Measurement of T₁ and T₂ in the cervical spinal cord at 3 tesla

Abstract

T 1 and T 2 were measured for white matter (WM) and gray matter (GM) in the human cervical spinal cord at 3T. T 1 values were calculated using an inversion-recovery (IR) and B 1 -corrected double flip angle gradient echo (GRE) and show significant differences (p ‫؍‬ 0.002) between WM (IR ‫؍‬ 876 ؎ 27 ms, GRE ‫؍‬ 838 ؎ 54 ms) and GM (IR ‫؍‬ 973 ؎ 33 ms, GRE ‫؍‬ 994 ؎ 54 ms Image contrast in conventional MRI relies on the distinct relaxation behavior of water spins residing in different tissue environments. Quantitative determination of the relaxation time constants is important for the derivation of experimental parameters that optimize image contrast. Furthermore, understanding the nature of relaxivity in different tissues facilitates the development of new imaging methods. As the use of higher field whole body MRI systems (i.e., Ͼ1.5T) is becoming more widespread, it should be recognized that tissue relaxation rates are fielddependent and that experimental parameters must be reoptimized to take full advantage of the benefits of higher field strength. In vivo human tissue relaxation parameters have recently been measured in the brain (1,2) and in blood (3) at 3T, but to our knowledge no studies of the human spinal cord have been reported at any clinical field strength. The small size and mobile nature of the spinal cord hamper quantitative measurements, and it has been necessary to assume that spinal cord white matter (WM) and gray matter (GM) relaxation rates will mimic those in the brain, in spite of histological indications that spinal cord tissues differ from brain tissue (4). The same difficulties that have deterred measurement of relaxation behavior have also slowed the development of spinal cord imaging in general (5,6). Recently, a number of techniques for highresolution imaging have been applied to the spinal cord (7-9), yielding important clinical information about several pathologies (10,11), most notably multiple sclerosis (MS). Further development (and thereby, widespread adoption) of these methodologies may be facilitated by quantitative measures of the relaxation times, as they allow optimization of imaging parameters, potentially yielding improvements in sensitivity and contrast.Several other approaches require knowledge of water relaxation times. For example, in the field of in vivo spectroscopy, it is necessary to quantify metabolite concentrations from signal intensities that are functions of concentration, relaxation rates and experimental parameters. Since the intensity of the unsuppressed water signal is often used as an internal standard (12), accurate quantification of the relaxation parameters of water is critical. In the case of magnetization transfer imaging, knowledge of the relaxation times is important for the quantification of magnetization transfer effects which can provide parameters that reflect macromolecular interactions with the water signal (e.g., bound pool fraction, exchange rate) (13,14), as well as the optimization of imaging sequences at higher field strength (15) In th...

Myelin water and T2 relaxation measurements in the healthy cervical spinal cord at 3.0T: Repeatability and changes with age

“…The geometric mean over the entire T 2 distribution (global GMT 2 ) times found here are in agreement with the T 2 times determined from a single exponential fit of an 8 echo decay curve reported recently (Smith et al, 2008), however in the present study the GMT 2 times between WM and GM reached statistical significance. Additionally, the T 2 times found in this study for the IE water follow the same , intra-and extra-cellular and global geometric mean T 2 (IE GMT 2 and GL GMT 2 , respectively) in the spinal cord white matter regions (dorsal column (DC), lateral columns (LC)) and grey matter (GM).…”

Optimal radiofrequency and gradient spoiling for improved accuracy of T1 and B1 measurements using fast steady‐state techniques

“…From a practical standpoint, periodic properties of the modified scheme should be taken into account, if the AFI sequence is applied with different n. As it was shown previously (13), n ¼ 4-6 provides optimal sensitivity of AFI to flip angle variations, though applications with smaller n also were reported (4,14). Spoiling behavior of flip angles simulated with both schemes at different n is compared in Fig.…”

“…Due to its time efficiency, AFI is useful for correction of errors caused by B 1 nonuniformities in quantitative in vivo imaging applications, and particularly, in VFA T 1 mapping (4,(13)(14)(15). Incomplete spoiling in AFI also was identified as a cause of B 1 measurement errors, and the use of diffusion-based gradient spoiling was shown to improve accuracy of this method (16,17).…”

Intervertebral disc height loss demonstrates the threshold of major pathological changes during degeneration

“…Then, the mean intensity in each disc was divided by the mean intensity in the spinal cord gray matter to obtain a metric that can be compared across subjects. Based on earlier reports [15], we expected that the inter-subject variations in T2W signal in spinal cord gray matter would be minimal in subjects with no spinal cord anomalies. …”