METHOD FELL THE QUANTITATIVE ASSESSMENT OF CONTRAST AGENT UPTAKE IN DYNAMIC CONTRAST-ENHANCED MRT

In previous papers relative signal intensity increase was used as a qu antitative assessment parameter for contrast uptake in contrast-enhanc ed MRI. However, relative signal intensity increase does not only refl ect contrast uptake but depends also on tissue parameters(native T-1 r elaxation time) and sequence parameters (repetition time and flip angl e); thus, the contrast uptake cannot be assessed accurately using rela tive signal intensity increase. Based on an analysis of the contrast b ehavior of spoiled gradient echo sequences, a method is described in t his paper that overcomes the limitations of relative signal intensity increase measurement. A parameter, called ''enhancement factor'' (EF) is introduced that approximates differential T-1 relaxation rate. The enhancement factor scales linearly with contrast uptake and is indepen dent of tissue and sequence parameters. The additional measurement tim e involved in determining the enhancement factor is less than 1 min an d computation is straightforward. The practicality of the new method w as confirmed by phantom measurements using T-1-weighted and proton den sity-weighted spoiled gradient echo sequences (FLASH-PD). Enhancing ti ssues were simulated by water phantoms doped with increasing concentra tions of Gd-DTPA.