Optimal smoothing splines improve efficiency of entropy imaging for detection of therapeutic benefit in muscular dystrophy

Abstract

We have reported previously on sensitivity comparisons of signal energy and several entropies to changes in skeletal muscle architecture in experimental muscular dystrophy before and after pharmacological therapeutic intervention [M. S. Hughes, IEEE Trans. UFFC. 54, 2291–2299 (2007)]. The study was based on a moving window analysis of simple cubic splines that were fit to the backscattered ultrasound and required that the radio frequency ultrasound (RF) be highly oversampled. The current study employs optimal smoothing splines instead to determine the effect of analyzing the same data with increasing levels of decimation. The RF data were obtained from selected skeletal muscles of muscular dystrophy mice (mdx: dystrophin -/-) that were randomly blocked into two groups: 4 receiving steroid treatment over 2 weeks, and 4 untreated positive controls. Ultrasonic imaging was performed on day 15. All mice were anesthetized then each forelimb was imaged in transverse cross sections using a Vevo-660 with a single-element 40 MHz wobbler-transducer (model RMV-704, Visualsonics). The result of each scan was a three dimensional data set 384 × 8192 × # frames in size. We find the equivalent sensitivity of this new approach for detecting treatment benefits as before (p<0.03), but now at a decimated sampling rate slightly below the Nyquist frequency. This implies that optimal smoothing splines are useful for analysis of data acquired from point of care imaging devices where hardware cost and power consumption must be minimized.