FR2490481A1 - Ultrasonic echograph for medical diagnosis of body organs - has transducer fixed to pantographic arm on which position sensors provide synchronised signals for display - Google Patents

Abstract

The pantograph (3) has two arms and is mounted on a base (4) to enable an ultrasonic probe (8) to be positioned over an organ in a body (1). Position sensors (5,6,7) enable instantaneous position data from the probe to be transferred to a data logging system (2) where it is processed for display on a screen (9). The probe is displaced manually along the skin on the body in the desired examination area and at the examination plane. The position sensors enable the probe movement under real or non real time conditions to be synchronised with the display by determination of the cartesian and angular coordinates from the probe position sensors.

Description

 The present invention relates to an ultrasound device for medical diagnosis. It uses the ultrasound technique and allows a better practice of the ultrasound examination.

 It is the examination according to the two-dimensional mode commonly called mode B or echotomography.

 It is known that this technique presents various easements.

Indeed, at the frequencies used, the air is absorbent, the bone is an obstacle.

 It follows that ultrasound allows the representation of anatomical images only of certain regions and certain organs, for example: soft but full organs: eye, neck, thyroid, breasts, heart, liver, spleen, vesicle biliary, pancreas, uterus, ovaries, fetus, bladder and superficially the limbs.

 This provided that these organs are not masked by bony or gaseous areas.

 Another constraint, derived from the absorption of air, is the necessary application against the skin, of the transducer transmitter and receiver of ultrasound, without air interface: we even add a fluid: oil or aqueous gel to improve acoustic contact.

 The art of the sonographer will consist in applying the probe containing the transducer with a view to targeting the organ (s) to be observed on a region of the skin forming an acoustic "window", that is to say free of obstacles such as bone, cartilage hard, or areas containing air.

 These "windows" are few and the sonographer will make the most of them by observing from the most open angle possible.

 In other words, the axis of the transducer will receive successively very variable angular orientations either automatically or manually in the case of observation through narrow windows.

 In the case of observation under larger windows, the angular variations are less, but the probe can be translated over a greater length to have a sufficiently wide and even very wide image.

 All ultrasound systems include one or more conductive trains whose position in space is identified by electro-mechanical devices (as well as the orientation of the acoustic propagation axis) relative to a provisionally fixed reference system.

 They include position sensors providing correlated electrical data which, when transmitted to a processing chain, make it possible to synchronize recording and display means generally comprising a television tube.

There are two types of ultrasound devices currently known:
1. Delayed 1 "devices using a single element probe, which is attached to a pantograph. This pantograph has a dual function: first, it allows the practitioner to select an examination plan; then, he ensures , at the joints of its elements, the emission of electrical signals characteristic of the geometric coordinates of the probe it carries, including its orientation.

 For example, these joints will be provided with sine-cosine potentiometers, or else digital coders.

 The transducer excited on emission by electrical pulses emits a beam of ultrasound in the direction of the main axis of the probe, through the patient's body. Any variation in the structure of the media crossed causes more or less intense echoes.

 These echoes are received by the transducer then operating as a receiver. Taking into account the time separating the emission from the reception, the position of the obstacle responsible for the echo is measured with precision.

 The received signal is transformed into an electrical signal which is studied in phase and amplitude by conventional means, enables image reconstruction to be carried out on conventional display means.

 2. The devices in "real time".

They do not include a pantograph, the reference system being the probe housing containing the transducer (s). They are divided into 2 categories according to the type of probe:
- phased array probes (themselves of 2 types)
- mechanical probes.

 Multi-element probes include several transducers assembled in a row and mounted on a backing fixed to the probe body.

The excitation of each transducer is determined by program according to two procedures specific to 2 subcategories of phased array probes:
- Linear scanning probes:
Construction much longer than wide, their length determines that of the anatomical cut observed. The contact surface with the skin is therefore significant. The excitation pulse generators of the transducers are successively switched on so that each transducer or each group of transducers in turn emits on its acoustic axis.

- Sectorial scanning probe:
More compact in construction, length and width are of the same order. The contact surface with the skin is small, like that of the monoelement probes.

