Blood Flow Imaging Technique for Intravascular Ultrasound

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1.RF echo processingWe developed a new time domain correlation technique for detecting displacement and velocity vectors. The technique is based on calculation of the correlation between RF echo detected by a single transducer at a fixed repetition rate. Relation between the velocity vector and correlation was derived theoretically. Advanced RF signal processing techniques for evaluation of structure and charactor of biological tissue were also discussed.2.Measurement system>>Transducers for IVUSSmall transducers (1.2mm * 0.8mm) which can be used in the IVUS catheter were developed. Improvement of spatial resolution and speckle reduction in the B-mode image were discussed.>>Data acquisition and processing systemRF echo signal of the 16 sequential radial scan images is digitized into a 4 Mbyte digital data and a correlation image is processed in several minutes using personal computer. A blood flow phantom was also diveloped for in vitro experiments.3.Experimental evaluation>>Measurement of flow velocity (1-D distribution)In vitro experiments to measure the one-dimensional distribution of the flow velocity in the flow phantom were carried out. The experimental results demonstrated the practicability of the flow velocity measurement in the IVUS using the correlation technique.>>Detection of vascular lumen (2-D imaging)Extension of the correlation technique to the radial scan image was discussed. In this case, it is difficult to measure the flow velocity using correlation technique. However, still it is possible to get the information whether it flows or not. In vitro experiment showed that the vascular lumen was clearly identified in the radial scan image using the correlation technique.