An optional sub-study examining test-retest reproducibility of MRS at 1.5 and 3T will be performed on selected participants willing to undergo a second scan. Details of this sub-study are provided below. As outlined above our preferred field strength for the assessment of PEDSR is 1.5T. However, due to higher signal to noise of 3T imaging, MRS for myocardial triglyceride may be better at 3T but there have been no direct comparisons.