?º
`
`United States Patent [19]
`McKenna
`
`US005448607A
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,448,607
`Sep. 5, 1995
`
`5,109,397 4/1992 Gordon et al. ......................... 378/4
`FOREIGN PATENT DOCUMENTS
`8703190 U 8/1988 Germany .
`Primary Examiner—David P. Porta
`Assistant Examiner—Don Wong
`Attorney, Agent, or Firm—Lappin & Kusmer
`
`[54] X-RAY TOMOGRAPHY SYSTEM WITH
`gºivor aspirasslation
`[75] Inventor: Gilbert W. McKenna, Revere, Mass.
`[73] Assignee: Analogic Corporation, Peabody,
`Mass.
`[21] Appl. No.: 193,562
`ppl. No.:
`3.
`[22] Filed:
`Feb. 8, 1994
`+.
`ABSTRACT
`[57]
`An improved, portable X-ray tomography system is
`6
`§ § º ------------------------------------------- #º: disclosed wherein lateral movement of the various to
`378/195; 378/198
`mography components relative to a stationary patient
`[58] Field of Search ................................ 37%iºs, during a scanning procedure is precisely controlled by
`378/11, 15, 4, 146, 17
`mechanical displacement means which, in turn, is cou
`pled to electro-mechanical means for simultaneously
`References Cited
`measuring and monitoring the amount of the displace
`U.S. PATENT DOCUMENTS
`ment.
`4,131,802 12/1978 Braden et al. .......................... 378/4
`4,928,283 5/1990 Gordon ................................... 378/4
`
`[56]
`
`
`
`32 Claims, 6 Drawing Sheets
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`Varian Exhibit 2002, Page 001
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`

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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
`Sep. 5, 1995
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`Sheet 1 of 6
`Sheet 1 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 002
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`Varian Exhibit 2002, Page 002
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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
`Sep. 5, 1995
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`Sheet 2 of 6
`Sheet 2 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 003
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`Varian Exhibit 2002, Page 003
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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
`Sep. 5, 1995
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`Sheet 3 of 6
`Sheet 3 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 004
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`Varian Exhibit 2002, Page 004
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`

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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
`Sep. 5, 1995
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`Sheet 4 of 6
`Sheet 4 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 005
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`Varian Exhibit 2002, Page 005
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`

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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
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`Sheet 5 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 006
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`Varian Exhibit 2002, Page 006
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`U.S. Patent
`U.S. Patent
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`Sep. 5, 1995
`Sep. 5, 1995
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`Sheet 6 of 6
`Sheet 6 of 6
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`5,448,607
`5,448,607
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`Varian Exhibit 2002, Page 007
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`Varian Exhibit 2002, Page 007
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`1
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`5,448,607
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`X-RAY TOMOGRAPHY SYSTEM WITH GANTRY
`PIVOT AND TRANSLATION CONTROL
`
`RELATED APPLICATIONS
`
`This application is related to U.S. patent application
`Ser. No. 08/193,783, filed in the name of Gilbert W.
`McKenna and entitled “X-ray Tomographic Scanning
`System” (Attomey’s Docket No. ANA-30); U.S. patent
`application Ser. No. 08/ 193,696, filed in the name of
`Gilbert W. McKenna and Ronald E. Swain and entitled
`“Tomographic Scanner Having Center of Rotation for
`all Physics” (Attomey’s Docket No. ANA-31); and
`U.S. patent application Ser. No. 08/193,782, filed in the
`name of Gilbert W. McKenna and entitled “Stabilized,
`Cantilevered, Patient Trauma Table System” (Attor-
`ney’s Docket No. ANA—58), all filed simultaneously
`herewith and assigned to the present assignee.
`FIELD OF INVENTION
`
`The present invention relates generally to X-ray to-
`mography systems and, more specifically, to a portable
`system for supporting and moving a tomography gantry
`assembly relative to a stationary support for supporting
`the object being scanned in order to provide limited,
`precisely controllable and measurable translation of the
`gantry assembly parallel to the stationary support, and
`also to provide limited, precisely controllable tilting of
`the gantry assembly relative to the object being
`scanned.
