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New real-time image fusion technique for characterization of tumor vascularisation and tumor perfusion of liver tumors with contrast-enhanced ultrasound, spiral CT or MRI: First results
Introduction
The detection and characterization of liver tumors can frequently only accomplished by combining different imaging techniques. The imaging modality of first choice in liver imaging is ultrasound including dedicated vascular imaging. However contrast-enhanced ultrasound (CEUS) is required for the detection of smaller liver lesions with sufficient confidence [1–6]. A certain disadvantage of ultrasound is the fact, that the method is dependent on the experience of the examiner. Contrast-enhanced multidetector- CT (MD-CT) can detect and characterize liver lesions with a high degree of diagnostic certainty since it involves imaging during the arterial and portal-venous contrast phase. On the other hand it is not possible to monitor the contrast enhancement of the lesions continually. This is not even possible with contrast-enhanced MRI. Additionally there are several contra-indications for contrast media application in CT and MRI [5]. Nevertheless, ultrasonic contrast media can be used even if the kidney function is reduced. Additionally, CEUS is being employed increasingly to determine the dynamic vascularisation and perfusion, and thereby to characterize liver lesions which cannot be detected by CT or MRI [7–12]. Frequently there are different numbers of lesions detected by CEUS, CT and MRI. This is especially the case with hypervascularised foci of hepatocellular carcinomas (HCC). Consequently a real-time fusion of CEUS with MD-CT or CEUS with MRI would be a perfect method to combine the continuous dynamics of CEUS with the tumor perfusion data and the high spatial resolution obtained with MD-CT and MRI. This could be applied for detection, characterization and monitoring of interventions.
With the development of a new ultrasound transducer together with a navigation system and dynamic positioning system (“Vnav”) it is becoming possible to combine current ultrasonic images with uploaded CT or MRI data. That enables us to combine the advantages of diverse imaging procedures within the framework of an ultrasonic examination and to enhance the certainty of a diagnosis. Modern probe technologies and very sensitive contrast-enhanced ultrasound imaging (amplitude modulation) with a low mechanical index (low MI technique) thereby afford us the prerequisites for an image fusion that enables an improved visualization of the microcirculation. There are only a few studies about imaging fusion with native US and CT or MRI [13–17].
The aim of this study is to present the first clinical results concerning the evaluation and characterization of the vascularisation and perfusion of liver tumors by means of real-time image fusion of CEUS and MD-CT or MRI with the help of a new ultrasound navigation technique.
Authors
E.M. Jung, A.G. Schreyer, D. Schacherer, C. Menzel, S. Farkas, M. Loss, S. Feuerbach, N. Zorger and C. Fellner