Olfactory nerve scintigraphy in patients with impaired sense of smell by per-nasal Tl-201 administration

Objectives At present, there is no method to visualize the olfactory nerve damage. It has been reported that thallium-201 (Tl) is transported to the olfactory nerve tract after nasal administration in rodents. The aim of this study was to assess whether olfactory nerve scinitigraphy by per-nasal cavity Tl administration is feasible in patients with impaired sense of smell.

Methods 12 patients with impaired sense of smell (6 males and 6 females, aged 53 ± 13) and 5 normal volunteers (5 male, aged 43 ± 8) were administered 18-37 MBq (74 MBq/ml) of Tl on the olfactory mucosa. 24-hr after the tracer administration, SPECT/CT was performed. CT image from SPECT/CT was fused with MRI image that obtained separately, then SPECT/MRI fused image was generated. On the SPECT/MRI coronal and sagittal fused images, ROIs were set to cover the area of Tl administered on the olfactory mucosa with the 50% threshold of maximum count, and another ROI was set on the olfactory bulb. The % uptake of the Tl of the olfactory bulb (U) was calculated as: U = 100 (counts of the olfactory bulb / counts of the olfactory mucosa).

Results In normal volunteers, significant Tl activity was observed in olfactory bulb, however, little activity was observed in patients with impaired sense of smell. Quantitatively, olfactory bulb Tl uptake was significantly lower in patients with impaired sense of smell than normal volunteers (4.8 ± 3.4 % vs 16.3 ± 3.4%, p<0.001).

Conclusions Tl transport from olfactory mucosa to olfactory bulb was reduced in patients with impaired sense of smell by per-nasal cavity administration of Tl, indicating the feasibility of olfactory nerve scintigraphy for the diagnosis of impaired olfactory nerve function