Abstract
This issue of Clinical Hemorheology and Microcirculation is dedicated to the developments in the application of high resolution ultrasound in clinical diagnostics.
The editors sought to provide information on the latest procedures for ultrasound bringing together outstanding original articles and reviews about new diagnostic information obtained by recent technological advances but also clarify well-established or controversial subjects. A very important step forward in ultrasound technology towards clinical application was the introduction of microbubbles as contrast enhancer. Contrast enhanced ultrasound (CEUS), performed with the intravenous injection of microbubble contrast agents applying the low mechanical index (MI) technique of contrast harmonic imaging has expanded the horizon for ultrasound imaging. CEUS provides a technique with superb sensitivity from early arterial phase up to late venous enhancement in dynamic realtime vascular imaging. For the first time, this ultrasound technology allows the non-invasive demonstration of blood flow of inner organs at a microcirculatory level [1, 2]. Further, the purely intravascular microbubbles enable ultrasound to be used to monitor changes in the blood flow of tumors and in inflamed areas in a diagnostic approach but also for therapy control. Its performance without any requirement for ionizing radiation and with no nephrotoxicity makes it a compelling choice in many clinical arenas and is now FDA approved for liver imaging, and also for children [1–8].
In this special issue, a first study evaluated factors which are associated with the initial incomplete ablation in radiofrequency ablation (RFA) for thyroid nodules [2]. Recent intraoperative studies reported the results of CEUS for immediate assessment of ablation status after RFA of hepatic malignancies [3]. These two articles showed the benefit of CEUS in the treatment control for ablation of solid nodules in various organs in terms of the virtues of CEUS such as real-time scanning, easy performance, and immediate assessment. In addition to qualitative evaluation for characterization [4, 5], quantitative evaluation of blood flow perfusion is also available with use of CEUS [6]. Other important applications are the assessment of vascular diseases such as vascular complications after liver transplantation or the detection of endoleaks after endovascular aortic repair (EVAR) [7, 8] or post-operative complications [9].
In addition and complement to CEUS, ultrasound elastography has gained increasing attention in recent years. There are two types of ultrasound elastography techniques: strain elastography and shear wave elastography (SWE). Both can be used to assess the tissue’s stiffness, whereas the former is qualitative and the latter is quantitative [11–14]. The tissue stiffness can be denoted by Young’s modulus (in kPa) or shear wave velocity (SWV) (in m/s). SWE such as transient elastography and the acoustic radiation force impulse technique of shear wave imaging are now also playing a pivotal role in the study of tissue fibrosis. Some studies have shown that elastography can detect both the progression and regression of fibrosis. Various SWE have been introduced in clinical practice and in this issue He et al. firstly evaluated the difference between two SWE in characterization of thyroid nodules [15]. Moreover, SWE might also be useful in assessing the patient’s prognosis in patients withmalignancy [16].
For both applications guidelines already exist [1, 9–11] and it can be anticipated that additional guidelines will be forthcoming as CEUS and elastography technology evolve and more clinical studies and new applications are developed.