Dynamic imaging of pancreatic diseases by contrast enhanced coded phase inversion harmonic ultrasonography

Abstract

Background: Coded phase inversion harmonic ultrasonography, a newly available sonographic technique, enables visualisation of slow flow in minute vessels in a real time fashion with the use of a sonographic contrast agent containing monosaccharide. Our purpose was to employ this novel technique to observe microvessels in pancreatic tumours.

Subjects and methods: Sixty five patients with suspicious pancreatic tumours received contrast enhanced coded phase inversion harmonic ultrasonography, contrast enhanced computed tomography, and endosonography. Final diagnoses based on histological findings were pancreatic ductal carcinomas in 49 patients, inflammatory pseudotumours with chronic pancreatitis in seven, and endocrine tumours in nine. For contrast enhanced coded harmonic ultrasonography, Levovist, a contrast agent, was injected intravenously as a bolus. When the first microbubble signal appeared in the pancreas, images of the ideal scanning plane were displayed in a real time continuous fashion (vessel images). Subsequently, interval delay scanning (perfusion images) was taken to demonstrate parenchymal flow. Tumour vascularity was evaluated by using the two types of imaging. Sensitivities for depicting pancreatic tumours were compared between three examinations.

Results: Contrast enhanced ultrasonography demonstrated tumour vessels in 67% of pancreatic ductal carcinomas, although most were relatively hypovascular compared with the surrounding pancreatic tissue. The vascular patterns of tumours obtained by contrast enhanced ultrasonography were closely correlated with those obtained by contrast enhanced computed tomography. Values for sensitivity in depicting pancreatic tumours of 2 cm or less in size were 68% for contrast enhanced computed tomography, 95% for endosonography, and 95% for contrast enhanced ultrasonography.

Conclusion: Contrast enhanced coded phase inversion harmonic ultrasonography successfully visualised fine vessels in pancreatic tumours and may play a pivotal role in the depiction and differential diagnosis of pancreatic tumours.

Figure 1

Classification of vascular patterns of pancreatic tumours. Type I: no vessels on the vessel image and no enhancement on the perfusion image. Type II: few vessels on the vessel image and heterogeneous enhancement in the hypovascular area on the perfusion image. Vascularity is less than in the surrounding pancreatic tissue. Type III: similar vascularity to the surrounding pancreatic tissue on the vessel image and homogenous isovascular enhancement on the perfusion image. Type IV: abundant vessels on the vessel image and hypervascular enhancement on the perfusion image.

Figure 2

Contrast indices of the four types of contrast enhanced ultrasonography classified tumours. p<0.05 was considered significant.

Figure 3

Typical case of a type I tumour. A 43 year old man with a pancreatic ductal cancer found by contrast enhanced ultrasonography (US). (A) Perfusion image of contrast enhanced US shows a hypovascular tumour of 1.3 cm in diameter adjacent to the splenic vein (SV). (B) Contrast enhanced computed tomography failed to depict the tumour.

Figure 4

Typical case of a type II tumour. A 71 year old man with a pancreatic ductal cancer. (A) Contrast enhanced computed tomography shows a low dense mass in the pancreatic body to the tail. (B) Fundamental B-mode ultrasonography (US) shows the swollen pancreas. However, the margin of the tumour is unclear. (C) Vessel image of contrast enhanced US. The architecture of the vessels (arrowheads) in the tumour was clearly observed. (D) Perfusion image of contrast enhanced US. A hypovascular tumour with heterogeneous network-like enhancement (arrowheads) was clearly depicted.

Figure 5

Typical case of a type III tumour. A 59 year- old man with an inflammatory pseudotumour with chronic pancreatitis. (A) Endoscopic retrograde cholangiopancreatography shows stenosis of the main duct of the pancreatic head (arrowheads). (B) Fundamental B-mode ultrasonography (US) shows a low echoic mass (arrow) in the pancreatic head. (C) Vessel image of contrast enhanced US. The splenic vein (SV) was enhanced at the dorsal side of the pancreatic body. Vessels in the mass were observed as those in the pancreatic body. (D) Perfusion image of contrast enhanced US. As the mass in the pancreatic head was enhanced homogeneously as in the other part of pancreas, there was no visible tumour-pancreas contrast.

Figure 6

Typical case of a type IV tumour. A 38 year old woman with a pancreatic islet tumour. (A) Contrast enhanced computed tomography does not depict any tumours in the pancreas. (B) Fundamental B-mode ultrasonography (US) shows a low echoic tumour (arrow) of 0.7 cm in diameter at the pancreatic tail. (C) Vessel image of contrast enhanced US. There were abundant vessels in a spherical tumour (arrow) at the pancreatic tail. (D) Perfusion image of contrast enhanced US. The tumour (arrow) was relatively hypervascular compared with the other part of the pancreas.