Hyperpolarized 13 C,15 N2 -Urea MRI for assessment of the urea gradient in the porcine kidney.

PURPOSE: A decline in cortico-medullary osmolality gradient of the kidney may serve as an early indicator of pathological disruption of the tubular reabsorption process. The purpose of this study was to investigate the feasibility of hyperpolarized 13 C,15 N2 -urea MRI as a biomarker of renal function in healthy porcine kidneys resembling the human physiology. METHODS: Five healthy female Danish domestic pigs (weight 30 kg) were scanned at 3 Tesla (T) using a 13 C 3D balanced steady-state MR pulse sequence following injection of hyperpolarized 13 C,15 N2 -urea via a femoral vein catheter. Images were acquired at different time points after urea injection, and following treatment with furosemide. RESULTS: A gradient in cortico-medullary urea was observed with an intramedullary accumulation 75 s after injection of hyperpolarized 13 C,15 N2 -urea, whereas images acquired at earlier time points postinjection were dominated by cortical perfusion. Furosemide treatment resulted in an increased urea accumulation in the cortical space, leading to a reduction of the medullary-to-cortical signal ratio of 49%. CONCLUSION: This study demonstrates that hyperpolarized 13 C,15 N2 -urea MRI is capable of identifying the intrarenal accumulation of urea and can differentiate acute renal functional states in multipapillary kidneys, highlighting the potential for human translation. Magn Reson Med 76:1895-1899, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Assessment of intramyocardial hemorrhage by T1-weighted cardiovascular magnetic resonance in reperfused acute myocardial infarction.

BACKGROUND: Intramyocardialhemorrhage (IMH) reflects severe reperfusion injury in acute myocardial infarction. Non-invasive detection of IMH by cardiovascular magnetic resonance (CMR) may serve as a surrogate marker to evaluate the effect of preventive measures to reduce reperfusion injury and hence provide additional prognostic information. We sought to investigate whether IMH could be detected by CMR exploiting the T1 shortening effect of methemoglobin in an experimental model of acute myocardial infarction. The results were compared to T2-weighthed short tau inversion recovery (T2-STIR), and T2*-weighted(T2*W) sequences. METHODS AND RESULTS: IMH was induced in ten 40 kg pigs by 50-min balloon occlusion of the mid LAD followed by reperfusion. Between 4-9 days (average 4.8) post-injury, the left ventricular myocardium was assessed by T1-weigthed Inversion Recovery(T1W-IR), T2-STIR, and T2*W sequences. All CMR images were matched to histopathology and compared with the area of IMH. The difference between the size of the IMH area detected on T1W-IR images and pathology was -1.6 ± 11.3% (limits of agreement, -24%-21%), for the T2*W images the difference was -0.1 ± 18.3% (limits of agreement, -36.8%-36.6%), and for T2-STIR the difference was 8.0 ± 15.5% (limits of agreement, -23%-39%). By T1W IR the diagnostic sensitivity of IMH was 90% and specificity 70%, for T2*W imaging the sensitivity was 70% and specificity 50%, and for T2-STIR sensitivity for imaging IMH was 50% and specificity 60%. CONCLUSION: T1-weigthed non-contrast enhanced CMR detects IMH with high sensitivity and specificity and may become a diagnostic tool for detection of IMH in patients with myocardial infarction.