Patent ID: 12226260

MORE DETAILED DESCRIPTION

FIG.1shows a device1in accordance with a first embodiment of the invention. It consists in a so called “1D” probe including three transducers2, T1and T2.

First transducer2is dedicated to generate a shear wave in tissue3.

It can be qualified as “pushing” transducer and works, for example at a central frequency of 3 MHz.

In such a case, it is designed to generate an ultrasound beam B, said beam B being advantageously of a few mm width and in a depth range between 2 and 6 cm.

Said ultrasound beam B can be of such a power that it can create a shear wave SW in the tissue3.

The two other transducers T1and T2are imaging transducers dedicated to image the tissue3along two ultrasound lines L1and L2. Said transducers T1and T2advantageously emit ultrasounds of central frequency 5 MHz. They are advantageously separated by 1-2 cm. Simultaneous or time-shifted emissions may be implemented.

Both ultrasound lines L1and L2are positioned in the vicinity of a region of interest for an elasticity measurement.

Said probe1is electronically controlled by one programmable emitting channel EC controlling the pushing element2and two programmable transmit/receive channels RC1and RC2controlling the imaging elements T1and T2. Said transmit/receive channels are connected to at least one memory4available to store in real time data coming from the imaging channels RC1and RC2.

Then, a processing is performed in real time on a computer having access to said memory4or on a dedicated processing system5including said memory4and connection to channels EC, RC1and RC2.

The purpose of this processing is to achieve a mean visco-elasticity measurement for the region of interest.

For such a purpose, the probe1is placed on the surface of the tissue3to be investigated, such as liver muscles or artery walls. A high power ultrasound beam B, for example at 3 MHz, is generated by the pushing element2to create a shear wave SW in the tissue3.

Then, the probe1is such that imaging transducers T1and T2send multiple pulses, for example at 5 MHz. These multiple pulses enable to track the induced displacements along the two ultrasound lines L1and12.

The pulses are sent at a PRF (for Pulse Repetition Frequency) high enough to correctly sample the medium transient response. Typically, PRF=1000 to 5000 Hz.

The use of lower frequency for the pushing sequence allows better pushing efficiency and less interference between pushing and imaging beams.

Such a measurement of displacements in a tissue is well known in the field of elastography and may be performed using any manner known to the person skilled in the art.

For example, processing consists in first applying motion estimation algorithms such as 1D cross correlation or Doppler based algorithms.

Tissue displacements or velocity V are then assessed along lines L1and L2as a function of time t: V1(z1,t) and V2(z2,t), where z1 et z2 are the respective depth along lines L1and L2and t is the time).

Displacement data is then used to deduce shear wave characteristics along the two lines L1and L2and then measure a global mechanical parameter of the medium located between the two lines L1and L2. An example of mechanical parameter estimated is the speed CTof the shear wave between those two points:
cT=argmaxCΣt,z2(Σz1V1(t,z1))(Σz2V2(t−d12/C,z2)),
where d12 is the distance between the two lines L1et L2.

The depth of interest on which the displacement field are summed can be chosen to cover the depth of field or just a small range. In the second case, measurements can be repeated for different slices located at different depths. In this case, an estimated parameter cT(z) which is a function of depth is available.

This first embodiment of the invention presents the advantage of being particularly compact because of the basic association of only three transducers.

FIG.2shows a second embodiment of a measurement device in accordance with the present invention. It consists in an implementation of the method in an echographic imaging system using an ultrasound array probe10to image the tissue3.

The following describes how a real time echographic system with mean visco-elasticity measurement and display is thus obtained.

Said echographic system is advantageously controlled in order to generate an ultrasound pushing beam B in the tissue3.

As illustrated onFIG.2, such beam B may be obtained by specific focusing of ultrasound emitted by a group GTb of transducers located on one of the sides of the transducer array10.

Two other transducers or group of transducers GT1, GT2are subsequently used to image two lines of interest L1and L2.

Advantageously, first, a classical ultrasound imaging sequence is performed to compute an ultrasound image of the region of interest. This is an approximately 20 ms long step.

Then the global elasticity measurement method according to the invention is performed using an ultrasound pushing beam B and at least one tracking line L1with the same probe10than the one used for ultrasound imaging. This is an approximately 20 ms long step.

Both sequences, ultrasound imaging and elasticity estimation, are then looped continuously to provide in real time both ultrasound images and global elasticity estimation to the user.

The elasticity value may be displayed on a side of the echographic image. This coupling appears very interesting as guidance for the physician to locate areas of pathological interest characterized by an increase of elasticity.

An alarm may also be emitted as soon as the estimated mean elasticity value reaches a predetermined threshold. The emitted sound warns the physician of the necessity of a more thorough investigation. This alarm feature may be implemented alone or in parallel with the displaying of the mean elasticity value.

A preferred use of the invention thus lies in the field of medical imaging, since it enables a fast preliminary scanning of elasticity characteristics of a region of interest. As elasticity abnormalities can reveal lesions, the method of the invention can help in localization and detection of illness.