CN110786854A - 一种水脂混合体系下的反转回复序列t1测量方法 - Google Patents
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Abstract
一种水脂混合体系下的反转回复序列T1测量方法,涉及磁共振成像技术,该方法具有以下步骤:步骤一、先采集一个多回波的图像用于水脂分离,计算出每个像素点或者ROI的脂肪质子密度分数;步骤二、采集自由衰减信号;步骤三、计算出像素点或者ROI的脂肪质子密度分数之后,对采集得到的自由衰减信号作多参数拟合,同时计算出水和脂的弛豫特征,解决了传统反转恢复T1测量无法在脂肪存在的情况下完成组织T1测量的缺陷。该方法不仅可以测得水组织的T1,在脂肪信号占比足够的情况下也可以同时测得脂肪的T1。
Description
技术领域
本发明涉及磁共振成像技术,具体涉及一种水脂混合体系下的反转回复序列T1测量方法。
背景技术
T1弛豫时间是磁共振成像中的一个重要参数,它表征磁共振成像中磁化矢量沿着主磁场方向恢复的快慢程度。自由水和体液弛豫慢,T1时间长;而在生物的组织中,由于水部分的被束缚在蛋白质上,增强了T1弛豫,因而弛豫时间通常为几百毫秒。正常组织中自由水和束缚水之间存在一个平衡,而病理条件会扰乱这种平衡,使得T1弛豫时间产生变化。因此,T1弛豫时间可以作为判断疾病进展情况的一个重要标志。T1定量技术目前已经被广泛用于心肌病变检测,脑诊断,肝纤维化分级等应用中。但由于部分器官的脂性病变,水信号与脂肪信号会在磁共振图像的同一个像素点或者同一个感兴趣区域(ROI)同时中存在,短T1的脂肪信号为影响到肝组织T1的测量。现有的基于翻转恢复的自旋回波T1测量方法无法排除脂肪的影响。
人体组织发生脂性病变时,磁共振图像中会出现脂肪与水信号在同一个像素点(或者ROI)中共存的情况。而脂肪与水有着不同的纵向弛豫特征。传统的反转恢复T1测量序列并未考虑到脂肪与水组织共存的情况,只能测得一个表观弛豫时间T1。这个表观弛豫时间会同时受到脂肪质子密度分数(protondensity fatfraction,PDFF),水组织T1,w,脂肪组织T1,f的影响,无法表征组织的固有弛豫特性,为了解决上述技术问题,特提出一种新的技术方案。
发明内容
本发明提出提出一种能够在水脂混合体系下完成组织T1测量的方法,克服现有的反转恢复T1测量序列会受到脂肪信号干扰的局限。
为实现上述目的,本发明提供如下技术方案一种水脂混合体系下的反转回复序列T1测量方法,该方法具有以下步骤:
步骤一、先采集一个多回波的图像用于水脂分离,计算出每个像素点或者ROI的脂肪质子密度分数;
步骤二、采集自由衰减信号;
步骤三、计算出像素点或者ROI的脂肪质子密度分数之后,对采集得到的自由衰减信号作多参数拟合,同时计算出水和脂的弛豫特征。
所述的参数拟合的公式为:
其中,S为各个时间点下采集得到的自由衰减信号幅值;T1为重复时间;M0为氢质子密度;考虑到实际的射频脉冲不一定正好是180°,假定一个0~2变化的参数α;T1为待测组织的纵向弛豫时间常数;d为系统设备的固定偏差。
所述的参数拟合的公式为:
其中,Mw、Mf分别为水、脂中氢质子密度,二者之和即为Mo;T1,w、T1,f分别为水、脂的纵向弛豫时间常数;αw和αf为射频脉冲对水、脂中氢质子产生的磁化矢量翻转效率。
所述的Mw、Mf可表示为:
Mw=(1-FF)·M0,Mf=FF·M0
FF即为脂肪质子密度分数。
与现有技术相比,本发明的有益效果是:解决了传统反转恢复T1测量无法在脂肪存在的情况下完成组织T1测量的缺陷。该方法不仅可以测得水组织的T1,在脂肪信号占比足够的情况下也可以同时测得脂肪的T1。
具体实施方式
下面将对本发明实施例中的技术方案进行清楚、完整地描述,显然,所描述的实施例仅仅是本发明一部分实施例,而不是全部的实施例。基于本发明中的实施例,本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例,都属于本发明保护的范围。
一种水脂混合体系下的反转回复序列T1测量方法,该方法具有以下步骤:
步骤一、先采集一个多回波的图像用于水脂分离,计算出每个像素点或者ROI的脂肪质子密度分数;
