Patent Publication Number: US-11026591-B2

Title: Intravascular pressure sensor calibration

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Patent Application No. 61/778,656, filed Mar. 13, 2013, which is incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to methods of calibrating a pressure sensor as part of a deliverable intravascular device. The invention can be used with pressure sensing catheters and guidewires. 
     BACKGROUND 
     Cardiovascular disease frequently arises from the accumulation of atheromatous deposits on inner walls of vascular lumen, particularly the arterial lumen of the coronary and other vasculature, resulting in a condition known as artherosclerosis. These deposits can have widely varying properties, with some deposits begin relatively soft and others being fibrous and/or calcified. In the latter case, the deposits are frequently referred to as plaque. These deposits can restrict blood flow, leading to myocardial infarction in more severe cases. 
     The severity of artherosclerosis can be quantified using Fractional Flow Reserve (FFR) techniques to assess blood flow at various points in the vasculature. FFR is determined by measuring the maximum myocardial flow in the presence of a stenosis (i.e., a narrowing of the blood vessel) divided by the normal maximum myocardial flow. The ratio is approximately equal to the mean hyperemic (i.e., dilated vessel) distal coronary pressure divided by the mean aortic pressure. 
     To measure FFR, distal coronary pressure is usually measured with a pressure sensor mounted on the distal portion of an intraluminal device, e.g., a guidewire after administering a hyperemic agent into the blood vessel. Mean aortic pressure is then measured using a variety of techniques in areas proximal of the stenosis, for example, in the aorta. A variety of intravascular pressure sensors are commercially-available for FFR measurements, and many include integrated software and displays to output the information in a useful format. 
     One shortcoming of current intravascular pressure sensors is that they require pre-calibration prior to administration and measurement to ensure that the sensor will be accurate when used in the body. This calibration is required due to the innate variability that exists in the microfabricated sensors used to detect pressure. The calibration typically includes span and temperature calibration over a range of pressures and temperature beyond that typically encountered in the body. The calibration data is stored in some manner and transmitted to the control system when the wire is attached to the system. The system uses this calibration information to adjust output of the sensor to be reflective of the calibrated condition. 
     Unfortunately, the factory calibration does not always correlate the performance of the sensor to the electrical output. That is, the calibration can slip for a number of reasons, such as improper storage or differences between the control electronics used in the operating room and the electronics used to perform the calibration. Because of this, it is still necessary to “double-check” the calibration of a sensor prior to use. If the calibration is off, it is often necessary to dispose of the entire sensor device, e.g., pressure guidewire. 
     It would be beneficial to develop a technique that allows calibration of an intravascular pressure sensor at the point of use. Such a technique would give a user confidence that the sensor is working properly and avoid the need to dispose of the device if the factory calibration is lost. 
     SUMMARY 
     The invention is a method for calibrating an intravascular pressure sensor at the point of use. By using data from a secondary pressure measurement device, e.g., an automated aortic pressure monitor, the pressure sensor can be easily calibrated over a range of temperatures and pressures relevant to the patient. Accordingly, an intravascular pressure sensor can be calibrated without undergoing a factory calibration. Additionally, in the event that the calibration is lost, the sensor can be recalibrated. 
     In place of pre-calibration and storage for transmission to the system, the invention involves using the peak-to-peak values of the pressure measurement, e.g., an aortic pressure measurement, to calibrate the sensor, e.g., the pressure wire sensor. That is, it is possible for a user to simply calibrate the sensor by leveraging a data stream from common pressure monitoring equipment, e.g., a surgical blood pressure cuff. Calibration of the pressure sensor against an existing stream of aortic pressure data allows for the elimination of several redundant testing steps during the manufacturing process, thereby reducing the time and cost of production. 
