在7T的健康和脱髓鞘活体小鼠中,基于综合定量磁化转移(qMT)方案,确定单点大分子质子分数(SP-MPF)映射的最佳约束组织参数和非共振序列参数。
使用3D宠坏的基于梯度回波的序列,通过对小鼠大脑的Z光谱进行采样来执行全面的qMT协议,在体内。提供额外的T1,B1+和B0图允许估计qMT组织参数,其中三个将受到限制,即自由池的纵向和横向松弛特性(R1,f,T2,f),交叉弛豫率(R)和束缚池横向弛豫时间(T2,r)。研究了不同的约束参数集,以减少基于综合协议的SP-MPF及其参考之间的偏差。
基于受约束参数的全脑直方图分析,使参考图和SP-MPF图之间的全局偏差最小化的最佳实验参数包括600°和6kHz的非共振辐照脉冲。在Bland-Altman对感兴趣区域进行分析之后,最优约束参数为R1,fT2,f=0.0129,R=26.5s-1,和T2,r=9.1µs,在所有小鼠中,产生10-4的总体MPF偏倚(一致性极限[-0.0068;0.0070])和参考方法与最佳单点方法之间的相对差异为0.64%±5.95%。
证明了估计动物模型和场相关约束参数的必要性。单点MPF方法可以在7T可靠地应用,作为小鼠常规临床前体内成像方案的一部分。
To determine optimal constrained tissue parameters and off-resonance sequence parameters for single-point macromolecular proton fraction (SP-MPF) mapping based on a comprehensive quantitative magnetization transfer (qMT) protocol in healthy and demyelinated living mice at 7T.
Using 3D spoiled gradient echo-based sequences, a comprehensive qMT protocol is performed by sampling the Z-spectrum of mice brains, in vivo. Provided additional T1 , B 1 + and B0 maps allow for the estimation of qMT tissue parameters, among which three will be constrained, namely the longitudinal and transverse relaxation characteristics of the free pool (R1,f T2,f ), the cross-relaxation rate (R) and the bound pool transverse relaxation time (T2,r ). Different sets of constrained parameters are investigated to reduce the bias between the SP-MPF and its reference based on the comprehensive protocol.
Based on a whole-brain histogram analysis about the constrained parameters, the optimal experimental parameters that minimize the global bias between reference and SP-MPF maps consist of a 600° and 6 kHz off-resonance irradiation pulse. Following a Bland-Altman analysis over regions of interest, optimal constrained parameters were R1,f T2,f = 0.0129, R = 26.5 s-1 , and T2,r = 9.1 µs, yielding an overall MPF bias of 10-4 (limits of agreement [-0.0068;0.0070]) and a relative variation of 0.64% ± 5.95% between the reference and the optimal single-point method across all mice.
The necessity of estimating animal model- and field-dependent constrained parameters was demonstrated. The single-point MPF method can be reliably applied at 7T, as part of routine preclinical in vivo imaging protocol in mice.