Contrast-enhanced ultrasonography: advance and current status in abdominal imaging

Abstract

In the field of contrast-enhanced ultrasonography (US), contrast agents are classified as either first- or second-generation agents depending on the gas within the microbubbles. In the case of first-generation contrast agents, a high-mechanical-index technique is used and only intermittent scanning is possible due to the early destruction of the microbubbles during the scanning. The use of second-generation contrast agents in a low-mechanical-index technique enables continuous scanning. Besides the detection and characterization of focal liver lesions, contrastenhanced US is helpful in the monitoring of radiofrequency ablation therapy and in the targeting step of an US-guided biopsy. Recently, there has been a demand for new criteria to evaluate the treatment response obtained using anti-angiogenic agents because morphologic criteria alone may not reflect the treatment response of the tumor and contrast-enhanced US can provide quantitative markers of tissue perfusion. In spite of the concerns related to its cost-effectiveness, contrast-enhanced US has the potential to be more widely used as a complimentary tool or to substitute the current imaging modalities in some occasions.

Keywords: Abdomen; Contrast media; Image enhancement; Microbubbles; Ultrasonography.

Fig. 1.. A 64-year-old male with focal nodular hyperplasia.

A. A T1-weighted magnetic resonance image showed a hypervascular nodular lesion in the right lobe of the liver (arrow). B. In the hepatobiliary phase, the lesion showed a higher signal intensity (arrow) than the adjacent liver parenchyma. C. In the arterial phase of contrast-enhanced ultrasonography (US), the lesion showed hypervascularity (arrowheads). D. In the portal venous phase, the lesion showed iso-echogenicity (arrowhead) relative to the adjacent liver. The lesion was confirmed as focal nodular hyperplasia by an US-guided biopsy.

Fig. 2.. A 64-year-old female with gallbladder carcinoma.

A. In the portal venous phase of computed tomography, a hypo-attenuating lesion was noted in segment 7 of the liver (arrow). B. In the portal venous phase of the ultrasonography (US), the lesion showed hypo-echogenicity compared with the adjacent liver. The lesion was confirmed as a metastasis by a US-guided biopsy (arrow).

Fig. 3.. A 57-year-old female with malignant portal vein thrombosis.

Computed tomography (A) and conventional ultrasonography (US) (B) showed tumor thrombosis (arrows) in the right and the main portal veins. C. On contrast-enhanced US, contrast enhancement suggesting tumor thrombosis was clearly noted within the thrombosis (arrowheads).

Fig. 4.. A 64-year-old female with metastatic neuroendocrine carcinoma in the liver.

A. The hepatobiliary phase of magnetic resonance showed a low signal intensity lesion in segment 4 (S4) of the liver (arrow). B. On conventional ultrasonography (US), the lesion was not clearly detected. C. After contrast enhancement, a low echoic lesion (arrow) was detected on S4 of the liver. US-guided biopsy was performed after lesion localization on contrast-enhanced US, and the lesion was confirmed as metastatic neuroendocrine carcinoma.

Fig. 5.. A 76-year-old male with gallbladder carcinoma.

A. On computed tomography, a nodular lesion with central necrosis was noted on S4 of the liver (arrow). B. Ultrasonography (US)-guided biopsy was performed, and the pathologic result was total necrotic tissue. C. On contrast-enhanced US, the lesion showed a peripheral enhancing area (arrow), which suggested a viable portion, with central necrosis (arrowheads). A re-biopsy was performed targeting the viable peripheral portion, and the final pathologic diagnosis was metastasis.

Fig. 6.. A 49-year-old female with vulvar cancer and acute pyelonephritis.

A. In the renal parenchyma phase of computed tomography (CT), a wedge-shaped hypo-attenuating lesion was newly detected in the mid pole of the left kidney (arrows). To exclude metastasis, an ultrasonography (US)-guided biopsy was planned. B. On conventional US, the lesion, which was noted on CT, was not detected. C. After contrast enhancement, a poorly enhancing wedge-shaped lesion was detected in the left kidney (arrowheads), enabling the US-guided biopsy.

Fig. 7.. A 49-year-old male underwent renal transplantation.

A. On contrast-enhanced ultrasonography, the hematoma (arrowheads) was well visualized around the transplanted kidney, but there was no evidence of active bleeding within the hematoma. B. A 2.8-cm unruptured aneurysm (arrow) was seen at the renal artery (arrowhead). C. On renal angiography, the renal artery aneurysm (arrow) was found to have originated from the transplanted renal artery. Stent graft placement was performed at the renal artery. D. After 1 week, the renal artery aneurysm was no longer visible. The arrowhead indicates the renal artery.

Fig. 8.. A 58-year-old male who underwent stent graft due to abdominal aortic aneurysm.

A. On contrast-enhanced computed tomography (CT), contrast agent extravasation (arrow) was suspected at the excluded aneurysmal sac. The patient had already undergone embolization therapy with Lipiodol and Histoacryl due to an endoleak (arrowhead). B. On contrast-enhanced ultrasonography, the contrast agent was observed in the excluded aneurysmal sac outside the aorta (arrow) but not from the abdominal aortic lumen, which was suggestive of a type-II endoleak. C. Embolization therapy was performed, and no evidence of a residual endoleak was found on the follow-up CT.