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標題: 立體磁振造影血管顯像術
Stereoscopic Magnetic Resonance Angiography
作者: 周正杰
出版社: 電機工程學系

Magnetic resonance angiography (MRA) is an imaging technique to show the blood vessels but suppress signals from all the other tissues. There are two approaches to acquire an image of MRA. One is done in two dimension by projecting 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 for 3-D MRA. When the scan time is limited, we must use 2-D MRA and the depth of information is sacrificed. In this thesis, we research on the subject of recovering the depth information by reconstructing 3-D vessels from two projective MRA images.
Stereoscopic angiography utilizes two images by projecting blood vessels onto 2-D plane in two angles. Two major modalities are digital subtraction angiography (DSA) and magnetic resonance angiography (MRA). For 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 and proton density). Therefore, it is difficult to obtain the relation between the shape of the vessels and the pixel intensity. Therefore, we attempt to reconstruct the shape of the vessels by geometry. We assume that the shape of the vessel on every cross-section is an ellipse. Then, we develop 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.
Eighty images of MRA were used to demonstrate the capability of our algorithm. From these images, we use fifty images to make two projective images. The two projections are 300 apart. We employ our algorithm to estimate all the ellipses and reconstruct the 3-D model of the vessels. Comparing the boundaries of the original projective images with the boundaries of the reconstructed 3-D model, the average error is 0.471 pixels.
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