Hi, I am trying to model HiFU through a heterogeneous medium but I am struggling with how best to approach assigning the alpha power coefficient as I am propagating the ultrasound through three different regions: water, fat and tissue.

Each region has a different alpha power value based on experimental data values. However, kWave only allows for a scalar value of alpha_power rather than a matrix. I discovered on the forum the function fitPowerLawParamsMulti, but this still requires picking a reference value y_ref.

Currently, the three values for alpha power are the following,

% define different absorption properties for different regions

medium.alpha_power = 1 * ones(Nx, Ny); % [dB/(MHz^y cm)] - Water

medium.alpha_power(Region_2{j}) = 0.4; % [dB/(MHz^y cm)] Region 2 - Fat

medium.alpha_power(Region_3{j}) = 1.41; % [dB/(MHz^y cm)] Region 3 - Tissue

When I use the function, it plots a graph, and based on the point where the lines overlap for each three regions, I changed the y_ref to be a value in between the points of overlap for Region 2 and 3, which is roughly 0.55. Is this the correct approach to define a y_ref, or am I misunderstanding how best to define y_ref? Any advice on how to go about this would be much appreciated!