Photon-Counting Detector CT Enables Quantification of Dorsal Root Ganglion Enlargement in Radiculopathy

Background/Objectives: Dorsal root ganglion (DRG) enlargement in radiculopathy reflects inflammatory nerve root responses and correlates with symptom severity. While DRG enlargement can be detected by MRI, it is unclear whether photon-counting detector CT (PCD-CT) acquired during routine periradicular therapy (PRT) enables detection and quantification of DRG volumetric changes in lumbosacral radiculopathy. Methods: This retrospective study included 28 selected patients with unilateral L5 or S1 radiculopathy undergoing PCD-CT-guided PRT followed by confirmed therapeutic response. Three independent blinded readers segmented DRGs on low-dose planning acquisitions. Affected and contralateral DRG volumes were compared using paired Wilcoxon signed-rank tests. Results: Affected DRGs exceeded contralateral volumes in 26 of 28 patients (92.9%). Median symptomatic DRG volume was 341.1 mm3 versus 282.3 mm3 contralaterally (p < 0.001). Median DRG enlargement was +24.0%. The result was consistent across L5 and S1 radiculopathy levels. Inter-reader agreements were high (median Dice similarity coefficients 0.78–0.85, median volumetric similarities 0.93–0.95). Conclusions: PCD-CT enables visualization and quantification of DRG volumetric changes on routine therapeutic imaging of selected patients, extracting biological information from procedural acquisitions. This establishes PCD-CT for investigating nerve pathophysiology and extends CT-based neuroradiological research into biological questions previously limited to MRI.