Synchronized inversion recovery‐spin echo sequences for precise in vivo T₁ measurement of human myocardium: A pilot study on 22 healthy subjects

Abstract

An ECG-triggered, two-sequence MRI technique is proposed for the precise measurement of proton T1 relaxation times of the human myocardium at a field strength of 0.5 T. The combination of an inversion recovery (IR) sequence and a spin echo (SE) sequence is not new. It is, however, rarely used in quantitative in vivo cardiac studies. Our approach employs a synchronization of the 90 degrees read pulse to the systolic period. In a study of 22 healthy volunteers, the globally measured T1 value was estimated to be 714 +/- 23 ms. Four of the volunteers also underwent additional imaging scans for the purposes of reproducibility assessment. The T1 precision was found to be 3.9 +/- 1.1% for the IR/SE combination and 16.9 +/- 5.3% for a combination of SE sequences. Total imaging time for the IR and SE sequences was 19.2 +/- 3.0 mins. The relative rapidity of this classic technique and the T1 precision obtained give this technique an obvious application in the discrimination of normal and diseased myocardium. In the same study, valuable supplementary tissue characterization is provided by T2, calculated from the SE sequence. T2 was evaluated to be 50 +/- 3 ms.

T 1 : The Longitudinal Relaxation Time

“…This can be achieved by gating the image acquisition point in the sequence, and gating the preparation period to a previous cardiac cycle. For instance, Walker et al (1993) used a two-point IR/SE sequence in this way. If the lengths of the cardiac cycles can be monitored accurately, then these values can be used in a nonsteady-state estimation of T 1 .…”

“…Therefore it can be checked experimentally by preceding a standard imaging sequence with a presaturation pulse in which the slice selection gradient is applied along the phase-encoding direction of the image. Signals should be integrated over the slice profile as discussed above control the T 1 and T 2 relaxation times of the phantoms (Walker et al, 1989). In this case the relaxation times at a given field strength will have to be determined empirically.…”

Improved quantitative myocardial T2 mapping: Impact of the fitting model

“…In terms of the curve‐fitting model, the two‐parameter fit has been used extensively in the literature, both with spin echo acquisitions or bSSFP acquisitions with various profile ordering schemes . However, the 2‐parameter model ignores the changes in the T 1 /T 2 contrast due to the imaging pulses until the acquisition of the center of k‐space when using a bSSFP sequence, with several start‐up pulses and especially with linear profile ordering.…”

Complementary radial tagging for improved myocardial tagging contrast

“…LV CRT images in the SA plane were simulated with the T 1 = 1000 ms , T 2 = 60 ms representing myocardium at 1.5 T.The magnetization of the myocardium at thermodynamic equilibrium was set to one. Based on the average size of a normal human heart , an annulus of myocardium in the SA plane was defined with an inner diameter of 3 cm and an outer diameter of 5 cm.…”