Newby, David

Henriksen, Peter

Stirrat, Colin Gordon

other

2018-06-05T09:11:03Z

2018-06-05T09:11:03Z

2018-06-30

Background Ultrasmall superparamagnetic particles of iron oxide (USPIO)- enhanced magnetic resonance imaging (MRI) can detect tissue-resident inflammatory macrophages and identify cellular inflammation. Clinical studies using this non-invasive technique are now emerging. Objectives The aims of this thesis were (i) to determine whether USPIO-enhanced MRI can detect and serially monitor myocardial inflammation after myocardial infarction (MI) using single and repeated USPIO administration, (ii) to report a range of normal R2* (1/T2*) values at 1.5 tesla (T) and 3 T in healthy myocardium and other tissues before and after USPIO administration, (iii) to determine whether USPIO-enhanced MRI can detect myocardial inflammation in acute myocarditis, and (iv) to determine whether USPIO-enhanced MRI can detect myocardial inflammation in patients with a prior cardiac transplant. Methods Thirty-one patients were recruited following acute MI and followed up for 3 months with repeated T2 and USPIO-enhanced T2* mapping 3 T MRI. Twenty healthy volunteers were recruited: 10 imaged each at 1.5 T and 3 T. T2 and USPIO-enhanced T2* mapping MRI was conducted. Fourteen patients with suspected acute myocarditis underwent T2 and USPIO-enhanced T2* mapping 3 T MRI, with further imaging at 3 months. Eleven patients with prior cardiac transplant underwent T2 and USPIO-enhanced T2* mapping 1.5 T MRI with further imaging at 3 months. Regions of interest within the myocardium, along with other tissues, were selected for analysis. Pre-contrast T2 values, and the change in R2* due to USPIO from baseline to 24 hours after USPIO were compared for each region of interest. Results In patients with MI, USPIO uptake in the infarct zone peaked at days 2-3, and greater USPIO uptake was detected in the infarct zone compared to remote myocardium in the first 2 weeks after myocardial infarction. In contrast, T2-defined myocardial oedema peaked at days 3-9 and remained increased in the infarct zone throughout the 3-month follow up period. Histology confirmed colocalisation of iron and macrophages within the infarcted, but not the non-infarcted, myocardium. In healthy volunteers, we reported a range of normal myocardial and tissue R2* values at baseline, and following USPIO. Tissues showing greatest USPIO enhancement were organs of the reticuloendothelial system: the liver, spleen and bone marrow. Myocarditis was confirmed in 9 of the 14 suspected cases of myocarditis. There was greater myocardial oedema, but no demonstrable difference in USPIO enhancement, in inflamed myocardial regions in patients with myocarditis when compared to healthy myocardium. We recorded an improvement in cardiac function and reduced imaging measures of inflammation after 3 months. Ten patients with cardiac transplant were retained for analysis. Measures of myocardial oedema were greater in patients with cardiac transplant than healthy volunteers. There was no difference in the change in R2* due to USPIO between patients with transplantation and healthy volunteers. Imaging recordings did not change when repeated at 3 months. Conclusions Myocardial macrophage activity can be detected using USPIO-enhanced MRI in the first 2 weeks following acute MI. This observed pattern of cellular inflammation is distinct, and provides complementary information to, the more prolonged myocardial oedema detectable using T2 mapping. In patients with acute myocarditis, USPIO-enhanced MRI does not provide additional clinically relevant information to standard clinical MRI sequences. This suggests that tissue-resident macrophages do not provide a substantial contribution to the myocardial inflammation in this condition. Stable patients with cardiac transplantation have increased myocardial T2 values, consistent with resting myocardial oedema or fibrosis. In contrast, USPIO-enhanced MRI is normal and stable over time suggesting the absence of chronic macrophage-driven cellular inflammation. In conclusion, this imaging technique holds promise as a non-invasive method of assessing and monitoring macrophage-driven myocardial inflammation after myocardial infarction with potential application to diagnosis, risk stratification and assessment of novel anti-inflammatory therapeutic interventions. It remains to be determined whether USPIO-enhanced MRI may be able to identify myocardial inflammation in other myocardial inflammatory conditions including acute cardiac transplant rejection.

http://hdl.handle.net/1842/31064

en

The University of Edinburgh

Alam SR, Tse GH, Stirrat C et al. Nanoparticle enhanced MRI scanning to detect cellular inflammation in experimental chronic renal allograft rejection. Int J Mol Imaging 2015;2015(5):507909-8.

Stirrat CG, Alam SR, MacGillivray TJ et al. Ferumoxytol-enhanced magnetic resonance imaging methodology and normal values at 1.5 and 3T. J Cardiovasc Magn Reson 2016;18(1):46.

Stirrat CG, Alam SR, MacGillivray TJ et al. Ferumoxytol-enhanced magnetic resonance imaging assessing inflammation after myocardial infarction. Heart 2017;103:1528-1535.

Stirrat CG, Vesey AT, McBride OMB et al. Ultra-small superparamagnetic particles of iron oxide in magnetic resonance imaging of cardiovascular disease. J Vasc Diagnostics 2014;2:99-112.

Stirrat CG, Newby DE, Robson JMJ, Jansen MA. The use of superparamagnetic iron oxide nanoparticles to assess cardiac inflammation. Curr Cardiovasc Imaging Rep 2014;7:9263. DOI 10.1007/s12410-014-9263-3.

Stirrat CG, Alam SR, MacGillivray TJ et al. Ferumoxytol-enhanced magnetic resonance imaging in acute myocarditis. Accepted by Heart 2017,

USPIO

cellular inflammation

MRI

USPIO-enhanced MRI

myocardial inflammation

macrophage activity

Detection of cardiac inflammation using ultrasmall superparamagnetic particles of iron oxide-enhanced magnetic resonance imaging

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy