Reducing Catheter Rotation Motor PWM Interference in Intravascular Ultrasound Imaging

Abstract

The method includes capturing an intravascular ultrasound image, a drive motor is used to actively drive an ultrasound transducer at a set rotational speed, a temporal sensing window is generated during which the ultrasound transducer is driven with a constant drive signal, and a plurality of signals are received from the ultrasound transducer during the temporal sensing window.

Description

[Technical Field]

[0001] TECHNICAL FIELD The present disclosure relates to intravascular ultrasound imaging. [Background technology]

[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. Each of these devices and methods has certain advantages and disadvantages. There is currently a need to provide alternative devices and methods. Summary of the Invention

[0003] The present disclosure provides design and use alternatives for medical devices and methods, including intravascular ultrasound imaging. As an example, a method for capturing intravascular ultrasound images using a mechanically steered transducer is disclosed. The method includes generating a pulse-width modulated (PWM) drive signal and using the PWM drive signal to operate a drive motor for an intravascular ultrasound catheter including the ultrasound transducer to rotate the ultrasound 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 multiple signals are received from the ultrasound 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 sensing window has ended. Alternatively or additionally, the method may further include modifying the PWM drive signal to adjust the rotation speed of the ultrasonic transducer relative to a set rotation 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 detection window.

[0006] Alternatively or additionally, the increased rotational speed may continue for a first period of time that ends at the start of the detection window. Alternatively or additionally, the method may further include modifying the PWM drive signal to adjust the rotation speed of the ultrasonic transducer relative to a set rotation speed immediately after the end of the detection window.

[0007] Alternatively or additionally, modifying the PWM drive signal to adjust the rotation 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 rotation speed immediately after the end of the detection window.

[0008] Alternatively or additionally, the method may further include modifying the PWM drive signal to return to rotating the ultrasonic transducer at the set rotational speed after a second period starting 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 sensing window is generated during which the drive motor drive signal is not switched, and a plurality of signals are received from the ultrasound transducer during the temporal sensing window.

[0010] Alternatively or additionally, the method may further include, upon expiration of the temporary sensing window, again allowing the drive motor drive signal to be switched to drive the ultrasonic transducer at the set rotational speed.

[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 of time before 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 below the set rotational speed for a short period of time immediately after the end of the temporary detection window.

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

[0014] Alternatively or additionally, the drive motor may be controlled via a pulse width modulated (PWM) drive signal. Alternatively or additionally, the state of the drive motor drive signal during the temporal sensing 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 including rotating an ultrasound transducer using a digital drive motor operating according to a varying drive signal, the ultrasound transducer being rotated using the digital drive motor operating according to a non-varying drive signal for a short period of time, and a signal from the ultrasound transducer being sensed for the short period of time.

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

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

[0018] Alternatively or additionally, the method may further include changing the rotational speed of the ultrasound transducer either immediately before or immediately after the short period of time. The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The following figures and detailed description more particularly exemplify these embodiments. [Brief explanation of the drawings]

[0019] The present disclosure can be more fully understood from the following detailed description considered in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of an exemplary intravascular ultrasound system. [Figure 2] FIG. 2 is a perspective view of an exemplary intravascular ultrasound catheter system. [Figure 3] FIG. 3 is a side view of a portion of an exemplary intravascular ultrasound catheter system. [Figure 4] FIG. 4 is a schematic diagram of an exemplary intravascular ultrasound system. [Figure 5A] FIG. 5A is an exemplary ultrasound image that does not contain artifacts due to motor noise. [Figure 5B] FIG. 5B is an exemplary ultrasound image containing artifacts due to motor noise. [Figure 6] FIG. 6 is a flow diagram illustrating an exemplary method for capturing an intravascular ultrasound image. [Figure 7] FIG. 7 is a flow diagram illustrating an exemplary method for capturing an intravascular ultrasound image. [Figure 8] FIG. 8 is a flow diagram illustrating an exemplary method for capturing an intravascular ultrasound image. [Figure 9] FIG. 9 is a flow diagram illustrating an exemplary method for capturing an intravascular ultrasound image. [Figure 10] FIG. 10 is a flow diagram illustrating an exemplary method for capturing intravascular ultrasound images. [Figure 11] FIG. 11 is a flow diagram illustrating an exemplary method for capturing intravascular ultrasound images. [Figure 12] FIG. 12 is a flow diagram illustrating an exemplary method for capturing an intravascular ultrasound image. [Figure 13] FIG. 13 is a flow diagram illustrating 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 representation of rotational speed versus time data. [Figure 17] FIG. 17 is a graphical representation 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] While the present disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[0021] For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification. All numerical values ​​are assumed to be modified herein by the term "about," whether explicitly stated or not. The term "about" generally refers to a range of numbers that one of ordinary skill in the art would consider equivalent to the recited value (e.g., having the same function or result). In many instances, the term "about" may include numbers that are rounded to the nearest significant figure.

