MINIATURE C-ARM APPARATUS WITH C-ARM MOUNTED COMPACT OIL IMMERSION POWER _ CROSS REFERENCE TO RELATED APPLICATION This application claims the priority benefit, under 35 U. S. C. §119 (e) (1), of applicants'copending United States provisional application Serial No. 60/102,128, filed September 28,1998, which is incorporated herein in its entirety by this reference.

BACKGROUND OF THE INVENTION This invention relates to mobile x-ray fluoroscopic imaging systems with miniature C-arm apparatus, and more particularly to miniature C-arm apparatus providing visual indicators to alert the physician and others to the activation of the x-ray source function of the system.

In present-day medical practice, x-ray fluoroscopic imaging systems provide images of bone and tissue that are similar to conventional film x-ray shadowgrams but are produced by conver- sion of an incident x-ray pattern to a"live"enhanced (intensi- fied) optical image that can be displayed on a video monitor directly, i. e., essentially contemporaneously with the irradia- tion of the patient's body or body portion being imaged. The term"fluoroscopic imaging"is used herein to designate such provision of directly video-displayed x-ray images. An imaging device, including an image intensifier, suitable for use in such a system is described in U. S. patent No. 4,142,101, which is incorporated herein in its entirety by this reference.

In some x-ray fluoroscopic imaging systems, the entire system is carried on an easily movable cart and an x-ray source and detector are mounted on a rotatable mini C-arm dimensioned

for examining smaller body parts such as the-extremities (wrists, ankles, etc.) of a human patient.

One illustrative example of a commercially available mini C-arm x-ray fluoroscopic imaging system is that sold under the trade name"FluoroScan III"by FluoroScan Imaging Systems, Inc., of Northbrook, Illinois. Further examples of mini C-arm x-ray fluoroscopic imaging systems are described in U. S. Patent 5,627,873 and copending U. S. patent application Serial No.

09/199,952, filed November 24,1998 (and assigned to the same assignee as the present application), both of which are incorpo- rated herein in their entirety by this reference.

Mini C-arm x-ray fluoroscopic imaging systems are also being used to measure bone mineral density (BMD) of bones in, for example, the forearm or wrist, or in the ankle or heel (calcaneal region) of a human patient. An example of such an x-ray fluoro- scopic imaging system is described in allowed copending U. S.

Patent Application No. 08/794,615 filed on February 3,1997 which is assigned to Hologic, Inc., the parent company of the assignee of the present application, and which is incorporated herein in its entirety by this reference.

Generally, such mini C-arm x-ray fluoroscopic imaging systems and x-ray bone densitometry systems are economical in space, conveniently movable (as within a hospital, clinic or physician's office) to a desired temporary location of use, and offer superior safety (owing to low levels of electric current utilization and reduced exposure of personnel to scatter radiation) as well as ease of positioning the x-ray source and detector relative to a patient's extremity for imaging. The various functions and operations of the system are conventionally controlled by buttons or switches on a control panel that is positionally associated with the cart.

X-ray fluoroscopic imaging systems of the type with which the present invention is concerned typically include a processing system, such as a computer, and peripheral devices enclosed within a portable cabinet and a C-arm apparatus that is mounted to the cabinet. The processing system controls the operation of the various components of the imaging system, provides a camera

or image processing to transform in real time image data received from an image receptor for display, printing or storage, and communicates with peripheral devices. The computer may also be configured to communicate with a local area network to transfer, for example, image data to locations remote from the sterile environment. An example of a suitable processing system is a personal computer running the Windows 95, DOS, UNIX, MacOS or other operating systems. Examples of peripheral devices include display monitors, image (or video) printers and image storage devices (or recorders).

The C-arm apparatus includes a C-arm assembly, a support arm assembly and an articulated arm assembly. The C-arm assembly includes a C-arm having a track for guiding rotational movement of the C-arm, an x-ray source assembly including an x-ray source and an x-ray detector assembly including an image receptor and camera. The x-ray source and detector assemblies are located at opposing ends of the C-arm so that the x-ray source and image receptor face each other and x-rays emitted by the x-ray source impinge on the image receptor.

The support arm assembly engages the C-arm track so that the C-arm is movable relative to the support arm, and the articulated arm assembly is provided to facilitate movement of, including change in the angular orientation of, the source and detector assemblies relative to a patient's body portion being imaged.

