SE537029C2 - Method for accurate positioning of the detector in a mobile imaging system - Google Patents

Description

30 30 35 40 45 50 537 029 different directions, by rotating the detector an angle (a) between each image recording; identifying the coordinates of the object's center of gravity in each projection; calculating the actual position of the imaged object using the coordinates of the projections; calculating the displacement of the detector from the center of gravity of the field of view of the system; and adjusting the position of the detector with this offset.

The positioning method and system includes several features that make it advantageous and these features are subject to dependent requirements.

Further applicability of the present invention will become apparent from the detailed description given below and the accompanying drawings which are given for illustrative purposes only and are thus not to be construed as limiting the invention, and in which Fig. 1 shows a mobile imaging system; Fig. 2 is a view of the mechanical positioning device; Fig. 3a shows the positioning device in an inoperative state; Fig. 3b shows the positioning device in an operative state; Figs. 4a-e illustrate a method of determining the necessary adjustment of the detector; Fig. 5 illustrates means for driving the wheels of the system; Fig. 6 is an example of a collimator with inclined holes; and Fig. 7 schematically illustrates a method in an arrangement with a patient.

Detailed description of preferred embodiments In order to obtain an optimal image, it is required that the heart (or other imaged object) is located within the field of view of the system. However, it is difficult to position the detector at an exact and correct position and readjustment of the apparatus some small distance such as one or a few centimeters is usually necessary.

A main object of the present invention is therefore to provide accurate positioning of the imaging apparatus by tuning / adjusting the position of the detector to optimize the imaging procedure. To achieve this purpose, new features are provided, each of which, separately or together, are useful for optimizing positioning.

The first feature is a visual interface that includes at least two projections of the heart taken at different angles, and a control unit / calculation unit that allows determination of the optimal detector position and subsequent accurate positioning of the detector. In order to enable a final accurate position adjustment of the detector in relation to the heart to be performed, a method and a device are provided which, based on at least two, preferably three projections of the heart recorded at different collimator rotation angles, make it possible to fine-tune the detector position to a correct position. This is referred to herein as "" sight system "" and "sight method" and will be described with reference to Figs. 4a-e.

Another feature is a mechanical position adjustment unit designed to significantly reduce the force required to move the rather heavy equipment in small increments to adjust the position of the detector. This mechanical unit is shown in Figs. 1-2 and is described in detail with reference to these figures.

Another feature which is optional is the provision of an automatic positioning of the detector when the optimum position has been determined by the control unit.

Fig. 1 schematically shows an embodiment of a complete mobile imaging system, generally designated 10. It comprises a chassis 11a and a substantially vertically arranged frame 11b, a main cabinet 12 which houses control electronics 12 ', a display 13, a detector 14a, suitably a so-called gamma camera (or scintillation camera also called Auger camera) mounted on a substantially horizontal beam 14b mounted on the frame 11b, a rotatable collimator 15, a height adjustment unit 16 and a mechanical positioning unit 17 for fine tuning the detector position. The system also has a front wheel pair FW and a rear wheel pair RW.

The detector in Fig. 6 comprises a processor P, an amplifier AMP, photomultipliers PM, a scintillation crystal SC, a collimator with inclined holes SHC made of lead, and schematically shows a means into which a substance emitting gamma radiation has been introduced.

For the purpose of this application, "Y-direction" refers to the long direction of the system and "X-direction" is a transverse direction in relation to the system, while "Z-direction" is a vertical direction.

The system is generally used as follows. Because it is equipped with wheels, ie is mobile and not so large, it is easily and quickly visible to a place where a patient is, instead of moving the patient. When the mobile system arrives at the patient, the front end of the chassis is driven 1 1 under the bed on which the patient is lying. The detector 14a is placed at a nominal height so that it is always free from the patient at this moment. When it has been positioned approximately correctly, the position adjustment system is activated. The detector 14 is then positioned correctly within only a few minutes, after which pictures can be taken.

Now, the mechanical positioning unit 17 will be described in detail with reference to the schematic illustrations in Figures 2 and 3a-b. As shown in Fig. 1, the mechanical positioning unit 17 is preferably located on the chassis 11a at its underside, in the vicinity of the entire front part of the apparatus, i.e. at a position substantially vertically below the detector 14a. and the collimator 15. In operation, the mechanical positioning unit 17, which acts as a jack, is activated, so that a support element will be lowered using, for example, hydraulics so that it is brought into contact with the ground or the floor. Continued activation will provide an upward force whereby the front part of the system is lifted. Thus, the front wheels will no longer rest against the floor. This is illustrated in Figures 3a and 3b.