[0022] The recitation of numerical ranges by endpoints includes all numbers within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally used in its sense including "and / or" unless the content clearly dictates otherwise.

[0023] It should be noted that references herein to "one embodiment," "some embodiments," "other embodiments," etc., indicate that the described embodiment may include one or more particular features, structures, and / or characteristics. However, such a description does not necessarily mean that all embodiments include the particular feature, structure, and / or characteristic. In addition, if a particular feature, structure, and / or characteristic is described in connection with one embodiment, it should be understood that such feature, structure, and / or characteristic may also be used in connection with other embodiments, whether or not explicitly described, unless expressly stated to the contrary.

[0024] The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

[0025] Ultrasound devices that can be inserted into patients have proven 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 blocked blood vessels and provide information 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 blood vessels. IVUS imaging systems can also be used to determine the presence of an obstruction or stenosis within a blood vessel, as well as the nature and extent of the obstruction or stenosis. IVUS imaging systems can also be used to visualize segments of the vasculature that may be difficult to visualize using other intravascular imaging techniques, such as angiography, due to, for example, motion (e.g., a beating heart) or obstructions by one or more structures (e.g., one or more blood vessels not desired 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). Additionally, IVUS imaging systems can be used to monitor one or more heart chambers.

[0026] IVUS imaging systems have been developed to provide diagnostic tools for visualizing various diseases or disorders. An IVUS imaging system can include a control module (with a pulse generator, an image processor, and a monitor), a catheter, and one or more transducers disposed in the catheter. The catheter containing the transducers can be positioned in a lumen or cavity within or adjacent to the region 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 the one or more transducers and converted into acoustic pulses that are transmitted through the patient tissue. Reflected pulses of the transmitted acoustic pulses can be absorbed by the one or more transducers and converted into electrical pulses. The converted electrical pulses can be delivered to an image processor and converted into an image displayable on a monitor.

[0027] 1 schematically illustrates 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 can 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 FIG. 3) disposed 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 FIG. 3 ) disposed in the catheter 102. In some examples, electrical signals transmitted from one or more transducers (312 in FIG. 3 ) may be input to the processor 106 for processing. In some examples, the processed electrical signals from the one or more transducers (312 in FIG. 3 ) may be displayed as one or more images on one or more displays 112. For example, a scan converter may be used to map scan line samples (e.g., radial scan line samples, etc.) onto a two-dimensional Cartesian grid to display one or more images on the 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 at least one of the frequency or duration of electrical pulses transmitted from the pulse generator 108, the speed of rotation of the imaging core (306 in FIG. 3) by the drive unit 110, the speed or length of pullback of the imaging core (306 in FIG. 3) by the drive unit 110, or one or more characteristics of one or more images formed on the 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 ultrasound transducers (312 in FIG. 3).

[0030] In some cases, the processor 106 can control the digital drive motor via a pulse-width modulated (PWM) drive signal. The PWM drive signal can vary between on (or high) and off (or low). The PWM drive signal can regulate the operation of the digital drive motor by adjusting how often the PWM drive signal is on (or high) and how often the PWM drive signal is off (or low). In some cases, the PWM drive signal can include a single signal or multiple signals. In some cases, the PWM drive signal may include a signal that is tri-stated rather than simply on (or high) or off (or low).

