Physiological fluorodeoxyglucose uptake of spinal cord in adults

Quantitative and Computational Spinal Imaging in Neurodegenerative Conditions and Acquired Spinal Disorders: Academic Advances and Clinical Prospects

Introduction: Quantitative spinal cord imaging has facilitated the objective appraisal of spinal cord pathology in a range of neurological conditions both in the academic and clinical setting. Diverse methodological approaches have been implemented, encompassing a range of morphometric, diffusivity, susceptibility, magnetization transfer, and spectroscopy techniques. Advances have been fueled both by new MRI platforms and acquisition protocols as well as novel analysis pipelines. The quantitative evaluation of specific spinal tracts and grey matter indices has the potential to be used in diagnostic and monitoring applications. The comprehensive characterization of spinal disease burden in pre-symptomatic cohorts, in carriers of specific genetic mutations, and in conditions primarily associated with cerebral disease, has contributed important academic insights. Methods: A narrative review was conducted to examine the clinical and academic role of quantitative spinal cord imaging in a range of neurodegenerative and acquired spinal cord disorders, including hereditary spastic paraparesis, hereditary ataxias, motor neuron diseases, Huntington's disease, and post-infectious or vascular disorders. Results: The clinical utility of specific methods, sample size considerations, academic role of spinal imaging, key radiological findings, and relevant clinical correlates are presented in each disease group. Conclusions: Quantitative spinal cord imaging studies have demonstrated the feasibility to reliably appraise structural, microstructural, diffusivity, and metabolic spinal cord alterations. Despite the notable academic advances, novel acquisition protocols and analysis pipelines are yet to be implemented in the clinical setting.

Physiologically intense FDG uptake of distal spinal cord on total-body PET/CT

OBJECTIVE

Physiologically mild-to-moderate FDG uptake of the spinal cord was reported. However, we noticed intense FDG uptake of distal spinal cord in several patients without definite spinal cord lesions on total-body PET/CT. Thus, this study aimed to investigate the frequency, pattern, intensity, and associations of FDG uptake in such cases on total-body PET/CT.

METHODS

The clinical characteristics of age, gender, body mass index (BMI), lower extremity symptom, diabetes, and fasting blood glucose level, and total-body FDG PET/CT metabolic parameters of maximum standard uptake value (SUVmax), SUVmax of lean body mass (SUVlbm), and SUVmax of body surface area (SUVbsa), were retrospectively analyzed in 527 patients without definite spinal cord lesions. Intense FDG uptake was defined as greater than liver glucometabolism on visual analysis, and T5 cord was selected as cord background.

RESULTS

Intense FDG uptake of distal spinal cord was observed in 87 out of 527 patients (16.5%) and involved with 2-3 vertebral segments including T11-T12 in 33 cases (38.0%), T12-L1 in 29 (33.3%), and T11-L1 in 25 (28.7%). No lesions were demonstrated on follow-up physical examinations, MRI or contrast-enhanced CT in these 87 cases with intense FDG accumulation in the distal spinal cord. The median SUVmax, SUVlbm, and SUVbsa of distal spinal cord with intense FDG uptake were 3.8 (2.7-5.5), 2.9 (2.2-4.3), and 1.0 (0.7-1.6), respectively. Significant differences in SUVmax, SUVlbm, and SUVbsa of distal cord and cord background were found between the groups with and without intense FDG uptake (P < 0.05). Moreover, significant differences in ratios of distal spinal cord-to-cord background, to mediastinal blood pool, and to liver were observed between two groups (P < 0.05). Intense FDG uptake of distal cord was associated with age, diabetic status, and blood glucose level.

CONCLUSIONS

Intense FDG uptake of distal spinal cord on total-body PET/CT may be physiological, more common in younger age, patients without diabetes, or lower fasting blood glucose.

Feasibility of imaging synaptic density in the human spinal cord using [11C]UCB-J PET

PURPOSE

Neuronal damage and synapse loss in the spinal cord (SC) have been implicated in spinal cord injury (SCI) and neurodegenerative disorders such as Amyotrophic Lateral Sclerosis (ALS). Current standards of diagnosis for SCI include CT or MRI imaging to evaluate injury severity. The current study explores the use of PET imaging with [11C]UCB-J, which targets the synaptic vesicle protein 2A (SV2A), in the human spinal cord, as a way to visualize synaptic density and integrity in vivo.

RESULTS

First, simulations of baseline and blocking [11C]UCB-J HRRT scans were performed, based on SC dimensions and SV2A distribution to predict VT, VND, and VS values. Next, human baseline and blocking [11C]UCB-J HRRT images were used to estimate these values in the cervical SC (cSC). Simulation results had excellent agreement with observed values of VT, VND, and VS from the real human data, with baseline VT, VND, and VS of 3.07, 2.15, and 0.92 mL/cm3, respectively, with a BPND of 0.43. Lastly, we explored full SC imaging with whole-body images. Using automated SC regions of interest (ROIs) for the full SC, cSC, and thoracic SC (tSC), the distribution volume ratio (DVR) was estimated using the brain gray matter as a reference region to evaluate SC SV2A density relative to the brain. In full body imaging, DVR values of full SC, cSC, and tSC were 0.115, 0.145, and 0.112, respectively. Therefore, measured [11C]UCB-J uptake, and thus SV2A density, is much lower in the SC than in the brain.

CONCLUSIONS

The results presented here provide evidence for the feasibility of SV2A PET imaging in the human SC, however, specific binding of [11C]UCB-J is low. Ongoing and future work include further classification of SV2A distribution in the SC as well as exploring higher-affinity PET radioligands for SC imaging.