Stereotactic mammography system imaging

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This invention relates to a patient-supporting table and associated equipment for X-ray mammography and stereotactic needle biopsy of breast tissue suspected to contain lesions requiring radiographic evaluation.

RELATED ART

Since the publication of an article entitled "Stereotaxic Instrument for Needle Biopsy of the Mamma" by Jan Bolmgren et al, published in the American Journal of Roentgenology Vol. 129, Page 121 in July 1977, needle biopsy of breast lesions to minimize unnecessary surgical invasion of the patient's tissue has achieved increasing acceptance. Guidance of the biopsy needle by stereotactic X-ray exposures traditionally required development of the two X-ray film images and their comparison to determine the X, Y and Z coordinates of the lesion in question. Insertion of the biopsy needle via a carefully placed needle guide directed toward the lesion site could be verified only by additional stereo X-ray film exposures.

Mammograms made while the patient sits erect before the X-ray equipment may introduce unavoidable patient movement and resulting inaccuracy, while conventional tables supporting the patient in the prone position with the breast depending through a suitable aperture in the table generally require a patient's arms to be raised, tensing arm muscles, straining or distorting the breast tissue and again introducing inaccuracies. In addition, relatively flat and rigid tables often impose undue stress and discomfort on the patient's joints and vertebra, inducing undesired restless movements.

SUMMARY OF THE INVENTION

The unique prone position mammography tables of the present invention provide comfortable support for the prone patient, with a front edge portion being removable, permitting the patient's arm and shoulder to be lowered to more normal positions and thus minimizing patient discomfort and involuntary movements, leaving the patient normally relaxed during the procedure. In addition, a central concave torso depression formed in these tables exposes the maximum volume of breast tissue for X-ray examination.

Furthermore, the central concave torso depression encircling the breast-receiving aperture is positioned at the center of a longer-than-normal table having an extensible footrest at each end, which is supported by a rear pedestal opposite the removable front edge portion. The X-ray tube and the biopsy needle guide are thus afforded access to the patient's pendulant breast from all possible angles, over a range of more than 360.degree..

With this invention, accurate placement of the biopsy needle is further achieved via electronic imaging of the tissue X-rayed utilizing charge coupled devices or CCDs, with computer enhancement software designed to increase the sharpness of contrast between portions of the image most indicative of particular lesion structures of possible interest. This CCD-based imaging system offers such advantages in visualization and differentiation of nonpalpable lesions that contrast resolution and system sensitivity exceed that available with conventional screen or film X-ray mammography, often permitting definitive diagnosis of equivocal findings without the need for biopsy. Visualization capabilities are further increased by electronic image processing techniques to enhance contrasts. Delays in film development and evaluation are eliminated by the systems of the present invention, providing virtually instant confirmation of proper biopsy needle placement, reducing patient discomfort during this critical phase of the procedure.

This virtually real time imaging of the stereotactic X-ray images, and their computer enhancement, are preferably facilitated by an optical system interposed in the position normally occupied by the X-ray film cassette. This preferred optical system employs a phosphor screen exposed to the arriving X-rays passing through the breast tissue, and the image created on the phosphor screen by the arriving X-rays is reflected by a mirror surface provided by a pellicle reflector, comprising an extremely thin sheet of select optical grade nitrocellulose, on the order of five to nine microns in thickness, stretched like a drumhead over a black anodized flat metal frame and bonded to the precision lapped edge of the frame. The X-radiation passes directly through this thin film to the phosphor screen, while the visible light image of the phosphor screen is reflected from the film's underside directly toward the camera lens, due to a reflective coating of metallic material such as aluminum silicate, deposited on the underside of the thin film. Suitable coatings produce up to nearly sixty percent reflectance, depending upon wavelength. In a preferred embodiment, a second flat mirror surface redirects the reflected image, thereby producing a compact folded optical system conveniently enclosed in a light-tight housing occupying very little more space than conventional X-ray film cassettes and associated film holder structures. The preferred camera is Peltier cooled, and incorporates a rectangular CCD format with one thousand or more pixels along each orthogonal edge.

The comfortable table for supporting the patient in the prone position with minimum distortion of normal breast configuration cooperates with the stereotactic X-ray projection system mounted directly under the table. When desired, the folded CCD imaging system replaces the normal X-ray film cassette, and the unique software enhances the contrast and sharpness of the resulting virtually real time image. Preferably the image-receptor and the X-ray tube are mounted on the same angularly movable C-arm, assuring that the X-ray image is always perpendicular to the optic axis of the arriving X-rays. This permits a bucky grid to have all of its grid planes permanently aligned with the X-ray source, minimizing lateral scatter radiation and producing X-ray images of maximum sharpness and clarity.

