TECHNICAL FIELD

This disclosure relates to an intravascular system and a method of operating the same.

BACKGROUND

Intravascular processes such as imaging processes or receiving other physiological measurements (e.g., measurements of blood parameters, such as blood pressure, oxygen saturation levels, blood pH, etc.) are often used to identify diagnostically significant characteristics of a vessel. For example, an intravascular imaging system may be used by a healthcare professional to help identify and locate blockages or lesions in a vessel. Common intravascular imaging systems include intravascular ultrasound (IVUS) systems as well as optical coherence tomography (OCT) systems.

Intravascular imaging involves one or more transducers emitting and/or receiving energy based on received electrical signals and sending return electrical signals based on signals reflected by various intravascular structures. Intravascular imaging is often used to generate images. In some instances, a console with a high-resolution display is able to display intravascular images in real-time. In this way, intravascular imaging can be used to provide in-vivo visualization of the vascular structures and lumens, including the coronary artery lumen, coronary artery wall morphology, and devices, such as stents, at or near the surface of the coronary artery wall. Intravascular imaging may be used to visualize diseased vessels, including coronary artery disease. In some instances, the transducer(s) can be carried near a distal end of an intravascular imaging catheter. Some intravascular imaging systems involve rotating the intravascular imaging catheter (e.g., mechanically, phased-array, etc.) for 360-degree visualization.

Many intravascular imaging systems are configured to perform translation operations, in which imaging components of the catheter are translated through a patient's blood vessel while acquiring images. The result is a 360-degree image with a longitudinal component. When performing a translation operation, it can be important to accurately determine at least the relative amount of translation of the catheter's imaging components in order to accurately construct the 360-degree image.

In other intravascular processes, intravascular blood pressure measurements may be used for evaluating the degree to which a stenotic lesion obstructs flow through a blood vessel, such as a Fractional Flow Reserve measurement (FFR). To calculate the FFR for a given stenosis, two blood pressure readings are taken using a pressure sensor, such as a monorail pressure sensor (MPS). One pressure reading is taken on the distal side of the stenosis (e.g., downstream from the stenosis), the other pressure reading is taken on the proximal side of the stenosis (e.g., upstream from the stenosis, towards the aorta). The FFR is defined as the ratio of maximal blood flow in a stenotic artery, taken distal to the lesion, to normal maximal flow, and is typically calculated based on a measured pressure gradient of the distal pressure to the proximal pressure. The FFR is therefore a unitless ratio of the distal and proximal pressures. The pressure gradient, or pressure drop, across a stenotic lesion is an indicator of the severity of the stenosis, and the FFR is a useful tool in assessing the pressure drop. The more restrictive the stenosis is, the greater the pressure drop, and the lower the resulting FFR. The FFR measurement may be a useful diagnostic tool.

One method of measuring the pressure gradient across a lesion is to use a small catheter connected to a blood pressure measurement sensor. The catheter would be passed over the guidewire which has already been placed across the lesion. The catheter would be advanced down the guidewire until the tip of the catheter crosses the lesion. The blood pressure on the distal side of the lesion is recorded. This pressure would be divided by the pressure value recorded in the aorta. A disadvantage of using this method is that some error may be introduced due to the cross sectional size of the catheter. As the catheter crosses the lesion, the catheter itself introduces blockage, in addition to that caused by the lesion itself. The measured distal pressure would therefore be somewhat lower than it would be without the additional flow obstruction, which may exaggerate the measured pressure gradient across the lesion.

Pressure drop can also be measured across a heart valve. When a heart valve is regurgitant, a less than optimal pressure drop is typically observed. Using a catheter to measure pressure drop is common across a heart valve. However, because of the catheter size, the heart valve may not seal well around the catheter. Leakage might also result from the presence of the catheter and may contribute to an inaccurate pressure drop reading. One example of where this could occur is in the mitral valve (e.g., mitral valve regurgitation).

