Positano Vincenzo, Pepe Alessia, Santarelli Maria Filomena, Scattini Barbara, De Marchi Daniele, Ramazzotti Anna, Forni Gianluca, Borgna-Pignatti Caterina, Lai Maria Eliana, Midiri Massimo, Maggio Aurelio, Lombardi Massimo, Landini Luigi
MRI Laboratory, Institute of Clinical Physiology, CNR, Pisa, Italy.
NMR Biomed. 2007 Oct;20(6):578-90. doi: 10.1002/nbm.1121.
A segmental, multislice, multi-echo T2* MRI approach could be useful in heart iron-overloaded patients to account for heterogeneous iron distribution, demonstrated by histological studies. However, segmental T2* assessment in heart can be affected by the presence of geometrical and susceptibility artefacts, which can act on different segments in different ways. The aim of this study was to assess T2* value distribution in the left ventricle and to develop a correction procedure to compensate for artefactual variations in segmental analysis. MRI was performed in four groups of 22 subjects each: healthy subjects (I), controls (II) (thalassemia intermedia patients without iron overload), thalassemia major patients with mild (III) and heavy (IV) iron overload. Three short-axis views (basal, median, and apical) of the left ventricle were obtained and analyzed using custom-written, previously validated software. The myocardium was automatically segmented into a 16-segment standardized heart model, and the mean T2* value for each segment was calculated. Punctual distribution of T2* over the myocardium was assessed, and T2* inhomogeneity maps for the three slices were obtained. In group I, no significant variation in the mean T2* among slices was found. T2* showed a characteristic circumferential variation in all three slices. The effect of susceptibility differences induced by cardiac veins was evident, together with low-scale variations induced by geometrical artefacts. Using the mean segmental deviations as correction factors, an artefact correction map was developed and used to normalize segmental data. The correction procedure was validated on group II. Group IV showed no significant presence of segmental artefacts, confirming the hypothesis that susceptibility artefacts are additive in nature and become negligible for high levels of iron overload. Group III showed a greater variability with respect to normal subjects. The correction map failed to compensate for these variations if both additive and percentage-based corrections were applied. This may reinforce the hypothesis that true inhomogeneity in iron deposition exists.
一种分段、多层、多回波T2磁共振成像方法可能有助于诊断心脏铁过载患者，组织学研究已证实该方法可用于解释铁分布的异质性。然而，心脏分段T2评估可能会受到几何和敏感性伪影的影响，这些伪影可能以不同方式作用于不同节段。本研究的目的是评估左心室T2值分布，并开发一种校正程序以补偿分段分析中的伪影变化。对四组每组22名受试者进行了磁共振成像：健康受试者（I组）、对照组（II组）（中间型地中海贫血且无铁过载患者）、轻度（III组）和重度（IV组）铁过载的重型地中海贫血患者。获取左心室的三个短轴视图（基底、中间和心尖），并使用自定义编写且先前已验证的软件进行分析。心肌自动分割为16节段的标准化心脏模型，并计算每个节段的平均T2值。评估T2在心肌上的逐点分布，并获取三个切片的T2不均匀性图。在I组中，未发现切片间平均T2有显著差异。T2在所有三个切片中均呈现出特征性的圆周变化。心脏静脉引起的敏感性差异的影响明显，同时几何伪影引起的低尺度变化也很明显。以平均节段偏差作为校正因子，开发了一个伪影校正图并用于标准化节段数据。该校正程序在II组上得到验证。IV组未显示出明显的节段伪影，证实了敏感性伪影本质上是累加的这一假设，并且对于高水平的铁过载来说可以忽略不计。III组相对于正常受试者表现出更大的变异性。如果同时应用累加校正和基于百分比的校正，校正图无法补偿这些变化。这可能强化了铁沉积中存在真正不均匀性的假设。