`
`BACKGROUND OF THE INVENTION
`
`The present invention is an improvement in portable
`X-ray tomography systems such as those described in
`U.S. Pat. Nos. 4,928,283 (issued May 22, 1990 to Ber-
`nard M. Gordon for X-Ray Tomography Apparatus,
`and assigned to the present assignee) and 5,109,397
`(issued Apr. 28, 1992 to Bernard M. Gordon et al. for
`X-Ray Tomography Apparatus With Lateral Move-
`ment Compensation, also assigned to the present as-
`signee); and helical scan tomography systems such as
`described in German Gebrauchsmuster File No. G 87
`03 190.6, filed by Siemens AG and published Aug. 11,
`1988, all three documents being incorporated herein by
`reference.
`
`Tomography systems have been used for many years
`to create images of cross-sectional slices through ob-
`jects, and are particularly useful as a diagnostic aid. CT
`(computed tomography) scan systems usually include a
`gantry assembly comprising a disk mounted for rotation
`within a gantry frame. In third generation machines, the
`disk supports X-ray imaging components including an
`X-ray source and X-ray detectors that rotate within a
`stationary frame. In fourth generation machines the
`X-ray detectors are secured equiangularly around the
`stationary frame, while the source rotates with the disk
`relative to the detectors. In both types of systems, the
`source may provide periodic X-ray pulses, or alterna-
`tively, continuous-wave (CW) X-rays. The disk of the
`gantry is normally adapted to rotate through a full 360°
`rotation so that the imaging components secured to the
`disk rotate through a plurality of incremental positions
`where a corresponding series or set of readings (called
`“views”) by the detectors are made. The number of
`photons absorbed along the various paths through the
`object, during each sampling period defining each view
`or set of readings, is a function of the absorption charac-
`teristics of the portions of the object along each path
`
`2
`during each set of readings. Thus, a plurality of views
`are taken through the portion of an object disposed
`within the common plane of rotation of the X-ray paths
`(hereinafter the “scanning plane”). The detectors gener-
`ate a corresponding plurality of analog information
`signals representative of X-ray flux detected by the
`detectors during each sampling period or projection
`view.
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`The output analog information signals of the X-ray
`detectors acquired from all of the views of the 360°
`rotation,
`i.e., through all of the incremental angular
`positions of the 360° rotation within the scanning plane,
`are processed, typically through a back projection pro-
`cessing technique, so as to create an image of the slice of
`the interior structure of the object exposed to the X-
`rays: In some CT scanners, provision is made to move
`the patient support while performing a scan in order to
`provide a helical scan so as to increase the scanned
`volume.
`
`An important consideration in CT scanning has al-
`ways been the accurate and consistent alignment of the
`tomography components and the patient both through-
`out the rotation and over the course of many scans and
`patients. Misalignment or movement can negatively
`influence the data of an entire scan. In order to deal
`with this factor, manufacturers of prior art CT scan
`apparatus typically have produced a very large and
`massive machine which includes a heavy gantry assem-
`bly for supporting the tomography components. The
`handling of this weight requires additional mass in the
`remainder of the apparatus and typically a large appara-
`tus overall. The rotating disk supporting at least the
`X-ray source is typically rotatably supported in a mas-
`sive,
`finely—machined bearing assembly, and an ex-
`tremely massive and heavy support system is provided
`for supporting the gantry assembly and tomography
`components. The very massiveness of these systems
`helps to minimize vibration and other lateral mechani-
`cal movements, which, for example, can occur with
`wear between parts moving relative to one another.
`But such massive systems are also extremely expen-
`sive to build and once located and constructed for use
`are extremely difficult to relocate. They require large
`amounts of floor space and thus can not be used in space
`limited environments. Thus, use of such systems, for
`example, within the operating theater are impractical.
`The result is that a very powerful data gathering diag-
`nostic system is not readily available to a surgeon when
`such data might be very helpful, or to trauma units
`when movement of the patient should be minimized.
`One ramification of the extra size and mass of these
`machines has been to provide a fixed gantry assembly so
`as to require a movable patient table, as the weight of
`the patient and the patient table is typically much less
`than the weight of the gantry assembly and its rotating
`components. A movable patient table is used not only to
`properly position the patient in the desired location
`relative to the fixed gantry assembly so that a scan can
`be performed through a select portion of the patient’s
`body; but in the case of machines capable of performing
`helical scans, to move the patient parallel to the rotation
`axis (referred to as the “Z-axis”) of the tomography
`imaging components, while the components are rotat-
`ing about the patient. But, the apparatus which has
`resulted from these various requirements has been typi-
`cally large, heavy, expensive, and difficult to relocate.
