Abstract:

Configuration and performance features of the newly developed L-band three-dimensional ESR imaging system were introduced. The main components of the ESRI system include a set of L-band ESR spectrometer, the three dimensional gradient magnetic field system  and the imaging reconstruction software. The microwave system worked at the frequency of 1.05 GHz with more than 500 mW microwave power. The phase-locking receiver was set to work at 100 kHz modulation frequency with a modulation amplitude of more than 0.5 mT. Receiver gain could be set up to 1×10⁺⁶ and time constant was adjustable from 0.02 ms to 1 s. The sample cavity was a threelooptwogap reentrance one which had an unloaded Q-value of more than 1 000 and had a cylindrical sensitive volume of 2 cm in diameter and 3 cm in length. The maximum gradient strength could be 2 mT/cm with spatial linearity of better than 5% in all three dimensions. Field stability was about 10^-5. Main magnet strength and the scanning range of the magnetic field were 1.6～96 mT and 0.2～16 mT respectively. Data system worked on a 12-bit A/D card for data acquisition. Three channels of 8-bit D/A converter were used for gradient control. Spectrum processing functions included integration, base line correction, resolution enhancement, spectrum deconvolution and noise filtering. Imaging functions included two and three dimensional imaging reconstruction, 2D image display of spin intensity isograms, 3D image display of contour and computed tomography. The preliminary results of imaging of biological equivalent samples, such as large volume solution phantoms, suggested that the present ESRI system was capable of imaging biological samples in combination with spin labeling techniques.

Key words: ESR, 3D-ESRI, L-band, system configuration, performance feature