     In one embodiment, an intravascular device having a pressure sensor can be calibrated using the following steps. First, the device is attached to supporting electronics which are also interfaced to an additional pressure monitor. Next the intravascular device is inserted into a guide lumen (inserter) or guide catheter until the sensor just protrudes into the vasculature past the inserter. In this configuration, the sensor is then calibrated so that the mean value of the pressure wire signal equals the mean value from the additional pressure monitor. Once this calibration is complete, the intravascular device is ready for use. 
     Additional methods of calibrating the intravascular pressure sensor are also disclosed in the following description, figures, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a guidewire with pressure measuring capabilities for use in practicing methods of the invention; 
         FIG. 2  illustrates an alternative view of the guidewire of  FIG. 1 ; 
         FIG. 3  is a flowchart of a method for calibrating a pressure sensing guidewire with external pressure data; 
         FIG. 4  is a graphical display of a Fractional Flow Reserve (FFR) determination; 
         FIG. 5  is an enlarged view of a subwindow provided in the graphical display of  FIG. 4 ; 
         FIG. 6  is a block diagram of an exemplary system for calibrating a pressure sensing intravascular device and using it to evaluate a patient; 
         FIG. 7  is a block diagram of an exemplary system for calibrating a pressure sensing intravascular device and using it to evaluate a patient. 
     
    
    
     DETAILED DESCRIPTION 
     The invention involves methods for calibrating intravascular pressure sensors using available streams of pressure data. By using data from a secondary pressure measurement device, e.g., an automated aortic pressure monitor, the pressure sensor can be easily calibrated over a range of temperatures and pressures relevant to the patient. 
     Calibration of a pressure sensor is typically performed at a manufacturing or test facility prior to sale or delivery of the sensor. Typical methods involve exposing the sensor to a specified range of pressures, typically between 0 and 300 mmHg, and a specified range of temperatures, typically 22 to 43° C., and calculating a calibration value for the sensor. This is routinely done at the sensor fabrication level and then again in the finished intravascular device, e.g., a pressure-sensing guidewire. The sensor output is then verified at the various pressure and temperature conditions and calibration information is stored on the pressure wire connector cable. In the operating room, the intravascular sensor is interfaced with a control system and the calibration value is uploaded to the control system. Next the pressure wire is zeroed outside the body to assure that the pressure sensor has an appropriate baseline. The zeroing step also identifies defective sensor conditions. Upon entry of the wire into the body, the sensor baseline is adjusted (normalized) to the aortic pressure that is measured with another device, for example a blood pressure cuff or an automated aortic pressure monitor. [Automated aortic pressure monitors are standard in most procedures requiring anesthesia.] The normalized baseline assures that the differential pressures measured during the procedure are of the correct magnitude. 
     Although methods of the invention encompass any physiological measurement, in preferred aspects, the physiological measurement is FFR. Fractional flow reserve (FFR) is a criteria typically used to assess blood flow. Fractional flow reserve is determined by measuring maximum flow in the presence of a stenosis (i.e., a narrowing of the blood vessel) divided by normal maximum flow. This ratio is approximately equal to the mean hyperemic (i.e., dilated vessel) distal coronary pressure divided by the mean aortic pressure. Distal coronary pressure is usually measured with a pressure sensor mounted on the distal portion of a guidewire after administering a hyperemic agent into the blood vessel. Mean aortic pressure is measured using a variety of techniques in areas proximal of the stenosis, for example, in the aorta. 
     FFR provides a convenient, cost-effective way to assess the severity of coronary and peripheral lesions. FFR also provides an index of stenosis severity that allows rapid determination of whether a blockage is significant enough to limit blood flow within the artery, thereby requiring treatment. The normal value of FFR is about 1.00. Values less than 0.80 are deemed significant and require treatment, which may include angioplasty and stenting. 
