Relaxation properties of human umbilical cord blood at 1.5 Tesla

Abstract

Purpose-To characterize the MRI relaxation properties of human umbilical cord blood at 1.5 Tesla.Methods-Relaxometry measurements were performed on cord blood specimens (N=88, derived from 6 caesarean deliveries) spanning a broad range of hematocrits (Hct=0.19-0.76) and oxygen saturations (sO 2 =4-100%), to characterize the dependence of T 1 and T 2 on these blood properties.Adult blood data (N = 31 specimens, derived from two volunteers) were similarly studied to validate our experimental methods by comparison with existing literature. Using biophysical models previously developed for adult blood, new model parameters were estimated, which relate Hct and sO 2 to the observed cord blood relaxation times.Results-Fitted biophysical models explained more than 90% of the variation in T 1 and T 2 . In general, T 2 relaxation times of cord blood were longer (by up to 35%) than those of adult blood, while T 1 relaxation times were slightly shorter (by up to 10%).Conclusion-The models and fitted parameters presented here can be used for calibration of future MRI investigations of fetal and neonatal blood physiology. This study is an important step in facilitating accurate, non-invasive assessments of fetal blood oxygen content, a valuable diagnostic parameter in the identification and treatment of fetal hypoxia.

MR imaging of the fetal heart

“…Recognizing that these differences would likely affect MRI relaxation properties, the relationships between fetal blood relaxation times and oxygen saturation and hematocrit at 1.5T and 3T have been characterized by using umbilical cord blood samples harvested from human cesarean deliveries. This approach confirmed the reliability of this method for calculating blood hematocrit and oxygen saturation from measurements of the T 1 and T 2 relaxation times of fetal blood …”

“…This approach confirmed the reliability of this method for calculating blood hematocrit and oxygen saturation from measurements of the T 1 and T 2 relaxation times of fetal blood. 58,63,64…”

Transverse signal decay under the weak field approximation: Theory and validation

“…As the field strength is decreased, the relative contribution of chemical exchange to relaxation is expected to increase, as its contribution changes at a less than quadratic rate with respect to B 0 , whereas the diffusion contribution is expected to change at a quadratic rate . That the results of the Luz‐Meiboom exchange model fits gave an exchange time of 2.2 ms, whereas the exchange lifetime of water in RBCs is generally considered to be approximately 10 ms , is evidence that the LM chemical exchange model alone is insufficient to describe transverse relaxation at 3 T. This finding of lower than expected τ ex is consistent with several earlier studies with B 0 of approximately 1.5 to 4.7 T . Invariably, both relaxation mechanisms contribute to T 2 decay, and to what extent is a complex issue that further underscores the limitations of describing the relaxation by a single mechanism.…”

Non‐invasive evaluation of blood oxygen saturation and hematocrit from T1 and T2 relaxation times: In‐vitro validation in fetal blood

“…Parameter values used in this study, along with those reported in previous work , were obtained from (and therefore apply to) measurements acquired at 37 °C. Normal variation in body temperature is small (36.5 °C–37.5 °C); however, fever can elevate temperatures to ∼40 °C.…”