High speed rotating gantry

A medical imaging apparatus includes a stationary gantry and a generally spool-shaped rotating gantry (304), which rotates about an examination region about a longitudinal axis. The rotating gantry includes a first flange (320), a second flange (322), and a plurality of elongate structural elements (402) that are disposed between and couple' the first and second flanges. The first flange (320) is rotatably coupled to the stationary gantry, and the second flange (322) extends radially in a plane perpendicular to the longitudinal axis, thereby providing radial stiffness for the rotating gantry. A radiation source is affixed to the rotating gantry between the first and second flanges, and a detector array is affixed to the rotating gantry between the first and second flanges, opposite the examination region from the radiation source.

The present application relates to a medical imaging system, and finds particular application to computed tomography (CT). It also amenable to other medical imaging applications and to non-medical imaging applications.

Generally, computed tomography (CT) scanners used for medical imaging applications include a stationary gantry/frame assembly and a rotating gantry/frame assembly, which rotates with respect to the stationary gantry about an examination region along a longitudinal or z-axis. The rotating gantry is supported on the stationary gantry via a bearing.

A radiation source and other components, such as a heat exchanger, a collimator, a power module and/or other components, are affixed to the rotating gantry and rotate about the examination region when the rotating gantry rotates about the examination region. In a third generation system, an array of radiation sensitive detectors is also affixed to the rotating gantry and is located opposite the radiation source with respect to the examination region. With a fourth generation system, the array of the radiation sensitive detectors is affixed to the stationary gantry.

In one configuration, the rotating gantry is based on a single plate rotor topology in which the radiation source and the detector array (third generation system) are affixed to a plate-shaped rotor such that the radiation source and the detector array cantilever from the plate-shaped rotor. An example of such a configuration is shown inFIGS. 1A,1B, and1C. In these figures, a radiation source102and a detector array104cantilever from a side of a plate-shaped rotor106, and the radiation source102produces a radiation beam108that traverse an examination region110and illuminates the detector array104.

Unfortunately, the single plate-shaped rotor106may physically distort in a direction along the z-axis, as shown inFIG. 1C, due to radial g-forces associated with the components supported on the plate-shaped rotor106when the single plate-shaped rotor106rotates. Generally, the physical distortion increases with rotor rotation speed such that the distortion is relatively greater, for example, at a rotor rotation speed of 180 revolutions per minute (RPM) as compared to a rotor rotation speed of 60 RPM. A consequence of such a distortion is that the radiation beam108drifts along the detector array104.FIG. 1Cshows an exaggerated drift.

With some lower rotor rotation speed (e.g., 60 RPM scanners) single and dual slice scanners, a width of the detectors in the detector array104along the z-axis is increased so that the radiation beam108illuminates the detector array104over a range of radiation beam drift. However, such an increase in detector width may lead to increased detector cost. Alternatively, a width of the radiation beam108along the z-axis may be increased so that the radiation beam108illuminates the detector array104over a range of radiation beam drift. However, widening the radiation beam may lead to decreased radiation efficiency, or increased patient/object dose. With some scanners, increasing the detector width and/or increasing the beam width may not be desirable.

In another configuration, the rotating gantry is based on a cylinder rotor topology in which the radiation source and the detector array (third generation system) are affixed to a cylindrically-shaped rotor. An example of such a configuration is shown inFIGS. 2A,2B, and2C. In these figures, a radiation source202and a detector array204are affixed to opposing sides of a cylindrically-shaped rotor206, and the radiation source202produces a radiation beam208that traverse an examination region210and illuminates the detector array204.

Unfortunately, the cylindrically-shaped rotor206may physically distort along a radial direction, as shown inFIG. 2C, due to radial g-forces associated with the components supported on the plate-shaped rotor206when the cylindrically-shaped rotor202rotates. As with the plate-shaped rotor topology, the corresponding distortion generally increases with rotor rotation speed such that the distortion is greater at higher rotor rotation speeds. Since reconstruction is dependant upon a substantially constant physical relationship between the radiation source202and the detector array204, such physical distortion or other geometrical distortion may introduce artifact that is propagated to the volumetric image data and images generated therefrom.

The single plate and the cylinder rotor topologies have been combined to provide incremental improvements over each of the single rotor plate and the rotor cylinder topologies with respect to the above-noted physical rotor distortions.

