[0001] This invention relates to a protective cover for use in connection with a radiologic imaging table. BACKGROUND OF THE INVENTION [0002] Radiologic imaging is used extensively for diagnostic procedures and the monitoring of patients. The imaging apparatus conventionally includes a table or other support on which a patient may lie for exposure to imaging apparatus having cooperable components positioned below and above the patient. The imaging components carried by the patient support are particularly vulnerable to fluids originating from a patient or spilled by technicians. Such fluids have a tendency to collect atop the patient support, or even seep into the support, resulting in contamination of the surface of the support and interference with the operation of the imaging apparatus. Further, the collection of fluids requires careful cleaning which often consumes so much time that the imaging apparatus cannot be used when needed. [0003] The problems associated with the collection of fluids atop patient supports have been considered heretofore and solutions proposed, but not all of the proposed solutions have been satisfactory for a number of reasons. For example, some protective covers proposed heretofore are exceedingly complicated in construction, thereby delaying the application and removal of such covers to and from a patient's support. If such a cover is one which cannot be cleaned and reused, the cost of utilization of such covers is unacceptably high. [0004] In some cases a patient who is unconscious or incapable of controlling his movements must be restrained so as to avoid injuring himself or rendering the imaging procedures ineffective. In some instances, however, fixed restraints such as straps cannot be used if they overlie or bear against a traumatized portion of the patient's body. However, not all restraining straps are sufficiently adjustable relative to the patient to provide the necessary restraint at an appropriate position of the patient's body. [0005] A principal object of the invention is to provide a protective cover and patient restraint construction that will overcome the disadvantages referred to above. SUMMARY OF THE INVENTION [0006] Apparatus constructed in accordance with the invention comprises a sheet formed of pliable, waterproof material which is adapted to overlie the patient supporting surface of a table or other support in which components of imaging apparatus are housed. The sheet has a length corresponding substantially to that of the support surface and a width greater than that of the support surface so that when the sheet is applied to the surface of the table a central section of the sheet rests upon the patient supporting surface of the table and is flanked by flaps which extend beyond and depend from the table surface. Preferably, the center section of the cover includes a pad of cushioning material so as to enhance the comfort of the patient. Preferably, the entire sheet, including the flaps, is encapsulated in a coating of pliable, durable, easily cleanable material so as to facilitate cleaning of the cover between successive uses thereof. [0007] Restraining straps are provided to restrain movements of a patient lying on the cover. Each strap is coupled to the cover in such manner as to enable the strap to be moved longitudinally of the cover to any selected position of adjustment. The coupling is one which not only permits such longitudinal adjustment, but also is quickly attachable to and detachable from the cover. The coupling apparatus is wholly external of the encapsulating coating. [0008] The flaps and the adjacent sides of the patient supporting table preferably are equipped with separable retainers for separably securing the flaps in depending relation to the table surface. [0009] The materials from which the apparatus is formed are inert insofar as the radiologic imaging apparatus is concerned, thereby avoiding any interference with the imaging procedures. THE DRAWINGS [0010] The preferred embodiment of the invention is illustrated in the accompanying drawings wherein: [0011] Figure 1 is an isometric view, with parts broken away, illustrating a cover adapted to be applied to an imaging table and in overlying relation therewith; [0012] Figure 2 is a greatly enlarged sectional view taken on the line 2-2 of Figure 1; [0013] Figure 3 is a view similar to Figure 1, but omitting the external coating and illustrating patient restraining straps coupled to the cover; [0014] Figure 4 is an enlarged sectional view taken on the line 4-4 of Figure 3. [0015] Figure 5 is an enlarged, fragmentary, isometric view of apparatus for coupling a restraining strap to the cover; [0016] Figure 6 is a fragmentary, isometric, exploded view illustrating one manner in which the cover may be separably secured to the upper part of a patient support; [0017] Figure 7 is an enlarged end elevational view of the strap coupling apparatus; and [0018] Figure 8 is an enlarged, isometric, exploded view of a cover and a pad prior to the pad's being adhered to a cover. THEPREFERREDEMBODIMENT [0020] Apparatus constructed in accordance with the invention is adapted for use with a support table 1 having a base 2 supporting a top 3 having an upper surface 4 flanked by longitudinally extending rails 5. The base 2, or the top 3, or both, include radiologic imaging components (not shown) which cooperate with other components contained in an overhead support (not shown) for producing diagnostic images of a patient lying atop the table. The rails 5 help define the area to be occupied by the patient during the diagnostic process. However, the rails, if used, tend to enable fluids to collect on the upper surface of the table, thereby making cleaning of the table between uses more complicated and, perhaps, enabling such fluids to seep into the interior of the support. [0021] The apparatus comprises a cover 6 formed from a sheet 7 of waterproof, pliable material such as polyvinyl chloride which is inert with respect to the imaging apparatus. The sheet 7 has a center section 8 having a length corresponding substantially to the length of the table top 3 and a width substantially greater than that of the table top so that, when the center section overlies the surface 4, the opposite sides of the sheet extend beyond the table top 3 and form flaps 9 which, because of the pliability of the sheet material, may depend and occupy positions adjacent the upper sides of the table. [0022] Secured to the center