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

PURPOSE

To develop a fast protocol for measuring T 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 T in the ICA at 3T. T 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 T 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 T 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 T 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. © 2016 International Society for Magnetic Resonance in Medicine.