EP1558147A1

EP1558147A1 - Pressure measuring unit for ultrasound measuring devices

Info

Publication number: EP1558147A1
Application number: EP03750234A
Authority: EP
Inventors: Ulrich André Baumann
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-28
Filing date: 2003-10-23
Publication date: 2005-08-03
Also published as: WO2004037091A1; AU2003269669A1; EP1415596A1

Abstract

The invention relates to a pressure measuring unit (5) for coupling to an ultrasound measuring head (7), said unit comprising a housing having a rear window consisting of a rigid, ultrasound-permeable material, e.g. PTFE with a maximum thickness of 1 mm, and a front opening which is sealed by a membrane consisting of a silicone elastomer, preferably having a thickness of between 0.4 and 0.5 mm. The inner region is filled with an ultrasound-permeable liquid, especially a glycerine-water mixture. The inventive pressure measuring unit can be used to carry out the known ultrasound measurements on organisms, with measurement of the bearing pressure.

Description

Pressure measuring device for ultrasonic measuring devices

The present invention relates to a pressure measuring device for performing ultrasound measurements on living beings, in particular humans, according to the preamble of claim 1. Furthermore, it relates to an ultrasound measuring device with such a device and uses of the pressure measuring device and the ultrasound measuring device.

In diagnostic ultrasound examinations, a commercial transducer is placed on the person to be examined using a contact gel, e.g. the skin of the abdominal wall. Commercially available equipment is used to generate an image from the signal emitted in the transducer and received again by reflection, which e.g. in medicine, the representation of organs and tissues lying deeper and hidden from the eye is permitted.

The use of pressure on the transducer to characterize pressure-related tissue and vascular changes is well established (e.g. nominal compressions for thrombosis diagnosis). However, the pressure on the ultrasonic measuring head and thus the contact surface was applied by the user in a purely emotional manner. The pressure exerted on the tissue / organ system to be examined during the ultrasound examination in medicine obviously differs from examiner to examiner and depends on his level of training and his experience.

To better display vascular structures, Doppler procedures are also used in medicine, which necessitate expensive additional equipment for commercial ultrasound devices. Such an arrangement is known from US-A-6 086 533. A bubble is placed in front of an ultrasonic measuring head. The bladder is filled with an acoustically permeable liquid. The whole arrangement is built into a cylindrical housing, at one open end of which the bladder is accessible. If the arrangement is placed on the skin, the contact pressure can be determined by measuring the internal pressure of the bladder, and an ultrasound signal can be radiated through the bladder into the tissue and the echo can be evaluated.

Practical tests with such arrangements have shown, however, that the spatial resolution of the ultrasound measuring heads customary in medicine is regularly severely impaired or becomes unusable by the provision of such a pressure measuring device.

An object of the present invention is to provide a pressure measuring device for an ultrasound measuring head which has less of an adverse effect on the measuring properties of the ultrasound measuring head.

Such a device is specified in claim 1. The other claims give preferred training,

Ultrasonic measuring devices with it and applications.

Accordingly, the pressure measuring device essentially consists of a rigid housing, for example in the form of a flat hollow cylinder. A rigid membrane is embedded on the back, which is used for coupling to the ultrasonic measuring head. The front is closed with a flexible membrane. The interior is filled with an ultrasound-permeable liquid as completely as possible, ideally free of bubbles. It has been shown that in particular the flexible membrane, which is applied to the body surface of the patient, but also the rigid membrane have a strong influence on the quality of the ultrasound images and, in particular, their spatial or two-dimensional resolution.

In the case of the rigid membrane, a sufficiently small thickness should be chosen in particular.

For the flexible membrane, the most suitable material in series tests was silicone, i.e. a silicone elastomer.

The liquid must generally be ultrasonically transparent. In general, water-containing liquids and in particular glycerol-water mixtures have proven successful. The liquid layers to be traversed by ultrasound should also be kept as thin as possible.

