laid thereon. Therefore, it is necessary to avoid contact of the subject with the gantry while actuating the table to move the subject toward a bore of the gantry. Especially in the case that the table is automatically operated, it is important to provide the CT apparatus with means for avoiding contact between the subject and the gantry. The CT apparatus described in PTL 1, however, has no such contact avoidance means. Therefore, according to PTL 1, while moving the subject toward the bore of the gantry, the operator has to pay attention to motion of the table with his/her hand constantly placed on a stop button of the gantry so that he/she can promptly stop movement of the table when the subject is about to collide with the gantry; this poses a problem that radiographers' work stress is difficult to fully mitigate.

Therefore, there is a need for a technique capable of automatically avoiding contact between the subject and the gantry.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the present invention is a contact avoidance apparatus for avoiding contact of a subject to be examined laid on a cradle of a table with a gantry, said apparatus comprising:

a sensor section for acquiring distance data for determining a distance between said sensor section and at least part of said subject laid on said cradle;

contour-data generating means for generating contour data representing a contour of said at least part of said subject, wherein the contour-data generating means determines information on positions of points on a body surface of said at least part of said subject with respect to said cradle based on said distance data, and generates said contour data based on said information on positions; and deciding means for deciding whether or not there is a risk for said subject to come into contact with said gantry while said gantry or said table is moving based on data representing a limit of a range up to which said subject can come close to said gantry and on said contour data.

A second aspect of the present invention is a medical apparatus comprising:

a gantry;

a cradle on which a subject to be examined is laid;

a sensor section for acquiring distance data for determining a distance between said sensor section and at least part of said subject laid on said cradle;

contour-data generating means for generating contour data representing a contour of said at least part of said subject, wherein the contour-data generating means determines information on positions of points on a body surface of said at least part of said subject with respect to said cradle based on said distance data, and generates said contour data based on said information on positions; and

deciding means for deciding whether or not there is a risk for said subject to come into contact with said gantry while said gantry or said table is moving based on data representing a limit of a range up to which said subject can come close to said gantry and on said contour data.

A third aspect of the present invention is a program applied to a contact avoidance apparatus for avoiding contact of a subject to be examined laid on a cradle with a gantry using distance data for determining a distance between a sensor section and at least part of said subject laid on said cradle, said program being for causing a computer to execute:

contour-data generating processing of generating contour data representing a contour of said at least part of said subject, wherein the contour-data generating processing determines information on positions of points on a body surface of said at least part of said subject with respect to said cradle based on said distance data, and generates said contour data based on said information on positions; and

deciding processing of deciding whether or not there is a risk for said subject to come into contact with said gantry while said gantry or said table is moving based on data representing a limit of a range up to which said subject can come close to said gantry and on said contour data.

Contour data representing a contour of the subject is generated. Therefore, by using data representing a limit of a range up to which the subject can come close to the gantry and the contour data, it is possible to recognize whether or not the subject is approaching beyond the range up to which the subject can come close to the gantry. Thus, it is possible to decide whether or not there is a risk for the subject to come into contact with the gantry.

DETAILED DESCRIPTION OF THE INVENTION

Now embodiments for practicing the invention will be described hereinbelow, although the present invention is not limited to the following embodiments.

FIG. 1is an external view of an X-ray CT apparatus in a first embodiment.

As shown inFIG. 1, the X-ray CT apparatus1comprises a gantry2, a table4, and an operation console6.

The gantry2and table4are installed in a scan room R1. The operation console6is installed in an operation room R2different from the scan room R1.

The gantry2is provided on its front surface with a sensor section19and a display section18. The sensor section19and display section18will be discussed later.

FIG. 2is a diagram schematically showing a hardware configuration of the X-ray CT apparatus1in accordance with the first embodiment.

The gantry2has an X-ray tube21, an aperture22, a collimator device23, an X-ray detector24, a data acquisition system (DAS)25, a rotating section26, a high-voltage power source27, an aperture drive apparatus28, a rotation drive apparatus29, and a gantry/table control section30. InFIG. 2, the sensor section19and display section18provided on the front surface of the gantry2are omitted in the drawing.

