基于能谱CT探讨低对比剂用量时肺动脉造影最佳单能量水平

Optimal Monochromatic Energy Levels in Dual-energy Spectral CT Pulmonary Angiography with Low Contrast Medium Dosage

目的:探讨低对比剂用量CTPA的能谱最佳单能量水平。方法:前瞻性收集临床拟诊肺动脉栓塞并行能谱扫描模式(GSI)低对比剂用量(25ml)患者30例。扫描条件为:扫描协议为GSI-36:260mA,对比剂用量25ml(350mgI/ml,4. 0ml/s),小剂量(8ml)团注测试法监测。扫描完成后采用自适应统计迭代算法(ASiR:50%)将图像重建为层厚为1. 25mm的60-80keV(间隔5keV) 5组单能量图像。分别测量5组单能量图像的主肺动脉(MPA)、右肺动脉(RPA)、左肺动脉(LPA)、右下肺动脉(RLPA)及左下肺动脉(LLPA)的CT值和SD值以及同层面背部肌肉的CT值,计算SNR及CNR并用于分析比较。由两名有经验的影像科医师采用5级评分法对5组图像进行主观评价。采用SPSS 19. 0统计学软件分析上述数据,以P <0. 05为差异有统计学意义。结果:5组单能量图像中各肺动脉的CT值随能量升高而降低,60keV-70keV单能量图像的肺动脉平均CT均大于300HU。65keV单能量图像的平均SNR及CNR最高,平均SD最低,与60keV和70keV图像两两比较差异均有统计学意义(p均<0. 05)。两名放射科医师对65keV图像评分最高,但与60keV和70keV图像两两比较差异均无统计学意义(p均>0. 05)。结论:能谱扫描模式低对比剂用量肺动脉造影中,65KeV图像平均SNR及CNR最高,平均噪声较最低,以及最高的主观评分,可作为低对比剂用量CTPA中的最佳单能量图像水平。

Purpose:To determine the optimal monochromatic energy levels in dual-energy Spectral CT pulmonary angiography(CTPA)with low contrast dosage.Materials and Methods:Thirty patients with suspected pulmonary embolism(PE) underwent dual-energy Spectral CTPA with low radiation and low contrast doses: scanning protocol of GSI-36 with 260mA, and 25ml contrast (350mgI/ml) with 4.0ml/s injection speed. The monochromatic images from 60-80keV(interval 5keV)were reconstructed using a 50% adaptive statistical iterative reconstruction (50%ASiR) algorithm at 1.25mm slice thickness.The CT attenuation and standard deviation (SD) values of the main, right, left, right lower and left lower pulmonary arteries and the back muscle at the same level were measured on the 60-80keV images, and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and analyzed. The subjective image quality was evaluated by two experienced radiologists using a 5-level scoring method independently. Measurements were analyzed using SPSS 19.0 statistical software.Results:CT attenuation values of the pulmonary arteries decreased with the increase of energy level in the five-energy groups, with valuesgreater than 300HU at 60keV-70keV energies.The 65keV image had the highest SNR and CNR and lowest SD, with significant differences compared with those of other image sets(p<0.05).The subjective quality scores for the 65keV image was judged to be the highest by the two radiologists, but was not significantly different from 60keV and 70keV (all p>0.05).Conclusions:The 65keV monochromatic images provided the highest SNR, CNR and subjective scores with the lowest image noise in dual-energy Spectral CTPA with low contrast dosage.