`It has required a large amount of floor space and thus
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`Varian Exhibit 2002, Page 008
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`Varian Exhibit 2002, Page 008
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`can not be used in space-limited environments. A fur-
`ther disadvantage caused by the size and weight of these
`apparatuses has been the wear experienced in the mov-
`ing parts thereof. Moreover, in the course of reposition-
`ing a movable patient table for successive scans or a
`helical scan, the momentum of the movement of the
`table can result in patient movement during the scan
`resulting in erroneous scanning data. This problem can
`be especially acute when the table moves abruptly at the
`beginning or end of a scan.
`At least one three dimensional CT scanning system
`has been suggested in German Gebrauchsmuster File
`No. G 87 03 190.6 (described above) in which the tomo-
`graphic elements move through a helical path about a
`stationary patient table. As described in the document, a
`rotating ring supports the X-ray source and X-ray re-
`ceiver. The rotating ring is provided with helical screw
`threads so that as the ring rotates within a shell during
`a scan it simultaneously moves parallel to the patient
`table so that the ring moves in a helical manner along
`the length of the patient table and so that a high three-
`dimensional volume can be measured. The data ac-
`quired during a three dimensional scan make it possible
`to reconstruct
`large volume images. However,
`the
`movement of the rotating ring is confined to helical
`movement so that the system is only capable of three-di-
`mensional scanning. Additionally, while the patent sug-
`gests that, depending on system design, it is possible to
`reconstruct images taken" during the three-dimensional
`scanning process for any theoretical rotating ring incli-
`nation (layer angle) on the basis of data taken during the
`scan even through the scanning plane established by the
`ring can not be tilted. This would require the ring to be
`laterally displaced parallel to the orientation of the
`patient table over a large distance. For example, to
`obtain data equivalent to a 45° inclined angle, the rotat-
`ing ring would have to transverse a distance equal to the
`distance between the source and detectors exposing the
`patient to excessive amounts of X-rays over a large
`period of time. Further, the ring appears to be large, and 40
`urmecessarily massive. The system therefore would not
`be practical as a portable system.
`The portable tomography apparatus described in
`U.S. Pat. No. 4,928,283 (Gordon) represents a signifi-
`cant improvement in the state of the art by providing an
`apparatus with a high degree of mobility. The tomogra-
`phy components are supported ‘on a structure that also
`serves to support a removable patient table. The gantry
`assembly is movable between a first position where the
`table is disposed within the gantry and a scan can be
`performed on a patient disposed on the patient table and
`a second position where the gantry assembly is oriented
`90° to the first position so that it can be more easily
`transported and stored. The gantry assembly can be
`tilted. The support structure in the Gordon patent also
`provides means for rotating the tomography compo-
`nents about the Z-axis and means for moving the tomog-
`raphy components linearly along the Z-axis relative to
`the table when the tomography components are ori-
`ented in the first direction. The patent suggests that the
`apparatus is thus capable of helical scanning.
`The apparatus of the Gordon patent is therefore an
`improvement over the much larger, essentially immo-
`bile tomography systems of the prior art. With the Gor-
`don apparatus, the tomography system can be brought
`to the patient, for example, instead of vice versa. But,
`the apparatus of the Gordon patent is still larger and less
`maneuverable than desired because this apparatus nec-
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`5,448,607
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`4
`essarily incorporates the support structure for the pa-
`tient table. Furthermore, this apparatus requires trans-
`ferring a patient to the special removable patient table,
`which inhibits use ofthe apparatus at critical times, such
`as during surgery, or during emergency situations. In
`addition, precise control and measurement of the posi-
`tion of the gantry assembly relative to the patient is an
`elusive problem, since reducing the overall weight and
`mass of the system increases the amount of vibration
`and mechanical noise to which the system will be sub-
`ject as the components rotate during a scan.
`U.S. Pat. No. 5,109,397 (Gordon et al.) attempts to
`overcome some of the problems endemic to a portable
`tomography system by incorporating means for provid-
`ing error information at incremental angular positions
`and means for compensating the data derived from the
`analog information signals. Another type of measure-
`ment system for providing such error information is
`described in U.S. patent application Ser. No. 08/ 162,653
`filed on Dec. 6, 1993 in the names of Bernard M. Gor-
`don, et al., for “Apparatus for and Method of Measur-
`ing Geometric, Positional and Kinematic Parameters of
`a Rotating Device” (Attomey’s Docket No. ANA-21)
`and assigned to the present assignee. It remains desir-
`able, nevertheless, to reduce or eliminate misalignment
`errors in portable tomography systems through more
`accurate control and measurement of the position and
`orientation of the tomography components.
