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Description
Ultrasound attenuation maps are an important imaging modality of medical ultrasound tomography. Many approaches however only put focus on the attenuation at a specific or dominant frequency with small bandwidth or the broad band attenuation of a signal with large bandwidth. Yet, attenuation by tissue is typically considered to be frequency dependent. In the literature this is modelled linearly or with a power law (Attenuation = $ a \cdot f^y$ in $\mathrm{\frac{dB}{cm}}$, where $a$ is attenuation coefficient in $\mathrm{\frac{dB}{MHz^y \cdot cm}}$, $f$ is frequency in $\mathrm{MHz}$ and $\mathrm{y}$ is attenuation exponent).
Using the approach of the power law attenuation, we developed a method to determine the according parameters (a and y) from measured data of KIT’s 3D USCT III with broadband signals (0.5-5 MHz). The individual broadband attenuation signals are being windowed and transformed into the Fourier domain to calculate an attenuation value for sub-bands of the available bandwidth. Subsequently an attenuation map is reconstructed for each sub-band. These attenuation maps are used to perform a parameter fit for each voxel to determine the two parameters a and y.
The method has been applied successfully on simulated 3D data using a ray based simulation suite to validate the approach (RMSE of a = 0.294 $\mathrm{\frac{dB}{MHz^y \cdot cm}}$, RMSE of y = 1.361). Furthermore the k-wave toolbox has been used to test the concept with 2D simulated data (RMSE of a = 0.0316 $\mathrm{\frac{dB}{MHz^y \cdot cm}}$, RMSE of y = 0.2197). In addition results with experimental data will be presented.