One method of measuring blood pressure in a patient is to use a pressure sensing guidewire. Such a device has a pressure sensor embedded within the guidewire itself. A pressure sensing guidewire can be used in the deployment of interventional devices such as angioplasty balloons or stents. Prior to the intervention, the pressure sensing guidewire would be deployed across a stenotic lesion so the sensing element is on the distal side of the lesion and the distal blood pressure is recorded. The guidewire may then be retracted so the sensing element is on the proximal side of the lesion. The pressure gradient across the stenosis and the resulting FFR value can then be calculated.

To use a guidewire-based pressure sensor in certain applications, the guidewire must be repositioned so the sensing element of the guidewire is correctly placed with respect to a stenotic lesion, for example. Blood pressure measurements for calculating FFR, for example, are generally taken on both sides of a given stenosis, so the guidewire is typically retracted across the stenosis to make the upstream measurement. After retracting the guidewire to make the proximal pressure measurement (aortic pressure or upstream coronary pressure), the guidewire may again be repositioned downstream of the lesion, for example, if it is determined (e.g., based on the FFR calculation) that an interventional device should be deployed. In cases where there are multiple lesions, the sensing element of a pressure sensing guidewire would need to be advanced and retracted across multiple lesions, and would potentially have to be advanced and repositioned again for each such lesion. Advancing and maneuvering a pressure sensing guidewire though stenotic lesions and the vasculature, for example, can be a difficult and/or time consuming task.

In existing systems, the amount of translation or maneuvering of intravascular catheter components is often estimated by attempting to translate portions of the catheter at a certain velocity for a certain amount of time. If the catheter's components are translated at a certain velocity for a certain time, the translated distance can be calculated. However, if the actual translation velocity is not the same as the commanded velocity, for example, or cannot be otherwise reliably measured or produced, inaccuracies in determining the amount of translation can occur. Inaccurate translation determinations can lead to errors in determining position-dependent information of the patient's vasculature. Additionally or alternatively, in some procedures, it may not be necessary or even desirable to pull the catheter back at a fixed velocity. For example, an operator may want to spend more time analyzing areas of interest, or to return to an area of interest by navigating the catheter in the opposite direction. In still further examples, velocity is not measured, and distances may simply be estimated by a system operator. Accordingly, more reliable position sensing mechanism may be useful in performing position-sensitive intravascular processes.

SUMMARY

Aspects of this disclosure include systems and methods for monitoring the position of one or more components of a catheter. Some exemplary systems include a catheter having a proximal end, a distal end, a sensor located at the distal end, and a cable extending from the proximal end of the catheter to the distal end of the catheter. The cable can be operatively connected to the sensor at the distal end, and the sensor can be configured to provide an intravascular signal representative of one or more intravascular properties of a patient. Exemplary sensors can include ultrasound transducers, pressure sensors, or the like.

Exemplary systems can include at least one friction wheel operatively engaging the cable of the catheter. The engagement between the at least one friction wheel and the cable can be such that distal and proximal motion of the cable causes rotation of the at least one friction wheel. In some examples, systems can include a first friction wheel and a second friction wheel positioned generally opposite one another such that the cable of the catheter extends between the first and second friction wheels. In some such examples at least one of the first and second friction wheels can be spring-biased against the catheter cable.

Systems can include a position sensor. Exemplary position sensors can include a reference element and a movable element, and can be configured to generate a position signal based on the relationship between the reference element and the movable element. In some embodiments, the movable element is configured to move relative to the reference element in response to rotation of at least one friction wheel.

Systems can include an intravascular processing engine in communication with the catheter sensor and the position sensor. The intravascular processing engine can be configured to receive the intravascular signal from the sensor of the catheter and also the position signal from the position sensor. In some examples, the received data in the intravascular signal can be associated with the positions in received position signal.

Aspects of the disclosure further include position sensing systems for an intravascular system. Such systems can include at least one friction wheel and a spring mechanism biased to press at least one friction wheel against a cable of the intravascular system. Exemplary sensing systems can include at least one detectable area disposed on at least one friction wheel and a detector configured to detect relative movement of the detectable area. In some embodiments, a position sensing assembly includes a housing configured to interface with a catheter, such as the catheter of an intravascular system. For instance in some examples, a position sensing assembly housing includes a groove configured to receive an anchor portion of a catheter.

