In vivo blood T₁ measurements at 1.5 T, 3 T, and 7 T

Abstract

The longitudinal relaxation time of blood is a crucial parameter for quantification of cerebral blood flow by arterial spin labeling and is one of the main determinants of the signal-to-noise ratio of the resulting perfusion maps. Whereas at low and medium magnetic field strengths (B0), its in vivo value is well established; at ultra-high field, this is still uncertain. In this study, longitudinal relaxation time of blood in the sagittal sinus was measured at 1.5 T, 3 T, and 7 T. A nonselective inversion pulse preceding a Look-Locker echo planar imaging sequence was performed to obtain the inversion recovery curve of venous blood. The results showed that longitudinal relaxation time of blood at 7 T was ∼ 2.1 s which translates to an anticipated 33% gain in the signal-to-noise ratio in arterial spin labeling experiments due to T1 relaxation alone compared with 3 T. In addition, the linear relationship between longitudinal relaxation time of blood and B0 was confirmed.

Relaxation properties of human umbilical cord blood at 1.5 Tesla

“…The adult T 1 data is consistent with the T 1 measurements reported in [24]. T 1 values of 1531±29 ms and 1429±21 ms were measured in the sagittal sinus of 3 females and 3 males, respectively.…”

In Vivo T1 of Blood Measurements in Children with Sickle Cell Disease Improve Cerebral Blood Flow Quantification from Arterial Spin-Labeling MRI

“…It is unlikely that we underestimated T1 blood due to sequence-related limitations because the Look-Locker T1 technique has previously provided robust results in the same ROI. 16,17,27 Reports of T1 blood values ranging from 1500 to 2100 ms follow a linear relationship with Hct between 23% and 50%. 13,16,18 It is possible that we did not have sufficient precision to detect this inverse relationship in our dataset or that the range of Hct values (A and B); T1 blood calculated from hematocrit (CBF T1 blood -Hct), T1 ϭ 0.5*Hctϩ0.37 (C and D) 16 ; in vivo-measured T1 blood (CBF T1 blood -measured) (E and F); and a fixed SCD value obtained from the mean of the in vivo-measured T1 blood (CBF T1 blood -SCD) (G and H).…”

“…[10][11][12] For healthy adults, with a stable Hct, a fixed T1 blood value of 1650 ms is recommended for CBF quantification from pseudocontinuous ASL (pCASL) at 3T. 13,14 T1 blood is inversely correlated with Hct, 10,13,[15][16][17][18][19] and a linear relationship has been proposed in the literature permitting the calculation of T1 blood from measured Hct values. 12,13,16 While Hct ranges from 38% to 45% in healthy children, 20 it is as low as 18%-30% in children with SCD.…”

“…12,22,23 Owing to recent developments in MR imaging, direct measurements of the inversion recovery of T1 blood are now possible by combining a global inversion pulse and a subsequent sectionselective Look-Locker readout in the sagittal sinus. 16,17 Patientspecific, in vivo T1 blood measurements are noninvasive, robust, and fast, making them preferable to calculating T1 blood from blood samples. Our first hypothesis was that in vivo-measured T1 blood would be higher in children with SCD than the adult reference value of 1650 ms due to anemia.…”

Tonotopic maps in human auditory cortex using arterial spin labeling

“…Other parameters in Eq. (1) are: $M_0$ representing the signal intensity of the M 0 image; $PLD$ the post labeling delay (adjusted for each slice according to the slice acquisition order); $\tau$ the label duration; ${T1}_{blood}$ the longitudinal relaxation time of blood in seconds ( ${T1}_{blood}=1.650s$ at 3T; Lu et al, 2004; Zhang et al, 2013); $\lambda$ the brain/blood partition coefficient in ml/g ( $\lambda =0.9ml/g$); and $\alpha$ the labeling efficiency ( $\alpha =0.85$ for pCASL). Finally, the factor 6000 converts the units from 1/s to ml/100g/min, which is the commonly used physiological unit for quantitative CBF.…”