Reduction of catheter rotation motor PWM interference in intravascular ultrasound imaging.

Abstract

We provide an intravascular ultrasound (IVUS) imaging system. [Solution] An intravascular ultrasound (IVUS) imaging system comprising an ultrasonic transducer and a drive motor is configured to use the drive motor to actively drive the ultrasonic transducer at a set rotational speed according to a time-varying drive motor drive signal, to generate a temporary detection window in which the drive motor drive signal is not switched, and to receive multiple signals from the ultrasonic transducer during the temporary detection window.

Description

Technical Field

[0001] The present disclosure relates to intravascular ultrasound imaging.

Background Art

[0002] A wide variety of medical devices have been developed for medical applications, such as intravascular applications. Some of these devices include intravascular ultrasound imaging devices. In addition, methods for intravascular ultrasound imaging have been developed. These devices and methods each have certain advantages and disadvantages. There is a current need to provide alternative devices and alternative methods.

Summary of the Invention

[0003] The present disclosure provides alternatives for the design and use of medical devices and methods, such as methods including intravascular ultrasound imaging. As an example, a method for capturing an intravascular ultrasound image using a mechanically steered transducer is disclosed. The method includes generating a pulse width modulation (PWM) drive signal and using the PWM drive signal to operate a drive motor for an intravascular ultrasound catheter including an ultrasonic transducer to rotate the ultrasonic transducer at a set rotational speed. To reduce electrical noise, a detection window is generated during which the PWM drive signal is not switched, and a plurality of signals are received from the ultrasonic transducer during the detection window.

[0004] Alternatively or additionally, the method may further include returning to a state that allows the PWM drive signal to be switched after the detection window ends. Alternatively or additionally, the method may further include changing the PWM drive signal to adjust the rotational speed of the ultrasonic transducer with respect to the set rotational speed immediately before the start of the detection window.

[0005] Alternatively or additionally, modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer may include modifying the PWM drive signal to rotate the ultrasonic transducer at an increased rotational speed greater than the set rotational speed, immediately before the start of the sensing window.

[0006] Alternatively or additionally, the increased rotation speed may be maintained over a first period ending at the start of the detection window. Alternatively or additionally, the method may further include modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer to a set rotational speed immediately after the end of the detection window.

[0007] Alternatively or additionally, modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer may include modifying the PWM drive signal to rotate the ultrasonic transducer at a reduced speed relative to the set rotational speed immediately after the end of the sensing window.

[0008] Alternatively or additionally, the method may further include modifying the PWM drive signal to return the ultrasonic transducer to a state where it rotates at a set rotational speed after a second period that begins at the end of the detection window.

[0009] As another example, a method for capturing intravascular ultrasound images is disclosed. The method includes using a drive motor to actively drive an ultrasound transducer at a set rotational speed according to a time-varying drive motor drive signal. A detection window is generated in which the drive motor drive signal is not switched, and multiple signals are received from the ultrasound transducer during the transient detection window.

[0010] Alternatively or additionally, the method may further include enabling the drive motor drive signal to be switched back to drive the ultrasonic transducer at a set rotational speed once the temporary detection window has ended.

[0011] Alternatively or additionally, the method may further include temporarily increasing the rotational speed of the ultrasonic transducer above the set rotational speed for a short period prior to the start of the temporary detection window.

[0012] Alternatively or additionally, the method may further include temporarily reducing the rotational speed of the ultrasonic transducer to below the set rotational speed for a short period immediately following the end of the temporary detection window.

[0013] Alternatively or additionally, the method may further include increasing the rotational speed of the ultrasonic transducer to be equal to the set rotational speed once the short period has ended.

[0014] Alternatively or additionally, the drive motor may be controlled via a pulse-width modulation (PWM) drive signal. Alternatively or additionally, the state of the drive motor drive signal during a temporary detection window may be dynamically determined based on the motor speed and / or load.

[0015] As another example, a method for capturing intravascular ultrasound images is disclosed. The method includes rotating an ultrasound transducer using a digital drive motor that operates according to a changing drive signal. The ultrasound transducer is rotated for a short period of time using a digital drive motor that operates according to a non-changing drive signal, and the signal from the ultrasound transducer is detected for a short period of time.

[0016] Alternatively or additionally, detecting signals from the ultrasonic transducer may further include not detecting signals from the ultrasonic transducer when the digital drive motor is operating according to a changing drive signal.

[0017] Alternatively or additionally, the state of the drive motor drive signal during a temporary detection window may be dynamically determined based on the motor speed and / or load. Alternatively or additionally, the method may further include controlling a digital drive motor using a pulse-width modulation (PWM) drive signal.

[0018] Alternatively or additionally, the method may further include changing the rotational speed of the ultrasonic transducer either immediately before or after a short period of time. The above summary of some embodiments is not intended to describe each disclosed embodiment or all implementations of this disclosure. The following drawings and detailed description illustrate these embodiments more specifically. [Brief explanation of the drawing]

[0019] This disclosure can be better understood by considering the following detailed description in relation to the attached drawings. [Figure 1] Figure 1 is a schematic diagram of an exemplary intravascular ultrasound system. [Figure 2] Figure 2 is a perspective view of an exemplary intravascular ultrasound catheter system. [Figure 3] Figure 3 is a partial side view of an exemplary intravascular ultrasound catheter system. [Figure 4] Figure 4 is a schematic diagram of an exemplary intravascular ultrasound system. [Figure 5A] Figure 5A is an exemplary ultrasound image free from artifacts caused by motor noise. [Figure 5B] Figure 5B is an exemplary ultrasound image that includes artifacts caused by motor noise. [Figure 6] FIG. 6 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 7] FIG. 7 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 8] FIG. 8 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 9] FIG. 9 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 10] FIG. 10 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 11] FIG. 11 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 12] FIG. 12 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 13] FIG. 13 is a flowchart showing an exemplary method for capturing an intravascular ultrasound image. [Figure 14] FIG. 14 is a schematic diagram of an exemplary control algorithm. [Figure 15] FIG. 15 is a schematic diagram of an exemplary control algorithm. [Figure 16] FIG. 16 is a graphical display of rotational speed versus time data. [Figure 17] FIG. 17 is a graphical display of rotational speed versus time data. [Figure 18] FIG. 18 is a schematic diagram of rotational speed versus time. [Figure 19] FIG. 19 is a schematic diagram of rotational speed versus time.

