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Myocardial Infarct Characterization using Relaxation along Fictitious Field in the nth Rotating Frame1Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland, 2Department of Radiology, Oulu University Hospital, Oulu, Finland, 3Department of Applied Physics, University of Eastern Finland, Kuopio, Finland, 4Department of Cardiology, Oulu University Hospital, Oulu, Finland
Synopsis
Based on the previous promising relaxation along fictitious field in nth frame (RAFFn) findings in myocardial infarct mouse model at 9.4 T, we adjusted RAFFn measurement to standard clinical 1.5 T scanner with γB1 = 500 Hz. We demonstrate with five myocardial infarct patients that fitted steady state from RAFF2 and RAFF3 weighted images can separate the infarct from remote myocardium using clinical main and RF fields. We also demonstrate association between RAFF3 steady state and extra cellular volume that is calculated based on pre and post contrast T1 maps and hematocrit.
Introduction
Qualitative determination of myocardial infarct (MI) and cardiac fibrosis have been based on late gadolinium enhancement in MRI. Lately quantitative extra cellular volume (ECV), exploiting T1 mapping before and after contrast agent injection and hematocrit from blood sample, has gained interest1. Both methods requires contrast agent injection and especially ECV suffers motion artifacts between the T1 measurements among other technical difficulties. Relaxation along Fictitious Field (RAFF)2 and RAFF in the nth rotating frame (RAFFn)3 have been recently introduced to measure accurately acute and chronic infarct scar in mouse model at high (9.4T) magnetic field4. Purpose of the study was to demonstrate the contrast at clinical 1.5 T field with standard body transmitter and compare RAFFn contrast to ECV.Methods
Study participants (n=5) were recruited from group of patients who have coronary artery disease and myocardial infarction. All the measurements were done at 1.5 T using a Siemens Aera (Siemens Healthineers GmbH, Erlangen Germany) scanner. The 18-channel body array coil together with receivers built in the bed were used with body transmitter. For RAFF2, the pulse duration was set to 2.83 ms and the maximum pulse amplitude (γB1) to 500 Hz, while maintaining the original waveform2, and 0, 12 and 24 pulses were added in to pulse train and experiment was repeated with initial inversion as before2. For RAFF3, the pulse duration was identical, however 0, 16 and 32 pulses with γB1=418 Hz were applied with original waveform3. For comparison, late gadolinium enhanced images, T1 map before and 10 minutes after gadolinium enhancement, T1ρ, and T2 map were acquired. For quality assurance, absolute B1 and qualitative B0 were mapped. Before calculating the relaxation times all data was motion corrected either with standard Siemens protocols (T1, and T2) or using Matlab (MathWorks Inc., MA, USA) (RAFF2 and RAFF3). Regions-of-interest were located on infarct scar and remote area based on high and low ECV values, respectively. ECV, relaxation times (TRAFF2, TRAFF3, T1ρ, T1 and T2) and fitted steady state (SS) fractions (S(∞) / S(0)) for RAFF2 and RAFF3 were averaged on the regions-of-interests. Association between ECV and RAFF3 SS was calculated.Results
The representative
relaxation time maps of RAFF2 and RAFF3 with respective steady state maps shows
reasonable relaxation weighting with clinically relevant RF peak power (γB1=500 Hz) and B0=1.5
T (Figure 1). Increased RAFF2 SS and RAFF3 SS in infarct area compared to
remote area are clearly visible (Figure 1). Significant differences were found
in the fitted steady state magnetization between MI and remote area in RAFF2
and RAFF3 (Table 1). Similarly, significant difference was found in ECV, as
expected. No differences were found in any of the endogenous relaxation times. Significant
Spearman correlation (R2=0.64, p<0.01) was observed between RAFF3
SS and ECV (Figure 2).Discussion
Previous results from mouse setup at 9.4 T and peak power of γB1=1250 Hz without taking into account the formation of steady state showed increased RAFF2, RAFF3 and RAFF4 relaxation times4. In this study, we took into account the formation of steady state, and observed that the differences between MI and remote areas were reflected rather in the steady state than in the relaxation time. The spatial distribution of large steady state values reflected the infarct area seen in the ECV maps and the RAFF3 SS among ECV were the only methods to separate infarct and remote areas without overlap of absolute values. Overall the relaxation times and the ECV values agree with previous findings.Conclusions
Steady state extraction from RAFF2 and RAFF3 maps may provide a contrast agent free alternative for ECV mapping.Acknowledgements
No acknowledgement found.References
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2Liimatainen T, Sorce DJ, Connell R, Garwood M, Michaeli S, MRI Contrast from Relaxation Along a Fictitious Field (RAFF). Magn Reson Med 2010;64:983-994.
3Liimatainen T, Hakkarainen H, Mangia S, Huttunen JM, Storino C, Idiyatullin D, Sorce D, Garwood M, Michaeli S, MRI contrasts in high rank rotating frames. Magn Reson Med 2015;73:254-262.
4Yla-Herttuala E, Laidinen S, Laakso H, Liimatainen T, Quantification of myocardial infarct area based on TRAFFn relaxation time maps - comparison with cardiovascular magnetic resonance late gadolinium enhancement, T1rho and T2 in vivo. J Cardiovasc Magn Reson 2018;20:34-018-0463-x.
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