Allkemper T, Reimer P, Schuierer G, Peters P E
Institute of Clinical Radiology, Westfalian Wilhelms University Muenster, Albert-Schweitzer-Strasse 33, D-48 129 Muenster, Germany.
Eur Radiol. 1998;8(5):834-8. doi: 10.1007/s003300050481.
The aim of this study was to evaluate the sensitivity of gradient-and-spin-echo (GRASE) sequences to susceptibility effects. GRASE sequences with 21 and 33 echoes per echo train were compared with a T2-weighted FSE sequence with an echo train length of 5 by means of MRI in phantoms, volunteers (n = 10), and patients (n = 19) with old hemorrhagic brain lesions. All experiments were performed on a 1.0-T clinical MR system (Impact Expert, Siemens AG, Erlangen, Germany) with constant imaging parameters. Contrast-to-noise ratios (CNRs) of tubes doped with iron oxides at different concentrations, of brain areas with physiological iron deposition (red nucleus, substantia nigra), and of areas of old brain hemorrhage were calculated for FSE and GRASE pulse sequences. Areas of old brain hemorrhage were also qualitatively analyzed for the degree of visible susceptibility effects by blinded reading. The CNR of iron oxide tubes and iron-containing brain areas decreased with increasing echo trains of GRASE sequences. The CNR of GRASE sequences decreased when compared with CNR of their FSE counterparts (GRASE 21 echo trains 23.8 +/- 0.8, FSE 5 echo trains 26.7 +/- 0.9; p </= 0.01). Qualitative analysis confirmed these measurements. FSE with an ETL of 5 demonstrated significantly stronger susceptibility effects than their GRASE counterpart with an ETL of 21. The results demonstrate that GRASE sequences do not necessarily compensate for the reduced sensitivity of FSE to susceptibility effects. The complex signal behavior of GRASE makes conventional SE, gradient echo, or FSE sequences containing shorter echo trains preferable when patients with intracranial hemorrhage are clinically evaluated.
本研究的目的是评估梯度自旋回波（GRASE）序列对磁化率效应的敏感性。通过在体模、志愿者（n = 10）和患有陈旧性脑内出血病变的患者（n = 19）中进行磁共振成像（MRI），将每个回波链有21个和33个回波的GRASE序列与回波链长度为5的T2加权快速自旋回波（FSE）序列进行比较。所有实验均在1.0-T临床磁共振系统（Impact Expert，西门子公司，埃尔朗根，德国）上进行，成像参数保持恒定。针对FSE和GRASE脉冲序列，计算了不同浓度掺杂氧化铁的试管、具有生理性铁沉积的脑区（红核、黑质）以及陈旧性脑出血区域的对比噪声比（CNR）。还通过盲法阅读对陈旧性脑出血区域的可见磁化率效应程度进行了定性分析。随着GRASE序列回波链的增加，氧化铁试管和含铁脑区的CNR降低。与FSE序列的CNR相比，GRASE序列的CNR降低（GRASE 21个回波链为23.8±0.8，FSE 5个回波链为26.7±0.9；p≤0.01）。定性分析证实了这些测量结果。回波链长度为5的FSE显示出比回波链长度为21的GRASE更强的磁化率效应。结果表明，GRASE序列不一定能弥补FSE对磁化率效应敏感性降低的问题。当对颅内出血患者进行临床评估时，GRASE复杂的信号行为使得包含较短回波链的传统自旋回波、梯度回波或FSE序列更可取。