The X-ray tube21and X-ray detector24are disposed to face each other sandwiching an imaging volume, i.e., a bore B of the gantry2, in which a subject5to be examined is placed.

The aperture22is disposed between the X-ray tube21and bore B. The aperture22shapes X-rays emitted from an X-ray focus of the X-ray tube21toward the X-ray detector24into a fan beam or a cone beam.

The collimator device23is disposed between the bore B and X-ray detector24. The collimator device23removes scatter rays that would otherwise impinge upon the X-ray detector24.

The X-ray detector24has a plurality of X-ray detector elements two-dimensionally arranged in directions of the span and the thickness of the fan-shaped X-ray beam emitted from the X-ray tube21. The X-ray detector elements each detect X-rays passing through the subject5placed in the bore B, and output electric signals depending upon their intensity.

The data acquisition system25receives the electric signals output from the X-ray detector elements in the X-ray detector24, and converts them into X-ray data for collection.

The table4has a cradle41and a drive apparatus42. The subject5is laid on the cradle41. The drive apparatus42drives the table4and cradle41so that the cradle41is movable in y- and z-directions.

The high-voltage power source27supplies high voltage and electric current to the X-ray tube21.

The aperture drive apparatus28drives the aperture22to modify the shape of its opening.

The rotation drive apparatus29rotationally drives the rotating section26.

The gantry/table control section30controls several apparatuses and sections in the gantry2, the drive apparatus42, etc.

The gantry2also has the display section (referred to as “gantry display section hereinbelow)18and the sensor section19in an upper portion of its surface on the side of the table4installed.

FIG. 3is an explanatory diagram for the sensor section19and gantry display section18.FIG. 3shows a side view of the gantry2and table4.

The gantry display section18has a display with touch-panel-driven GUI (Graphical User Interface). The gantry display section18is connected to the operation console6via the gantry/table control section30. A radiographer50performs a touch-panel operation on the gantry display section18, whereby he/she can achieve several kinds of operations and settings related to the X-ray CT apparatus1. The gantry display section18can also display several kinds of setting screens, graph displays, images, etc., on its display.

The sensor section19has a number of pixels of n by m, and is configured to acquire image data and distance data. The numbers n and m are, for example, n=640 and m=480. Each pixel in the sensor section19has an imaging section for acquiring the image data.

The imaging section is a CCD (Charge Coupled Device) for acquiring color information in, for example, RGB (Red Green Blue), or a monochrome CCD. The imaging section outputs the image data for the subject5laid on the cradle41of the table4.

In addition to the imaging section described above, each pixel in the sensor section19is provided with a light receiving section for acquiring the distance data. The light receiving section receives reflected rays of infrared rays emitted from an infrared source provided in the sensor section19toward the subject5, and based on the received reflected rays, outputs the distance data for determining a distance between the sensor section19and each position on the surface of the subject5. The sensor section19that may be used is, for example, a TOF camera manufactured by Panasonic Photo & Lighting Co., Ltd. It should be noted that infrared rays may be replaced with ultrasound or laser light for use to acquire the distance data.

InFIG. 3, a range of a field of view of the sensor section19is defined so that the portion of the table4on the side of the gantry2falls within a field-of-view region RV while the portion of the table4on the side opposite to the gantry2falls outside the field-of-view region RV. However, the field-of-view region RV of the sensor section19may be defined so that the whole table4falls within the field-of-view region RV.

The gantry/table control section30drives the drive apparatus42as needed based on input signals from the gantry display section18and/or sensor section19.

Returning toFIG. 2, the explanation will be continued below.

The operation console6accepts several kinds of operations from the radiographer. The operation console6has an input device61, a display device62, a storage device63, and a computational processing device64.

As used herein, a direction of the body axis of the subject5, i.e., a direction of carrying of the subject5by the table4will be referred to as z-direction. A vertical direction will be referred to as y-direction, and a horizontal direction orthogonal to the y- and z-directions will be referred to as x-direction.

