Breast lesion characterization by parametric imaging of subharmonic signals from ultrasound contrast agents

Parametric imaging of contrast media perfusion in breast lesions may be a useful tool in determining malignancy and grade of suspected breast tumors. Traditional ultrasound contrast modes have applied this technique, but they often suffer from reduced blood-to-tissue signal due to the tissue´s ability to express signal at the transmit and higher harmonic frequencies. Alternatively, it has been shown that imaging at the subharmonic frequency (transmit at f₀, receive at f₀/2) results in near complete tissue signal suppression. In this regard, parametric subharmonic imaging (SHI) may be an ideal tool for breast lesion characterization, because the signal is generated almost exclusively by contrast microbubbles within the vasculature. In this study, we examined the ability of parametric SHI to characterize breast lesions. Digital SHI clips of 16 breast lesions from 14 women were acquired during contrast injection and used to generate parametric maps of cumulative maximum intensity (CMI), time to peak (TTP), estimated perfusion (EP) and area under the time-intensity curve (AUC). No significant variations were detected with CMI (p = 0.80), TTP (p = 0.35) or AUC (p = 0.65), while a statistically significant variation was detected for the average pixel EP (p = 0.002). While our initial sample size is limited, preliminary results indicate parametric SHI may be a useful tool for breast lesion characterization.