What about the speed of sound in different frames

EP1987774A1 - Measurement of sonographic speed of sound using a marker device - Google Patents

Measurement of the sonographic speed of sound using a marker device Download PDF

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Publication number
EP1987774A1
EP1987774A1EP07107418AEP07107418AEP1987774A1EP 1987774 A1EP1987774 A1EP 1987774A1EP 07107418 AEP07107418 AEP 07107418AEP 07107418 AEP07107418 AEP 07107418AEP 1987774 A1EP1987774 A1EP. 1987774 A1EP1987774A1EP
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European Patent Office
Prior art keywords
data
marker
ultrasound
reflection
sonography
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EP07107418A
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English (en)
French (fr)
Inventor
Fritz Vollmer
Ingmar Thiemann
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Brainlab AG
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Brainlab AG
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Publication of EP1987774A1publicationCriticalpatent / EP1987774A1 / de
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Classifications

    • A — HUMAN NECESSITIES
    • A61-MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B-DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8 / 00 — Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8 / 08 — Detecting organic movements or changes, e.g. tumors, cysts, swellings
    • A61B8 / 0833 — Detecting organic movements or changes, e.g. tumors, cysts, swellings involving detecting or locating foreign bodies or organic structures
    • A — HUMAN NECESSITIES
    • A61-MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B-DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B34 / 00 — Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
    • A61B34 / 20 — Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
    • A — HUMAN NECESSITIES
    • A61-MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B-DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8 / 00 — Diagnosis using ultrasonic, sonic or infrasonic waves
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    • A61B8 / 0875 — Detecting organic movements or changes, e.g. tumors, cysts, swellings for diagnosis of bone
    • A — HUMAN NECESSITIES
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    • A61B8 / 42 — Details of probe positioning or probe attachment to the patient
    • A61B8 / 4245 — Details of probe positioning or probe attachment to the patient involving determining the position of the probe, e.g. with respect to an external reference frame or to the patient
    • A — HUMAN NECESSITIES
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    • A61B2034 / 2055-Optical tracking systems
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    • A61B34 / 25 — User interfaces for surgical systems
    • A61B2034 / 256 — User interfaces for surgical systems having a database of accessory information, e.g. including context sensitive help or scientific articles
    • A — HUMAN NECESSITIES
    • A61-MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B-DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90 / 00 — Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1 / 00 - A61B50 / 00, e.g. for luxation treatment or for protecting wound edges
    • A61B90 / 36 — Image-producing devices or illumination devices not otherwise provided for
    • A61B90 / 37 — Surgical systems with images on a monitor during operation
    • A61B2090 / 378 — Surgical systems with images on a monitor during operation using ultrasound
    • A — HUMAN NECESSITIES
    • A61-MEDICAL OR VETERINARY SCIENCE; HYGIENE
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    • A61B8 / 0808 — Detecting organic movements or changes, e.g. tumors, cysts, swellings for diagnosis of the brain

Abstract

Description

  • The present invention relates to the measurement of the speed of sound of the ultrasound which is used for sonography (also echography). In particular, the speed of sound is to be measured in an anatomical body structure in which the ultrasound can propagate. Examples of such body structures (of a person or animal) are in particular water-containing body structures, for example soft tissues, tissues, liver, internal organs, in particular the brain or extremities.
  • In sonography, the evaluation of the measurement data, in particular for scaling an ultrasound image, is based on a speed of sound that is assumed to be the same for all body structures regardless of the specific body structure. Since the speed of sound is included in the determination of distances determined by means of sonography, an incorrect assumption about the speed of sound can lead to incorrect distance determinations, in particular incorrect scaling of sonographic images.
  • The object of the invention is to improve the determination of the speed of sound.
  • The above problem is solved by the subjects of the independent claims. Advantageous further developments emerge from the dependent claims.