FIG. 4is a block diagram of main functions of the X-ray CT apparatus. While in practice, the X-ray CT apparatus has a large number of functional blocks, only those necessary in the explanation of the first embodiment are shown here.

In the first embodiment, the X-ray CT apparatus has, as its main functional blocks, an image producing section101, a display control section102, a contour-data generating section103, a detecting section104, a calculating section105, a first deciding section106, and a second deciding section107.

The image producing section101produces an image of the subject5based on the image data obtained from the sensor section19.

The display control section102controls the gantry display section18so that an image and/or necessary information etc. are displayed in the gantry display section18.

The contour-data generating section103generates contour data representing a contour of the subject5based on the distance data obtained from the sensor section19. A method of generating the contour data will be discussed later.

The detecting section104detects a body part to be imaged of the subject5based on the distance data obtained from the sensor section19.

The calculating section105calculates an amount Δycof movement of the cradle41in the y-direction and an amount Δzcof movement of the cradle41in the z-direction required to carry the body part to be imaged of the subject5to a prespecified position within the bore B of the gantry2. A method of the calculation will be discussed later.

The first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on a limit surface representing a limit of a range up to which the subject5can come close to the gantry2. Now the limit surface will be described below.

FIG. 5is an explanatory diagram for the limit surface.

A limit surface Sb represents a limit of the range up to which the subject5can come close to the gantry2. Data of the limit surface Sb is stored in, for example, the storage device63. In the present embodiment, the limit surface Sb is defined to represent a limit of a range up to which the subject5can come close to a front surface2aand an inner wall surface2bof the gantry2. The limit surface Sb may be defined so that, for example, it covers the front surface2aof the gantry2at a position away from the front surface2aof the gantry2by a distance Δd1and also it covers the inner wall surface2bof the gantry2at a position away from the inner wall surface2bof the gantry2by a distance Δd2. The distances Δd1and Δd2may be set so that Δd1=Δd2or Δd1≠Δd2. Δd1and Δd2may be set at a value of a few centimeters, for example. The value of Δd1may be identical all over the front surface2aof the gantry2, or it may be set at different values by hypothetically dividing the front surface2aof the gantry2into a plurality of facets and setting different values on a facet-by-facet basis. Likewise, the value of Δd2may be identical all over the inner wall surface2bof the gantry2, or it may be set at different values by hypothetically dividing the inner wall surface2bof the gantry2into a plurality of facets and setting different values on a facet-by-facet basis.

The first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2in the case that at least part of the subject5comes close to the gantry2beyond the limit surface Sb. A particular method for the decision method will be discussed later.

The second deciding section107decides whether or not the cradle41has moved by the amounts Δycand Δzcof movement, which will be discussed later.

The image producing section101constitutes an example of the image producing means, the contour-data generating section103constitutes an example of the contour-data generating means, and the first deciding section106constitutes an example of the deciding means.

Programs for implementing these functional blocks may be stored in the storage device63in the operation console6, or stored in at least one of a storage section in the gantry2and that in the table4. The gantry2, table4, and operation console6serve as computers for executing the programs stored in the storage device or storage section(s), and the computers function as respective functional blocks by executing the programs stored in the storage device or storage section(s). It is possible to store at least part of the programs into a storage section or a storage medium90(seeFIG. 2) externally connected with the operation console6. Details of the functions shown inFIG. 4will be described later in explaining the processing flow in the X-ray CT apparatus.

In the present embodiment, the CT apparatus1comprises a contact avoidance apparatus for avoiding contact of the subject5with the gantry2while the subject5is being carried toward the bore B of the gantry2. Therefore, the subject5can be safely carried toward the bore B of the gantry2. Now the flow of carrying the subject5toward the bore B of the gantry2will be described referring toFIG. 6.

FIG. 6is a diagram showing an exemplary operation flow in the first embodiment.

