- Meeting abstract
- Open Access
1077 susceptibility-related signal loss compensation in myocardial T2*-quantification
Journal of Cardiovascular Magnetic Resonance volume 10, Article number: A202 (2008)
Cardiac magnetic resonance T2*-quantification in the mid-ventricular septum is a valid method to assess myocardial iron overload . 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  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).
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).
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.
Westwood M, et al: A single breath-hold multiecho T2* cardiovascular magnetic resonance technique for diagnosis of myocardial iron overload. J Magn Reson Imaging. 2003, 18: 33-10.1002/jmri.10332.
Atalay MK, et al: Cardiac susceptibility artifacts arising from the heart-lung interface. Magn Reson Med. 2001, 45: 341-10.1002/1522-2594(200102)45:2<341::AID-MRM1043>3.0.CO;2-Q.
Reeder SB, et al: In vivo measurement of T2* and field inhomogeneity maps in the human heart at 1.5 T. Magn Reson Med. 1998, 39: 988-10.1002/mrm.1910390617.
Constable RT, et al: Composite image formation in z-shimmed functional MR imaging. Magn Reson Med. 1999, 42: 110-10.1002/(SICI)1522-2594(199907)42:1<110::AID-MRM15>3.0.CO;2-3.
Westwood MA, et al: Interscanner reproducibility of cardiovascular magnetic resonance T2* measurements of tissue iron in thalassemia. J Magn Reson Imaging. 2003, 18: 616-10.1002/jmri.10396.
Tanner MA, et al: Multi-center validation of the transferability of the magnetic resonance T2* technique for the quantification of tissue iron. Haematologica. 2006, 91: 1388-
About this article
Cite this article
Goetschalckx, K., Klarhöfer, M., Buser, P. et al. 1077 susceptibility-related signal loss compensation in myocardial T2*-quantification. J Cardiovasc Magn Reson 10 (Suppl 1), A202 (2008). https://doi.org/10.1186/1532-429X-10-S1-A202
- Cardiac Magnetic Resonance
- Signal Decay
- Myocardial Iron
- Parallel Imaging Technique
- Inferior Segment