Sheth Vipul R, Fan Shujuan, He Qun, Ma Yajun, Annese Jacopo, Switzer Robert, Corey-Bloom Jody, Bydder Graeme M, Du Jiang
Department of Radiology, University of California, San Diego, CA, United States.
The Institute for Brain and Society, San Diego, CA, United States.
Magn Reson Imaging. 2017 May;38:87-94. doi: 10.1016/j.mri.2016.12.025. Epub 2016 Dec 28.
Multiple sclerosis (MS) causes demyelinating lesions in the white matter and increased iron deposition in the subcortical gray matter. Myelin protons have an extremely short T2* (<1ms) and are not directly detected with conventional clinical magnetic resonance (MR) imaging sequences. Iron deposition also reduces T2*, leading to reduced signal on clinical sequences. In this study we tested the hypothesis that the inversion recovery ultrashort echo time (IR-UTE) pulse sequence can directly and simultaneously image myelin and iron deposition using a clinical 3T scanner. The technique was first validated on a synthetic myelin phantom (myelin powder in DO) and a Feridex iron phantom. This was followed by studies of cadaveric MS specimens, healthy volunteers and MS patients. UTE imaging of the synthetic myelin phantom showed an excellent bi-component signal decay with two populations of protons, one with a T2* of 1.2ms (residual water protons) and the other with a T2* of 290μs (myelin protons). IR-UTE imaging shows sensitivity to a wide range of iron concentrations from 0.5 to ~30mM. The IR-UTE signal from white matter of the brain of healthy volunteers shows a rapid signal decay with a short T2* of ~300μs, consistent with the T2* values of myelin protons in the synthetic myelin phantom. IR-UTE imaging in MS brain specimens and patients showed multiple white matter lesions as well as areas of high signal in subcortical gray matter. This in specimens corresponded in position to Perl's diaminobenzide staining results, consistent with increased iron deposition. IR-UTE imaging simultaneously detects lesions with myelin loss in the white matter and iron deposition in the gray matter.
多发性硬化症（MS）会导致白质脱髓鞘病变，并使皮质下灰质中的铁沉积增加。髓磷脂质子的T2极短（<1ms），常规临床磁共振（MR）成像序列无法直接检测到。铁沉积也会降低T2，导致临床序列上的信号减弱。在本研究中，我们检验了以下假设：反转恢复超短回波时间（IR-UTE）脉冲序列可使用临床3T扫描仪直接并同时成像髓磷脂和铁沉积。该技术首先在合成髓磷脂模型（溶解于去离子水中的髓磷脂粉末）和菲立磁铁模型上得到验证。随后对尸体MS标本、健康志愿者和MS患者进行了研究。合成髓磷脂模型的UTE成像显示出优异的双成分信号衰减，有两类质子群，一类T2为1.2ms（残留水质子），另一类T2为290μs（髓磷脂质子）。IR-UTE成像对0.5至约30mM的广泛铁浓度范围显示出敏感性。健康志愿者大脑白质的IR-UTE信号显示出快速的信号衰减，T2约为300μs，与合成髓磷脂模型中髓磷脂质子的T2值一致。MS脑标本和患者的IR-UTE成像显示出多个白质病变以及皮质下灰质中的高信号区域。在标本中，这与Perl二氨基联苯胺染色结果在位置上相对应，与铁沉积增加一致。IR-UTE成像可同时检测白质中髓磷脂丢失的病变和灰质中的铁沉积。