However, continuing advances in scanner related technology are leading to scanners that are capable of rotating at much higher speeds, for example, over 200 RPM. As the rotor rotation speed increases, the rotor is exposed to a greater g-force, for example, a g-force of 30 g or greater in the radial direction. As a consequence, the above-noted physical rotor distortions are exaggerated and more prominent.

Aspects of the present application address the above-referenced matters and others.

According to one aspect, a medical imaging apparatus includes a stationary gantry and a generally spool-shaped rotating gantry, which rotates about an examination region about a longitudinal axis. The rotating gantry includes a first flange, a second flange, and a plurality of elongate structural elements that are disposed between and couple the first and second flanges. The first flange is rotatably coupled to the stationary gantry, and the second flange extends radially in a plane perpendicular to the longitudinal axis, thereby providing radial stiffness for the rotating gantry. A radiation source is affixed to the rotating gantry between the first and second flanges, and a radiation sensitive detector is affixed to the rotating gantry between the first and second flanges, opposite the examination region from the radiation source.

According to another aspect, a rotating gantry includes a first flange configured for rotatably coupling to a stationary gantry. The rotating gantry further includes a second flange that provides radial stiffness for the rotating gantry when the rotating gantry rotates. A plurality of elongate structural elements are disposed between and couple the first and second flanges.

According to another aspect, a method includes rotating a spool-shaped rotating gantry about an examination region. The spool-shaped rotating gantry includes a radiation source and a detector array. The method further includes generating a radiation beam with the radiation source, detecting radiation emitted by the radiation source with the detector array, and generating volumetric image data from a signal indicative of the detected radiation.

Initially with reference toFIG. 3, a computed tomography (CT) scanner300includes a stationary gantry302and a rotating gantry304. The stationary gantry302is stationary in that it is generally stationary during a scan. However, it may be configured to tilt or otherwise be moved.

The rotating gantry304is supported on the stationary gantry302via a bearing (not visible). Non-limiting examples of suitable bearings include a mechanical bearing, such as one with rolling balls interposed between two raceways, a fluid bearing, such as an air bearing that provides an air barrier between the rotating gantry304and the stationary gantry302, and other bearings. An example of a suitable fluid bearing is described in patent application Ser. No. 09/428, 431, filed Oct. 27, 1999, and entitled “Aerostatic CT suspension.”

The rotating gantry304rotates about a z-axis306around an examination region308. In the illustrated example, the rotating gantry304is configured to rotate at rotation speeds greater than 200 revolutions per minute (RPM) such as 220 RPM or more. The rotating gantry304is also configured to rotate at lower rotation speeds.

The rotating gantry304supports a radiation source310, such as an x-ray tube that emits radiation. The rotating gantry304also supports a source collimator312that collimates the radiation emitted by the radiation source310to produce a generally conical or fan shaped radiation beam314. As shown, the radiation beam314traverses the examination region308.

With the illustrated third generation CT scanner300, the rotating gantry304also supports a radiation sensitive detector array316that subtends an angular arc on a side of the examination region308opposite the radiation source310. A fourth generation CT configuration is also contemplated. The illustrated detector array316includes multiple rows of radiation sensitive detector elements that extend in the z-axis direction, and multiple columns of radiation sensitive detector elements that extend in a traverse direction. A single row detector array is also contemplated. The detector elements detect radiation that traverses the examination region308.

The rotating gantry304also supports a heat exchanger318, a power module319, and/or various other components such as one or more patient positioning lasers, a rotor angular position measurement device, a data transfer module, cabling, balancing weights, and/or other components.

In the illustrated embodiment, the rotating gantry304includes a spool-shaped rotor that it includes flanges320and322coupled together by elongate structural elements402(FIG. 4) disposed therebetween. As described in greater detail below, in one instance the flanges320and322include a dimension such as shape and a size configured to provide radial stiffness and the elongate structural elements402include a dimension and location configured to provide axial stiffness. As a result, in one instance the rotating gantry304may be less prone to physical distortions due to radial g-forces when the rotating gantry304rotates at relatively high rotation speeds, such as rotation speeds greater then 200 RPM, relative to an embodiment in which the flanges320and322and the elongate structural elements402are otherwise configured.

