الفهرس 
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Abstract
Conventional MRI (cMRI), as well as different advanced MRI techniques, including magnetic resonance spectroscopy (MRS), diffusion-weighted and diffusion tensor imaging (DWI/DTI) and functional MRI (fMRI), are helpful to distinguish PD from APDs, especially in early stage of disease where a differentiation of these conditions is not easy (4) .
The midbrain, or mesencephalon, is the most rostral part of the brainstem and sits above the pons and is adjoined rostrally to the thalamus. During development, the midbrain forms from the middle of three vesicles that arise from the neural tube. The cerebral peduncles (also known as the cerebral crus) are the part of the midbrain that link the remainder of the brainstem to the thalami and there by, the cerebrum. They are the most anterior structure in the midbrain and contain the large ascending and descending tracts that run to and from the cerebrum(6).
When viewed in cross-section, the midbrain can be divided into three portions:
Tectum (posterior),Tegmentum and Cerebral peduncles (anterior).
The tectum is composed of the tectal (quadrigeminal) plate and superior and inferior colliculi. The tectum is unique to the midbrain and does not have a counterpart in the rest of the brainstem(5,6).
The tegmentum (Latin for ”covering”) is the phylogenetically-old part of the brainstem and runs through the pons and medulla oblongata. In the adult brain, it contains all the brainstem nuclei(6).
The overwhelming advantage of MR imaging is its ability to provide images with increased signal to noise ratios. Tissue characteristics with respect to different imaging sequences provide valuable clues when interpreting an MR image of the brain. Therefore, it is important to understand the accentuated tissue features on each scan. T1-weighted images provide good tissue discrimination and, in conjunction with the post contrast scans, allow assessment or tissue enhancement. Pre contrast and post contrast scans must be obtained with identical imaging parameters to truly assess contrast enhancement (T1-weighted and T2-weighted images are complementary to each other because the T2-weighted images are sensitive to increased water content within tissues and to differences in susceptibility between tissues. Gradient echo images are susceptible to in homogeneities in the magnetic field, accentuating blood products, iron, calcium, and manganese within tissues. This sequence is routinely performed during evaluation for stroke and trauma because hemorrhage is well seen. Fluid-attenuated inversion recovery (FLAIR)sequence can be used to obtain T2-weighted contrast while voiding the signal from cerebrospinal fluid, allowing a pathologic process to be identified with more confidence (12).
Parkinson’s disease (PD) and the different forms of atypical parkinsonism (AP) are clinical diagnoses. Differentiating PD and AP on clinical parameters is challenging, especially in early disease courses. This is due to large overlap in symptoms and because the so called red flags, i.e. symptoms indicating AP, have not (fully) developed (52-55).
Brain MRI can aid to improve the accuracy and confidence about the diagnosis, which is relevant for treatment decision making. It also important for prognosis estimation and to exclude other possible and sometimes treatable causes of parkinsonism (56,57).
Furthermore, brain MRI can support the possible or probable diagnosis of aspecific form of AP (56-58).
For more accurate and early diagnosing of different types of parkinsonism we recommend more advanced techniques such as MRI 7T, functional MRI, DTI, PET and SPECT scan.