Fig. 2 shows the details of the positioning system 17.

The positioning unit 17 is essentially an "X / Y" table, which is a mechanism well known per se.

Here, the unit comprises a pair of elements referred to herein as sliding blocks, a lower sliding block 19 and an upper sliding block 20. Each sliding block comprises two parts. The lower sliding block 19 has a lower part 19 'which rests on the floor in operative position, i.e. when the unit 17 has been lowered to lift the chassis 11, and an upper part 19 "which is slidably connected to the lower part. In the same way, the upper sliding block 20 comprises a lower part 20 'and an upper part 20' which are slidably connected to each other. In one embodiment, the coupling is a rail-like structure. However, any arrangement can be used as long as it provides slidability.

As a result, the respective upper and lower parts of each sliding block have a very low friction between them, which makes them easily movable without the need for appreciable force.

Between the upper part 19 "of the lower sliding block 19 and the lower part 20 'of the upper sliding block 20 there is arranged a bearing arrangement 21 (pivot bearing) which makes it possible to rotate the two sliding blocks relative to each other. This bearing arrangement is necessary for the function as it will address the angular displacement of the two sliding blocks when the detector fl is moved laterally (X-direction). In this way, simple X-Y movement of the entire system is allowed so that accurate positioning of the detector and the collimator unit 14a, 15 is possible.

N is a correct position has been reached, the system is locked in this position during image registration.

In the operative position, the upper part 20 'of the upper sliding block 20 is rigidly connected to the chassis 11. The lower part 19' of the lower sliding block 19 rests against the ground or floor and is thus stationary during position adjustment.

Preferably, the sliding blocks 19 and 20, respectively, are arranged perpendicular to each other if they have a non-square geometry.

Thus, when the adjusting device 17 is in the operative position, as shown in Fig. 3b, the low friction pivot bearing arrangement 21 will allow small movements with very little power consumption and the displacement of the whole system in relation to the ground will be occupied by the slidable coupling between the parts of each sliding block 19, 20.

A mechanism is also provided for lowering the adjusting unit 17.

This mechanism comprises in one embodiment a linear actuator 23, which may comprise a hydraulic, pneumatic or electric actuator coupled to an actuating rod 24 which is also coupled to the upper part 20 "of the upper sliding block 20. The upper part 20 "of the upper sliding block 20 is also connected to the chassis 11 via link units 25 in the form of yokes which are rotatably connected to the upper part 20" and to the chassis 11, which is clearly shown in Figures 3a and 3b.

In the non-operational position (Fig. 3a), the entire position adjustment unit 17 is retracted so that it moves free from the ground or floor when the mobile imaging system is transported. When the line actuator 23 is started, it will pull on the upper part 20 "of the upper sliding block 20, the whole unit 17 will pivot downwards due to the clutch yoke 25 being rotatably coupled as shown.

When the lower part 19 'of the lower sliding block 19 goes against the ground, the continued pulling action exerted by the linear actuator 23 will cause the front of the entire mobile imaging system to rise so that the wheels move free of the ground by approximately 5 mm (Fig. 3b), rather similar to the function of a standard jack.

As already mentioned, in the raised position it is very easy to adjust the detector with very little use of force.

Now, the screening method and system will be described in detail with reference to Figs. 4a-e.

The mobile imaging system comprising a chassis 11a with a front end and a rear end, where the front end is configured to be insertable under a bed on which a patient is located, a rotatable detector 14a with a collimator 15, attached to the chassis so that it can be positioned over the patient in the bed configured to record images of an internal organ such as the patient's heart, thus also includes control electronics 12 ', a device for accurately positioning the detector, comprising a display unit 13 for displaying at least two, preferably three projections of a objects to be imaged from different directions, which projections are obtained with the detector 14a; a screen cursor is displayed on the display unit for each projection shown, and is superficial to a position substantially centered over the object in the corresponding projection; means for positioning at least two of the markers substantially centered over the object in corresponding projection; means for calculating the projected coordinates of the center of the object, i.e. the point where the projected lines from two markers intersect, which lines have the same direction as the corresponding collimator heel; means for calculating the displacement required to move the detector to a position where the center of the projected object substantially coincides with the center of the field of view and means for adjusting the position of the detector by fl moving the detector to the calculated displacements in X. - respective Y-direction.

