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

Abstract

Background Fast and accurate T1ρ mapping in myocardium is still a major challenge, particularly in small animal models. The complex sequence design owing to electrocardiogram and respiratory gating leads to quantification errors in in vivo experiments, due to variations of the T1ρ relaxation pathway. In this study, we present an improved quantification method for T1ρ using a newly derived formalism of a T1ρ* relaxation pathway. Methods The new signal equation was derived by solving a recursion problem for spin-lock prepared fast gradient echo readouts. Based on Bloch simulations, we compared quantification errors using the common monoexponential model and our corrected model. The method was validated in phantom experiments and tested in vivo for myocardial T1ρ mapping in mice. Here, the impact of the breath dependent spin recovery time Trec on the quantification results was examined in detail. Results Simulations indicate that a correction is necessary, since systematically underestimated values are measured under in vivo conditions. In the phantom study, the mean quantification error could be reduced from − 7.4% to − 0.97%. In vivo, a correlation of uncorrected T1ρ with the respiratory cycle was observed. Using the newly derived correction method, this correlation was significantly reduced from r = 0.708 (p < 0.001) to r = 0.204 and the standard deviation of left ventricular T1ρ values in different animals was reduced by at least 39%. Conclusion The suggested quantification formalism enables fast and precise myocardial T1ρ quantification for small animals during free breathing and can improve the comparability of study results. Our new technique offers a reasonable tool for assessing myocardial diseases, since pathologies that cause a change in heart or breathing rates do not lead to systematic misinterpretations. Besides, the derived signal equation can be used for sequence optimization or for subsequent correction of prior study results.

Robust cardiac T1ρ$$ {\mathrm{T}}_{1_{\boldsymbol{\rho}}} $$ mapping at 3T using adiabatic spin‐lock preparations

“…17,18 More recently, quantitative T 1ρ maps have demonstrated improved differentiation between infarcted and remote myocardium in swine models, compared with native T 1 and T 2 maps, yielding comparable contrast-to-noise ratio (CNR) to LGE images. 13,19,20 Similar results have been reported in mice [21][22][23] and monkeys. 24 In vivo T 1ρ mapping has been successfully applied in patients with ischemic and nonischemic cardiomyopathies at 1.5T.…”

Corrections for Rabi oscillations in cardiac chemical exchange saturation transfer MRI under the influence of very short preparation pulses

“…Pulsed CEST acquisition necessitates intricate numeric integration for optimizing CEST parameters, 12 while SL techniques rely on meticulous sequence design and quantification. 13 By contrast, continuous wave (cw-) CEST* experiments, containing one single RF pulse for saturation, benefit from a straightforward optimization of CEST parameters and from a facile sequence design. However, to match the cardiac cycle and reduce motion artifacts during acquisition, cw-CEST pulse length should not exceed a duration of approximately 140 ms, although this may cause additional signal modulation in the CEST spectra, induced by Rabi oscillations.…”

“…Although several improvements have already been established to overcome the technical limitations in cardiac imaging, such as, for example, a long scan time, respiratory and cardiac motion, or B 0 field inhomogeneities, 3,10,11 significant challenges remain. Pulsed CEST acquisition necessitates intricate numeric integration for optimizing CEST parameters, 12 while SL techniques rely on meticulous sequence design and quantification 13 . By contrast, continuous wave (cw‐) CEST* experiments, containing one single RF pulse for saturation, benefit from a straightforward optimization of CEST parameters and from a facile sequence design.…”