Measuring Myocardial Iron
Non-invasive cardiac imaging modalities, such as echocardiography (echo), are of limited utility in identifying left ventricular myocardial iron deposition: First, morphological changes in the myocardium (e.g., in myocardial wall thickness and in the end-diastolic diameter of the left ventricle), resulting from iron deposition, may be modest— thereby limiting sensitivity. Second, ventricular dysfunction and dilation that may be detected on echo often do not appear until the iron concentration reaches a critical concentration. Finally, while echo may be employed to detect abnormal wall motion (e.g., reduced longitudinal shortening), it is not specific to myocardial iron overload. Therefore, the use of other noninvasive imaging modalities is warranted.
Cardiac magnetic resonance imaging (MRI) is useful in detecting iron in specific tissues, quantifying its concentration, and monitoring the efficacy of subsequent treatments (e.g., iron chelation therapy). Using gated, short-axis images taken from breath-hold, multi-echo fast gradient echo sequences, iron concentration may be acquired in the myocardium (F1). A sizeable region of interest is drawn on the interventricular septum of the mid left ventricle (F1A). From this suiteHEART® software displays a T2* relaxation curve (F1B, F2) and a T2* value (F2), which may indicate pathology: The general idea is that the presence of iron in the myocardium disrupts magnetic field homogeneity, thus shortening relaxation time and decreasing the value of myocardial T2* compared with unaffected tissue.
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