Purpose: High intensity focused ultrasound (HIFU) has the potential to locally and non-invasively treat cancer with fewer side effects than alternative therapies. However, motion and tissue heterogeneity in the abdomen can compromise the HIFU focus and confound current thermometry methods.
Methods: The proposed thermometry method combines principal component analysis (PCA), as a multi-baseline technique, and projection onto dipole fields (PDF), as a near-referenceless method. PCA forgoes tracking tools by projecting incoming images onto a subspace spanning the motion history. PDF is subsequently used to synthesize the naturally feasible components of the residual phase using a magnetic dipole model. This leaves only the phase shifts that are induced by HIFU.
Results: With in vivo measurements, in porcine and human kidneys, the mean pixel-wise temperature SD was 0.86 ± 0.41°C in selected regions of interest (ROIs) across all data sets, without any user-interaction or supplementary tracking tools. This is an improvement over a benchmark hybrid method, which scored 1.36 ± 1.20°C on the same data. Uncorrected subtraction of the data yielded a score of 3.02 ± 2.87°C.
Conclusion: The PCA-PDF hybrid method achieves superior artifact correction by exploiting the motion history and intrinsic magnetic susceptibility of the underlying tissue.
Keywords: HIFU; MR thermometry; artifacts; motion compensation; susceptibility.
© 2018 International Society for Magnetic Resonance in Medicine.