IVUS beyond the horizon Antonius F.W. van der Steen 1,2 *, Radj A. Baldewsing 1 , F. Levent Degertekin 3 , Stanislav Emelianov 4 , Martijn. E. Frijlink 1 , Yuji Furukawa 5 , Dave Goertz 1,2 , Mustafa Karaman 6 , Pierre T. Khuri-Yakub 7 , Kang Kim 8 , Frits Mastik 1 , T. Moriya 9 , Ömer Oralkan 7 , Yoshifumi Saijo 10 , Johannes A Schaar 1 , Patrick W Serruys 1 , Shriram Sethuraman 4 , Akira Tanaka 11 , Hendrik. J. Vos 1,12 , Russell Witte 8 , Matthew O’Donnell 8 1. Biomedical Engineering, Thorax Center Erasmus MC, Rotterdam, The Netherlands; 2. Interuniversity Cardiology Institute of the Netherlands; 3. Georgia Institute of Technology, Atlanta, Georgia, USA; 4. Department of Biomedical Engineering, The University of Texas at Austin, USA; 5. Tokyo University of Agriculture and Technology, Tokyo, Japan; 6. Isik University, Istanbul, Turkey; 7. E. L. Ginzton Laboratory, Stanford University, Stanford, California, USA; 8. Department of Biomedical Engineering, Univ. of Michigan, Ann Arbor, USA; 9.Tokyo Metropolitan University, Tokyo, Japan; 10. Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan; 11. Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, Japan; 12. Seismics and acoustics, Technical University Delft, The Netherlands Introduction Intravascular Ultrasound is a clinically available technique that can image the vessel wall and atherosclerotic plaque 1 . Although the first patent on this technique dates from 1972 2,3 , the first catheters for clin- ical use were only available in the late eighties 4,5 . Since then this diag- nostic technique is ever evolving. The main clinical applications to date have been assessment of free lumen and atherosclerotic plaque area 6 , volume and therapy guidance 7,8 and guidance of stent placement 9 . To a lesser extent, it has been used for dosimetry in brachytherapy 10 and for assessing the true 3D orientation of coronary arteries and plaque to perform haemodynamic and shear stress studies 11-13 . At present, IVUS has only been used to a limited percentage of its potential. Most concepts mature outside the view of a clinical audi- ence, but are widely discussed in the technical ultrasonics and bio- medical engineering societies before they become available prod- ucts. Probably the most appropriate platform for this has been the annually held IEEE Ultrasonics Symposium. Most IVUS equipment and signal processing methods were discussed here long before they became available in the clinic 14,15 . The array catheter and its beam forming were introduced in 1991 16 . Also forward looking IVUS has been discussed by several groups 17,18 . Qualitative flow 19,20 and quantitative flow 21-23 assessment derived from IVUS data were intro- duced here as well as tissue characterization using RF data, now available under the name Virtual Histology 24-27 . Also IVUS Elastography, Palpography and tissue velocity imaging 28-32 were nurtured at this symposium. This paper gives a review of IVUS techniques under development that were discussed at the 2005 IEEE Ultrasonics symposium. Although not all will become products, it gives a good impression of what is cooking in engineering kitchens. Forward-Viewing IVUS using CMUTs Forward-viewing ultrasound volume images are desired for many intravascular and intracardiac applications such as guiding treat- ment of chronic total occlusion, helping stent deployment, and monitoring ablation procedures in the heart. Because of the requirements for a guidewire in catheters, an annular ring is the preferred geometry for transducer arrays. However, it is very chal- lenging to implement this geometry in a very small scale (1-2 mm) using existing piezoelectric transducer technology 18 . * Corresponding author: Biomedical Engineering, Thorax Center Ee 23.02, Erasmus MC Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands E-mail: a.vandersteen@erasmusmc.nl © Europa Edition 2006. All rights reserved. - 132 - Expert review EuroInterv.2006;2:132-142