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  • Workshop presentation
  • Open Access

Non-contrast T1 and T2 relaxometry characterizes reperfusion injury of acute MI in swine

  • 1, 2,
  • 3,
  • 4, 5,
  • 4,
  • 4,
  • 4, 6 and
  • 2
Journal of Cardiovascular Magnetic Resonance201517 (Suppl 1) :W14

https://doi.org/10.1186/1532-429X-17-S1-W14

  • Published:

Keywords

  • Myocardial Infarction
  • Acute Myocardial Infarction
  • Reperfusion Injury
  • Balloon Occlusion
  • Microvascular Obstruction

Background

Reperfusion injury in acute myocardial infarction (MI) results in edema, necrosis, microvascular obstruction (MVO), and intramyocardial hemorrhage (IMH), the latter presents an interesting clinical target. [1] Cardiovascular MRI has been shown capable of characterizing all of these tissue components. Other than MVO, which is currently detected by flow-deficient regions in contrast enhanced imaging, all other tissue components can be identified by T1 and T2 (T2*). Theoretically, the byproducts of blood breakdown observed with IMH lead to decreased T1 and T2 (T2*). [2] Conversely, free water accumulation (edema) and necrosis lead to increased T1 and T2. [2] Hence, direct and quantitative measurement of relaxation rates is promising in myocardial tissue characterization, avoiding ambiguity typical of weighted images (i.e. T2-weighted spin-echo), undesired signal loss from T2* (weighted) images or the uncertainty introduced by contrast agent kinetics. Hypothesis: Combined T1 and T2 mapping can characterize reperfused MI without contrast agents.

Methods

MI was induced in swine by 1 (N=3) or 2 (N=3) hr balloon occlusion of the LAD after the first diagonal, with MRI 7-9 days post MI (Achieva TX, Philips). Relaxometry: 3D respiratory navigator-gated T2-mapping [3]; 2D Breath-hold T1-mapping (MOLLI) [4]. Clinical standard: breath-hold black-blood T2W TSE (BB-T2-STIR) [5]; early (3 min post) gadolinium-enhanced images (EGE) using PSIR and 0.2 mmol/kg Magnevist. [6]. IMH was identified in T2W images/T1/T2 maps as areas of hypointensity surrounded by hyperintense signal/T1/T2 representing edema. MVO was defined in EGE images as hypointense areas surrounded by enhanced MI. The co-localization of tissue types among techniques was examined.

Results

IMH was detected in all animals with 2 hr occlusions, identified by decreased T1 and T2, and was spatially consistent with the hypoenhanced core in BB-T2-STIR and with MVO in EGE. Edema was observed in all animals (elevated T1and T2). (Fig. 1)
Figure 1
Figure 1

Matched representative SAX images from swine without hemorrhage after 1 hr LAD occlusion (Case #1) (a-d) and with hemorrhage after a 2 hr occlusion (Case #2) (e-h). In Case #1, significant T1 and T2 elevation are present in both maps (c,d), though no MVO was observed with EGE (b) nor was a hypointense core present in T2W images (a). In comparison, Case #2 shows clear IMH, demarked by decrease in T1 and T2, surrounded by edema, shown by increased T1 and T2 (g and h), all of which are excellently co-localized with that in T2W (e) and EGE (f). Green arrowhead indicates edema; red arrowhead indicates the core of IMH. Note that T1 mapping is influenced by off-resonance and lower image resolution. As the result of competing effects on T1 and T2 from IMH and edema, partial volume averaging makes the T2 in IMH close to that of normal myocardium.

Planimetry showed that relative to remote myocardium, T1 and T2 of edema were significantly higher (p < 0.001 and p <1e-5, respectively), while within IMH T1 was lower (p = 0.001) and T2 the same (p = 0.28). (Fig. 2)
Figure 2
Figure 2

a. ROI-based T1 & T2 for edema, IMH and remote myocardium from matched T1 and T2 maps. b. Changes in T1 & T2 after subtraction of the reference values of remote myocardium. Edema had higher T2 than both remote myocardium or IMH. T1 can be used to discriminate between edema, IMH and normal myocardium, though the distributions may overlap. Edema and IMH can be classified with higher specificity using both T1 and T2.

Conclusions

Though either T1 or T2 can be used to separate tissues, combined T1 and T2 mapping may allow for more accurate detection of IMH in reperfusion injury, without variability from contrast kinetics, or BB-T2-STIR artifacts. [7] Based on a small number of animals, T2 was superior in edema detection, while T1 performed better in IMH detection. Combined relaxometry may identify tissues with better specificity than individual and may help clarify the link between MVO and IMH. High-resolution relaxometry may be necessary to avoid partial volume.

Funding

Funded in part by the American Heart Association - 11SDG5280025.

Authors’ Affiliations

(1)
Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China
(2)
Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, USA
(3)
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins School of Medicine, Baltimore, MD, USA
(4)
Department of Medicine, Cardiology, Johns Hopkins School of Medicine, Baltimore, MD, USA
(5)
Department of Radiology, Mercy Fitzgerald Hospital, Darby, PA, USA
(6)
Heart Institute, Sheba Medical Center, Tel Aviv University, Ramat Gan, Israel

References

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Copyright

© Ding et al; licensee BioMed Central Ltd. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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