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

[0032] FIG. 3 is a schematic perspective view of one embodiment of the distal end 208 of the elongate member 202 of the catheter 102. The elongate member 202 includes a sheath 302 having a longitudinal axis 303 and a lumen 304. An imaging core 306 is disposed 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 are attached to the imaging device 308 and may be 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 hypotubing, or the like, or combinations thereof.

[0033] In some examples, an array of transducers 312 is attached to the imaging device 308, as shown in FIG. 3 . Alternatively, a single transducer may be used. Any suitable number of transducers 312 may 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. As will be appreciated, other numbers of transducers may also be used. When multiple transducers 312 are employed, the transducers 312 may be configured in any suitable arrangement, including, for example, a circular arrangement, a rectangular arrangement, etc.

[0034] The one or more transducers 312 may be formed from a material capable of converting applied electrical pulses into pressure strains on the surface of the one or more transducers 312, and vice versa. Examples of suitable materials include piezoelectric ceramic materials, piezoelectric composites, piezoelectric plastics, barium titanate, lead zirconate titanate, lead metaniobate, polyvinylidene fluoride, etc. Other transducer technologies include composite materials, single crystal composites, and semiconductor devices (e.g., capacitive micromachined ultrasonic transducers (“cMUTs”), piezoelectric micromachined ultrasonic transducers (“pMUTs”), etc.).

[0035] Pressure distortions on the surface of the one or more transducers 312 form acoustic pulses at a frequency based on the resonant frequency of the one or more transducers 312. The resonant frequency of the one or more transducers 312 can be affected 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 can be disk-shaped, block-shaped, rectangular-shaped, elliptical-shaped, etc. The one or more transducers can be formed into the desired shape by any process, including, for example, dicing, die-and-fill, machining, micromachining, etc.

[0036] As an example, each of the 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 acoustically absorbing material (e.g., an epoxy substrate with tungsten particles). During operation, the piezoelectric layer can be electrically excited to cause the emission of an acoustic pulse.

[0037] The one or more transducers 312 can be used to form radial cross-sectional images of the surrounding space. Thus, for example, when the one or more transducers 312 are disposed within the catheter 102 and inserted into a patient's blood vessel, the one or more transducers 312 can be used to form images of the walls of the blood vessel and the tissue surrounding the blood vessel.

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

[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 arrives at the transducer with sufficient energy to be detected is converted to an electrical signal at the receiving transducer. The one or more converted electrical signals are transmitted to a control module (104 in FIG. 1 ), where a processor 106 processes the electrical signal characteristics to form a displayable image of the imaged area based at least in part on the collection of information from each of the transmitted acoustic pulses and received echo pulses. In some examples, rotation of the imaging core 306 is driven by a drive unit 110 located within the control module (104 in FIG. 1 ). In an alternative embodiment, the one or more transducers 312 are fixed in place and do not rotate. In that case, the drive shaft 310 may instead rotate a mirror that reflects acoustic signals to and from the fixed one or more transducers 312.

[0040] As one or more transducers 312 are rotated about the longitudinal axis 303 of the catheter 102 that emits the acoustic pulses, multiple images can be formed that collectively form a radial cross-sectional image (e.g., a tomographic image) of a portion of the area surrounding the one or more transducers 312, such as the wall of a blood vessel of interest and the tissue surrounding the blood vessel. 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, such that multiple cross-sectional images may be formed along the longitudinal length of the blood vessel. During an imaging procedure, the one or more transducers 312 may be retracted (e.g., pulled back) along the longitudinal length of the catheter 102. The catheter 102 may include at least one telescoping section that may be retracted during the retraction of the one or more transducers 312. In some examples, the 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 may be any suitable distance, including, for example, at least 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, or more. Regardless of whether the imaging core 306 moves longitudinally independently of the catheter 102, the entire catheter 102 may be retracted during an imaging procedure.

[0042] A motor may optionally be used to retract the imaging core 306. The motor may retract the imaging core 306 a short distance, stop long enough for the one or more transducers 306 to capture an image or series of images, then retract the imaging core 306 another short distance, again to capture another image or series of images, and so on.