步骤二、采集自由衰减信号;
步骤三、计算出像素点或者ROI的脂肪质子密度分数之后,对采集得到的自由衰减信号作多参数拟合,同时计算出水和脂的弛豫特征。
所述的参数拟合的公式为:
其中,S为各个时间点下采集得到的自由衰减信号幅值;T1为重复时间;M0为氢质子密度;考虑到实际的射频脉冲不一定正好是180°,假定一个0~2变化的参数α;T1为待测组织的纵向弛豫时间常数;d为系统设备的固定偏差。
考虑到水脂混合体中,同时会存在两种不同物质——水和脂,我们可以对传统的反转恢复信号拟合公式作如下更改,所述的参数拟合的公式为:
其中,Mw、Mf分别为水、脂中氢质子密度,二者之和即为Mo;T1,w、T1,f分别为水、脂的纵向弛豫时间常数;αw和αf为射频脉冲对水、脂中氢质子产生的磁化矢量翻转效率。
所述的Mw、Mf可表示为:
Mw=(1-FF)·M0,Mf=FF·M0
FF即为脂肪质子密度分数。可以通过已有文献中的多回波水脂分离算法得到。即结合水脂分离算法后,可以将公式
可改写为
其中,未知量有六个,T1,w、T1,f、M0、d、αw、αf,按照上式进行参数拟合,即可同时得到水、脂的纵向弛豫时间常数。
为了验证算法可行性,我们在自制仿体上完成了相关实验。仿体中脂肪含量分别按照0,5%,10%,15%,20%,25%,30%用纯水和花生油配制,同时添加了一定量的防腐剂以及表面活性剂。反转恢复序列的反转时间分别设置为100ms,600ms,1100ms,1600ms,2100ms以及2600ms,重复时间TR=3000ms,层厚3mm,带宽500Hz,脂肪定量图像采集所用序列为2D多回波GRE序列,层厚5mm,重复时间TR=19ms,翻转角2°,回波时间分别设置为2.43ms,4.11ms,5.79ms,7.47ms,9.15ms,10.83ms,实验平台为联影uMR790系统。通过已有水脂分离算法,利用采集得到的多回波图像,分别算的每个试管中的脂肪含量分别为0.29%,4.54%,8.51%,12.55%,16.97%,21.62%,27.43%。因为第一个试管中只有纯水,因而原有反转恢复拟合的方式是适用的,并且1号管的T1值可以作为2~7号试管的参考。
各管中水的T1值如下表所示,对应的B-A分析结果。从结果可以看出,由于受到脂肪信号的影响,2~7号试管测得的T1值与1号试管的T1值存在较大明显偏差,无法完成水T1的测量;与之对比的是,此方法,在不同的脂肪含量下,均能够准确的测得水的T1。
由此可见此方法不仅可以用于水脂T1测量,同样可以应用于其他含量已知的混合体系T1定量,只需要在
中增加更多衰减项以及对应物质比例即可。
解决了传统反转恢复T1测量无法在脂肪存在的情况下完成组织T1测量的缺陷。该方法不仅可以测得水组织的T1,在脂肪信号占比足够的情况下也可以同时测得脂肪的T1。
尽管已经示出和描述了本发明的实施例,对于本领域的普通技术人员而言,可以理解在不脱离本发明的原理和精神的情况下可以对这些实施例进行多种变化、修改、替换和变型,本发明的范围由所附权利要求及其等同物限定。
Claims (4)
1.一种水脂混合体系下的反转回复序列T1测量方法,其特征在于:该方法具有以下步骤:
步骤一、先采集一个多回波的图像用于水脂分离,计算出每个像素点或者ROI的脂肪质子密度分数;
步骤二、采集自由衰减信号;
步骤三、计算出像素点或者ROI的脂肪质子密度分数之后,对采集得到的自由衰减信号作多参数拟合,同时计算出水和脂的弛豫特征。
4.根据权利要求3所述的水脂混合体系下的反转回复序列T1测量方法,其特征在于:所述的Mw、Mf可表示为:
Mw=(1-FF)·M0,Mf=FF·M0
FF即为脂肪质子密度分数。
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CN117310581B (zh) * | 2023-10-11 | 2024-05-10 | 安徽峻德医疗科技有限公司 | 一种核磁共振信号衰减拟合方法、系统、设备及存储介质 |
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