A method for rapid in vivo measurement of blood T₁

Abstract

We present a technique to measure the longitudinal relaxation time constant of venous blood (T(1b) ) in vivo in a few seconds. The MRI sequence consists of a thick-slab adiabatic inversion, followed by a series of slice-selective excitations and single-shot echo planar imaging readouts. The time intervals between excitations were chosen so that blood in macroscopic vessels is fully refreshed between excitations, making the blood signal follow an unperturbed inversion recovery curve. Static tissue, which experiences the inversion and all excitation pulses, quickly reaches a steady state at a low signal as a result of partial saturation. This allows blood-filled voxels to be discriminated from those containing static tissue, and to be fitted voxel-by-voxel to a simple inversion recovery model. The sequence was tested on a flow phantom with the proposed method, yielding T(1) values consistent to within 3% of those obtained using a conventional inversion recovery sequence with a spin-echo readout. The method was applied to seven adult volunteers and 18 neonates. The blood T(1) of the neonates (1799 ± 206 ms; range, 1393-2035 ms) was found to be more variable than that of adults (1717 ± 39 ms; range, 1662-1779 ms). A linear correlation between the inverse of T(1b) and the haematocrit was established in 12 neonates (R(2) = 0.90).

Accuracy of Parenchymal Cerebral Blood Flow Measurements Using Pseudocontinuous Arterial Spin-Labeling in Healthy Volunteers

“…The T1 relaxation of blood (T1 b ) can influence the accuracy of ASL perfusion measurements. 26,37 Previous studies have shown higher mean T1 b values (6%-9%) in women than in men, and the lower blood hematocrit level in women than in men may explain this observed sex difference in mean T1 b . [38][39][40] In a previous study, Piechnik et al 40 found significantly higher mean T1 b values in women than in men (1577 vs 1491 ms, respectively).…”

Brain Perfusion Imaging in Neonates: An Overview

“…65 Blood T1 variations have a greater effect on perfusion than tissue T1 variations. 69 Varela et al 70 established a linear correlation between the inverse of blood T1 and hematocrit in 12 neonates. This may offer the possibility of blood T1 estimations from recent hematocrit measurements.…”

Calibrated MRI to Evaluate Cerebral Hemodynamics in Patients with an Internal Carotid Artery Occlusion

“…For the blood T 1 maps, a T 1 inversion recovery sequence was used that consisted of a presaturation pulse followed by a single adiabatic inversion pulse and single-shot echo planar imaging as a readout. 17 Scan parameters were TR/TE/ΔTI/TI1: 15 seconds/20 ms/150 ms/20 ms, 60 phases, scan matrix 128 × 128, field of view 240 × 240, flip angle 95º, slice thickness 3mm, and sense 2.5. The imaging plane of the blood T 1 sequence was positioned perpendicular to the superior sagittal sinus based on the sagittal angiography image.…”