Balchandani Priti, Pauly John, Spielman Daniel
Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
Magn Reson Med. 2008 May;59(5):973-9. doi: 10.1002/mrm.21539.
Proton magnetic resonance spectroscopic imaging ((1)H MRSI) is a useful technique for measuring metabolite levels in vivo, with Choline (Cho), Creatine (Cre), and N-Acetyl-Aspartate (NAA) being the most prominent MRS-detectable brain biochemicals. (1)H MRSI at very high fields, such as 7T, offers the advantages of higher SNR and improved spectral resolution. However, major technical challenges associated with high-field systems, such as increased B(1) and B(0) inhomogeneity as well as chemical shift localization (CSL) error, degrade the performance of conventional (1)H MRSI sequences. To address these problems, we have developed a Position Resolved Spectroscopy (PRESS) sequence with adiabatic spatial-spectral (SPSP) refocusing pulses, to acquire multiple narrow spectral bands in an interleaved fashion. The adiabatic SPSP pulses provide magnetization profiles that are largely invariant over the 40% B(1) variation measured across the brain at 7T. Additionally, there is negligible CSL error since the transmit frequency is separately adjusted for each spectral band. in vivo (1)H MRSI data were obtained from the brain of a normal volunteer using a standard PRESS sequence and the interleaved narrow-band PRESS sequence with adiabatic refocusing pulses. In comparison with conventional PRESS, this new approach generated high-quality spectra from an appreciably larger region of interest and achieved higher overall SNR.
质子磁共振波谱成像（¹H MRSI）是一种用于测量体内代谢物水平的有用技术，胆碱（Cho）、肌酸（Cre）和N-乙酰天门冬氨酸（NAA）是最主要的可通过磁共振波谱检测到的脑生化物质。在7T等超高场强下进行¹H MRSI，具有更高的信噪比和更好的光谱分辨率等优势。然而，与高场系统相关的主要技术挑战，如B₁和B₀不均匀性增加以及化学位移定位（CSL）误差，会降低传统¹H MRSI序列的性能。为了解决这些问题，我们开发了一种带有绝热空间光谱（SPSP）重聚焦脉冲的定位分辨波谱（PRESS）序列，以交错方式获取多个窄光谱带。绝热SPSP脉冲提供的磁化分布在7T磁场下大脑中测量到的40%B₁变化范围内基本不变。此外，由于每个光谱带的发射频率是单独调整的，CSL误差可以忽略不计。使用标准PRESS序列和带有绝热重聚焦脉冲的交错窄带PRESS序列从一名正常志愿者的大脑中获取了体内¹H MRSI数据。与传统PRESS相比，这种新方法从明显更大的感兴趣区域生成了高质量光谱，并实现了更高的整体信噪比。
