||Apply High-frequency Ultrasound to Microcirculation Assessment in Small Animals
||Institute of Biomedical Engineering
high-frequency ultrasound imaging system
微循環血流的變化和疾病有很大的關聯，其中又以腫瘤的生成為最典型的例子，因此對於腫瘤微循環狀態的評估，在診斷和治療效果上皆可提供臨床重要醫學資訊。腫瘤生長的過程中，血管新生扮演很重要的角色，因此我們選擇高頻超音波影像系統為診斷工具。高頻超音波(> 15 MHz)相較於傳統超音波(2-15 MHz)在於工作頻率的提高，使得解析度可達微米等級，故足以解析微循環細小的血流資訊。因此本研究中，首先希望藉由高頻超音波影像統來長期觀察腫瘤內部微循環血流變化，並且評估腫瘤內部中心與周圍的血流變化；同時也比較放射性治療前後血流的改變情況。在血流評估方法上，本研究採用掃掠式掃描來評估血流。在小動物活體實驗部份，我們採用C57BL/6老鼠，同時選擇四種量化參數來評估腫瘤的生長狀況，分別為血流能量、血流量、血管數目密度、及新生血管的程度，並且定義腫瘤中心為腫瘤內徑的50 %，外圍50 %為腫瘤周圍。根據研究結果顯示，隨著腫瘤體積的生長，腫瘤內部的血流能量、血流量、血管數目、及新生血管的程度都會有增加的趨勢，因此推論腫瘤隨著體積的增加其代謝會愈旺盛。另外當腫瘤體積大於10-15 mm3，腫瘤內部中心與周圍血流差異會最大，也就是說腫瘤內部的血流供應是以周圍的50 %血管來主宰。為了評估放射性治療效果，本研究給予單一劑量(25 Gy)放射性照射治療，並觀察治療後的第4小時及24小時的血流改變情形。結果顯示放射性治療後24小時內，血流量的增加並不明顯，但是血流速度以及血管數目都會有明顯的增加及減少，因此推論腫瘤經由放射性治療之後會抑制腫瘤血管的新生。未來，我們可以持續探討，在不同比例下腫瘤中心與周圍的比值來比較血流分布的情形，並且延長放射性治療後實驗追蹤的時間，同時我們也希望藉由增加老鼠的實驗數量來做更完整的統計分析。
Microcirculation blood flow is related to many diseases among which tumor angiogenesis is one of the typical of models. It is known that angiogenesis plays an important role in the cancer proliferation and metastasis. Since the microvascular status can yield clinically significant information, assessing the microcirculation would be of particular interest in tumor diagnosis and prognosis. The primary advantages of high-frequency ultrasound imaging system, operated at a frequency greater than 15 MHz, are higher spatial resolution which can be used as noninvasive approach for small vessel imaging. In this study, we investigated in vivo assessment of tumor microcirculation blood flow in C57BL/6 mice using our developed high frequency ultrasound system. The vascularity in the core and periphery of tumor was first observed in time course scheme. Then, the changes of microcirculation blood flow were recorded at 4 and 24 hours post radiotherapy. We demonstrated that blood flow energy, volumetric blood flow, color pixel density, and neovascularity could estimate tumor microcirculation blood flow. As tumor growth, these tumor quantitative parameters were increased with the increase of tumor volume. In addition, these parameters in the tumor periphery region were much larger than those in tumor core when the tumor volume was larger than 10-15 mm3. After radiation therapy, the microcirculation flow increased slowly but the blood velocity significantly increased; however, the numbers of vessels was decreased within 24 hours. Future work should focus on extension of the tracing days for exploring the post-radiotherapy mechanism and for observing the vascular pattern changes in varied ratio of tumor core and periphery which should be further verified from histological studies.
List of Figures VI
List of Tables IX
Chapter 1: Introduction 1
1.1 High-frequency Ultrasound Imaging 1
1.2 Measurement of Blood Flow by Doppler Ultrasound 2
1.3 Microcirculation Blood Flow in Tumor 5
1.4 Motivations and Scope of the thesis 8
Chapter 2: Methods and Materials 10
2.1 Doppler Flow Estimation 10
2.1.1 Clutter Filter 13
2.1.2 One-Dimensional Autocorrelation 15
2.1.3 Blood Noise Discrimination 17
2.2 High-frequency Ultrasound Instrument 17
2.3 Animals Preparation 19
2.4 Assessment Tumor Microcirculation Blood Flow with Time-course Study 21
2.4.1 Experimental Setup 21
2.4.2 Analysis Method 21
2.5 Assess Post-radiotherapy Microcirculation Blood flow Changes 24
Chapter 3: Results 25
3.1 In Vivo Assessment Tumor Microcirculation with Time-course Study 25
3.2 In Vivo Assessment Post-radiotherapy Microcirculation Blood Flow Changes 33
Chapter 4: Discussion and Conclusions 40
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