The CG volume differences were attributed to underestimation in apex-to-base regions (B-mode: −10.8% ± 13.9%, ARFI: −28.8% ± 9.4%) and overestimation of the lateral dimension (B-mode: 18.4% ± 13.9%, ARFI: 21.5% ± 14.3%) due to poor contrast caused by extraprostatic fat. Recently, a comparison of prostatic volume estimation using B-mode/ARFI images and MR T2-weighted images, conducted by Palmeri et al., reported that both US and ARFI volumes yielded a good correlation with MR results in the CG (R2 = 0.77 and 0.85, respectively). However, the low resolution and limited depth penetration (22 mm) presented challenges when discriminating among PCa, BPH, and the discrete structures using the implemented qualitative ARFI. Unlike B-mode images, ARFI images were characterized by higher contrast of the prostate structures. PCa was present in most patients as bilaterally asymmetric stiff structures, while benign prostatic hyperplasia (BPH) appeared heterogeneous with a nodular texture. This study used custom ARFI imaging sequences implemented with a scanner modified with a 3D wobbler, end-firing, transcavity transducer to image prostates of 19 patients before and after undergoing RP. A decade later, the potential of this technique to guide prostate needle biopsy within specific structures of human prostates was shown in vivo. The clinical viability of this method was studied as an approach to detect local variations in the mechanical properties of soft tissues by applying radiation force to small volumes of tissue (2 mm 3) to exert displacements around 10 μm. Similar to SE images, the information provided is qualitative, where regions of decreased displacement suggest stiffer tissues. The differential displacement with respect to the moment before applying the pulse is monitored using traditional B-mode US. ARFI imaging applies a focused US pulse (<1 ms) whose energy displaces the prostatic tissue to about 10 μm. The acoustic radiation force impulse (ARFI) method remotely palpates tissues through absorption of ultrasonic energy. Our approach is related to the treatment of lattice vibrations in Chapter 6, and sound waves may be viewed as the long-wavelength limit of phonons. However, they can no longer be classified as pure longitudinal and transverse waves, and the phase velocity is not parallel to, or equal in magnitude to, the group velocity except in certain symmetry directions of the lattice. In a single crystal there are still three modes for sound waves, with velocities expressed in the elastic constants of the medium and the crystallographic direction of the wave vector. The transverse mode is degenerate its vibrations can be along any of two (arbitrary) directions perpendicular to the velocity vector. In this case there is no distinction between phase velocity and group velocity. Here ρ is the mass density of the medium. The longitudinal mode has the velocity C L = 1 / 2. a texture-free piece of polycrystalline iron, there are two kinds of sound waves, corresponding to longitudinal and transverse vibrations. In an isotropic engineering material, e.g. GÖRAN GRIMVALL, in Thermophysical Properties of Materials, 1999 1 Introduction
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