Free-breathing myocardial T2* mapping using GRE-EPI and automatic non-rigid motion correction

J Cardiovasc Magn Reson. 2015 Dec 23;17:113. doi: 10.1186/s12968-015-0216-z.

Abstract

Background: Measurement of myocardial T2* is becoming widely used in the assessment of patients at risk for cardiac iron overload. The conventional breath-hold, ECG-triggered, segmented, multi-echo gradient echo (MGRE) sequence used for myocardial T2* quantification is very sensitive to respiratory motion and may not be feasible in patients who are unable to breath-hold. We propose a free-breathing myocardial T2* mapping approach that combines a single-shot gradient-echo echo-planar imaging (GRE-EPI) sequence for T2*-weighted image acquisition with automatic non-rigid motion correction (MOCO) of respiratory motion between single-shot images.

Methods: ECG-triggered T2*-weighted images at different echo times were acquired by a black-blood, single-shot GRE-EPI sequence during free-breathing. A single image at a single TE is acquired in each heartbeat. Automatic non-rigid MOCO was applied to correct for in-plane respiratory motion before pixel-wise T2* mapping. In a total of 117 patients referred for clinical cardiac magnetic resonance exams, the free-breathing MOCO GRE-EPI sequence was compared to the breath-hold segmented MGRE approach. Image quality was scored independently by 2 experienced observers blinded to the particular image acquisition strategy. T2* measurements in the interventricular septum and in the liver were compared for the two methods in all cases with adequate image quality.

Results: T2* maps were acquired in all 117 patients using the breath-hold MGRE and the free-breathing MOCO GRE-EPI approaches, including 8 patients with myocardial iron overload and 25 patients with hepatic iron overload. The mean image quality of the free-breathing MOCO GRE-EPI images was scored significantly higher than that of the breath-hold MGRE images by both reviewers. Out of the 117 studies, 21 breath-hold MGRE studies (17.9% of all the patients) were scored to be less than adequate or very poor by both reviewers, while only 2 free-breathing MOCO GRE-EPI studies were scored to be less than adequate image quality. In a comparative evaluation of the images with at least adequate quality, the intra-class correlation coefficients for myocardial and liver T2* were 0.868 and 0.986 respectively (p < 0.001), indicating that the T2* measured by breath-hold MGRE and free-breathing MOCO GRE-EPI were in close agreement. The coefficient of variation between the breath-hold and free-breathing approaches for myocardial and liver T2* were 9.88% and 9.38% respectively. Bland-Altman plots demonstrated good absolute agreement of T2* in the interventricular septum and the liver from the free-breathing and breath-hold approaches (mean differences -0.03 and 0.16 ms, respectively).

Conclusion: The free-breathing approach described for T2* mapping using MOCO GRE-EPI enables accurate myocardial and liver T2* measurements and is insensitive to respiratory motion.

Publication types

  • Multicenter Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Automation
  • Biomarkers / metabolism
  • Cardiac-Gated Imaging Techniques
  • Cardiomyopathies / diagnosis*
  • Cardiomyopathies / metabolism
  • Cardiomyopathies / physiopathology
  • Child
  • Electrocardiography
  • Female
  • Heart Rate
  • Humans
  • Image Interpretation, Computer-Assisted
  • Iron / metabolism*
  • Iron Overload / diagnosis*
  • Iron Overload / metabolism
  • Iron Overload / physiopathology
  • London
  • Magnetic Resonance Imaging*
  • Male
  • Middle Aged
  • Myocardium / metabolism*
  • Myocardium / pathology
  • Observer Variation
  • Ohio
  • Predictive Value of Tests
  • Prognosis
  • Reproducibility of Results
  • Respiratory Mechanics*
  • Severity of Illness Index
  • Young Adult

Substances

  • Biomarkers
  • Iron