Empirical model of human blood transverse relaxation at 3 T improves MRI T₂oximetry

Abstract

Purpose We sought a human blood T2-oximetery calibration curve over the wide range of hematocrits commonly found in anemic patients applicable with T2 Relaxation Under Spin Tagging (TRUST). Methods Blood was drawn from 5 healthy control subjects. Ninety-three in vitro blood transverse relaxation (T2b) measurements were performed at 37° C over a broad range of hematocrits (10–55%) and oxygen saturations (14–100%) at 3T. In vivo TRUST was performed on 35 healthy African American control subjects and 11 patients with chronic anemia syndromes. Results 1/T2 rose linearly with hematocrit (r2 = 0.96), for fully saturated blood. Upon desaturation, 1/T2 rose linearly with the square of the oxygen extraction, (1−Y)2, and the slope was linearly proportional to hematocrit (r2= 0.88). The resulting bilinear model between 1/T2, (1−Y)2 and hematocrit had a combined r2 of 0.96 and a coefficient of variation of 6.1%. Using the in-vivo data, the bilinear model had significantly lower bias and variability than existing calibrations, particularly for low hematocrits. In-vivo Bland Altman analysis demonstrated clinically relevant bias that was −6% (absolute saturation) for hematocrits near 30% and rose to +6% for hematocrits near 45%. Conclusion This work introduces a robust bilinear calibration model that should be used for MRI oximetry.

Diminished cerebral oxygen extraction and metabolic rate in sickle cell disease using T2 relaxation under spin tagging MRI

“…The remaining CPMG T 2 preparation sequence parameters included a repetition time of 1978 ms, 110 cm FOV, 5‐mm slice thickness and in plane resolution of 1.7 mm. These modifications did not alter the fundamental measured T 2b .…”

“…Following completion of the ex vivo T 2b measurements, T 2b was derived by applying monoexponential fitting to the blood pool signal and the values were fit to a bilinear relationship of hematocrit (Hct) and oxygen saturation (Y) as follows: where A 1 , A 2, A 3 , and A 4 are empirically determined coefficients .…”

Pseudo continuous arterial spin labeling quantification in anemic subjects with hyperemic cerebral blood flow

“…Numerical simulations revealed that velocity and B1 + strength were the strongest contributors to diminished labeling efficiency and resultant errors between PCASL and PC CBF measurements. At typical carotid velocities and oxygen saturations, differences in T 2 values for healthy and anemic subjects (200ms-300ms) contributed <1.5% to labeling efficiency(10). …”

“…The model parameters used were chosen similar to arterial human blood including T 2 = 200ms(10), T 1 = 1600ms(9). Numerical simulations were performed on resonance, in the rotating frame with a numerical step size of 3.6 μs.…”

“…Anemic subjects have elevated CBF(6), high blood velocities(7), shorter vascular transit times(8) and longer blood relaxation times(9,10). In sickle cell disease (SCD), quantification is complicated further by abnormal blood properties (shorter T1 for a given hematocrit(11)) and cerebrovascular disease (stroke(12,13), vessel tortuosity(14)).…”