基于敏感编码并行采集技术的MR血流定量测量在主动脉的初步研究

Flow quantification of aorta by phase-contrast MR combined with sensitivity-encoded technique:an initial study

目的探讨基于敏感编码并行采集(SENSE)技术的 MR 相位对比血流测量法扫描(PC-MRI)的可行性和应用价值。方法对14例健康志愿者进行 SENSE 技术加二维(2D)PC-MRI 法检查,改变 SENSE 技术中的参数缩减因子(R),探讨在不同 R 值下的主动脉成像结果。从成像时间、图像信噪比(SNR)、速度噪声比(VNR)、峰值流速4个方面研究基于 SENSE 技术 PC-MRI 的图像特点和准确性。结果结合 SENSE 技术后,PC-MRI 的扫描速度成倍提高。R 值大小直接影响扫描时间和图像质量,R 取2、3、4时,扫描时间分别减少了49.6%(131/264)、66.3%(175/264)和74.6%(197/264)。随着 R 值的增加,SNR 和 VNR 逐渐下降,R 取2、3、4时,升(降)主动脉的 SNR 分别为707±170(737±179)、530±151(567±162)、430±86(451±97),与 R 取1时(即标准 PC 法)的结果1305±538(1320±576)比较,差异均有统计学意义[t 值分别为5.71(5.24)、6.76(6.29)、6.47(6.24),P 值均<0.01];VNR 分别为575±174(527±144)、509±137(488±121)、483±97(457±101),与标准 PC 法的结果630±188(577±163)比较,差异均有统计学意义[t 值分别为6.49(4.07)、6.72(5.43)、4.27(5.39),P 值均<0.05]。SNR 下降的程度明显低于相同 R 值下 VNR 下降的程度。应用 SENSE 技术后,不同 R 值下,升(降)主动脉峰值流速测量结果与标准法一致性好,相关系数分别为0.97(0.96)、0.98(0.90)、0.97(0.92)。对于升主动脉等管径较大的血管,在 R 取4时,测得的血流速度平均偏差仅为-1.53 cm/s,偏差的范围为-8.79～5.72 cm/s,血流速度的结果仍然是准确的。结论结合 SENSE 技术后,PC 法测量血流的效率成倍提高,对大血管流速的测量结果仍然准确。更快的扫描有望为 MRI 血流测量开拓新的应用空间。

Objective To evaluate the feasibility and clinical value of phase-contrast MRI （ PC- MRI） combined with sensitivity encoded （SENSE） technique for the flow quantification of aorta. Methods 2D-PC MR scanning combined with SENSE technique was performed for fourteen healthy volunteers. Overall scanning time, signal-to-noise ratio （SNR）, velocity-to-noise ratio （VNR） and peak velocity of aorta were compared respectively by changing the parameter of reduce factor （ R）. Results The scan time was shortened markedly with SENSE technique. The value of R significantly influenced the scan time and quality of imaging. When R value was set to 2,3,4, the scan time was reduced 49.6% ,66.3% and 74.6% respectively. SNR and VNR decreased gradually with the increasing R value. When R value was 2,3,4, the SNR of the ascend aorta （ descend aorta） was 707 ± 170 （737 ± 179 ）, 530 ± 151 （ 567 ± 162 ）, 430 ± 86 （451 ±97）and the VNR was 575 ± 174 （527 ± 144）,509 ± 137 （488 ± 121 ）,483 ± 97 （457 ± 101 ） respectively. When compared with R = 1 （standard PC MRI technique）, both SNR and VNR results showed statistical difference[ t =5.71（5.24） ,6.76（6.29）,6.47（6.24）, P 〈0.01 ] ; and It =6.49（4.07）, 6. 72 （5.43） ,4. 27 （ 5.39 ）, P 〈 0. 05 ] respectively. The downtrend degree of SNR was more remarkable than VNR when using the same R value. The agreement of peak velocity between SENSE and non-SENSE was considerably good, r values being 0. 97 （0. 96） ,0. 98 （0. 90） ,0. 97 （0. 92） respectively. Even under the condition of R was 4, the bias was - 1.53 cm/s, the limits of agreement between the two methods were narrow： -8.79 to 5. 72 cm/s, reflecting a high degree of agreement. Conclusion PC-MRI protocol combined with SENSE technique is a promising method in the measurement of flow velocity of great vessels with a relatively short scanning time.