The pressure measuring device according to the invention is used for the first time in the examination of pressure-dependent changes in the tissue of a patient, the examining person also being provided with the usual ultrasound images and information derived therefrom in addition to the pressure data.

The device according to the invention is also used in training: as is known, the ultrasound technique of the individual examiner differs individually. With the device, these different examination techniques / contact pressures of the transducer can be harmonized during training or when comparing results and / or trainees can learn the correct transducer contact pressure right from the start. The contact pressure of the ultrasound head on the skin also plays a major role when assessing the blood flow to tissues. If the impression is too strong, the

Blood flow to the underlying tissue. This is particularly important when characterizing tumors using modern ultrasound contrast agents. In order to achieve comparable results, the contact pressure on the skin must be standardized. This is essentially only possible through a diameter.

Furthermore, it is conceivable that, by means of simple quantifiable statements with the presented invention, expensive additional examinations such as color duplex are no longer necessary or only have to be used in a targeted manner.

The invention will be further explained using exemplary embodiments with reference to figures. Show it:

Fig. 1: Schematic of an ultrasonic measuring head with pressure measuring device in side view;

2: a rear view of the pressure measuring device;

3 shows a section according to III-III in FIG. 2; and

4: an ultrasound recording of an ultrasound measuring head with a pressure measuring device according to the invention.

The exemplary embodiment according to the invention is characterized in that the contact pressure, ie the directed force 1 of the ultrasound head 2 on the tissue 4 (for example the skin of a person), is quantitative during the examination is measured and displayed. For this purpose, a sound-permeable pressure measuring device in the form of a measuring capsule 5 is coupled to a commercially available transducer 7. It is also conceivable for the pressure measuring device to be integrated into the transducer. The size and shape of the measuring capsule 5 can be varied depending on the application and task. In addition to the fixed coupling or constructive integration on or in the transducer, various couplings to known transducers are conceivable. As a rule, between the pressure measuring device and the

Ultrasound head also applied a gel 8 to improve the coupling.

Various measurement solutions are possible within the scope of the invention, such as a pressure measurement by commercial pressure transducers in the liquid located between the transducer and the support membrane, pressure change in the support membrane, etc.

The arrangement of a pressure measuring cell or a pressure sensor in the measuring capsule offers the particular advantage that long, liquid-filled lines from the measuring capsule to the measuring device are no longer necessary. Such lines are bulky compared to electrical lines and, if broken, lead to the system having to be refilled.

In the exemplary embodiment, the liquid 11 in the interior of the measuring capsule 5 for the pressure measurement is connected via a line 12 to a pressure measuring device (not shown). Suitable pressure measuring devices are known per se and are therefore not described. Ideally, the liquid must be completely transparent for ultrasound. A glycerin-water mixture in a mass ratio of 85:15 has proven itself. The measuring capsule 5 is closed by a flexible, ultrasound-permeable membrane 13 on the side, which serves to rest on the tissue 4.

Practical tests have shown that the material and the design of this membrane have a major influence on the quality of the ultrasonic measurement. In numerous tests, silicone elastomer was found to be suitable, preferably the type MVQ (international code), which is characterized by the following data: hardness 50 ° Shore A density 1.15 g / cm ³ appearance milky transparent The thickness of the membrane should also be as small as possible be, for example 0.4 to 0.5 mm, the material MVQ could easily be used with a thickness of 1 mm. Smaller thicknesses would be an advantage, but are easier to damage. By contrast, thicker membranes, in particular thicker than 3 mm, impair the ultrasound measurement result 13 too much.

As usual, a gel 17 is also applied between the membrane and the tissue surface 15 in order to improve the ultrasound coupling.

A window 20 is embedded in the rear side 19 of the measuring capsule 5. The window 20 consists of an ultrasound-permeable material, which preferably has a low flexibility. When the ultrasound head 7 is placed on the back 19, the membrane can thus adapt somewhat to the shape of the forehead 22 of the measuring head, which is often more or less rounded. Teflon ^® (polyfluoroethylene, Du Pont) has a thickness of 0.5 for the window up to 0.7 mm proved to be suitable. A significant deterioration in the quality of the ultrasound measurement was observed from a thickness of 1 mm, and the measurements were practically unusable from a thickness of 3 mm.