Preferably, the displacement calculating means is configured to calculate the distance between the surface of the detector and the center of the object such as Z = r * tan (o), where r is the distance between one of the markers and the center of the projected object and o is the angle between the detector surface and the corresponding collimator holes. wherein the required displacement in the Z-direction is dZ = R * tan (o) * 0.5-Z, where R is the radius of the detector, and where the means for adjusting the position of the detector is also configured to enable the detector to be moved in the Z-direction.

Suitably the marker is a ring whose size is preferably adjustable, or at least large enough to enclose the projection of the heart.

Thus, to enable a final accurate positional adjustment of the detector relative to the heart, a method and apparatus are provided which, based on at least two, preferably three, different projections of the heart, recorded at different angles of rotation of the collimator, allow very fine adjustment of the detector position to a correct position.

By using only two or three projections instead of all the projections required for a complete image, the imaging during the positioning adjustment can be performed much faster than shooting a complete image, thus simplifying and speeding up the detector's alignment.

For correct image capture, it is important that the object to be imaged is within the system's field of view. In tomography with limited field of view (“limited view tomography”), the field of view is a cone, a truncated cone, a double cone or a truncated double cone with its axis coinciding with the axis of rotation of the collimator.

The position of an object in relation to the detector is uniquely determined by its positions in two different projections taken at different collimator angles of rotation. If the object is visible and is part of three projections taken at three different collimator angles of rotation, it will, due to the symmetry of the field of view, be present within the field of view of the system.

The preferred embodiment of the sight system presents three projections of the object in question, exemplified herein by the heart muscle, recorded at three different collimator angles of cil, C12 and (13, typically 0, 120 and 240 degrees, on a monitor screen. of steps are shown in Figures 4a-e.

Furthermore, three markers are represented here re-represented by rings 41 42 43, which is a 7 7 7 7 preferred embodiment of the monitor screen. These rings can be taken like a cursor 7 on the monitor screen using an input device such as a computer mouse. 10 15 20 25 30 35 40 45 537 029 In particular, they can be surface centered over the projection of the heart muscle displayed on the monitor. It is not strictly necessary to use rings, any marker that can be placed so that it is centered over the object in question, such as a heart, would work. The position of the third cursor is calculated automatically as described below.

Thus, each marker belongs to one of the cardiac projections, which projections are denoted P1, P2 and P3, respectively, in the following. In Fig. 4a, three projections P1, P2, P3 are shown on the monitor M. Here, the projected heart is ideally positioned and fully visible within the field of view. It can be seen that the centers of the three cardiac projections form an equilateral triangle (indicated by a dashed line) with the center of gravity in the center of the detector.

Fig. 4b illustrates a typical situation before position adjustment has been made. Two of the projections are not completely within the field of view.

In Fig. 4c, two markers 41, 42 have been placed on the projections P1 and P2, respectively. In 4d a third marker is automatically placed on the third projection P3, and finally in Fig. 4e the situation is shown in Which detector is correctly positioned, i.e. the center of gravity of the triangle formed by the projections P1, P2, P3 coincides with the center of gravity of the field of view CGFV.

The operator thus centers two of the rings over the projections of the imaged object by means of a mouse or other device. Two of the three rings can be placed this way. Using the coordinates of the two rings positioned manually, the system calculates a third position in a symmetrical triangle, and thus the third ring is automatically placed on the third projection. The diameter of the rings can be adjusted to fit the object in question or alternatively they can at least be so large that they can completely enclose the projections of the object to be imaged.

Once the camera has been positioned correctly and projections have been obtained, each ring will be centered over each corresponding projection of the object and each ring will be located in the center of the projection and housed within the corresponding projection.

It should be noted that in the above description three projections are foreseen, however, two are sufficient. The third projection, which can be excluded, is used for increased operator comfort and convenience.

