T₁, T₂ relaxation and magnetization transfer in tissue at 3T

Abstract

magnetization transfer (MT) measurements were performed in vitro at 3 T and 37°C on a variety of tissues: mouse liver, muscle, and heart; rat spinal cord and kidney; bovine optic nerve, cartilage, and white and gray matter; and human blood. The MR parameters were compared to those at 1.5 T. As expected, the T 2 relaxation time constants and quantitative MT parameters (MT exchange rate, R, macromolecular pool fraction, M 0B , and macromolecular T 2 relaxation time, T 2B ) at 3 T were similar to those at 1.5 T. Longitudinal, T 1 , and transverse, T 2 , relaxation time measurements are relevant in understanding water molecular dynamics in biologic systems. T 1 , T 2 relaxation times and MT depend on the chemical and physical environments of water protons in tissue. MRI contrast between normal and pathologic tissue is often based on differences in tissue microstructure and, therefore, different T 1 and T 2 relaxation times. Moreover, T 1 , T 2 , and MT provide quantitative assessment of tissue pathology. In particular, they offer additional information about the processes of demyelination and axonal loss (1-4), inflammation (5), infarction (6), white matter edema (7), tumor malignancy (8), and ischemia (9). Both tissue relaxation and MT parameter estimates are important in designing MRI pulse sequences that aim to accentuate contrast between normal and pathologic tissue. Since MRI at higher fields (particularly 3 T) has become more common, it is important to evaluate MR parameters of tissue quantitatively to determine MRI sequence parameters, such as TE (echo time), TR (repetition time), or MT saturation schemes, that provide an optimal contrast. The literature data regarding MR parameters at high fields (such as 3 T) is surprisingly limited. The goal of this study is to provide a comprehensive evaluation of MR parameters at 3 T to serve as reference for further MRI pulse sequence optimization. Therefore, T 1 and T 2 relaxation, and MT parameters at 3 T and 37°C for a wide range of tissues: liver, muscle, optic nerve, spinal cord, heart, kidney, white (corpus callosum) and gray matter (brain cortex), cartilage, and blood were measured and compared to those at 1.5 T. EXPERIMENTAL METHODS MR MeasurementsAll 3 T, MR measurements were performed at 37°C using a research-dedicated, whole body GE SIGNA magnet. MR pulse sequences and data acquisition were controlled by an NMR spectroscopy console (SMIS, Surrey, England). Rectangular radiofrequency (RF) pulses were transmitted by an RF amplifier (American Microwave Technology, Brea, CA; model 3205) and solenoid RF coil designed to accommodate in vitro tissue measurements in test tubes (9 turns, 8 mm in diameter, 15 mm length). Immediately after tissue excision, the samples (approximately 300 L by volume) were immersed in non-protonated, MR-compatible fluid (Fluorinert; 3M, London, Canada) to avoid dehydration and reduce magnetic susceptibility effects. Temperature was controlled by an air-flow mechanism with MR-compatible thermocouple (Luxtron) inserted into the measured sam...

Influence of fat on liver T1 measurements using modified Look–Locker inversion recovery (MOLLI) methods at 3T

“…T 1 and T 2 values for fat and liver components were: T 1fat = 382 msec, T 2fat = 68 msec,24 T 1hepatic = 812 msec,25 T 2hepatic = 34 msec 24. Separate signals corresponding to each component of a multiple‐peak lipid spectrum were weighted by their relative amplitude provided by Hamilton et al26 and summed to obtain a single fat signal.…”

Effect of multislice acquisition on T1 and T2 measurements of articular cartilage at 3T

“…The contrast agent gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA 2-) (Magnevist; Schering, Berlin, Germany), was added into each set of the collagen gel phantoms to obtain a Gd-DTPA 2-concentration of 0, 0.05, 0.1, 0.15, 0.2, 0.5, 1.0, or 1.5 mmol/L (mM). The concentration of contrast agent was determined to cover the estimated range of T 1 and T 2 values in articular cartilage (21,22).…”

Optimized T1- and T2-weighted volumetric brain imaging as a diagnostic tool in very preterm neonates

“…However, image contrast and signal intensity changes occurring during the first year of life necessitate careful optimization of the experimental parameters used in neonatal MRI [13][14][15][16][17][18]. In neonates, image contrast is inverted relative to adults [19][20][21][22], as relaxation times of white matter (WM) are longer than those of gray matter (GM) [15,23]. Decreases in brain water content, neuronal and synaptic development and increases in the concentration of macromolecules associated with myelin cause T1 and T2 relaxation times to decrease significantly during the first 2 years [1,2,5,8,18].…”