Jose L. Agraz, PhD

Conclusions

The use of LabVIEW to control PHIP instrumentation has strong potential for aiding in the maximum polarization levels of different metabolites with high reliability and at an affordable price. In addition, the use of LabVIEW for the automation of metabolite hyperpolarization improves the instrument accuracy, shortens development time, and decreases hardware costs. The operational test shows that the LabVIEW-based hyperpolarization instrumentation system is stable and reliable, crucial aspects for metabolite hyperpolarization.
We have modeled and implemented a VCCS for the generation of precision Bo in PHIP instrumentation. The design shows a much lower i n and i D and a 100% increase in HEP polarization compared to previous methods of B o generation. The VCCS model, confirmed by experimental results with a 0.02% correlation at 0Hz, shows that i n and i D are principally dependent on the control of current flow. Because of the reduction in i n and i D , we were able to achieve higher levels of polarization. Specifically, for 10mM of HEA, 2mM of catalyst solution, and the Goldman RF sequence, the HEP polarization increased an average of 115%, with a minimum at 20% & a maximum of 152% from using a VCCS. Although, the measured noise is much greater than in integrated circuits (IC) for low current application, the VCCS design shows very low noise levels at high currents (1Amp). Also, the VCCS design has the capabilities of handling much larger currents with minimum design changes at virtually the same noise levels measured here. Further design improvement, such design simplicity, could come from redesigning the circuit using TF with negative feedback and lower noise levels and drift may be achieved by using digital control. We have presented the results for the implementation of a VCCS for doubling the hyperpolarization of endogenous substances, more specifically, HEP. We deduced that the use of an ultra low noise, high stability voltage reference driving a current sink generates a stable Io to 15ppm, resulting in a stable B o for the hyperpolarization of HEP. This has led us to propose a new definition for the generation of a precision B o for hyperpolarization applications. This new approach is fundamentally different from the traditional generation of B o using VCVS devices, which does not control the flow of current.
We have calculated the TF’s solutions and examined the circuit stability. Although the circuit is stable for 0Hz (where the circuit usually performs), the stability of the current sink section in the circuit begins to decreases at higher frequencies, thus the negative poles. More specifically, the instability resides at 380KHz with a 200KHz bandwidth and a peak gain of 2. Because of the dominant pole at 49 Hz, this characteristic should only affect in & iD at a minimum beyond thermal and 1/f noise frequencies (≤1KHz). Our definition of precision Bo generation suggests new approaches worth exploring, and more detail of circuitry optimization using TFs, board layout, & measurements on the VCCS’ thermal and 1/f noise could be particularly rewarding. For example, minimizing the amount of poles and including negative feedback will produce a more efficient circuit with less components and a lower in & iD . Most importantly, the circuit will be more immune to external influences such as electrical noise and temperature changes.