[0043] The quality of images produced at different depths from one or more transducers 312 may be affected by one or more factors, including, for example, bandwidth, transducer focus, beam pattern, and frequency of the acoustic pulses. 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 the one or more transducers 312. Generally, as the frequency of the acoustic pulses decreases, the penetration depth of the acoustic pulses within 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 may electrically couple the transducer 312 to the control module 104 (see, e.g., FIG. 1 ). In that case, the one or more conductors 314 may extend along the longitudinal length of the rotatable drive shaft 310.

[0045] A catheter 102 with one or more transducers 312 attached to the distal end 208 of the imaging core 308 may be percutaneously inserted into a patient via an accessible vessel, such as the femoral artery, femoral vein, or jugular vein, at a site remote from a selected portion of a selected region, such as a blood vessel, to be imaged. The catheter 102 may then be advanced through the patient's blood vessels 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 emitted into 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 pullback of the imaging device 308 along the target imaging location. It should be understood that frames may be acquired with or without rotation of the imaging device 308, and with or without pullback. Furthermore, it will be understood that frames may be acquired using other types of movement procedures in addition to or instead of at least one of rotation or pullback of the imaging device 308.

[0047] In some examples, when pullback is performed, the pullback may be at a constant speed, thus providing a tool for potential applications that can calculate longitudinal vessel / plaque measurements. In some examples, the imaging device 308 is pulled back at a constant speed of at least 0.3 mm / sec. In some examples, the imaging device 308 is pulled back at a constant speed of at least 0.4 mm / sec. In some examples, the imaging device 308 is pulled back at a constant speed of at least 0.5 mm / sec. In some examples, the imaging device 308 is pulled back at a constant speed of at least 0.6 mm / sec. In some examples, the imaging device 308 is pulled back at a constant speed of at least 0.7 mm / sec. In some examples, the imaging device 308 is pulled back 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 pullback procedure. However, it may be useful to simultaneously display at least two images in real time during an IVUS procedure (e.g., a pullback 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] 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 FIG. 1. Various features described herein as part of the IVUS imaging system 100 may also be considered part of the IVUS imaging system 400. Similarly, various features described herein as part of the IVUS imaging system 400 may also be considered 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 ultrasound transducer 404, may 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, although in some cases a brushed motor is envisioned. The drive motor 406 may be operated according to a PWM drive signal. In some cases, the PWM drive signal may be generated by the processor 106 shown in FIG. 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 may vary according to how often the PWM drive signal goes high (on, or set equal to 1) and how often the PWM drive signal goes low (off, or set equal to 0).

[0053] The gear reduction mechanism 408 can provide a reduction in the rotational speed of 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 reduction or a 5:1 reduction. In some cases, the gear reduction mechanism 408 can provide a reduction that is approximately 4.5:1 reduction. As an example, the drive motor 406 can rotate at 5000 to 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 ultrasound transducer being able to capture 30 frames per second. These are merely examples.

[0054] The transformer 410 provides electrical coupling to the imaging core 402. The transformer 410 includes a first winding 410a that rotates and is coupled to the imaging core 402, and a second winding 410b that is fixed. 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 ultrasound transducer 404 can be transmitted from the imaging core 402 to the IVUS image 412. It will be appreciated that the signal from the ultrasound 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 provides advantages such as, but not limited to, fewer components, which may mean that using a PWM drive can result in cost savings, reduced power consumption, and improved reliability. Using a PWM drive may mean faster response to command changes. In some cases, using a PWM drive signal may cause noise in the corresponding IVUS image. Because the PWM drive signal alternates between high and low, each time the PWM drive signal switches, various electrical noises may be generated, which may appear as speckle on the IVUS image. Speckle is an undesirable image component created by the detection circuit detecting electrical noise rather than actual (real or expected) data from the ultrasound transducer.

