Time intensity curve analysis of subharmonic transabdominal and harmonic endoscopic contrast-enhanced ultrasound of pancreatic masses

Abstract

Pancreatic cancer is associated with poor clinical outcomes primarily due to the advanced stage at the time of diagnosis. Endoscopic harmonic ultrasound imaging (HI) is being used to characterize pancreatic masses. Alternatively, transabdominal subharmonic imaging (SHI) may limit invasiveness and better suppress nonlinear tissue echoes. In both approaches, time-intensity curve (TIC) analysis can be performed to quantify blood flow dynamics. The purpose of this study was to compare TICs from both HI and SHI ultrasound of pancreatic masses. Patients underwent both endoscopic HI and SHI prior to an endoscopic biopsy of a pancreatic mass. SHI (transmitting/receiving at 2.5/1.25 MHz) was performed on a modified Logiq 9 system with a 4C probe (GE Healthcare, Milwaukee, WI), while endoscopic HI ultrasound (transmitting/receiving at 4.7/9.4 MHz) was performed with a radial endoscope (GF-UTC180; Olympus, Tokyo, Japan) and a ProSound SSD α-10 scanner (Hitachi-Aloka, Tokyo, Japan). TIC analysis was performed on a pixel by pixel basis to generate parametric images of peak intensity, time to peak, perfusion, and area under the curve and compared by modality to pathology. To date, TIC processing has been completed on 10 cases that were not compromised by excessive motion. No significant differences were observed between imaging modes for time to peak, perfusion, or area under the curve (p>0.11), while peak intensity was different (p=0.01) most likely due to scanner-specific properties such as transmit power, etc. When grouped by pathology (adenocarcinoma vs. other masses), neither modality showed significant differences in any TIC parameter, with peak intensity being the closest to demonstrating differences (p= 0.06). While the feasibility of parametric imaging of pancreatic masses has been demonstrated, future efforts with increased sample size and motion correction are likely needed to better elucidate any differences in blood flow TIC parameters between benign and malignant pancreatic lesions.