Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/8125
標題: 以立體血管顯像術重健三維血管模型的新方法
New Methods to Reconstruct 3-D Blood Vessel Models from Stereoscopic Magnetic Resonance Angiography
作者: 郭蕾欣
Kuo, Lei-Hsin
關鍵字: MRA;磁振造影血管顯影術;projection;blood vessel;reconstruction;投影;血管;重建
出版社: 電機工程學系
摘要: 
磁振造影血管顯影術是一種將人體內血管顯示出來但不顯示其它任何組織的造影技術,其產生影像有兩種方法,一種為將三度空間的血管投影到二維平面的投影影像(二維血管顯影術),另一種則是取得完整的三度空間資訊的三度空間醫學影像(三維血管顯影術),三維血管顯影術的優點在於可以隨心所欲去觀察任一角度的資訊,缺點則是造影的時間非常長,為了縮短造影時間,通常是使用二維血管顯影術來診斷病變,但是這樣會犧牲掉深度資訊,因此在本篇論文中我們研究利用兩張二維投影影像重建立體血管的方法。
立體磁振造影血管顯像術,是利用兩個角度的血管投影影像,來重建立體血管影像,和一般X光血管顯像術所產生的投影影像比較,X光投影影像中像素亮度值,可視為光線行進路徑上所有物質衰減值的積分,因此可由此積分進而反推物體的形狀。但是磁振造影血管顯像術成像的參數很多(例如:T1、T2、質子密度、與共振偏移等),影響像素亮度的參數也非常多,所以很難由像素亮度值直接推得與物體形狀的關係,因此我們改以空間幾何的方式來還原物體形狀,假設血管為傾斜直圓柱而血管切面形狀則會近似於橢圓形,再將從投影影像中取得的邊界值,配合所導出的演算法,求得橢圓形的參數,即可還原血管切面形狀,而得到立體血管影像。
一般要表示一個橢圓形是利用它的長短軸及其對座標軸的傾斜角度來表示之,雖然這個表示法可以令人很直覺的了解,但是對於重建問題卻顯得有些複雜,因此我們將橢圓形以對稱矩陣的方式來表示,這樣橢圓形和它的投影就會是一個簡單的向量關係。
本篇論文也以實際的例子,來重建實際的三度空間血管影像。由從台中榮總醫院所獲得的80張磁振造影血管影像,我們取其中50張影像,分別作左右各150的投影,當作實際血管投影影像,然後取得邊界值,以推導而得的演算法算出切面形狀的參數,重建血管三度空間模型,然後將重建之立體血管影像再作同樣角度的投影,將獲得的邊界值與原始的邊界值做比較,其平均誤差為0.1011。

Magnetic resonance angiography (MRA) is an imaging technique to show the blood vessels without all the other tissues. There are two approaches to acquire an image of MRA. One is to project the 3-D vessels onto 2-D plane; the other is to directly obtain the complete 3-D information. The advantage of 3-D MRA is that one can view the data from arbitrary direction. However, the scan time is usually very long. To shorten the scan time, 2-D MRA is used, but the depth of information will be sacrificed. Therefore, we researched on the subject of reconstructing 3-D vessels from two projective MRA images.
Stereoscopic magnetic angiography utilizes two images by projecting blood vessels onto 2-D plane in two angles. For digital subtraction angiography (DSA), the pixel value is the integration of the attenuation value in the path of the X-ray. We can use this property to derive the shape of the vessels by solving the integrals. On the other hands, there are many imaging parameters in MRA(such as T1, T2, proton density, and so on). Therefore, it is difficult to obtain the relation between the shape of the vessels and the pixel intensity. For this reason, we attempt to reconstruct the shape of the vessels by geometry. We assume that blood vessels are tilted circular tube and the shape of blood vessels on every cross-section is approximately an ellipse. Based on these assumptions, we developed an algorithm to estimate the parameters of the ellipse from the boundaries of the projective images. The reconstructed ellipses are then taken as the 3-D shape of the vessels.
To describe of an ellipse, we needed its semiaxis lengths together with its rotation angles with respect to the coordinate system. While this representation was intuitive, it proved inconvenient for reconstruction as it led to complicated equations. Alternatively, we represented an ellipse using a symmetric matrix. This representation ed to a simple linear relationship between the ellipse and its orthogonal projection.
In the thesis, eighty images of MRA were used to demonstrate the capability of our algorithm. From these images, we used fifty images to make two projective images. The two projections are 150 apart. We used our algorithm to estimate all the ellipses and reconstructed the 3-D model of the vessels, and then we compared the boundaries of the original projective images with the boundaries of the re-projective images of the reconstructed 3-D model, the average error is 0.1011.
URI: http://hdl.handle.net/11455/8125
Appears in Collections:電機工程學系所

Show full item record
 

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.