Histological validation of ShMOLLI equilibrium contrast CMR for the measurement of diffuse myocardial fibrosis
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Histological validation of ShMOLLI equilibrium contrast CMR for the measurement of diffuse myocardial fibrosis Steven K White1,2*, Stefan K Piechnik3, Stefan Neubauer3, Matthew D Robson3, James Moon1 From 15th Annual SCMR Scientific Sessions Orlando, FL, USA. 2-5 February 2012 Background Diffuse myocardial fibrosis can be measured using pre and post contrast T1 relaxation time changes. Newer, faster sequences for T1 mapping promise whole heart coverage and improved clinical utility, but have not been validated against histology. Methods In fourteen patients with symptomatic severe aortic stenosis awaiting valve surgery, we performed equilibrium contrast CMR (EQ-CMR: [Flett AS et al. Circulation 2010;122(2):138-44]) to calculate Vd(m) using ShMOLLI (Shortened Modified Look-Locker Inversion recovery [Piechnik at al. JCMR 2010;12:69]) and standard multibreathold (FLASH) mapping, for the pre and equilibrium contrast T1 mapping. We compared the results to surgical biopsy. Vd(m) was calculated by Vd(m)=(1-hematocrit)xΔ(1/ T1)myo ÷ Δ(1/T1)blood. Surgical left ventricular septal biopsies were fixed and stained with picrosirius red and then digitally photographed. Collagen volume fraction (CVF%) was calculated by a blinded observer using in-house software (macro written in Image J) for automated analysis. Patients with LGE in the biopsy area were pre-specified as being excluded from analysis. Results FLASH T1 mapping was not possible in 2 out of 14 patients due to: 1) inability to breath hold & 2) persistent ectopy. ShMOLLI assessment was possible in all subjects. No patient was excluded for LGE in the biopsy
area, but 2 biopsy specimens were excluded because they were thought histologically to be superficial with extremes of fibrosis (patchy fibrosis). There was a strong correlation between histological CVF% and both FLASH Vd(m) (r=0.772, p=0.021) and ShMOLLI Vd(m) (r=0.748, p=0.007), as shown in Figures 1 and 2.
Conclusions Rapid T1 mapping with ShMOLLI can be used to measure Vd(m) by EQ-CMR. The histological calibration here permits conversion of ShMOLLI Vd(m) to % fibrosis, but also, potentially, whole heart fibrosis assessment,
Figure 1 MRI measured myocardial volume of distribution Vd(m) against histological CVF% (n=11, r=0.772, p=0.021). Vd(m) calculated using T1 values obtained by Inversion Recovery FLASH acquired over multiple breath-holds with different TI delays.
1 The Heart Hospital Imaging Centre, The Heart Hospital, London, UK Full list of author information is available at the end of the article
© 2012 White et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
White et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):O111 http://www.jcmr-online.com/content/14/S1/O111
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Figure 2 MRI measured
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