  • According to the invention, the speed of the ultrasound is measured, the ultrasound being transmitted and detected by a sonography device. The sonography device can be designed "in one piece", i.e. it can have a combined transmitter and receiver, in particular an ultrasound probe which sends and receives ultrasound waves. In this sonography device, referred to herein as "one-piece", in particular the location where the ultrasonic waves leave the sonography device and the location where they are received by the sonography device for detection coincide or the aforementioned two locations have a fixed, predetermined, in particular unchangeable relative position to each other. The latter can be the case, for example, if the transmitter and detector are located next to one another in the head of an ultrasonic probe. The invention also relates to a sonography device in which the aforementioned two locations do not coincide and the relative position of the two locations to one another can be changed. This sonography device is referred to herein as a "two-part" sonography device. The two-part sonography device comprises a first location for emitting the ultrasound in a first part of the sonography device (ultrasound transmitter) and a second location, which is spatially separated from the first, for receiving the ultrasound in a second part of the sonography device (ultrasound receiver), both parts being relative are movable to each other, so that the relative position between the two locations is variable. In particular, the body structure to be examined lies between the ultrasound transmitter (first part) and the ultrasound receiver (second part) of the two-part sonography device. The sonography device referred to herein as one-piece works as follows: It emits ultrasound waves that pass through a body structure, are then reflected, again pass through the body structure and are then detected by the one-piece sonography device (the ultrasound probe). The reflection can take place on a part of the body structure (reflection part) which results in an ultrasound reflection. An example of this would be a bone structure. The reflection results from the changing propagation properties of the ultrasound when the ultrasound wave reaches the reflection part. In other words, the reflection takes place at the interface between the upstream body structure (in the direction of propagation of the ultrasound) and in the reflection part. As far as a reflection at the reflection part is spoken of here, the reflection at the aforementioned interface is meant. The reflection takes place when the ultrasonic wave reaches a transition between two different materials (with different ultrasonic propagation properties). One example is the transition from tissue to bone. The reflective part should, however, have the property that it does not absorb ultrasound, as is the case, for example, with air-filled cavities (intestines).
  • The reflection can take place on a bone structure but also on a non-body part, for example on a plate that reflects ultrasound, the body structure to be examined being arranged between the plate and the ultrasound probe. The above terms "one-part" and "two-part" do not exclude that the sonography device comprises more than one or two parts, e.g. in addition to the transmitter and receiver, also a monitor and a computer.
  • The method according to the invention comprises in particular the following steps: Data are preferably provided which relate to the reflection of the ultrasound and which are referred to below as “reflection data”. The reflection data contain information about the position of the reflection part relative to a reflection marker device. The reflection marker device is a marker device which has a fixed spatial relationship to the reflection part, that is to say, for example, is firmly connected to the reflection part. The marker device can be designed to be active or passive, i.e. actively emitting rays or waves or passively reflecting them. Examples of waves or rays are light, in particular infrared light or sound waves. The marker device can in particular comprise reflective spheres which are in a fixed spatial relationship to one another.
  • Furthermore, data are preferably provided which relate to the location of the transmission and reception of the ultrasonic waves and are referred to below as “location data”. The location data describe the relative position of a sonography device marker device to an output location and a receiving location for the ultrasonic waves. The sonography device marker device is a marker device (in particular as described above) which, in particular, has a fixed relative position relative to the sonography device, in particular is firmly connected to the sonography device. In particular, the relative position between the location at which the ultrasonic waves are emitted from the sonography device is fixed relative to the sonography marker device. In particular, the relative position between the receiving location of the ultrasonic waves and the sonography device marker device is fixed.
  • Furthermore, data are preferably provided which relate to the position of the marker devices. These data are referred to herein as "marker data". The marker data describe the relative position of the sonography marker device relative to the reflection marker device.
  • Further data relating to the running time are advantageously provided. This data is called "runtime data". The transit time data describe the transit time of the sound wave from the point of origin to the point of reception.
  • The path of the sound wave from the point of origin to the place of reception, in particular the length of the path, is the path from the place of origin to the place where the ultrasonic wave is reflected and from there to the place of reception. This path length covered by the ultrasonic wave is preferably calculated based on the reflection data, the location data and the marker data.
  • If the path length is known, the speed of sound of the ultrasound can be determined using the transit time described by the transit time data. More precisely, it is the mean speed of sound that the sound wave has during its travel time. If the body structure that is permeable to ultrasound is heterogeneous in terms of the speed of sound, the determined speed of sound can deviate locally from the actual speed of sound.