The articulated arm assembly includes at least one movable arm wherein a first end portion of the arm is connected to the support arm assembly and a second end portion of the arm is connected to a mobile base or portable cabinet. Preferably, the first end portion is so connected to the support arm assembly that the support arm assembly can be rotated relative to the movable arm.

During surgical procedures a sterile field is created around a patient to ensure that foreign substances or organisms do not infect the patient. Any instruments or persons within this field have to be sterile or covered by a sterile draping material. The sterile field is generally defined by the American College of Surgeons and published by the Association of Operating Room

Nurses (AORN). Generally, the sterile field is defined as the area occupied by the sterile draping material on any operating room table, including the patient table and instrument tables.

To permit sterile personnel to position the x-ray fluoroscopic imaging system C-arm assembly in the sterile field a clear surgical drape covers the C-arm assembly.

In the x-ray fluoroscopic imaging system described in U. S. provisional patent application Serial No. 60/078,491 filed by one of the applicants herein (jointly with other persons) on March 18,1998, and in U. S. patent application Serial No. 09/270,373 filed by the same one of the applicants herein (jointly with the same other persons) on March 16,1999, the entire disclosures of which are both incorporated herein by this reference, to permit surgeons to activate certain functions of the x-ray fluoroscopic imaging system within this sterile field, either the x-ray source assembly or the x-ray detector assembly, which are used within the sterile field, includes a control panel that provides a physician with easy access to predefined imaging control functions associated with the x-ray fluoroscopic imaging system within the sterile field. By locating the control panel on the ends of the C-arm, a surgeon can activate the functions without placing a hand or arm in the path of the x-ray beam. Preferably, the control panel includes an array of membrane switches, wherein each switch in the array is provided to activate a function performed by the x-ray fluoroscopic imaging system. Examples of functions controlled by the control panel switches include: x-ray source activation; image printing; image noise suppression; camera rotation; and x-ray source voltage/current control-.

The x-ray fluoroscopic imaging system may also include a foot control panel which is similar to the above-described control panel but permits foot activation of predefined functions of the x-ray fluoroscopic imaging system including but not limited to x-ray activation, image printing and image storing.

SUMMARY OF THE INVENTION The present invention broadly contemplates the provision of an x-ray fluoroscopic imaging system comprising a portable cabinet; a support arm assembly ; an articulated arm assembly having at least one movable arm and connecting the support arm assembly to the cabinet; and a C-arm assembly having a C-arm carried by the support arm assembly, an x-ray source assembly including an x-ray source and an x-ray detector assembly including an image receptor located at opposing locations on the C-arm such that the x-ray source and image receptor face each other so that x-rays emitted by the x-ray source impinge on the image receptor; wherein the improvement comprises the provision of a compact oil immersion power supply mounted in the C-arm and providing power at least for the x-ray source.

Further in accordance with the invention, the power supply is immersed in a suitable high dielectric strength oil that permits proper high voltage dielectric breakdown strength, proper cooling and increased maintainability. The power supply provides activation of x-rays, high voltage and current required as functions of the system as a minimum; other functions may be added.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified and partly schematic side elevational view of mini C-arm x-ray fluoroscopic imaging apparatus incorpo- rating an illustrative embodiment of the present invention; FIGS. 2A, 2B, 2C and 2D are reduced-scale views of the apparatus of FIG. 1, respectively in side elevation with the arm assembly extended (showing different positions thereof), in plan with the arm assembly extended, in side elevation with the arm assembly folded, and in plan with the arm assembly folded;

FIGS. 3A, 3B, 3C and 3D are enlarged views of a portion of FIG. 1, respectively in side elevation, top plan, fragmentary bottom plan, and front elevation, wherein FIG. 3A shows the location of the compact oil immersion power supply in the illus- trated embodiment of the _ FIG. 4 is a system block diagram of the apparatus of FIG.

