Synchronized inversion recovery-spin echo sequences for precise in vivo T1 measurement of human myocardium: a pilot study on 22 healthy subjects

Improved quantitative myocardial T2 mapping: Impact of the fitting model

PURPOSE

To develop an improved T₂ prepared (T₂ prep) balanced steady-state free-precession (bSSFP) sequence and signal relaxation curve fitting method for myocardial T₂ mapping.

METHODS

Myocardial T₂ mapping is commonly performed by acquisition of multiple T₂ prep bSSFP images and estimating the voxel-wise T₂ values using a two-parameter fit for relaxation. However, a two-parameter fit model does not take into account the effect of imaging pulses in a bSSFP sequence or other imperfections in T₂ prep RF pulses, which may decrease the robustness of T₂ mapping. Therefore, we propose a novel T₂ mapping sequence that incorporates an additional image acquired with saturation preparation, simulating a very long T₂ prep echo time. This enables the robust estimation of T₂ maps using a 3-parameter fit model, which captures the effect of imaging pulses and other imperfections. Phantom imaging is performed to compare the T₂ maps generated using the proposed 3-parameter model with the conventional two-parameter model, as well as a spin echo reference. In vivo imaging is performed on eight healthy subjects to compare the different fitting models.

RESULTS

Phantom and in vivo data show that the T₂ values generated by the proposed 3-parameter model fitting do not change with different choices of the T₂ prep echo times, and are not statistically different than the reference values for the phantom (P = 0.10 with three T₂ prep echoes). The two-parameter model exhibits dependence on the choice of T₂ prep echo times and are significantly different than the reference values (P = 0.01 with three T₂ prep echoes).

CONCLUSION

The proposed imaging sequence in combination with a three-parameter model allows accurate measurement of myocardial T₂ values, which is independent of number and duration of T₂ prep echo times. Magn Reson Med 74:93-105, 2015. © 2014 Wiley Periodicals, Inc.

Complementary radial tagging for improved myocardial tagging contrast

PURPOSE

To develop and evaluate complementary radial tagging (CRT) for improved myocardial tagging contrast.

METHODS

We sought to develop and evaluate CRT, which aims to preserve the radial tag contrast throughout the cardiac cycle. Similar to complementary spatial modulation of magnetization, CRT acquires two sets of images with a phase shift in the tag pattern. The combination of a ramped imaging flip angle and image subtraction enhances tag contrast throughout the cardiac cycle. The proposed CRT technique uses a small table shift away from the isocenter to improve the uniformity of the radial tag pattern. We provide a mathematical solution for the optimal table shift and validate the solution in using a retrospective analysis of images from 500 patients in the Cardiac Atlas Project database.

RESULTS

CRT simulations, phantom experiments, and in vivo images all demonstrate the improved tag contrast of CRT compared to RT. The retrospective evaluation demonstrated that acceptable CRT images could be acquired in over 98% of the clinical exams.

CONCLUSION

The CRT technique improves radial tag contrast throughout the cardiac cycle and should produce high quality tag patterns in nearly all patients.

Detection and prediction of acute heart transplant rejection with the myocardial T2 determination provided by a black-blood magnetic resonance imaging sequence

OBJECTIVES

This study aimed to determine whether the myocardial T2 relaxation time, determined using a black-blood magnetic resonance imaging (MRI) sequence, could predict acute heart transplant rejection.

BACKGROUND

The use of black-blood MRI sequences allows suppression of the confusing influence of blood signal when myocardial T2 is calculated to detect myocardial edema.

METHODS

A total of 123 investigations, including cardiac MRI and myocardial biopsy, were performed 8 +/- 11 months after heart transplantation. Myocardial T2 was determined using an original inversion-recovery/spin-echo sequence.

RESULTS

A higher than normal T2 (> or = 56 ms) allowed an accurate detection of the moderate acute rejections evidenced at baseline biopsy (> or = International Society for Heart and Lung Transplantation grade 2): sensitivity, 89% and specificity, 70% (p < 0.0001). T2 was increased in grade 2 (n = 11) compared with grade 0 (n = 49, p < 0.05), grade 1A (n = 34, p < 0.05) and grade 1B (n = 21, p < 0.05); T2 was further increased in grade 3 (n = 8) compared with grade 2 (p < 0.05). In addition, in patients without rejection equal to or greater than grade 2 at baseline, a T2 higher than normal (> or = 56 ms) was correlated with the subsequent occurrence of equal or greater than grade 2 rejection within the next three months: sensitivity 63% (12/19) and specificity 78% (64/82) (p = 0.001).

CONCLUSIONS

Myocardial T2 determined using a black-blood MRI sequence, is sufficiently sensitive to identify most of the moderate acute rejections documented with biopsy at the same time, but is also a predictor of the subsequent occurrence of such biopsy-defined rejections.

Comparison of T1 estimation techniques in cardiac MRI

We have shown that the use of a simple combination of inversion recovery/spin-echo (IR/SE) sequences provides undeniably superior precision in quantitative in vivo myocardium T1 estimation than the standard multiple spin-echo approach. On a group of 25 healthy subjects, the T1 dispersion was, respectively, 3.8% for the IR/SE combination and 19.6% for the best SE pair combination. Moreover, repeated measurements were carried out on seven of the volunteers in order to assess T1 reproducibility. The mean intra-individual T1 precision was found to be 2.8% for the IR/SE pair and 20.0% for the best SE pair. The in vivo imaging work was supported and corroborated by a thorough treatment of the theoretical T1 errors. We also highlight the importance of quality control in quantitative MRI; a correction being required in the SE sequences to bring measured signal intensities into line with those predicted from simple theory.