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。
Background The breathhold contrast-enhanced three-dimensional magnetic resonance angiography （MRA） using Tl-weighted gradient-echo imaging sequence is the standard technique for MRA of the thorax. However, this technique is not desirable for certain patients with respiratory insufficiency, serious renal impairment, or allergy to contrast agents. The objective of this study was to optimize and evaluate a non-contrast-enhanced free-breathing pulmonary MRA protocol at 3 Tesla. Methods The time-of-flight protocol was based on a two-dimensional Tl-weighted turbo field echo sequence with slice-selective inversion recovery and magnetization transfer preparation together with respiratory navigator gating, cardiac gating, and parallel imaging. Optimal values for time of inversion delay, flip angle and slice thickness were experimentally determined and used for all subjects. Results Excellent pulmonary MRA images, in which the 7th order branches of pulmonary arteries could be reliably identified, were obtained in the 12 free-breathing healthy volunteers. TI of -300 ms provides the best suppression of background thoracic and cardiac muscles and effective inflow enhancement. With increasing flip angle, the pulmonary vessels gradually brightened and exhibited optimal contrast at 20°-30°. The 2 mm slice thickness and 0.5 mm slice overlap is suitable for visualization of the peripheral pulmonary vessel. Conclusions The MRA protocol at 3 Tesla may have clinical significance for pulmonary vascular imaging in patients who are not available for contrast-enhanced 3D MRA and CT angiography examination or are unable to sustain a long breath-hold.
YANG JianWANG WeiWANG Ya-rongNIU GangJIN Chen-wangWU Ed Xuekui
