Assessment of effects of attenuation and excitation modes on ultrasonic Nakagami parameter
| Autor: | Jiue-JiaWu, 吳珏佳 |
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| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 Statistical models, frequently adopted for describing the probability distribution function (PDF) of ultrasonic backscattered envelopes, have been utilized for tissue characterization. Due to the attenuation increase with ultrasonic frequency, the estimated statistical parameter can be affected by the broad-band attenuation in tissues and distortion of acquired echo signals. Hence, different ultrasonic frequencies and excitation signals were implemented to investigate the attenuation effect on statistical analysis of ultrasonic backscattered signals. Measurements were performed from tissue-mimicking phantoms, which were consisted of gelatin and glass beads with concentrations of 16 and 64 scatterers/mm3, using 3.5 and 7.5 MHz focus transducers. Per each experiment, a phantom was placed between the transducer and tissue-mimicking phantom for creating attenuation. Ultrasound signals were generated by exciting transducers with 1, 3, 5, and 10 cycles sinusoidal signals. The Nakagami statistical model was used to analyze the PDF of ultrasonic backscattered envelopes. This study further indicated that the attenuation could significantly vary the PDF of ultrasonic envelopes especially for the transducer was excited by monocycle sinusoidal signals. As a narrower bandwidth associated with the increase of cycles of tone burst was implemented, the attenuation effect was substantially reduced. The sinusoidal signals of 3 cycles among other excitation signals demonstrated the most appropriate performance to accommodate between attenuation effect and image resolution. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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