1; FIGS. 5A, 5B and 5C are views respectively in side eleva- tion, front elevation and plan of the apparatus of FIG. 1; FIGS. 6A, 6B and 6C are various views of the compact oil immersion power supply mounted in the C-arm in the illustrated embodiment of the invention; FIG. 7 is a block diagram of the power supply of FIGS. 6A-6C and its interaction with the system computer; FIGS. 8, 9 and 10 are respectively front elevational, side elevational and plan views of the x-ray source assembly oh the mini C-arm of the system of FIG. 1, further illustrating the disposition of the compact oil immersion power supply therein; FIGS. 11A, 11B, 11C, 11D, 11E, 11F, 11G and 11H are perspec- tive (exploded) and detail views of various elements and subassemblies of the power supply and associated x-ray tube; FIGS. 12A, 12B, 12C, 12D, 12E and 12F are further perspec- tive and detail views of various elements and subassemblies of the power supply and associated x-ray tube; FIG. 13 is an exploded perspective view of the power supply; FIG. 14 is a view of the filament drive assembly; and FIG. 15 is a simplified and partly schematic side eleva- tional view of a mini C-arm x-ray fluoroscopic imaging system arranged for use to measure forearm BMD of a human patient, in which an embodiment of the present invention may be incorporated.

DETAILED DESCRIPTION An exemplary x-ray fluoroscopic imaging system incorporating one embodiment of the present application is shown in FIGS. 1-5.

In this embodiment, the imaging system 10 is entirely contained

in a wheeled cart or portable cabinet 11 that can easily be rolled from place to place. The cabinet includes a generally rectangular, upright body 12 that supports a display 14 (e. g., dual video monitors) on its top surface and an articulated arm assembly 18 secured thereto. The cabinet also contains a computer for processing data as hereinafter further discussed.

It will be understood that images taken by the imaging system can be shown on only a single monitor, or printed on a printer which is preferably enclosed within the cabinet.

In this embodiment, the articulating arm assembly 18 includes two arms 18a and 18b. The distal end of arm 18b is connected to a support arm assembly 20 that has a C-arm locking mechanism 22. A C-arm 24 of mini C-arm assembly 26 is carried by the support arm assembly 20 such that a track 28 of the C-arm is slidable within the C-arm locking mechanism 22. The mini C- arm assembly 26 also includes an x-ray source assembly 30 and an x-ray detector assembly 34 respectively mounted at opposite extremities of the C-arm in facing relation to each other so that an x-ray beam 36 from an x-ray source 32 within the source assembly impinges on the input end 38 of the detector assembly 34. The x-ray source 32 and detector end 38 are spaced apart by the C-arm sufficiently to define a gap 40 between them, in which the limb or extremity of a human patient 42 can be inserted in the path of the x-ray beam 36.

The support arm assembly 20 connected to the end of arm 18b provides 3-way pivotal mounting that enables the C-arm 24 to be swivelled or rotated through 360° in each of three mutually perpendicular (x, y, z) planes and to be held stably at any desired position, while the arm 18a of the articulating arm assembly 18 is mounted to the portable cabinet 11 at point"A" and jointed to enable its distal end and the C-arm to be angularly displaced both horizontally and vertically. The multidirectional angular movability of the C-arm assembly facilitates the positioning of the x-ray source and detector assemblies in relation to a patient body portion to be irradiat- ed.

A suitable power supply for the x-ray source (hereinafter further described), and instrumentalities for controlling or varying current (mA) and voltage (kV), not shown, are incorporat- ed in the system as well.

As noted, the C-arm 24 is movable within the C-arm locking mechanism 22. To fix the position of the C-arm relative to the support arm assembly 20, the C-arm locking mechanism is used.

The C-arm locking mechanism may be a clamp assembly (not shown) which is compressed against the C-arm when tightened, but preferably the C-arm locking mechanism is of the type described in pending U. S. Provisional Patent Application No. 60/066,966 filed on November 28,1997, which is incorporated herein in its entirety by this reference.

Preferably, either the x-ray source assembly or the x-ray detector assembly includes a control panel 50 that is mounted thereon (i. e. at one or the other of the opposed extremities of the C-arm) and is coupled to the imaging system computer to provide a physician with easy access within the sterile field to predefined imaging control functions associated with the x-ray fluoroscopic imaging system. With the control panel 50 included in either the source or detector assembly, a physician can activate certain (or all) functions of the x-ray fluoroscopic imaging system from within the sterile field and without placing a hand or arm within the path of the x-ray beam. One result of this configuration is that it gives a physician immediate control of the operating characteristics of the fluoroscope in the event that a regular operator is unavailable or unable to operate controls located outside of the sterile field.