[0056] 5A shows a first IVUS image 512 without speckles, and FIG. 5B shows a second IVUS image 514 similar to the first IVUS image 512 but including multiple speckles. These speckles, and any other visible signs of electrical noise, can make it difficult to obtain clear IVUS images and to properly interpret the IVUS images relative to the anatomical structures depicted in those IVUS images. FIGS. 6-13 are flow diagrams illustrating an exemplary method for capturing ultrasound images in a manner that reduces or even eliminates 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] FIG. 6 is a flow diagram illustrating an exemplary method 600 for capturing intravascular ultrasound images using a mechanically steered transducer. The method 600 includes generating a pulse-width modulated (PWM) drive signal, as shown in block 602. As shown in block 604, the PWM drive signal is used to operate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in FIGS. 1-3 or imaging core 402 shown in FIG. 4) that includes 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 an operator, or may be factory-set, for example. The set rotational speed represents a target operating speed.

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

[0059] The detection window may last for a short period of time or may occur periodically. For example, in some cases, the detection window may last for 0.1% to 0.5% of the time it takes for the imaging core to complete one rotation. The motor speed may range from 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] Multiple signals may be received from the ultrasonic transducer during the detection window, as shown in block 608. In some cases, once the detection window ends, the PWM drive signal reverts to a time-varying signal, as shown in block 610. It will be appreciated that the detection window may be generated periodically by preventing the PWM drive signal from switching for a period corresponding to the detection window, with intervening periods allowing the PWM drive signal to switch between high and low to maintain the desired rotation speed.

[0061] FIG. 7 is a flow diagram illustrating an exemplary method 612 for capturing intravascular ultrasound images. The method 612 includes generating a pulse-width modulated (PWM) drive signal, as indicated in block 614. As indicated in block 616, the PWM drive signal is used to operate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in FIGS. 1-3 or imaging core 402 shown in FIG. 4) that includes 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 an operator, or may be factory-set, for example. The set rotational speed represents a target operating speed.

[0062] As shown in block 618, a detection window is generated during which the PWM drive signal is temporarily held stable. Holding the PWM drive signal constant means that the PWM drive signal is high or on, meaning that the rotation speed can 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, meaning that the rotation speed can drop below the set rotation speed during the detection window. The detection window may last for a short period of time or may occur periodically. For example, in some cases, the detection window may last for 0.1% to 0.5% of the time it takes for the imaging core to complete one full rotation. The motor speed may range from 1000 RPM to 2000 RPM. Therefore, the detection window may have a duration ranging from 30 microseconds to more than 200 microseconds and a frequency ranging from 4 kHz to 33 kHz. As shown in block 620, multiple signals may be received from the ultrasound 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 ultrasound transducer relative to a set rotational speed just before the start of the detection window, as shown in block 622. In some examples, this may include modifying the PWM drive signal just before the start of the detection window to rotate the ultrasound transducer at an increased rotational speed greater than the set rotational speed. Depending on the duration of a particular detection window and the size and other characteristics of the ultrasound catheter, if the detection window means that the PWM drive signal is constrained low or off, the ultrasound catheter may slow down too much during the detection window when the drive motor is essentially coasting. Therefore, a small speed increase just before the detection window can help maintain the rotational speed of the ultrasound catheter and / or ultrasound transducer. The increased rotational speed can continue for a first period ending at the start of the detection window. The first period can have a duration ranging from approximately zero to the entire period between sampling windows. This period can vary dynamically depending on the motor speed and load.

[0064] In some examples, modifying the PWM drive signal immediately before the start of the detection window may include 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. Because the rotation speed of the ultrasonic transducer increases during the detection window when the PWM drive signal is constrained high or on, it may be desirable to reduce the rotation speed immediately before the start of the detection window when the PWM drive signal is constrained high or on during the detection window. In some cases, whether the PWM drive signal is modified immediately before the start of the detection window may vary, for example, to accommodate a particular pattern in the PWM drive signal.

[0065] FIG. 8 is a flow diagram illustrating an exemplary method 624 for capturing intravascular ultrasound images. The method 624 includes generating a pulse-width modulated (PWM) drive signal, as shown in block 626. As shown in block 628, the PWM drive signal is used to operate a drive motor (e.g., drive motor 406) for an intravascular ultrasound catheter (e.g., catheter 102 shown in FIGS. 1-3 or imaging core 402 shown in FIG. 4) including 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 an operator, or may be factory-set, for example. The set rotational speed represents a target operating speed.

