Patent Number: 052788873
Section: summary

FIELD OF THE INVENTION The present invention relates to an apparatus and method for reducing the dosage of X-ray radiation received by both a patient and medical personnel during an X-ray fluoroscopic procedure, and more particularly to such apparatus and methods that confine full X-ray dosage to a central area, compensating for the reduced X-ray dosage in the peripheral areas by computer imaging enhancement. BACKGROUND OF THE INVENTION Interventional radiology procedures are becoming more prevalent for the detection and treatment of many diseases and injuries. Often an interventional radiology procedure involves the viewing of a catheter, or needle, as it is directed into a desired position within the body. Catheter based medical procedures are commonplace and include such medical treatments as balloon angioplasty, laser ablation, the installation of stints and many other valuable treatments. In such medical procedures the progress of the catheter is typically monitored, within a patient's body, by an X-ray fluoroscope imaging system. During a catheterization procedure, physicians and technicians need to position themselves next to the patient, in order to control the catheter. The overall X-ray exposure to such medical personnel can be higher than the X-ray exposure to the patient because medical personnel may do several X-ray fluoroscopic procedures in a single day and receive multiple dosages of X-ray radiation. For example, neuroangiographic procedures to repair an aneurysm or malformation may take as long as ten hours, during which the patient and physician are exposed to X-ray radiation much of the time. If the physician performs several such procedures a year, the physician quickly may exceed the recommended maximum dosage of radiation. The results of this potential for overexposure has been for highly trained physicians and other technical medical personnel to reduce their work load or to not wear their radiation monitor. Similarly, concern over overexposure may cause a physician to hurry a procedure, thus increasing the chances of making a mistake. One way to reduce X-ray exposure from fluoroscopy is to use various shielding techniques. Staff can be protected with lead aprons, imaging chain canopies, lead gloves, and eye shields. Patients can be protected with gonad shields, etc. Many of these techniques are not often used because they interfere with the clinical procedure in one way or another. In X-ray fluoroscopy it is well known that the dosage of the X-ray radiation is inversely proportional to the quantum noise in the viewed image. Prior art methods of X-ray dose reduction have addressed lowering the rate of dosage. For example, a nominal operational rate for X-ray fluoroscope is 30 frames/sec which may result in an exposure of approximately 10R/min skin dose. Prior art methods have attempted to reduce exposure by reducing the operational rate, for example, from 30 frames/sec. to 15 frames/sec. Such techniques have not been successful since a reduced frame rate necessitates an increased dosage rate per frame to minimize the quantum noise, the net result being no significant reduction in exposure. Other techniques for reducing the dosage of X-ray radiation include operating the fluoroscopy imaging system in a zoom mode; in other words, limiting the X-ray radiation to a small region and electronically magnifying that region to form the entire viewed image. Zoom mode imagery is not popular among some medical personnel because the zoomed image only permits a physician to view a small segment of a patient's body. Such a limited view makes it difficult for a physician to orient the placement of a catheter in a body, and prevents a physician from anticipating upcoming obstacles in the body until they appear in the zoomed image. In addition, in zoom mode, some X-ray systems increase the X-ray tube output dose such as to maintain a constant level of light output from the image intensifier. In that case, there is no dose saving to the patient. It is therefore a primary objective of the present invention to provide an apparatus and method for reducing X-ray radiation exposure to both patients and medical personnel without adversely affecting either the area of interest the X-ray fluoroscope procedure is being used to view, or the physician's ability to view the peripheral regions surrounding the area of interest. SUMMARY OF THE INVENTION The present invention relates to an apparatus and method for reducing the dosage of X-ray radiation incurred by a patient and medical personnel during a fluoroscopic procedure. During a fluoroscopic procedure X-rays are passed through a patient and are converted into a viewed image. Traditionally, the input X-ray beam is unattenuated across the entire field of view, even though it is herein recognized that, with some procedures, only a small area of the field of view actually requires high definition imaging. The present invention includes a filter member that attenuates the X-ray radiation