Feasibility of relaxation along a fictitious field in the 2nd rotating frame (T_RAFF2) mapping in the human myocardium at 3 T

Purpose: Evaluate the feasibility of quantification of Relaxation Along a Fictitious Field in the 2nd rotating frame (RAFF2) relaxation times in the human myocardium at 3 T.

Methods: ${\text{T}}_{\mathrm{RAFF}2}$ mapping was performed using a breath-held ECG-gated acquisition of five images: one without preparation, three preceded by RAFF2 trains of varying duration, and one preceded by a saturation prepulse. Pixel-wise ${\text{T}}_{\mathrm{RAFF}2}$ maps were obtained after three-parameter exponential fitting. The repeatability of ${\text{T}}_{\mathrm{RAFF}2}$ , ${\text{T}}_1$ , and ${\text{T}}_2$ was assessed in phantom via the coefficient of variation (CV) across three repetitions. In seven healthy subjects, ${\text{T}}_{\mathrm{RAFF}2}$ was tested for precision, reproducibility, inter-subject variability, and image quality (IQ) on a Likert scale (1 = Nondiagnostic, 5 = Excellent). Additionally, ${\text{T}}_{\mathrm{RAFF}2}$ mapping was performed in three patients with suspected cardiovascular disease, comparing it to late gadolinium enhancement (LGE), native ${\text{T}}_1$ , ${\text{T}}_2$ , and ECV mapping.

Results: In phantom, ${\text{T}}_{\mathrm{RAFF}2}$ showed good repeatability (CV < 1.5%) while showing no ( $R^2=0.09$ ) and high ( $R^2=0.99$ ) correlation with ${\text{T}}_1$ and ${\text{T}}_2$ , respectively. Myocardial ${\text{T}}_{\mathrm{RAFF}2}$ maps exhibited overall acceptable image quality (IQ = 3.0 $\pm$ 1.0) with moderate artifact levels, stemming from off-resonances near the coronary sinus. Average ${\text{T}}_{\mathrm{RAFF}2}$ time across subjects and repetitions was 79.1 $\pm$ 7.3 ms. Good precision (7.6 $\pm$ 1.4%), reproducibility (1.0 $\pm$ 0.6%), and low inter-subject variability (10.0 $\pm$ 1.8%) were obtained. In patients, visual agreement of the infarcted area was observed in the ${\text{T}}_{\mathrm{RAFF}2}$ map and LGE.

Conclusion: Myocardial ${\text{T}}_{\mathrm{RAFF}2}$ quantification at 3 T was successfully achieved in a single breath-hold with acceptable image quality, albeit with residual off-resonance artifacts. Nonetheless, preliminary clinical data indicate potential sensitivity of ${\text{T}}_{\mathrm{RAFF}2}$ mapping to myocardial infarction detection without the need for contrast agents, but off-resonance artifacts mitigation warrants further investigation.