A patient support324, such as a couch, supports a patient in the examination region308. The patient support324is movable along the z-axis306in coordination with the rotation of the rotating gantry304to facilitate helical, axial, or other desired scanning trajectories.

A reconstructor326reconstructs projection data from the detectors to generate volumetric data indicative of the interior anatomy of the patient. An image processor328processes the volumetric image data generated by the reconstructor326for display in human readable form.

A general purpose computing system serves as an operator console330. The operator console330includes human readable output devices such as a display332and/or printer and input devices such as a keyboard and/or mouse. Software resident on the console330allows the operator to control the operation of the system300, for example, by allowing the operator to select a scan protocol, initiate scanning, terminate scanning, view and/or manipulate the volumetric image data, and/or otherwise interact with the system300.

The rotating gantry304is now described in further detail in connection withFIGS. 4 and 5. Initially referring toFIG. 4, a perspective view of the rotating gantry304, without the components supported thereby, is illustrated. As briefly discussed above, the rotating gantry304includes the first and second flanges320and322coupled together by the elongate structural elements402.

The first flange320includes first and second major surface404and406, both extending generally perpendicular to the longitudinal axis306(FIG. 3). The first major surface404is operatively coupled to the bearing (not visible). The second major surface406is operatively coupled to the elongated structural elements402. The second flange322includes first and second major surface408and410, both extending generally perpendicular to the longitudinal axis306. The first major surface408faces away from the elongate structural elements402, and the second major surface410is operatively coupled to the elongate structural elements402. As shown, in this example the first and second flanges320and322are positioned generally parallel to each other, with their respective second surfaces406and410facing each other.

The dimensions of the second flange322, in a plane perpendicular to the longitudinal axis306, is application dependent. In the illustrated example, the second flange402includes a shape and size that is determined based on the operable rotor rotation speeds, the mass of the components supported on the rotating gantry304, a level of acceptable radial distortion, and component accessibility. By way of example, for a particular level of distortion and known mass, the shape and size may correspond to a shape and size that provides suitable radial stiffness at a maximum or other rotor rotation speed so that the radial distortion of the rotating gantry304, if any, does not exceed the particular level of distortion. The particular level of distortion may be based on image quality, the ability to correct for distortion (via hardware and/or software techniques), and/or other considerations. In general, the larger the flange is in the plane perpendicular to the longitudinal axis306, the greater the radial stiffness. However, the shape and size is also determined in a manner to reduce or minimize the need to remove the second flange322or maximize access to the components when accessing the components supported on the rotating gantry304. The illustrated shape and size is one non-limiting example of a suitable shape and size for the illustrated CT scanner300. It is to be appreciated that the second flange322and the first flange320may be substantially equal in size. Other factors may alternatively or additionally be considered when determining the shape and size of the second flange322.

Turning toFIG. 5, a sectional view ofFIG. 4is illustrated. The dimensions and locations of the elongate structural elements402are determined based on a location of the supported components, the rotor rotation speeds, the mass of the supported components, and a level of acceptable axial distortion.

By way of example, structural elements4021and4022are positioned on the first flange320in manner that leaves a first opening506therebetween dimensioned so that at least a first portion of the radiation source310(FIG. 3) is disposed between the structural elements4021and4022when the radiation source310is installed on the rotating gantry304. The structural elements4021and4022extend perpendicularly from the first flange404, extend radially in a plane parallel to the longitudinal axis, and have a non-zero finite width. In this example, the height of the structural elements4021and4022extends a sub-portion of a distance between an inner perimeter502and an outer perimeter504of the first flange320, and the structural elements4021and4022are positioned nearer to the inner perimeter502with respect to the outer perimeter504. Such dimensions and locations of the structural elements4021and4022can provide substantial symmetrical structural stiffness about the installed radiation source310, for example, for the particular rotation speed, known mass, and particular acceptable level of rotor physical distortion. The illustrated dimensions and locations of the structural elements4021and4022is one non-limiting example of suitable dimensions and locations for the illustrated CT scanner300.

