Combined Visualization of Nigrosome-1 and Neuromelanin in the Substantia Nigra Using 3T MRI for the Differential Diagnosis of Essential Tremor and de novo Parkinson's Disease

Distinguishing essential tremor from Parkinson's disease: clinical and experimental tools

INTRODUCTION

Essential tremor (ET) and Parkinson's disease (PD) are the most common causes of tremor and the most prevalent movement disorders, with overlapping clinical features that can lead to diagnostic challenges, especially in the early stages.

AREAS COVERED

In the present paper, the authors review the clinical and experimental studies and emphasized the major aspects to differentiate between ET and PD, with particular attention to cardinal phenomenological features of these two conditions. Ancillary and experimental techniques, including neurophysiology, neuroimaging, fluid biomarker evaluation, and innovative methods, are also discussed for their role in differential diagnosis between ET and PD. Special attention is given to investigations and tools applicable in the early stages of the diseases, when the differential diagnosis between the two conditions is more challenging. Furthermore, the authors discuss knowledge gaps and unsolved issues in the field.

EXPERT OPINION

Distinguishing ET and PD is crucial for prognostic purposes and appropriate treatment. Additionally, accurate diagnosis is critical for optimizing clinical and experimental research on pathophysiology and innovative therapies. In a few years, integrated technologies could enable accurate, reliable diagnosis from early disease stages or prodromal stages in at-risk populations, but further research combining different techniques is needed.

Loss of the "swallow tail sign" on susceptibility-weighted imaging in the diagnosis of dementia with Lewy bodies: a systematic review and meta-analysis

INTRODUCTION

Loss of dorsolateral nigral hyperintensity (DNH) on iron-sensitive brain MRI is useful for Parkinson's disease detection. DNH loss could also be of diagnostic value in dementia with Lewy bodies (DLB), an a-synuclein-related pathology. We aim to quantitatively synthesize evidence, investigating the role of MRI, a first-line imaging modality, in early DLB detection and differentiation from other dementias.

METHODS

Our study was conducted according to the PRISMA statement. MEDLINE, Scopus, Web of Science, and Cochrane Library were searched using the terms like "dementia with Lewy bodies", "dorsolateral nigral hyperintensity", and "MRI". Only English-written peer-reviewed diagnostic accuracy studies were included. We used QUADAS-2 for quality assessment.

RESULTS

Our search yielded 363 search results. Three studies were eligible, all with satisfying, high quality. The total population of 227 patients included 63 with DLB and 164 with other diseases (Alzheimer disease, frontotemporal dementia, mild cognitive impairment). Using a univariate random-effects logistic regression model, our meta-analysis resulted in pooled sensitivity, specificity and DOR of 0.82 [0.62; 0.92], 0.79 [0.70; 0.86] and 16.26 ([3.3276; 79.4702], p = 0.0006), respectively, for scans with mixed field strength (1.5 and 3 T). Subgroup analysis of 3 T scans showed pooled sensitivity, specificity and DOR of 0.82 [0.61; 0.93], 0.82 [0.72; 0.89] and 18.36 ([4.24; 79.46], p < 0.0001), respectively.

DISCUSSION

DNH loss on iron-sensitive MRI might comprise a supportive biomarker for DLB detection, that could augment the value of the DLB diagnostic criteria. Further evaluation using standardized protocols is needed, as well as direct comparison to other supportive and indicative biomarkers.

Neuromelanin-sensitive magnetic resonance imaging: Possibilities and promises as an imaging biomarker for Parkinson's disease

