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In vivo validation of a theory-based single-point T1 mapping pulse sequence for quantitative first-pass cardiac perfusion MRI

Introduction

In quantitative analysis of first-pass contrast-enhanced cardiac perfusion MRI, the signal-time curves must be converted to contrast agent (gadolinium-DTPA) concentration-time curves. A theory-based single-point T1 measurement method has been proposed and validated in phantoms at 1.5 T [1, 2] and 3 T (unpublished).

Purpose

To validate in vivo the accuracy of the proposed single-point T1 mapping pulse sequence against a reference pulse sequence.

Methods

Two healthy volunteers were imaged in a short-axis plane of the heart on a 3 T whole-body MR scanner (Tim-Trio, Siemens) at 9 time points: pre-contrast, 5, 10, 15, and 20 min post first injection (0.1 mmol/kg, Magnevist) of Gd-DTPA, and 5, 10, 15, and 20 min post second injection of Gd-DTPA. A saturation-recovery TurboFLASH sequence was implemented with the following parameters: FOV = 320 mm × 262 mm, slice thickness = 8 mm, matrix = 144 × 94, TE/TR = 1.24 ms/2.4 ms, flip angle = 10°, T-SENSE-factor = 2, centric k-space trajectory, effective saturation pulse [3] with delay time (TD) = 50 ms, and total image acquisition time = 176 ms. The effective longitudinal magnetization in the center of k-space was calculated using the Bloch equation. A proton density-weighted image was acquired in the first heartbeat, without the saturation pulse, in order to normalize the image signal, and obtain a theoretical relationship between the signal and T1(Fig. 1a). Contours for the myocardium and left ventricular (LV) cavity were drawn manually (Fig 1b).

Figure 1
figure1

a) Theoretical normalized signal intensity vs T 1 (calculated for the sequence parameters)/b) Representative LV cavity (black) and wall (white) ROIs.

Reference T1 measurements were performed with a multi-point saturation recovery TurboFLASH sequence with variable TD and a centric k-space trajectory. A varying trigger delay was introduced to acquire in mid-to-late-diastole, 550 ms after QRS detection. A least square linear regression was used to fit the experimental 6-point-curve (no saturation pulse - TD = 200-300-400-500-550 ms). The single-point and reference T1 measurement pulse sequences were performed during separate breathholds of 8 s and 6 s respectively. Measured T1s were converted to Gd-concentrations ([Gd]) assuming fast water exchange condition [4] and T1 relaxivity of 3.8 L/mmol/s [5, 6].

Results

Figure 2a/b show respectively the single point T1/[Gd] plotted against the reference T1/[Gd] in the LV cavity and the myocardium. A strong linear correlation was found for all curves (Pearson correlation coefficient = 0.98; p < 0.001). Representatives LV cavity and wall [Gd]-time curves calculated from data acquired during first passage of Gd-DTPA are shown in (fig. 2c).

Figure 2
figure2

a) Linear correlation bw. single-point and reference T 1 . b) Linear correlation bw. single-point and references Gd-DTPA concentrations. c) LV cavity and wall GD-time curve of a cardiac first-pass perfusion, calculated from the single-point T1 method.

Conclusion

The study shows that our theory-based single-point T1 measurement method and the multi-point T1 measurement method produce quantitatively equivalent [Gd] values. Future studies include in vivo validation in patients.

References

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Correspondence to Elodie Breton.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Breton, E., Eum, H., Chung, S. et al. In vivo validation of a theory-based single-point T1 mapping pulse sequence for quantitative first-pass cardiac perfusion MRI. J Cardiovasc Magn Reson 12, M7 (2010). https://doi.org/10.1186/1532-429X-12-S1-M7

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Keywords

  • Saturation Pulse
  • Leave Ventricular Cavity
  • Saturation Recovery
  • Trigger Delay
  • TurboFLASH Sequence