`It is desirable to provide an improvement over the
`X-ray system described in U.S. Pat. No. 4,928,283 (Gor-
`don), by providing an improved X-ray tomography
`system with translation and pivoting control so that
`precise positioning of the components relative to a sta-
`tionary patient table can be easily accomplished.
`OBJECTS OF THE INVENTION
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`Accordingly, it is a general object of this invention to
`provide a tomography apparatus which substantially
`reduces or overcomes the above-noted problems.
`More specifically, it is an object of this invention to
`provide tomography apparatus with means for pre-
`cisely controlling and measuring the position of the
`scanning plane vis-a-vis a stationary patient during a
`scanning procedure.
`Another object of this invention is to provide a porta-
`ble tomography apparatus with means for precisely
`controlling and measuring the longitudinal position of
`the gantry assembly relative to the longitudinal axis of a
`patient’s body or limb.
`And another object of this invention is to provide a
`portable tomography apparatus with means for pre-
`cisely controlling and measuring the tilting of the gan-
`try assembly relative to the longitudinal axis of a pa-
`tient’s body or limb.
`It is also an object of this invention to provide a por-
`table tomography system which is readily adaptable for
`use with a patient in either a recumbent or a sitting
`position.
`A further object of this invention is to provide a
`portable tomography system which is independent of
`the patient support means.
`Specifically, it is an object of this invention to pro-
`vide a portable tomography apparatus wherein lateral
`translation of the gantry assembly relative to the sup-
`port structure is regulated by mechanical displacement
`means which, in turn, is coupled to electro-mechanical
`means for simultaneously measuring and monitoring the
`amount of the displacement.
`'
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`Varian Exhibit 2002, Page 009
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`5,448,607
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`5
`Still another object of this invention is to provide a
`portable tomography apparatus capable of carrying out
`either a sequence of precisely controlled individual
`X-ray scans or a continuous, helical scan.
`Other objects of the invention will in part be obvious
`and will in part appear hereinafter. The invention ac-
`cordingly comprises the apparatus possessing the con-
`struction, combination of elements and arrangement of
`parts exemplified in the following detailed disclosure
`and the accompanying drawings, and the scope of the
`application of which will be indicated in the claims.
`SUMMARY OF THE INVENTION
`
`The present invention comprises tomography appara-
`tus wherein lirnited lateral movement of a gantry assem-
`bly relative to a stationary patient is precisely con-
`trolled by coupling mechanical displacement means to
`electro-mechanical means for simultaneously control-
`ling and measuring the amount of the displacement. A
`support structure for the gantry assembly preferably
`comprises a cart-like apparatus on wheels being adapted
`to: support a translatable and pivotable gantry assembly
`so as to provide limited, precisely controlled and moni-
`tored lateral movement of the gantry assembly relative
`to the patient and the support structure; and limited,
`precisely controlled tilting of the gantry assembly rela-
`tive to the axis of a patient’s limb or body. The resulting
`tomography system is compact, readily mobile, and
`easily maneuverable while at the same time generating
`highly accurate and dependable scanning data.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`detectors diametrically opposite the X-ray source, a
`power source, and other components as described in
`U.S. Pat. No. 4,928,283. For additional details relating
`to the gantry assembly see copending U.S. patent appli-
`cation Ser. No. 08/193,783, filed in the name of Gilbert
`W. McKenna and entitled “X-ray Tomographic Scan-
`ning System” (Attomey’s Docket No. ANA-30); and
`U.S. patent application Ser. No. 08/193,696, filed simul-
`taneously herewith in the name of Gilbert W. McKenna
`and Ronald E. Swain and entitled “Tomographic Scan-
`ner Having Center of Rotation for all Physics” (Attor-
`ney’s Docket No. ANA-31), assigned to the present
`assignee, and incorporated herein by reference. In order
`to protect and conceal the components distributed
`around the frame of gantry assembly 12, a skin or cover
`24 of an X-ray transparent material (shown schemati-
`cally in FIG. 1), such as a polycarbonate plastic or the
`like, may be provided and secured in place by a plural-
`ity of bands or fasteners 26 distributed around the cir-
`cumference of the gantry assembly. Means (not shown)
`are provided for rotating the tomography components
`mounted on gantry assembly 12, such as the means
`described in U.S. Pat. No. 4,928,283.
