Standardized T₂* map of normal human heart in vivo to correct T₂* segmental artefacts

Abstract

A segmental, multislice, multi-echo T 2 Ã MRI approach could be useful in heart iron-overloaded patients to account for heterogeneous iron distribution, demonstrated by histological studies. However, segmental T 2 Ã 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 T 2 Ã 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 T 2 Ã value for each segment was calculated. Punctual distribution of T 2 Ã over the myocardium was assessed, and T 2 Ã inhomogeneity maps for the three slices were obtained. In group I, no significant variation in the mean T 2 Ã among slices was found. T 2 Ã 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.

Cardiac iron and cardiac disease in males and females with transfusion-dependent thalassemia major: a T2* magnetic resonance imaging study

“…10 A T2* value greater than 20 ms was considered as a conservative cut-off for all 16 segments, for the mid-ventricular septum and for the entire heart. 11,12 The intraobserver, inter-observer and inter-study variabilities of the proposed methodology have been previously assessed. 5,7 The transferability of multislice multiecho T2* within the MIOT network has been previously validated.…”

Single region of interest versus multislice T2* MRI approach for the quantification of hepatic iron overload

“…We developed a susceptibility artifacts map to take into account artifactual T2* fluctuations. We adopted the same approach used to build a T2* correction map applied to cardiac images (22). Briefly, it could be expected that systematic drift of T2* segmental values from the mean T2* liver values in subjects without iron overload is due only to susceptibility artifacts.…”

Influence of myocardial fibrosis and blood oxygenation on heart T2* values in thalassemia patients

“…After the delay time, only 20.3 msec were used for the acquisition of the nine k-space segments. This time covered the tele-diastolic phase, which was when heart motion can be negligible (12). Analysis on T2* images was performed by one experienced observer using dedicated software (HIPPO MIOT IFC-CNR) to provide the T2* value on each of the 16 segments of the left ventricle (according to the standard AHA/ACC model (23)) as well as the global T2* value averaged over all segmental T2* values and the T2* value in the mid-ventricular segment averaged over the mid-anterior septum and the mid-inferior septum (Fig.…”

“…1). As previously demonstrated, the developed procedure was able to correct for cardiac/visceral geometrical and susceptibility artifacts, exploiting an appropriate correction map (12). A T2* value Ͼ 20 ms was taken as the "conservative" normal value for all 16 segments and for the global T2* value (7)(8)(9)12).…”