64层螺旋CT的层敏感度曲线测试

目的 测试和评价64层螺旋CT的层敏感度曲线（SSP）及有效层厚半高宽（FWHM）。方法 对Somatom Sensation 64层螺旋CT，使用临床常用的腹部螺旋扫描模式和CT质控delta（8）体模，分别以螺距（pitch）=0．50、0．75、1．00、1．25、1．50，重建层厚0．6mm（标称值）进行扫描和重建。对于pitch=1．00，再分别以层厚1．0、1．5mm进行重建。然后测试各种情况的SSP和有效层厚。结果 对于标称层厚0．6mm，不同pitch时测试的有效层厚分别为0．67、0．67、0．66、0．69、0．69mm；pitch=1．00时，标称层厚0．6、1．0、1．5mm的有效层厚分别为0．66、1．06、1．52mm。有效层厚均略大于标称层厚，但与标称层厚相比均不超过0．1mm。测试的SSP形状近似钟形，左右分布基本对称，没有延伸较长的尾部；随着重组层厚的增加，SSP逐渐变平阔；当pitch改变时，SSP变化轻微。结论 对于Sensation64层螺旋CT，pitch的变化对SSP、有效层厚和z轴空间分辨率的影响很小。这一结论有助于临床应用中优化CT扫描方案。

Measurement of slice sensitivity profile for a 64-slice spiral CT system

Objective To measure and evaluate slice sensitivity profile(SSP)and the full width at half-maximum(FWHM)for a 64-slice spiral CT system.Methods Using the same CT technique and body mode as those used for clinical CT,delta phantom was scanned with Somatom Sensation 64-slice spiral CT.SSPs and FWHM were measured both with reconstruction slice width of 0.6 mm at pitch = 0.50,0.75,1.00,1.25,1.50 and with reconstruction slice width of 0.6,1.0,1.5 mm at pitch = 1 respectively.Results For normal slice width of 0.6 mm,the measured FWHM,i.e.effective slice width,is 0.67,0.67,0.66,0.69,0.69 mm at different pitch.All the measured FWHM deviate less than 0.1mm from the nominal slice width.The measured SSPs are symmetrical,bell-shaped curves without far-reaching tails,and show only slight variations as a function of the spiral pitch.When reconstruction slice width increase,relative SSP become wider.Conclusions The variation of pitch hardly has effect all on SSP,effective slice width,and z-direction spatial resolution for Sensation 64-slice spiral CT system,which is helpful to optimize CT scanning protocol.