     As encompassed by the invention, a baseline FFR measurement is taken prior to conducting the therapeutic procedure. The procedure is then performed, and a subsequent post-therapy FFR measurement is taken. The post-therapy measurement is compared to the baseline measurement, and the degree in improvement is ascertained. As described herein, the degree of improvement resulting from the therapy is known as functional gain. For example, the FFR of an apparently occluded blood vessel is ascertained to be 0.75. As this is below the threshold value for therapeutic intervention, the patient will receive a stent to restore flow in the vessel. After the stent procedure, FFR is again assessed in the area of interest. This time, the FFR is determined to be 0.97. Comparing the second FFR reading to the first, the patient has a functional gain of 29%. While the second FFR determination does indicate that the operation is a success, (the blood flow is now essentially at normal levels), it does not quantify the degree of success. Methods of the invention provide just that, the ability to determine and document the degree of improvement after a therapeutic procedure has been performed. Accordingly, methods of the invention provide highly practical tools to monitor a patient&#39;s progress after therapeutic intervention. 
     Determination of FFR typically involves the insertion of a pressure sensing guidewire into a blood vessel and measuring pressure inside the vessel with the device. The actual parameters and calculations for determining FFR are well known in the art and are described above. 
     In practice, measuring pressure inside the vessel may also involve injecting a local anesthetic into the skin to numb the area of the patient prior to surgery. A puncture is then made with a needle in either the femoral artery of the groin or the radial artery in the wrist before the provided guidewire is inserted into the arterial puncture. Once positioned, the guidewire may then be used to measure pressure in the vessel, and subsequently FFR. 
     In a typical procedure, the guidewire may be advanced to a location on the distal side of the stenosis. The pressure may then be measured at a first flow state. Then, the flow rate may be significantly increased, for example by the use of drugs such as adenosine, and the pressure measured in this second, hyperemic, flow state. The pressure and flow relationships at these two flow states are then compared to assess the severity of the stenosis and provide improved guidance for any coronary interventions. As explained above, FFR is a comparison of the pressure within a vessel at positions prior to the stenosis and after the stenosis. The level of FFR determines the significance of the stenosis, which allows physicians to more accurately identify clinically relevant stenosis. For example, an FFR measurement above 0.80 indicates normal coronary blood flow and a non-significant stenosis. A measurement below 0.80 indicates the necessity of therapeutic intervention 
     Any medical device can be used in conjunction with the provided methods for taking physiological measurements (e.g., FFR), before and after a therapeutic procedure. In certain embodiments, the device is configured for insertion into a bodily lumen, such as a guidewire or catheter. In other embodiments, the medical device is a pressure-sensing guidewire or catheter. In additional embodiments, the medical device is flow-sensing guidewire or catheter. In further embodiments, the encompassed guidewire or catheter has both flow and pressure measuring capabilities. 
     An exemplary guidewire for practicing methods of the invention is depicted in  FIGS. 1 and 2 . The exemplary guidewire shown has pressure capabilities, and optionally other measurement capabilities such as imaging or flow-sensing. A guidewire with a pressure sensor provides a desirable environment in which to calculate fractional flow reserve (FFR). Moreover, the invention is equally applicable to any type of physiological measurement, including fractional flow reserve (FFR), instant free-wave ratio (IFR), coronary flow reserve (CFR), hyperemic stenosis resistance (HSR), hyperemic microvascular resistance (HMR), and index of microvascular resistance (IMR). Intravascular devices incorporating the invention may also be applied to intravascular imaging (IVUS) or optical coherence tomography (OCT). Any of these physiological measurements can be taken prior to therapeutic invention, subsequent to therapeutic invention, and have the two values compared to determine functional gain. 
     Turning to  FIGS. 1 and 2 , a sensor tip  100  for practicing the invention is illustrated. The sensor tip  100  includes a flow sensor  101 , for example an ultrasound transducer, a Doppler flow sensor or any other suitable flow sensor, disposed at or in close proximity to the distal end  102  of the combination sensor tip  100 . The ultrasound transducer  101  may be any suitable transducer, and may be mounted in the distal end using any conventional method, including the manner described in U.S. Pat. No. 5,125,137, which is fully incorporated herein by reference. Conductors (not shown) may be secured to the front and rear sides of the ultrasound transducer  101 , and the conductors may extend interiorly to the proximal extremity of a guide wire. 
