We found a wide variability of the T1 of blood related to haematocrit variability.
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We demonstrated the implications in methods relying on the T1 of blood value.
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The T1 of blood can be estimated from arterial-obtained haematocrit.
Abstract
Background and purpose
The longitudinal relaxation time of blood (T1b) is influenced by haematocrit (Hct) which is known to vary in neonates. The purpose of this study was threefold: to obtain T1b values in neonates, to investigate how the T1b influences quantitative arterial spin labelling (ASL), and to evaluate if known relationships between T1b and haematocrit (Hct) hold true when Hct is measured by means of a point-of-care device.
Materials and methods
One hundred and four neonates with 120 MR scan sessions (3 T) were included. The T1b was obtained from a T1 inversion recovery sequence. T1b-induced changes in ASL cerebral blood flow estimates were evaluated. The Hct was obtained by means of a point-of-care device. Linear regression analysis was used to investigate the relation between Hct and MRI-derived R1 of blood (the inverse of the T1b).
Results
Mean T1b was 1.85 s (sd 0.2 s). The mean T1b in preterm neonates was 1.77 s, 1.89 s in preterm neonates scanned at term-equivalent age (TEA) and 1.81 s in diseased neonates. The T1b in the TEA was significantly different from the T1b in the preterm (p < 0.05). The change in perfusion induced by the T1b was −11% (sd 9.1%, p < 0.001). The relation between arterial-drawn Hct and R1b was R1b = 0.80 × Hct + 0.22, which falls within the confidence interval of the previously established relationships, whereas capillary-drawn Hct did not correlate with R1b.
Conclusion
We demonstrated a wide variability of the T1b in neonates and the implications it could have in methods relying on the actual T1b as for instance ASL. It was concluded that arterial-drawn Hct values obtained from a point-of-care device can be used to infer the T1b whereas our data did not support the use of capillary-drawn Hct for T1b correction.
Keywords
Blood T1
Neonates
Arterial spin labelling
Cerebral blood flow
Haematocrit
MRI
Abbreviations
ASL
arterial spin labelling
CBF
cerebral blood flow
CBF1.6
cerebral blood flow quantified with a T1b of 1.6 s
CBF1.85
cerebral blood flow quantified with a T1b of 1.85 s
CBFcor
cerebral blood flow quantified with the corrected T1b
CBFmean
cerebral blood flow quantified with the mean T1b found in our study
Hct
haematocrit
Hctcd
haematocrit measured on a capillary-drawn blood sample
Hctad
haematocrit measured on an arterial-drawn blood sample