Quadrupole-Dips Measured by Whole-Body Field-Cycling Relaxometry and Imaging
Quadrupole-Dips Measured by Whole-Body Field-Cycling Relaxometry and Imaging
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通过全身场循环松弛测量和成像测量四极杆倾斜
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发表时间：
1999
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影响因子：
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通讯作者：
D. Lurie
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作者：
D. Lurie
过渡。这种效应在20世纪80年代早期至中期得到了广泛研究，并在水合蛋白质和各种生物样本中测量了四极下降[1]。Kimmich等人首次在体内证实了这一现象，他研究了活水蛭[2]。然而，据作者所知，到目前为止，还没有其他的四极子倾角的体内测量。在这项工作中，四极骤降已被测量的第一次在人体肌肉在体内使用全身大小的场循环松弛和成像系统。还获得了人前臂的场循环反转恢复图像，使得能够通过四极倾角效应进行间接NQR成像。方法使用全身场循环MRI系统进行实验，该系统最初是为使用Overhauser效应进行场循环PEDRI自由基成像而开发的[3]。成像器使用具有59 mT垂直场的全身永磁体（Field Effects Inc.，MA，USA），其提供检测磁场。场循环通过场补偿方法来实现：电阻性鞍形磁体（Magnex Scientific Ltd.，UK）被装配到永磁体的孔中，并且来自该次级磁体的场可以添加到永磁体的场或从永磁体的场减去。在10 ms内可以实现30 mT的磁场变化。由于永磁体由铁氧体制成，并且支撑结构也是不导电的，因此不存在涡流问题。场梯度线圈被集成到永磁体的结构中，并且次级磁体线圈的可用孔的直径为52 cm，足以用于人类受试者。本工作采用了内径为14 cm的分裂式螺线管线圈，用于2.5MHz的NMR发射和接收。成像器由商业NMR控制台（SMIS Ltd.，英国）。场循环、交错反转恢复/饱和恢复脉冲序列用于通过两点法测量T1值;脉冲序列如图1所示。在极化周期（长度T pol）期间，磁化强度在测量场处平衡。应用10 ms绝热快速通道（AFP）反演，并且场返回到测量值，其中磁化强度随着自旋-晶格弛豫时间恢复。该序列的饱和恢复部分是相同的，除了不应用AFP。在30 mT至80 mT的范围内，以1 mT的间隔收集T1数据。还使用了交错场循环反转恢复成像脉冲序列，使用该序列的改编版本在57.5 mT和65 mT下收集图像。
transitions. This effect was studied extensively in the early to mid 1980s, and quadrupole dips were measured in hydrated proteins and various biological samples [1]. The first in vivo demonstration of the phenomenon was carried out by Kimmich et al., who studied living leeches [2]. To the author’s knowledge, however, no other in vivo measurements of quadrupole dips have been made until now. In this work, quadrupole dips have been measured for the first time in human muscle in vivo using a whole-body sized field-cycling relaxometry and imaging system. Field-cycled inversion recovery images have also been obtained of the human forearm, enabling indirect NQR imaging via the quadrupole dip effect. METHODS Experiments were carried out using a whole-body field-cycling MRI system, originally developed for field-cycled PEDRI free radical imaging using the Overhauser effect [3]. The imager uses a whole-body permanent magnet with a vertical field of 59 mT (Field Effects Inc., MA, USA) which provides the detection magnetic field. Field cycling is accomplished by the fieldcompensation method: a resistive, saddle-shaped magnet (Magnex Scientific Ltd., UK) is fitted into the bore of the permanent magnet, and the field from this secondary magnet can add to or subtract from the field of the permanent magnet. A field change of 30 mT can be achieved in 10 ms. There are no problems with eddy currents because the permanent magnet is made of ferrite, and the support structures are also non-conducting. Field gradient coils are integrated into the structure of the permanent magnet, and the useable bore of the secondary magnet coil is 52 cm in diameter, sufficient for human subjects. In this work, a splitsolenoid coil with i/d 14 cm was used for NMR transmit and receive at 2.5 MHz. The imager is controlled by a commercial NMR console (SMIS Ltd., UK). A field-cycled, interleaved inversion-recovery / saturation-recovery pulse sequence was used to measure T 1 values by a two-point method; the pulse sequence is shown in Figure 1. During the polarisation period (length T pol ) the magnetisation equilibrates at the measurement field. A 10 ms adiabatic fast passage (AFP) inversion is applied and the field is returned to the measurement value where the magnetisation recovers with the spin-lattice relaxation time. The saturation recovery part of the sequence is identical, except that the AFP is not applied. T 1 data was collected over the range 30 mT to 80 mT, at intervals of 1 mT. An interleaved field-cycled inversion recovery imaging pulse sequence was also used, collecting images at 57.5 mT and 65 mT using an adapted version of the sequence.