     The combination sensor tip  100  also includes a pressure sensor  104  also disposed at or in close proximity to the distal end  102  of the combination sensor tip  100 . The pressure sensor  104  may be of the type described in U.S. Pat. No. 6,106,476, which is fully incorporated herein by reference. For example, the pressure sensor  104  may be comprised of a crystal semiconductor material having a recess therein and forming a diaphragm bordered by a rim. A reinforcing member may be bonded to the crystal to reinforce the rim of the crystal, and may have a cavity therein underlying the diaphragm and exposed to the diaphragm. A resistor having opposite ends may be carried by the crystal and may have a portion thereof overlying a portion of the diaphragm. Leads may be connected to opposite ends of the resistor and extend proximally within the guide wire. Additional details of suitable pressure sensors that may be used as the pressure sensor  104  are described in U.S. Pat. No. 6,106,476. U.S. Pat. No. 6,106,476 also describes suitable methods for mounting the pressure sensor  104  within the combination sensor tip  100 . In one embodiment, the pressure sensor  104  is oriented in a cantilevered position within a sensor housing  103 . For example, the sensor housing  103  preferably includes a lumen surrounded by housing walls. When in a cantilevered position, the pressure sensor  104  projects into the lumen of the sensor housing  103  without contacting the walls of the sensor housing  103 . 
     The procedure for using calibrating a pressure-sensing guidewire is rather straightforward, and described in the flow chart of  FIG. 3 . In the operating or procedure room the product packaging is opened and the guidewire is placed on a sterile field. With the wire in the spiral, the signal cable is removed from the spiral by pulling on the plug, and then the cable is connected a compatible instrument (described generally as a controller). The controller has already been interfaced with an external pressure monitor, i.e., an aortic pressure monitor. As discussed above, the baseline is first zeroed extracorporally. Typically, this merely involves clicking a mouse button or having an assistant initiate the zeroing procedure. During the zeroing, the controller also initiates a self-test. 
     Once the sensor has been zeroed, the connector body is removed from the spiral clip and withdrawn from the spiral. At this time, the guide wire tip may be shaped with standard tip-shaping practices, if desired. The working length of the guidewire is then wet with normal saline, and inserted through the appropriate introducer components and guiding catheter into the desired blood vessel. Once the guidewire has passed through the guiding catheter (shallow insertion) the guidewire is stopped, and the reading of the guidewire pressure sensor is synchronized with the reading from the external pressure sensor, i.e., the sensed range of arterial pressure is assigned to the range sensed by the external sensor. Typically, the calibration is merely a matter of clicking a mouse button or having an assistant otherwise initiate the calibration, which is done automatically. 
     Once the guidewire is calibrated, it can be advanced under fluoroscopic guidance, with contrast injections, as needed, to verify the guidewire location. The sensor can then be advanced (deep insertion) to the desired measurement location, and pressure measurements made as appropriate. Optionally, when the procedure is complete, the guidewire can be withdrawn to a position just prior to entering the guide catheter and the sensor pressure and the external pressure monitor readings can be compared to verify that pressures are equal. 
     Methods of the invention also encompass displaying the obtained information, including the pre-therapy FFR, post-therapy-FFR, and functional gain in a format that is convenient and easily understandable to the physician. This may encompass displaying such information visually on a monitor or on a printed medium. The information may also be presented textually (using letters and/or numbers), graphically (e.g., bar graphs, pie charts, etc.), or a combination of the two. The display of such information is facilitated by systems of the invention, described in more detail below. 
