摘要
Empirical mode decomposition (EMD) is an adaptive method for decomposing a signal into intrinsic mode functions (IMFs). This study explored using EMD of ultrasound imaging for gain-independent measurements on tissue echogenicity. The IMF-based echogenicity ratio (IER) was proposed using the first (C-1) and second IMFs (C-2) of ultrasound radiofrequency data. Experiments on lipid phantoms were conducted to investigate the practical performance of IER. Phantoms with lipid concentrations 0%-30% (n = 36) were scanned using a clinical ultrasound scanner to acquire the radiofrequency data under different gains (12-33 dB) for EMD and IER calculations. Experiments on a tissue-mimicking phantom were further performed using the same ultrasound system and data acquisition procedure to investigate the effect of ultrasound frequency on the IER at 5-8 MHz. Experimental results showed that the IER measured under 33-dB gain decreased from 6.65 +/- 0.23 to 3.97 +/- 0.10 when the lipid concentrations were increased from 0% to 30%. When 12-dB gain was used, the IER decreased from 6.21 +/- 0.29 to 3.39 +/- 0.07. However, whenincreasing the frequency, the IER had a mean decreasing rate of 8.67% per MHz, which was lower than those of the C-1 and C-2 intensities. The proposed IER may allow gain-independent measurement on tissue echogenicity.