in areas of the field of view that are not of primary interest. With the filter member in place, a physician can still visualize the entire field of view for the purposes of orientation and placement, except that now the areas in the viewed image outside the point of interest are of lower quality. By attenuating the X-ray radiation in the areas outside the point of interest, the integrated-area dosage of X-rays is greatly reduced, as is the chance of overexposure to either the patient or the physician. There is an analogy to the retina fovea mechanism of the human eye to track an object of interest. Thus the concept of the present invention is also referred to herein as an "X-ray fovea". The attenuation of the X-ray radiation in selective areas changes in the brightness of the viewed image. Thus, the areas of the viewed image created by the attenuated X-rays are amplified to match the brightness of the viewed image created by the unattenuated X-rays. To prevent a distinct division of the viewed image between the areas formed by the attenuated and unattenuated X-rays, special image processing algorithms must be used. In addition, the filter member can have a varying transparency to X-rays, such that a smooth transition is made between the various regions of the viewed image and no discernable transition line appears in the image. In addition to compensating the brightness in the peripheral area, one may also introduce temporal or spatial filtering to reduce noise. In accordance with an aspect of the invention, in an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source to an X-ray detector, through a subject body; a radiation reduction device comprises: a filter member, being semi-transparent to X-rays, and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; and wherein the X-rays passing through the filter member are attenuated and strike the subject body in a pattern that surrounds, and is adjacent to, the common region. In accordance with another aspect of the invention, the filter member includes a transition area surrounding the at least one aperture, the transition area having an increased transparency to X-rays as the transition area approaches the at least one aperture. In accordance with yet another aspect of the invention, the filter member is a substantially planar structure having a single aperture formed therethrough, the planar structure decreasing in thickness in the transition area such that the thickness of the planar structure is at a minimum at the edge of the aperture. In accordance with an aspect of the invention, in an X-ray fluoroscopic procedure wherein an image is produced by passing X-ray radiation through a subject body a method of reducing the dosage of X-ray radiation striking the subject body, comprises the steps of: selectively filtering the X-ray radiation such that attenuated and unattenuated X-ray radiation strike the subject body, the unattenuated X-ray radiation being confined to a predetermined common area surrounded by the attenuated X-ray radiation. In accordance with still yet another aspect of the invention, in an X-ray fluoroscopic procedure wherein a viewed image is produced, for monitoring the advancement of a medical instrument within a patient, by passing X-ray radiation through a patient; a method for reducing the dosage of X-ray radiation being exposed to the patient comprises the steps of: selectively filtering the X-ray radiation such that attenuated and unattenuated X-ray radiation pass through the patient, the unattenuated X-ray radiation being confined to a common region; calculating the size and position of the common region striking the patient; and altering the position of the common region to follow the advancement of the medical instrument, such that a point of interest on the medical instrument is viewed within the common region. In accordance with another aspect of the invention, an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source arrangement through a subject body to an X-ray detector arrangement, including image processing arrangement coupled thereto; a radiation reduction device comprises: a controllable filter member arrangement being responsive to a control signal, and including a filter member being semi-transparent to X-rays and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; wherein the X-rays passing through the filter member are attenuated and strike the subject body in a pattern that surrounds, and is adjacent to, the common region; and a control arrangement coupled to the X-ray source arrangement, to the image processing arrangement, and to the controllable filter member arrangement. In accordance with yet another aspect of the invention, the control arrangement provides the control signal to the controllable filter member arrangement for selectably placing the filter member in an operative mode. In accordance with still yet another aspect of the apparatus and method forming the context for the description of the invention, in an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source