Value of transverse relaxometry difference methods for iron in human brain

详细信息    查看全文

• 作者：Md. Nasir Uddin ; R. Marc Lebel¹ ; Alan H. Wilman ; ^{wilman@ualberta.ca" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Iron ; Transverse relaxometry ; R2&rsquo ; Stimulated echo compensation ; FDRI
• 刊名：Magnetic Resonance Imaging
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：34
• 期：1
• 页码：51-59
• 全文大小：1380 K

文摘

To investigate the brain iron dependence of transverse relaxation rate difference methods derived from spin echo and gradient echo measurements from two field strengths.

<h4 id="absSec_2">Methodsh4>

Transverse relaxation rates R₂ and R₂^⁎ were measured in human brain in 17 healthy subjects at 1.5 T and 4.7 T using multi-slice, multiecho spin echo and gradient echo sequences. R₂ quantification used stimulated echo compensation and R₂^⁎ quantification used linear background gradient correction at 4.7 T only. Subtraction of R₂ from R₂^⁎ within each field strength yielded R₂^’, and R₂ subtraction across fields yielded Field Dependent R₂ Increase (FDRI). All transverse relaxation measures were then correlated with published post-mortem iron concentrations using linear regression analysis. Regional differences were tested using paired t-tests. Phantom measurements of FDRI were also performed.

<h4 id="absSec_3">Resultsh4>

In deep grey matter, all transverse relaxation rates (R₂, R₂^⁎, R₂^’) at both 1.5 T and 4.7 T, and FDRI had moderate to strong correlations (r > 0.71, p < 0.0001) with estimated non-heme iron. The 4.7 T methods and FDRI had higher correlations (r > 0.9) than 1.5 T measures. R₂, R₂^⁎, R₂’ at 4.7 T and FDRI had slopes 0.49, 1.96, 1.48 and 0.33 [s^− 1/mg Fe/100 g wt. tissue] and intercepts 14.40, 16.87, 2.47 and 3.21 [s^− 1] respectively. Even though FDRI yielded a zero intercept in phantom, in vivo FDRI was found to be ineffective at fully removing non-iron contributions and yielded a large intercept. The slope for R₂^’ was 3.4 times greater at 4.7 T than 1.5 T. For white matter fiber tracts oriented predominantly perpendicular versus parallel to B₀, R₂^’ increased by ~ 50% at 4.7 T and ~ 30% at 1.5 T, while R₂ and FDRI in white matter was insensitive to its orientation with respect to B₀.

<h4 id="absSec_4">Conclusionh4>

The transverse relaxation difference methods FDRI and R₂^’ at 4.7 T had high correlations to predicted iron content similar to R₂ and R₂^⁎ at 4.7 T. Although R₂^’ had smaller y-intercept with estimated iron concentration than FDRI, in white matter R₂^’ demonstrated strongest dependence on fiber orientation with respect to B_0. These results suggest that for brain iron correlation, there is minimal value of transverse difference methods over a single R₂^⁎ measurement at highest available field, which was 4.7 T.