  • The reflection part can have an extended area, so that the ultrasonic waves traveling along the aforementioned path can potentially be reflected at different locations of the reflection part. In order to be able to determine the path length from the point of origin of the ultrasonic waves to the point of reflection and from there to the point of reception, the point of reflection is preferably based on information about a surface of the reflection part where the sound waves can be reflected and information about the direction of propagation of the sound wave determined by the starting point. The point of intersection between the sound wave propagating from the starting point in the known direction along a propagation line and the surface of the reflection part thus represents the reflection point.
  • As an alternative to the aforementioned determination of the location of the reflection or in addition to the aforementioned determination, the location of the reflection can also be determined according to the principle of angle of incidence equal to the angle of reflection for a given area of ​​the reflection part, in particular if the starting location does not match the receiving location.
  • If the reflection part is outside the body of a patient, the reflection data can be determined simply, e.g. by scanning, scanning or optical detection of the reflection part in order to determine the position of the reflection part relative to the reflection marker device. If the reflection part is inside the patient's body, i.e. if it is, for example, a bone structure, in particular a skull bone, the reflection data is preferably determined by means of a medical analysis method that uses waves or rays in particular to obtain scaled information about the position or position to gain spatial distribution of components of a body structure. In particular, X-ray analysis methods (such as CT or X-ray images or fluoroscopy images, in particular 3D images reconstructed from this X-ray analysis method) or magnetic resonance images (NMR, differential NMR, etc.) are used. The analysis is preferably carried out with the marker device attached to the patient's body. The marker device is preferably designed in such a way that it can be detected both by the analysis device and by a marker detection device (e.g. camera or sensor that responds to reflected waves or rays). For example, marker spheres are used that reflect light and contain a metal core that can be detected in the X-ray machine. The marker spheres are preferably firmly connected to the bone structure. For example, a ball holder is screwed into the bone structure.In this way, the relative position of the reflection marker device can be determined relative to the components of the body structure, in particular relative to a part of the body structure (e.g. bones) on which the sound waves are potentially reflected. The information about the position of the aforementioned surface of the reflection part includes, in particular, information about the extent and / or course of the surface. In particular, the surface (and its course) can be described by a mathematical function in order to determine the aforementioned point of intersection between the propagation line and the reflection surface.
  • In the medical analysis method mentioned above for determining the position of a reflective body structure in order to determine the reflection data, an analysis method is preferably used that is not sonography, i.e. in particular no ultrasound waves are used, so that the analysis data obtained are not depend on the speed of sound of the ultrasound.
  • As already stated above, the sonography device can also be in two parts. In this case too, the path of the ultrasonic waves from the point of origin to the point of reception can run via a reflection part. Usually, however, this will not be the case with the two-part sonography device, but rather the ultrasound passes through the body structure starting from the starting point and then hits the receiving part of the sonography device. In the latter case, the path is determined by the distance between the starting point and the receiving point. In the first case, it is calculated as has already been explained above with regard to the one-piece sonography device.
  • In the two-part sonography device there are in particular two separate marker devices for the sonography device, namely a receiver marker device which has a fixed relative position to the receiving location of the ultrasonic waves and is attached in particular to the receiving part of the sonography device, and a transmitter marker device which has a fixed relative position has to the starting point of the ultrasonic waves and is attached in particular to the transmitting part of the sonography device. By determining the position of the transmitter marker device and the receiver marker device and based on the aforementioned known relative position between the transmitter marker device and the starting point and the receiver marker device and the receiving location, the distance between the starting location and the receiving location can be determined by detecting the marker device. This also determines the length of the path that the sound wave travels.
  • Medical analysis methods, in particular those already mentioned above, are preferably used in order to obtain information about the body structure to be examined or examined with sonography. In particular, these medical analysis methods are preferably used to identify different types of body structures in the case of a heterogeneous body structure and, in particular, to determine their extent and / or position, in particular relative to a marker device (e.g. reflection marker device).
