Applications:
Tissue stiffness is a known marker of disease, but it is
difficult to see in conventional imaging. Significant change in tissue stiffness
can occur without a related change in ultrasound echogenicity or x-ray
density. Quantitative measurements of stiffness, in terms of the
shear modulus, would be useful clinically in the diagnosis of liver fibrous, and
for finding tumors the 40% of all prostrate tumors which are not visible in
ordinary ultrasound, but which can be detected by palpation because of a tissue
stiffness.
Acoustic radiation force impulse (ARFI) ultrasound is
currently limited to “focal” disease states, in which there are well defined
areas of modified stiffness; it cannot image disease states in which the
stiffness increase is general and diffuse in the organ, but our spatially
modulated ARFI can obtain a quantitative measure of stiffness in such an organ
and provide an indication of the degree of disease. Other applications
include diffuse vascular diseases, which causes a systemic stiffness increase,
which cannot be detected by current conventional acoustic radiation force
impulse (ARFI) ultrasound, but could be detected with our spatially modulated
ARFI technique. The technique could also be useful in RF ablation therapy for
liver cancer, in which the progress of the therapy must now be checked by an
off-line CT scan, but which could be monitored real-time with our SM-ARFI
ultrasound.
Advantages:
Acoustic radiation force impulse (ARFI) ultrasound
provides an indication of the local shear modulus of tissue, which is fast, has
good penetration, works by local generation of shear wave which minimizes shear
wave attenuation difficulties. but it is not quantitative. This Spatially
Modulated ARFI method provides a quantitative measurement, in addition to the
other benefits of ARFI. An alternative method, transient
elastography is quantiative, but is noise sensitive. Sonoelastography is
potentially quantitative, but it is difficult to propagate shear waves tgo the
region of interest because of attentuation and refraction.
Vibroacoustaography can be quantitative but it is both very slow and sensitive
to background noise. A biopsy is quantitative and definitive but is
not fast, is invasive, expensive and can be done only on a limited number of
small samples. Palpation is fast and inexpensive, but is not quantitative
and can only be used in areas of limited
pentetration.