The Impact of Flip Angle and TR on the Enhancement Ratio of Dynamic Gadobutrol-enhanced MR Imaging: <i>In Vivo</i> VX2 Tumor Model and Computer Simulation

Abstract

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is widely used to diagnose cancer and monitor therapy. The maximum enhancement ratio (ER max ) obtained from the curve of signal intensity over time could be a biomarker to distinguish cancer from normal tissue or benign tumors. We evaluated the impact of flip angle (FA) and repetition time (TR) on the ER max values of dynamic gadobutrol-enhanced MR imaging, obtaining T 1 -weighted (T 1 W) MR imaging of VX2 tumors using 2-dimensional fast spoiled gradient echo (2D FSPGR) with various FAs (30°, 60°and 90°) at 1.5 tesla before and after injection of 0.1 mmol/kg gadobutrol. In vivo study indicated significant differences between ER max values and area under the ER-time curve (AUC 100 ) of VX2 tumors and muscle tissue, with the highest ER max and AUC 100 at FA 90°. Computer simulation also demonstrated the ER as a strictly increasing monotonic function in the closed interval [0°, 90°] for a given TR when using T 1 W FSPGR, and the highest ER value always occurred at FA 90°. The FA for the highest ER differed from that for the highest signal-to-noise or contrast-to-noise ratio. For long TR, the ER value increases gradually. However, for short TR, the ER value increases rapidly and plateaus so that the ER value changes little beyond a certain FA value. Therefore, we suggest use of a higher FA, near 90°, to obtain a higher ER max for long TR in 2D SPGR or FSPGR and a smaller FA, much less than 90°, to reach an appropriate ER max for short TR in 3D SPGR or FSPGR. This information could be helpful in setting the optimal parameters for DCE-MRI.

Preoperative prediction of sentinel lymph node metastasis in breast cancer by radiomic signatures from dynamic contrast‐enhanced MRI

“…Although the ratios are functions of TR, these functions are relatively slow varying. 42 A carefully designed prospective study is warranted to investigate the findings of this study. Another limitation is that most of the DCE-MRI images were collected after biopsy of the primary tumor.…”

“…One such variation is the change of TR and TE among DCE-MRI acquisitions; however, difference in the original MR signal intensity was not a major concern in this study as the radiomic features were extracted from three ratio maps which reflect contrast agent concentration changes. Although the ratios are functions of TR, these functions are relatively slow varying(42). A carefully designed prospective study is warranted to investigate the findings of this study.…”

Radiomics of dynamic contrast-enhanced magnetic resonance imaging parametric maps and apparent diffusion coefficient maps to predict Ki-67 status in breast cancer

“…One source of variation was the changes in repetition time during DCE-MRI acquisition; however, the difference in MR signal intensity was not the principal factor in our study, because the radiomics features were derived from three parametric maps reflecting the changes in contrast medium concentration. Although the enhancement ratio is a function of repetition time, these functions change relatively slowly ( 43 ). Therefore, a well-designed prospective study supporting the results of this study is necessary.…”