In the exemplary system illustrated in the drawings, the control panel has an array of switches, one of which controls the x-ray source to generate a single image or for continuous imaging. For example, to generate a single image, a physician may depress the x-ray control switch twice in rapid succession and then release the switch so that the x-ray source (or tube) is activated for a single image or strobe shot. For continuous im- aging, a physician depresses the x-ray control switch twice in rapid succession and then continues to depress (or hold down) the

switch so that the x-ray source is activated and continues to produce x-rays for as long as the switch is depressed to create a real time continuous or cinematic fluoroscopic picture.

As thus far described, the system 10 is essentially identical to currently available mini C-arm x-ray fluoroscopic imaging systems. Thus, the system 10 may be a"FluoroScan IV" system, produced by FluoroScan Imaging Systems, Inc., having the following specifications: OUTPUT FORMAT: Standard 2,200 Image Storage; Optional 4,000 Image Storage; Digital Video Output; Composite Video Output VIDEO PROCESSING: Last Image Hold for 4 Images; Real Time Edge Enhancement; User Selectable Real Time Recursive Averaging; Noise Suppression; Automatic Contrast Enhancement; Automatic Brightness Control INPUT POWER: 110V-60Hz Nominal; 90V-to 132V-Actual ; 47Hz to 63Hz Actual; Non Dedicated, Grounded WARM UP: 3 Seconds X-RAY POWER SUPPLY: Continuous Duty kV-40kV to 75kV in 2.15kV Increments ANODE CURRENT: 20yA (0. 020mA) to 100yA (O. lmA) in 3.6fiuA Increments FOCAL SPOT: 85 Micron (0.085 mm) TUBE TYPE: Custom Designed Cold Anode TUBE COOLING: Maximum Tube Temperature is 50°C at Maximum Power After 4 Hours of Continuous Duty TARGET: Tungsten COLLIMATION: Fixed to Field of View Size FIELDS OF VIEW: 150mm (6"Nominal) IMAGE INTENSIFIER: High Gain Micro Channel Plate with Minimum of 40,000 Gain

PIXEL ARRAY: 768 pixels by 600 lines DUAL VIDEO MONITORS: 15" (39cm) SVGA High Resolution Video Monitor Video Standard NTSC/VHS OVERALL HEIGHT: 60 inches OVERALL FLOOR SPACE: 8.0 ft2 (36"wide by 32"deep) In accordance with the present invention, in the exemplary embodiment now to be described, there is provided a compact oil immersion power supply 54 (FIG. 3A) to provide power for certain functions of the imaging system, including, at least, the power required for the x-ray source 32. The power supply 54 is mounted in the C-arm assembly, and specifically, as shown in FIGS. 3A and 8-10, in the x-ray source assembly 30.

Preferably, further in accordance with the invention, the power supply 54 comprises a power supply assembly 55 (FIG. 13) mounted in a compact aluminum container 56 (FIG. 6) filled with oil. The compact power supply generates all of the high voltages and currents required and is operatively combined with an x-ray tube to convert the high voltage to a beam of x-rays required for the operation of the x-ray fluoroscopy system. The entire power supply is self-contained in a modular container filled with insulating oil. This approach provides an x-ray power supply assembly that is modular, efficient, easily repairable and provides effective cooling of all of the high voltage components.

Typical units today are potted modules that cannot be repaired.

The power supply 54, shown in FIGS. 6-10, has the following pertinent high voltage specifications: HIGH VOLTAGE RANGE 40 to 75 kVp 150-.) CURRENT RANGE 20 to 100 yA DUTY CYCLE Continuous duty FOCAL SPOT SIZE 0.085 millimeter maximum

FIG. 7 is a block diagram of the power supply and its interaction with the system computer. The power supply is under control of the system PC controller at all times.

More particularly, and referring to FIGS. 11-13, the power supply assembly 55 includes a high voltage transformer 58 with primary coil 59, secondary coil 60 and ferrite U-core 61; a high voltage multiplier 62 with capacitors 63 and high voltage multiplier printed circuit board (PCB) 64; a filament transformer 65 with primary coil 66, secondary coil 67 and ferrite core 68; a kV feedback PCB 69; and a transformer side PCB 70, arranged within a compact volume and mechanically interconnected by threaded rods 71 and nuts 72. The electrical interconnection and functioning of these elements to constitute a power supply having the above-stated purposes will be readily apparent to persons skilled in the art, and accordingly need not be further de- scribed. The filament drive assembly 73 is shown in detail in FIG. 14.