DETAILED DESCRIPTION OF THE INVENTION

[0020] This disclosure follows various modifications and alternative forms, the details of which are shown in the drawings as examples and described in detail. However, it should be understood that the intent is not to limit the invention to any particular embodiment described. On the contrary, the invention encompasses all modifications, equivalents, and alternative forms that fall within the technical concept and scope of this disclosure.

[0021] The terms defined below shall apply unless otherwise given in the claims or elsewhere in this specification. All numerical values ​​herein are assumed to be modified by the term “approximately,” whether expressly indicated or not. The term “approximately” generally refers to a range of numbers that a person skilled in the art would consider equivalent to (e.g., having the same function or result as) the stated value. Often, the term “approximately” may include numbers rounded to the nearest significant figure.

[0022] Numerical ranges specified by endpoints include all numbers within that range (for example, 1-5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). As used herein and in the appended claims, the singular forms “a,” “an,” and “the” refer to multiple subjects unless the context clearly indicates otherwise. As used herein and in the appended claims, the term “or” is generally used to include “and / or” unless the context clearly indicates otherwise.

[0023] Please note that references in this specification to “one embodiment,” “several embodiments,” and “other embodiments” indicate that the embodiments described may include one or more specific features, structures, and / or characteristics. However, such descriptions do not necessarily mean that all embodiments include specific features, structures, and / or characteristics. In addition, if specific features, structures, and / or characteristics are described in relation to one embodiment, please understand that such features, structures, and / or characteristics may be used in relation to other embodiments, whether explicitly described or not, unless explicitly stated otherwise.

[0024] The following detailed description should be read with reference to the drawings, where similar elements in different drawings are numbered the same. The drawings are not necessarily to scale and illustrate exemplary embodiments; they are not intended to limit the scope of the invention.

[0025] Ultrasound devices that can be inserted into patients have demonstrated diagnostic capabilities for a variety of diseases and disorders. For example, intravascular ultrasound (IVUS) imaging systems can be used as an imaging modality to diagnose and inform about occluded vessels to assist physicians in selecting and placing stents and other devices to restore or increase blood flow. IVUS imaging systems can also be used to diagnose the accumulation of atherosclerotic plaque at specific locations within vessels. IVUS imaging systems can also be used to determine the presence of obstructions or stenosis within vessels, as well as the nature and extent of such obstructions or stenosis. IVUS imaging systems can also be used to visualize segments of the vascular system that may be difficult to visualize using other intravascular imaging techniques, such as angiography, due to movement (e.g., a beating heart) or obstructions caused by one or more structures (e.g., one or more vessels that are not to be imaged). IVUS imaging systems can also be used to monitor or evaluate ongoing intravascular treatments, such as angiography and stent placement, in real time (or near real time). Furthermore, an IVUS imaging system can be used to monitor one or more cardiac chambers.

[0026] IVUS imaging systems have been developed to provide a diagnostic tool for visualizing various diseases or disorders. An IVUS imaging system may include a control module (equipped with a pulse generator, an image processor, and a monitor), a catheter, and one or more transducers positioned within the catheter. The catheter, including the transducers, may be positioned within or adjacent to a lumen or cavity in the area to be imaged, such as a blood vessel wall or patient tissue adjacent to the blood vessel wall. The pulse generator in the control module can generate electrical pulses, which are delivered to one or more transducers and converted into acoustic pulses transmitted through the patient tissue. Reflected pulses of the transmitted acoustic pulses may be absorbed by one or more transducers and converted into electrical pulses. The converted electrical pulses may be delivered to an image processor and converted into an image that can be displayed on a monitor.

[0027] Figure 1 schematically shows an exemplary IVUS imaging system 100. The IVUS imaging system 100 includes a catheter 102 that can be coupled to a processing unit or control module 104. The control module 104 may include, for example, a processor 106, a pulse generator 108, a drive unit 110, and one or more displays 112. In some examples, the pulse generator 108 forms electrical pulses that can be input to one or more transducers (312 in Figure 3) placed in the catheter 102.

[0028] In some examples, mechanical energy from the drive unit 110 may be used to drive an imaging core (306 in Figure 3) located in the catheter 102. In some examples, electrical signals transmitted from one or more transducers (312 in Figure 3) may be input to a processor 106 for processing. In some examples, the processed electrical signals from one or more transducers (312 in Figure 3) may be displayed as one or more images on one or more displays 112. For example, a scan converter can be used to map scan line samples (e.g., radial scan line samples) to a two-dimensional Cartesian grid to display one or more images on one or more displays 112.

[0029] In some examples, the processor 106 may be used to control the function of one or more of the other components of the control module 104. For example, the processor 106 may be used to control the frequency or duration of electrical pulses transmitted from the pulse generator 108, the rotational speed of the imaging core (306 in Figure 3) by the drive unit 110, the speed or length of the retraction of the imaging core (306 in Figure 3) by the drive unit 110, or at least one of the characteristics of one or more images formed on one or more displays 112. In some examples, the processor 106 may control the operation of the drive unit 110. In some examples, the drive unit 110 may include a digital drive motor adapted to drive and rotate the catheter 102 or a portion thereof, such as one or more ultrasonic transducers (312 in Figure 3).

[0030] In some cases, the processor 106 can control a digital drive motor via a pulse-width modulation (PWM) drive signal. The PWM drive signal can vary between on (or high) and off (or low). The operation of the digital drive motor can be adjusted by varying the frequency of the PWM drive signal being on (or high) and the frequency of the PWM drive signal being off (or low). In some cases, the PWM drive signal may consist of a single signal or multiple signals. In some cases, the PWM drive signal may consist of a tristate signal rather than simply being on (or high) or off (or low).

