3.0T和1.5T MRI定量地中海贫血心、肝脏铁沉积的对比研究

Using a novel iron overloaded rabbit model, we have proved determine the feasibility of liver and cardiac iron concentration quantification by 1.5T MRI. But, is there the same rule at 3.0T? What is the patient's diagnosis criteria at 3.0T? Because 3.0T is becoming increasingly widespread now, and some hospitals have only 3T scanner, in particular in China where the ownership of 3T is relatively high. Since relaxation rates are in general field-dependent, the diagnosis criteria of liver and cardiac iron-load established at 1.5T do not apply at 3.0T. So it is important to be able to interpret 3.0T relaxation rates in terms of liver and cardiac iron concentration. Through an observation study, we found liver or cardiac T2* values of same rabbit were linearly positive correlated between 1.5T and 3.0T, and liver R2* values was linearly positive correlated with liver iron concentration, cardiac R2* values was linearly positive correlated with cardiac iron concentration. Therefore, we speculate that assessment of liver or cardiac iron burden by T2* imaging is feasible at 3.0T. This study aims to establish iron overloaded rabbit model and to explore the relationship of liver and cardiac R2* values between 3.0T and 1.5T, and the relationship between liver R2* values and liver iron concentration, cardiac R2* values and cardiac iron concentration at 3.0T. The conclusion could be applied to clinical application, to establish the relationship between 1.5T and 3.0T by comparing T2* measurements of cardiac iron burden at 3.0T with those obtained at 1.5T in the same patients, then deducted the regression equation between them. Obtained the cut-off T2* values used to evaluate the severity of the cardiac iron loading at 3.0T through the prediction equation. Through the liver iron concentration obtained by 1.5T MRI, the relationship between liver R2* values and liver iron concentration at 3.0T to be explored, then deducted the regression equation between them.

通过建立铁超负荷兔模型，我们已经证明1.5T MRI可以定量心、肝铁沉积，那么3.0T是否存在相同规律？诊断标准是什么？因为3.0T MRI在世界范围内，尤其是亚洲，数量增长迅速，我国有的医疗机构甚至只有3.0T。由于弛豫时间具有场强依赖性，1.5T获得的诊断标准并不适用于3.0T，这使利用MRI定量心、肝铁含量的这种无创、准确、可反复的方法遭受到了新挑战。通过预实验我们发现同一家兔的心肌、肝脏分别在3.0T和1.5T的弛豫参数之间存在相关，心肌、肝脏在3.0T场强下的弛豫参数与实际心、肝铁浓度之间有线性相关趋势。因此，我们推测3.0T MRI定量心、肝脏铁沉积具有可行性。本研究旨在通过建立铁超负荷兔模型，探讨3.0T场强下心、肝脏弛豫参数与实际铁含量之间的关系及3.0T和1.5T场强下心、肝脏弛豫参数之间的关系，将得到的结论应用于临床对比研究，获得3.0T诊断患者心、肝铁沉积的标准。

依靠反复输血治疗的地中海贫血患者一年之内即有可能发生铁超负荷。心肌铁沉积所致的心力衰竭等心脏并发症是患者最主要的死亡原因之一。如果能持续监测心肌铁沉积程度，及时去铁治疗，不仅可以预防心肌铁沉积的发生，还可以逆转早期铁沉积导致的心脏并发症。肝脏是人体过量的铁最主要沉积部位（70-90％），肝铁浓度是反映体内铁含量最直接也是最重要的指标。持续监测肝脏铁浓度，早期诊断铁超负荷，制定去铁方案及时治疗，可以避免并发症的发生。本研究通过建立铁超负荷家兔模型，探讨3.0T和1.5T场强下获取的心肌、肝脏MRI数据之间的关系及3.0T场强下MRI数据与家兔心肌、肝脏铁含量实测值之间的相关性，并建立预测心肌、肝脏铁浓度的直线回归方程。以动物实验获得的结论为基础，对不同程度铁超负荷患者（重型和中间型地中海贫血患者）分别同时进行3.0T和1.5T MRI扫描，测量心肌、肝脏T2*值。探讨获取的3.0T 和1.5T场强下患者心肌、肝脏的MRI数据之间的关系，探讨3.0T场强下肝脏的MRI数据与肝脏铁含量实测值之间的相关性，并建立两者之间的直线回归方程。铁超负荷家兔心肌R2*值与CIC之间高度线性相关（r=0.854，P＜0.001）。两者之间的一元回归方程为：Y = 0.004 X + 0.213（F =96.056，P＜0.001）X：心肌R2*值；Y：CIC。肝脏R2值与LIC呈显著直线正相关（r=0.948, P=0.000）。SIR（肝脏/肌肉）与LIC呈显著直线负相关（r=﹣0.845, P=0.000)。分别建立两者之间的回归方程：Y1=96.426X1﹣0.92(F=235.843，P=0.000)；Y2=-5.924X2+10.581(F=96.338，P=0.000) X1：R2，X2:SIR（肝脏/肌肉），Y为预测的LIC。3.0T和1.5T场强下患者心肌T2*之间高度相关（（r =0.935，P＜0.001）。两者之间的直线回归方程：T2*（3T）= 0.447 T2*（1.5T）+ 0.965。患者的肝脏R2*值与LIC之间高度线性相关（r=0.963，P＜0.0001）；两者之间的回归方程为：LIC=0.04R2*-3.804。MRI 评价地贫患者心肌、肝脏铁沉积程度，进一步确定是否需要去铁治疗及治疗方案的制定，为临床铁超负荷患者提供一项无创、有效的检查方法。