Fiat D, Dolinsek J, Hankiewicz J, Dujovny M, Ausman J
Department of Physiology and Biophysics, University of Illinois at Chicago 60680.
Neurol Res. 1993 Aug;15(4):237-48. doi: 10.1080/01616412.1993.11740143.
17O natural abundance imaging in a whole body imager is demonstrated using standard MRI spectrometer and 1H imaging methods. A novel design of a highly sensitive 17O/1H doubly tuned surface head coil is shown. The head probe allows simultaneous acquisition of 17O and 1H images using a single coil. The relatively low 17O signal intensity due to the low natural abundance of 17O (0.037 atom percent) is partially compensated by fast repetition of the pulse sequence, achievable due to the short spin lattice relaxation time, T1. A small number of signal averages (e.g., NEX = 50) is sufficient for obtaining images having signal to noise of about 5:1. Due to the short longitudinal relaxation time of 17O, i.e., 2-5 msec, short TR values can be used. 128 phase encoding steps with TR = 10-25 msec correspond to total acquisition time of 1 to 2.5 min. Due to the small gyromagnetic ratio of 17O and the relatively small gradients in a standard whole body system, i.e. 0.5 G/cm, the image in-plane resolution is about 3 mm and a slice thickness of 15 mm. In vivo 17O MRS and MRI natural abundance spectroscopic signals and images of human brain have been observed. The transverse relaxation time, T2 was found to be 2.00 +/- 0.17 msec at 1.5 T. MRS 17O measurements of signal intensity in the occipital cortex during inhalation of oxygen gas, 21.8% 17O enriched, showed a maximum signal enhancement of 25% within the inhalation period. The rate of the metabolism of oxygen (CMRO2) in the occipital cortex was found to be 1.5 mumole/(g tissue) in good agreement with the value of 1.435 mumole/(g tissue) given in the literature. Current measurements using higher 17O enrichments and larger quantities of 17O enriched oxygen gas will enhance resolution and provide more accurate determination of the rate of oxygen metabolism rate and blood flow. The potential of 17O imaging is thus demonstrated in physiological in vivo studies of cerebral metabolism of oxygen and blood flow.
利用标准的磁共振波谱仪和氢质子成像方法，在全身成像仪中实现了氧 - 17自然丰度成像。展示了一种新型的高灵敏度氧 - 17/氢质子双调谐表面头部线圈设计。该头部探头允许使用单个线圈同时采集氧 - 17和氢质子图像。由于氧 - 17的自然丰度较低（0.037原子百分比）导致其信号强度相对较低，这可通过快速重复脉冲序列得到部分补偿，这是由于其短的自旋晶格弛豫时间T1得以实现。少量的信号平均次数（例如，NEX = 50）就足以获得信噪比约为5:1的图像。由于氧 - 17的纵向弛豫时间短，即2 - 5毫秒，所以可以使用短的TR值。128个相位编码步长且TR = 10 - 25毫秒，对应的总采集时间为1至2.5分钟。由于氧 - 17的旋磁比小以及标准全身系统中的梯度相对较小，即0.5 G/cm，图像的平面分辨率约为3毫米，切片厚度为15毫米。已观察到人体大脑的体内氧 - 17磁共振波谱和磁共振成像自然丰度光谱信号及图像。在1.5 T时，横向弛豫时间T2为2.00±0.17毫秒。在吸入含21.8%氧 - 17富集的氧气期间，对枕叶皮质进行的氧 - 17磁共振波谱信号强度测量显示，在吸入期内信号最大增强了25%。发现枕叶皮质中的氧代谢率（CMRO2）为1.5微摩尔/（克组织），与文献中给出的1.435微摩尔/（克组织）的值吻合良好。目前使用更高的氧 - 17富集度和大量的氧 - 17富集氧气进行测量，将提高分辨率，并能更准确地测定氧代谢率和血流速度。因此，氧 - 17成像在大脑氧代谢和血流的生理体内研究中的潜力得以展现。
