Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
2001-05-31
2004-03-16
Casler, Brian L. (Department: 3763)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
C600S473000, C604S099010, C606S194000
Reexamination Certificate
active
06706004
ABSTRACT:
TECHNICAL FIELD
This invention relates to catheters, and more particularly to balloon catheters.
BACKGROUND
Certain types of plaques in a patient's vasculature are likely to rupture. These plaques, once ruptured, are extremely dangerous and can swiftly cause the patient's death. It is therefore desirable to detect the existence of such high-risk plaques so that they can be disposed of before they rupture.
High-risk plaques are believed to be characterized by large lipid pools hidden behind vascular walls. Because these lipid pools are covered by vascular walls, they cannot be seen by visible light. However, infrared light can penetrate short distances into the vascular wall and can therefore be used to detect such plaques, as well as other intravascular pathology.
A difficulty associated with intravascular use of infrared radiation is that blood absorbs and scatters such radiation. This results in a reduction in the signal-to-noise ratio. As a result, it is desirable to minimize the extent to which infrared radiation propagates through the blood.
One approach to removing blood from a measurement site is to purge or flush the site with saline. This technique provides a short window of opportunity during which a measurement can be taken through the transparent saline. However, once the saline disperses, blood flows back into the measurement site and obscures the vascular wall.
Another approach to removing blood from a measurement site is to displace it with an inflated balloon catheter. However, if the balloon is not sufficiently inflated, considerable blood remains between the balloon and the vascular wall. If the balloon is so inflated that it makes contact with the vascular wall, blood flow is obstructed. This can lead to ischemia at points downstream from the balloon. In addition, the pressure of the balloon on the vascular wall can trigger a rupture of the plaque.
SUMMARY
The invention is based on the discovery that if the inflation level, and hence diameter, of a catheter balloon is carefully controlled in real time, the balloon can displace a maximal amount of blood without touching the inner wall of the blood vessel. This reduces scattering and absorption by the blood while avoiding irritation and injury to the inner walls of the blood vessel.
The present invention features catheters for inspecting intravascular structure with infrared radiation. The catheters include balloons that can be inflated to displace blood from the field of view. The extent to which the balloon is inflated is controlled by a feedback loop in which the measured extent of a gap between the outer wall of the balloon and the inner wall of the blood vessel is compared with a desired extent of that gap. The difference between the measured extent and the desired extent provides a basis for either inflating or deflating the balloon.
Another aspect of the invention features a plurality of individually controllable balloons circumferentially disposed around a catheter. A corresponding plurality of measurements provides an estimate of the gap between each of the circumferentially disposed balloons and an arcuate segment of the vascular wall directly opposed from that balloon. By individually controlling each of the balloons, the catheter can be centered within the blood vessel.
In one embodiment, the invention provides an apparatus for controlling an extent of a gap between a wall of a balloon mounted on a catheter and a wall of a lumen into which the catheter is inserted. The apparatus includes a radiation detector or optical fiber mounted within the balloon for generating a feedback signal having information indicative of whether the extent of the gap is greater than or less than a desired value, and a feedback loop for receiving the feedback signal and controlling a size of the balloon to cause the extent of the gap to approach the desired value.
In another embodiment, the invention provides an apparatus having a catheter for insertion into a lumen and a balloon disposed on the catheter. The balloon defines a gap between a wall of the lumen and a wall of the balloon. A radiation source is disposed within the balloon for transmitting radiation through the balloon wall and into coupling fluid present in the gap. The apparatus also includes a feedback loop having a radiation detector or optical fiber disposed within the balloon to receive radiation from the coupling fluid through the balloon wall, and a processor in communication with the radiation detector for determining, on the basis of a signal provided by the radiation detector, a measured extent of the gap. A controller in communication with the processor controls the inflation of the balloon to achieve a desired extent of the gap in response to the measured extent of the gap.
The radiation source can be an infrared emitter and the radiation detector can be an infrared detector. However, the principles of the invention are applicable to emitters and detectors adapted for operation at other frequencies of electromagnetic radiation. In addition, the radiation emitter and detector need not operate at the same frequencies.
The processor can be configured to determine the extent of the gap on the basis of absorption of radiation transmitted by the radiation source, the extent of the absorption being indicative of the extent of the gap. Alternatively, the processor can be configured to determine the extent of the gap on the basis of velocity of coupling fluid in the gap, the velocity of the coupling fluid being indicative of the extent of the gap. In one aspect of the invention, a calibration database in communication with the processor provides information to enable the processor to correct for variations due to wave propagation effects that vary among individuals.
The controller can be configured to control inflation of the balloon by changing a quantity of control fluid in the balloon. The quantity of control fluid can be changed by incremental amounts until the difference between the measured extent of the gap and the desired extent of the gap is within a pre-selected range. Alternatively, the quantity can be changed by an amount that depends on the difference between the measured extent of the gap and the desired extent of the gap.
In another embodiment of the invention, a plurality of balloons is circumferentially disposed around the distal end of the catheter. Each balloon has a size that can be controlled by the controller independently of the other balloons. An embodiment having a plurality of balloons is useful to center the catheter within a lumen or to maintain a spatially constant gap between the wall of each balloon and the wall of the lumen when the cross-section of the lumen is not circular.
The method also includes methods for controlling an extent of a gap between a wall of a balloon mounted on a catheter and a wall of a lumen into which the catheter is inserted.
In one practice, the method includes obtaining a feedback signal having information indicative of whether the extent of the gap is greater than or less than a desired value. In response to the feedback signal, the size of the balloon is controlled to cause the extent of the gap to approach the desired value.
In another practice, the invention includes a method for controlling an extent of a gap between a wall of a balloon catheter and a wall of a lumen, the gap being filled with a coupling fluid. The method includes transmitting first radiation through the coupling fluid and receiving second radiation. The second radiation contains information indicative of propagation effects encountered by the first radiation. On the basis of the second radiation, a measured extent of the gap is determined. The balloon is then inflated to minimize a difference between the measured extent of the gap and a desired extent of the gap.
In one aspect of the invention, the transmitted radiation is infrared radiation. However, the method can include transmitting radiation having any frequency. Similarly, the detected, or received radiation can be infrared radiation. However, the method can i
Bouma Brett E.
Furnish Simon
Ryan S. Eric
Tang Jing
Tearney Guillermo J.
Casler Brian L.
Fish & Richardson P.C.
Infraredx, Inc.
Thissell Jeremy
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