Shepp-Logan phantom dataset

Is there any biological word for tha small ellipses in the lower portion of the image. For example in human head data we call the inner part as corpus callopsum?

Answer 1

[Johannes Fischer]

In their paper from 1974, they call these ellipses tumors (see caption of Figure 1)

https://web.archive.org/web/20160304035526/http://stat.wharton.upenn.edu/~shepp/publications/33.pdf

[Humera Yasir]

Thankyou!!