`As best seen in FIGS. 1 and 2, cart apparatus 14 is
`generally of a U—shaped configuration comprising a
`transverse base member 16 supported on a plurality of
`wheels 18, upwardly projecting wall members 20 and
`22, which may be either extensions of or fastened to
`base member 16, and means for supporting gantry as-
`sembly 12 on wall members 20 and 22. In place of
`wheels 18, any equivalent multi-directional movement
`or rolling means, such as ball-and-socket rollers, may be
`substituted. In a preferred embodiment, wall members
`20 and 22 include inwardly sloping lower portions (as
`best seen in FIG. 2) such that wall members 20 and 22
`together with base member 16 comprise a protective
`cradle for the lower half of gantry 12 which flanks the
`outer circumferential walls of the gantry assembly. One
`or both wall members 20 and 22 further comprise a
`gantry displacement mechanism 70, generally indicated
`in FIG. 1 (and described in greater detail in connection
`with FIG. 5), wherein a portion of which is visible as
`rod members 80, and a gantry tilt control mechanism
`(not seen in FIGS. 1 and 2, but described in greater
`detail hereinafter in connection with FIG. 6).
`For reference purposes, FIGS. 1-3 also show a sepa-
`rate, movable, X-ray transparent patient table or gurney
`40 generally comprising a transverse base member 42
`supported on a plurality of wheels 44 in combination
`with upright support members 46 supported on base
`member 42 at the lower ends thereof. Members 46 in
`
`turn support table means 48 at their upper extremities. It
`will be appreciated that patient table 40 may instead be
`stationary,
`in which case no wheels 44 would be
`needed, without in any way affecting the operation of
`the tomography apparatus of this invention. In a pre-
`ferred embodiment, upright table support members 46
`may comprise telescoping tubes or similar means by
`which the height of the foot and head ends of table
`means 48 above the floor can be readily and indepen-
`dently adjusted by conventional automated or manual
`means. Such table height adjustment means facilitates
`positioning a patient at the center of the tomography
`apparatus, as better seen in FIG. 2 where the dotted
`outline of patient support member 56, as described be-
`low, indicates the table in the elevated position. In an-
`other preferred embodiment, as seen in FIG. 2, table
`means 48 may comprise two laterally extending,
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`Varian Exhibit 2002, Page 010
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`For a fuller understanding of the nature and objects 0
`of the present invention, reference should be made to
`the following detailed description taken in connection
`with the accompanying drawings wherein:
`FIG. 1 is a schematic perspective view of the tomog-
`raphy apparatus of the present invention illustrated in
`relationship to a separate patient table;
`FIG. 2 is a schematic end view of the tomography
`apparatus and patient table illustrated in FIG. 1;
`FIG. 3 is a schematic side view of the tomography
`apparatus and patient table illustrated in FIG. 1;
`FIG. 4 is a schematic side view of the tomography
`apparatus, similar to FIG.‘ 3, but shown in use with a
`patient chair and arm support;
`-
`FIG. 5 is an enlarged, schematic, partially cutaway
`isometric view of the mechanical displacement mecha-
`nism used to achieve lateral movement of the gantry I
`assembly and of the associated electro-mechanical sys-
`tem for measuring and monitoring the amount of the
`displacement; and
`FIG. 6 is an enlarged, schematic, isometric side view
`of the tomography apparatus of FIG. 1 illustrating the
`relationship of the mechanical displacement mechanism
`of FIG. 5 relative to the tomography apparatus and also
`illustrating the tilt control mechanism of this invention.