[0066] As shown in block 630, a detection window is generated during which the PWM drive signal is temporarily held stable. Holding the PWM drive signal constant means that the PWM drive signal is high or on, meaning that the rotation speed can 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, meaning that the rotation speed can drop below the set rotation speed during the detection window. The detection window may last for a short period of time or may occur periodically. For example, in some cases, the detection window may last for 0.1% to 0.5% of the time it takes for the imaging core to complete one full rotation. The motor speed may range from 1000 RPM to 2000 RPM. Therefore, the detection window may have a duration ranging from 30 microseconds to more than 200 microseconds and a frequency ranging from 4 kHz to 33 kHz. As shown in block 632, multiple signals may be received from the ultrasound 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 relative to the 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 shock 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, method 624 may further include modifying the PWM drive signal to return to rotating the ultrasonic transducer at the set rotational speed after a second period starting at the end of the detection window, as shown in block 636. The second period may have a duration ranging from 30 microseconds to more than 200 microseconds.

[0068] 9 is a flow diagram illustrating an example method 638 for capturing intravascular ultrasound images. The method 638 includes actively driving an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed using a drive motor (such as drive motor 406) 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, for example, by an operator, or may be factory-set. The set rotational speed represents a target operating speed.

[0069] A temporary detection window is generated during which the drive motor drive signal is held constant, i.e., is not allowed to change or switch, as shown in block 642. Method 638 includes receiving a plurality of signals from the ultrasonic transducer during the temporary detection window, as shown in block 644. In some cases, method 638 may include once again actively driving the ultrasonic transducer at a set rotational speed upon expiration of the temporary detection window, as shown in block 646. For example, in some cases, the detection 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] 10 is a flow diagram illustrating an example method 648 for capturing intravascular ultrasound images. The method 648 includes actively driving an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed using a drive motor (such as drive motor 406) 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, for example, by an operator, or may be factory-set. The set rotational speed represents a target operating speed.

[0071] As shown in block 652, a temporary detection window is generated during which the drive motor drive signal is held constant, i.e., is not allowed to change or switch. In some cases, the detection 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. Method 648 includes receiving a plurality of signals from the ultrasonic transducer during the temporary detection 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 of time prior to the start of the temporary detection window, as shown in block 656.

[0072] 11 is a flow diagram illustrating an exemplary method 658 for capturing intravascular ultrasound images. The method 658 includes actively driving an ultrasound transducer (such as ultrasound transducer 312 or ultrasound transducer 404) at a set rotational speed using a drive motor (such as drive motor 406) 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, for example, by an operator, or may be factory-set. The set rotational speed represents a target operating speed.

[0073] A temporary detection window is generated during which the drive motor drive signal is held constant, i.e., is not allowed to change or switch, as shown in block 662. In some cases, the detection 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. Method 658 includes receiving a plurality of signals from the ultrasonic transducer during the temporary detection window, as shown in block 664.

[0074] In some cases, method 658 may further include temporarily reducing the rotational speed of the ultrasonic transducer below the set rotational speed for a short period of time immediately following the end of the temporary detection 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 upon the end of the short period of time, as shown in block 668, for example. The short period of time may range from approximately zero duration to the entire period between sampling windows. This period may vary dynamically depending on the motor speed and load.

[0075] 12 is a flow diagram illustrating an example method 670 for capturing intravascular ultrasound images. The 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) operating according to a time-varying drive motor drive 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, for example, by an operator, or may be factory-set. The set rotation speed represents a target operating speed.

[0076] The ultrasonic transducer is rotated using a digital drive motor operating according to a constant drive signal for a short period of time, as shown in block 674. For example, the short period, which may represent a detection 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. Method 670 includes detecting a signal from the ultrasonic transducer during the 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 the time-varying drive signal. In some cases, method 670 may further include changing the rotational speed of the ultrasonic transducer either immediately before or immediately after the short period of time, as shown in block 678.

