title: Impact of neonate haematocrit variability on the longitudinal relaxation time of blood: Implications for arterial spin labelling MRI.
abstract: OBJECTIVE
  The longitudinal relaxation time of blood (T 1b) is influenced by haematocrit (Hct) which is known to vary in neonates. The purpose of this study was threefold: to obtain T 1b values in neonates, to investigate how the T 1b influences quantitative arterial spin labelling (ASL), and to evaluate if known relationships between T 1b and haematocrit (Hct) hold true when Hct is measured by means of a point-of-care device.
  
  
  METHODS
  One hundred and four neonates with 120 MR scan sessions (3 T) were included. The T 1b was obtained from a T 1 inversion recovery sequence. T 1b-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 T 1b).
  
  
  RESULTS
  Mean T 1b was 1.85 s (sd 0.2 s). The mean T 1b 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 T 1b in the TEA was significantly different from the T 1b in the preterm (p < 0.05). The change in perfusion induced by the T 1b 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.
  
  
  CONCLUSIONS
  We demonstrated a wide variability of the T 1b in neonates and the implications it could have in methods relying on the actual T 1b 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 T 1b whereas our data did not support the use of capillary-drawn Hct for T 1b correction.
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: J B
authors.initials: JB
authors.lastname: De Vis
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Hendrikse
authors.affiliation: Department of Neonatology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: F
authors.initials: F
authors.lastname: Groenendaal
authors.affiliation: Department of Neonatology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: L S
authors.initials: LS
authors.lastname: de Vries
authors.affiliation: Department of Neonatology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: K J
authors.initials: KJ
authors.lastname: Kersbergen
authors.affiliation: Department of Neonatology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: M J N L
authors.initials: MJ
authors.lastname: Benders
authors.affiliation: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands ; Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: E T
authors.initials: ET
authors.lastname: Petersen
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology*; D002536:Cerebral Arteries / Q000033:anatomy & histology / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006400:Hematocrit / Q000379:methods*; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: ASL, arterial spin labelling; Arterial spin labelling; Blood T1; 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; Cerebral blood flow; Haematocrit; Hct, haematocrit; Hctad, haematocrit measured on an arterial-drawn blood sample; Hctcd, haematocrit measured on a capillary-drawn blood sample; MRI; MRI, magnetic resonance imaging; NPD, normalized perfusion difference; Neonates; PCA, postconceptional age; PNA, postnatal age; POCT, point-of-care test; R1b, longitudinal relaxation rate constant of blood; T1b, longitudinal relaxation time of blood; TEA, term-equivalent age