Regularized ultrasound phantom-free local Attenuation Coefficient Slope (ACS) imaging in homogeneous and heterogeneous tissues
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IEEE Transactions on ultrasonics, ferroelectrics and frequency control ; vol. 69, no 12, p. 3338-3352.Éditeur·s
Institute of electrical and electronics engineersRésumé·s
Attenuation map or measurements based on local
attenuation coefficient slope (ACS) in quantitative ultrasound
(QUS) has shown potential for diagnosis of liver steatosis. In liver
cancers, tissue abnormalities and tumors detected using ACS are
also of interest to provide new image contrast to clinicians.
Current phantom-based approaches have the limitation of
assuming comparable speed of sound between the reference
phantom and insonified tissues. Moreover, these methods present
the inconvenience for operators to acquire data on phantoms as
well as on patients. The main goal was to alleviate these drawbacks
by proposing a methodology for constructing phantom-free
regularized (PF-R) local ACS maps and investigate the
performance in both homogeneous and heterogeneous media. The
proposed method was tested on two tissue mimicking media with
different ACS constructed as homogeneous phantoms, side-byside and top-to-bottom phantoms, and inclusion phantoms with
different attenuations. Moreover, an in-vivo proof-of-concept was
performed on healthy, steatotic and cancerous human liver
datasets. Modifications brought to previous works include: a) a
linear interpolation of the power spectrum in log-scale; b) the
relaxation of the underlying hypothesis on the diffraction factor;
c) a generalization to nonhomogeneous local ACS; and d) an
adaptive restriction of frequencies to a more reliable range than
the usable frequency range. Regularization was formulated as a
generalized LASSO, and a variant of the Bayesian Information
Criterion (BIC) was applied to estimate the Lagrangian multiplier
on the LASSO constraint. In addition, we evaluated the proposed
algorithm when applying median filtering before and after
regularization. Tests conducted showed that the PF-R yielded
robust results in all tested conditions, suggesting potential for
additional validation as a diagnosis method.
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