快速电影相位对比序列磁共振成像中流速编码的选择

Selection of velocity encoding in fast CINE phase contrast magnetic resonance imaging

目的探讨应用MRI快速电影相位对比序列研究时流速编码大小和方向的正确选择。方法将内径为3 mm塑料管固定在水模中,用高压注射器以平均流速42.46 cm/s向管腔内注射0.9%氯化钠溶液,应用3.0 T高场强MRI扫描仪快速电影相位对比序列进行扫描。分别设置不同的流速编码值(40、60、80、100、120、140、160、180、200、220、240、260、280、300、350、400、500 cm/s)和流速编码方向[S→I;Slice;ALL(oblique S/I Flow);ALLs(oblique R/L Flow、oblique A/P Flow和oblique S/I Flow)]对模型进行扫描,测量实际平均流速及峰值流速。分析流速编码大小和方向的选择对液体实际流速大小和方向的影响。结果当流速编码=40 cm/s及60 cm/s时,管腔内出现混淆伪影;当流速编码=80 cm/s时,混淆伪影消失。当流速编码≥80 cm/s时,测量流速与实际流速间差异有统计学意义(t=2.52,P<0.05)。测量流速与流速编码之间无相关性(P>0.05)。当流速编码=100 cm/s时,所测得的流速与真实值最接近。当流速编码方向分别选择为S→I、Slice、ALL(obligue S/I Flow)、ALLs(obligue R/L Flow,obligue A/P Flow和obligue S/I Flow)时相位图均能正确显示液体流动方向,各方向时所测流速与实际流速间差异无统计学意义(t=0.29,P>0.05)。结论临床血流测量中要根据峰值流速大小选取适当的流速编码值才能确保测量的准确性,不能过大也不能过小;流速编码方向选择Slice,能够满足大多数血流动力学测量的需要。

Objective To study the suitable choice of size and direction in velocity encoding（VENC） by using fast CINE phase contrast（PC） magnetic resonance imaging（MRI）. Methods The plastic tube with inner diameter of 3 mm was fixed in water phantom, and the high pressure injector injected 0.9 % sodium chloride solution with 42.46 cm/s, then fast CINE PC sequence for scanning by 3.0 T high field MRI scanner was performed. The different sizes（40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240,260, 280, 300, 350, 400, 500 cm/s） and different directions of VENC[S →I; Slice; ALL（oblique S/I Flow）; ALLs（oblique R/L Flow, oblique A/P Flow and oblique S/I Flow）] were sited to scan, the mean velocity and peak velocity were measured. The influence of choosing the size and direction of VENC for acutal velocity and direction was analyzed. Results The artifacts showed confusion artifacts at VENC = 40 cm/s and 60 cm/s; Confusion artifacts were disappeared at VENC = 80 cm/s. The difference was statistically significant between measurement velocity and actual VENC at ≥ 80 cm/s（t = 2.52, P〈0.05）, and there was no correlation between measurement velocity and VENC（P〈0.05）. The mearurement velocity was similar with acutal at VENC = 100 cm/s.The PC image was displayed correct direction in VENC was S→I, Slice, ALL（obligue S/I Flow） and ALLs（obligue R/L Flow,obligue A/P Flow and obligue S/I Flow）, and there was no difference between measurement velocity and actual VENC（t = 0.29, P〈0.05）. Conclusion It is demonstrated that clinical measurements should be based on peak size to select appropriate VENC,neither too big nor too small, so VENC direction of Slice could meet the needs of most hemodynamic measurements.