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1077 susceptibility-related signal loss compensation in myocardial T2*-quantification

Introduction

Cardiac magnetic resonance T2*-quantification in the mid-ventricular septum is a valid method to assess myocardial iron overload [1]. However, in non-midseptal heart segments, T2*-quantification is compromised by macroscopic susceptibility effects [2, 3]. We studied the intra-, interstudy and inter-observer reproducibility of circumferential myocardial T2* measurements in normal individuals and evaluated reduced slice thickness and a z-shim technique [4] on their potential to reduce susceptibility artefacts.

Materials and methods

8 healthy volunteers underwent a cardiac 1,5 Tesla-MR-examination twice (Siemens Avanto). Within a single breath-hold 8 echo images with TEs from 2.3 ms to 18.6 ms were acquired with a multi-echo gradient echo sequence. Slice thicknesses of 8 and 6 mm were used. For the z-shim technique 11 acquisitions were performed on 8 mm slices with compensation moments between -M0 and M0 added to the exact rephasing moment M0. T2* calculation (a mono-exponential signal decay was assumed) and ROI analysis was performed in Matlab (The MathWorks, Inc., Natick, USA). Z-shim corrected images were calculated using a maximum intensity (MIP) as well as a square root of the sum of squares (SSQ) method. Statistical analysis was performed in SPSS (SPSS 14.0 Inc., Chicago, USA).

Results

The intra-study coefficient of variation (CoV) of midseptal T2* in 8 mm slices was 7.5%, inter-study CoV 6.8% and inter-observer CoV 6.0%. Both slice thickness reduction and z-shim-application resulted in less negative percentual deviation from the 8 mm midseptal T2* value for the lateral and inferior segments (Fig. 1), indicating less signal decay (Fig. 2). Moreover, circumferential homogeneity is improved, especially by the z-shim-SSQ technique. On the other hand slice thickness reduction resulted in an increase of midseptal CoV from 6.8% to 13.2% (p = 0,161). After z-shim application, larger deviations from the 8 mm midseptal T2* were measured for all except lateral segments (Fig. 1). Compared to the MIP approach, deviations were smaller using the SSQ technique (p = 0,042).

Figure 1
figure1

Circumferential T"-variation. Circumferential T2*-quantification is compromised by susceptibility effects. We aimed to evaluate the effect of slice thickness reduction and a z-shim technique on susceptibility-related signal loss. Both techniques resulted in better T2*-homogeneity, at the cost of SNR or scan time, respectively.

Figure 2
figure2

Uncorrected (top) and z-shim corrected (bottom) first and last echo images. The corresponding signal decays over all echo times in septal and inferior segments are shown in the centre.

Discussion

Our reproducibility-data on myocardial T2*-quantification in healthy volunteers resulted in intra-, inter-study and inter-observer CoV comparable to literature standards [5, 6]. Diminishing field variations across the slice by reducing its thickness resulted in slower signal decay for the lateral and inferior wall, but at the same time in a decreased inter-study reproducibility. This is most probably due to lower fit quality, caused by a lower signal to noise ratio. Additional gradient moments in slice direction enabled signal recovery especially in lateral and inferior segments (Fig. 2), improving circumferential T2*'-homogeneity. However, it has to be clarified why falsly high T2* values were obtained mainly in the inferior segment after signal combination using MIP or SSQ techniques. In future T2*-quantification studies, the application of an optimized set of less compensation moments in combination with parallel imaging techniques might allow single breath-hold z-shimmed acquisitions, reducing errors caused by cardiac motion.

References

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Author information

Correspondence to Kaatje Goetschalckx.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Goetschalckx, K., Klarhöfer, M., Buser, P. et al. 1077 susceptibility-related signal loss compensation in myocardial T2*-quantification. J Cardiovasc Magn Reson 10, A202 (2008). https://doi.org/10.1186/1532-429X-10-S1-A202

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Keywords

  • Cardiac Magnetic Resonance
  • Signal Decay
  • Myocardial Iron
  • Parallel Imaging Technique
  • Inferior Segment