arrangement through a subject body to an X-ray detector arrangement, including image processing arrangement including image intensifier arrangement, coupled thereto for providing an image and including a radiation reduction device comprising: a controllable filter member arrangement being responsive to a control signal, and including a filter member being semi-transparent to X-rays and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; wherein the X-rays passing through the filter member are attenuated and strike the subject body in a pattern that surrounds, and is adjacent to, the common region; control arrangement coupled to the X-ray source arrangement, to the image processing arrangement, and to the controllable filter member arrangement, a method for tracking a catheter or probe, the catheter being characterized by at least some of the following characteristics: A. relatively thin, less than 2 mm, wire-like shape; PA0 B. begins in periphery of the image; PA0 C. has smooth edges; PA0 D. does not bend much; and PA0 E. X-ray dense as compared to the surround; PA0 1. morphologically processing the image to enhance an image of the catheter; PA0 2. threshold ENHANCED giving binary image, BINARY whereby the binary image contains silhouettes including a silhouette of the catheter; PA0 3. analyzing regions or blobs, in BINARY to find the image of the catheter using properties of the catheter including the catheter being thin, relatively rigid, and X-ray dense; PA0 4. finding the end of the catheter selected: PA0 5. ending. PA0 1. Entering a user-selected value for m in the equation PA0 2. obtaining a value of b necessary to give similar gray values in a center region and the peripheral region, whereby pixel values are average in annuli in central and peripheral regions giving G.sub.c and G.sub.p, respectively, deriving an appropriate value for b by computing EQU b=G.sub.c -m G.sub.p ; and PA0 3. given b and m, calculating new pixel values in said peripheral region using the equation G'.sub.p =mG.sub.p +b. PA0 1. segmenting the transition region symmetrically into a plurality of arcuate segments; PA0 2. obtaining the average overall intensity for a given arcuate segment over a range of radii, ranging from an inside boundary of the transition region to an outside boundary thereof; PA0 3. calculating an intensity profile of the given arcuate segment; and PA0 4. deriving from the intensity profile and applying to the given arcuate segment an intensity correction factor. PA0 a. calculating an average intensity of the given arcuate segment for the outside boundary of the transition region; PA0 b. calculating an average intensity of the given arcuate segment 42 for the inside boundary of the transition region; PA0 c. applying linear interpolation to the inside and outside boundary average intensity values to approximate what the average intensity ought to be for the full range of radii of the given arcuate segment; PA0 d. determining the difference between the overall average intensity of the given arcuate segment and the interpolated intensity, at a given radius to create a correct compensation factor for the given arcuate segment; PA0 e. adding the difference to the interpolated intensity and repeat for the entire range of radii; and PA0 f. repeating the foregoing for each of the arcuate segments into which the transition region 32 has been divided. PA0 1. recursively forming a gradient image of the common region; PA0 2. creating projections of the gradient image in the horizontal, vertical and two 45.degree. directions, whereby peaks occur in the data of each projection where the projections pass tangentially near the gradient image and the distance between two peaks on a single projection represents a possible diameter of the gradient image; PA0 3. matching peaks of the various projections to deduce the actual center and radius of the gradient image. PA0 4. smoothing the data to eliminate smaller, inconsequential peaks in the data; PA0 5. locating all pairs of peaks in the horizontal projection while ignoring all pairs of peaks which are separated by a distance that falls outside a range of possible diameters for the gradient image; PA0 6. repeating for the vertical projection, as well as the two projections in the 45.degree. direction, whereby the sampling distance along the two projections in the 45.degree. directions is 1/.sup.