ABSTRACT
Joshua R. Doherty, Mark L. Palmeri, Gregg E. Trahey, and Kathryn R. Nightingale 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
8.2 ARF-Induced Tissue Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 8.2.1 Soft Tissue Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 8.2.2 ARF Derivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 8.2.3 Shear Wave Generation and Propagation . . . . . . . . . . . . . . . . . . . . . . . . 236 8.2.4 Force Field Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
8.3 Monitoring Tissue Deformation Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 8.3.1 Cross-Correlation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 8.3.2 Phase Shift Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 8.3.3 Sources of Bias and Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
8.4 ARF-Based Elasticity Imaging Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 8.4.1 (Quasi)Static Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
8.4.1.1 Acoustic Streaming in Diagnostic Ultrasound . . . . . . . . . . . . . 246 8.4.1.2 Sonorheometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
8.4.2 Transient (Impulsive) Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 8.4.2.1 On-Axis Tracking (Qualitative) Methods . . . . . . . . . . . . . . . . . . . 246 8.4.2.2 Off-Axis Tracking (Quantitative) Methods . . . . . . . . . . . . . . . . . 247
8.4.3 Harmonic Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 8.4.3.1 Vibroacoustography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 8.4.3.2 Harmonic Motion Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 8.4.3.3 Shear Wave Dispersion Ultrasound Vibrometry . . . . . . . . . . . . 252 8.4.3.4 Crawling Wave Sonoelastography . . . . . . . . . . . . . . . . . . . . . . . 253
8.5 Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
8.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
8.1 Introduction Since ancient Egyptian medicine, manual palpation has been used to detect the size, location, and stiffness of superficial structures within the body [1]. By assessing the elasticity (i.e., stiffness) of structures compared with surrounding tissues, the information gleaned by palpation can help clinicians determine states of disease associated with various pathologic processes. For instance, the presence of a stiff mass within otherwise healthy breast tissue can be an indication of breast cancer [2-5]. Although indispensable for medical diagnosis, manual palpation methods do not allow clinicians to “see” changes deep within the tissue. Furthermore, because these pathologic processes are associated with changes in the mechanical properties of tissue, they can often go unnoticed by conventional imaging techniques, such as diagnostic ultrasound, which distinguishes features based on the acoustic properties of tissue. To that end, ultrasound elasticity imaging methods have been developed as noninvasive tools for probing the elasticity of tissue deep within the body.