  • A database is preferably also provided which assigns different types of parts of the body structure to different speeds of sound of the ultrasound. The speed of sound can differ in different types (e.g. blood or tissue). While the different types of body structure are recognized by means of Kemspin, for example, and their position and extent are determined, the speed of sound can be assigned to the individual types so that, in particular, a spatial distribution of the ultrasound speed in the body structure can be determined. This spatial distribution can then be calibrated by determining the ultrasonic speed according to the invention. The calibration can be designed in such a way that the mean speed of sound is adapted by the body structure to that determined according to the invention. This can be done, for example, in such a way that a mean speed of sound (based on the database) (database speed of sound) is determined, as would result from the stored data and the medical analysis along the sound path. This value is compared with the (measured) speed of sound determined according to the invention, which represents a mean value along the measuring path. The sound velocity values ​​resulting from the database for the individual areas of the body structure are then raised or lowered, for example by a certain percentage, until the mean database sound velocity matches the measured mean sound velocity. In this way, a calibrated spatial distribution of the speed of sound in the body structure has been achieved. This spatial distribution can then be used to further increase the accuracy of the scaling of the ultrasound image.
  • Another example of different types of body structures are healthy and diseased tissue, for example healthy areas of the brain and a brain tumor. If one takes into account the different speed of sound applicable in each case in the different body structure types and then calibrates this according to the method described above on the basis of the measurement of the mean speed of sound, the accuracy of the scaling can be further increased. As a medical analysis method for typing the body structure and spatially resolved measurement and position determination, in addition to the medical analysis methods mentioned above by way of example, sonography in particular can also be used.
  • The present invention is also directed to an apparatus which in particular comprises a data processing device. The data processing device is designed to process the aforementioned data in the aforementioned manner. In particular, the device comprises an input means for inputting the data to be processed. Furthermore, the device preferably comprises a sonography device, which is used in particular to determine the transit time data. A detection device, for example a camera, is preferably also provided, which is designed to measure signals.
  • The device according to the invention can furthermore comprise a medical analysis device, such as an NMR device or a CT device, for example, the measurement data being transmitted to the data processing device.
  • The present invention is further directed to a program which carries out a method according to the invention when it runs on a computer. The data to be processed by the program are transmitted to the program in the usual way. The data can be transmitted to a computer, for example via conventional input means, such as a keyboard or interfaces to data memories (e.g. drive for optical disc) or databases or the Internet.
  • In the following detailed description, further advantages and features of the invention are disclosed. The figures show the following:
    • shows the ultrasound measurement on a brain.
    • shows the principle of ultrasonic velocity measurement.
    • shows the measurement with a two-part sonography device.
    • shows the structure of a device according to the invention.
  • In particular, the present invention enables the mean speed of sound to be determined in a body structure, for example in the living brain or in other body structures. The body structures can be homogeneous or heterogeneous. In the case of heterogeneous body structures, additional data material from medical analysis facilities is preferably used (see above). In the following, it is assumed that the body structure to be examined is a homogeneous tissue. In particular, another type of body structure can adjoin this homogeneous tissue which differs in terms of its ultrasound propagation properties in such a way that it leads to a reflection. For example, the tissue can be partially surrounded by bone, as is the case with the brain.
  • The position of the sonography device, in particular the transmitter and receiver or the ultrasound probe, is preferably monitored by means of a navigation device. For this purpose, marker devices such as reference stars are preferably attached to the transmitter, receiver and / or ultrasound probe so that navigation of the ultrasound probe is possible, as is customary in particular with IGS (Image Guided Surgery). In particular, it is possible to measure the position of the transmitter, receiver and / or ultrasound probe by means of a detection device, which is in particular part of a navigation device.
  • The ultrasonic measurement takes place, for example, in the so-called A-mode or B-mode. Several ultrasound scans are preferably carried out in order to increase the accuracy of the measurement data. In addition to the ultrasound measurement, another medical analysis device is preferably used, in particular to determine the above-mentioned reflection data and / or body structure data. For example, a CT or MRI is used here. The data obtained by means of the medical analysis device are preferably analyzed. The analysis can be carried out manually, for example by a doctor, or automatically. The analysis is aimed at recognizing types with different ultrasound properties, in particular different echogenicity, and in particular determining their position relative to markers and / or relative to homogeneous, ultrasound-permeable tissue.
  • If one obtains a value for the speed of sound cs of the ultrasound, it can be used to correct the ultrasound setting of the sonography device. Usually a sonography device (ultrasound device) uses a fixed value of 1540 m / s for cs. This value can be corrected in the aforementioned manner in order, in particular, to scale the ultrasound images more precisely and to be able to determine distances more precisely by means of ultrasound. In particular, a higher accuracy is achieved in navigated sonography (ultrasound imaging technology).
