Resolution Improvement in Positron Emission Tomography Using Anatomical Magnetic Resonance Imaging

Enhanced hyperpolarized chemical shift imaging based on a priori segmented information

PURPOSE

The purpose of the study was to develop an approach for improving the resolution and sensitivity of hyperpolarized ¹³ C MRSI based on a priori anatomical information derived from featured, water-based ¹ H images.

METHODS

A reconstruction algorithm exploiting ¹ H MRI for the redefinition of the ¹³ C MRSI anatomies was developed, based on a modification of the spectroscopy with linear algebraic modeling (SLAM) principle. To enhance ¹³ C spatial resolution and reduce spillover effects without compromising SNR, this model was extended by endowing it with a search allowing smooth variations in the ¹³ C MR intensity within the targeted regions of interest.

RESULTS

Experiments were performed in vitro on enzymatic solutions and in vivo on rodents, based on the administration of ¹³ C-enriched hyperpolarized pyruvate and urea. The spectral images reconstructed for these substrates and from metabolic products based on predefined ¹ H anatomical compartments using the new algorithm, compared favorably with those arising from conventional Fourier-based analyses of the same data. The new approach also delivered reliable kinetic ¹³ C results, for the kind of processes and timescales usually targeted by hyperpolarized MRSI.

CONCLUSION

A simple, flexible strategy is introduced to boost the sensitivity and resolution provided by hyperpolarized ¹³ C MRSI, based on readily available ¹ H MR information.

Initial Investigation of preclinical integrated SPECT and MR imaging

Single-photon emission computed tomography (SPECT) can provide specific functional information while magnetic resonance imaging (MRI) can provide high-spatial resolution anatomical information as well as complementary functional information. In this study, we utilized a dual modality SPECT/MRI (MRSPECT) system to investigate the integration of SPECT and MRI for improved image accuracy. The MRSPECT system consisted of a cadmium-zinc-telluride (CZT) nuclear radiation detector interfaced with a specialized radiofrequency (RF) coil that was placed within a whole-body 4 T MRI system. The importance of proper corrections for non-uniform detector sensitivity and Lorentz force effects was demonstrated. MRI data were utilized for attenuation correction (AC) of the nuclear projection data and optimized Wiener filtering of the SPECT reconstruction for improved image accuracy. Finally, simultaneous dual-imaging of a nude mouse was performed to demonstrated the utility of co-registration for accurate localization of a radioactive source.