Characterization of renal masses with harmonic and subharmonic contrast-enhanced ultrasound

The objective of this study was to compare coded harmonic imaging (HI) to pulse-inversion subharmonic imaging (SHI) in the characterization of renal masses. Twelve patients with 13 renal masses provided informed consent for an off-label CEUS exam prior to renal mass biopsy and cryoablation. All scanning was performed on a modified Logiq 9 ultrasound scanner with a 4C probe (GE Healthcare, Milwaukee, WI). Following baseline imaging, patients received a 2 ml bolus IV injection of the ultrasound contrast agent Optison (GE Healthcare, Princeton, NJ) and 10 ml flush during simultaneous 2D dual imaging in both grayscale (f = 4.0 MHz) and SHI (ftransmit = 2.5 MHz, frecieve= 1.25 MHz). Following a 15 min wait, patients received a 1 ml contrast injection during imaging with the unit's HI package (ftransmit = 2.0 MHz, frecieve= 4.0 MHz). A blinded radiologist with experience in CEUS evaluated the heterogeneity, intensity, and wash-in/wash-out kinetics of enhancement in the mass relative to the renal cortex. Additionally, contrast signal time intensity curves (TICs) were constructed from both the renal mass and cortex, fit to a contrast wash-in model, and used to calculate the time to peak, perfusion, maximum intensity, and area under the curve. Finally, the radiologist and TIC findings from each CEUS imaging mode were compared to pathology. Biopsy findings showed the 13 renal masses consisted of 9 renal cell carcinomas, 2 areas of benign renal parenchyma, 1 area of renal necrosis, and 1 oncocytoma. All masses showed heterogeneous enhancement with both SHI and HI. Increased enhancement of the mass relative to the renal cortex was observed during the early contrast wash-in phase in 2/9 malignant and 3/4 benign lesions on SHI, and 3/9 malignant and 1/4 benign lesions on HI. Early contrast wash out in the mass relative to the cortex was observed in 6/9 malignant and 0/4 benign lesions in SHI (sensitivity = 67%, specificity = 100%), and 8/9 malignant and 1/4 benign lesions in HI (sensitivity = 89%, specificity = 75%). Comparison of the TIC parameters obtained from the renal mass and cortex of malignant lesions showed no statistically significant differences when compared to benign lesions (p > 0.2). Thus, visualization of early contrast washout on HI or SHI appears to be a reliable indicator of renal carcinoma on CEUS; albeit based on a limited sample size.