Pulsed EPR imaging: image reconstruction using selective acquisition sequences.

Pulsed nuclear magnetic resonance imaging (NMRI) apparatus has developed very quickly. On the other hand, the development of apparatus for pulsed electron paramagnetic resonance imaging (EPRI) has been very slow. This fact is due to the extremely reduced relaxation times of the paramagnetic probes. EPR linewidths are larger than typical NMR linewidths. These large linewidths are also responsible for a substantial worsening of spatial resolution. Due to the brevity of the electronic relaxation times, not all the acquisition/reconstruction techniques currently used in NMRI (such as spin-echo, gradient-echo, etc) can be applied in pulsed EPRI. In fact, the usable sequences in pulsed EPRI are only acquisitions from projections, where it is possible to use stationary magnetic field gradients. Moreover, the use of high fixed magnetic field gradients induces a short decay time constant T2*. The low T2* value can make it impossible for the analogue to digital conversion system (ADC) to reproduce signal variations during the whole acquisition interval and the resolution can worsen. A new pulsed EPRI acquisition sequence from projections, based on selective reception, is presented that is particularly useful in solving the problems of worsening of spatial resolution associated with the use of an ADC. In order to demonstrate the capabilities of our acquisition method, simulated numerical tests will also be reported.