Mechanical Imaging - a Technology for 3-D Visualization and Characterization of Soft Tissue Abnormalities. A Review

Abstract

Mechanical Imaging (MI) is a branch of Elastography. MI differs from conventional ultrasonic and MR elastography in that it evaluates soft tissue mechanical structure using stress data rather than dynamic or static strain data. MI closely mimics manual palpation because the MI probe with a force sensor array attached to its tip acts as a palpating finger. MI is intrinsically a three-dimensional imaging modality because the surface stress patterns obtained at different levels of tissue compression are defined by three-dimensional mechanical structure of the tissue. This review presents the biomechanical basis of MI and its applications for breast cancer screening, and the differentiation of benign and malignant lesions, the visualization and evaluation of prostate conditions, and for the characterization of vaginal wall elasticity.

Keywords: Elastography; breast; cancer; elasticity imaging; mechanical imaging; prostate; soft tissue; tactile imaging.

Figures

Fig. (1)

Dependence of pressure profile data on parameters of a nodule. Adapted from [28]. See text.

Fig. (2)

Dependence of the pressure profile maximum (normalized to ΔP/P0 for E/E0=100) on the relative elasticity of the nodule.

Fig. (3)

Experiments have demonstrated the use of the pressure profile for estimating integral elasticity. Experimental results (right panel) agree well with finite element simulations (left panel).

Fig. (4)

Pressure profiles for different inclusion diameter, d and depth h. See text.

Fig. (5)

Spatial-temporal pressure profiles obtained by moving a linear array of sensors over a phantom with an inclusion. Reproduced with permission from [1].

Fig. (6)

Image matching procedure yields a compound image which closely corresponds to the examined structure. See text.

Fig. (7)

Compound image shows good correspondence with the examined object. See text.

Fig. (8)

Illustration of an algorithm for 3-D image reconstruction. A - a schematic top view of a test phantom (E = 8 kPa) with 3 inclusions (E = 125 kPa, D1 = 15mm, D2 = 8mm and D3 = 5mm) at about 8 mm depth; B – a sequence of 2-D stress patterns obtained at different levels of compression; C - reconstructed 3-D image. See text for details.

Fig. (9)

PMI closely mimics DRE while offering superior sensitivity and capability of 3-D imaging and storing examination data.

Fig. (10)

General view of the Prostate Mechanical Imager.

Fig. (11)

General view of Breast Mechanical Imager. The device comprises a probe with 2-D pressure sensor array (1), an electronic unit (2), and a laptop computer with touch screen capability. Reproduced with permission from [26].

Fig. (12)

Processed data for two clinical cases demonstrate the ability of MI technology to produce 3-D images of lesions. A - two cysts; B - invasive ductal carcinoma.

Fig. (13)

Mechanical imaging of anterior and posterior vaginal walls allows visualization and quantitative elasticity evaluation of increased rigidity at mesh grafts. Adapted with permission from [29].

Fig. (14)

Box plots demonstrating discrimination of normal from prolapse vaginal wall conditions assessed by VTI. Adapted with permission from [29].