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Type:
Educational Exhibit
Keywords:
Tissue characterisation, Neoplasia, Experimental investigations, Diagnostic procedure, Ultrasound, Experimental, Elastography, Ultrasound physics, Pancreas, Abdomen
Authors:
S. Crosara, M. D'Onofrio, R. De Robertis, S. Canestrini, E. Demozzi, R. Pozzi Mucelli; Verona/IT
DOI:
10.1594/ecr2014/C-0686
Background
TECHNOLOGY
Elastography is a new technique applied to US imaging [1].
The challenge of this new technique is to distinguish different tissues on the basis of their specific consistency (Fig.
1),
reflected by the deformation generated in the tissue itself by an imparted force on the target organ [2,3].
ARFI imaging is able to qualitatively and quantitatively define the tissue stiffness with no need for an external compression,
so reducing the interobesrver variability.
It exploits short duration acoustic radiation forces to generate localized tissue displacements that are registered by the US scanner.
Such displacements are related to the viscoelastic properties of local soft tissue [4].
ARFI has the advantage of being integrated into a conventional ultrasound system and therefore can be performed during a standard examination [5].
ARFI can be used in two different ways.
One is qualitative,
called Virtual Touch Tissue Imaging,
which employs a short acoustic impulse of high intensity to deform the tissue elements and create a static map (elastogram) of the relative stiffness of the tissues included in the region of interest (ROI).
The system is set up to use a hue chromatic (gray scale or red-green-blue) map.
One limitation of this technique is that the complete chromatic spectrum encoding the tissue is applied to each elastographic record and indicates the grade of relative elasticity within the sample area,
thus there is not an absolute chromatic scale of tissue stiffness.
Another application (Fig.
2),
called Virtual Touch Tissue Quantification,
is quantitative: after the preliminary selection of a target ROI of fixed dimensions (10x15 mm) on a conventional US image,
an acoustic push pulse departing from the probe is transmitted through the tissue by side of the target ROI and induces sound waves from the deformation of the tissue itself.
A numeric value of the wave speed (meters/second) is then reported as a result of multiple measurements automatically made for that spatial location: the stiffer a tissue is,
the greater the numerical value will be [6].
IMAGING INTERPRETATION
According to preliminary results,
the internal structure of the pancreas is normally uniformly iso/hyper-echoic compared to the liver.
It appears as intermediately soft,
characterized by a homogeneous soft tissue area .
The mean velocity value measured through the normal pancreatic parenchyma (Fig.
3) is approximately 1.40 m/s [7-9].
Embriologically the pancreas develops from two primordia,
the dorsal and the ventral.
The dorsal primordium can rise above the surrounding tissue as a band-shaped hypoechoic structure and should not be confused with local inflammation or a tumor.
ARFI provides similar values in both parts of a healthy pancreas [9].
With advancing age,
pancreatic echogenicity increases significantly,
as a result of fat and connective tissue deposits; the elastographic image becomes heterogeneous and the velocity values becomes higher [9].