Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Heidelberg University, Theodor- Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
Acad Radiol. 2013 Apr;20(4):407-13. doi: 10.1016/j.acra.2012.10.009.
(23)Na magnetic resonance imaging is a promising technique for the noninvasive imaging of renal function. Past investigations of the renal corticomedullary [(23)Na] gradient have relied on imaging only in the coronal plane and on cumbersome calculations of [(23)Na], which require the use of external phantoms. The aim of this study is therefore two-fold: to use an isotropic three-dimensional data set to compare coronal measurements of renal [(23)Na] relative to measurements obtained in planes along the corticomedullary gradients and to investigate cerebrospinal fluid (CSF) (23)Na signal as an internal reference standard, obviating the need for time-intensive [(23)Na] calculations.
Nominal isotropic three-dimensional (23)Na MRI data sets were obtained in 14 healthy volunteers before and after a water load. Images were reconstructed in the coronal plane and in planes angled along the direction of the corticomedullary sodium gradients. [(23)Na] values and values of the corticomedullary [(23)Na] gradient were measured by placement of a linear region of interest along corticomedullary gradients in both the coronal/nonangled [(23)Na(non-ang)] and the angled [(23)Na(ang)] image reconstructions. CSF [(23)Na] was also acquired at multiple levels. Ratios of renal (23)Na and CSF (23)Na signal were calculated to construct a semiquantitative parameter, [(23)NaCSF]. Results of water stimulation as measured by [(23)NaCSF] and [(23)Na(ang)] were then compared.
Mean values of [(23)Na(ang)] were statistically significantly greater than those of [(23)Na(non-ang)] (P < .0001), although these values were linearly correlated (R = 0.553, P < .0001) and exhibited similar extents of decreases in absolute terms (P = .2) and in terms of the corticomedullary gradient following the water load. CSF [(23)Na] did not statistically significantly differ at any level after the water load (P > .5) but tended to increase in the cranial direction (P < .001). [(23)NaCSF] measures demonstrated analogous statistical properties to [(23)Na(ang)] before and after the water load.
Assessment of renal corticomedullary [(23)Na] gradients using isotropic data sets with image reconstructions along the gradients is likely more accurate than measurements in the coronal plane. Because CSF [(23)Na] differs based on anatomic levels, such measures are useful as an internal reference only if region of interest placement is consistent. With this caveat in mind, normalization of renal to CSF (23)Na signal provides a feasible, less cumbersome alternative to [(23)Na] calculations in intraindividual studies.
（23）Na 磁共振成像是一种有前途的无创性肾功能成像技术。过去对肾皮质髓质[（23）Na]梯度的研究依赖于仅在冠状面进行成像和对[（23）Na]进行繁琐的计算，这需要使用外部体模。因此，本研究的目的有两个：使用各向同性三维数据集比较肾[（23）Na]相对于沿皮质髓质梯度获得的平面测量的冠状测量值，并研究脑脊液（CSF）[（23）Na]信号作为内部参考标准，避免需要耗时的[（23）Na]计算。
在 14 名健康志愿者水负荷前后获得名义各向同性三维（23）Na MRI 数据集。图像在冠状面和沿皮质髓质钠梯度方向的平面上重建。通过在冠状/非成角度[（23）Na（非角）]和成角度[（23）Na（角）]图像重建中沿皮质髓质梯度放置线性感兴趣区，测量[（23）Na]值和皮质髓质[（23）Na]梯度值。还在多个水平采集 CSF [（23）Na]。计算肾[（23）Na]和 CSF [（23）Na]信号的比值，以构建半定量参数[（23）NaCSF]。然后比较水刺激测量的[（23）NaCSF]和[（23）Na（角）]结果。
尽管这些值呈线性相关（R = 0.553，P <.0001），且绝对值（P =.2）和水负荷后皮质髓质梯度的降低程度相似，但[（23）Na（角）]的平均值统计学上显著大于[（23）Na（非角）]（P <.0001）。CSF [（23）Na]在水负荷后任何水平均无统计学差异（P >.5），但有向颅侧增加的趋势（P <.001）。水负荷前后，[（23）NaCSF]测量值表现出与[（23）Na（角）]相似的统计学性质。
使用沿梯度的各向同性数据集进行皮质髓质[（23）Na]梯度的评估可能比在冠状面进行测量更准确。由于 CSF [（23）Na]基于解剖水平而有所不同，因此如果感兴趣区的放置一致，这种测量值仅作为内部参考才有意义。考虑到这一点，肾与 CSF[（23）Na]信号的归一化提供了一种可行的、不那么繁琐的替代[（23）Na]计算的方法，用于个体内研究。