[0031] Figure 2 is a schematic side view of one embodiment of a catheter 102 of an IVUS imaging system (100 in Figure 1). The catheter 102 includes an elongated member 202 and a hub 204. The elongated member 202 includes a proximal end 206 and a distal end 208. In Figure 2, the proximal end 206 of the elongated member 202 is coupled to the catheter hub 204, and the distal end 208 of the elongated member is configured and positioned for percutaneous insertion into the patient. Optionally, the catheter 102 may define at least one flush port, such as a flush port 210. The flush port 210 may be defined within the hub 204. The hub 204 may be configured and positioned to be coupled to a control module (104 in Figure 1). In some examples, the elongated member 202 and the hub 204 are formed as a single unit. In other examples, the elongated member 202 and the catheter hub 204 are formed separately and then assembled together.

[0032] Figure 3 is a schematic perspective view of one embodiment of the distal end 208 of the elongated member 202 of a catheter 102. The elongated member 202 includes a sheath 302 having a longitudinal axis 303 and a lumen 304. An imaging core 306 is located within the lumen 304. The imaging core 306 includes an imaging device 308 coupled to the distal end of a drive shaft 310 that is rotatable manually or using a computer-controlled drive mechanism. One or more transducers 312 may be attached to the imaging device 308 and employed to transmit and receive acoustic signals. The sheath 302 may be formed from any flexible biocompatible material suitable for insertion into a patient. Examples of suitable materials include, for example, polyethylene, polyurethane, plastic, spiral-cut stainless steel, nitinol hypotube, or combinations thereof.

[0033] In some examples, an array of transducers 312 is mounted on the imaging device 308, as shown in Figure 3, for example. Alternatively, a single transducer may be used. Any appropriate number of transducers 312 can be used. For example, there may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 20, 25, 50, 100, 500, 1000 or more transducers. Other numbers of transducers may also be used as recognized. When multiple transducers 312 are employed, the transducers 312 can be configured in any appropriate arrangement, including, for example, a ring arrangement, a rectangular arrangement, etc.

[0034] One or more transducers 312 can be formed from a material capable of converting applied electrical pulses into pressure strain on the surface of one or more transducers 312, and vice versa. Examples of suitable materials include piezoelectric ceramic materials, piezoelectric composite materials, piezoelectric plastics, barium titanate, lead zirconate titanate, lead metaniobate, and polyvinylidene fluoride. Other transducer technologies include composite materials, single-crystal composite materials, and semiconductor devices (e.g., capacitive micromachine ultrasonic transducers ("cMUT"), piezoelectric micromachine ultrasonic transducers ("pMUT"), etc.).

[0035] Pressure strain on the surface of one or more transducers 312 forms acoustic pulses of a frequency based on the resonant frequencies of the one or more transducers 312. The resonant frequencies of the one or more transducers 312 may be influenced by the size, shape, and material used to form the one or more transducers 312. The one or more transducers 312 can be formed in any shape suitable for placement within the catheter 102 and for propagating acoustic pulses of a desired frequency in one or more selected directions. For example, the transducers may be disk-shaped, block-shaped, rectangular, elliptical, etc. The one or more transducers can be formed into the desired shape by any process, including, for example, dicing, die-and-fill, machining, micro-machining, etc.

[0036] As an example, each of one or more transducers 312 may include a layer of piezoelectric material sandwiched between a matching layer and a conductive backing material formed from an acoustic absorbing material (e.g., an epoxy substrate having tungsten particles). During operation, the piezoelectric layer can be electrically excited to cause the emission of acoustic pulses.

[0037] One or more transducers 312 can be used to form radial cross-sectional images of the surrounding space. For example, when one or more transducers 312 are placed in the catheter 102 and inserted into the patient's blood vessel, one or more transducers 312 can be used to form images of the blood vessel wall and the surrounding tissue.

[0038] The imaging core 306 is rotated about the longitudinal axis 303 of the catheter 102. As the imaging core 306 rotates, one or more transducers 312 emit acoustic signals in different radial directions (e.g., along different radial scan lines). For example, one or more transducers 312 may emit acoustic signals in regular (or irregular) increments, such as 256 radial scan lines per rotation. Alternatively, it will be understood that it is possible to emit any other number of radial scan lines per rotation.

[0039] When an emitted acoustic pulse with sufficient energy encounters one or more medium boundaries, such as one or more tissue boundaries, a portion of the emitted acoustic pulse is reflected back to the emitting transducer as an echo pulse. Each echo pulse that reaches the transducer with enough energy to be detected is converted into an electrical signal in the receiving transducer. One or more converted electrical signals are transmitted to a control module (104 in Figure 1), where a processor 106 processes the electrical signal characteristics to form a displayable image of the imaged region, based at least partially on the set of information from each of the transmitted acoustic pulses and received echo pulses. In some examples, the rotation of the imaging core 306 is driven by a drive unit 110 located within the control module (104 in Figure 1). In an alternative embodiment, one or more transducers 312 are fixed in place and do not rotate. In that case, the drive shaft 310 can instead rotate mirrors that reflect acoustic signals to and from the fixed one or more transducers 312.

[0040] When one or more transducers 312 are rotated about the longitudinal axis 303 of the catheter 102 that emits acoustic pulses, multiple images can be formed that collectively form radial cross-sectional images (e.g., tomographic images) of a portion of the region surrounding one or more transducers 312, such as the wall of a vessel of interest and the surrounding tissue. The radial cross-sectional images can optionally be displayed on one or more displays 112. At least one of the imaging cores 306 can be rotated manually or using a computer-controlled mechanism.

[0041] The imaging core 306 may move longitudinally along the blood vessel into which the catheter 102 is inserted, so that multiple cross-sectional images can be formed along the longitudinal length of the blood vessel. During the imaging procedure, one or more transducers 312 can be retracted (e.g., pulled back) along the longitudinal length of the catheter 102. The catheter 102 may include at least one expandable section that can be retracted during the retraction of one or more transducers 312. In some examples, a drive unit 110 drives the retraction of the imaging core 306 within the catheter 102. The retraction distance of the imaging core by the drive unit 110 can be any suitable distance, for example, at least 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, or more. Whether or not the imaging core 306 moves longitudinally independently of the catheter 102, the entire catheter 102 can be retracted during the imaging procedure.