 In a sector scan, the transducers all receive a train of pulses. But between each transducer and the transmission-reception chain is interposed an adjustable phase delay line which, in cooperation with other delay lines, simulates a plane wave whose propagation axis can be tilted at will, thus achieving a sector scan.

 The main advantage of phased array, linear or sector probes is the use of powerful microprogrammed means (microprocessors, digital memories, etc.). But they suffer from parasitic emissions in other directions than the scanning direction (problems of the side lobes). Mechanical probes are much less subject to these drawbacks. A transducer system comprising- at least one piezoelectric element emits an acoustic wave which mechanical means distribute in various directions around the axis of the probe, in a predetermined plane, by the position of the probe body.

 This comprises means for locating the angle made between its main axis and the instantaneous acoustic emission axis.

Thus the user currently sees advantages and limitations to the 2 main types of ultrasound systems in B mode:
- "Delayed time" devices with small transducer. The practitioner applies the probe to the patient's skin and prints movements in the plane of the pantograph.

 These movements are of 2 types: angulation to obtain a sectorial image through small anatomical windows, ie outside the bony walls or gaseous regions; translation to obtain an image on a fairly wide section from the surface, possibly a complete section of the trunk.

 Practically these two movements are more or less simultaneous and require from the operator a certain skill which he acquires by a fairly long training.

 The formation of a cut is done in 2s 1 or 2 seconds, so that the moving organs are not visible (kinetic blurring).

 Several prior cuts are necessary before the diagnosis.

 For these reasons a complete examination is quite long and therefore expensive (w hour to 314 hour).

 - The devices in "real time" include a fast probe which provides an instant image by simply placing the probe on the patient. We can therefore also visualize the moving organs (echoscopy). Currently we get frame rates of 20 to 50 frames per second, if necessary beyond.

 We then observe the heart, even that very fast of the young fetuses and generally all the more or less mobile organs for various causes (repercussion of the cardiac activity, respiration, movements of the patient or of the practitioner's hand).

 In summary, we get rid of kinetic blur. The major drawback is the small size of the sections obtained, so that certain organs are not seen completely (liver, developed fetus) and that one does not obtain a section complete enough to see several organs simultaneously, with their relationships between them.

 Linear scanning probes give rectangular images. Sector scanning probes give triangular or trapezoidal images. It has been proposed to mount a linear element phased array probe on a pantograph, to allow both rapid cuts and extended cuts (see for example French patent application 76/167 44 published under the number 2.353.370). However, such an arrangement has the drawback of not allowing precise examinations through narrow windows, since such a linear bar probe has too long a contact length with the skin.

 The present invention provides a remedy to all these drawbacks of the prior art.

 That is to say, it reconciles the following advantages: images in real time, without kinetic blurring, image under variable incidences possibly very inclined through narrow anatomical windows, image extended in possibly very wide sections, very manipulation easy for the practitioner who is freed from the pivoting movement ensured automatically by the sectoral probe and mainly ensures only the translational movement manually.

 The present invention provides a remedy to these various drawbacks of the prior art. Indeed, it relates to an ultrasound device intended for medical diagnosis, which comprises an ultrasonic probe mounted on a pantograph, the probe being connected to a transmission-reception chain which cooperates with signal processing means intended to control means of writing on display means, the probe and the pantograph being provided with means for detecting the instantaneous position and orientation of the beam of ultrasonic waves which control means for synchronizing the writing means; and is characterized in that the probe is of the sectoral scanning type and in that the various coordinates representing the position and the orientation of the ultrasonic beam coming from both the probe and the pantograph are added, the sectoral exploration plan being identical or parallel to the plane of the pantograph.

The invention will be better understood using the description of the appended figures which are:
FIG. 1: an ultrasound diagram of the "deferred time" type,
FIG. 2: a diagram of a sectoral scanning probe,
- Figure 3: an example of ultrasound examination according to the invention.

 In FIG. 1, which illustrates the so-called "delayed-time" technique, a cross section 1 of the human body has been shown which one seeks to visualize on the data entry assembly 2. The pantograph 3 is mounted on a base 4 linked to the ground and comprises two arms and position sensors 5, 6 and 7 which determine the position and orientation of the probe 8. The signals which pass through a cable.

are processed in the data entry set 2 and displayed on screen 9.

 To obtain an image, the doctor chooses a cutting plane or examination plane 1 by orienting the base 4 of the pantograph 3. The probe 8 can then be moved along the patient's skin in the examination plane and be rotated according to different incidences. The doctor can thus enrich the image as and when he registers on the screen 9.

 In Figure 2, there is shown a mechanical probe. It comprises in a body 10, a support member 14 movable in rapid rotation by a motor not shown. This support member 14 supports for example three transducers 11-13 distributed in such a way that there is always an ultrasonic beam passing through the diaphragm 19 of the probe. There is shown the axis 17 of the probe, the two extreme axes 15 and 18 of the sector scanning and the instantaneous acoustic axis 16 of emission from the transducer 12 which is in the emissive field of the probe. The representation of FIG. 2 is given by way of nonlimiting example. The probe can be rotatable with any number of elements. The probe can be oscillating. The probe can be fixed with an oscillating or rotating mirror.

 In FIG. 3, there is shown a section of a body lengthwise 20.

The probe has been shown in four successive positions. According to the invention, this sector scanning probe is mounted on a pantograph and can be moved manually. The probe, which has a small contact surface, can therefore be of the multi-element type as well as of the mechanical type. The sectors dotted on each position of the probe correspond to the sector automatically scanned for a mechanical position of the probe.

 In position 21, the probe emits in a narrow anatomical window between two bones 26, 27. This window looks onto an organ 25 of which it is possible to make a representation thanks to the small surface of the probe. The doctor moves the probe to position 22 by providing it with a certain manual angulation up to position 23. It can be seen in FIG. 3 that it is thus possible by the three scanned sectors to completely cover the member 25.

 To continue a long cut along the vein 28 to the organ 29, the doctor can move the probe continuously to position 24.

 The particular advantage of the pantograph probe assembly is that it allows a perfect transformation between examination section and image, each position of the probe being identified by position sensors on the pantograph and each position of the beam can be identified by means of detection of the angle made between the instantaneous acoustic axis 16 with the axis 17 of the probe, this axis being of orientation known by the pantograph sensors. To synchronize the recording means of the display means such as the screen 9, it suffices to add the Cartesian and angular coordinates supplied on the one hand by the probe and on the other hand by the pantograph.

 The probe, mounted on a pantograph, can advantageously be provided with beam focusing means. This allows for precise examination as is known elsewhere. The focusing means also cooperating with the means for synchronizing the writing means, for example on the screen 9 by determining exactly the point of impact of the writing beam.

 Various improvements can be made to the invention making it benefit from digital electronic computing means such as, for example, memories for freezing the image on a screen without persistence.

It is thus possible for the doctor to carry out three types of examination:
- an examination in deferred time with a sectorial scanning probe in the locked position, making it possible to make slow and determined acquisition by the doctor of image information, (as with a conventional device in "deferred time" with single element probe and pantograph),
- an automatic examination in real time of a quasi-fixed point, even by reduced anatomical windows, allowing a sectorial image,
- a compound examination, the doctor scanning the chosen examination section himself with the sectoral scanning probe allowing an image that is both extensive, precise and under great incidence even by narrow windows and without kinetic blurring even on organs with fast movement.

Claims (3)

 1. Ultrasound apparatus for medical diagnosis, which comprises an ultrasonic probe (8) mounted on a pantograph (3), the probe (8) being connected to a reception transmission chain which cooperates with signal processing means intended to control recording means on display means (9), the probe (8) and the pantograph (3) being provided with detection means (5-7) of the instantaneous position and orientation of the beam of ultrasonic waves which control means of synchronization of the recording means, characterized in that the probe is of the sector scanning type and in that the different coordinates representing the position and the orientation of the ultrasonic beam coming from both the probe that of the pantograph are added.  2. Apparatus according to claim 1, characterized in that the probe (8> is of the transducer multi-element type.  3. Apparatus according to claim 1, characterized in that the probe (8) is of the type with mechanical scanning