Method for the quantitative assessment of contrast agent uptake in dynamic contrast‐enhanced MRI

Abstract

In previous papers relative signal intensity increase was used as a quantitative assessment parameter for contrast uptake in contrast-enhanced MRI. However, relative signal intensity increase does not only reflect contrast uptake but depends also on tissue parameters (native T1 relaxation time) and sequence parameters (repetition time and flip angle); thus, the contrast uptake cannot be assessed accurately using relative signal intensity increase. Based on an analysis of the contrast behavior of spoiled gradient echo sequences, a method is described in this paper that overcomes the limitations of relative signal intensity increase measurement. A parameter, called "enhancement factor" (EF) is introduced that approximates differential T1 relaxation rate. The enhancement factor scales linearly with contrast uptake and is independent of tissue and sequence parameters. The additional measurement time involved in determining the enhancement factor is less than 1 min and computation is straightforward. The practicality of the new method was confirmed by phantom measurements using T1-weighted and proton density-weighted spoiled gradient echo sequences (FLASH-2D). Enhancing tissues were simulated by water phantoms doped with increasing concentrations of Gd-DTPA.

Neoadjuvant chemotherapy in breast cancer: early response prediction with quantitative MR imaging and spectroscopy

“…In-house software (developed using the IDL language, Research Systems Inc., Boulder, CO, USA) was then used to measure the mean pixel signal intensity (SI) within the ROI for the proton density image (SI PD ) and each of the images in the T 1 -weighted series (SI T1 ). These data were then used to calculate an enhancement factor (EF) time series proportional to the concentration of gadopentetate dimeglumine, with differences/changes in the native tissue T 1 between patients/visits being corrected for using the proton density SI and the mean pre-contrast T 1 SI as obtained from a user-defined number of baseline points (SI 0 ) (Hittmair et al, 1994). The equations for EF calculation were EFðtÞ ¼ 1=ðKTR T1 Þ ln½ðSI max À SI 0 Þ=ðSI max À SI T1 ðtÞÞ and SI max ¼ SI PD  sinða T1 =a PD Þ, where a T1 and TR T1 are the flip angle and TR for the dynamic T 1 -weighted series and a PD is the flip angle for the proton density-weighted image.…”

Method for quantitative mapping of dynamic MRI contrast agent uptake in human tumors

“…These image data were combined with the dynamic Gd contrast-enhancement image data to calculate concentration Gd (a.u.) using the method described by Hittmair et al (22).…”

Limitations of dynamic contrast‐enhanced MRI in monitoring radiation‐induced changes in the fraction of radiobiologically hypoxic cells in human melanoma xenografts

“…Tumor images were analyzed on a voxel-by-voxel basis by using software developed in IDL (Interactive Data Language, Boulder, CO). Gd-DTPA concentrations were calculated from signal intensities by using the method of Hittmair et al (22), and to determine values for E ⅐ F and , the modified Kety equation (10) was fitted to plots of Gd-DTPA concentration versus time by using the arterial input function determined by Benjaminsen et al (15). The uncertainty in the assessment of E ⅐ F and was investigated by Monte Carlo analysis, using noise randomly generated from the Gaussian distribution of the residuals of the Kety curve fits.…”