[0042] A motor may optionally be used to pull back the imaging core 306. The motor can pull back the imaging core 306 by a short distance, stopping for a length sufficient for one or more transducers 306 to capture one image or a series of images, and then pull back the imaging core 306 by another short distance to capture yet another image or a series of images, and so on.

[0043] The quality of images generated at different depths from one or more transducers 312 may be influenced by one or more factors, including, for example, bandwidth, transducer focus, beam pattern, and acoustic pulse frequency. The frequency of the acoustic pulses output from one or more transducers 312 may also affect the penetration depth of the acoustic pulses output from one or more transducers 312. Generally, as the frequency of the acoustic pulse decreases, the penetration depth of the acoustic pulse in patient tissue increases. In some examples, the IVUS imaging system 100 operates within a frequency range of 5 MHz to 100 MHz.

[0044] One or more conductors 314 can electrically couple the transducer 312 to the control module 104 (see, for example, Figure 1). In this case, one or more conductors 314 can extend along the longitudinal length of the rotatable drive shaft 310.

[0045] A catheter 102, equipped with one or more transducers 312 attached to the distal end 208 of an imaging core 308, can be percutaneously inserted into a patient via an accessible blood vessel, such as a femoral artery, femoral vein, or jugular vein, at a site away from a selected portion of a selected area, such as a blood vessel to be imaged. The catheter 102 may then be advanced through the patient's blood vessel to a selected imaging site, such as a portion of a selected blood vessel.

[0046] An image or image frame ("frame") can be generated each time one or more acoustic signals are output to the surrounding tissue and one or more corresponding echo signals are received by the imaging device 308 and transmitted to the processor 106. Alternatively, an image or image frame may be a composite of scan lines from a full or partial rotation of the imaging core or device. Multiple frames (e.g., a sequence of frames) may be acquired over time during any type of movement of the imaging device 308. For example, frames may be acquired during rotation and retraction of the imaging device 308 along a target imaging position. It should be understood that frames may be acquired with or without rotation of the imaging device 308, and with or without retraction. Furthermore, it will be understood that frames may be acquired using, in addition to or instead of, at least one of rotation or retraction of the imaging device 308, other types of movement procedures.

[0047] In some examples, when the retraction is performed, the retraction may be at a constant speed, thus providing a tool for potential applications where longitudinal vessel / plaque measurements can be calculated. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.3 mm / sec. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.4 mm / sec. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.5 mm / sec. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.6 mm / sec. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.7 mm / sec. In some examples, the imaging device 308 is retracted at a constant speed of at least 0.8 mm / sec.

[0048] In some examples, one or more acoustic signals are output to the surrounding tissue at regular time intervals. In some examples, one or more corresponding echo signals are received by the imaging device 308 and transmitted to the processor 106 at regular time intervals. In some examples, the resulting frames are generated at regular time intervals.

[0049] At least some conventional IVUS imaging systems display only a single image (e.g., cross-sectional, longitudinal, etc.) during or after an IVUS procedure, such as a retraction procedure. However, it may be useful to display at least two images simultaneously in real time during an IVUS procedure (e.g., a retraction procedure), such as the most recently processed image and a previously acquired image having certain or selected image characteristics (e.g., maximum or minimum lumen area or diameter).

[0050] Figure 4 is a schematic diagram of an exemplary IVUS imaging system 400. The IVUS imaging system 400 may be considered an example of the exemplary IVUS imaging system 100 shown in Figure 1. Various features described herein as part of the IVUS imaging system 100 may similarly be considered as part of the IVUS imaging system 400. Similarly, various features described herein as part of the IVUS imaging system 400 may similarly be considered as part of the IVUS imaging system 100.

[0051] The IVUS imaging system 400 includes an imaging core 402, which may be considered an example of the catheter 102 shown in Figure 1. The imaging core 402 includes an ultrasound transducer 404, which may be considered an example of the ultrasound transducer 312 shown in Figure 3. Although a single ultrasound transducer 404 is shown, it should be understood that the imaging core 402 may have any number of ultrasound transducers 404.

[0052] The imaging core 402, and therefore the ultrasonic transducer 404, can be rotationally driven via a drive motor 406 operably coupled to the imaging core 402 via a gear reduction mechanism 408. The drive motor 406 may be, for example, a brushless digital motor, but in some cases a brushed motor is assumed. The drive motor 406 can be operated according to a PWM drive signal. In some cases the PWM drive signal may be generated by a processor 106 shown in Figure 1. The PWM drive signal is a digital signal that is either high (on) or low (off) and has a value of either 1 or 0. The operating speed of the drive motor 406 can be varied according to how often the PWM drive signal is high (on, or set to equal to 1) and how often the PWM drive signal is low (off, or set to equal to 0).

[0053] The gear reduction mechanism 408 can provide a reduction in the imaging core 402 relative to the rotational speed of the drive motor 406. For example, the gear reduction mechanism 408 can provide a 4:1 or 5:1 reduction. In some cases, the gear reduction mechanism 408 can provide a reduction that is approximately 4.5:1. As an example, the drive motor 406 can rotate at 5000-6000 revolutions per minute (RPM), while the imaging core 402 can rotate at a reduced speed in the range of approximately 1800 RPM. This rotational speed corresponds to the ultrasonic transducer being able to capture 30 frames per second. These are just examples.

[0054] The transformer 410 provides electrical coupling with the imaging core 402. The transformer 410 includes a first winding 410a that rotates in coupling with the imaging core 402 and a fixed second winding 410b. The electric field generated by the moving first winding 410a can be picked up via the second winding 410b. As a result, the signal from the ultrasonic transducer 404 can be transmitted from the imaging core 402 to the IVUS image 412. It will be understood that the signal from the ultrasonic transducer 404 may undergo various processing before being displayed as the IVUS image 412.