section 8 of the sheet 7 inboard of the flaps 9 is a pad 10 formed of cushioning material which is inert to the imaging apparatus. The material could be an open cell foam, such as polyurethane, or a closed cell ethylenevinyl acetate foam. The pad 10 may be cemented by any suitable adhesive to one side only of the sheet 7, but it is preferred to use two identical halves 11 and 12 between which the center section 8 of the sheet is sandwiched. This construction is preferred because it enables openings 13 to be provided in the center section 8 of the sheet, thereby permitting each half to be adhered not only to the sheet itself, but to each other via the openings 13. This construction provides an extremely secure attachment of the pad to the sheet. [0023] Preferably, but not necessarily, the assembly of the sheet 7 and the pad 10 is encapsulated by a pliable, waterproof coating 14 which forms the exterior surface of the cover. The material from which the coating is formed is a suitable liquid such as a commercially available vinyl emulsion or solution containing known percentages of polymeric resins, other materials, and water or solvents. The coating may be applied in liquid form by dipping, brushing, or spraying, followed by curing of the coating in an over or at ambient temperature. A suitable coating is available from Contour Fabricators, Inc. of Fenton, Michigan, under the trademark SCANCOAT. However, any coating which has the desired characteristics of being waterproof, washable, and durable may be used, as long as the material of the coating enhances X-ray radiolucency and diminishes computerized tomography artifacting. [0024] In some of the drawing figures the coating is shown with an exaggerated thickness, whereas in others the coating is omitted for purposes of clarity. [0025] The apparatus preferably includes a plurality of pairs of restraining straps 15 and 16. The two straps 15 are identical to one another and the two straps 16 are identical to one another, and the pairs of straps 15 and 16 are the same except for width. Each of the straps is formed from a radiologic inert material such as rayon, nylon, or other strong, flexible material and each strap is coupled at one of its ends to an associated flap 9 of the cover 6 adjacent the pad 10. The coupling means is designated generally by the reference character 17 in Figures 5 and 7 and, in each instance, includes an anchor strip 18 stitched or otherwise suitably secured to a flap 9 adjacent and longitudinally parallel to the pad 10. The anchor strip 18 may be secured to the flap 9 by stitching, heat sealing or welding, adhesively, or in any other conventional manner. Preferably, the anchor strip 18 is external of the coating 14 on the flaps 9 and is formed from radiologic inert material such as a polyester available under the trademark MYLAR and having sufficient stiffness to be form stable. At its free end the anchor strip 18 terminates in an integral enlargement or bead 19 of substantially semispherical configuration in cross section. The outer surface 20 (Figures 7) of the enlargement 19 is arcuate, whereas the inner surface is flat and forms a pair of coplanar shoulders 21 flanking the strip 18. [0026] Each of the straps 15, 16 has one end stitched or otherwise suitably secured at one end to an anchor strip 18a which is identical to the strip 18 and has a corresponding semihemispherical enlargement or bead 19. Each of the anchor strips 18, 18a is adapted for removable and slideable mounting in a coupling body member 22 having a pair of spaced, semispherical channels 23 therein, each of which communicates with an access slot 24 of such width as slideably to accommodate the associated strip 18, 18a. Each channel 23 has flanges 25 on opposite sides of the slot, and the inner surfaces of such flanges form coplanar stops against which the planar shoulders 21 of the beads 19 bear. [0027] From the foregoing description it will be clear that the coupling means by which each strap is secured to the cover includes two anchor strips, two enlargements or beads, and one coupling body member having a pair of channels therein. [0028] The construction and arrangement of the coupling means are such that the body member 22 can be secured to the strip 18 by fitting the enlargement 19 at one end of the strip into one of the channels 23 and by fitting the enlargement 19 at the free end of the strip 18a into the other channel 23 from one end of the body member 22. The body member then may be slid longitudinally of the strips 18, 18a to any desired position along the length of the cover. [0029] The planar configuration of the shoulders 21 and the flanges 25 cooperate to retain the enlargements in the channels more securely than if the surfaces of the enlarge¬ ments confronting the flanges were rounded. This is because the presence of rounded surfaces on the enlargements would enable the latter to act as cams and spread the flanges 25. [0030] Each of the straps 15, 16 is of such length as to overlie the pad and at least a portion of a patient lying on the pad. The two free ends of each pair of straps may be fastened to one another by suitable fastening means, such as confronting hook and pile sections 26 like that sold by Velcro, Inc. under the trademark VELCRO. However, other separable fasteners may be used. For example, the straps could be provided with radiologic inert buckles, grippers, or releasable contact adhesives so as to provide a secure, but separable, means for fixing the straps in overlying relation to a patient lying on the cover. [0031] If desired, the cover may be releasably fastened to the table 3 in any one of a number of different ways. For example, a pair of supports 27 may be stitched, adhesively, or otherwise secured to the lower surfaces of the flaps 9 and each support may be provided with appropriately placed VELCRO or other fasteners 29 for cooperation with correspondingly placed VELCRO fasteners 30 secured to the table 3. The support 28 is shown in Figure 6 as being right angular in configuration, but it should be understood that such supports are formed of pliable materials like those referred to earlier so that they do not interfere with the flaps 9 assuming their depending positions. By securing the cover to the table the restraining force that can be applied via the straps 15, 16 to a patient is enhanced. [0032] The disclosed embodiment is representative of a presently preferred form of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.