Elastography

Physicians have been palpating lumps and bumps for centuries.  One of the features of a mass assessed with palpation is the stiffness/hardness of the mass.  In general, stiff, hard masses are more worrisome for malignancy than softer, more deformable masses.  Likewise, a stiff, hard liver is more concerning for cirrhosis than a soft malleable liver.

Elastography is an ultrasound application that can also assess the stiffness of a lesion.  Some people have called it 'echopalpation'.

There are two basic types of elastography:

• strain elastography

• shear wave elastography

Strain elastography is a qualitative technique in which the tissue is compressed manually by the sonographer using the transducer.  This induces a pressure wave that travels through the lesion and will alter the echoes from the lesion proportional to the lesion's stiffness.  These echoes are then assessed by the system's computer.  The stiffness of the lesion can be displayed in a grayscale overlay or displayed in color according to a color map.  A typical map may indicate stiff lesions as blue and less stiff lesions as red.   The image produced is called an elastogram.

Here's a short video from GE describing the strain elastography process.  

Shear wave elastography is a quantitative technique in which the pressure wave is produced by the transducer.  This generates a transverse shear wave within the tissue.  The speed of the shear wave is proportional to the tissue stiffness.  Stiffer lesions produce faster shear waves.  Using a region of interest, the sonographer can obtain a value for the speed of the shear wave, thereby obtaining a quantitative value for tissue stiffness. 

Here is an excellent video demonstrating the use of shear wave elastography in the evaluation of the stiffness of a variety of lesions.

More detailed information can also be found in my two videos on recent advances.