At Step S1, the radiographer lays the subject5on the cradle41of the table4(seeFIG. 7). The radiographer also sets scan conditions (a body part to be imaged, for example) for the subject5. While the body part to be imaged is considered as a head part here, it is not limited thereto and may be any other body part, such as a shoulder part, a chest part, an abdominal part, or a leg part. After the subject5is laid on the cradle41as shown inFIG. 7, the process goes to Step S2.

At Step S2, the image producing section101(seeFIG. 4) produces an image of the subject5based on image data obtained from the sensor section19. The display control section102(seeFIG. 4) controls the gantry display section18so that the image produced by the image producing section101is displayed in the gantry display section18.FIG. 7schematically shows the image displayed in the gantry display section18.

Moreover, at Step S2, the contour-data generating section103(seeFIG. 4) generates contour data representing a contour of the subject5in the z-direction falling within the field-of-view region RV of the sensor section19based on distance data obtained by the sensor section19.FIG. 8is an explanatory diagram for an exemplary method of generating the contour data.

In the present embodiment, the contour data is determined based on information on positions at points on the surface of the subject5. In determining the value of the contour data at z=za, for example, a maximum of y-coordinates y1, y2, . . . , yk, . . . , ynof points P(x1, y1, za), P(x2, y2, za), . . . , P(xk, yk, za), . . . , P(xn, yn, za) at z=zaon the body surface of the subject5can be set for the value of the contour data at z=za. It should be noted that the value of the contour data is not limited to the maximum of y1, y2, . . . , yk, . . . , yn, and it may be an average of y1, y2, . . . , yk, . . . , yn, for example.

The contour data D generated is schematically shown inFIG. 7. In the present embodiment, the contour data D is generated as a contour line representing the contour of the subject5in the z-direction. After generating the contour data D, the process goes to Step S3.

At Step S3, the detecting section104(seeFIG. 6) generates, based on the distance data, three-dimensional (3D) data representing the 3D shape of the body surface of the subject5in the field-of-view region RV, and executes processing for detecting the body part to be imaged from the 3D data. Since the head part is set for the body part to be imaged here, the detecting section104executes processing for detecting the head part of the subject5. An exemplary method of detecting the body part to be imaged comprises preparing beforehand templates representing the standard shapes of body parts to be imaged, such as the head part, shoulder part, chest part, abdominal part, and leg part, and performing matching of the 3D data with each template to detect the body part to be imaged. Referring toFIG. 7, the head part, which is the body part to be imaged, falls within the field-of-view region RV. Thus, the detecting section104can detect the head part based on the distance data.FIG. 9shows a position Pv of the detected head part as Pv=(yi, zi). The position yiof the head part in the y-direction here is calculated as a mid-position between a maximum yvof the position on the surface of the head part of the subject5in the y-direction, and a position y0of the cradle41in the y-direction, that is, y=(y0+yv)/2. The position ziof the head part in the z-direction is calculated as a mid-position in a range zi1to zi2of the head part of the subject5in the z-direction, that is, z=(zi1+zi2)/2. However, any position offset from the mid-positions described above may be calculated as the position of the head part.

After detecting the head part, the process goes to Step S4.

At Step S4, the calculating section105(seeFIG. 4) calculates amounts Δycand Δzcof movement of the cradle41required to position the head part of the subject5at a prespecified position (yr, zr) in the bore B of the gantry2(seeFIG. 10).

FIG. 10is an explanatory diagram for an exemplary method of calculating the amounts Δycand Δzcof movement of the cradle41.

Δycis the amount of movement of the cradle41in the y-direction required to position the head part of the subject5at the prespecified position yrin the bore B of the gantry2in the y-direction. On the other hand, Δzcis the amount of movement of the cradle41in the z-direction required to position the head part of the subject5at the prespecified position zrin the bore B of the gantry2in the z-direction. Since the position of the body part to be imaged in the y-direction is yihere, the calculating section105calculates Δyc=yr−yi. Similarly, since the position of the body part to be imaged in the z-direction is zi, the calculating section105calculates Δzc=zi−zr. After calculating the amounts Δycand Δzcof movement, the process goes to Step S5.

