Hirsch Matthew L, Smith Bryce A, Mattingly Mark, Goloshevsky Artem G, Rosay Melanie, Kempf James G
Bruker Biospin Corp., Billerica, MA 01821, USA.
Bruker Biospin Corp., Billerica, MA 01821, USA.
J Magn Reson. 2015 Dec;261:87-94. doi: 10.1016/j.jmr.2015.09.017. Epub 2015 Oct 24.
We demonstrate transport of hyperpolarized frozen 1-(13)C pyruvic acid from its site of production to a nearby facility, where a time series of (13)C images was acquired from the aqueous dissolution product. Transportability is tied to the hyperpolarization (HP) method we employ, which omits radical electron species used in other approaches that would otherwise relax away the HP before reaching the imaging center. In particular, we attained (13)C HP by 'brute-force', i.e., using only low temperature and high-field (e.g., T<∼2K and B∼14T) to pre-polarize protons to a large Boltzmann value (∼0.4% (1)H polarization). After polarizing the neat, frozen sample, ejection quickly (<1s) passed it through a low field (B<100G) to establish the (1)H pre-polarization spin temperature on (13)C via the process known as low-field thermal mixing (yielding ∼0.1% (13)C polarization). By avoiding polarization agents (a.k.a. relaxation agents) that are needed to hyperpolarize by the competing method of dissolution dynamic nuclear polarization (d-DNP), the (13)C relaxation time was sufficient to transport the sample for ∼10min before finally dissolving in warm water and obtaining a (13)C image of the hyperpolarized, dilute, aqueous product (∼0.01% (13)C polarization, a >100-fold gain over thermal signals in the 1T scanner). An annealing step, prior to polarizing the sample, was also key for increasing T1∼30-fold during transport. In that time, HP was maintained using only modest cryogenics and field (T∼60K and B=1.3T), for T1((13)C) near 5min. Much greater time and distance (with much smaller losses) may be covered using more-complete annealing and only slight improvements on transport conditions (e.g., yielding T1∼5h at 30K, 2T), whereas even intercity transfer is possible (T1>20h) at reasonable conditions of 6K and 2T. Finally, it is possible to increase the overall enhancement near d-DNP levels (i.e., 10(2)-fold more) by polarizing below 100mK, where nanoparticle agents are known to hasten T1 buildup by 100-fold, and to yield very little impact on T1 losses at temperatures relevant to transport.
我们展示了超极化冷冻的1-（13）C丙酮酸从其产生位点运输到附近设施的过程，在该设施中，从水性溶解产物获取了（13）C图像的时间序列。可运输性与我们采用的超极化（HP）方法相关，该方法省略了其他方法中使用的自由基电子物种，否则这些自由基电子物种会在到达成像中心之前使HP弛豫消失。具体而言，我们通过“强力”方法实现了（13）C超极化，即仅使用低温和高场（例如，T<∼2K和B∼14T）将质子预极化到较大的玻尔兹曼值（∼0.4%的（1）H极化）。在使纯净的冷冻样品极化后，快速喷射（<1s）使其通过低场（B<100G），通过称为低场热混合的过程在（13）C上建立（1）H预极化自旋温度（产生∼0.1%的（13）C极化）。通过避免溶解动态核极化（d-DNP）这种竞争方法超极化所需的极化剂（也称为弛豫剂），（13）C弛豫时间足以在最终溶解于温水中并获得超极化、稀释的水性产物的（13）C图像（∼0.01%的（13）C极化，在1T扫描仪中比热信号增益超过100倍）之前运输样品约10分钟。在极化样品之前的退火步骤也是在运输过程中将T1提高约30倍的关键。在那段时间里，仅使用适度的低温和磁场（T∼60K和B = 1.3T）来维持HP，此时（13）C的T1接近5分钟。使用更完全的退火以及仅对运输条件进行轻微改进（例如，在30K、2T时产生T1∼5小时），可以覆盖更长的时间和距离（损失更小），而在6K和2T的合理条件下甚至可能实现城市间转移（T1>20小时）。最后，通过在低于100mK的温度下极化，可以将整体增强提高到接近d-DNP水平（即多100倍），已知纳米颗粒剂在该温度下可使T1积累加快100倍，并且在与运输相关的温度下对T1损失的影响非常小。
