Comparison of 3 T and 1.5 T for T2* magnetic resonance of tissue iron

Abstract

BackgroundT2* magnetic resonance of tissue iron concentration has improved the outcome of transfusion dependant anaemia patients. Clinical evaluation is performed at 1.5 T but scanners operating at 3 T are increasing in numbers. There is a paucity of data on the relative merits of iron quantification at 3 T vs 1.5 T.MethodsA total of 104 transfusion dependent anaemia patients and 20 normal volunteers were prospectively recruited to undergo cardiac and liver T2* assessment at both 1.5 T and 3 T. Intra-observer, inter-observer and inter-study reproducibility analysis were performed on 20 randomly selected patients for cardiac and liver T2*.ResultsAssociation between heart and liver T2* at 1.5 T and 3 T was non-linear with good fit (R2 = 0.954, p < 0.001 for heart white-blood (WB) imaging; R2 = 0.931, p < 0.001 for heart black-blood (BB) imaging; R2 = 0.993, p < 0.001 for liver imaging). R2* approximately doubled between 1.5 T and 3 T with linear fits for both heart and liver (94, 94 and 105 % respectively). Coefficients of variation for intra- and inter-observer reproducibility, as well as inter-study reproducibility trended to be less good at 3 T (3.5 to 6.5 %) than at 1.5 T (1.4 to 5.7 %) for both heart and liver T2*. Artefact scores for the heart were significantly worse with the 3 T BB sequence (median 4, IQR 2–5) compared with the 1.5 T BB sequence (4 [3–5], p = 0.007).ConclusionHeart and liver T2* and R2* at 3 T show close association with 1.5 T values, but there were more artefacts at 3 T and trends to lower reproducibility causing difficulty in quantifying low T2* values with high tissue iron. Therefore T2* imaging at 1.5 T remains the gold standard for clinical practice. However, in centres where only 3 T is available, equivalent values at 1.5 T may be approximated by halving the 3 T tissue R2* with subsequent conversion to T2*.

High resolution in‐vivo DT‐CMR using an interleaved variable density spiral STEAM sequence

“…Although the T2* correction sharpens the images, it also increases the noise by adding weight to high spatial frequencies. Furthermore, the T2* value is calculated from the whole FOV and the T2* decay is likely underestimated …”

“…Furthermore, the T2* value is calculated from the whole FOV and the T2* decay is likely underestimated. 51 The proposed sequence depends on subjects holding their breath. In particular, during the beginning of the breath-hold, as bulk motion results in an inaccurate estimation of the field map, this, in turn, corrupts the diffusion weighted images during the off-resonance correction.…”

Accurate simultaneous quantification of liver steatosis and iron overload in diffuse liver diseases with MRI

“…Iron-related R2* quantification is also dependent on the magnetic field strength and the quantitative MR protocol [6]. Nevertheless, hepatic R2* quantification seems to be reproducible at 1.5 T and 3 T [43] and using fat-corrected models might be more advantageous [6,22,44]. Further calibration studies with phantoms are necessary to guarantee robustness, precision, and reproducibility of the measurements.…”

Assessment of cardiac function, blood flow and myocardial tissue relaxation parameters at 0.35 T

“…The availability of parameter‐mapping sequences specifically designed for the heart has facilitated quantitative myocardial tissue characterization; 48 these techniques are increasingly being used to determine extracellular volume fraction, 30,49,50 detect edema and inflammation, 31,51 and diagnose and quantify myocardial iron deposition 35,52,53 . We demonstrated the feasibility of quantitative myocardial relaxation parameter measurement at 0.35 T using the sequences commonly employed at 1.5 and 3 T, and also evaluated the differences in myocardial T1, T2 and T2* at these three field strengths.…”