     A visual display in accordance with the invention is provided in  FIG. 4 , which depicts FFR data in a visual format for display on a monitor. Subwindow  501  provides data from FFR measurements conducted before and after therapeutic intervention. An enlarged view of data presented in subwindow  501  is presented in  FIG. 5 . As presented, subwindow  501  provides pre-therapy FFR data (Pre-RCA Mid 0.75) and post-therapy FFR data (Post-RCA Mid 0.97). Although the therapeutic procedure performed here involved a stent delivery, the invention encompasses any therapeutic procedure, particular cardiovascular procedures. Additional exemplary therapeutic procedures include, without limitation, angioplasties, ablations, and excisions. Any therapeutic procedure may be performed and its effectiveness assessed using the methods provided herein. 
     As noted above, it is contemplated that certain aspects of the invention are particularly amenable for implementation on computer-based systems. Accordingly, the invention also provides systems for practicing the above methods. The system may comprise a processor and a computer readable storage medium instructions that when executed, cause the computer to determine a baseline measurement prior to conducting a therapeutic procedure and determine a post-therapy measurement after conducting the therapeutic procedure. The instructions may also cause the computer to compare the post-therapy measurement to the baseline measurement, thereby determining the degree of post-therapy improvement after conducting the therapeutic procedure. In further aspects, the system displays the various measurements and comparisons in a form that is ready understandable to the operator, for example, in a textual or graphical format. 
     A system of the invention may be implemented in a number of formats. An embodiment of a system  300  of the invention is shown in  FIG. 6 . The core of the system  300  is a computer  360  or other computational arrangement comprising a processor  365  and memory  367 . The memory has instructions which when executed cause the processor to determine a baseline measurement prior to conducting a therapeutic procedure and determine a post-therapy measurement after conducting the therapeutic procedure. The instructions may also cause the computer to compare the post-therapy measurement to the baseline measurement, thereby determining the degree of post-therapy improvement after conducting the therapeutic procedure. The physiological measurement data of vasculature will typically originate from an intravascular measurement device  320 , which is in electronic and/or mechanical communication with a sensing catheter  325 . Having collected the baseline measurement and post-therapy measurement, the processor then processes and outputs the results. The results are typically output to a display  380  to be viewed by a physician or technician. In some embodiments the display will include pre-therapy data, post-therapy data, and functional gain data that correlate the pre- and post-therapy data, as shown in  FIG. 4 . In certain embodiments, the displayed information is presented in a textual format as shown in  FIG. 5 . In other embodiments, the information may be presented in graphical format, like a pie chart or bar graph. 
     Data for calibrating the sensor is provided by pressure monitor  350 , which is typically an automatic aortic pressure monitoring system, such as commonly used during surgical procedures. In addition to outputting a display of pressure measured by the device, the monitor  350  also provides the measured range of pressures and/or traces to the computer  360  for calibration purposes. The pressure monitor  350  may communicate the calibration data to the computer with a wired connection, wirelessly, or through a network. 
     Systems of the invention may rely on the operator instructing the computer which measurement is the baseline measurement and which is the post-procedure measurement. Based on those instructions, the computer would then determine the functional gain achieved as a result of the procedure. It is contemplated that computers may one day be able to determine which measurements are which without operator intervention. For example, the software run by the computer may use coregistration to know that certain measurements were made at the same spot and are thus related. It is also contemplated that systems of the invention may integrate with the case log and determine that a measurement has been made in the same location immediately after stent deployment, and therefore assign a post-therapy designation to the measurement. 
     In advanced embodiments, system  300  may comprise an imaging engine  370  which has advanced image processing features, such as image tagging, that allow the system  300  to more efficiently process and display intravascular and angiographic images. The imaging engine  370  may automatically highlight or otherwise denote areas of interest in the vasculature. The imaging engine  370  may also produce 3D renderings or other visual representations of the physiological measurements. In some embodiments, the imaging engine  370  may additionally include data acquisition functionalities (DAQ)  375 , which allow the imaging engine  370  to receive the physiological measurement data directly from the catheter  325  or collector  347  to be processed into images for display. 
