Advances in computed tomography and magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma(HCC)is the most common primary liver cancer.Imaging is important for establishing a diagnosis of HCC and early diagnosis is imperative as several potentially curative treatments are available when HCC is small.Hepatocarcinogenesis occurs in a stepwise manner on a background of chronic liver disease or cirrhosis wherein multiple genes are altered resulting in a range of cirrhosisassociated nodules.This progression is related to increased cellularity,neovascularity and size of the nodule.An understanding of the stepwise progression may aid in early diagnosis.Dynamic and multiphase contrast-enhanced computed tomography and magnetic resonance imaging still form the cornerstone in the diagnosis of HCC.An overview of the current diagnostic standards of HCC in accordance to the more common practicing guidelines and their differences will be reviewed.Ancillary features contribute to diagnostic confidence and has been incorporated into the more recent Liver Imaging Reporting and Data System.The use of hepatocyte-specific contrast agents is increasing and gradually changing the standard of diagnosis of HCC;the most significant benefit being the lack of uptake in the hepatocyte phase in the earlier stages of HCC progression.An outline of supplementary techniques in the imaging of HCC will also be reviewed.

Focal liver lesions:Practical magnetic resonance imaging approach

With the widespread of cross-sectional imaging, a growth of incidentally detected focal liver lesions(FLL) has been observed. A reliable detection and characterization of FLL is critical for optimal patient management. Maximizing accuracy of imaging in the context of FLL is paramount in avoiding unnecessary biopsies, which may result in post-procedural complications. A tremendous development of new imaging techniques has taken place during these last years. Nowadays, Magnetic resonance imaging(MRI) plays a key role in management of liver lesions, using a radiation-free technique and a safe contrast agent profile. MRI plays a key role in the non-invasive correct characterization of FLL. MRI is capable of providing comprehensive and highly accurate diagnostic information, with the additional advantage of lack of harmful ionizing radiation. These properties make MRI the mainstay for the noninvasive evaluation of focal liver lesions. In this paper we review the state-of-the-art MRI liver protocol, briefly discussing different sequence types, the unique characteristics of imaging non-cooperative patients and discuss the role of hepatocyte-specific contrast agents. A review of the imaging features of the most common benign and malignant FLL is presented, supplemented by a schematic representation of a simplistic practical approach on MRI.

In vivo hyperthermia effect induced by high-intensity pulsed ultrasound

Hyperthermia effects （39-44 ℃） induced by pulsed high-intensity focused ultrasound （HIFU） have been regarded as a promising therapeutic tool for boosting immune responses or enhancing drug delivery into a solid tumor. However, previous studies also reported that the cell death occurs when cells are maintained at 43 ℃ for more than 20 minutes. The aim of this study is to investigate thermal responses inside in vivo rabbit auricular veins exposed to pulsed HIFU （1.17 MHz, 5300 W/cm2, with relatively low-duty ratios （0.2%-4.3%）. The results show that： （1） with constant pulse repetition frequency （PRF） （e.g., 1 Hz）, the thermal responses inside the vessel will increase with the increasing duty ratio; （2） a temperature elevation to 43 ℃ can be identified at the duty ratio of 4.3%; （3） with constant duty ratios, the change of PRF will not significantly affect the temperature measurement in the vessel; （4） as the duty ratios lower than 4.3%, the presence of microbubbles will not significantly enhance the thermal responses in the vessel, but will facilitate HIFU-induced inertial cavitation events.

Nanoparticles as contrast agents for photoacoustic brain imaging

Photoacoustic(PA)imaging has emerged as a promising technique for real-time detection and diagnosis of brain-related pathologies,due to its advantages in deep penetration of ultrasound imaging and high resolution of optical fluorescence imaging.We herein provide an overview on the latest developments of nanoparticles as contrast agents specifically designed for PA imaging of brain tumor,and brain vascular and other brain-related diseases.Five design considerations of high-performance PA contrast agents for brain-related disease diagnosis are discussed,which include(1)strong absorption in NIR or NIR-Ⅱ window,(2)good biocompatibility,(3)high photothermal conversion efficiency,(4)precise nanostructure control,and(5)spe-cific targeting capability.Challenges and perspectives of developing more robust and universal contrast agents for enhanced PA imaging are discussed at the end.