Type:
Educational Exhibit
Keywords:
Breast, Mammography, Physics, Diagnostic procedure, Artifacts, Calcifications / Calculi
Authors:
K. Rangarajan1, S. Hari2; 1New Delhi/IN, 2NEW DELHI, DELHI/IN
DOI:
10.1594/ecr2013/C-1711
Background
- Digital Breast Tomosynthesis is an exciting new technology that holds promise in improving cancer detection by removal of overlap of tissue in mammography[1,2,3,4].
- The technology represents a compromise between obtaining a 3rd dimension and minimizing radiation exposure to the exquisitely radiation-sensitive organ.
It is thus,
prone to a number of artifacts.
Principle
- The basic principle of tomosynthesis is similar to stereovision- the mechanism by which the human brain perceives the depth of an object by comparing images formed by the two eyes(fig 1).
Fig. 1: The mechanism by which the human brains perceives depth - by comparing images formed by the 2 eyes
- Unlike in conventional 2- dimentional mammography where the tube is stationary,
in tomosynthesis the tube rotates to acquire different projections.
By comparing the displacement of a mass within the breast with movement of the tube,
the depth of the mass can be gauged (fig 2),thus adding the 3rd dimension.[9]
Fig. 2: Baic principle of tomosynthesis : deeper the mass in the breast, further the displacement with rotation of the tube
Genesis of artifacts
Although the in-plane resolution is excellent,
the limited angle of rotation of the tube makes the z axis depiction of the object far from perfect.
Unlike in computed tomography where the tube rotates atleast 180 degrees,
in tomosynthesis exact location on the z axis is not possible.
This “uncertainty” along the z- axis is the source of most artifacts[9].
(fig 3).
Fig. 3
The accuracy of location along the z-axis would depend on-
- Number of projections
- Angular range covered by the projections