Fast measurement of blood T₁ in the human carotid artery at 3T: Accuracy, precision, and reproducibility

Purpose: To develop a fast protocol for measuring T₁ values in the internal carotid artery (ICA), to validate this technique with in vitro measurements, and to evaluate its reproducibility. Methods: A modified Look–Locker sequence was optimized to enable rapid determination of T₁ in the ICA at 3T. T₁ values from the ICA were compared with in vitro measurements on individually sampled venous blood oxygenated to arterial levels. A test–retest reproducibility study was also conducted. Results: The group-averaged arterial blood T₁ value was 1908 ± 77 ms for six women (hematocrit = 0.39 ± 0.03) and 1785 ± 55 ms for seven men (hematocrit = 0.45 ± 0.02), which is 100–200 ms longer than the widely adopted value obtained from bovine blood experiments. The arterial T₁ value per subject correlated significantly with individual hematocrit values. The intrasession and intersession coefficients of variation were 1.1% and 2.1%, respectively, indicating good precision and reproducibility of our method. Reasonable agreement was observed between the in vivo and in vitro results with a correlation coefficient of 0.78. Conclusion: The proposed method can provide fast arterial T₁ measurement on individual subjects. When not performing such a subject-specific measurement, we recommend the use of 1908 ms and 1785 ms for healthy women and men, respectively, or 1841 ms for adults in general. Magn Reson Med 77:2296–2302, 2017.