At Step S5, whether or not the radiographer has input a command to carry the subject5into the bore B of the gantry2is decided. In the case that the command of carrying is input, the process goes to Step S6. On the other hand, in the case that the command of carrying is not input, the process waits until the command of carrying is input.

Once the radiographer has input the command to carry the subject5into the bore B of the gantry2via the input device, the process goes to Step S6.

At Step S6, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour data (contour line) D. Now a method of the decision will be particularly described below.

The first deciding section106reads out, from the storage section, the limit surface Sb (seeFIG. 5) representing the limit of the range up to which the subject5can come close to the gantry2. The first deciding section106then decides whether or not the contour line D that the contour data represents is tangent to or intersects the limit surface Sb. In the case that the contour line D is tangent to or intersects the limit surface Sb, the first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2. In this case, the process goes to Step S17, where the cradle (table) stops and the flow is terminated. On the other hand, in the case that the contour line D that the contour data represents is not tangent to or does not intersect the limit surface Sb, the first deciding section106decides that there is no risk for the subject5to come into contact with the gantry2, and the process goes to Step S7.

InFIG. 10, the contour line D lies farther away from the gantry2with respect to the limit surface Sb. Therefore, the first deciding section106decides that the contour line D is not tangent to or does not intersect the limit surface Sb. In this case, the first deciding section106decides that there is no risk for the subject5to come into contact with the gantry2, and accordingly, the process goes to Step S7.

At Step S7, the control section30controls the table4so that the cradle41starts moving in the y-direction. Thus, movement of the cradle41in the y-direction is started.FIG. 11shows a condition in which the cradle41has moved by Δy=Δy1in the y-direction.

At Step S8, the image producing section101produces an image of the subject5based on image data obtained from the sensor section19. The display control section102controls the gantry display section18so that the image produced by the image producing section101is displayed in the gantry display section18. InFIG. 11is schematically shown the image at a time point when the cradle41has moved by Δy=Δy1in the y-direction.

Moreover, the contour-data generating section103generates contour data at the time point when the cradle41has moved by Δy=Δy1in the y-direction based on distance data obtained from the sensor section19.

At Step S9, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour line D. In the case that the contour line D is tangent to or intersects the limit surface Sb, the first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2. In this case, the process goes to Step S17, where the cradle (table) stops and the flow is terminated. InFIG. 11, the contour line D lies farther away from the gantry2with respect to the limit surface Sb. Therefore, the first deciding section106decides that the contour line D is not tangent to or does not intersect the limit surface Sb, so that it is decided that there is no risk for the subject5to come into contact with the gantry2, and the process goes to Step S10.

At Step S10, the second deciding section107(seeFIG. 4) decides whether or not the cradle41has moved by Δycin the y-direction. As shown inFIG. 11, the cradle41has moved only by Δy=Δy1(<Δyc) yet. Accordingly, the process goes back to Step S8.

At Step S8, while the cradle41is moving in the y-direction, the contour-data generating section103generates the contour line D and updates the contour data (contour line) D to the latest data each time the position of the cradle41in the y-direction is changed. On the other hand, at Step S9, each time the contour data (contour line) D is updated, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour line D and limit surface Sb, and in the case that there is no risk for the subject5to come into contact with the gantry2, the second deciding section107decides whether or not the cradle41has moved by Δycat Step S10.

Therefore, in the case that it is decided that there is no risk for the subject5to come into contact with the gantry at Step S9, and at the same time it is decided that the cradle41has not moved by Δycin the y-direction at Step S10, a loop of Steps S8, S9, and S10is repetitively executed.

FIG. 12is a diagram showing a condition in which the cradle41has moved by Δy=Δycin the y-direction.

Once the cradle41has moved by Δy=Δyc, the position Pv of the head part reaches Pv=(yr, zi). In this case, at Step S10, the second deciding section107decides that the cradle41has moved by Δy=Δyc. Accordingly, the process goes to Step S11.

