Machann J, Schnatterbeck P, Raible A, Lutz O, Claussen C D, Schick F
Department of Diagnostic Radiology, Institute of Physics, Eberhard-Karls-University Tübingen, Germany.
Invest Radiol. 2000 Jul;35(7):393-400. doi: 10.1097/00004424-200007000-00001.
Density of trabecular bone structures in human heel bones was assessed by 3D magnetic resonance (MR) gradient echo imaging (GEI) with multiple echoes. Different spatial resolutions were applied to investigate the influence of the pixel size on signal characteristics in GEI and to find suitable measuring parameters for a maximum correlation between GEI and bone mineral density obtained by quantitative computed tomography (QCT).
Thirty-five patients aged 31 to 65 years with suspected osteoporosis underwent MR and QCT examinations of the heel bones. The MR protocol included 3D GEI with three echo times (TE1 = 9.3, TE2 = 27.9, and TE3 = 46.5 ms) and isotropic pixel sizes of (0.6 mm)3, (1.2 mm)3, and (2.4 mm)3. Several subregions in the heel bones were analyzed. For determination of signal reduction with increasing TE, signal intensity ratios were calculated pixelwise from images with TE2/TE1 and TE3/TE1.
All examinations showed that the T2*-related signal decrease was more pronounced for lower spatial resolution. In the dorsal part of the heel bones, the correlation between signal ratios in GEI and QCT-based bone mineral density values was between r = -0.86 for a spatial resolution of (0.6 mm)3 and r = -0.73 for (2.4 mm)3. Areas with low trabecular density in the ventral part of the heel bones showed clearly lower correlation coefficients (-0.65 < r < -0.67).
Spatial resolution in 3D GEI clearly influences the T2*-related signal characteristics. Despite measuring different physical properties of spongy bone by GEI and QCT, a relatively high correlation between GEI with small pixel sizes and QCT was obtained in the dorsal part of the heel bones, but not in the ventral part with partly thickened trabeculae and irregular distribution. However, standardized measuring protocols with preferably small pixel sizes (as low as [0.6 mm]3) should be applied, and correlation curves must be determined, dependent on the actual bone marrow site, before clinical routine MR osteodensitometry becomes possible.
采用具有多个回波的三维磁共振（MR）梯度回波成像（GEI）评估人跟骨小梁骨结构的密度。应用不同的空间分辨率来研究像素大小对GEI中信号特征的影响，并找到合适的测量参数，以使GEI与定量计算机断层扫描（QCT）获得的骨矿物质密度之间具有最大相关性。
35例年龄在31至65岁之间疑似骨质疏松症的患者接受了跟骨的MR和QCT检查。MR检查方案包括具有三个回波时间（TE1 = 9.3、TE2 = 27.9和TE3 = 46.5毫秒）且各向同性像素大小为(0.6 mm)3、(1.2 mm)3和(2.4 mm)3的三维GEI。对跟骨中的几个子区域进行了分析。为了确定随着TE增加信号的衰减情况，从TE2/TE1和TE3/TE1图像逐像素计算信号强度比。
所有检查均表明，对于较低的空间分辨率，与T2*相关的信号衰减更为明显。在跟骨的背侧部分，GEI中的信号比与基于QCT的骨矿物质密度值之间的相关性在空间分辨率为(0.6 mm)3时r = -0.86，在(2.4 mm)3时r = -0.73。跟骨腹侧部分小梁密度低的区域显示出明显较低的相关系数（-0.65 < r < -0.67）。
三维GEI中的空间分辨率明显影响与T2*相关的信号特征。尽管GEI和QCT测量的是松质骨的不同物理特性，但在跟骨背侧部分，小像素大小的GEI与QCT之间获得了相对较高的相关性，而在小梁部分增厚且分布不规则的腹侧部分则没有。然而，在临床常规MR骨密度测定成为可能之前，应采用最好是小像素大小（低至[0.6 mm]3）的标准化测量方案，并根据实际骨髓部位确定相关曲线。
