(Barannik 2002)Doppler Ultrasound Detection of Shear Waves Remotely Induced in Tissue Phantoms and...

7/30/2019 (Barannik 2002)Doppler Ultrasound Detection of Shear Waves Remotely Induced in Tissue Phantoms and Tissue in

1/4

Doppler ultrasound detection of shear waves remotely inducedin tissue phantoms and tissue in vitro

E.A. Barannik a,*, A. Girnyk a, V. Tovstiak a, A.I. Marusenko b, S.Y. Emelianov c,A.P. Sarvazyan d

a PhysicalTechnical Department, Kharkiv National University, 4 Svobody Sq., Kharkiv 61077, Ukraineb JSC Research Development Institute of Radio Engineering Measurements, 271 Ac. Pavlov Av., Kharkiv 61054, Ukraine

c Biomedical Engineering Department, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109, USAd Artann Laboratories, 1 Riva Avenue, North Brunswick, NJ 08902, USA

Abstract

In shear wave elasticity imaging (SWEI), mechanical excitation within the tissue is remotely generated using radiation force of

focused ultrasound. The induced shear strain is subsequently detected to estimate visco-elastic properties of tissue and thus aid

diagnostics. In this paper, the mechanical response of tissue to radiation force was detected using a modified ultrasound Doppler

technique. The experiments were performed on tissue mimicking and tissue containing phantoms using a commercial diagnostic

scanner. This scanner was modified to control both the pushing and probing beams. The pushing beam was fired repetitively along a

single direction while interlaced probing beams swept the surrounding region of interest to detect the induced motion.

The detectability of inhomogeneous inclusions using ultrasonic Doppler SWEI method has been demonstrated in this study. The

displacement fields measured in elastic phantoms clearly reveal the oscillatory nature of the mechanical relaxation processes in

response to impulsive load due to the boundary effects. This relaxation dynamics was also present in cooked muscle tissue, but was

not detected in more viscous and less elastic phantom and raw muscles. Presence of a local heterogeneity in the vicinity of the focal

region of the pushing beam results in generation of a standing wave field pattern which is manifested in the oscillatory response ofthe excited region of the tissue. There has been made an assumption that dynamic characteristics of the relaxation process may be

used for visualization of inhomogeneities. 2002 Published by Elsevier Science B.V.

Keywords: Shear wave; Elasticity; Doppler; Phantom; Tissue

1. Introduction

Several imaging modalities can provide information

about elastic properties of tissue. These methods include

shear wave elasticity imaging or SWEI [15], acoustic

remote palpation [69], sonoelasticity imaging [1013]

and elastography [1416]. These methods are based on

formation of elastic deformations inside the tissue under

study with the help of an exterior power source that can

be of various physical nature. In particular, in sono-

elasticity imaging a vibration power source is used, and

in elastography the elasticity is evaluated from internal

strain in tissues subjected to a given external load. All

these methods suggest a considerable clinical potential

and may add a new quality to the conventional ultra-

sonic imaging.

In SWEI as well as in acoustic remote palpation ini-

tial shear displacements are remotely generated using

the acoustic radiation force. Induced shear strains can

be detected then by the ultrasound Doppler technique,

which is commonly used for color blood flow mapping,

or by the speckle-tracking method. The SWEI method

is based on the analysis of the mechanical response

of tissue to the radiation force and space distribution of

maximum tissue displacement caused by propagation of

induced shear waves. The main objective of this paper is

to investigate the relaxation dynamics of the local shear

strain in the presence of an inhomogeneous inclusion,

and to study a possibility to visualize tissue inhomoge-

neity in phantoms.

Ultrasonics 40 (2002) 849852

www.elsevier.com/locate/ultras

* Corresponding author. Tel.: +380-572-353733; fax: +380-572-

353977.

E-mail address: [email protected] (E.A. Baran-

nik).

0041-624X/02/$ - see front matter 2002 Published by Elsevier Science B.V.

PII: S 0 0 4 1 - 6 2 4 X ( 0 2 ) 0 0 2 4 3 - 3


2/4

2. Methods

In present experiments all of the ultrasonic pushing

(i.e., motion inducing) beams were fired in a single di-

rection defined by the axis of the pushing transducer.

Probing (i.e., motion sensing) beams irradiated by a

single crystal ultrasound transducer swept the sur-rounding region of interest to detect the induced motion.

The experiments were performed with a commercial

diagnostic scanner ULTIMA developed in Kharkiv

(Radmir, Ukraine). The scanner has been modified to

allow a user to control the characteristics of the pushing

and probing beams and other experimental conditions.

In particular, a pre-defined number of probing pulses

followed every pushing pulse because the pulse repeti-

tion frequencies of pushing (3.67 MHz) and probing

(14.59 MHz) beams were multiple and were defined

by the scanner clock rate. Experiments were performed

with the lowest possible intensity of pushing ultrasonic

beams, which is important for eventual medical appli-

cations. Radiation force was generated by a focused

transducer of 8 cm aperture, 7 cm focal length and 4 mm

focal area diameter (6 dB). The carrier frequency was 1

MHz with intensity ISPPA about 145 W/cm2 and dura-

tion of pushing pulses equal to 2.18 ms. Parameters of

probing pulses are common for color Doppler mapping.

The probing transducer operating at 3.5 MHz was in-

stalled in the center of the pushing transducer (Fig. 1).

A technique to reduce the interference between

pushing and probing beams was utilized. This technique

includes coherent accumulation of Doppler signals ob-

tained after each of the pushing beams and non-coher-ent accumulation of output data. The mixture of these

two methods and developed procedure of Doppler sig-

nal processing based on the autocorrelation method al-

lowed estimation of the displacement with accuracy

about 10%. The Table 1 presents the parameters of two

gel-based tissue phantomsviscous phantom (due to

glycerol additive) and elastic phantom. As a result, in

the viscous phantom shear wave attenuation is greater,

while the elastic phantom has a greater ultrasound

absorption. Indeed, absorption of shear waves in the

medium is related only to dynamic viscosity, while

absorption of compressional waves depends also on

bulk viscosity, heat conductivity and bulk compress-

ibility.

3. Results and conclusion

The maximum displacements are detected in the focal

region of pushing beams where the maximum radiation

pressure occurs. The obtained 2-D graphs, which por-

tray the space distribution of tissue displacement, are

similar for the viscous and elastic phantoms. The dis-

placement magnitude registered in the less elastic but vis-

cous phantom is lower than that in the elastic onethis

is due to the small duration of pushing pulses. Note that

the value of shear strain for the level of intensity used isin agreement with the theoretical assessments [1] and

experimental results [6,7]. As expected, the maximum

displacement for probing points with the non-zero radial

coordinate r is registered with a greater time delay for

the viscous phantom that has lower shear waves veloc-

ity. The time difference of delays reflects apparently the

difference of shear elasticity moduli of the phantoms.

Fig. 1. Assembled unit of pushing and probing transducers.

Table 1

Gel-based tissue phantoms

Parameters Viscous phantom Elastic phantom

Water (l) 1.1 2.5

Gelatin (g) 130 240

Glycerol (l) 1.26

Shear wave velocity (m/s) 2.3 3.6

Speed of sound (m/s) 1810 1560Ultrasound absorption

(dB/MHz cm)

0.36 0.51

850 E.A. Barannik et al. / Ultrasonics 40 (2002) 849852


3/4

Typical relaxation processes in the elastic phantom at

two positions with different radial coordinate in the fo-

cal plane are shown in Fig. 2. The mechanical relaxation

processes in response to impulsive load exhibit a fuzzysecond maximum indicating weak oscillation. One of

possible causes of such behavior is a registration of waves

reflected from the boundary between the phantom and

water where phantom and transducer assembly are po-

sitioned during the experiment. Boundary effects in the

elastic phantom cannot be neglected due to relatively

small absorption of shear waves with a great wave

length, and, therefore, the induced shear wave distur-

bance cannot be described by a homogeneous model.

The viscous phantom with a local elastic inclusion

was used to study the impact of inhomogeneity on the

relaxation of the induced shear wave disturbance. The

approximately 1 cm3 inclusion was visible on the B-

image (Fig. 3) due to the small additive of aluminum

oxide powder. The obtained 2-D map of the displace-

ment in this inhomogeneous phantom does not permit

direct identification of the inclusion because of the dis-

tortion due to the space distribution of radiation pres-

sure. To eliminate the difference in displacement caused

by radiation pressure distribution within the focal area,

the original 2-D image was normalized to the space dis-

tribution of displacement in homogeneous phantoms.

Normalization procedure allows us to identify the in-

clusion with certainty on the 2-D image using the datareflecting the difference in displacement amplitudes of

the viscous and elastic phantom. Just as the B-image in

Fig. 3, the SWEI image of the inclusion in Fig. 4 is lo-

cated asymmetrically relative to the axis of pushing

beams.

The typical relaxation dynamics for the probing point

near the inclusion, which is marked on the B-image, is

shown in Fig. 5. This dynamics is contrasted with the

one obtained from the cooked beef muscle tissue at the

point remote from the focal area of the pushing beam.

The used sample of muscle tissue was cut out along the

fibers and boiled for 1 h. Curves of relaxation in the

Fig. 5. Displacement through time from elastic phantom at the point

marked on the B-image (1) and typical displacement through time

from the boiled muscle tissue at point distant from the pushing beam

axis.

Fig. 2. Relaxation dynamics in the elastic phantom: (1) r 0 mm,

Dmax 17:6 lm; (2) r 11 mm, Dmax 3:9 lm (tpush 2:18 ms).

Fig. 3. Ultrasonic B-mode image of inhomogeneous inclusion.

Fig. 4. Normalized 2-D image of displacement in phantom with in-

clusion.

E.A. Barannik et al. / Ultrasonics 40 (2002) 849852 851


4/4

phantom obtained for other probing points away from

the inclusion are also of oscillatory nature, in some cases

are rather complicated. Such behavior may be explained

if we take into account that for small values of inho-

mogeneity (approximately several wave lengths) the su-

perposition of direct waves and shear waves reflected

from the inhomogeneity boundary can cause a compli-cated oscillatory motion of both the boundary and points

close to it. Using the cooked muscle tissue we tried to

imitate the muscle tonus, i.e. to increase the shear elas-

ticity modulus and to decrease viscosity. The presented

relaxation curve was obtained for the fiber orientation,

which was transverse relative to the axis of pushing

beams. Damped oscillation is rather evident in this figure

and may be related both to boundary effects and to the

presence of inhomogeneities.

In conclusion, the ultrasonic Doppler SWEI method

for remote palpation of tissue has been experimentally

examined, and mechanical response of gel-based tissue

phantoms has been studied. It has been shown that the

difference in the visco-elastic properties of gel-based

tissue phantoms is the cause for observed difference of

displacement magnitudes. There has been experimental

demonstration of the principal detectability of inho-

mogeneous inclusions with the aid of ultrasonic Dopp-

ler SWEI method. The results from examined elastic

phantoms clearly demonstrate the oscillatory nature of

the mechanical relaxation processes in response to im-

pulsive load due to the boundary effects. This relaxation

dynamics was also present in some tissues such as boiled

muscle tissue, but was not detected in the more viscous

and less elastic tissue phantom and raw muscles. Pres-ence of a local heterogeneity in the vicinity of the focal

region of the pushing beam results in generation of a

standing wave field pattern which is manifested in the

oscillatory response of the excited region of the tissue.

Further research will be directed towards to better un-

derstanding of dynamic processes associated with SWEI

and their use for visualization of inhomogeneities.

Acknowledgements

This work is supported by the Science and Technol-ogy Center in Ukraine under grant no. 865.

References

[1] A.P. Sarvazyan, O.V. Rudenko, S.D. Swanson, J.B. Fowlkes, S.Y.

Emelianov, Shear wave elasticity imaging: a new ultrasonic

technology of medical diagnostics, Ultrasound Med. Biol. 24 (9)

(1998) 1419.

[2] A.P. Sarvazyan, A.R. Skovoroda, S.Y. Emelianov, J.B. Fowlkes,

J.G. Pipe, R.S. Adler, R.B. Buxton, P.L. Carson, Biophysicalbases of elasticity imaging, Acoust. Imaging 21 (1995) 223.

[3] A.P. Sarvazyan, Method and device for shear wave elasticity

imaging, US Patent 5,606,971, 1997.

[4] V.G. Andreev, V.N. Dmitriev, O.V. Rudenko, A.P. Sarvazyan,

Remote generation of shear wave in soft tissue by pulsed radiation

pressure, J. Acoust. Soc. Am. 102 (1997) 3155.

[5] E.A. Barannik, S.A. Girnyk, V.V. Tovstiak, A.P. Sarvazyan,

Doppler ultrasound detection of shear wave remotely induced in

tissue phantoms by focused ultrasound, in: Joint 140th Meeting

ASA/NOISE-CON 2000, J. Acoust. Soc. Am. 108 (5) (2000) 2549,

abstract.

[6] K. Nightingale, R. Nightingale, M. Palmeri, G. Trahey, A finite

element model of remote palpation of breast lesions using

radiation force: factors affecting tissue displacement, Ultrason.

Imaging 22 (1) (2000) 35.[7] K. Nightingale, M. Palmeri, R. Nightingale, G. Trahey, On the

feasibility of remote palpation using acoustic radiation force, J.

Acoust. Soc. Am. 110 (1) (2001) 625.

[8] W. Walker, Internal deformation of a uniform elastic solid by

acoustic radiation force, J. Acoust. Soc. Am. 105 (4) (1999)

2508.

[9] W. Walker, F. Fernandez, L. Negron, A method of imaging

viscoelastic parameters with acoustic radiation force, Phys. Med.

Biol. 45 (6) (2000) 1437.

[10] Y. Yamakoshi, J. Sato, T. Sato, Ultrasonic imaging of the internal

vibration of soft tissue under forced vibration, IEEE Trans.

Ultrason. Ferroelectr. Freq. Control 37 (1990) 45.

[11] R.M. Lerner, S.R. Huang, K.J. Parker, Sonoelasticity images

derived from ultrasound signals in mechanically vibrated tissues,

Ultrasound Med. Biol. 16 (1990) 231.[12] T.A. Krouskop, D.R. Dougherty, S.F. Levinson, A pulsed

Doppler ultrasonic system for making non-invasive measurements

of the mechanical properties of soft tissue, J. Rehabil. Res. Dev.

24 (2) (1987) 1.

[13] M. Fatemi, J. Greenleaf, Probing the dynamics of tissue at low

frequencies with the radiation force of ultrasound, Phys. Med.

Biol. 45 (6) (2000) 1449.

[14] J. Ophir, I. Cespedes, H. Ponnekanti, Y. Yazdi, X. Li, Elasto-

graphy: a quantitative method for imaging the elasticity of

biological tissues, Ultrason. Imaging 13 (1991) 111.

[15] M.O. Donnell, A.R. Skovoroda, B.M. Shapo, S.Y. Emelianov,

Internal displacement and strain imaging using ultrasonic speckle

tracking, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 41

(1994) 314.

[16] E.E. Konofagou, T. Varghese, J. Ophir, Spectral estimators inelastography, Ultrasonics 38 (2000) 412.

852 E.A. Barannik et al. / Ultrasonics 40 (2002) 849852

(Barannik 2002)Doppler Ultrasound Detection of Shear Waves Remotely Induced in Tissue Phantoms and...

Documents

Transcript of (Barannik 2002)Doppler Ultrasound Detection of Shear Waves Remotely Induced in Tissue Phantoms and...