     Other advanced embodiments use the I/O functionalities  362  of computer  360  to control the intravascular measurement  320 . In these embodiments, computer  360  may cause the imaging assembly of catheter  325  to travel to a specific location, e.g., if the catheter  325  is a pull-back type. While not shown here, it is also possible that computer  360  may control a manipulator, e.g., a robotic manipulator, connected to catheter  325  to improve the placement of the catheter  325 . 
     A system  400  of the invention may also be implemented across a number of independent platforms which communicate via a network  409 , as shown in  FIG. 7 . Methods of the invention can be performed using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations (e.g., imaging apparatus in one room and host workstation in another, or in separate buildings, for example, with wireless or wired connections). 
     As shown in  FIG. 7 , the intravascular detecting system  320  facilitate obtaining the data, however the actual implementation of the steps can be performed by multiple processors working in communication via the network  409 , for example a local area network, a wireless network, or the internet. The components of system  400  may also be physically separated. For example, terminal  467  and display  380  may not be geographically located with the intravascular detection system  320 . 
     As shown in  FIG. 7 , imaging engine  859  communicates with host workstation  433  as well as optionally server  413  over network  409 . In some embodiments, an operator uses host workstation  433 , computer  449 , or terminal  467  to control system  400  or to receive images. An image may be displayed using an I/O  454 ,  437 , or  471 , which may include a monitor. Any I/O may include a monitor, keyboard, mouse, or touch screen to communicate with any of processor  421 ,  459 ,  441 , or  475 , for example, to cause data to be stored in any tangible, nontransitory memory  463 ,  445 ,  479 , or  429 . Server  413  generally includes an interface module  425  to communicate over network  409  or write data to data file  417 . Input from a user is received by a processor in an electronic device such as, for example, host workstation  433 , server  413 , or computer  449 . In certain embodiments, host workstation  433  and imaging engine  855  are included in a bedside console unit to operate system  400 . 
     In some embodiments, the system may render three dimensional imaging of the vasculature or the intravascular images. An electronic apparatus within the system (e.g., PC, dedicated hardware, or firmware) such as the host workstation  433  stores the three dimensional image in a tangible, non-transitory memory and renders an image of the 3D tissues on the display  380 . In some embodiments, the 3D images will be coded for faster viewing. In certain embodiments, systems of the invention render a GUI with elements or controls to allow an operator to interact with three dimensional data set as a three dimensional view. For example, an operator may cause a video affect to be viewed in, for example, a tomographic view, creating a visual effect of travelling through a lumen of vessel (i.e., a dynamic progress view). In other embodiments an operator may select points from within one of the images or the three dimensional data set by choosing start and stop points while a dynamic progress view is displayed in display. In other embodiments, a user may cause an imaging catheter to be relocated to a new position in the body by interacting with the image. 
     In some embodiments, a user interacts with a visual interface and puts in parameters or makes a selection. Input from a user (e.g., parameters or a selection) are received by a processor in an electronic device such as, for example, host workstation  433 , server  413 , or computer  449 . The selection can be rendered into a visible display. In some embodiments, an operator uses host workstation  433 , computer  449 , or terminal  467  to control system  400  or to receive images. An image may be displayed using an I/O  454 ,  437 , or  471 , which may include a monitor. Any I/O may include a keyboard, mouse or touch screen to communicate with any of processor  421 ,  459 ,  441 , or  475 , for example, to cause data to be stored in any tangible, nontransitory memory  463 ,  445 ,  479 , or  429 . Server  413  generally includes an interface module  425  to effectuate communication over network  409  or write data to data file  417 . Methods of the invention can be performed using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations (e.g., imaging apparatus in one room and host workstation in another, or in separate buildings, for example, with wireless or wired connections). In certain embodiments, host workstation  433  and imaging engine  855  are included in a bedside console unit to operate system  400 . 