The container 56 includes an open-topped aluminum tank 74 of generally rectangular-solid configuration, dimensioned to receive the assembly 55, and an aluminum cover plate 75 for closing the open top of the tank. A"Mylar>"liner (represented by broken lines 76 in FIG. 13) is placed in the bottom of the tank. An O-ring 77 is inserted within a groove, not shown, on the upper lip of the tank, to provide a seal between the tank and cover so that, when the cover is mounted on the tank, the tank and cover cooperatively constitute a liquid-tight container capable of being filled with oil.

The assembly 55, secured to a mounting shelf 78, and the x- ray tube 79 of the x-ray source 32, with its associated shielding hardware 80, disposed in interfitted relation to minimize space, are mounted on the cover plate 75 in such arrangement that when the cover plate is placed on the open top of the tank, the assembly 55 and the tube 79 are received together within and enclosed by the container 56. The cover plate is formed with a first aperture 81 for the x-ray tube; a second, elongated aperture 82 for a mount 83 for a rubber oil expansion diaphragm

84; a third aperture 85 for connector 86, and a fourth aperture 87, closed by a plug 88, for filing the container with oil.

Thus, in the illustrated embodiment, the power supply assembly 55 and the x-ray tube 79 are placed within the container 56, which is filled with oil under vacuum. The container 56 is then placed into the x-ray source assembly 30 as shown in FIGS.

8-10 and is oriented so that the x-ray tube exit port 90 is posi- tioned toward the rear of the assembly.

It is currently preferred to use one of two types of dielec- tric oil to fill the container 56. One of these, at present especially preferred, is the oil available from Shell Oil under the trade name"DIALA."The second is a compound available under the designations"FC40"or"FLUORINERT" (trade name) electronic fluid, which is a product of 3M.

A wide variety of additional alternatives are embraced within the scope of the invention in its broader aspects. For instance, the image intensifier employed in the detector may be either of a type that intensifies optical images (as in the above-described"FluoroScan IV"system) or of a type that intensifies x-ray images. Again, in place of an image intensifi- er and video camera, the detector may be a direct digital 2- dimensional x-ray detector; an example of such a device is the "FlashScan 20"high resolution flat panel device of dpiX, A Xerox Company, which is an amorphous silicon image sensor that acquires conventional x-ray images and converts them to digital form in a way that can provide fluoroscopic imaging in real time.

An alternative embodiment of an x-ray fluoroscopic imaging system in which the present invention can be incorporated i-s that described in the aforementioned copending U. S. patent application Serial No. 08/794,615, which describes various alternative embodiments and modifications suitable for such use.

Such an alternative embodiment of the x-ray fluoroscopic imaging system which can be used to measure bone mineral density (BMD) in, for example, the forearm, wrist, ankle or heel of a human patient will be described with reference to FIG. 13. This imaging system 200 is also entirely contained in a wheeled cart or cabinet 210 that can easily be rolled from place to place.

The cabinet includes a generally rectangular, upright body 212 that supports dual video monitors 214 (only one being shown) on its top surface and has, in its upper portion, a keyboard 216 and an articulated member 218; the cabinet also contains a computer (not shown) for processing data as hereinafter further discussed.

It will be understood that the present method can be practiced with use of only a single monitor, or indeed without a monitor (e. g., employing a printer to produce the BMD measurement data).

The outer end of articulated member 218 carries a mini C-arm 220 having an x-ray source 222 and a detector 224 respectively fixedly mounted at its opposite extremities so that an x-ray beam 226 from source 222 impinges on the input end 228 of the detector, the source and detector being spaced apart by the C-arm sufficiently to define a gap 229 between them, in which the limb or extremity of a human patient 230 can be inserted in the path of the x-ray beam 226. The C-arm is connected to the end of member 218 by a 3-way pivotal mounting 232 that enables the C-arm to be swivelled or rotated through 360° in each of three mutually perpendicular (x, y, z) planes and to be held stably at any desired position, while the member 218 is itself mounted and jointed to enable its outer end and the C-arm to be angularly displaced both horizontally and vertically. The multidirectional angular movability of the mini C-arm facilitates the positioning of the source and detector in relation to a patient body portion to be irradiated.

