Departament of Information Technology and Electrical Engineering, University and ETH Zurich, and Institute of Neuroradiology, University Hospital of Zurich, Zurich, Switzerland.
Magn Reson Med. 2013 May;69(5):1253-60. doi: 10.1002/mrm.24387. Epub 2012 Jun 28.
Magnetic resonance spectroscopy enables insight into the chemical composition of spinal cord tissue. However, spinal cord magnetic resonance spectroscopy has rarely been applied in clinical work due to technical challenges, including strong susceptibility changes in the region and the small cord diameter, which distort the lineshape and limit the attainable signal to noise ratio. Hence, extensive signal averaging is required, which increases the likelihood of static magnetic field changes caused by subject motion (respiration, swallowing), cord motion, and scanner-induced frequency drift. To avoid incoherent signal averaging, it would be ideal to perform frequency alignment of individual free induction decays before averaging. Unfortunately, this is not possible due to the low signal to noise ratio of the metabolite peaks. In this article, frequency alignment of individual free induction decays is demonstrated to improve spectral quality by using the high signal to noise ratio water peak from non-water-suppressed proton magnetic resonance spectroscopy via the metabolite cycling technique. Electrocardiography (ECG)-triggered point resolved spectroscopy (PRESS) localization was used for data acquisition with metabolite cycling or water suppression for comparison. A significant improvement in the signal to noise ratio and decrease of the Cramér Rao lower bounds of all metabolites is attained by using metabolite cycling together with frequency alignment, as compared to water-suppressed spectra, in 13 healthy volunteers.
磁共振波谱能深入了解脊髓组织的化学成分。然而，由于技术挑战，脊髓磁共振波谱在临床工作中很少应用，这些挑战包括该区域的强磁化率变化和脊髓直径小，这会扭曲谱线形状并限制可达到的信噪比。因此，需要进行广泛的信号平均，这增加了由受试者运动（呼吸、吞咽）、脊髓运动和扫描器引起的频率漂移引起的静态磁场变化的可能性。为了避免非相干信号平均，在平均之前对单个自由感应衰减进行频率对准将是理想的。不幸的是，由于代谢物峰的信噪比低，这是不可能的。在本文中，通过使用代谢物循环技术，利用来自非水抑制质子磁共振波谱的高信噪比水峰，展示了单个自由感应衰减的频率对准，以改善光谱质量。使用代谢物循环和水抑制进行比较，以心电图（ECG）触发点分辨波谱（PRESS）定位进行数据采集。与水抑制谱相比，在 13 名健康志愿者中，使用代谢物循环和频率对准可显著提高所有代谢物的信噪比，并降低克拉默-劳下限。