[0055] In some cases, as described above, a PWM drive signal may be used to control the operation of the drive motor 406. Using a PWM drive signal offers advantages such as fewer components, though not limited to them, and means that using PWM drive can result in cost savings, reduced power consumption, and improved reliability. Using PWM drive can mean a faster response to command changes. In some cases, using a PWM drive signal can introduce noise into the corresponding IVUS image. Because the PWM drive signal alternates between high and low, each time the PWM drive signal switches, various electrical noises can be generated, and this noise can appear as speckles on the IVUS image. Speckles are undesirable image components generated when the sensing circuit detects electrical noise instead of actual (real or expected) data from the ultrasonic transducer.

[0056] Figure 5A shows a first IVUS image 512 without speckles, and Figure 5B shows a second IVUS image 514 similar to the first IVUS image 512 but containing multiple speckles. These speckles, and any other signs of visible electrical noise, can make it difficult to obtain clear IVUS images and to properly interpret them for the anatomical structures represented in those IVUS images. Figures 6–13 are flowcharts illustrating an exemplary method of capturing ultrasound images to reduce or even eliminate any visual signs of electrical noise that may be caused by a PWM drive signal switching between high (or on) and low (or off) while capturing intravascular ultrasound images.

[0057] Figure 6 is a flowchart illustrating an exemplary method 600 for capturing intravascular ultrasound images using a mechanically steered transducer. Method 600 includes generating a pulse-width modulation (PWM) drive signal, as shown in block 602. As shown in block 604, the PWM drive signal is used to activate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in Figures 1-3 or imaging core 402 shown in Figure 4) containing an ultrasound transducer (e.g., ultrasound transducer 312 or ultrasound transducer 404) to rotate the ultrasound transducer at a set rotational speed. The set rotational speed may be set or adjusted by the operator, for example, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0058] To reduce electrical noise, a sensing window is generated in which the PWM drive signal is temporarily not switched, as shown in block 606. Keeping the PWM drive signal constant means that the PWM drive signal is high or on, and that the rotational speed may exceed the set rotational speed during the sensing window. Keeping the PWM drive signal constant means that the PWM drive signal is low or off, and that the rotational speed may decrease to below the set rotational speed during the sensing window. In some cases, determining the state of the PWM drive signal during the sensing window may be determined dynamically based on the motor speed and / or load immediately before the sensing window. If the motor speed is below the desired speed immediately before the sensing window, the PWM drive signal may be set to high or on during the sensing window. If the motor speed is above the desired speed immediately before the sensing window, the PWM drive signal may be set to low or off during the sensing window.

[0059] The detection window may last for a short period of time or occur periodically. For example, in some cases, the detection window may last only 0.1% to 0.5% of the time it takes for the imaging core to complete one rotation. The motor speed may be in the range of 1000 RPM to 2000 RPM. Thus, the detection window may have a duration ranging from 30 microseconds to over 200 microseconds and a frequency ranging from 4 kHz to 33 kHz.

[0060] As shown in block 608, multiple signals can be received from the ultrasonic transducer during a sensing window. In some cases, once the sensing window ends, the PWM drive signal reverts to a time-varying signal, as shown in block 610. It will be understood that the sensing window can be generated periodically by intervening a period during which the PWM drive signal remains stationary for a duration corresponding to the sensing window, and allowing the PWM drive signal to switch between high and low to maintain the desired rotational speed.

[0061] Figure 7 is a flowchart illustrating an exemplary method 612 for capturing intravascular ultrasound images. Method 612 includes generating a pulse-width modulation (PWM) drive signal, as shown in block 614. As shown in block 616, the PWM drive signal is used to activate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in Figures 1-3 or imaging core 402 shown in Figure 4) containing an ultrasound transducer (e.g., ultrasound transducer 312 or ultrasound transducer 404) to rotate the ultrasound transducer at a set rotational speed. The set rotational speed may be set or adjusted by the operator, for example, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0062] As shown in block 618, a detection window is generated in which the PWM drive signal is temporarily held stably. Holding the PWM drive signal constant means that the PWM drive signal is high or on, and that the rotation speed may exceed the set rotation speed during the detection window. Holding the PWM drive signal constant means that the PWM drive signal is low or off, and that the rotation speed may decrease to below the set rotation speed during the detection window. The detection window may last for a short period of time or occur periodically. For example, in some cases, the detection window may last only 0.1% to 0.5% of the time it takes for the imaging core to complete one rotation. The motor speed may be in the range of 1000 RPM to 2000 RPM. Thus, the detection window may have a duration in the range of 30 microseconds to over 200 microseconds and a frequency in the range of 4 kHz to 33 kHz. As shown in block 620, multiple signals can be received from the ultrasonic transducer during the detection window.

[0063] In some cases, method 612 further includes modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer to a set rotational speed immediately before the start of the sensing window, as shown in block 622. In some examples, this may include modifying the PWM drive signal to rotate the ultrasonic transducer at an increased rotational speed greater than the set rotational speed immediately before the start of the sensing window. Depending on the duration of a particular sensing window, as well as the size and other characteristics of the ultrasonic catheter, the ultrasonic catheter may decelerate too much during the sensing window, if the sensing window means that the PWM drive signal is constrained to low or off, while the drive motor is operating substantially by inertia. Therefore, slightly increasing the speed immediately before the sensing window may help maintain the rotational speed of the ultrasonic catheter and / or ultrasonic transducer. The increased rotational speed may be maintained over a first period ending at the start of the sensing window. The first period may have a duration ranging from nearly zero to the entire period between sampling windows. This period may vary dynamically depending on the motor speed and load.

[0064] In some examples, changing the PWM drive signal immediately before the start of a detection window may involve adjusting the PWM drive signal to rotate the ultrasonic transducer at a reduced rotation speed lower than the set rotation speed immediately before the start of the detection window. Since the rotation speed of the ultrasonic transducer increases during the detection window when the PWM drive signal is constrained to high or on, it may be desirable to decrease the rotation speed immediately before the start of the detection window if the PWM drive signal is constrained to high or on during the detection window. In some cases, whether the PWM drive signal is changed immediately before the start of a detection window may vary, for example, to adapt to a particular pattern within the PWM drive signal.

