Stereotactic MR imaging for planning neural transplantation: a reliable technique at 3 Tesla?

Emerging Imaging Modalities in Regenerative Medicine

The field of regenerative medicine has experienced considerable growth in recent years as the translation of pre-clinical biomaterials and cell- and gene-based therapies begin to reach clinical application. Until recently, the ability to monitor the serial responses to therapeutic treatments has been limited to post-mortem tissue analyses. With improvements in existing imaging modalities and the emergence of hybrid imaging systems, it is now possible to combine information related to structural remodeling with associated molecular events using non-invasive imaging. This review summarizes the established and emerging imaging modalities that are available for in vivo monitoring of clinical regenerative medicine therapies and discusses the strengths and limitations of each imaging modality.

Clinical imaging in regenerative medicine

In regenerative medicine, clinical imaging is indispensable for characterizing damaged tissue and for measuring the safety and efficacy of therapy. However, the ability to track the fate and function of transplanted cells with current technologies is limited. Exogenous contrast labels such as nanoparticles give a strong signal in the short term but are unreliable long term. Genetically encoded labels are good both short- and long-term in animals, but in the human setting they raise regulatory issues related to the safety of genomic integration and potential immunogenicity of reporter proteins. Imaging studies in brain, heart and islets share a common set of challenges, including developing novel labeling approaches to improve detection thresholds and early delineation of toxicity and function. Key areas for future research include addressing safety concerns associated with genetic labels and developing methods to follow cell survival, differentiation and integration with host tissue. Imaging may bridge the gap between cell therapies and health outcomes by elucidating mechanisms of action through longitudinal monitoring.

Stereotactic targeting of the ventrointermediate nucleus of the thalamus by direct visualization with high-field MRI

OBJECTIVE

To evaluate the ability of high-field MRI to consistently produce high-resolution, anatomical images of the thalamic ventrointermediate nucleus (Vim) suitable for stereotactic targeting.

METHODS

MR images of the thalamus of patients treated for essential tremor were acquired prior to treatment using a 3-tesla MR system. Similar images were acquired in 6 volunteers using, for comparison, both a 1.5-tesla and a 3.0-tesla system.

RESULTS

The thalamic Vim was clearly and consistently delineated on the 3-tesla images. These images were successfully used for target localization in essential tremor patients. In the volunteers data, images acquired using the 1.5-tesla system were inferior to those acquired using the 3-tesla system, lacking the ability to consistently provide reliably defined borders of the Vim.

CONCLUSION

3-Tesla MRI can provide high-quality depiction of the Vim, potentially enabling accurate treatment planning by direct visualization and definition of the targeted Vim.

Imaging in cell-based therapy for neurodegenerative diseases

Fetal cell transplantation for the treatment of Parkinson's and Huntington's diseases has been developed over the past two decades and is now in early clinical testing phase. Direct assessment of the graft's survival, integration into the host brain and impact on neuronal functions requires advanced in vivo neuroimaging techniques. Owing to its high sensitivity, positron emission tomography is today the most widely used tool to evaluate the viability and function of the transplanted tissue in the brain. Nuclear magnetic resonance techniques are opening new possibilities for imaging neurochemical events in the brain. The ultimate goal will be to use the combination of multiple imaging modalities for complete functional monitoring of the repair processes in the central nervous system.