For a better adaptation to the forehead 22 of the measuring head 7, the window can also be curved as shown in FIG. 3.

The window 20 and the membrane 13 are held in a frame 24 made of metal. The basic principle is that all the housing components of the measuring capsule 5, apart from the membrane 13, are made as rigid as possible. With regard to the frame 24, which does not have to have any special properties with regard to ultrasound, it can also be used on others

Materials such as hard plastics, possibly with inserts.

At the rear of the measuring capsule 5, holders 26 are fastened to the frame, between which the measuring head 7 is inserted. The holders 26 can e.g. be equipped with spring elements (not shown) to hold the measuring head 7. A variant with Velcro fasteners 28 is shown, which permit stable, but pressure-free fixing of the measuring head 7 on the measuring capsule 5. For this purpose, the holders 26 are designed as wings 30 which can be pivoted about the rods 32 and which have a Velcro strip on their sides.

A large number of variants are conceivable for the implementation of the connection between measuring capsule 5 and measuring head 7

In extreme cases, the design as an inseparable connection, i.e. as an ultrasonic measuring head with pressure measuring device.

Figg. 2 and 3 show a concrete construction of the measuring capsule 5. The basic element is a ring 36 with a rectangular one Cross-section. An edge is chamfered on the outside at the bottom to form a contact surface 38 around the flexible membrane 13. The membrane 13 is pressed on the circumference by a projection 40 of a first clamping ring 41 onto the bearing surface 38 and is thus fastened. The clamping ring 41 can be clamped onto the ring 36 alone, but another fastening, such as gluing or screwing, is also conceivable in addition or as an alternative.

A second, flat clamping ring 42 rests on the top of the ring 36. The window 20 is clamped between the clamping ring 42 and a step 43 on the underside of the ring 36. An O-ring 45 is placed around the window 20 for sealing.

The cavity filled by the liquid 11 has a height of approximately 1 mm. This value is not critical in itself, but is favorable for measurements with high frequencies (see below).

The window 20 has a thickness on the circumference 47 corresponding to the distance between the clamping ring 42 and the projection 43. The central zone 48, on the other hand, has a small thickness as described above, e.g. 0.5 - 0.7 mm in order to obstruct the ultrasonic passage as little as possible. A curved design is shown as an adaptation to an ultrasound head with a curved forehead.

A bore 50 runs through the ring 36, into which the connection nipple 51 for the line 12 to the pressure measuring device is inserted. Further blind holes 53 are used to attach the holder 26 and to fasten the clamping ring 42 on the ring 36.

A disk-shaped design is shown, but other shapes such as, for example, rectangular are also conceivable Adaptation to the often rectangular forehead of ultrasonic measuring heads.

The interior 55 is filled with the ultrasound-transparent liquid as free of bubbles as possible. For example, vacuum can be applied via the nipple 51. Then you let the liquid flow in automatically, which then completely fills the interior.

A measurement with an ultrasound measuring head 7 with an upstream measuring capsule 5 is carried out essentially like a normal ultrasound measurement. 4 shows an ultrasound image that can be obtained in this way. The arrows 60, 61 point to the internal jugular vein, no pressure being exerted in the illustration on the left in FIG. 4, but pressure being exerted on the right. The vein walls can be clearly seen in the normal (arrow 60) and in the compressed state (arrow 61).

In addition, the pressure on the body surface can now be changed. This enables the changes in the tissue caused by the locally changed pressure, such as e.g. to watch vein compression.

If the measuring arrangement is first placed on the body surface without pressure before starting the measurement, a zero adjustment can be carried out in this state and then the contact pressure can be measured absolutely.

The rigid housing of the measuring capsule also has an advantageous effect, since it reduces the yielding and thus deformation of the flexible membrane when the contact pressure changes.

