Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, USA.
J Cardiovasc Magn Reson. 2019 Jan 10;21(1):5. doi: 10.1186/s12968-018-0507-2.
Endogenous contrast T1ρ cardiovascular magnetic resonance (CMR) can detect scar or infiltrative fibrosis in patients with ischemic or non-ischemic cardiomyopathy. Existing 2D T1ρ techniques have limited spatial coverage or require multiple breath-holds. The purpose of this project was to develop an accelerated, free-breathing 3D T1ρ mapping sequence with whole left ventricle coverage using a multicoil, compressed sensing (CS) reconstruction technique for rapid reconstruction of undersampled k-space data.
We developed a cardiac- and respiratory-gated, free-breathing 3D T1ρ sequence and acquired data using a variable-density k-space sampling pattern (A = 3). The effect of the transient magnetization trajectory, incomplete recovery of magnetization between T1ρ-preparations (heart rate dependence), and k-space sampling pattern on T1ρ relaxation time error and edge blurring was analyzed using Bloch simulations for normal and chronically infarcted myocardium. Sequence accuracy and repeatability was evaluated using MnCl phantoms with different T1ρ relaxation times and compared to 2D measurements. We further assessed accuracy and repeatability in healthy subjects and compared these results to 2D breath-held measurements.
The error in T1ρ due to incomplete recovery of magnetization between T1ρ-preparations was T1ρ = 6.1% and T1ρ = 10.8% at 60 bpm and T1ρ = 13.2% and T1ρ = 19.6% at 90 bpm. At a heart rate of 60 bpm, error from the combined effects of readout-dependent magnetization transients, k-space undersampling and reordering was T1ρ = 12.6% and T1ρ = 5.8%. CS reconstructions had improved edge sharpness (blur metric = 0.15) compared to inverse Fourier transform reconstructions (blur metric = 0.48). There was strong agreement between the mean T1ρ estimated from the 2D and accelerated 3D data (R = 0.99; P < 0.05) acquired on the MnCl phantoms. The mean R1ρ estimated from the accelerated 3D sequence was highly correlated with MnCl concentration (R = 0.99; P < 0.05). 3D T1ρ acquisitions were successful in all human subjects. There was no significant bias between undersampled 3D T1ρ and breath-held 2D T1ρ (mean bias = 0.87) and the measurements had good repeatability (COV = 6.4% and COV = 7.1%).
This is the first report of an accelerated, free-breathing 3D T1ρ mapping of the left ventricle. This technique may improve non-contrast myocardial tissue characterization in patients with heart disease in a scan time appropriate for patients.
内源性对比 T1ρ 心血管磁共振（CMR）可检测缺血性或非缺血性心肌病患者的瘢痕或浸润性纤维化。现有的 2D T1ρ 技术具有有限的空间覆盖范围或需要多次屏气。本项目的目的是开发一种加速的、自由呼吸的 3D T1ρ 映射序列，使用多通道、压缩感知（CS）重建技术对欠采样 k 空间数据进行快速重建，具有整个左心室覆盖范围。
我们开发了一种心脏和呼吸门控的自由呼吸 3D T1ρ 序列，并使用可变密度 k 空间采样模式（A=3）采集数据。使用 Bloch 模拟分析了瞬态磁化轨迹、T1ρ 准备之间的磁化不完全恢复（心率依赖性）以及 k 空间采样模式对 T1ρ 弛豫时间误差和边缘模糊的影响。使用具有不同 T1ρ 弛豫时间的 MnCl 幻影评估序列的准确性和可重复性，并与 2D 测量值进行比较。我们还在健康受试者中评估了准确性和可重复性，并将这些结果与 2D 屏气测量值进行了比较。
由于 T1ρ 准备之间的磁化不完全恢复引起的 T1ρ 误差为 60bpm 时为 6.1%和 10.8%，90bpm 时为 13.2%和 19.6%。在 60bpm 的心率下，由于读出相关磁化瞬变、k 空间欠采样和重排的综合影响，T1ρ 误差为 12.6%和 5.8%。CS 重建具有改善的边缘锐度（模糊度指标=0.15）与逆傅里叶变换重建（模糊度指标=0.48）。在 MnCl 幻影上获得的 2D 和加速 3D 数据的平均 T1ρ 估计之间存在很强的一致性（R=0.99；P<0.05）。从加速的 3D 序列中估计的平均 R1ρ 与 MnCl 浓度高度相关（R=0.99；P<0.05）。3D T1ρ 采集在所有人体受试者中均成功完成。欠采样的 3D T1ρ 和屏气的 2D T1ρ 之间没有显著的偏差（平均偏差=0.87），并且这些测量具有良好的可重复性（COV=6.4%和 COV=7.1%）。
这是首次报道左心室加速、自由呼吸 3D T1ρ 映射。该技术可在适用于患者的扫描时间内改善心脏病患者的非对比心肌组织特征。
