Gd-DTPA : Concentration Versus MR Signal Intensity

Abstract

Purpose : To determine the relationship between Gd-DTPA concentration and Signal intensity (Sl) in MR imaging. Material and Methods : Gd-DTPA supplied in a vial of 0.5 molar solution was mixed with distilied water to prepare solutions with 1, 1/2, 1/4, -,-,-, 1/2^(n,(n-0.20)) of the original concentration. With 5 cc plastic phantoms containing the solutions at the center of a head coil, spin-echo images were obtained in a 1.5 T unit (GE Signa) using acquisition parameters of TR/TE 400/15, FOV 16 cm, matrix size 256x256, and thickness 5 ㎜. Sl of each phantom was measured relative to that of a pure water phantom and was plotted against Gd-DTPA concentration into a log_(1/2) curve to determine the relationship between the two variables. Results : At each of the progressive half-dose concentrations of Gd-DTPA, respective Sl of 0.067, 0.072, 0.081, 0.096, 1.084, 3.796, 6.749, 8.412, 8.210, 6.536, 4.737, 3.056, 2.077, 1.443, 1.154, 1.067, 1.020, 0.938, 0.907, 0.902, 0.932 were observed. Sl remained dose to 0.0 when the concentration was between 1/2^(0) and 1/2^(3) of the original. In relation to further reduction in concentration, Sl lineariy increased (r²=0.988) and reached maximum of 8.41 at the concentration 1/2^(7) of the original. On the contrary, Sl lineariy decreased (r²=0.972) in relation to the concentration between 1/2^(8) and 1/2^(13) of the original which is the clinical range during the Span of a typical MR scanning. Beyond this range, Sl remained dose to the value of 1. Conclusion : There was a linear log_(1/2) relationship between Sl and clinical range of Gd-DTPA concentration. Considering the inverse relationship at higher concentration, Gd-DTPA should be administered in a proper dosage which should be adjusted in dehydrated subjects.