[0065] Figure 8 is a flowchart illustrating an exemplary method 624 for capturing intravascular ultrasound images. Method 624 includes generating a pulse-width modulation (PWM) drive signal, as shown in block 626. As shown in block 628, the PWM drive signal is used to activate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in Figures 1-3 or imaging core 402 shown in Figure 4) containing an ultrasound transducer (e.g., ultrasound transducer 312 or ultrasound transducer 404) to rotate the ultrasound transducer at a set rotational speed. The set rotational speed may be set or adjusted by the operator, for example, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0066] As shown in block 630, a detection window is generated in which the PWM drive signal is temporarily held stably. Holding the PWM drive signal constant means that the PWM drive signal is high or on, and that the rotation speed may exceed the set rotation speed during the detection window. Holding the PWM drive signal constant means that the PWM drive signal is low or off, and that the rotation speed may decrease to below the set rotation speed during the detection window. The detection window may last for a short period of time or occur periodically. For example, in some cases, the detection window may last only 0.1% to 0.5% of the time it takes for the imaging core to complete one rotation. The motor speed may be in the range of 1000 RPM to 2000 RPM. Thus, the detection window may have a duration in the range of 30 microseconds to over 200 microseconds and a frequency in the range of 4 kHz to 33 kHz. As shown in block 632, multiple signals can be received from the ultrasonic transducer during the detection window.

[0067] In some cases, method 624 further includes modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer to a set rotational speed immediately after the end of the detection window, as shown in block 634. In some cases, this includes modifying the PWM drive signal to rotate the ultrasonic transducer at a reduced speed relative to the set rotational speed immediately after the end of the detection window. In some cases, using a reduced speed immediately after the end of the detection window can reduce the impact applied to the ultrasonic transducer. In some cases, modifying the PWM drive signal may include modifying the PWM drive signal to rotate the ultrasonic transducer at an increased speed relative to the set rotational speed immediately after the end of the detection window. In some cases, as shown in block 636, method 624 may further include modifying the PWM drive signal to return the ultrasonic transducer to a state where it rotates at a set rotational speed after a second period beginning at the end of the detection window. The second period may have a duration ranging from 30 microseconds to more than 200 microseconds.

[0068] Figure 9 is a flowchart illustrating an exemplary method 638 for capturing intravascular ultrasound images. Method 638 includes using a drive motor (such as drive motor 406) to actively drive an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed according to a time-varying drive motor drive signal, as shown in block 640. In some cases, the time-varying drive motor signal may include, for example, a PWM drive motor signal. The set rotational speed may be set or adjusted by, for example, an operator, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0069] As shown in block 642, a temporary sensing window is generated in which the drive motor drive signal is held constant, i.e., not allowed to change or switch. Method 638 includes receiving multiple signals from the ultrasonic transducer during the temporary sensing window, as shown in block 644. In some cases, Method 638 may include actively driving the ultrasonic transducer again at a set rotational speed when the temporary sensing window ends, as shown in block 646. For example, in some cases, the sensing window may have a duration ranging from 30 microseconds to over 200 microseconds and occur at a frequency ranging from 4 kHz to 33 kHz.

[0070] Figure 10 is a flowchart illustrating an exemplary method 648 for capturing intravascular ultrasound images. Method 648 includes using a drive motor (such as drive motor 406) to actively drive an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed according to a time-varying drive motor drive signal, as shown in block 650. In some cases, the time-varying drive motor signal may include, for example, a PWM drive motor signal. The set rotational speed may be set or adjusted by, for example, an operator, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0071] As shown in block 652, a temporary sensing window is generated in which the drive motor drive signal is held constant, i.e., not allowed to change or switch. In some cases, the sensing window may have a duration ranging from 30 microseconds to over 200 microseconds and may occur at frequencies ranging from 4 kHz to 33 kHz. Method 648 includes receiving multiple signals from the ultrasonic transducer during the temporary sensing window, as shown in block 654. In some cases, Method 648 may also include temporarily increasing the rotational speed of the ultrasonic transducer above a set rotational speed for a short period before the start of the temporary sensing window, as shown in block 656.

[0072] Figure 11 is a flowchart illustrating an exemplary method 658 for capturing intravascular ultrasound images. Method 658 includes using a drive motor (such as drive motor 406) to actively drive an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed according to a time-varying drive motor drive signal, as shown in block 660. In some cases, the time-varying drive motor signal may include, for example, a PWM drive motor signal. The set rotational speed may be set or adjusted by, for example, an operator, or it may be a factory setting. The set rotational speed represents the target operating speed.

[0073] As shown in block 662, a temporary sensing window is generated in which the drive motor drive signal is held constant, i.e., not allowed to change or switch. In some cases, the sensing window may have a duration ranging from 30 microseconds to over 200 microseconds and may occur at frequencies ranging from 4 kHz to 33 kHz. Method 658 includes receiving multiple signals from an ultrasonic transducer during the temporary sensing window, as shown in block 664.

[0074] In some cases, method 658 may further include temporarily reducing the rotational speed of the ultrasonic transducer to below the set rotational speed for a short period immediately following the end of the transient sensing window, as shown in block 665. Method 658 may further include increasing the rotational speed of the ultrasonic transducer to equal the set rotational speed once the short period has ended, as shown, for example, in block 668. The short period may range from a duration of nearly zero to the entire duration between sampling windows. This period may vary dynamically depending on the motor speed and load.

[0075] Figure 12 is a flowchart illustrating an exemplary method 670 for capturing intravascular ultrasound images. Method 670 includes rotating an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) using a digital drive motor (such as drive motor 406) that operates according to a time-varying drive motor signal, as shown in block 672. In some cases, the time-varying drive motor signal may include, for example, a PWM drive motor signal. The set rotation speed may be set or adjusted by, for example, the operator, or it may be a factory setting. The set rotation speed represents the target operating speed.

