諧波成像衰減補償

Abstract

超音波影像解析度深受發射訊號的頻寬影響。欲得到高解析度影像則需要較高頻寬，目前常用來提升影像解析度是組織二倍頻諧波成相技術。然而，發射訊號頻寬與發射訊號週期數成反比，二倍頻產生能力與發射訊號週期數成正比。為了得到更高解析度得影像反而降低回波訊號的能量。因此，先前有人提出了合頻技術，運用窄頻寬利於二倍頻產生的特性，提升回波訊號的能量且透過提升合頻個數達到與脈衝反向技術相同的解析度。因此合頻技術可以擁有高對比度與解析度特性。然而合頻與寬頻脈衝反向技術同樣面臨組織衰減，散射子問題。因此本篇研究利用合頻的窄頻特性，提出衰減與散射子補償辦法使合頻的解析度與對比度獲得更好的提升。

The resolution of Ultrasound images is limited by the bandwidth of emitted signal; wider bandwidth is required for images with better resolution. Nowadays, tissue harmonic imaging utilized its broader bandwidth to achieve high-resolution images. However, the number of pulse cycles is reciprocal to the bandwidth of emitted signal but proportional to the production of Tissue Harmonic Signal. In order to break the trade-off between pulse cycles and image resolution, Synthetic Spectrum Imaging (SSI) was presented previously, the principle of which is based on the advantage that narrow band is beneficial to the production of Tissue Harmonic Signal. Under this advantage, the power of THS can be improved and the resolution can be raised to the same level with Pulse Inversion (PI) by increasing the number of synthetic bands. Thus, Synthetic Spectrum technique is capable to acquire high resolution and SNR images. Nevertheless, Synthetic Spectrum imaging has its challenge comes from the absorption effect of tissues, the main reason to reduce the benefits of SSI. Consequently, we presented a correction method to compensate the absorption effect of tissues for maintaining the high SNR and resolution benefits from SSI. Keywords: Synthetic Spectrum Imaging; tissue harmonic imaging; attenuation correction image; attenuation measurement; Pulse inversion.