Fast myocardial T1ρ mapping in mice using k-space weighted image contrast and a Bloch simulation-optimized radial sampling pattern

Abstract

Purpose T1ρ dispersion quantification can potentially be used as a cardiac magnetic resonance index for sensitive detection of myocardial fibrosis without the need of contrast agents. However, dispersion quantification is still a major challenge, because T1ρ mapping for different spin lock amplitudes is a very time consuming process. This study aims to develop a fast and accurate T1ρ mapping sequence, which paves the way to cardiac T1ρ dispersion quantification within the limited measurement time of an in vivo study in small animals. Methods A radial spin lock sequence was developed using a Bloch simulation-optimized sampling pattern and a view-sharing method for image reconstruction. For validation, phantom measurements with a conventional sampling pattern and a gold standard sequence were compared to examine T1ρ quantification accuracy. The in vivo validation of T1ρ mapping was performed in N = 10 mice and in a reproduction study in a single animal, in which ten maps were acquired in direct succession. Finally, the feasibility of myocardial dispersion quantification was tested in one animal. Results The Bloch simulation-based sampling shows considerably higher image quality as well as improved T1ρ quantification accuracy (+ 56%) and precision (+ 49%) compared to conventional sampling. Compared to the gold standard sequence, a mean deviation of − 0.46 ± 1.84% was observed. The in vivo measurements proved high reproducibility of myocardial T1ρ mapping. The mean T1ρ in the left ventricle was 39.5 ± 1.2 ms for different animals and the maximum deviation was 2.1% in the successive measurements. The myocardial T1ρ dispersion slope, which was measured for the first time in one animal, could be determined to be 4.76 ± 0.23 ms/kHz. Conclusion This new and fast T1ρ quantification technique enables high-resolution myocardial T1ρ mapping and even dispersion quantification within the limited time of an in vivo study and could, therefore, be a reliable tool for improved tissue characterization.

Quantification correction for free-breathing myocardial T1ρ mapping in mice using a recursively derived description of a T1ρ* relaxation pathway

“…By choosing high flip angles and multiple readouts, the signal equation approaches the monoexponential model ( ). Nevertheless, this was not the case in studies that previously dealt with T 1ρ quantification in small animals [ 39 – 42 ]. Given the parameters in other studies (e.g.…”

“…After a standard planning procedure, a midventricular short-axis imaging slice has been selected for the T 1ρ measurements. Compared to the phantom experiment, accelerated data acquisition based on a radial gradient echo readout and a KWIC-filtered (k-space weighted image contrast) view sharing method was used [ 42 ]. The acquisition window for the readout was positioned in end diastole using a variable trigger delay dependent on the respective SL preparation time.…”

“…Similarly accelerated quantification techniques were presented by Khan et al [ 40 ] and Yla-Herttuala [ 41 ], with additional T 2 and T RAFFn preparations being considered. Finally, in [ 42 ], a significantly accelerated technique for myocardial T 1ρ quantification in mice was presented, in which radial gradient echo readouts and a KWIC filtered view sharing method were used.…”

“…In summary, gradient echo readouts have become the quasi standard for myocardial T 1ρ quantification in small animals due to shorter repetition times and faster k-space acquisition [ 39 – 42 ]. However, in the studies available to date, the influence of the readout on the T 1ρ relaxation pathway was neglected for the in vivo scenario.…”

“…In the context of CMR, multiple gradient echo readouts are usually acquired in the transient signal evolution towards steady-state after each preparation (Fig. 1 ) [ 39 – 42 ]. However, an analytical description of the signal equation was only derived for the case of NR = 1 acquisition after each preparation [ 43 ].…”