| Cardiovascular disease is the leading cause of death in our society. Intravascular ultrasound (IVUS) is now an established modality in the management of coronary artery disease. However, conventional IVUS systems using circumferential arrays fire beams orthogonal to the main axis of the mounting catheter. The system produces high resolution cross-sectional images but must be guided by conventional X-ray angiography. A real-time forward-viewing array, integrated into the same catheter, could greatly reduce radiation exposure from angiographic guidance. Unfortunately, the mounting requirement of a catheter guide wire prohibits a full-disk imaging aperture. Given only an annulus of array elements, this dissertation discusses a design that uses a total of 210 transceiver firings with synthetic beamforming for a given 3-D image frame. Simulation results demonstrate this design can achieve side-lobes near −40dB for on-axis situations and about −30dB for steering to the edge of a 60°cone.; A scheme, called Coded EXcitation with Spectrum Inversion (CEXSI) has been proposed to improve SNR in this system. An established optimal binary code whose spectrum has no nulls and possesses the least variation is used for transmission. Decoding is a simple matter of spectrum inversion. Various transmission techniques can be employed to improve energy coupling within the transducer pass-band. CEXSI has the potential to achieve very low (<−80dB) side-lobes. For a 2.6μs code, an array element on the ring-annular array with a center frequency of 10MHz and fractional bandwidth of 38%, range side-lobes of about −40dB have been achieved experimentally with a negligible compromise in range resolution. SNR improvement also has been characterized at about 14dB.; The 3-D data set from such an array opens up opportunities for compounding in both axial and lateral directions. To explore this potential, simulation studies analyzing 3-D ultrasound data from various phantom geometries have been performed. For a vessel phantom, the results indicate compounding could boost contrast to noise ratio (CNR) (up to a factor of 4 in the results) without a significant compromise in image resolution. For an isotropic cyst phantom, axial and lateral compounding perform similarly. Such improvement should be helpful for guidance in interventional procedures.; Initial experiments have been performed on a prototype ultra-sparse array. The results so far demonstrated the potential of the system. |