`DETAILED DESCRIPTION OF THE
`DRAWINGS
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`FIGS. 1-3 show an X-ray tomography apparatus 10
`generally including a doughnut-like gantry assembly 12
`mounted on a movable cart apparatus 14. As schemati-
`cally shown in FIG. 2, gantry assembly 12 comprises a
`stationary annular frame 28, and a disk 30 mounted for
`rotation within the armular frame 28 and supporting
`conventional
`tomography components,
`typically in-
`cluding an X-ray source, a plurality or array of X-ray
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`5,448,607
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`7
`grooved side or rail members 52 and 54 and a flat or
`curved patient support member 56 adapted along its
`lateral edges to be slidably engaged by the grooves of
`members 52 and 54. The table 40 includes a coupling
`mechanism generally indicated at 58 in FIG. 3. Such a
`patient table or gurney specially adapted for use in
`combination with the tomography system of this inven-
`tion is described in a copending U.S. patent application
`Ser. No. 08/193,782, filed simultaneously herewith in
`the name of Gilbert W. McKenna and entitled “Stabi-
`lized, Cantilevered, Patient Trauma Table System”
`(Attorney’s Docket No. ANA-58), assigned to the pres-
`ent assignee and incorporated herein by reference.
`Thus, in preparation for a CT scan, as best seen in
`FIGS. 1 and 3, cart 14 carrying gantry assembly 12 and
`one end of table 40 would be moved together and joined
`by mechanism 58. Table means 48, if necessary, would
`be elevated to the desired height for centering with
`respect to gantry assembly 12. Then, patient support
`member 56 carrying the subject patient would be slid
`into the inner, annular region of gantry assembly 12 for
`generally positioning the patient. Once the patient is
`thus initially positioned vis-a-vis the tomography appa-
`ratus, further movement of the patient or patient table is
`unnecessary with the apparatus of this invention. In-
`stead, the gantry displacement mechanism 70 is capable
`of limited, controlled lateral translation of gantry as-
`sembly 12 generally along the longitudinal axis of the
`table in order to generate the sequential X-ray data
`needed for large volume and helical scan imaging. In
`one embodiment of this invention,
`therefore, X-ray
`imaging is performed step-wise in conjunction with
`incremental, precisely measured, discrete displacements
`of the gantry assembly with respect to the patient,
`which displacements are effected by briefly and repeat-
`edly activating the gantry displacement mechanism. In
`an alternative embodiment, X-ray imaging can also be
`carried out continuously as a helical scan by activating
`the gantry displacement mechanism for gradual, contin-
`uous and precisely measured lateral displacement of the
`gantry assembly while the tomography system is in
`operation with the disk 30 rotating within the annular
`frame 28. Although a patient table such as that illus-
`trated in FIG. 1 is particularly well adapted to perform-
`ing CT scans with the apparatus of this invention, as
`described above, this invention is not to be construed as
`being limited in any way to use in combination with
`patient table 40 as described above. It should be appre-
`ciated that the tomography apparatus of this invention
`has utility with other types of patient tables and with
`other types of patient supports, such as a chair as illus-
`trated in FIG. 4.
`FIG. 4 shows a plan view of an alternative utilization
`of the tomography apparatus of this invention, again
`wherein corresponding numbers identify corresponding
`members. As shown in FIG. 4, limb support means 60,
`comprising a frame 62 supporting a limb platform 64, is
`mounted on cart 14. The tomography apparatus thus
`adapted is suitable for performing CT scans on a pa-
`tient’s limb, such as an arm, while the patient sits or
`reclines alongside can 14.
`FIG. 5 shows an enlarged, partially cutaway view of
`the gantry displacement apparatus as of this invention.
`Preferably a pair of identical gantry displacement appa-
`ratus 70, one being shown in FIG. 5 as being fixed along
`one side thereof to base or surface member 72 for illus-
`tration, are respectively adapted to be incorporated into
`or secured to the wall members 20 and 22 of cart 14 as
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`described hereinafter. Each displacement apparatus 70
`generally comprises an elongated ball screw element 74,
`connected to drive means such as a reversible drive
`electric stepping motor 76, and displacement member
`78 functioning in cooperation with screw element 74,
`such as a ball nut, and connected to the gantry assembly
`12. Displacement member 78 is adapted for two-way
`movement along a track generally defined by screw
`element 74. The movement track has a length that is
`somewhat less than the width of cart 14. Screw element
`74 and the associated displacement member 78 are at
`least partly enclosed by housing means 90. In one em-
`bodiment, electric stepping motor 76 may be mounted
`externally of one wall of housing means 90 and con-
`nected to screw element 74 through an aperture in that
`housing waH. For example, a stepping motor having 200
`steps per five millimeters permits a very fine adjustment
`resolution of 0.001 inches/step. Housing means 90 may
`further comprise apertures 92 in two opposite end walls
`in order to accommodate the opposite ends of a guiding
`rod member 80 as hereinafter described. As seen in
`FIG. 5, displacement member 78 comprises an inter-
`nally threaded block which engages screw element 74
`such that, as motor 76 rotates screw element 74 in a
`clockwise direction, member 78 is moved along the
`screw element in a first direction; and, as motor 76
`rotates screw element 74 in a counterclockwise direc-
`tion, member 78 is moved along the screw element in a
`second, opposite direction.
