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Strain ratios obtained from elastograms over a 9 month period for phantom D (○) and a 7 month period for phantom E (□). The dashed horizontal lines correspond to the mean of all strain ratios for each phantom, excluding the initial values in each case. The numerical mean value corresponding to the dashed line appears at the right end of the line. The position of the letter P on each dashed line indicates the time of production of the phantom.
