Table 4.

Mean Attenuation Coefficient versus Frequency Slope Values (dB/cm-MHz) Estimated Using the Three Clinical Ultrasound Imaging Systems

		Layer 1 (dB/cm-MHz)		Layer 2 (dB/cm-MHz)		Layer 3 (dB/cm-MHz)
Clinical System	Transducer	Const-α	Const-BSC	Const-α	Const-BSC	Const-α	Const-BSC
Lab characterization		0.52	0.48	0.54	0.73	0.52	0.47
UltraSonix RP	L14-5/38	0.46	0.46	0.48	0.64	0.31	0.41
Siemens Acuson S2000	18L6	0.48	0.48	0.53	0.71	0.44	0.43
	9L4	0.49	0.5	0.52	0.7	0.55	0.45
VisualSonics Vevo 2100	MS200	0.67	0.46	0.55	0.69	0.53	0.5

Const-α = constant attenuation; Const-BSC = constant backscatter. The mean value was obtained by averaging estimates from different alpha-estimation blocks and from uncorrelated image frames for each layer. For the UltraSonix and Siemens systems, the transducers were placed in contact with Layer 1 and then directed to the more distal layers; for the high-frequency VisualSonics, the transducer was in contact with Layer 3, providing a shorter path to the distal layer (see Figure 1).