  • Usually it is assumed that the speed of sound of the ultrasound in a tissue corresponds to an average value, as it is given in a healthy tissue or a tissue with a defined change (e.g. fatty liver). However, some diseases change the ultrasound speed, for example by increasing the amount of water in the tissue (for example in cysts or in compressed tissue (e.g. hyperdense tumors). The speed of sound changed, for example, by changing the water content, if it is unknown, can be measured by the present invention and In particular, a database can be filled with the data measured in this way, ie with data for the ultrasound speed, which depend on the respective type of body structure and are specific for this type the examined body structure can be used, for example, by determining the database speed of sound.
  • In particular, the invention allows in vivo measurements of the speed of sound, e.g., in the brain or other body structures of a patient. As explained above, the value for the speed of sound, which is fixed in the prior art, can be corrected in order to increase the accuracies. In this way, the accuracy in navigation, e.g. of an instrument or an implant, can be increased and the scaling and length measurement in ultrasound images can be improved.
  • Since the measurement according to the invention allows the determination of the ultrasound speed, a conclusion about the properties of the body structure can also be drawn in this way. If, for example, a speed of sound that differs from healthy tissue is measured, it can be concluded that there is a disease. For example, a tumor can be detected or changes in the speed of sound property of the tumor can be determined in order to detect a possible malignant change in the tumor.
  • The principle of ultrasonic measurement is as follows. The mean speed of the ultrasound through a body structure results from the distance covered by the ultrasound divided by the time (transit time) that the signal needs to cover the distance. For example, if the ultrasound requires the time t to get from an ultrasound probe 10 (see) to a bone structure 20, which is an example of a reflection part, and if the ultrasound is reflected by the bone structure 20 and then measured again by the same ultrasound probe 10, for a distance between the probe and the reflecting bone structure d, the speed of sound c is calculateds as follows:
  • In order to determine the path length that the ultrasound travels from the probe head to the bone, a navigation system is preferably used which detects the position of the marker devices 30 and 40. In addition, data are used from which the position of the bone structure relative to the marker device 40 results. For this purpose, CT data, for example of the head, are preferably used, the marker device 40 being recorded by the CT image. The distance between the reflective part of the bone structure 20 and the head of the ultrasonic probe 10 is denoted by d in FIG. The ultrasonic wave traveling back and forth between the head and the reflective part is indicated by a black line with arrows. The brain 50 is shown hatched.
  • The position of the reflective part of the bone structure 20 can be determined by a doctor and input into the device according to the invention as input data. This position can also be determined automatically by determining the direction of the sound waves from the position of the ultrasound probe. The place of reflection is where a line running in this direction intersects with the bone structure. The relative position of the ultrasound probe 10 relative to the bone structure 20 results, as explained above, from the detection of the marker devices 30 and 40. In this way, the data (analysis data) from the medical analysis method (in the case of ultrasound is not used but e.g. X-ray) compare with the ultrasound data. For this purpose, bone structures are preferably automatically recognized by segmentation (structure recognition method) in the CT image.
  • Preferably, at least some of the following circumstances exist in order to determine the ultrasound speed, for example by means of analysis data (e.g. CT data), in particular with the one-piece sonography device:
    • The registration of the patient data (analysis data) in a reference system (for example the reference system of a navigation system) is possible.
    • The medical analysis data (data that were not obtained by means of ultrasound) enable the bony structure of the body to be identified, on which ultrasound waves can be reflected. This detection can take place automatically or manually (e.g. by the doctor).
    • The tissue between the ultrasound head and the bone is preferably homogeneous, so that the determined mean ultrasound speed is meaningful.
    • The tissue examined with ultrasound is surrounded by a bone structure or at least partially adjoins a bone structure, so that the ultrasound can be reflected back to the probe head.
    • The distance to the bone (or to another structure, in particular a rigid structure on which an ultrasound is reflected) can be achieved by the ultrasound waves. This means that the probe head is sufficiently dimensioned, in particular with regard to power and frequency, so that the waves arrive at the reflecting structure and can be reflected there.