Lockard Carly A, Damon Bruce M, Serrai Hacene
Stephens Family Clinical Research Institute, Carle Health, Urbana, Illinois, United States of America.
Carle Illinois Advanced Imaging Center, Urbana, Illinois, United States of America.
PLoS One. 2025 Apr 17;20(4):e0310590. doi: 10.1371/journal.pone.0310590. eCollection 2025.
Zero echo time (ZTE) sequences capture signal from tissues with extremely short T2* and are useful for qualitative and quantitative imaging of musculoskeletal tissues' ultrashort-T2* components. One such sequence is Pointwise Encoding Time Reduction with Radial Acquisition (PETRA). While this sequence has shown promising results, it has undergone only limited testing at 7 tesla (T). The purpose of this work was to evaluate PETRA at 7T in its standard, commercially available form and with sequence code modifications to allow extended echo times for the purpose of performing ultrashort-T2* mapping. We acquired PETRA images of MnCl2 and collagen phantoms and of the knee in eight participants (5 for optimization and 3 for ultrashort-T2* mapping assessment; 5 male/3 female, 39 ± 11 years old). Images were acquired using a 1-transmit/28-receive-channel knee coil. Artifacts, signal, signal-to-noise ratio (SNR), ultrashort-T2*, the corresponding curve fit quality, and repeatability were assessed. In knee tissues, SNR was higher at TE = 0.07 msec than in a conventional-TE sequence (Dual-Echo Steady State with TE = 2.55 msec), with values of 68-337 for PETRA versus 16-30 for the same regions in the conventional-TE series. Acquisition of series for ultrashort-T2* maps was feasible at 1.50 mm isotropic acquisition resolution and TE ≤ 0.58 msec. Strong linear correlations were observed between relaxation rates (R2*) and MnCl2 concentration, and between signal and collagen concentration. Ultrashort-T2* signal decay curve fit R2 and repeatability were high for phantom and knee ultrashort-T2* <1 msec. PETRA imaging with minimal artifacts, high SNR, and scan time < 11 minutes was achieved at 7T at high (0.34 mm isotropic) resolution at TE = 0.07 msec and lower resolution (1.52 mm isotropic) at echo times ≤ 0.58 msec. Ultrashort-T2* mapping provided acceptable curve-fitting results for substances with sub-millisecond T2*.
零回波时间（ZTE）序列可采集来自具有极短T2的组织的信号，对肌肉骨骼组织的超短T2成分进行定性和定量成像很有用。一种这样的序列是径向采集逐点编码时间减少（PETRA）。虽然该序列已显示出有前景的结果，但仅在7特斯拉（T）下进行了有限的测试。这项工作的目的是评估7T下标准的市售形式的PETRA，并通过序列代码修改以允许延长回波时间，用于执行超短T2映射。我们采集了八名参与者（5名用于优化，3名用于超短T2映射评估；5名男性/3名女性，39±11岁）的MnCl2和胶原蛋白模型以及膝盖的PETRA图像。使用1发射/28接收通道的膝盖线圈采集图像。评估了伪影、信号、信噪比（SNR）、超短T2*、相应的曲线拟合质量和重复性。在膝盖组织中，TE = 0.07毫秒时的SNR高于传统TE序列（双回波稳态，TE = 2.55毫秒），PETRA的值为68 - 337，而传统TE系列中相同区域的值为16 - 30。在1.50毫米各向同性采集分辨率和TE≤0.58毫秒下采集超短T2图的系列是可行的。在弛豫率（R2）与MnCl2浓度之间以及信号与胶原蛋白浓度之间观察到强线性相关性。对于模型和膝盖超短T2*<1毫秒，超短T2信号衰减曲线拟合R2和重复性很高。在7T下，在TE = 0.07毫秒时以高（0.34毫米各向同性）分辨率以及在回波时间≤0.58毫秒时以较低分辨率（1.52毫米各向同性）实现了具有最小伪影、高SNR且扫描时间<11分钟的PETRA成像。超短T2映射为具有亚毫秒级T2*的物质提供了可接受的曲线拟合结果。