[0076] The ultrasonic transducer is rotated using a digital drive motor that operates according to a constant drive signal for a short period of time, as shown in block 674. For example, a short period that may represent a detection window may have a duration ranging from 30 microseconds to over 200 microseconds and may occur at a frequency ranging from 4 kHz to 33 kHz. Method 670 includes detecting a signal from the ultrasonic transducer during a short period of time, as shown in block 676. In some cases, detecting a signal from the ultrasonic transducer may further include not detecting a signal from the ultrasonic transducer when the ultrasonic transducer is actively driven by a time-varying drive signal. In some cases, Method 670 may further include changing the rotational speed of the ultrasonic transducer either immediately before or after the short period of time, as shown in block 678.

[0077] Figure 13 is a flowchart illustrating an exemplary method 680 for capturing intravascular ultrasound images. Method 680 includes rotating an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) using a PWM drive signal to control a digital drive motor (such as drive motor 406), as shown in block 682. The set rotation speed may be set or adjusted by the operator, for example, or it may be a factory setting. The set rotation speed represents the target operating speed.

[0078] The ultrasonic transducer is rotated using a digital drive motor that operates according to a constant drive signal for a short period of time, as shown in block 684. The short period can represent, for example, a detection window, having a duration ranging from 30 microseconds to over 200 microseconds and occurring at a frequency ranging from 4 kHz to 33 kHz. Method 680 includes detecting a signal from the ultrasonic transducer during the short period, as shown in block 686.

[0079] Figure 14 is a schematic diagram of an exemplary control algorithm 700. The exemplary control algorithm 700 may be implemented, for example, via a processor 106 (Figure 1) when controlling the operation of a drive motor 702 that rotates an ultrasonic transducer(s). The control algorithm 700 can be thought of as a PID (Proportional Integral Derivative) control algorithm, although in some cases one or more of the proportional (P), integral (I), and derivative (D) terms may be set to zero. As shown, the derivative (D) term is set to zero, which means that the control algorithm 700 essentially represents a PI (Proportional Integral) control algorithm.

[0080] The speed reference 704 is provided to the summing point 706, as well as the feedback term 708 for generating an error signal. After passing through the proportional (P) term 710, the integral (I) term 712, and optionally the differential (D) term 714, the signal is passed to another summing point 716. After passing through the current amplifier 718, the drive signal reaches the drive motor 702. The state from the drive motor 706 is measured via an encoder 720, etc.

[0081] Figure 15 is a schematic diagram of an exemplary control algorithm 730, similar to control algorithm 730 but including several additional logic components. The additional logic components include a blackout logic block 732 and an additional add point 734. The current amplifier 718 is modified so that its state can be forced to either an on or off state regardless of the input drive signal. In some cases, the blackout logic block 732 is useful for modifying time-varying drive motor drive signals, such as, but not limited to, PWM drive motor drive signals, to provide a sensing window for acquiring a signal from an ultrasonic transducer without the emergence of electronic noise caused by a PWM drive signal that changes while attempting to acquire the signal.

[0082] For example, the blackout logic block 732 may consider the current state of the PWM drive signal immediately before the detection window to determine whether the PWM drive signal is constrained to remain high or on during the detection window, or to remain low or off during the detection window. If the PWM drive signal is constrained to remain high or on during the detection window, it means that the ultrasonic transducer is likely to accelerate during the detection window, and the blackout logic block 732 may decide to reduce the speed before reaching the detection window. If the PWM drive signal is constrained to remain low or off during the detection window, it means that the ultrasonic transducer is likely to decelerate during the detection window, and the blackout logic block 732 may decide to increase the speed before reaching the detection window and / or decrease the drive speed when the detection window ends. These are just examples.

[0083] Figure 16 is a speed-versus-time graph, where the vertical axis represents rotational speed in revolutions per minute (RPM) and the horizontal axis represents time in seconds. The first plot line 740 represents the speed-versus-time performance of a particular ultrasonic transducer rotated by an analog motor at a speed corresponding to 30 frames per second (FPS). The second plot line 742 represents the speed-versus-time performance of a particular ultrasonic transducer rotated by a PWM-controlled drive motor at the same speed. In the case of a PWM-controlled drive motor, the drive motor is controlled according to a periodic sensing window in which the PWM drive signal is kept constant and is not allowed to change during the sensing window. As can be seen, the performance of the PWM-controlled motor far surpasses that of the analog system because the speed fluctuations are small.

[0084] Figure 17 is a speed-versus-time graph, where the vertical axis represents rotational speed in revolutions per minute (RPM) and the horizontal axis represents time in seconds. The first plot line 750 represents the speed-versus-time performance of a particular ultrasonic transducer rotated by a PWM-controlled motor at a speed corresponding to approximately 30 FPS relative to a speed reference represented by plot line 752. Plot line 754 represents a threshold set to equal speed reference plus 1.5 percent, and plot line 756 represents a threshold set to equal speed reference minus 1.5 percent. As can be seen, the use of PWM motor control, in combination with the use of a sensing window, helps to stabilize low-frequency vibrations, pushing the remaining stability up to very high frequencies where they are not a problem. Overall, this demonstrates that the use of PWM motor control provides precise control.

[0085] Figure 18 is a speed-versus-time graph display providing an example of how rotation speed can change during a detection window. As seen in Figure 18, plot line 760 shows rotation speed over time, and plot line 775 shows an exemplary set rotation speed. The rotation speed decreases during detection window 762 relative to the set rotation speed 775. This illustrates what can happen if the PWM motor drive signal is constrained to remain low or off during detection window 762. The rotation speed returns to the pre-detection window 762 set rotation speed 775 in a short time after detection window 762 ends. The rotation speed decreases during detection window 764. Again, this illustrates what can happen if the PWM motor drive signal is constrained to remain low or off during detection window 764. If the PWM motor drive signal is constrained to remain high or on during detection window 762 and / or detection window 764, it will be understood that the rotation speed will instead increase during detection windows 762 and 764, respectively.

