Radiolabeling, Characterization and Diagnostic imaging of 99mTc-TRODAT-1 SPECT-CT in Parkinson disease

Objectives Dopamine transporter (DAT) imaging is usually performed using Iodine 123-ioflupane. Tc99m-TRODAT-1, a tropane derivative, also has potential for in-vivo assessment of the loss of dopamine neurons in Parkinson's and other neurodegenerative diseases. The objectives of this study were to label & characterize 99mTc-TRODAT-1 for imaging in the diagnosis of Parkinson’s disease.

Methods A total of 75 patients with clinically suspected Parkinson’s disease and other atypical parkinsonian disorders such as Multiple System Atrophy (MSA), Progressive Supranuclear Palsy (PSP) and Cortico-Basal Ganglionic Degeneration (CBGD) were included. All the patients were recently diagnosed/ suspected cases with no prior history of treatment with anti Parkinsonian drugs. Thorough clinical history of symptoms, laterality, duration and any drug intake were obtained prior to the imaging. All the patients were injected with 20-25mCi Tc99m-TRODAT-1, prepared in-house. Brain SPECT/CT imaging was performed approximately 4 hours after administration using a dual headed gamma camera (Symbia T-16 SPECT/CT; SIEMENS) equipped with LEHR collimators (128 x 128 matrix: 3 degree angular rotation, 180 degree/ detector; 64 frames with frame duration of 30 seconds). Images were reconstructed with attenuation correction and reorientation of the individual slices was done parallel to the orbitomeatal line. Tracer uptake in the striatum and its sub-regions, including the putamen and caudate nucleus was visually interpreted and compared for symmetry.

Results Of the 75 patients, 16 patients revealed adequate and symmetrical tracer binding in the bilateral striatum correlating well with the lower level of clinical suspicion in those cases. 28 patients had unilateral involvement of putamen out of which 21 patients had putamen involvement contralateral to the side with dominant symptoms, while 7 patients showed putamen involvement ipsilateral to side with dominant symptoms suggesting unilateral early stage presynaptic dopaminergic dysfunction. 5 patients revealed severely reduced tracer binding in entire contralateral striatum while 16 patients revealed severely reduced tracer binding in the bilateral putamen suggesting higher degree of disease severity. 6 patients who were suspected with atypical Parkinsonism / Parkinson Plus disease revealed inhomogeneous tracer uptake in the cortex and severely reduced tracer binding in the bilateral striatum.4 patients who had history of ongoingtreatment for other diseases like depression, anxiety etc. showed no tracer uptake in the bilateral striatum with increased tracer uptake in rest of the brain parenchyma; drug interference was considered in such case as the scans that were performed on the same day showed normal tracer binding ruling out the error with the radiopharmaceutical to be the cause for the same.

Conclusions Tc99m-TRODAT-1 is a good tracer imaging for in the diagnosis of Parkinson’s disease. It assists in the differentiation of conditions with and without presynaptic dopaminergic deficit. A normal DAT-SPECT supports the diagnosis of drug induced psychogenic and vascular Parkinsonism by excluding underlying true nigrostriatal dysfunction