Abstract
The contrast agent concentration, the time of repetition (TR) and magnetic field strength are significant parameters that influence for the accurate signal intensity (SI) in quantitative Magnetic Resonance Imaging (MRI). Therefore, this study was conducted to investigate and refine the dependence and the optimal effect of Time of Repetition (TR) on the relationship between signal intensity and Gd-DTPA (Gadolinium-diethylene-triaminepenta-acetic acid) concentration, after applying two-dimensional (2D) Spin Echo (SE) pulse sequence under low-field MRI. In addition to that, the optimal concentration of Gd-DTPA at given sequence parameters at low-field MRI was also evaluated. A water-filled phantom was constructed for a range of Gd-DTPA concentrations (0 - 6 mmol/L) and the mean signal intensities (SIs) were assessed in the defined region of interest on T1-weighted images with different TR values (40 - 2000 ms). The generated signal-concentration curves for Gd-DTPA revealed that increasing TR was associated with the increase of the overall SIs and the maximum relationship between SI to concentration. Moreover, the required Gd-DTPA concentration to produce the maximum SI was associated to decrease with the increase of TR. In addition to this, the application of beyond 100 ms TR values in this study with relatively higher concentrations (beyond 1 - 2 mmol/L) has resulted predominantly non-linear patterns in the signal-concentration curves and it appears the saturation or decay of the SIs due to T2 effect. From these results, it can be suggested that the selection of relatively lower Gd-DTPA concentration ( mmol/L) with less than 800 ms (<800 ms) TR values can produce a better linear relationship between the concertation and SIs in T1-weighted SE low field contrast-enhanced MRI. Furthermore, this study also outlined the significance and necessity of the optimization of TR in SE sequence in low field MRI prior to a particular examination.
Highlights
After introducing Magnetic Resonance Imaging (MRI) contrast agents (CAs) into the clinical setting, it has become a powerful medical imaging tool with a wide array of applications [1]
An optimal time of repetition (TR) value is essential in any magnetic field for deriving an accurate signal to concentration curves in quantitative MRI
The results of the present study clearly indicate that TR is one of the major influential factors for generating the signal intensity (SI) depending on Gd-DTPA concentrations
Summary
After introducing Magnetic Resonance Imaging (MRI) contrast agents (CAs) into the clinical setting, it has become a powerful medical imaging tool with a wide array of applications [1]. Gadolinium (Gd3+) based paramagnetic agents are the most commonly utilized CAs in the clinical setting as they have a range of applicability [2] [3]. Due to the low intrinsic sensitivity of MRI, the higher local concentration of the CA at the target site may be necessary to produce higher image contrast [2]. The contrast enhancement of GdDTPA (Gadolinium-diethylene-triaminepenta-acetic acid) does not linearly correlate with higher concentrations [5], [6]. The intrinsic and extrinsic factors such as proton density, spin relaxation time [5], image acquisition parameters [4], [8], magnetic susceptibility effect [9], magnetic field strengths [1] and type of pulse sequence [6], [8] play significant roles in the association of signal enhancement and quality of the acquired information
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