With P1 having the coordinates (X1, y1) and P2 having the coordinates (X2, y2), o the angle of the collimator holes and the radius of the detector, the position of the imaged object (X, y, z) relative to the detector will be (the scale is assumed here for simplicity's sake be l: 1): y: - - rgfß m:: gta 2 :: jt -: gigs lf; 53 x 07 These x, y values represent the position in a plane, while, as indicated earlier, the height above the patient may also need to be adjusted. This height is represented by the Z-value: Furthermore, the center coordinates of P3 will be: Z The necessary adjustments of the detector position will be: dx: -v fl êy = -3 x mi: - i These values of X-, Y- and Z the movements of the detector will be displayed on the monitor. This makes it easy to adjust the position.

The displacement in the X and Y directions can be performed manually or by means of motors connected to the rear wheels. The displacement in the Z-direction is suitably performed by displacing the horizontal beam 14b, either manually but preferably using a motor. Although it is convenient for many reasons to have operator control as described above, it is also within the inventive concept that this process is performed automatically. This can be accomplished by using image recognition software to identify the position of the center of gravity of the projection of the imaged object. In such a case, there is no need for operator intervention and no monitor screen is really needed to display the projections. For control purposes, however, it is a preferred feature to display the projection for visual verification of the correctness of the position.

The sequence of steps when performing the operator intervention method is as follows. 10 15 20 25 30 35 40 45 537 029 Fig. 4b shows the display on the monitor in an initial position for adjustment. Only one ring 42 is in the correct position in relation to the heart. Now fl one of the other rings 43 is manually moved on the monitor screen so that it covers the heart, see Fig. 4c.

The center of gravity 45 of the triangle formed by the three rings is automatically moved to a new position. Then a third ring 44 is automatically flattened so that it covers a third projection of the heart, Fig. 4d. The center of gravity 45 changes again and now deviations between the prevailing and optimal position will be calculated. This deviation is shown on the monitor and adjustments can be easily made either manually or automatically as described below, and the display will then look like in Fig. 4e.

After the adjustment, a new set of projections can optionally be taken up to verify the correctness of the position.

In an automated mode, the control electronics suitably running an image recognition software would process data for each image and provide the identification of the center of gravity of the object in each projection, and calculate the triangle thus formed, i.e., tensed by the centers of gravity.

Then a deviation between the prevailing and optimal position is calculated, as above, and adjustment is performed as before.

Preferably, the adjustment of the detector position in accordance with the calculated required displacement is effected automatically. This can be implemented, as shown in Fig. 5, by providing electric motors 51, 52 which are arranged to drive the rear wheels RW of the mobile apparatus. Thus, when it is desired to move the detector in the Y direction, the motors will drive each wheel in the same direction, while if movement in the X direction is required, the motors will drive the wheels in opposite directions.

In order to register the actual displacement during the adjustment step, in one embodiment a means is provided for detecting the position in relation to the ground or the floor. The position information is synchronized with data from the mechanical positioning adjustment unit 17, and this enables a determination of when the detector has reached an optimal position.

The position detection can be implemented with the help of the technology on which a so-called optical mouse is based, see Fig. 3a. An image recording device (camera) C continuously records the ground or floor and by means of digital image processing changes in the image are recorded by sequentially comparing the recorded images, and sold, the speed and direction of the displacement can be determined. Preferably, a light source such as an LED is provided to enhance the image.

Of course, any other type of position detection could be used as long as the speed and direction of the displacement can be recorded and fed back to the system. 537 029 The method is illustrated in some further detail in Fig. 7. It comprises recording successive projections of e.g. a heart at different, preferably, three different angles using the detector 60. The signals from the detector 60 representing each projection are stored in a memory 62 such as pixels representing images that can be displayed on a display screen or monitor 64.

In one embodiment, the control electronics 66 are programmed to execute an image recognition software. Thus, data, image pixels, from the memory, and the control electronics are retrieved, by executing the image recognition software, identifying the imaged objects and their respective centers of gravity, and selling the coordinates of said centers of gravity.

The center of gravity of each of the projections recorded at different angles by the detector each represents a corner of an equilateral triangle, which in turn has a center of gravity given directly by the coordinates of the centers of gravity in the projections by simple geometric considerations.

Thus, since the field of view of the system is known in terms of coordinates in the frame of reference of the apparatus itself, the deviation is calculated in centers of gravity of the geometric figure tensioned by these projections by means of the control electronics, and the deviation is presented as a required displacement of the detector and optionally the Z directions, so that the detector can be positioned correctly for the examination.

