Sonazoid microbubble is one of the second generation ultrasound contrast agents. Sonazoid is unique between second generation contrast agents because it is recognized and phagocytosed by macrophages during flowing in the circulating blood. Kupffer imaging is obtained the liver imaging 10 minutes after intravenous injection of Sonazoid. Kupffer imaging is obtained using harmonic imaging technique at a low mechanical index (MI). Harmonic imaging used for Sonazoid imaging is phase and amplitude modulation harmonic imaging. A low MI, 0.2 is used for Kupffer imaging. If the same dose of Sonazoid as vascular imaging is used, Kupffer imaging lasts for long time, 3 to 4 hours.
The most useful indication of Kupffer imaging is detection of liver timorous lesions. Small sized liver metastatic tumors are detectable using the Kupffer imaging. In the case of small sized tumor, the size being 1cm or less, the detectable tumor number using Sonazoid study is 40% increased comparing with dynamic CT.
In hepatocellular carcinoma (HCC), the number of the Kupffer cell in the tumor tissue is not decreased in well differentiated HCCs while the Kupffer cells are completely absent in the metastatic liver tumor. Therefore, the detectability of HCCs using Sonazoid Kupffer study is lower than that of metastatic liver tumors. Kupffer cells are present but their number is decreased in moderately differentiated HCCs and it is remarkably decreased in poorly differentiated HCCs. Therefore, Kupffer imaging can be used for histological differentiation of HCCs.
Kupffer imaging is also used for puncture guidance and treatment efficacy evaluation of RFA in liver cancer management. The low MI harmonic imaging of the Kupffer imaging is so stable that it is used as puncturing guidance. In this case, the tumor is shown clearly as a signal deficit from resonating microbubbles.
It is known that the number and function of Kupffer cells decrease in various liver diseases. They are remarkably decreased in non-alcoholic steato-hepatitis (NASH) even when the disease stage of NASH is not yet advanced, e.g. F1 to F3. The Kupffer imaging can be used for not only distinguishing NASH from NAFLD (non-alcoholic fatty liver disease) but also the evaluation of treatment efficacy of NASH because the decrease in signal intensity of the Kupffer imaging dramatically recovers following the dietary and exercise therapies.
In summary, Kupffer imaging of the liver using Sonazoid has high potential in the diagnosis and treatment of various liver diseases.