Radial imaging techniques, such as projection-reconstruction （PR）, are used in magnetic resonance imaging （MRI） for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion ar...Radial imaging techniques, such as projection-reconstruction （PR）, are used in magnetic resonance imaging （MRI） for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion artifacts, and support fast imaging with short echo times. However, aliasing and streaking artifacts are two main sources which degrade radial imaging quality. For a given fixed number of k-space projections, data distributions along radial and angular directions will influence the level of aliasing and streaking artifacts. Conventional radial k-space sampling trajectory introduces an aliasing artifact at the first principal ring of point spread function （PSF）. In this paper, a shaking projection （SP） k-space sampling trajectory was proposed to reduce aliasing artifacts in MR images. SP sampling trajectory shifts the projection alternately along the k-space center, which separates k-space data in the azimuthal direction. Simulations based on conventional and SP sampling trajectories were compared with the same number projections. A significant reduction of aliasing artifacts was observed using the SP sampling trajectory. These two trajectories were also compared with different sampling frequencies. ASP trajectory has the same aliasing character when using half sampling frequency （or half data） for reconstruction. SNR comparisons with different white noise levels show that these two trajectories have the same SNR character. In conclusion, the SP trajectory can reduce the aliasing artifact without decreasing SNR and also provide a way for undersampling recon- struction. Furthermore, this method can be applied to three-dimensional （3D） hybrid or spherical radial k-space sampling for a more efficient reduction of aliasing artifacts.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos.10527003,60672104the National Basic Research Program of China under Grant No.2006CB705705+2 种基金the Joint Research Subject of Beijing Education Committee of China under Grant No.JD100010607the Beijing Municipal Natural Science Foundation of China under Grant No.3073019the Upgrading Subject of Instrument in Science and Technological Ministry of China under Grant No.2006JG1000~~
文摘目的研究免服泻药管电压切换型双能CT结肠成像低浓度小剂量泛影葡胺标记肠内容物的效果。方法 46例没有影响胃肠道运动功能病史的健康成年志愿者,CT检查前1天低纤维、低残渣饮食,分5次口服4.0%泛影葡胺60mL标记肠内容物,每餐后喝水量大于200mL。采用Toshiba医疗系统Aquilion One 640管电压切换型CT机仰卧位双能容积扫描,获得双能融合图像。统计分析志愿者肠道准备依从性、肠内容物存留状态及肠内容物的1级标记效果。结果 95.7%、4.3%的志愿者肠道准备依从性分别为容易接受、尚可接受。11.2%肠段没有液体和固体内容物存留,44.9%、43.9%肠段分别以液体、固体内容物存留为主。升结肠、横结肠、降结肠内容物的1级标记效果分别为91.3%、100.0%、93.5%,盲肠、乙状结肠、直肠内容物的1级标记效果分别为67.4%、80.4%、73.9%。升结肠、横结肠、降结肠内容物总体上的1级标记效果(94.9%)明显好于盲肠、乙状结肠、直肠内容物总体上的1级标记效果(73.9%),差异有统计学意义(P<0.01)。液体肠内容物的1级标记效果(96.7%)明显好于固体肠内容物的1级标记效果(67.8%),差异有统计学意义(P<0.01)。结论免服泻药管电压切换型双能CT结肠成像低浓度小剂量泛影葡胺对升结肠、横结肠、降结肠内容物及液体肠内容物的标记效果良好。
基金Project supported by the National Basic Research Program of China(Grant No.2011CB707701)the Innovation Fund for Technology Based Firms,China(Grant No.11C26221103870)+1 种基金the National High Technology Research and Development Program of China(Grant Nos.2011BAI12B05 and 2011BAI23B07)the National Natural Science Foundation of China(Grant Nos.81171330,81271664,and 81230035)
文摘Radial imaging techniques, such as projection-reconstruction （PR）, are used in magnetic resonance imaging （MRI） for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion artifacts, and support fast imaging with short echo times. However, aliasing and streaking artifacts are two main sources which degrade radial imaging quality. For a given fixed number of k-space projections, data distributions along radial and angular directions will influence the level of aliasing and streaking artifacts. Conventional radial k-space sampling trajectory introduces an aliasing artifact at the first principal ring of point spread function （PSF）. In this paper, a shaking projection （SP） k-space sampling trajectory was proposed to reduce aliasing artifacts in MR images. SP sampling trajectory shifts the projection alternately along the k-space center, which separates k-space data in the azimuthal direction. Simulations based on conventional and SP sampling trajectories were compared with the same number projections. A significant reduction of aliasing artifacts was observed using the SP sampling trajectory. These two trajectories were also compared with different sampling frequencies. ASP trajectory has the same aliasing character when using half sampling frequency （or half data） for reconstruction. SNR comparisons with different white noise levels show that these two trajectories have the same SNR character. In conclusion, the SP trajectory can reduce the aliasing artifact without decreasing SNR and also provide a way for undersampling recon- struction. Furthermore, this method can be applied to three-dimensional （3D） hybrid or spherical radial k-space sampling for a more efficient reduction of aliasing artifacts.
