Background:MRI is not able to directly measure the concentration of contrast agent. It is measured indirectly from the signal intensity (SI). It is very important to know how much contrast agent should be injected to receive a maximum SI in the region of interest (ROI).
Objectives:The aim of this study was to investigate the maximum relationship between contrast concentration and signal intensity (SI) on T1-weighted images using spin echo (SE), fast spin echo (FSE) and inversion recovery (IR) sequences.
Materials and Methods:To assess the relationship between SI and concentration, a water-filled phantom containing vials of different concentrations of gadolinium DTPA (Gd-DTPA) (0 to 19.77 mmol/L) or a constant concentration (1.2 mmol/L) of contrast agent was used. The vials of constant concentration were used to measure coil nonuniformity. The mean SI was obtained in the ROI using T1-weighted images. All studies were carried out using a 0.3 T clinical MR scanner with a standard head coil.
Results:This study shows that maximum SI will appear at different ranges in different sequences. The maximum SI can be seen at concentrations of 5.95, 4.96 and 3.98mmol/L for SE, FSE and IR, respectively.
Conclusion:Using standard imaging parameters, each MRI sequence reaches its maximum SI in a specific contrast concentration, which is highest in SE and least in IR in a comparison between SE, FSE and IR sequences.
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