At Step S11, the movement of the cradle41in the y-direction stops, and movement of the cradle41in the z-direction is started.FIG. 13is a diagram showing a condition in which the cradle41has moved from z=z0to z=z1(the cradle41has moved by Δz=Δz1).

At Step S12, the image producing section101produces an image of the subject5based on image data obtained from the sensor section19. The display control section102controls the gantry display section18so that the image produced by the image producing section101is displayed in the gantry display section18. InFIG. 13is schematically shown the image at a time point when the cradle41has moved by Δz=Δz1in the z-direction.

Moreover, the contour-data generating section103generates contour data at the time point when the cradle41has moved by Δz=Δz1in the z-direction based on distance data obtained from the sensor section19.

At Step S13, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour line D. In the case that the contour line D is tangent to or intersects the limit surface Sb, the first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2. In this case, the process goes to Step S17, where the cradle (table) stops and the flow is terminated. InFIG. 13, the contour line D lies farther away from the gantry2with respect to the limit surface Sb. Therefore, the first deciding section106decides that the contour line D is not tangent to or does not intersect the limit surface Sb, so that it is decided that there is no risk for the subject5to come into contact with the gantry2, and the process goes to Step S14.

At Step S14, the second deciding section107decides whether or not the cradle41has moved by Δzcin the z-direction. Here, the cradle41has moved only by Δz=Δz1(<Δzc) yet. Accordingly, the process goes back to Step S12.

At Step S12, while the cradle41is moving in the z-direction, the contour-data generating section103generates the contour line D and updates the contour data (contour line) D to the latest data each time the position of the cradle41in the z-direction is changed. On the other hand, at Step S13, each time the contour data (contour line) D is updated, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour line D and limit surface Sb, and in the case that there is no risk for the subject5to come into contact with the gantry2, the second deciding section107decides whether or not the cradle41has moved by Δzcat Step S14.

Therefore, in the case that it is decided that there is no risk for the subject5to come into contact with the gantry at Step S13, and at the same time it is decided that the cradle41has not moved by Δzcin the z-direction at Step S14, a loop of Steps S12, S13, and S14is repetitively executed.

FIG. 14is a diagram showing a condition in which the cradle41has moved by Δz=Δzcin the z-direction.

At a time point when the cradle41has reached z=z1(seeFIG. 13), the head part of the subject5falls within the field-of-view region RV of the sensor section19. However, when the cradle41further moves into the gantry2beyond z=z1, the head part of the subject5gradually falls outside the field-of-view region RV, as shown inFIG. 14. Accordingly, in the present embodiment, when the cradle41further moves into the gantry beyond z=z1, the contour-data generating section103shifts the positions of points in the contour data (contour line) D in the z-direction when the cradle41has reached z=z1(seeFIG. 13) by an amount Δziof movement from z=z1, and generates contour data (contour line) D after the shift as the contour data (contour line) D of the subject5in a range z1<z≤zs. When the cradle41has reached z=zs, the amount Δziof movement is Δzi=Δzs, so that the contour data (contour line) D when the cradle41has reached z=zsis derived by shifting the position in the z-direction by Δzsrelative to the contour data (contour line) D when the cradle41has reached z=z1(seeFIG. 13).

Once the cradle41has moved by Δz=Δzc, the position Pv of the head part reaches Pv=(yr, zr). In this case, at Step S14, the second deciding section107decides that the cradle41has moved by Δz=Δzc. Accordingly, the process goes to Step S15.

At Step S15, the control section30controls the cradle41to stop. The process then goes to Step S16, where a scan is performed and the flow is terminated.

As described referring toFIGS. 7 to 14, in the period of time from when the cradle41starts moving until when the head part of the subject5reaches the prespecified position (yr, zr), the contour line D is not tangent to or does not intersect the limit surface Sb. Therefore, it can be seen that there occurs no risk for the subject5to come into contact with the gantry2in the period of time from when the cradle41starts moving until when the head part of the subject5reaches the prespecified position (yr, zr).

