Impact of field strength and iron oxide nanoparticle concentration on the linearity and diagnostc accuracy of off-resonance imaging
Impact of field strength and iron oxide nanoparticle concentration on the linearity and diagnostc accuracy of off-resonance imaging
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DOI：
10.1002/nbm.1209
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发表时间：
2008-06-01
影响因子：
2.9
通讯作者：
Sosnovik, David E.
中科院分区：
文献类型：
--
作者：
Farrar, Christian T.;Dai, Guangping;Sosnovik, David E.
非共振成像（ORI）技术正越来越多地用于对氧化铁成像剂如单晶氧化铁纳米颗粒（MION）进行成像。然而，ORI的诊断准确性，线性度和场依赖性尚未得到充分表征。因此，在本研究中，ORI的灵敏度、特异性和线性作为MION浓度和磁场强度（4.7和14 T）的函数进行了检查。对具有和不具有空气界面的MION体模以及愈合心肌梗死的小鼠模型中的MION摄取进行成像。MION的共振位移随MION浓度线性增加。相比之下，ORI信号/灵敏度是高度非线性的，最初随着MION浓度增加，直到T-2变得与TE相当，然后降低。发现ORI区分MION诱导的共振位移与共振水的特异性随着场的增加而降低，因为共振水线宽增加（4.7T时为15 Hz，14 T时为45 Hz）。在体外和体内，在4.7 T的空气界面处观察到大的共振位移（类似于300 Hz），并导致MION浓度低于150 μ g Fe/mL时ORI特异性较差。体内ORI灵敏度足以检测MION在浸润愈合心肌梗死的巨噬细胞中的积聚，但特异性受到胸壁和降主动脉的空气/组织界面处的非特异性阳性对比区域的限制。然而，可以预期在较低的磁场下可以改善特异性和线性度，其中观察到共振水线宽降低、空气引起的共振位移减少和T-2弛豫时间延长。因此，ORI的最佳性能可能在低场、中等MION浓度和含有非常短TE的序列中看到。版权所有（C）2007约翰威利父子有限公司
Off-resonance imaging (ORI) techniques are being increasingly used to image iron oxide imaging agents such as monocrystalline iron oxide nanoparticles (MION). However, the diagnostic accuracy, linearity, and field dependence of ORI have not been fully characterized. In this study, the sensitivity, specificity, and linearity of ORI were thus examined as a function of both MION concentration and magnetic field strength (4.7 and 14 T). MION phantoms with and without an air interface as well as MION uptake in a mouse model of healing myocardial infarction were imaged. MION-incluced resonance shifts were shown to increase linearly with MION concentration. In contrast, the ORI signal/sensitivity was highly non-linear, initially increasing with MION concentration until T-2 became comparable to the TE and decreasing thereafter. The specificity of ORI to distinguish MION-induced resonance shifts from on-resonance water was found to decrease with increasing field because of the increased on-resonance water linewidths (15Hz at 4.7T versus 45Hz at 14T). Large resonance shifts (similar to 300 Hz) were observed at air interfaces at 4.7 T, both in vitro and in vivo, and led to poor ORI specificity for MION concentrations less than 150 mu g Fe/mL. The in vivo ORI sensitivity was sufficient to detect the accumulation of MION in macrophages infiltrating healing myocardial infarcts, but the specificity was limited by non-specific areas of positive contrast at the air/tissue interfaces of the thoracic wall and the descending aorta. Improved specificity and linearity can, however, be expected at lower fields where decreased on-resonance water linewidths, reduced air-induced resonance shifts, and longer T-2 relaxation times are observed. The optimal performance of ORI will thus likely be seen at low fields, with moderate MION concentrations and with sequences containing very short TEs. Copyright (C) 2007 John Wiley & Sons, Ltd.