Parkinson's disease (PD) is an age-related progressive neurodegenerative disorder characterized by both motor and non-motor symptoms resulting from the death of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and noradrenergic neurons in the locus coeruleus (LC). The current diagnosis of PD primarily relies on motor symptoms, often leading to diagnoses in advanced stages, where a significant portion of SNpc dopamine neurons has already succumbed. Therefore, the identification of imaging biomarkers for early-stage PD diagnosis and disease progression monitoring is imperative. Recent studies propose that neuromelanin-sensitive magnetic resonance imaging (NM-MRI) holds promise as an imaging biomarker. In this review, we summarize the latest findings concerning NM-MRI characteristics at various stages in patients with PD and those with atypical parkinsonism. In conclusion, alterations in neuromelanin within the LC are associated with non-motor symptoms and prove to be a reliable imaging biomarker in the prodromal phase of PD. Furthermore, NM-MRI demonstrates efficacy in differentiating progressive supranuclear palsy (PSP) from PD and multiple system atrophy with predominant parkinsonism. The spatial patterns of changes in the SNpc can be indicative of PD progression and aid in distinguishing between PSP and synucleinopathies. We recommend that patients with PD and individuals at risk for PD undergo regular NM-MRI examinations. This technology holds the potential for widespread use in PD diagnosis.

Diagnostic utility of 7T neuromelanin imaging of the substantia nigra in Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that presents a diagnostic challenge due to symptom overlap with other disorders. Neuromelanin (NM) imaging is a promising biomarker for PD, but adoption has been limited, in part due to subpar performance at standard MRI field strengths. We aimed to evaluate the diagnostic utility of ultra-high field 7T NM-sensitive imaging in the diagnosis of PD versus controls and essential tremor (ET), as well as NM differences among PD subtypes. A retrospective case-control study was conducted including PD patients, ET patients, and controls. 7T NM-sensitive 3D-GRE was acquired, and substantia nigra pars compacta (SNpc) volumes, contrast ratios, and asymmetry indices were calculated. Statistical analyses, including general linear models and ROC curves, were employed. Twenty-one PD patients, 13 ET patients, and 18 controls were assessed. PD patients exhibited significantly lower SNpc volumes compared to non-PD subjects. SNpc total volume showed 100% sensitivity and 96.8% specificity (AUC = 0.998) for differentiating PD from non-PD and 100% sensitivity and 95.2% specificity (AUC = 0.996) in differentiating PD from ET. Contrast ratio was not significantly different between PD and non-PD groups (p = 0.07). There was also significantly higher asymmetry index in SNpc volume in PD compared to non-PD cohorts (p < 0.001). NM signal loss in PD predominantly involved the inferior, posterior, and lateral aspects of SNpc. Akinetic-rigid subtype showed more significant NM signal loss compared to tremor dominant subtype (p < 0.001). 7T NM imaging demonstrates potential as a diagnostic tool for PD, including potential distinction between subtypes, allowing improved understanding of disease progression and subtype-related characteristics.

Comparison of automated and manual quantification methods for neuromelanin-sensitive MRI in Parkinson's disease

Neuromelanin-sensitive magnetic resonance imaging quantitative analysis methods have provided promising biomarkers that can noninvasively quantify degeneration of the substantia nigra in patients with Parkinson's disease. However, there is a need to systematically evaluate the performance of manual and automated quantification approaches. We evaluate whether spatial, signal-intensity, or subject specific abnormality measures using either atlas based or manually traced identification of the substantia nigra better differentiate patients with Parkinson's disease from healthy controls using logistic regression models and receiver operating characteristics. Inference was performed using bootstrap analyses to calculate 95% confidence interval bounds. Pairwise comparisons were performed by generating 10,000 permutations, refitting the models, and calculating a paired difference between metrics. Thirty-one patients with Parkinson's disease and 22 healthy controls were included in the analyses. Signal intensity measures significantly outperformed spatial and subject specific abnormality measures, with the top performers exhibiting excellent ability to differentiate patients with Parkinson's disease and healthy controls (balanced accuracy = 0.89; area under the curve = 0.81; sensitivity =0.86; and specificity = 0.83). Atlas identified substantia nigra metrics performed significantly better than manual tracing metrics. These results provide clear support for the use of automated signal intensity metrics and additional recommendations. Future work is necessary to evaluate whether the same metrics can best differentiate atypical parkinsonism, perform similarly in de novo and mid-stage cohorts, and serve as longitudinal monitoring biomarkers.

Simple quantitative planimetric measurement of nigrosome-1 for clinical settings

INTRODUCTION

Loss of MRI hyperintense signal in nigrosome-1 (assessed with susceptibility-weighted imaging) is a biomarker for Parkinson's disease (PD). Current clinical practice involves subjectively rating the appearance of nigrosome-1 which is challenging. The study aimed to test and compare a simple method for quantifying nigrosome-1 with the current subjective rating method.

METHODS

Two experienced neuroradiologists measured area of hyperintense signal in nigrosome-1 (quantitative method) and rated nigrosome-1 appearance (as normal, attenuated, or absent; subjective method) in 42 patients encompassing the full spectrum of nigrosome-1 integrity (21 patients aged 55.5 ± 20.9 years with Essential tremor (ET) and a subset of 21 patients aged 69.6 ± 8.6 years with PD). Neuroradiologists were blinded to each other's measurements, clinical notes, and patient group.

RESULTS

Both methods yielded a significant difference between the groups (PD vs ET; p < 0.001). Pooled (across sides) area of nigrosome-1 hyperintense signal was significantly smaller in the PD group (median = 2.1 mm2, range = 0-15.8 mm2) than ET group (median = 8.3 mm2, range = 0-15.7 mm2; p < 0.001). Inter-rater reliability was high to very high for both methods (subjective: weighted kappa = 0.640, p < 0.001; quantitative: W = 0.733, p = 0.004). Our primary hypothesis that area of nigrosome-1 hyperintense signal exhibits higher inter-rater reliability than subjective rating of nigrosome-1 appearance was not supported.

CONCLUSION

The simple quantitative method, used with subjectively rated nigrosome-1 appearance, may improve confidence in longitudinal clinical reporting, when nigrosome-1 is attenuated. However, further work on the incremental diagnostic value of planimetry and bias, repeatability and reproducibility are needed before it can be recommended in clinical practice.

Quantitative MRI protocol and decision model for a 'one stop shop' early-stage Parkinsonism diagnosis: Study design

Differentiating among early-stage parkinsonisms is a challenge in clinical practice. Quantitative MRI can aid the diagnostic process, but studies with singular MRI techniques have had limited success thus far. Our objective is to develop a multi-modal MRI method for this purpose. In this review we describe existing methods and present a dedicated quantitative MRI protocol, a decision model and a study design to validate our approach ahead of a pilot study. We present example imaging data from patients and a healthy control, which resemble related literature.

Locus coeruleus and substantia nigra neuromelanin magnetic resonance imaging differentiates Parkinson's disease and essential tremor

BACKGROUND

Differential diagnosis of essential tremor (ET) and Parkinson's disease (PD) can still be a challenge in clinical practice. These two tremor disorders may have different pathogenesis related to the substantia nigra (SN) and locus coeruleus (LC). Characterizing neuromelanin (NM) in these structures may help improve the differential diagnosis.

METHODS

Forty-three subjects with tremor-dominant PD (PDTD), 31 subjects with ET, and 30 age- and sex-matched healthy controls were included. All subjects were scanned with NM magnetic resonance imaging (NM-MRI). NM volume and contrast measures for the SN and contrast for the LC were evaluated. Logistic regression was used to calculate predicted probabilities by using the combination of SN and LC NM measures. The discriminative power of the NM measures in detecting subjects with PDTD from ET was assessed with a receiver operative characteristic curve, and the area under the curve (AUC) was calculated.

RESULTS

The NM contrast-to-noise ratio (CNR) of the LC, the NM volume, and CNR of the SN on the right and left sides were significantly lower in PDTD subjects than in ET subjects or healthy controls (all P < 0.05). Furthermore, when combining the best model constructed from the NM measures, the AUC reached 0.92 in differentiating PDTD from ET.

CONCLUSION

The NM volume and contrast measures of the SN and contrast for the LC provided a new perspective on the differential diagnosis of PDTD and ET, and the investigation of the underlying pathophysiology.

