T2-mapping – Clinical Experience

3D whole-heart isotropic-resolution motion-compensated joint T1 /T2 mapping and water/fat imaging

PURPOSE

To develop a free-breathing isotropic-resolution whole-heart joint T₁ and T₂ mapping sequence with Dixon-encoding that provides coregistered 3D T₁ and T₂ maps and complementary 3D anatomical water and fat images in a single ~9 min scan.

METHODS

Four interleaved dual-echo Dixon gradient echo volumes are acquired with a variable density Cartesian trajectory and different preparation pulses: 1) inversion recovery-preparation, 2) and 3) no preparations, and 4) T₂ preparation. Image navigators are acquired to correct each echo for 2D translational respiratory motion; the 8 echoes are jointly reconstructed with a low-rank patch-based reconstruction. A water/fat separation algorithm is used to obtain water and fat images for each acquired volume. T₁ and T₂ maps are generated by matching the signal evolution of the water images to a simulated dictionary. Complementary bright-blood and fat volumes for anatomical visualization are obtained from the T₂ -prepared dataset. The proposed sequence was tested in phantom experiments and 10 healthy subjects and compared to standard 2D MOLLI T₁ mapping, 2D balance steady-state free precession T₂ mapping, and 3D T₂ -prepared Dixon coronary MR angiography.

RESULTS

High linear correlation was found between T₁ and T₂ quantification with the proposed approach and phantom spin echo measurements (y = 1.1 × -11.68, R² = 0.98; and y = 0.85 × +5.7, R² = 0.99). Mean myocardial values of T₁ /T₂ = 1116 ± 30.5 ms/45.1 ± 2.38 ms were measured in vivo. Biases of T₁ /T₂ = 101.8 ms/-0.77 ms were obtained compared to standard 2D techniques.

CONCLUSION

The proposed joint T₁ /T₂ sequence permitted the acquisition of motion-compensated isotropic-resolution 3D T₁ and T₂ maps and complementary coronary MR angiography and fat volumes, showing promising results in terms of T₁ and T₂ quantification and visualization of cardiac anatomy and pericardial fat.

3D Whole-heart free-breathing qBOOST-T2 mapping

PURPOSE

To develop an accelerated motion corrected 3D whole-heart imaging approach (qBOOST-T2) for simultaneous high-resolution bright- and black-blood cardiac MR imaging and quantitative myocardial T2 characterization.

METHODS

Three undersampled interleaved balanced steady-state free precession cardiac MR volumes were acquired with a variable density Cartesian trajectory and different magnetization preparations: (1) T2-prepared inversion recovery (T2prep-IR), (2) T2-preparation, and (3) no preparation. Image navigators were acquired prior the acquisition to correct for 2D translational respiratory motion. Each 3D volume was reconstructed with a low-rank patch-based reconstruction. The T2prep-IR volume provides bright-blood anatomy visualization, the black-blood volume is obtained by means of phase sensitive reconstruction between first and third datasets, and T2 maps are generated by matching the signal evolution to a simulated dictionary. The proposed sequence has been evaluated in simulations, phantom experiments, 11 healthy subjects and compared with 3D bright-blood cardiac MR and standard 2D breath-hold balanced steady-state free precession T2 mapping. The feasibility of the proposed approach was tested on 4 patients with suspected cardiovascular disease.

RESULTS

High linear correlation (y = 1.09 × -0.83, R² = 0.99) was found between the proposed qBOOST-T2 and T2 spin echo measurements in phantom experiment. Good image quality was observed in vivo with the proposed 4x undersampled qBOOST-T2. Mean T2 values of 53.1 ± 2.1 ms and 55.8 ± 2.7 ms were measured in vivo for 2D balanced steady-state free precession T2 mapping and qBOOST-T2, respectively, with linear correlation of y = 1.02x+1.46 (R² = 0.61) and T2 bias = 2.7 ms.

CONCLUSION

The proposed qBOOST-T2 sequence allows the acquisition of 3D high-resolution co-registered bright- and black-blood volumes and T2 maps in a single scan of ~11 min, showing promising results in terms of T2 quantification.

Mapping the future of cardiac MR imaging: case-based review of T1 and T2 mapping techniques

Cardiac magnetic resonance (MR) imaging has grown over the past several decades into a validated, noninvasive diagnostic imaging tool with a pivotal role in cardiac morphologic and functional assessment and tissue characterization. With traditional cardiac MR imaging sequences, assessment of various pathologic conditions ranging from ischemic and nonischemic cardiomyopathy to cardiac involvement in systemic diseases (eg, amyloidosis and sarcoidosis) is possible; however, these sequences are most useful in focal myocardial disease, and image interpretation relies on subjective qualitative analysis of signal intensity. Newer T1 and T2 myocardial mapping techniques offer a quantitative assessment of the myocardium (by using T1 and T2 relaxation times), which can be helpful in focal disease, and demonstrate special utility in the evaluation of diffuse myocardial disease (eg, edema and fibrosis). Altered T1 and T2 relaxation times in disease states can be compared with published ranges of normal relaxation times in healthy patients. In conjunction with traditional cardiac MR imaging sequences, T1 and T2 mapping can limit the interpatient and interstudy variability that are common with qualitative analysis and may provide clinical markers for long-term follow-up.