Reflections of the ultrasound in the measuring capsule can be felt or even to an imperceptible level can be reduced if at least the radiation surface of the ultrasound head rests only on the window 20 and in particular contact with the ring 41, 42 is avoided. The measuring capsule is preferably made so large that the window 20 is larger than the front of the ultrasound head.

The rigid design of the window allows this oversizing because it forms a rigid rear wall. In the case of a movable or stretchable window, the ultrasound head would be pressed into the window and surrounding, exposed areas of the window would bulge, as a result of which the measurement conditions would change overall and measurement errors would result. In addition, there is a risk that the window will touch the front membrane 13 under the pressure of the ultrasound head, which would seriously falsify the measurement.

However, it is conceivable to adapt a measuring capsule specifically to an ultrasound head so that it completely covers the window. In this case, a soft membrane can also be used because, despite its flexibility, it can no longer deform.

If the ultrasound head rests on the housing ring 41, 42, which is significantly more rigid than the window 20, it can also cause more force to be transmitted directly to the skin via the ring, this contact pressure not being fully recorded.

These requirements are further exacerbated, in particular, on a universally usable measuring capsule by the high frequencies used up to 15 MHz, typically around 7 MHz. At 15 MHz, the range of the ultrasound into the skin is still approx. 4 cm, so that the measuring capsule must be significantly thinner. There is only a very thin layer of liquid in the measuring capsule, which means that the Condition that disc and membrane must not touch each other is tightened again.

The membrane 13 on the front is tensioned in the unfilled state, so that it is also in the filled state

Measuring capsule is essentially flat. It should be noted that too dry glycerin can have an adverse effect in this regard: due to its high hygroscopy, it inevitably absorbs water over a long period of time. The corresponding change in volume causes the membrane to deform.

The pressure measuring range is 0 to 700 mbar (millibars), especially for the main application, venous pressure determination. Usual pressure sensors for this area offer a resolution of 1 to 2 bar.

The filling of the measuring capsule is carried out in a vacuum, preferably in a high vacuum, in order to achieve the best possible bubble and gas-free filling. The liquid is also degassed before filling. It was observed that the reaction time of the system in particular decreases with a removable gas component. With a high gas content, on the other hand, the compressibility increases noticeably, which creates the risk that the membrane 13 is pressed in and bears against the window 20.

The measuring capsule can therefore be used with various ultrasonic measuring heads and, due to its low height, is also compatible with high frequencies.

The inventors also see one in particular

Possible application in ultrasound training in medical diagnostics and possibly also in the replacement of expensive additional equipment or invasive Medical examinations (e.g. invasive blood pressure measurement in vessels). The invention can also be used for measurements on animals.

Various materials can be used for the housing of the pressure measuring device, e.g. Sound-permeable plastic casting alone or in combination with reinforcing metal parts.

The effect of the tissue / vessel change caused by the different contact pressure depends on the

Contact surface of the measuring head and the pressure measuring device. Depending on the question, they can be built in different shapes and sizes.

A preferred application is seen in the non-invasive measurement of venous pressure, in particular the pressure of the central veins. A cardiac catheter is currently used for these measurements. This procedure is relatively complex and invasive. 6 - 12% complications are observed, even with serious consequences (David C. McGee NEJM 2003). On the other hand, measuring the venous pressure using the measuring capsule is obviously risk-free and can be carried out quickly. In particular, several measurements can also be carried out in a short time in order to achieve a higher measurement accuracy by averaging.

The following procedure was developed for such measurements:

1) Zero point calibration: The measuring head with measuring capsule is held in the immediate vicinity of the measuring location, but still without contact with the patient's skin. The pressure now measured is set as the zero point. This zero point calibration near the measuring point has proven to be proven important for the quality of the measurements.

2) The measuring head is pressed on until the vein shows a visible narrowing in the ultrasound image. This corresponds to a reduction in the cross-sectional area by approx. 25%. The pressure measured by the measuring capsule is called "base pressure".

3) The measuring head is pressed on until the vein is closed. The measured pressure is the

"Collapse pressure".

