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  • Oral presentation
  • Open Access

T2-mapping of ischaemia/reperfusion-injury in the in vivo mouse heart

  • 1,
  • 1,
  • 2,
  • 1 and
  • 1
Journal of Cardiovascular Magnetic Resonance201012 (Suppl 1) :O61

https://doi.org/10.1186/1532-429X-12-S1-O61

  • Published:

Keywords

  • Left Ventricular Volume
  • Left Coronary Artery
  • Mouse Heart
  • Healthy Mouse
  • Basal Section

Introduction

Oedema is a key feature of acute ischaemia/reperfusion (IR) injury. As such, it is a diagnostic - and potentially therapeutic - target, assessable using MRI. To date, its application in the mouse heart is limited due to the challenges associated with low SNR inherent in T2-weighting, miniscule anatomy, and rapid motion. Absolute quantification of transverse relaxation time (T2-mapping) circumvents SNR constraints and may be an alternative to T2-weighted imaging. We have therefore measured myocardial T2 in IR-mice and related T2-maps to the histological area-at-risk (AAR)

Methods

The left coronary artery (LCA) was occluded for 45 minutes followed by 24 hours of reperfusion. For histology, hearts were excised, cannulated, dye-perfused after LCA-reocclusion, and sliced. AAR was determined planimetrically (ratio of unstained to stained myocardium, %LV). Myocardial T2 was measured in healthy and IR mice (n = 5/9) on a 9.4 Tesla MR system using a double-gated spin-echo pulse-sequence (matrix 128 × 128; field-of - view 25.6 × 25.6 mm; 6-8 contiguous slices (1 mm); 8 echo-times (TE, 7-34 ms); repetition time = 1 respiratory cycle. Regions of interest (40-80 voxels) were placed in healthy (septal) and IR (anterior) myocardium. High-T2 myocardium was quantified using a semi-automated threshold tool (cut-off T2NORMAL + 1, 2 and 3 standard-deviations, SD), expressed as fraction of left ventricular volume (%LV) and the spatial extent compared with histology (n = 4). In order to improve congruence with histology, the 1SD datasets were manually corrected (1SD-c) by excluding high-T2 pixels located remotely to the LCA territory. Correlation (r2) between methods was determined.

Results

Myocardial T2 in healthy mice was 21.3 +/- 1 ms. Septal T2 in IR mice was normal (21.2 +/- 2 ms; p = 0.8) while anterior T2 was elevated (27.9 +/- 2 ms; P < 0.01, Figure 1). Histologically, the AAR was 53 +/- 7%LV. T2-AAR was 58.3 +/- 4 (1SD), 37.8 +/- 5 (2SD) and 23.3 +/- 11%LV (3SD). AAR-size in the 1SD-c datasets was 48.7 +/- 6%LV. The correlation between methods was best when remote high-T2 pixels were excluded prior to volume measurements: r2 = 0.99, 0.713, 0.06 and 0.21 for 1SD-c and 1×, 2× and 3× SD, respectively.

Figure 1

Conclusion

The area-at-risk exhibits prolonged T2, likely reflecting myocardial oedema. T2-mapping can be used to identify and quantify the AAR non-invasively and without the SNR constraints impeding T2-weighted imaging. Semi-automated analysis requires a low T2-cut-off. However, accuracy can be improved by manual exclusion of remote pixels, which would otherwise be erroneously included in the threshold-measurements. This problem is most prominent in basal sections where bright flow and motion artifacts exist.

Authors’ Affiliations

(1)
University of Oxford, British Heart Foundation Experimental MR Unit, Oxford, UK
(2)
Franz Volhard Klinik, Charite University Medicine Berlin, HELIOS Clinics, Berlin, Germany

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