- 學位論文
乳房鈣化點光聲陣列造影之可行性研究
Photoacoustic Array Imaging of Breast Calcifications: Feasibility Study
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摘要
本研究中我們基於醫用超音波陣列影像系統開發高穿透深度之光聲陣列造影系統，並以鈣化點仿體實驗驗證此整合式之光聲造影系統於乳房鈣化點偵測的可行性及造影穿透深度。實驗以伴隨惡性腫瘤之成份的羥基磷灰石（hydroxyapatite，HA）鈣化顆粒的吉利丁與雞胸肉仿體為掃瞄標的，使用此整合式之光聲影像系統，以5 MHz陣列超音波探頭搭配最佳化之700 nm光聲激發波長，以側向式(Sideward mode)與逆向式(Backward mode)對仿體鈣化點進行造影。並針對逆向式造影模式設計出光聲探頭，以蒙地卡羅模擬來最佳化光纖束與超音波探頭之配置，並與側向式造影做為比較。系統於3 cm深度的軸向解析度為 0.54 mm，橫向解析度為0.35 mm，elevational解析度估計為1.25 mm，目前成像速度最高可達10 frames/sec。實驗數據經由延遲相加波束合成技術(delay and sum, DAS)重建影像與使用可適性同調權重技術(coherence factor weighting, CF weighting)來提高影像之對比度，由目前實驗結果，此系統可取得0.3 mm－0.5 mm之鈣化點影像。針對0.5 mm鈣化點，在雞胸肉3 cm深度中影像訊雜比可達14 dB，可與乳房中之血液光聲訊號相比擬，我們亦將超音波影像與光聲影像疊合成為雙模態影像，可加強鈣化點影像之判讀以及作為乳房鈣化點切片之影像導引。另外，我們分析鈣化點的訊雜比，計算出此陣列光聲造影系統對於0.5 mm之鈣化點於真實乳房中的可偵測深度為3.0－3.5 cm，符合實際臨床乳房鈣化點可能出現之深度0.6 cm－3.0 cm，並提出雙波長切換法來嘗試分辨乳房中血液與鈣化點的訊號，結果顯示為可行的。未來希望能取得臨床的鈣化點來做進一步的驗證，也希望能提供另一種代表良性的鈣化點草酸鈣(calcium oxalate，COD)與HA的分辨法，以及利用超音波都卜勒來提供影像上血液資訊。
並列摘要
In this study, based on a medical ultrasound array imaging platform, we developed a high penetration photoacoustic (PA) array imaging system for visualization of breast calcifications. Phantom studies were used to verify the imaging capability and penetration depth of the developed PA system for calcification imaging. In our phantom studies, intralipid and chicken breast phantoms embedded with different-sized hydroxyapatite (HA) particles, major components of breast calcification associated with malignant breast cancer, were imaged. A laser at 700 nm was used for photoacoustic excitation and imaging was performed in sideward mode and backward mode. A PA transducer made by integrating the fiber bundle with the ultrasound transducer was applied for backward-mode photoacoustic signal detection; its configuration was optimized through Monte Carlo simulation. Currently, the axial, lateral, and elevational resolution of this developed PA array imaging system are 0.54 mm, 0.35 mm, and 1.25 mm, respectively, and its highest frame rate is 10 frames/sec, which is limited by the laser pulse rate. The image was reconstructed by delay-and-sum algorithm while contrast enhancement was performed by coherence factor weighting. Experimental results demonstrated that this system is capable of calcification imaging of 0.3 - 0.5 mm HA particles. For the 0.5 mm HA particles at depth of 3 cm, the imaging signal-to-noise ratio was about 14 dB, comparable to that of blood. We then developed a dual-modal PA and ultrasound imaging to further enhance the calcification imaging capability, which may facilitate needle biopsy guidance for clinical use. Additionally, we analyzed the signal-to-noise ratio of HA and calculated the capable detection depth of 0.5-mm HA in human breast at approximately 3.0 - 3.5 cm. This is compatible with clinical applications, as calcifications are usually found at a depth of 0.6 – 3.0 cm. Moreover, based on the distinct optical absorption spectra of blood and HA in the near infrared wavelength range, we can also use PA signals from two selected wavelengths to differentiate the HA from the blood. Future work will focus on further validation of photoacoustic imaging of clinical breast calcifications. In addition, we wish to distinguish between calcium oxalate (COD) and HA, which are the components of breast calcifications associated with benign and malignant breast tumor, respectively. We also want to provide blood-flow information on our image by using Doppler ultrasound.
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