Now an exemplary case in which there is a risk, on the other hand, for the subject5to come into contact with the gantry2during movement of the cradle41will be described referring toFIG. 15.

InFIG. 15, a case in which the body part to be imaged is the chest part is shown, wherein is shown a condition in which the subject5raises his/her arms to prevent the arm part from falling within an imaged range.FIG. 15shows a case in which the contour line D is tangent to the limit surface Sb in the course of the cradle41moving in the z-direction.

In this case, at Step S13, the first deciding section106decides that the contour line D is tangent to the limit surface Sb. Therefore, the first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2when the cradle41continues to move. Accordingly, the process goes to Step S17.

At Step S17, the control section30controls the cradle41to stop, and the flow is terminated. Thus, a risk for the subject5to come into contact with the cradle41can be avoided.

As described above, in the present embodiment, it is decided whether or not there is a risk for the subject5to come into contact with the gantry2in the period of time from when the cradle41starts moving in the y-direction until when the head part of the subject5reaches the prespecified position (yr, zr). In the case that there is no risk for the subject5to come into contact with the gantry2, the head part of the subject5reaches the prespecified position (yr, zr). Thus, the operator can start a scan.

On the other hand, in the case that the contour line D is tangent to or intersects the limit surface Sb (seeFIG. 15) in the period of time from when the cradle41starts moving in the y-direction until when the head part of the subject5reaches the prespecified position (yr, zr), it is decided that there is a risk for the subject5to come into contact with the gantry2. In this case, the cradle41stops even when the head part of the subject5has not reached the prespecified position (yr, zr). Thus, a risk for the subject5to come into contact with the gantry2can be avoided.

In the present embodiment, moreover, by deciding whether or not the contour data for the subject5is tangent to or intersects the limit surface Sb, contact of the subject5to the gantry2can be avoided, which eliminates the need for a sensor for detecting contact between the subject5and the gantry2. Thus, manufacturing costs can also be reduced.

The first embodiment addresses a case of avoiding contact between the gantry2and the subject5by generating contour data for the subject5in the z-direction. In a second embodiment, a case of avoiding contact with the subject5by generating contour data for the subject5as viewed from directly above (contour data for the subject5in a zx-plane) will be described below.

The operation flow in the second embodiment will be described referring to the flow inFIG. 6, as with the first embodiment.

At Step S1, the subject5is laid on the cradle41, and then, the process goes to Step S2.

At Step S2, the image producing section101produces an image of the subject5based on image data obtained from the sensor section19. The display control section102controls the gantry display section18so that the image produced by the image producing section101is displayed in the gantry display section18.

Moreover, at Step S2, the contour-data generating section103generates contour data D representing a contour of the subject5in the zx-plane falling within the field-of-view region RV of the sensor section19based on distance data obtained from the sensor section19.FIG. 16schematically shows the contour data D in the zx-plane by a bold curved line. After generating the contour data D, the process goes to Step S3.

Steps S3to S5are identical to those in the first embodiment, the explanation of which will be omitted. Once the radiographer has input the command to carry the subject5into the bore B of the gantry2via the input device at Step S5, the process goes to Step S6.

At Step S6, the first deciding section106decides whether or not there is a possibility for the subject5to come into contact with the gantry2.

The first deciding section106decides whether or not the contour data (contour line) D is tangent to or intersects the limit surface Sb. InFIG. 16, the contour data (contour line) D lies away from the limit surface Sb. In this case, the contour line D is not tangent to or does not intersect the limit surface Sb, so that the first deciding section106decides that there is no risk for the subject5to come into contact with the gantry2.

At Step S7, the control section30controls the table4so that the cradle41starts moving in the y-direction.

