Determining the Degree of Dopaminergic Denervation Based on the Loss of Nigral Hyperintensity on SMWI in Parkinsonism

Abstract

BACKGROUND AND PURPOSE: Nigrostriatal dopaminergic function in patients with Parkinson disease can be assessed using 123I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)-nortropan dopamine transporter (123I-FP-CIT) SPECT, and a good correlation has been demonstrated between nigral status on SWI and dopaminergic denervation on 123I-FP-CIT SPECT. Here, we aim to correlate quantified dopamine transporter attenuation on 123I-FP-CIT SPECT with nigrosome-1 status using susceptibility map-weighted imaging (SMWI). MATERIALS AND METHODS: Between May 2017 and January 2018, consecutive patients with idiopathic Parkinson disease (n\u2009=\u2009109) and control participants (n\u2009=\u200929) who underwent 123I-FP-CIT SPECT with concurrent 3T SWI were included. SMWI was generated from SWI. Two neuroradiologists evaluated nigral hyperintensity from nigrosome-1 on each side of the substantia nigra. Using consensus reading, we compared the 123I-FP-CIT–specific binding ratio according to nigral hyperintensity status and the 123I-FP-CIT specific binding ratio threshold to confirm the loss of nigral hyperintensity was determined using receiver operating characteristic curve analysis. RESULTS: The concordance rate between SMWI and 123I-FP-CIT SPECT was 65.9%. The 123I-FP-CIT–specific binding ratios in the striatum, caudate nucleus, and putamen were significantly lower when nigral hyperintensity in the ipsilateral substantia nigra was absent than when present (all, P\u2009<\u2009.001). The 123I-FP-CIT–specific binding ratio threshold values for the determination of nigral hyperintensity loss were 2.56 in the striatum (area under the curve, 0.890), 3.07 in the caudate nucleus (0.830), and 2.36 in the putamen (0.887). CONCLUSIONS: Nigral hyperintensity on SMWI showed high positive predictive value and low negative predictive value with dopaminergic degeneration on 123I-FP-CIT SPECT. In patients with Parkinson disease, the loss of nigral hyperintensity is prominent in patients with lower striatal specific binding ratios.