Cutting-edge brain imaging with positron emission tomography

Simulation Study of a Frame-Based Motion Correction Algorithm for Positron Emission Imaging

Positron emission tomography (PET) is a functional non-invasive imaging modality that uses radioactive substances (radiotracers) to measure changes in metabolic processes. Advances in scanner technology and data acquisition in the last decade have led to the development of more sophisticated PET devices with good spatial resolution (1-3 mm of full width at half maximum (FWHM)). However, there are involuntary motions produced by the patient inside the scanner that lead to image degradation and potentially to a misdiagnosis. The adverse effect of the motion in the reconstructed image increases as the spatial resolution of the current scanners continues improving. In order to correct this effect, motion correction techniques are becoming increasingly popular and further studied. This work presents a simulation study of an image motion correction using a frame-based algorithm. The method is able to cut the acquired data from the scanner in frames, taking into account the size of the object of study. This approach allows working with low statistical information without losing image quality. The frames are later registered using spatio-temporal registration developed in a multi-level way. To validate these results, several performance tests are applied to a set of simulated moving phantoms. The results obtained show that the method minimizes the intra-frame motion, improves the signal intensity over the background in comparison with other literature methods, produces excellent values of similarity with the ground-truth (static) image and is able to find a limit in the patient-injected dose when some prior knowledge of the lesion is present.

Using fast-scan cyclic voltammetry to evaluate striatal dopamine release elicited by subthalamic nucleus stimulation

Deep brain stimulation (DBS), an effective neurosurgical therapy for Parkinson's disease (PD), may act via eliciting neurotransmitter release. However, the precise relationships between DBS and neurotransmitter release are not established. One issue in these studies may be analytical limitations of microdialysis and positron emission tomography, the primary measurement technologies employed. Limitations may be overcome by microsensors, which exhibit improved temporal and spatial resolution. Here we assess fast-scan cyclic voltammetry (FSCV) at a carbon-fiber microelectrode (CFM) for monitoring a putative DBS neurotransmitter, dopamine, during stimulation of the subthalamic nucleus (STN), a DBS target for PD. These results, obtained in the anesthetized rat, suggest that real-time microsensors are a suitable approach for testing the neurotransmitter release hypothesis of DBS action.

Improved work-up procedure for the production of [(18)F]flumazenil and first results of its use with a high-resolution research tomograph in human stroke

INTRODUCTION

The central benzodiazepine receptor (cBZR)-gamma-aminobutyric acid (GABA(A)) receptor complex in the human brain plays an important role in many neurological and psychiatric disorders. (18)F-Labeled flumazenil ([(18)F]FZ) provides a potentially useful tracer to investigate those disorders by means of positron emission tomography (PET).

METHODS

[(18)F]Flumazenil was synthesized from its nitro-precursor Ro 15-2344 in DMF at high temperatures between 150 degrees C and 160 degrees C. Other solvents like acetonitrile and dimethylsulfoxide were also investigated as reaction media. A new HPLC method for the final purification of [(18)F]FZ was developed to circumvent some difficulties associated with a previously published procedure sometimes led to a contamination of [(18)F]FZ with Ro 15-2344. The final purification of the radiotracer was achieved using a Waters Symmetry Prep C18 HPLC column with elution with 0.05 M sodium acetate (NaOAc) buffer (pH 5)/THF/MeOH (80:10:10).

RESULTS

[(18)F]FZ could be synthesized in reproducible radiochemical yields (RCYs) of 15-20% (decay corrected to EOB) after 80 min overall synthesis time. The synthesized [(18)F]FZ was applied for the first time in a human PET study in a patient with ischemic right middle cerebral artery stroke using the HRRT high-resolution research scanner (Siemens Medical Solution, Knoxville, TN, USA).

CONCLUSIONS

[(18)F]FZ is a potentially useful GABA receptor-binding PET ligand. A modified procedure for its preparation in reproducibly high radiochemical yields has been described and the [(18)F]FZ thus produced has been used successfully in a pilot clinical study.

Biomarkers and imaging: physics and chemistry for noninvasive analyses

The era of ‘modern medicine’ has changed its name to ‘molecular medicine’, and reflects a new age based on personalized medicine utilizing molecular biomarkers in the diagnosis, staging and monitoring of therapy. Alzheimer’s disease has a classical biomarker determined at autopsy with the histologic staining of amyloid accumulation in the brain. Today we can diagnose Alzheimer’s disease using the same classical pathologic biomarker, but now using a noninvasive imaging probe to image the amyloid deposition in a patient and potentially provide treatment strategies and measure their effectiveness. Molecular medicine is the exploitation of biomarkers to detect disease before overt expression of pathology. Physicians can now find, fight and follow disease using imaging, and the need for other disease biomarkers is in high demand. This review will discuss the innovative physical and molecular biomarker probes now being developed for imaging systems and we will introduce the concepts needed for validation and regulatory acceptance of surrogate biomarkers in the detection and treatment of disease.

[Central nervous system involvement in Wegener's granulomatosis]

INTRODUCTION

Wegener's granulomatosis (WG) is a systemic necrotizing vasculitis associated with c-ANCA antibodies. The involvement of the central nervous system in WG is uncommon and usually caused by in situ vasculitis, intracranial granuloma formation or contiguous invasion from extracranial sites.

CASE REPORT

Here, we report on a tumour-like expansion of a severe nasosinusal WG into the brain, which was confirmed by brain biopsy examination.

CONCLUSION

The positivity of positron emission tomography in our observation supports the potential role of such functional imaging in the staging, as well as in the follow-up of WG.