- 2 of the horizontal and vertical sampling distance; PA0 7. rescaling of the projection data relating to the two 45.degree. directions prior to computation; PA0 8. establishing for each projection a list of pairs of peaks that represent possible gradient pairs; PA0 9. for each pair of projections, identifying all pairs of peaks in one projection that are separated by the same distance as any of the pairs of peaks in the other projection, whereby six listings are obtained of pairs of peaks that represent possible gradient images; PA0 10. determining the center and inner radius for each possible gradient image 52 in the listings; PA0 11. comparing the center and inner radius on each list to find a close match on another list; PA0 12. identifying a close match as probably being the gradient image. wherein the method comprises the following steps: opening an input image, INPUT, with a flat, structuring element; PA1 subtracting the opened image from INPUT, to given ENHANCED; PA1 for each blob, make at least some of the following calculations: PA1 for each potential blob, compute a score which is a function of measures identified above; PA1 select identification of the catheter as a blob from the set of potential catheters having the highest score; PA1 the location of one endpoint of the medial axis farther away from the boundary is the end of the catheter selected; and apply a thinning algorithm to obtain a medial axis; PA2 compute length of the medial axis, MEDIAL.sub.-- LENG; PA2 compute AREA and PERIMETER. PA2 DISTANCE.sub.-- TO.sub.-- PERIPHERY.sub.-- i (i=1,2), the distance of two endpoints of the medial axis to a periphery of the image intensifier; PA2 AREA.sub.-- TO.sub.-- PERIMETER, a ratio of the area to the perimeter; PA2 PERIMETER.sub.-- TO.sub.-- MEDIAL.sub.-- LENG, a ratio of the perimeter to the length of the medial axis; PA2 BENDING, an average local curvature of the medial axis; PA2 compute a mean intensity within the blob from ENHANCED; PA2 identify potential catheters by the following properties: a. One of the DISTANCE.sub.-- TO.sub.-- PERIPHERY measure should be close to zero; PA3 b. AREA.sub.-- TO.sub.-- PERIMETER should be close to half the width of the catheter; PA3 c. PERIMETER.sub.-- TO.sub.-- MEDIAL.sub.-- LENG should be close to 2.0; PA3 d. BENDING should be small; PA3 e. mean intensity should be within a predetermined value. In accordance with still yet another aspect of the invention, in an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source arrangement through a subject body to an X-ray detector arrangement, including image processing arrangement including image intensifier arrangement, coupled thereto for providing an image and including a radiation reduction device comprising: a controllable filter member arrangement being responsive to a control signal, and including a filter member being semi-transparent to X-rays and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; wherein the X-rays passing through the filter member are attenuated and strike the subject body in an attenuated pattern that surrounds, and is adjacent to, the common region; control arrangement coupled to the X-ray source arrangement, to the image processing arrangement, and to the controllable filter member arrangement, a method for correcting gray-scale values in the attenuated pattern region, comprises the following steps: for corrected values in a peripheral region, G'.sub.p EQU G'.sub.p =mG.sub.p +b; In accordance with still yet another aspect of the invention, in an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source arrangement through a subject body to an X-ray detector arrangement, including image processing arrangement including image intensifier arrangement, coupled thereto for providing an image and including a radiation reduction device comprising: a controllable filter member arrangement being responsive to a control signal, and including a filter member being semi-transparent to X-rays and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; and wherein the X-rays passing through the filter member are attenuated and strike the subject body in an attenuated pattern that surrounds, and is adjacent to, the common region, with an annular transition region between the attenuated pattern and the common region; a method for compensating for differences in image intensity in the transition region, comprises the following steps: In accordance with a further, other aspect of the invention, steps 3 and 4 of the foregoing method comprise: In accordance with another, further aspect of the apparatus and method forming the context for the description of the invention, in an X-ray fluoroscopic apparatus for passing X-rays from an X-ray source arrangement through a subject body to an X-ray detector arrangement, including image processing arrangement coupled thereto for providing an image; a radiation reduction device comprising: a controllable filter member arrangement being responsive to a control signal, and including a filter member being semi-transparent to X-rays and having at least one aperture formed therethrough, such that X-rays passing through the at least one aperture remain unattenuated and strike the subject body in a common region; wherein the X-rays passing through the filter member are attenuated and strike the subject body in a pattern that surrounds, and is adjacent to, the common region; a method for locating an edge portion of the at least one aperture comprises the following steps: In accordance with still another, further aspect of the apparatus and method forming the context for the description of the invention, step 3 of the foregoing method for locating an edge portion comprises: