Imaging the elastic properties of tissue: the 20 year perspective (original) (raw)
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An overview of elastography-an emerging branch of medical imaging
Current Medical Imaging Reviews, 2011
From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field.
Imaging of the elastic properties of tissue--a review
Ultrasound in medicine & biology, 1996
Recently, a number of methods have been developed that make it possible to image the elastic properties of soft tissues. Because certain types of tissues such as malignant lesions, for example, have elastic properties that are markedly different from surrounding tissues, elasticity imaging could provide a significant adjunct to current diagnostic ultrasonic methods. Further, elasticity imaging techniques could be used to augment the study of tissues that change their elastic properties, such as skeletal and cardiac muscle. In this paper, we survey some of the previous work done in the related field of biomechanics, and we review measurement techniques from the 1950s to the 1980s. Different approaches to elastic imaging and signal processing are then discussed and a lexicography for elastic imaging is introduced. It is hoped that this nomenclature will provide a meaningful categorization of various approaches and will make evident the inherent parameters displayed and conditions appl...
A unified view of imaging the elastic properties of tissue
Journal of The Acoustical Society of America, 2005
A number of different approaches have been developed to estimate and image the elastic properties of tissue. The biomechanical properties of tissues are vitally linked to function and pathology, but cannot be directly assessed by conventional ultrasound, MRI, CT, or nuclear imaging. Research developments have introduced new approaches, using either MRI or ultrasound to image the tissue response to some stimulus. A wide range of stimuli has been evaluated, including heat, water jets, vibration shear waves, compression, and quasistatic compression, using single or multiple steps or low-frequency ͑Ͻ10 Hz͒ cyclic excitation. These may seem to be greatly dissimilar, and appear to produce distinctly different types of information and images. However, our purpose in this tutorial is to review the major classes of excitation stimuli, and then to demonstrate that they produce responses that fall within a common spectrum of elastic behavior. Within this spectrum, the major classes of excitation include step compression, cyclic quasistatic compression, harmonic shear wave excitation, and transient shear wave excitation. The information they reveal about the unknown elastic distribution within an imaging region of interest are shown to be fundamentally related because the tissue responses are governed by the same equation. Examples use simple geometry to emphasize the common nature of the approaches.
Editorial: Innovative developments in multi-modality elastography
Frontiers in Physics, 2022
Editorial on the Research Topic Innovative developments in multi-modality elastography At the crossroads between biomechanics, medical imaging and wave physics, elastography has been widely developed over the last 30 years. These innovations go hand in hand with the tremendous expansion of knowledge and technological leaps medical imaging has undergone in the past decades. Whatever the modality, elastography relies on three key steps: 1) biological soft tissue is stressed; 2) the resulting displacement, strain or strain rate fields are encoded on images; 3) mechanical property maps are reconstructed from the previously encoded fields. Since the initial proposal of static elastography [1], numerous static [2,3], strain [4-7] and dynamic shear wave [8] imaging methods have emerged. Today, the most widely deployed, dynamic methods include vibro-acoustography [9], Acoustic Radiation Force Impulse (ARFI) [10-12], Transient Elastography (TE) [13-15], Shear Wave Elasticity Imaging (SWEI) [8,16], MRI Elastography (MRE) [17,18] and Optical Coherence Elastography (OCE) [19,20]. Reference is made here to some of the main founding studies of these different approaches, many of which have been widely extended subsequently. Each of these methods has its own advantages and disadvantages with respect to the application to which they are dedicated, and it is important to emphasize their complementarity. For example, MRE methods, even if more complex to implement, allow to obtain measurements with a contrast and an attenuation independent of the penetrated tissues when using ultrasonic or optical methods which, for their part, provide a much more "real-time" information. These aspects have been widely compared in the past in comparative studies and literature reviews [21,22]. However, and as it appears later via the different articles presented in this topic, the overlapping of these different methods
Physical Principles of Elastography: A Primer for Radiologists
Indographics, 2021
Elastography is the noninvasive method of qualitative and quantitative evaluation of strain and elastic modulus distribution in soft tissues. In simpler terms, elastography is the science of measuring tissue stiffness, the deviation of which correlates with pathology of the tissue/organs being evaluated. Whereas, elasticity, refers to the property of solid matter to return to their original shape and size after removal of the deforming forces. In all forms of elastography, irrespective of the types of deforming forces or moduli, the deformation of tissue occurs in the form of shear deformation. The velocity of shear waves in the deformed tissue depends on its density and on the shear modulus. The direction of propagation of shear wave is perpendicular to the inciting mechanical or acoustic wave. The shear wave is then subsequently tracked using multiple tracking pulses, which measures tissue displacement in response to the passing shear wave. The calculated speed of the shear wave is then converted to conventional Young's modulus for the purpose of computing the tissue stiffness. The currently used elastography techniques are static or quasi-static elastography and dynamic elastography. Strain elastography (a form of static or quasi-static elastography) is based on the principle of acquisition of radio-frequency (RF) signals before and after the application of a deforming force in the form of slight compression of tissue by a transducer. RF signals are compared between the pre-compression image data set and the post-compression image data set and correlated between the two data sets. Dynamic elastography may be either ultrasound (US) based or magnetic resonance (MR) based. The types of dynamic US elastography are: acoustic radiation force impulse imaging (ARFI), transient elastography (TE), point shear wave elastography (pSWE), and shear wave elastography (SWE). ARFI uses a standard transducer to produce and propagate rapid bursts of long focused ultrasound pulses, also called as "push pulses" which cause tissue deformity, the propagation of which is tracked using radiofrequency echo tracking. In TE, a probe mounted on a vibrator is used to produce a small thump by piston like motion of transducer. The shear wave which arises from the edges of the transducer is tracked using high pulse repetition frequency tissue Doppler
Ultrasound in Medicine & Biology, 2008
Real-time elastography is a method for visualization of the elastic properties of soft tissue and may potentially enable differentiation between malignant and benign pathologic lesions. Our aim was to validate the method on a tissue-mimicking (TM) phantom and to evaluate the influence of different scanning parameters and investigator variability. A TM-phantom containing eight spherical inclusions with known storage modulus was examined using two different transducers on an ultrasound (US) scanner equipped with software for real-time elasticity imaging. The ultrasound transducers were moved vertically in a repetitive manner to induce strain. Two investigators performed series of standardized elastography scans applying a 0-4 categorical quality scale to evaluate the influence of seven parameters: dynamic range of elasticity, region-of-interest, frequency of transducer movement, rejection of elastogram noise, frame rate, persistence and smoothing. Subsequently, repeated examinations of four selected inclusions were performed using a visual analog scale (VAS) where investigators marked a 100 mm horizontal line representing the span in image quality based on experience from the first examination. The hardest and softest inclusions were imaged more clearly than the inclusions with elasticity more similar to the background material. Intraobserver agreement on elastogram quality was good (kappa: 0.67 -0.75) and interobserver agreement average (kappa: 0.55 -0.56) when using the categorical scale. The subsequent VAS evaluation gave intraclass-correlation coefficients for the two observers of 0.98 and 0.93, respectively, and an interclass-correlation coefficient of 0.93. Real-time elastography adequately visualized isoechoic inclusions with different elastic properties in a TM-phantom with acceptable intra-and interobserver agreement. Dynamic range of elasticity was the parameter with most impact on the elastographic visualization of inclusions. (E-mail: roald.flesland.havre@helse-bergen.no)
2008
ShearWave TM Elastography (SWE) is a new real time ultrasound imaging mode that quantitatively measures local tissue elasticity in kPa. Based on the Supersonic Shear Imaging concept (developped at the Laboratoire Ondes et Acoustique, Paris), this new concept may appear as a promising tool to improve breast lesion characterization. In vitro experimental measurements have been performed to quantify SWE mode performances in terms of resolution, penetration and the ability to measure quantitatively elasticity. Results show that the SWE mode exhibits a millimetric resolution and quantifies properly tissue elasticity on a wide range of elastic contrasts (from 7 to 110 kPa). The real time capabilities and the robustness of the mode have been tested in clinical conditions, on breast lesions. 150 patients have been scanned with SWE mode in three different sites. Results show that SWE performs well on breast pathologies and presents a very good inter-site reproducibility. Finally, the quantitative elasticity value was analyzed as a function of pathology using FNA or core biopsy as the reference diagnostic method.
Mechanical imaging in medical applications
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2009
Mechanical Imaging (MI), a.k.a. tactile imaging or stress imaging, is a branch of Elasticity Imaging, a medical diagnostic technique based on the visualization of tissue internal structures in terms of their elasticity modulus. During the last decade, numerous methods and devices have been developed implementing MI technology in various medical applications, such as the visualization and evaluation of prostate conditions, breast cancer screening, the differentiation of benign and malignant lesions, and the characterization of vaginal wall elasticity. This paper presents an overview of MI technology and its applications, strengths and limitations. Results of laboratory and clinical studies clearly indicate that Mechanical Imaging devices have the potential to be used as a cost effective means for cancer screening as well as diagnostics of various diseases accompanied by changes of mechanical properties of soft tissues.