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

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

[0079] 14 is a schematic diagram of an exemplary control algorithm 700. The exemplary control algorithm 700 may be implemented, for example, via the processor 106 (FIG. 1) in controlling the operation of a drive motor 702 that rotates the ultrasonic transducer(s). The control algorithm 700 may be considered 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 equal to zero. As shown, the derivative (D) term is set equal to zero, meaning that the control algorithm 700 essentially represents a PI (Proportional Integral) control algorithm.

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

[0081] 15 is a schematic diagram of an example control algorithm 730 similar to control algorithm 730 but including some additional logic components. The additional logic components include a blackout logic block 732 and an additional summing point 734. The current amplifier 718 is altered so that its state can be forced to an on or off state regardless of the input drive signal. In some cases, the blackout logic block 732 serves to modify a time-varying drive motor drive signal, such as, but not limited to, a PWM drive motor drive signal, to provide a detection window for acquiring a signal from an ultrasonic transducer without the appearance of electronic noise caused by the varying PWM drive signal while attempting to acquire the signal.

[0082] For example, the blackout logic block 732 can 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 whether the PWM drive signal is constrained 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, meaning the ultrasonic transducer is likely to accelerate during the detection window, the blackout logic block 732 can determine to reduce the speed before the detection window is reached. If the PWM drive signal is constrained to remain low or off during the detection window, meaning the ultrasonic transducer is likely to decelerate during the detection window, the blackout logic block 732 can determine to increase the speed before the detection window is reached and / or reduce the drive speed when the detection window ends. These are just examples.

[0083] FIG. 16 is a graphical representation of speed versus time, with the vertical axis representing rotational speed in revolutions per minute (RPM) and the horizontal axis representing time in seconds. A first plot line 740 represents the speed versus time performance of a particular ultrasonic transducer being rotated by an analog motor at a speed corresponding to 30 frames per second (FPS). A second plot line 742 represents the speed versus time performance of a particular ultrasonic transducer being rotated at the same speed by a PWM-controlled drive motor. In the case of the PWM-controlled drive motor, the drive motor is controlled according to a periodic detection window in which the PWM drive signal is held constant and not allowed to change during the detection window. As can be seen, the performance of the PWM-controlled motor significantly exceeds that of the analog system due to the smaller speed fluctuations.

[0084] FIG. 17 is a graphical representation of speed versus time, with the vertical axis representing rotational speed in revolutions per minute (RPM) and the horizontal axis representing time in seconds. A first plot line 750 represents the speed versus time performance of a particular ultrasonic transducer being rotated by a PWM-controlled drive 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 equal to the speed reference plus 1.5 percent, and plot line 756 represents a threshold set equal to the speed reference minus 1.5 percent. As can be seen, the use of PWM motor control, combined with the use of a detection window, helps stabilize low-frequency vibrations, pushing remaining stability up to much higher frequencies where they are not an issue. Overall, this demonstrates that the use of PWM motor control provides tight control.

[0085] FIG. 18 is a graphical representation of speed versus time that provides an example of how the rotation speed may change during a detection window. As seen in FIG. 18, plot line 760 shows the rotation speed over time, and plot line 775 shows an exemplary set rotation speed. The rotation speed decreases relative to the set rotation speed 775 during detection window 762. This represents what could happen if the PWM motor drive signal were constrained to remain low or off during detection window 762. The rotation speed returns to the set rotation speed 775 before detection window 762 a short time after detection window 762 ends. The rotation speed decreases during detection window 764. Again, this represents what could happen if the PWM motor drive signal were constrained to remain low or off during detection window 764. It will be appreciated that if the PWM motor drive signal were constrained to remain high or on during detection window 762 and / or detection window 764, the rotation speed would instead increase during detection windows 762 and 764, respectively.

[0086] FIG. 19 is a graphical representation of speed versus time that provides an example of how rotational speed may change during a detection window. As seen in FIG. 19, plot line 770 shows rotational speed over time, and plot line 775 shows an exemplary set rotational speed. FIG. 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 prior to 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 if the PWM drive signal is constrained off or low during the first detection window 772.