At Step S8, the image producing section101produces an image, and the contour-data generating section103generates contour data D for the subject5in the zx-plane. Then, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour data D at Step S9, and the second deciding section107decides whether or not the cradle41has moved by Δycin the y-direction at Step S10. While the cradle41is moving in the y-direction, the contour line D of the subject5is not tangent to or does not intersect the limit surface Sb. Therefore, while the cradle41is moving in the y-direction, the loop of Steps S8, S9, and S10is repetitively executed.

Once the cradle41has moved by Δycin the y-direction, the process goes to Step S11, where the cradle41starts moving in the z-direction.

At Step S12, the image producing section101produces an image, and the contour-data generating section103generates contour data D for the subject5in the zx-plane. Then, the first deciding section106decides whether or not there is a risk for the subject5to come into contact with the gantry2based on the contour data D at Step S13, and the second deciding section107decides whether or not the cradle41has moved by Δzcin the z-direction at Step S14.

Therefore, in the case that it is decided that there is no risk for the subject5to come into contact with the gantry at Step S13, and at the same time it is decided that the cradle41has not moved by Δzcin the z-direction at Step S14, the loop of Steps S12, S13, and S14is repetitively executed.

FIG. 17is a diagram showing the cradle41having reached z=z2.

Referring toFIG. 17, the contour line D is tangent to the limit surface Sb at z=z2. Therefore, the first deciding section106decides that there is a risk for the subject5to come into contact with the gantry2when the cradle41continues to move. In the case that there is a risk for the subject5to come into contact with the gantry2, the process goes to Step S17.

At Step S17, the control section30controls the cradle41to stop. Once the cradle41has stopped, the flow is terminated.

In the second embodiment, again, in the case that contour line D is tangent to or intersects the limit surface Sb in the period of time from when the cradle41starts moving in the y-direction until when the head part of the subject5reaches the prespecified position in the gantry, it is decided that there is a risk for the subject5to come into contact with the gantry2. In this case, the cradle41stops even when the head part of the subject5has not reached the prespecified position in the gantry. Thus, a risk for the subject5to come into contact with the gantry2can be avoided.

The first embodiment illustrates a case involving generating contour data representing the contour of the subject5in the z-direction, while the second embodiment illustrates a case involving generating contour data representing the contour of the subject5in the zx-plane. However, the contour data is not limited to these cases. For example, it may be contemplated to generate contour data as 3D data defined in an xyz-space, decide whether or not a contour plane that the contour data as 3D data represents is tangent to or intersects the limit surface Sb based on data from the sensor section19, and thereby decide whether or not there is a risk for the subject5to come into contact with the gantry.

While described in the embodiments above is a case in which a risk for the subject5to come into contact with the gantry2during movement of the table4is avoided, the present invention is not limited to these embodiments. For example, in the case that the gantry2is provided with a tilt mechanism to allow it to be tilted with respect to the cradle41, a risk for the subject5to come into contact with the gantry2may be avoided while the gantry2is moving (seeFIG. 18).

FIG. 18is an explanatory diagram for contact avoidance in the case that the gantry2is provided with a tilt mechanism.

FIG. 18shows a condition in which the contour data is tangent to the limit surface Sb in the course of the gantry2tilting. In this case, the control section30controls the gantry2to stop its tilting action. Thus, contact of the subject5with the gantry2can be avoided.

In the first and second embodiments, each time the cradle41is moved, distance data is acquired from the sensor section19and new contour data D is generated. However, it may be contemplated, after generating the contour data D at Step S2, to calculate amounts Δycand Δzcof movement of the cradle41at Step S4, and add Δy (0<Δy≤Δyc) to the y-coordinates at each point in the contour data D generated at Step S2and add Δz (0<Δz≤Δzc) to the z-coordinates at each point in the contour data D before actually moving the cradle41(table4), to thereby estimate the contour data D during movement of the cradle41. This makes it possible to decide whether or not the subject5comes into contact with the gantry2without actually moving the cradle41.

While in the first and second embodiments, the present invention is described focusing upon a CT apparatus, it may be applied to any medical apparatus (for example, an MRI apparatus) different from the CT apparatus.