The Comparison of the Contrasts of Magnetic Resonance Images of Plants

摘要

To obtain an image with the largest information value, the best image contrast during the measurement of the object in the magnetic resonance tomograph is necessary to achieve. This contrast depends on the physical properties of the object, in particular a proton density and relaxation properties of the material. Furthermore, the contrast depends on parameter characteristic for each MR method: Spin Echo, Gradient Echo and Inversion Recovery. The echo time and repetition time are included between the two most important parameters of pulse sequence. We can create four different variants of contrast by combining these two mentioned times: the contrast spin density, the T_1 weighted contrast, the T_2 weighted contrast, and the last one is inappropriate setting for the contrast. Each resulting contrast is suitable for displaying different plant stem tissues. An increase in the contrast can also be achieved by adding contrast (paramagnetic) substances for differentiation of isomagnetics tissues. The aim of this paper is to display the internal morphology of plants by various methods with subsequent comparison of contrast and identification of an appropriate method for the study of transport of substances in the stem of the plant. Euphorbia cactus was chosen for the study of the image contrasts. This plant was inserted into working space of the tomograph. Images of the plant stem were acquired by a magnetic resonance tomograph with the magnetic field induction of 4.7 T (200 MHz). The evaluation of the results obtained via the applied methods as related the last measurement. The data processing was performed by using Marevisi and Matlab programs. Monitored parameters of individual plant samples were inserted into a table and inserted into graphs. By evaluating and comparing the relaxation times, it can be determined that, in the same selected points, the relaxation time T_2 exhibits shorter values than the relaxation time T_1. This holds true despite the fact that method for weighted by relaxation time T_2 is a faster method. Moreover, the final image acquired via this method is of inferior quality. The resulting image after weighted relaxation time T_1 nevertheless exhibits a lower value of image intensity.