Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1999-01-07
2003-11-18
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C378S004000, C378S901000
Reexamination Certificate
active
06649914
ABSTRACT:
APPENDIX
Attached hereto is APPENDIX A, which contains the program listings for the preferred software modules for the programmable logic devices employed in an embodiment of the present invention. The contents of APPENDIX A are hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention pertains to diagnostic x-ray imaging equipment. More particularly, the present invention pertains to real-time scanning-beam x-ray imaging systems and to devices incorporating a marker, such as a medical catheter incorporating an x-ray sensor, which allows the determination of the device's precise position within another object.
2. Description of Related Art
Real-time x-ray imaging is increasingly being required by medical procedures as therapeutic technologies advance. For example, many electro-physiologic cardiac procedures, peripheral vascular procedures, PTCA procedures (percutaneous transluminal catheter angioplasty), urological procedures, and orthopedic procedures rely on real-time x-ray imaging. In addition, modern medical procedures often require the use of instruments, such as catheters, that are inserted into the human body. These medical procedures often require the ability to discern the exact location of instruments that are inserted within the human body, often in conjunction with an accurate image of the surrounding body through the use of x-ray imaging.
Current clinical real-time x-ray equipment produces high levels of x-ray exposure to both patients and attending staff. The United States Food and Drug Administration (F.D.A.) has reported anecdotal evidence of acute radiation sickness in patients, and concern among physicians of excessive occupational exposure. (Radiological Health Bulletin, Vol. XXVI, No. 8, August 1992).
A number of real-time x-ray imaging systems are known. These include fluoroscope-based systems where x-rays are projected into an object to be x-rayed and shadows caused by relatively x-ray opaque matter within the object are displayed on the fluoroscope located on the opposite side of the object from the x-ray source. Scanning x-ray tubes have been known in conjunction with the fluoroscopy art since at least the early 1950s. Moon,
Amplifying and Intensifying the Fluoroscopic Image by means of a Scanning X
-
ray Tube,
Science, Oct. 6, 1950, pp. 389-395.
Reverse-geometry scanning-beam x-ray imaging systems are also known. In such systems, an x-ray tube is employed to generate x-ray radiation. Within the x-ray tube, an electron beam is generated and focussed upon a small spot on the relatively large anode (transmission target) of the tube, inducing x-ray radiation emission from that spot. The electron beam is deflected (electromagnetically or electrostatically) in a raster scan pattern over the anode target. A small x-ray detector is placed at a distance from the anode target of the x-ray tube. The detector typically converts x-rays which strike it into an electrical signal in proportion to the detected x-ray flux. When an object is placed between the x-ray tube and the detector, x-rays are attenuated and scattered by the object in proportion to the x-ray density of the object. While the x-ray tube is in the scanning mode, the signal from the detector is inversely proportional to the x-ray density of the object
Examples of known reverse-geometry scanning-beam x-ray systems include those described in U.S. Pat. No. 3,949,229 to Albert; U.S. Pat. No. 4,032,737 to Albert; U.S. Pat. No. 4,057,745 to Albert; U.S. Pat. No. 4,144,457 to Albert; U.S. Pat. No. 4,149,076 to Albert; U.S. Pat. No. 4,196,351 to Albert; U.S. Pat. No. 4,259,582 to Albert; U.S. Pat. No. 4,259,583 to Albert; U.S. Pat. No. 4,288,697 to Albert; U.S. Pat. No. 4,321,473 to Albert; U.S. Pat. No. 4,323,779 to Albert; U.S. Pat. No. 4,465,540 to Albert; U.S. Pat. No. 4,519,092 to Albert; and U.S. Pat. No. 4,730,350 to Albert.
In a typical known embodiment of a reverse-geometry scanning-beam system, an output signal from the detector is applied to the z-axis (luminance) input of a video monitor. This signal modulates the brightness of the viewing screen. The x and y inputs to the video monitor are typically derived from the signal that effects deflection of the electron beam of the x-ray tube. Therefore, the luminance of a point on the viewing screen is inversely proportional to the absorption of x-rays passing from the source, through the object, to the detector.
Medical x-ray systems are usually operated at the lowest possible x-ray exposure level at the entrance of the patient that is consistent with the image quality requirement (particularly contrast resolution and spatial resolution requirements) for the procedure and the system. Typical patient entrance exposure in conventional 9″ filed of view image intensifier systems used in cardiac procedures, in the AP (anterior posterior) view with a standard adult chest, is approximately 2.0 to 2.8 R/min. The term “low dosage” used herein refers to a factor of 2 to 20 less than this.
Time and area distributions of x-ray flux follow a Poisson distribution and have an associated randomness which is unavoidable. The randomness is typically expressed as the standard deviation of the mean flux, and equals its square root. The signal-to-noise ratio of an x-ray image under these conditions is equal to the mean flux divided by the square root of the mean flux, i.e., for a mean flux of 100 photons, the noise is +/−10 photons, and the signal-to-noise ratio is 10.
Accordingly, the spatial resolution and the signal-to-noise ratio of x-ray images formed by known reverse-geometry scanning x-ray imaging systems are dependent, to a large extent, upon the size of the sensitive area of the detector. If the detector aperture is increased in area, more of the diverging rays are detected, effectively increasing sensitivity and improving the signal-to-noise ratio. At the same time, however, the larger detector aperture reduces attainable spatial resolution as the “pixel” size (measured at the plane of the object to be imaged) becomes larger. This is necessarily so because most objects to be imaged in medical applications (e.g., structures internal to the human body) are some distance from the x-ray source. In the known systems, therefore, the detector aperture size has been selected so as to effect a compromise between resolution and sensitivity, it not being previously possible to maximize both resolution and sensitivity simultaneously.
In the medical field, several conflicting factors, among them patient dosage, frame rate (the number of times per second that the object is scanned and the image refreshed), and resolution of the image of the object, often work to limit the usefulness of an x-ray imaging system. For example, a high x-ray flux may easily yield high resolution and a high frame rate, yet result in an unacceptably high x-ray dosage to the patient and attending staff.
Similarly, lower dosages may be achieved from the known systems at the cost of a low resolution image or an inadequate refresh rate. A preferred medical imaging system should provide low patient dosage, high resolution and an adequate refresh rate of up to at least about 15 images per second —all at the same time. Therefore, systems such as the known reverse-geometry scanning-beam x-ray imaging systems described above are not acceptable for diagnostic medical procedures where exposure times are relatively long and where, as is always the case with live patients, the x-ray dose received by the patient should be kept to a minimum.
Minimally invasive procedures in medicine are typically characterized by access to areas inside the body using existing orifices such as the ureter or by percutaneous entry such as a puncture of the femoral vein. In such procedures, various tools and catheters may than be progressed into the body and maneuvered using a real-time x-ray imaging for guidance. An estimated 3,000,000 medical procedures of this type were performed in 1993 under x-ray fluoroscopy guidance. Many of t
Fiekowsky Peter J.
Melen Robert E.
Moorhouse Abigail A.
Moorman Jack W.
Skillicorn Brian
Cardiac Mariners, Inc.
Ham Seungsook
Hanig Richard
Lyon & Lyon LLP
Wilent Virginia B.
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