4) The difference between collapse pressure and base pressure is a measure of venous pressure.

Collapse pressure and base pressure are the pressure with which the ultrasound button is pressed onto the surface, i.e. the measured value of the measuring capsule. Venous pressure is the pressure of the blood in the vein.

On the basis of the description given, a multitude of modifications are accessible to the person skilled in the art without leaving the scope of the invention as defined in the claims. For example, following modifications:

1. Instead of the liquid-filled measuring chamber, an elastic, sound-permeable material is used and the deformation is measured.

2. Instead of measuring the pressure in the pressurized liquid, the deformation of the support membrane is measured, e.g. with pressure gauges.

3. A pressure measurement can also be a simple water column, ^'in the in communication with the fluid Pressure gauge stands, take place.

4. The height of the liquid in the measuring capsule can be up to 5 mm or up to 1 cm.

Claims

claims

1. Pressure measuring device (5) for ultrasonic devices (7) for performing ultrasonic measurements, in particular on living beings and / or humans, with spatial resolution of the measurement result in at least one dimension, in particular in two dimensions, the pressure measuring device (5) measuring the contact pressure of the Ultrasonic measuring device is used, characterized in that the pressure measuring device comprises a housing with a front side and an opposite rear side, an ultrasound-permeable, essentially ^" rigid window (20) is inserted into the back, a flexible, ultrasound-permeable membrane ( 13) is present, the window and membrane represent walls of the housing, the housing and the window are essentially rigid at the pressures to be measured, and the pressure measuring device is filled with an ultrasound-permeable liquid, so that it passes through the pressure measuring device by means of an Fenst he coupled ultrasound measuring device ultrasound measurements are possible.

2. Pressure measuring device according to claim 1, characterized in that the membrane (13) consists of a silicone elastomer.

3. Pressure measuring device according to claim 1 or 2, characterized in that the window (20) consists of a fluorinated ethylene polymer, in particular poly-tetrafluoroethylene.

4. Pressure measuring device (5) according to claim 3, characterized in that the window (20) in the area which is provided for the ultrasound radiation has a thickness of at most 1 mm and preferably of 0.5-0.7 mm

5. Pressure measuring device (5) according to one of claims 1 to 4, characterized in that the membrane (13) has a thickness of 0.4 to 0.5 mm.

6. Pressure measuring device according to one of claims 1 to 5, characterized in that the liquid (11) contains water.

7. Pressure measuring device according to claim 6, characterized in that the liquid is a glycerol

Water mixture is, preferably in a mass ratio of about 85:15.

8. Pressure measuring device (5) according to one of claims 1 to 7, characterized in that the layer thickness of the

Liquid at least in the area intended for the passage of ultrasound is at most 1 cm, preferably at most 5 mm and particularly preferably at most 1 mm.

9. Pressure measuring device (5) according to one of claims 1 to 8, characterized in that it is connected to a pressure measuring device in order to be able to determine the pressure on the membrane (13) by measuring the pressure in the liquid (11).

10. Ultrasonic measuring device (7) with a pressure measuring device (5) coupled to the measuring surface (22) according to one of claims 1 to 9, wherein the window (20) of the pressure measuring device on the measuring surface of the

Ultrasonic device is present, preferably with a gel (8) to improve the coupling.

11. Ultrasonic measuring device (7) with a pressure measuring device (5) coupled to the measuring surface (22) According to one of claims 1 to 9, characterized in that the pressure measuring device (5) forms an integrated part of the ultrasonic measuring device.

12. Use of an ultrasonic measuring device (5, 7) according to one of claims 10 or 11 or a pressure measuring device (5) according to one of claims 1 to 9 for carrying out ultrasonic measurements on living beings with the contact pressure of the ultrasonic measuring device as an additional evaluation parameter.

13. Use of an ultrasonic measuring device (5,7) according to one of claims 10 or 11 or a pressure measuring device (5) according to one of claims 1 to 9 for training people to perform

Ultrasound measurements to train and adjust the pressure during a measurement.