These aspects of the invention all combine to produce a highly useful prone patient-supporting table for X-ray mammography and an effective stereotactic mammography system serving to minimize patient discomfort and trauma while permitting highly precise location and needle biopsy of suspected breast lesions, avoiding invasive surgery in a large number of cases.

Thus, a principal object of the present invention is to provide highly precise mammography systems providing uniquely accurate images of the observed breast structures of the patient.

Another object of the invention is to provide such systems incorporating prone patient supporting tables designed to expose the breast for mammographic examination while also assuring its undistorted orientation and the optimum comfort and relaxation for the patient during the procedure.

Still another object of the invention is to provide such systems with the capability for accurate guidance of needle biopsy procedures employing virtually real time electronic imaging and needle placement verification, eliminating delays for film cassette loading, changing, unloading, developing and evaluation.

A further object of the invention is to provide such systems which-are capable of stereotactic imaging of the maximum volume of the patient's breast tissue to provide three dimensional location of internal lesions or other internal sites requiring surgical examination.

A still further object of the invention is to provide folded CCD optical systems taking advantage of large CCD devices to provide extremely high resolution images of the patient tissue sites under study.

Another object of the invention is to provide digital X-ray image processing techniques using window and level manipulation, region of interest analysis, filters and edge enhancement, providing definitive X-ray diagnosis in many cases.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

THE DRAWINGS

For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a top perspective view of the prone patient supporting mammography table of the present invention;

FIG. 2 is an end perspective view of the same table showing the base, pedestal and angularly movable C-arm carrying the X-ray tube and the image receptor, as well as the separate compression arm carrying compression plates and needle guide;

FIG. 3 is a front elevation view of the same table supporting a prone female patient at maximum elevation above the floor, delivering X-radiation to the underside of the breast, toward the table's right end;

FIG. 4 is a schematic top plan view of the table showing the range of X-ray tube positions made possible by the rear pedestal construction of the unit;

FIG. 5 is a top plan view of the table of FIGS. 1-3, with the C-arm positioned for delivering X-radiation from the side of the patient;

FIG. 6 is a schematic front elevation view of the same table, with the C-arm positioned for delivering X-radiation toward the table's left end;

FIGS. 7A, 7B and 7C are corresponding successive fragmentary top plan schematic views showing the compression arm carrying the breast compression plates and needle guide in a fixed position beneath the table, while the underlying C-arm carrying the X-ray tube and image receptor is moved to different angular positions;

FIG. 8 is a schematic diagram of the stereotactic mammography procedure of this invention, comparing the X-radiation paths through a suspect lesion and a reference point on the compression plate for two angularly offset tubehead source positions, when the image receptor pivots with the tubehead on the C-am;

FIG. 9 is a fragmentary enlarged schematic diagram showing the lower end of FIG. 8 in more detail;

FIG. 10 is a schematic diagram of the two images produced at the image receptor by X-radiation from the same two source positions;

FIGS. 11 and 12 are schematic diagrams of the X-radiation paths for two angularly offset stereo tubehead source positions utilizing a folded CCD optical imaging system inserted in the position occupied by the X-ray film cassette in film mammography but with the digital CCD optical imaging system of FIGS. 13-17 pivoting with the tubehead.

FIG. 13 is a top plan schematic view of the conventional stereotactic mammography procedure performed on prior art devices, showing the X-radiation arriving at significant angles of inclination from the perpendicular, introducing undesired image degradation, when the image receptor is stationary.

FIG. 14 is a schematic diagram illustrating the stereotactic images employed to identify the coordinates of the target lesion with the imaging system of FIG. 13;

FIG. 15 is a perspective top view of the folded optical system employed in the stereotactic CCD imaging system of FIGS. 11 and 12, with a portion of the light-tight housing removed to reveal the location of the various components of the optical system;

FIG. 16 is a top plan view of the thin film pellicle mirror employed in the optical system of FIG. 15;

FIG. 17 is an edge elevation view of the same pellicle mirror;

FIG. 18 is a schematic diagram showing the imaging of the patient's compressed breast on a phosphor plate in the optical system delivering a focussed image to the CCD sensor and the proc