[0087] The rotational speed shown in 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 back to a lower rotational speed than before, as shown by curve 780. Similarly, the rotational speed shown in plot line 770 increases just before the second detection window 774. This bump 778 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 if the PWM drive signal is constrained 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 back to a lower rotational speed than the set rotational speed.

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

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

[0090] U.S. Patent Application Publication No. 2015 / 0073279 is incorporated herein by reference. It will be understood that this disclosure is, in many respects, merely illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps, without exceeding the scope of the disclosure. This may include, to the extent appropriate, the use of any of the features of one illustrative embodiment used in other embodiments. The scope of the invention will, of course, be defined in the language in which the appended claims are expressed.

Claims

1. 1. A system for capturing intravascular ultrasound images using a mechanically steered transducer, comprising: an intravascular ultrasound catheter including an ultrasound transducer; a processor coupled to the intravascular ultrasound catheter; wherein the processor: generating a pulse width modulated (PWM) drive signal; using the PWM drive signal to operate a drive motor for the intravascular ultrasound catheter to rotate the ultrasound transducer at a set rotational speed; creating a detection window during which the PWM drive signal is not switched to reduce electrical noise; receiving a plurality of signals from the ultrasonic transducer during the detection window; The system is configured as follows:

2. The system of claim 1 , wherein the processor is further configured to return to a state that allows the PWM drive signal to be switched after the sensing window ends.

3. 3. The system of claim 1, wherein the processor is further configured to modify the PWM drive signal to adjust the rotational speed of the ultrasonic transducer relative to the set rotational speed immediately before the start of the detection window.

4. 4. The system of claim 3, wherein modifying the PWM drive signal to adjust the rotational speed of the ultrasonic transducer comprises 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.

5. 3. The system of claim 1, wherein the processor is further configured to modify the PWM drive signal to adjust the rotational speed of the ultrasonic transducer relative to the set rotational speed immediately after the end of the detection window.

6. 6. The system of claim 5, 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 reduced speed relative to the set rotational speed immediately after the end of the detection window.

7. 7. The system of claim 6, wherein the processor is further configured to modify the PWM drive signal to return the ultrasonic transducer to rotating at the set rotational speed after a second period beginning at the end of the detection window.

8. 1. A system for capturing intravascular ultrasound images, comprising: an intravascular ultrasound catheter including an ultrasound transducer; a processor coupled to the intravascular ultrasound catheter; wherein the processor: using a drive motor to actively drive the ultrasonic transducer at a set rotational speed in accordance with a time-varying drive motor drive signal; creating a temporal detection window during which the drive motor drive signal is not switched; receiving a plurality of signals from the ultrasonic transducer during the temporal detection window; The system is configured as follows:

9. 9. The system of claim 8, wherein the processor is further configured to increase the rotational speed of the ultrasonic transducer above the set rotational speed for a short period of time before the start of the temporary detection window.

10. 9. The system of claim 8, wherein the processor is further configured to reduce the rotational speed of the ultrasonic transducer below the set rotational speed for a short period of time immediately after the end of the temporary sensing window.

11. 11. The system of claim 10, wherein the processor is further configured to increase the rotational speed of the ultrasound transducer to equal the set rotational speed upon expiration of the short period of time.

12. 12. The system of claim 9, wherein the processor is further configured to dynamically determine a state of the drive motor drive signal during the temporal sensing window based on motor speed and / or load.

13. 1. A system for capturing intravascular ultrasound images, comprising: an intravascular ultrasound catheter including an ultrasound transducer; a processor coupled to the intravascular ultrasound catheter; wherein the processor: rotating the ultrasonic transducer using a digital drive motor operating according to a varying drive signal; rotating the ultrasonic transducer using the digital drive motor operating according to a drive signal that does not change for a short period of time; Detecting a signal from the ultrasonic transducer during the short period of time. The system is configured as follows:

14. 14. The system of claim 13, wherein the processor is further configured to dynamically determine a state of the drive motor drive signal during the short period based on motor speed and / or load.

15. 15. The system of claim 13 or 14, wherein the processor is further configured to control the digital drive motor using a pulse width modulated (PWM) drive signal.

Images