Regatte Ravinder Reddy, Akella Sarma V S, Wheaton Andrew J, Borthakur Arijitt, Kneeland J Bruce, Reddy Ravinder
Metabolic Magnetic Resonance Research and Computing Center (MMRRCC), Department of Radiology, Stellar-Chance Laboratories, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-6100, USA.
J Magn Reson Imaging. 2003 Sep;18(3):336-41. doi: 10.1002/jmri.10358.
To demonstrate the in vivo feasibility of measuring spin-lattice relaxation time in the rotating frame (T(1rho)); and T(1rho)-dispersion in human femoral cartilage. Furthermore, we aimed to compute the baseline T(1rho)-relaxation times and spin-lock contrast (SLC) maps on healthy volunteers, and compare relaxation times and signal-to-noise ratio (SNR) with corresponding T(2)-weighted images.
All MR imaging experiments were performed on a 1.5 T GE Signa scanner (GEMS, Milwaukee, WI) using a custom built 15-cm transmit-receive quadrature birdcage radio-frequency (RF) coil. The T(1rho)-prepared magnetization was imaged with a single-slice two-dimensional fast spin-echo (FSE) pulse sequence preencoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. T(1rho)-dispersion imaging was performed by varying the spin-lock frequency from 100 to 500 Hz in five steps in addition to varying the length of the spin-lock pulse.
The average T(1rho)-relaxation times in the weight-bearing (WB) and nonweight-bearing (NWB) regions of the femoral condyle were 42.2 +/- 3.6 msec and 55.7 +/- 2.3 msec (mean +/- SD, N = 5, P < 0.0001), respectively. In the same regions, the corresponding T(2)-relaxation times were 31.8 +/- 1.5 msec and 37.6 +/- 3.6 msec (mean +/- SD, N = 5, P < 0.0099). T(1rho)-weighted images have approximately 20%-30% higher SNR than the corresponding T(2)-weighted images for similar echo time. The average SLC in the WB region of femoral cartilage was 30 +/-4.0%. Furthermore, SLC maps provide better contrast between fluid and articular surface of femoral-tibial joint than T(1rho)-maps. The T(1rho)-relaxation times varied from 32 msec to 42 msec ( approximately 31%) in the WB and 37 msec to 56 msec ( approximately 51%) in NWB regions of femoral condyle, respectively, in the frequency range 0-500 Hz (T(1rho)-dispersion).
The feasibility of performing in vivo T(1rho) relaxation mapping in femoral cartilage at 1.5T clinical scanner without exceeding Food and Drug Administration (FDA) limits on specific absorption rate (SAR) of RF energy was demonstrated.
证明在旋转坐标系中测量自旋晶格弛豫时间（T(1ρ)）以及人体股骨软骨中T(1ρ)弥散的体内可行性。此外，我们旨在计算健康志愿者的基线T(1ρ)弛豫时间和自旋锁定对比（SLC）图，并将弛豫时间和信噪比（SNR）与相应的T(2)加权图像进行比较。
所有磁共振成像实验均在1.5T GE Signa扫描仪（通用电气医疗系统公司，威斯康星州密尔沃基）上进行，使用定制的15厘米发射 - 接收正交鸟笼式射频（RF）线圈。用由两个硬90度脉冲和一个低功率自旋锁定脉冲组成的三脉冲簇预编码的单切片二维快速自旋回波（FSE）脉冲序列对T(1ρ)准备的磁化进行成像。除了改变自旋锁定脉冲的长度外，通过以五个步骤将自旋锁定频率从100 Hz变化到500 Hz来进行T(1ρ)弥散成像。
股骨髁负重（WB）和非负重（NWB）区域的平均T(1ρ)弛豫时间分别为42.2±3.6毫秒和55.7±2.3毫秒（平均值±标准差，N = 5，P < 0.0001）。在相同区域，相应的T(2)弛豫时间分别为31.8±1.5毫秒和37.6±3.6毫秒（平均值±标准差，N = 5，P < 0.0099）。对于相似的回波时间，T(1ρ)加权图像的SNR比相应的T(2)加权图像高约20% - 30%。股骨软骨WB区域的平均SLC为30±4.0%。此外，SLC图在股骨 - 胫骨关节的液体和关节表面之间提供了比T(1ρ)图更好的对比度。在0 - 500 Hz频率范围内（T(1ρ)弥散），股骨髁WB区域的T(1ρ)弛豫时间分别从32毫秒变化到42毫秒（约31%），NWB区域从37毫秒变化到56毫秒（约51%）。
证明了在1.5T临床扫描仪上对股骨软骨进行体内T(1ρ)弛豫映射且不超过美国食品药品监督管理局（FDA）对RF能量比吸收率（SAR）限制的可行性。