     Processors suitable for the execution of computer program include, by way of example, both general and special purpose microprocessors, and any one or more processor of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, (e.g., EPROM, EEPROM, NAND-based flash memory, solid state drive (SSD), and other flash memory devices); magnetic disks, (e.g., internal hard disks or removable disks); magneto-optical disks; and optical disks (e.g., CD and DVD disks). The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, the subject matter described herein can be implemented on a computer having an I/O device, e.g., a CRT, LCD, LED, or projection device for displaying information to the user and an input or output device such as a keyboard and a pointing device, (e.g., a mouse or a trackball), by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well. For example, feedback provided to the user can be any form of sensory feedback, (e.g., visual feedback, auditory feedback, or tactile feedback), and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     The subject matter described herein can be implemented in a computing system that includes a back-end component (e.g., a data server  413 ), a middleware component (e.g., an application server), or a front-end component (e.g., a client computer  449  having a graphical user interface  454  or a web browser through which a user can interact with an implementation of the subject matter described herein), or any combination of such back-end, middleware, and front-end components. The components of the system can be interconnected through network  409  by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include cell networks (3G, 4G), a local area network (LAN), and a wide area network (WAN), e.g., the Internet. 
     The subject matter described herein can be implemented as one or more computer program products, such as one or more computer programs tangibly embodied in an information carrier (e.g., in a non-transitory computer-readable medium) for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). A computer program (also known as a program, software, software application, app, macro, or code) can be written in any form of programming language, including compiled or interpreted languages (e.g., C, C++, Perl), and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. Systems and methods of the invention can include programming language known in the art, including, without limitation, C, C++, Perl, Java, ActiveX, HTML5, Visual Basic, or JavaScript. 
     A computer program does not necessarily correspond to a file. A program can be stored in a portion of file  417  that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. 
     A file can be a digital file, for example, stored on a hard drive, SSD, CD, or other tangible, non-transitory medium. A file can be sent from one device to another over network  409  (e.g., as packets being sent from a server to a client, for example, through a Network Interface Card, modem, wireless card, or similar). 
     Writing a file according to the invention involves transforming a tangible, non-transitory computer-readable medium, for example, by adding, removing, or rearranging particles (e.g., with a net charge or dipole moment) into patterns of magnetization by read/write heads, the patterns then representing new collocations of information desired by, and useful to, the user. In some embodiments, writing involves a physical transformation of material in tangible, non-transitory computer readable media with certain properties so that optical read/write devices can then read the new and useful collocation of information (e.g., burning a CD-ROM). In some embodiments, writing a file includes using flash memory such as NAND flash memory and storing information in an array of memory cells include floating-gate transistors. Methods of writing a file are well-known in the art and, for example, can be invoked automatically by a program or by a save command from software or a write command from a programming language. 
     In certain embodiments, display  380  is rendered within a computer operating system environment, such as Windows, Mac OS, or Linux or within a display or GUI of a specialized system. Display  380  can include any standard controls associated with a display (e.g., within a windowing environment) including minimize and close buttons, scroll bars, menus, and window resizing controls. Elements of display  380  can be provided by an operating system, windows environment, application programming interface (API), web browser, program, or combination thereof (for example, in some embodiments a computer includes an operating system in which an independent program such as a web browser runs and the independent program supplies one or more of an API to render elements of a GUI). Display  380  can further include any controls or information related to viewing images (e.g., zoom, color controls, brightness/contrast) or handling files comprising three-dimensional image data (e.g., open, save, close, select, cut, delete, etc.). Further, display  380  can include controls (e.g., buttons, sliders, tabs, switches) related to operating a three dimensional image capture system (e.g., go, stop, pause, power up, power down). 
     In certain embodiments, display  380  includes controls related to three dimensional imaging systems that are operable with different imaging modalities. For example, display  380  may include start, stop, zoom, save, etc., buttons, and be rendered by a computer program that interoperates with IVUS, OCT, or angiogram modalities. Thus display  380  can display an image derived from a three-dimensional data set with or without regard to the imaging mode of the system. 
     INCORPORATION BY REFERENCE 
     References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. 
     EQUIVALENTS 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.