In one embodiment, data representing the offsets are fed as control signals to a pair of motors 68 which individually drive the rear wheels 69, whereby an automatic adjustment of the detector is possible. 10

Claims (15)

10 15 20 25 30 35 537 029 PATENT REQUIREMENTS A method for adjusting the position of a detector in a mobile gamma camera system for imaging internal means so that the inner means is centered in the respective projection, which system comprises a gamma camera (14a) with a rotatable collimator (15) having collimator holes. arranged at an oblique angle (o), control electronics (12 '); wherein the method is characterized by: using the gamma camera to record at least two, preferably three projections of an internal member to be imaged, from different directions by rotating the collimator between each projection shot; identifying the projection coordinates of the center of gravity of the imaged internal organ in each projection; calculating the actual position of the imaged internal body using the coordinates of the projections; calculating the required displacement of the gamma camera from the center of gravity of the field of view of the system, the field of view of the system being a cone, a truncated cone, a double cone or a truncated double cone whose axis coincides with the axis of rotation of the collimator; and adjusting the position of the gamma camera according to the calculated offset. Method according to claim 1, characterized in that the identification of the coordinates of the center of gravity of each organ in each projection is done by running a program comprising algorithms for image recognition in the control electronics. 11 10 15 20 25 30 35 537 029 Method according to claim 1 or 2, characterized in that the identification of the coordinates of the center of gravity of each member in each projection comprises that the projections are displayed on a presentation unit, such as a graphic display unit; that a moving cursor is provided for each projection on the display unit; and placing the markers at the center of gravity of each projection; and that the coordinates of the center of gravity of each projection are stored for further calculations. Method according to claim 1, characterized in that the detector generates signals representing picture elements in pictures and where the picture elements belonging to each projection are stored in a memory. Method according to claim 1, characterized in that the step of identifying the projection coordinates comprises retrieving data from the memory and that via the images represented by this data on a display divided into three segments, angularly evenly distributed on the display, the center of the display representing the center of gravity of the system field of view, so that a projection is displayed in each display segment; that a cursor is generated on the display for each projection, where the position of each cursor is controllable by an operator; and that the cursor is centered on the center of gravity of each member in each projection. Method according to claim 3, characterized by recording the coordinates of the markers and entering the coordinates in the control electronics, which is programmed to calculate the coordinates of the center of gravity in the geometric figure clamped by the projections, e.g. a triangle, and calculating the deviation of these coordinates from the center of gravity of the system field of view. Method according to claim 1, characterized in that the step of identifying the projection coordinates comprises retrieving data from the memory and processing the data using image processing software by means of the control electronics to identify the center of gravity of each organ in each projection. Method according to one of the preceding claims, characterized by calculating the center of gravity of the geometric figure which is clamped by the projections, i.e. a triangle which is clamped by the three projections, and calculating this geometric deviation of the coordinates of the figure from the center of gravity of the system field of view, and adjustment of the position of the detector accordingly. Method according to one of the preceding claims, characterized in that the adjustment is carried out by manually moving the detector the required distances in the X and Y directions, respectively. Method according to one of the preceding claims 1-8, characterized in that the adjustment is made by feeding signals corresponding to the required displacement of the detector to the control electronics, which generate actuation signals for motors which individually drive a respective rear wheel on the movable gamma camera system. Method according to any one of the preceding claims, characterized in that the calculation of the position of the imaged means is performed according to the following equations: where X1 and y1, and X2 and y2 represent the coordinates of two projections and where a1, C12 represents rotation of the detector at a predetermined angle, and x and y represent the true coordinates of the organ in the plane. Method according to claim 4, further characterized by calculations of the height of the detector above the patient, wherein this height is represented by a third coordinate: za * ~ L? Method according to claim 5, characterized in that the required adjustment of the detector position is given by 13 537 029 where dx, dy and dz are the distances it is necessary to move the detector in each direction x, y and z, respectively. Method according to claim 1, characterized in that the positioning of the markers at the center of gravity of each member in each projection is done manually. A mobile gamma camera system for imaging internal means, characterized by a chassis (11a) having a front end and a rear end, the front end being configured to be insertable under a bed on which a patient is located, a gamma camera (14) with a rotatable collimator (15) with collimator holes arranged at an oblique angle (o); control electronics (12 '); A presentation unit; wherein the control electronics are programmed to perform the method according to any one of claims 1-14. 25 14