`The displacement apparatus may further comprise a
`guiding rod member 80 disposed in a linear bearing
`comprising a hemispherical or semi-tubular passageway
`82 extending through displacement member 78 (which
`is coupled to the gantry assembly as described in greater
`detail in FIG. 6), or through another member which is
`fastened to member 78, wherein the longitudinal axis of
`the hemispherical passageway 82 is substantially paral-
`lel to the longitudinal axis of ball screw 74. The ball
`screw 74 is suitably joumaled in the housing 90 so that
`it freely rotates in response to the operation of the step-
`per motor 76 without moving longitudinally. The pas-
`sageway 82 has a diameter slightly greater than that of
`rod member 80 and may lubricated or be fitted with ball
`bearings such that displacement member 78 slides along
`rod member 80 as ball screw 74 is driven by motor 76.
`As previously noted, the opposite ends of rod member
`80 are further supported by passing through apertures
`92 in two opposite end walls of housing 90. While the
`two displacement members 78, positioned on respective
`diametrically opposite sides of the gantry assembly, are
`preferably oriented parallel to one another, in order to
`accommodate minor non-parallel misalignments be-
`tween the two, apertures 92 have diameters slightly
`larger than that of rod member 80 such that a limited
`degree of lateral movement or tolerance of rod member
`80 is provided in order to accommodate such minor
`misalignments during the repositioning the tomography
`apparatus.
`Displacement apparatus 70 further comprises means
`for measuring the amount of any displacement, so that if
`necessary it can be monitored and/or controlled. In a
`preferred embodiment,
`the displacement monitoring
`means comprises electro-mechanical apparatus, such as
`a potentiometer 94, suitably biased with a supply volt-
`age (not shown) for providing a voltage output as a
`function of the position of the displacement member 78.
`As seen in FIG. 5, potentiometer 94 is secured relative
`to the surface member 72, preferably at one end of the
`
`Varian Exhibit 2002, Page 011
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`Varian Exhibit 2002, Page 011
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`9
`screw 74. Potentiometer 94 includes a pulley wheel 96
`which when turned varies the resistance of and thus the
`voltage output of the potentiometer 94. A second, fol-
`lower pulley 96 is preferably secured relative to the
`surface 72, preferably at the other end of screw 74. A
`cable 98 is looped around the two pulleys and is fixed at
`one end by suitable means, such as a cable connector 88,
`to the displacement member 78 and its other end to a
`spring 86 for tensioning the cable, said spring 86 also
`being connected to the displacement member 78, prefer-
`ably via the connector 88 as illustrated. Extremely pre-
`cise monitoring of the amount and direction of any
`movement of displacement member 78 (and thus longi-
`tudinal movement of the gantry assembly) is realized by
`conventional means for monitoring the electrical volt-
`age across the potentiometer. In a preferred embodi-
`ment of this invention, a pair of displacement appara-
`tuses 70 as shown in FIG. 5 are respectively incorpo-
`rated into or mounted on each of wall members 20 and
`22 of cart apparatus 14 (FIG. 1) so that both sides of 20
`gantry assembly 12 can be moved smoothly and simul-
`taneously.
`FIG. 6 shows a schematic side view of gantry assem-
`bly 12, with skin 24 removed for illustrative purposes,
`mounted on cart apparatus 14 (FIG. 1) and connected
`to a gantry displacement apparatus 70 similar to that
`shown in FIG. 5. As discussed with respect to FIG. 5,
`in FIG. 6 an elongated ball screw 74 is at least partly
`housed in housing 90 and is driven by stepper motor 76
`mounted externally of housing 90 and connected to ball
`screw 74 through an aperture in the adjacent wall of
`housing 90. The ball screw is suitably journaled in the
`housing 90 so that it freely rotates in response to stepper
`motor 76. The longitudinal axis of screw element 74 is
`subst