[0086] Figure 19 is a speed-versus-time graph display providing an example of how rotational speed can change during a detection window. As seen in Figure 19, plot line 770 shows rotational speed over time, and plot line 775 shows an exemplary set rotational speed. Figure 19 shows a first detection window 772 and a second detection window 774. Moving from left to right, it can be seen that the rotational speed shown in plot line 770 increases just before the first detection window 772. This bump 776 in plot line 770 represents an increase in rotational speed that may be commanded, for example, in response to various size parameters of the ultrasound catheter and / or when the PWM drive signal is constrained to off or low during the first detection window 772.

[0087] The rotational speed shown on plot line 770 decreases during the first detection window 772. In some cases, upon exiting the first detection window 772, the rotational speed may be commanded to return to a lower rotational speed than before, as shown by curve 780. Similarly, the rotational speed shown on plot line 770 increases immediately before the second detection window 774. This bump 778 on plot line 770 represents an increase in rotational speed that may be commanded, for example, in response to various size parameters of the ultrasound catheter and / or when the PWM drive signal is constrained to off or low during the second detection window 774. In some cases, upon exiting the second detection window 774, the rotational speed may be commanded to return to a rotational speed lower than the set rotational speed.

[0088] The process and / or display output may be used to extract clinically relevant IVUS features, guide therapeutic strategies such as calcium management, present intuitive maps, and / or combine information on a single display unit or a set of display units.

[0089] For example, several exemplary IVUS imaging systems that may be used in conjunction with the methods disclosed herein include, but are not limited to, those disclosed in, U.S. Patent Nos. 7,246,959, 7,306,561, and 6,945,938, and U.S. Patent Publication Nos. 2006 / 0100522, 2006 / 0106320, 2006 / 0173350, 2006 / 0253028, 2007 / 0016054, and 2007 / 0038111, all of which are incorporated herein by reference.

[0090] The specification of U.S. Patent Application Publication No. 2015 / 0073279 is incorporated herein by reference. It should be understood that this disclosure is illustrative in many respects. Modifications can be made without exceeding the scope of this disclosure, particularly with respect to details, shape, size, and step arrangement. This may include, to a reasonable extent, the use of any feature of one exemplary embodiment used in other embodiments. The scope of the invention is, of course, defined in the language in which the appended claims are expressed.

Claims

1. An intravascular ultrasound (IVUS) imaging system comprising an ultrasonic transducer and a drive motor, wherein the IVUS imaging system is Using the aforementioned drive motor, the ultrasonic transducer is actively driven at a set rotational speed according to a time-varying drive motor drive signal. A temporary detection window is generated in which the drive motor drive signal cannot be switched. Receiving multiple signals from the ultrasonic transducer during the aforementioned temporary detection window An IVUS imaging system configured as follows.

2. The IVUS imaging system according to claim 1, further configured to temporarily increase the rotational speed of the ultrasonic transducer above the set rotational speed for a short period of time prior to the start of the temporary detection window.

3. The IVUS imaging system according to claim 1 or 2, further configured to temporarily reduce the rotational speed of the ultrasonic transducer to a set rotational speed for a short period immediately following the end of the temporary detection window.

4. The IVUS imaging system according to claim 3, further configured to increase the rotational speed of the ultrasonic transducer to equal the set rotational speed when the short period has ended.

5. The IVUS imaging system according to any one of claims 2 to 4, wherein the state of the drive motor drive signal during the temporary detection window is dynamically determined based on the motor speed and / or load.

6. The IVUS imaging system according to any one of claims 1 to 5, further comprising a catheter and a control module, wherein the ultrasonic transducer is disposed within the catheter, the control module includes a drive unit, and the drive unit includes a drive motor.

7. The IVUS imaging system according to claim 6, wherein the control module comprises a processor configured to process the plurality of signals from the ultrasonic transducer, a pulse generator configured to form electrical pulses input to the ultrasonic transducer, and one or more displays configured to display the plurality of signals processed by the processor as one or more images.

8. The IVUS imaging system according to claim 7, wherein the processor is configured to control at least one of the following: the frequency or duration of electrical pulses transmitted from the pulse generator, the rotational speed of the ultrasonic transducer by the drive motor, the speed or length of the retraction of the ultrasonic transducer by the drive motor, and one or more characteristics of the one or more images on the one or more displays.

9. The IVUS imaging system according to any one of claims 1 to 8, wherein the time-varying drive motor drive signal is a pulse-width modulated (PWM) drive signal.

10. The IVUS imaging system according to claim 9, wherein the IVUS imaging system is further configured to generate the PWM drive signal.

11. The IVUS imaging system according to claim 9 or 10, further configured to allow the PWM drive signal to be switched after the detection window has ended.

12. The IVUS imaging system is further configured to modify the PWM drive signal to adjust the rotational speed of the ultrasonic transducer to the set rotational speed immediately before the start of the detection window. Preferably, the IVUS imaging system according to any one of claims 9 to 11, wherein modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer includes modifying the PWM drive signal to rotate the ultrasonic transducer at an increased rotational speed greater than the set rotational speed immediately before the start of the detection window.

13. The IVUS imaging system is further configured to modify the PWM drive signal immediately after the end of the detection window in order to adjust the rotation speed of the ultrasonic transducer to the set rotation speed. Preferably, the IVUS imaging system according to any one of claims 9 to 12, wherein modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer includes modifying the PWM drive signal to rotate the ultrasonic transducer at a speed reduced from the set rotational speed immediately after the end of the detection window.

14. The IVUS imaging system according to claim 13, further configured to modify the PWM drive signal to return to a state in which the ultrasonic transducer rotates at the set rotational speed after a second period which begins at the end of the detection window.

15. Intravascular ultrasound imaging system, A catheter to which an ultrasonic transducer is attached, A drive motor coupled to the catheter, Control unit and The control unit is equipped with, Using the aforementioned drive motor, the ultrasonic transducer is actively driven at a set rotational speed according to a time-varying drive motor drive signal. A temporary detection window is generated in which the drive motor drive signal cannot be switched. Receiving multiple signals from the ultrasonic transducer during the aforementioned temporary detection window A system that is configured in such a way.

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