Preferably, either the x-ray source or the x-ray detector includes a control panel 250 that is coupled to the imaging system computer to provide a physician with easy access within the sterile field to predefined imaging control functions associated with the x-ray fluoroscopic imaging system. The control panel 250 is illustrated in FIG. 13 as being mounted on the detector 224. Preferably, the control panel 250, like the panel 50 of FIG. 8, includes an array of membrane switches, each of which is provided to activate at least one function performed by the x-ray fluoroscopic imaging system. In one embodiment, each switch in the array has a raised button profile which provides tactile feedback, completes a signal circuit when

contact material mounted on the underside-of the raised button profile which provides tactile feedback is depressed to a base layer and breaks the signal circuit when pressure on the contact material is released.

The beam 226 emitted by the x-ray source 222 is a cone- shaped beam (i. e. a volume beam as opposed to a pencil beam-or fan beam) that impinges on a flat x-ray-sensitive receiving surface of the detector 224 at or adjacent the detector input end; this receiving surface faces the source across the gap 229 and is perpendicular to the axis of the beam path, so that the intersection of the receiving surface and the conical x-ray beam is an extended circular (2-dimensional) area. The term"field of view"is used herein to refer to the latter circular area, or that portion of it to which the detector responds, and also to designate the region, within the beam path or gap 229, the contents of which will be imaged by the detector. It will be understood that the area of the field of view as measured in a plane transverse to the beam path axis is sufficient to encompass objects of the size desired to be imaged or otherwise studied, e. g. a human wrist or heel.

The receiving surface of the detector 224 is a surface of an x-ray-to-visible-light converter, such as a layer of phosphor or scintillator material covered externally by a light shield, that converts impinging x-rays to visible light. The detector may include a Cesium Iodide vacuum tube image intensifier or an image intensifier of the high-gain microchannel plate type, and a planar output surface on which is produced an output visible- light image of the field of view, in accordance with well-known principles of fluoroscopic imaging. The combined converter and image intensifier elements of the detector 224 may be as described in the aforementioned U. S. patent No. 4,142,101 which is incorporated herein by reference.

In addition, the detector assembly includes a video camera (not separately shown) for viewing the image on the aforemen- tioned planar output surface and producing a signal output representative of that viewed image. The video camera can be a television camera and can operate according to a video standard

such as NTSC or CCIR. When the system is employed for fluoro- scopic imaging, the signal output of the video camera is processed by the onboard computer to produce video images on one or both monitors 214; the system also includes devices for recording and, optionally, printing out these video fluoroscopic images. _ As thus far described, the system 200 is essentially identical to currently available mini C-arm x-ray fluoroscopic imaging systems, e. g. having specifications as set forth above for the system 10 of FIG. 1.

A power supply for the x-ray source in accordance with the present invention as described above with reference to the apparatus of FIG. 1, and instrumentalities for controlling or varying current (mA) and voltage (kV), not shown, are incorporat- ed in the system as well.

Since the detector in the fluoroscopic imaging system detects x-ray emission from a cone-beam source over an extended two-dimensional area (the cross-section of the x-ray beam path in the plane of the detector receiving surface), there is inherent variation (i. e., variation attributable to the source and/or the detector having the image intensifier, independent of attenuation by any object interposed in the beam path) in received radiation intensity over the field of view. The image data obtained for the wrist and calibration bone sample by the steps described above are corrected for this inherent variation in order to enable more accurate calculation of BMD.

The calculation of data to produce BMD measurements could be performed with an onboard computer in a mini C-arm fluoroscop- ic system such as the"FluoroScan III"system, or in another computer. The functions of data acquisition/storage and BMD computation therefrom could be performed by different computers.

Also, instead of digitizing the detector output data before conversion to logarithms, the logarithmic conversion could be performed first (e. g. with a log amplifier) and digitized thereafter. Moreover, in addition to or in place of the fixtures described above for holding the body portion stationary,

appropriate software could be employed to re-register the images if there is movement.

A more detailed description of this embodiment and its operation is provided in the aforementioned U. S. Application No.

08/794,615 which is incorporated herein by reference.

It is to be understood that the invention is not limited to the procedures and embodiments hereinabove specifically set forth, but may be carried out in other ways without departure from its spirit.