Structural element4023and4024are positioned on the first flange320in manner that leaves a second opening508, in which at least a sub-portion of the detector array316(FIG. 3) fits between when the detector array316is installed on the rotating gantry304. Likewise, the structural element4023and4024extend perpendicularly from the first flange320and have a non-zero, finite width and height in a plane parallel to the longitudinal axis. As shown, the height of the structural elements4023and4024extend along a sub-portion of a distance between the inner and outer perimeters502and504, and are located nearer to the inner perimeter502. Such dimensions and locations of the structural elements4023and4024can provide substantial symmetrical structural stiffness about the installed detector array316, for example, for the particular rotation speed, known mass, and the particular level of rotor physical distortion. The illustrated dimensions and locations of the structural elements pairs4023/4024and4025/4026is one non-limiting example of suitable dimensions and locations for the illustrated CT scanner300.

The structural element pairs4023/4025and4024/4026define third and fourth opening510and512for installation of the power modules319(FIG. 3), and the structural element pairs4021/4025define a fifth opening514for installation of the heat exchanger318(FIG. 3). The dimensions and locations of the structural elements pairs4023/4025,4024/4026, and4021/4025provide structural stiffness about the installed power modules319and installed heat exchanger318.

InFIG. 5, connecting supports516,518, and520are employed. In particular, the connecting support516is disposed between and couples the structural elements4023and4025, the connecting support518is disposed between and couples the structural elements4024and4026, and the connecting support520is disposed between and couples the structural elements4022and4026. As can be seen, in one instance the connecting supports are employed between structural elements where such a connecting support would not interfere with a component supported on the rotating gantry304. Such supports516,518, and520may provide further axial stiffness. The supports516,518, and520may also provide shear stiffness. As such, the major surfaces406and408remain concentric. The connecting supports516,518, and520may also be omitted.

It is noted that the components installed on the rotating gantry304, for example, the radiation source310, the collimator312, the detector array316, the heat exchanger318, and the power module319, may also provide further structural stiffness for the rotating gantry304.

In the illustrated configuration, when the radiation source310, the detector array316, and the heat exchanger318are installed on the rotating gantry304, the combination of the structural elements402, the connecting supports516,518, and520, and the installed components aggregately form a generally cylindrical section between the first and second flanges320and322.

With respect toFIGS. 3,4and5, in the illustrated embodiment the first and second flanges320and322are formed from steel or the like, and the structural elements402are formed from aluminum or the like. The first and second flanges320and322are both fastened to the structural elements402. In one instance, the first and second flanges320and322and the structural elements402are fastened together via bolts, rivets or the like, and then the various components are affixed to the rotating gantry304. In another instance, the first flange320and the structural elements402are fastened together, the various components are affixed to the rotating gantry304, and then the second flange322and the structural elements402are fastened together. Other approaches for affixing the components to the rotating gantry304(the flanges320and322, and the structural elements402) and the components supported on the rotating gantry304are also contemplated.

Variations are contemplated.

As noted above, the illustrated first and second flanges320and322are formed from steel and the structural elements402are formed from aluminum. In another embodiment, the rotating gantry304, including the first and second flanges320and322and the structural elements402, is formed as a single unitary structure via an aluminum or other casting. In yet another embodiment, the first and second flanges320and322are substantially permanently mounted to the structural elements402, for example, via welding.

In the embodiment illustrated in the figures, the second flange322is a single unitary structure that is fastened with the structural elements402. In another embodiment, the second flange322includes two or more separate sub-sections that individually fasten to different pairs of the structural elements402. In yet another embodiment, the two or more separate sub-sections are affixed to different components, and affixing the components to the rotating gantry304affixes the second flange322to the rotating gantry304.

As shown inFIG. 5, the structural elements402are disposed nearer an inner perimeter502of the first flange320. However, in another embodiment, the structural elements402are disposed nearer an outer perimeter504. With this configuration, the connecting supports516-520may also be affixed to end regions of the structural elements that nearer to the outer perimeter504. In yet another embodiment, the structural elements402are approximately centered between the inner and outer perimeters502and504. In yet another embodiment, the structural elements402substantially extend the distance between the inner and outer perimeters502and504. In such an instance, connecting supports similar to the connecting supports516-520may alternatively or additionally be coupled to the end regions of the structural elements that are nearer to the outer perimeter504.

It is also to be appreciated that the rotating gantry304can be used in connection with other imaging systems, for example, positron emission and single photon emission tomography, in which it is desirable to rotate one or more components.

It is also to be appreciated that the stiffness of the rotating gantry304may also facilitate reducing radiation exposure, reducing imaging system calibration, mitigating active pre-examination region collimation, mitigating active post-examination region collimation.