• Tissues are inhomogenous and contain substructures. Hence varying amounts of ultrasound at different frequencies are scattered by tissue into different directions.
  This is known as the directivity pattern.
• Studies have shown that different tissue structures have different directivity patterns. It is also not unreasonable to expect that changes in tissue morphology will result in changes in directivity pattern
• We hypothesize that directivity patterns can aid in the detection of cancerous breast tumors.

Sound Scatter in the Breast

• Collagen is a primary source of ultrasound scatter. Other proteins form structures too small to be resolved by sound
• This molecule is a major constituent of the breast, and very commonly, its production is increased in breast lesions
• Past experiments seem to indicate that normal breast tissue has pronounced scattering into forward angles (< ± 90° from the incident beam direction)
• Increases in collagen likely give rise to:
  • more scatter in all directions originating from the lesion
  • more scatter in certain preferential directions due to increased backscatter from the sides of the fibrous region (directivity pattern will exhibit less forward scattering)