What is the current situation in liver imaging?

Abstract

IntroductionImaging algorithms of the liver have undergone continuous change over the last 15 years. While liver sonography was a first-choice modality in the past, computed tomography (CT) has become the leading modality in most institutions because of multiphasic and dynamic imaging capabilities. With the introduction of new breath-hold sequences and specific contrast agents during the last decade, the role of magnetic resonance (MR) imaging has changed from a pure problem-solver in lesion characterization to a first-step modality in hepatic imaging. Recent advances in functional imaging have introduced contrast-enhanced sonography and 18-FDG-PET as innovative and promising techniques into the broad spectrum of liver imaging. Imaging methods SonographySince sonography is easily available, noninvasive, and provides a depth-dependent spatial resolution combined with a good signal-to-noise ratio in most pathologic entities of the liver, it plays an important role in the firststep imaging evaluation providing high detection and specificity rates in capable hands. However, because sonography is highly operator-and equipment-dependent, sensitivity and specificity values vary significantly from institution to institution and are generally inferior to those of dynamic helical (multidetector) CT and MR imaging.The sensitivity of conventional "gray-scale" sonography in the detection of liver metastases, as reported in the literature, is highly dependent on the study design and the referred "gold standard" and ranges between 53% and 77% [1, 2]. Thus, sonography commonly yields lover detection rates than contrast-enhanced CT or MR imaging, which may be caused either by iso-echogenic focal lesions with a poor lesion-to-liver contrast, diminished spatial resolution with increasing insonation depth, poor acoustic properties in obese patients, or generally by a disadvantageous anatomical location.With the development of first-generation microbubble suspensions containing air, which act as acoustic backscatter, dynamic imaging of the liver was introduced into sonography. Second-generation agents, such as SonoVue (Bracco Imaging, Milan, Italy), taking advantage of stable phospholipid-coated gas particles, can withstand much better the acoustic pressure of insonation resulting in an increased half-time of the agent and thus providing a prolonged diagnostic window. These agents are used not only to increase the Doppler signal amplitude during the vascular phase, but also to differentiate hepatocellular tissue from neoplastic disease. The selective uptake of these microbubbles by ultrastructurally normal liver parenchyma with a probable interaction with the reticuloendothelial system (RES) during the "late phase", i.e. 2-4 min after contrast administration, will increase the lesion-to-liver contrast. Since nonhepatocellular tissue, e.g. metastases, is not able to "store" the microbubbles, it appears as hypoechoic "hole" in contrast-enhanced sonography (Fig. 1). This fact has led to the ongoing routine use of secondgeneration ultras...

Liver specific magnetic resonance imaging contrast medium for evaluation of focal liver lesions – Initial experience at a service hospital

“…3 MR imaging has the single-window potential to provide comprehensive and accurate information in hepatic imaging. 1 It can detect diffuse and focal liver lesions, with the added advantage of tissue characterization and multi-planar anatomy, thus obviate need for other imaging modalities. 6 The augmentation of imaging with MRI contrast media further provides essential information regarding vascular dynamics of any lesion, comparable to the multi-phase CECT studies.…”

“…1 The past two decades have seen widespread use of ultrasonography (USG), contrast enhanced computerized tomography (CECT) and magnetic resonance imaging (MRI). 2 While USG remains the modality of choice for screening purposes in liver imaging, CECT liver performed using multi-detector scanners with volumetric data acquisition and multi-planar reconstruction capabilities has been the preferred hepatic imaging modality.…”