Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-10-23
2001-01-23
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S160000, C600S342000, C348S077000
Reexamination Certificate
active
06178346
ABSTRACT:
FIELD OF INVENTION
This invention relates to the endoscopic imaging of structures in a liquid with suspended particles, such as blood, and apparatus for accomplishing such imaging.
BACKGROUND
Heart disease is the number one killer in the U.S. and many other countries. In the United States, heart disease results in the death of almost one million people per year. The high mortality and morbidity rate has led to many drug and device therapies to intervene in the progression of heart disease. Aggressive therapy for many forms of heart disease involve interventions where a cardiologist inserts a catheter in the patients artery or vein and performs procedures such as angioplasty, pacemaker or implantable defibrillator lead insertion or electrical mapping. These procedures have grown dramatically on a cost-basis: 947 million dollars were spent in 1990 vs.4.6 billion dollars spent in 1996.
Interventional procedures in cardiology are all the more remarkable since these procedures are performed only under radiographic guidance. Radiography presents the physician with a faint outline of the heart and its relation to the catheter. While radiography provides the cardiologist a crude guide, it does not allow examination of surfaces of the heart and vasculature or provide enough vision to guide procedures such as angioplasty or ablation.
In other body cavities, not filled with blood, such as the stomach or esophagus, fluid can be evacuated permitting visible wavelengths to be used in endoscope imaging. Visualizing the structure allows minimally invasive procedures such as ablating, stapling and suturing to be performed. These procedures, called laparoscopic procedures, are guided by the insertion of an endoscope, permitting visual examination of the treatment. These procedures are done in a saline bath or air to permit clear viewing. For example, minimally invasive orthopedic procedures rely on the endoscopic image to guide treatment. It is unfortunate cardiology has not had access to this technology since the common procedures would benefit from visualization.
The advantages to seeing structures in the cardiovascular system are numerous. Current methods of visualizing structures in the cardiovascular system are limited to radiography, ultrasound and angioscopy. Radiography is the standard visual tool used to image interventional cardiology procedures. It is applied by a large X-ray apparatus on a C-arm that will rotate around the patient through 180 degrees. The heart appears as a faint outline; while the metallic catheters are brightest. This allows for gross estimation of the catheter end to faint landmarks of the heart. The C-arm is frequently repositioned to give better viewing perspectives. Once the catheter has been navigated to the heart it can be placed in a coronary artery. In a self-contained entity such as an artery or vein, flouroscopic sensitive dye can be injected out the distal end of the catheter and viewed on the radiography camera for a short distance before it diffuses with blood. This technique is used to spot constricted areas in the coronary arteries. It has been shown that radiography, however, usually underestimates the degree of stenosis and therefore is only useful in providing a gross measure of flow.
More accurate assessments of coronary flow have been pioneered in the coronary arteries to evaluate angioplasty treatment. In the vasculature, the current angioplasty procedure for revascularization of an occluded coronary artery is to insert a catheter in the arterial tree, select the appropriate coronary artery, place an expandable balloon across the lesion and apply external pressure. As the pressure is reduced an expandable metallic structure (stent) remains opened to provide a scaffold, preventing the coronary artery from closing. This procedure is only effective long-term about 75-80% of the time. It is thought that many of these restenosis are due to inappropriate pressure application or inadequate stent placement. Oftentimes, postmortems have revealed stent buckling which can obstruct the flow rate in the coronary artery.
This information is so important, a form of endoscopy for the coronary arteries has been developed; called angioscopy. Examples of the art are contained in U.S. Patents since these devices operate in the visible spectrum, the blood must be removed and replaced with saline to permit viewing. Since blood is opaque at visible wavelengths, angioscopy only works when the blood is pumped out of the artery and replaced with clear saline solution. As stated in
Arterial Imaging: Text and Atlas
(White, D. M., Chapman and Hall, 1993), “In order to obtain adequate visualization within the vessel lumen, blood must be removed from the field of vision as even small amounts of red cells can obscure the clarity of the image.” In angioscopy, the catheter is directed to the arterial segment of interest and two occluding balloons are pressurized allowing the intervening blood to be removed and replaced with saline. An angioscopic catheter requires multiple ports: fluid pressure ports, an irrigation port and a port for the endoscope. Consequently, the devices are difficult to operate, since the physician must position the catheter, activate distal and proximal balloons, extract the blood from a port between the balloon and replace with saline. This cumbersome procedure, developed in the 1980's, has been used infrequently since it was very time consuming and presents a danger to the patient. The bulkiness of the angioscopic catheter, the complicated procedure and the inherent risk to the patient in having an artery totally occluded for the time of the procedure has made this procedure unpopular and relegated it to a few research-oriented hospitals. The disappointment with this technology has led to the development of a catheter ultrasonic technique called intraluminal ultrasound.
In an effort to produce visualization at the site of angioplasty for the surgeons, intraluminal ultrasound (for example, U.S. Pat. No. 4,917,097) devices have been designed. The intraluminal device is a modification of the familiar external ultrasound device used to visualize prenatal infants and heart valves. External ultrasound devices only have resolutions in the centimeter region. Greater resolution requires a higher greater frequency. The physics of the instrument dictate that the higher the frequency of the ultrasound transducer, the greater the potential for higher resolution and concomitant shorter penetration through the tissue. Higher frequencies do not penetrate as far requiring the transducers to be very near the structure. To visualize angioplasty procedures the resolution needs to be about 0.2 mm, requiring a 20 MHz device. A 20 MHz device will only penetrate about 1 cm of tissue before it is drowned in background noise. Consequently, for application in the coronary vasculature most of the device must be miniaturized so it can be inserted in the artery close to the blockage area. At a frequency of 20 MHz, it is possible to view the structures of the coronary artery only within a centimeter distance, requiring the transducers to be inserted in the artery. In one embodiment (U.S. Pat. No. 4,917,097) of this technology, a multitude of ultrasonic transducer crystals (
64
) are placed on the end an around the circumference of a 1.2 mm catheter to produce a visual view of the site of angioplasty. The catheter's construction is bulky because both the transducers and three integrated circuit signal processing chips have to be placed on the catheter tip. It is necessary to process the small signal with as little transmission through conductive wires. The positions of the electrical driver components (being external rather than internal) will generate ambient electronic noise, which contributes to the limitation of resolution from the catheter. The resultant picture is of marginal resolution quality because of the limited number or density of transducers, which corresponds to a 64-pixel image. The geometry of the catheter allows each pixel approximately 6 degree field-o
Amundson David C.
Hanlin H. John
Gibson Dunn & Crutcher, LLP
Lateef Marvin M.
Shaw Shawna J.
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