Intracranial CT angiography obtained from a cerebral CT perfusion examination
Intracranial CT angiography obtained from a cerebral CT perfusion examination
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DOI：
10.1118/1.3078043
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发表时间：
2009-04-01
期刊：
影响因子：
3.8
通讯作者：
Streekstra, G. J.
中科院分区：
文献类型：
--
作者：
van Andel, H. A. F. Gratama;Venema, H. W.;Streekstra, G. J.
脑部CT灌注(CTP)检查越来越多地用于评估蛛网膜下腔出血后中风和血管痉挛患者的脑血流。对于同一患者，通常还会进行CT血管造影(CTA)检查。本研究探讨从CTP检查中获得CTA图像的可能性，从而可能避免CTA检查。这将节省患者受到辐射、对比度和时间的影响。每个CTP帧都是具有不同对比度增强和高噪声的CTA图像。为了提高对比度噪声比(CNR)，我们在配准后将所有3D图像合并为一幅3D图像，以校正时间帧之间的患者运动。图像组合包括加权平均，其中每一帧的加权因子与动脉对比度成正比。结果表明，在此过程中，动脉的CNR达到最大。使用时间序列的CTP图像的另一个优点是可以自动区分动脉和静脉。这一功能被用来在生成的3D图像中屏蔽静脉，以增强最大强度投影(MIP)图像中动脉的可见性。在飞利浦华晨CT机(64×0.625 mm)上，采用翻转台技术对8例患者进行了80 mm的CTP检查。CTP检查包括15幅3D图像(2x64x0.625 mm；80kV；150mAs)，间隔4个S，分别测量加权平均图像、平面平均图像和最大动脉增强图像的CNR值。作者还将图像的CNR和质量与常规CTA检查进行了比较，并检查了MIP图像中自动静脉掩蔽的有效性。在CTP序列中，加权平均图像的CNR平均是最大动脉增强时图像的CNR的1.73倍，而使用平面平均仅使CNR增加1.49倍。加权平均图像的质量接近于CTA图像，尽管在本研究中CTA图像的质量还未完全达到。静脉的自动掩蔽是有效的，在掩蔽的图像中有时只有少量残留的静脉。加权平均可以从CTP检查中创建CNR明显高于最大动脉增强图像的CTA图像。所得图像的质量接近CTA图像的质量，并提供了自动区分动脉和静脉的额外优势。
CT perfusion (CTP) examinations of the brain are performed increasingly for the evaluation of cerebral blood flow in patients with stroke and vasospasm after subarachnoid hemorrhage. Of the same patient often also a CT angiography (CTA) examination is performed. This study investigates the possibility to obtain CTA images from the CTP examination, thereby possibly obviating the CTA examination. This would save the patient exposure to radiation, contrast, and time. Each CTP frame is a CTA image with a varying amount of contrast enhancement and with high noise. To improve the contrast-to-noise ratio (CNR) we combined all 3D images into one 3D image after registration to correct for patient motion between time frames. Image combination consists of weighted averaging in which the weighting factor of each frame is proportional to the arterial contrast. It can be shown that the arterial CNR is maximized in this procedure. An additional advantage of the use of the time series of CTP images is that automatic differentiation between arteries and veins is possible. This feature was used to mask veins in the resulting 3D images to enhance visibility of arteries in maximum intensity projection (MIP) images. With a Philips Brilliance 64 CT scanner (64x0.625 mm) CTP examinations of eight patients were performed on 80 mm of brain using the toggling table technique. The CTP examination consisted of a time series of 15 3D images (2x64x0.625 mm; 80 kV; 150 mAs each) with an interval of 4 s. The authors measured the CNR in images obtained with weighted averaging, images obtained with plain averaging, and images with maximal arterial enhancement. The authors also compared CNR and quality of the images with that of regular CTA examinations and examined the effectiveness of automatic vein masking in MIP images. The CNR of the weighted averaged images is, on the average, 1.73 times the CNR of an image at maximal arterial enhancement in the CTP series, where the use of plain averaging increases the CNR only with a factor of 1.49. The quality of the weighted averaged images approaches that of CTA images, although in the present study the image quality of CTA was not quite reached. The automatic masking of veins is effective and only small remnants of veins were sometimes present in the masked images. Weighted averaging makes it possible to create CTA images from a CTP examination with a CNR considerably higher than that of images with maximal arterial enhancement. The quality of the resulting images approaches that of CTA images and offers the additional advantages to automatically differentiate between arteries and veins.