The major role of the imaging used to be ruling out other disorders which present the symptoms of Parkinsonism. However, there are several imaging method which can visualize the abnormality in the Parkinson’s disease including neuromelanin image, diffusion images or susceptibility weighted imaging. This lecture will discuss on the recently developed imaging method for Parkinson’s disease or related disorders.
TARGET AUDIENCE
Researchers and clinicians interested in Parkinson’s desease
Parkinson’s disease is a degenerative disease that shows degeneration of melanin cells within substantia nigra. The major symptoms of the disease are tremor, rigidity, akinesia and postural reflex disturbance due to dysfunction of dopaminergic nigrostriatal pathway. The major role of the imaging used to be ruling out other disorders which present the symptoms of Parkinsonism. There is a tendency that the area of the higher signal intensity of the pars compacta in the substantia nigra decreases in the cases with Parkinson’s disease due to the signal decrease by iron deposition within this structure. However, this finding is not specific to the Parkinson’s disease and can be seen in the cases with secondary Parkinsonism or even in normal aged brain. In 2006, Sasaki et al. introduced neuromelanin image for diagnosis of the Parkinson’s disease (1). In Parkinson's disease patients, the signal intensity in the locus ceruleus and substantia nigra pars compacta are reduced, suggesting depletion of neuromelanin-containing neurons.
Susceptibility weighted image (SWI) uses a fully flow compensated, long echo, gradient echo scan to acquire images and post-processing that makes sensitive detection of paramagnetic effects using information from the phase image. SWI is one of the most sensitive methods for detect iron deposition, as it can identify susceptibility differences between tissues. Recently, in vivo visualization of the nigrosome 1 in the pars compacta of substantia nigra by using SWI is introduced. Nigrosome 1 is one of subgroups of dopamine containing neurons within the pars compacta. The absence of nigrosome 1 in the pars compacta of substantia nigra on SWI can be useful in developing a neuroimaging diagnostic test for PD (2).
Diffusion tensor image is the method to evaluate anisotropic motion of water molecules which is modulated by the random movement of water molecules within tissue. Fractional anisotropy (FA) is one of the parameters of the degree of anisotropy of diffusion. On Parkinson disease, a large, prospective, case control study is reported. In the report, the FA value in the substantia nigra on DTI was lower in Parkinson disease patients compared with healthy controls, and correlated inversely with the clinical severity of Parkinson disease (3). Recently developed non-Gaussian diffusion processing method named neurite orientation dispersion and density imaging (NODDI) is likely to be useful for diagnosing PD and assessing its progression. There is a report that indicate intracellular volume fraction and orientation dispersion index given by NODDI in the pars compacta of substantia nigra and putamen showed significant negative correlations with disease severity (4).
Another contribution of imaging for this disorder is the targeting for deep brain stimulation electrode. Brain imaging is used for the selection of patients for DBS, to localize the target nucleus, to detect complications, and to evaluate the final electrode contact position (5). T2 weighted image is usually applied in targeting the subthalamic nucleus, however, short tau inversion recovery with short echo time is also useful (6).
1. Sasaki M, Shibata E, Tohyama K, Takahashi J, Otsuka K, Tsuchiya K, et al. Neuromelanin magnetic resonance imaging of locus ceruleus and substantia nigra in Parkinson's disease. Neuroreport 2006;17(11):1215-8.
2. Blazejewska AI, Schwarz ST, Pitiot A, Stephenson MC, Lowe J, Bajaj N, et al. Visualization of nigrosome 1 and its loss in PD: pathoanatomical correlation and in vivo 7 T MRI. Neurology 2013;81(6):534-40.
3. Chan LL, Rumpel H, Yap K, Lee E, Loo HV, Ho GL, et al. Case control study of diffusion tensor imaging in Parkinson's disease. J Neurol Neurosurg Psychiatry 2007;78(12):1383-6.
4. Kamagata K, Hatano T, Okuzumi A, Motoi Y, Abe O, Shimoji K, et al. Neurite orientation dispersion and density imaging in the substantia nigra in idiopathic Parkinson disease. Eur Radiol 2016;26(8):2567-77.
5. Dormont D, Seidenwurm D, Galanaud D, Cornu P, Yelnik J, Bardinet E. Neuroimaging and deep brain stimulation. AJNR Am J Neuroradiol 2010;31(1):15-23.
6. Taoka T, Hirabayashi H, Nakagawa H, Sakamoto M, Kitano S, Takahama J, et al. "Sukeroku sign" and "dent internal-capsule sign"--identification guide for targeting the subthalamic nucleus for placement of deep brain stimulation electrodes. Neuroradiology 2009;51(1):11-6.