Moreover,B0 will no longer level along the z direction,making coordinate method defining the regional area and the gradient components place dependent.The calculated relaxation price is shown in Fig.4,and has the exciting attribute that for any worth of ?,the maximum rest charge takes place at almost precisely the same worth of z since the greatest on-axis rate.The rest price increases quickly with ?,reaching three.6 ? ten?two s?1 at ? = twenty cm,the biggest radial distance for which a relaxation rate may very well be reliably calculated.As expected,when ? exceeds the radius on the solenoid in the order masitinib model,the relaxation price begins to reduce.Hence,this numerical evaluation exhibits that is definitely most likely to get a maximum with the edge from the solenoid and will exceed the peak relaxation rate observed on axis by almost an purchase of magnitude.Lastly,note the gradients are right proportional to the field strength.As a result,Eq.signifies the relaxation prices do not depend on B0,but rather only to the unique geometry on the current configuration of the magnet.Hence,the calculations we have done for our 2-T,compact animal imaging magnet should certainly be equally applicable to a 4.7-T or 7-T program of very similar geometry,and people for the 1.
5-T clinical magnet would be equally applicable at 3-T.Despite the fact that we’ve got not reported direct measurements for 129Xe,it may possibly fairly be surmised that gradient-induced rest rate can be ~35-times slower than that observed for 3He.This huge difference arises through the substantially smaller free diffusion coefficient of 5.71? ten?two cm2/s for 129Xe in comparison to 3He.So,gradient rest will need to be deemed for 129Xe,nevertheless it is unlikely to become as sizeable a problem as for 3He.For example,the worst ?spot? in the on-axis fringe field within the 2-T tiny bore magnet gives a rest STI-571 time about 140 min for 129Xe,that is to the very same purchase since the relaxation time because of the wall rest.Conclusion We now have proven that the minimal relaxation time for 3He from the vicinity of an unshielded small-bore MR program is often as quick as 4 min on axis and it is decreased to 0.5 min,when moving out 20 cm inside the radial path.Moreover,the minimum on-axis 3He relaxation time would drop to approximately 1.two min,when the magnet had been self-shielded.Gradient-induced relaxation in a standard self-shielded clinical magnet is less significant,but nevertheless important and is anticipated to contribute a minimum on-axis 3He relaxation time of approximately twelve min.We’ve got also shown that the cylindrical symmetry of most magnet programs allows the off-axis fringe discipline to be predicted just by measuring the on-axis field.Furthermore,any model that adequately captures the behavior from the fringe-field may be used to calculate the gradient induced longitudinal relaxation.We’ve proven to the cases regarded right here,that a simple solenoid model is ample.