Application of Neuromelanin MR Imaging in Parkinson Disease

MRI has been used to develop biomarkers for movement disorders such as Parkinson disease (PD) and other neurodegenerative disorders with parkinsonism such as progressive supranuclear palsy and multiple system atrophy. One of these imaging biomarkers is neuromelanin (NM), whose integrity can be assessed from its contrast and volume. NM is found mainly in certain brain stem structures, namely, the substantia nigra pars compacta (SNpc), the ventral tegmental area, and the locus coeruleus. Another major biomarker is brain iron, which often increases in concert with NM degeneration. These biomarkers have the potential to improve diagnostic certainty in differentiating between PD and other neurodegenerative disorders similar to PD, as well as provide a better understanding of pathophysiology. Mapping NM in vivo has clinical importance for gauging the premotor phase of PD when there is a greater than 50% loss of dopaminergic SNpc melanized neurons. As a metal ion chelator, NM can absorb iron. When NM is released from neurons, it deposits iron into the intracellular tissues of the SNpc; the result is iron that can be imaged and measured using quantitative susceptibility mapping. An increase of iron also leads to the disappearance of the nigrosome-1 sign, another neuroimage biomarker for PD. Therefore, mapping NM and iron changes in the SNpc are a practical means for improving early diagnosis of PD and in monitoring disease progression. In this review, we discuss the functions and location of NM, how NM-MRI is performed, the automatic mapping of NM and iron content, how NM-related imaging biomarkers can be used to enhance PD diagnosis and differentiate it from other neurodegenerative disorders, and potential advances in NM imaging methods. With major advances currently evolving for rapid imaging and artificial intelligence, NM-related biomarkers are likely to have increasingly important roles for enhancing diagnostic capabilities in PD. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 2.

Regional age-related changes of neuromelanin and iron in the substantia nigra based on neuromelanin accumulation and iron deposition

OBJECTIVES

To investigate age-related neuromelanin signal variation and iron content changes in the subregions of substantia nigra (SN) using magnetization transfer contrast neuromelanin-sensitive multi-echo fast field echo sequence in a normal population.

METHODS

In this prospective study, 115 healthy volunteers between 20 and 86 years of age were recruited and scanned using 3.0-T MRI. We manually delineated neuromelanin accumulation and iron deposition regions in neuromelanin image and quantitative susceptibility mapping, respectively. We calculated the overlap region using the two measurements mentioned above. Partial correlation analysis was used to evaluate the correlations between volume, contrast ratio (CR), susceptibility of three subregions of SN, and age. Curve estimation models were used to find the best regression model.

RESULTS

CR increased with age (r = 0.379, p < 0.001; r = 0.371, p < 0.001), while volume showed an age-related decline (r =  -0.559, p < 0.001; r =  -0.410, p < 0.001) in the neuromelanin accumulation and overlap regions. Cubic polynomial regression analysis found a small increase in neuromelanin accumulation volume with age until 34, followed by a significant decrease until the 80 s (R² = 0.358, p < 0.001). No significant correlations were found between susceptibility and age in any subregion. No correlation was found between CR and susceptibility in the overlap region.

CONCLUSIONS

Our results indicated that CR increased with age, while volume showed an age-related decline in the overlap region. We further found that the neuromelanin accumulation region volume increased until the 30 s and decreased into the 80 s. This study may provide a reference for future neurodegenerative elucidations of substantia nigra.

KEY POINTS

• Our results define the regional changes in neuromelanin and iron in the substantia nigra with age in the normal population, especially in the overlap region. • The contrast ratio increased with age in the neuromelanin accumulation and overlap regions, and volume showed an age-related decline, while contrast ratio and volume do not affect each other indirectly. • The contrast ratio of hyperintense neuromelanin in the overlap region was unaffected by iron content.

Iron- and Neuromelanin-Weighted Neuroimaging to Study Mitochondrial Dysfunction in Patients with Parkinson's Disease

The underlying causes of Parkinson's disease are complex, and besides recent advances in elucidating relevant disease mechanisms, no disease-modifying treatments are currently available. One proposed pathophysiological hallmark is mitochondrial dysfunction, and a plethora of evidence points toward the interconnected nature of mitochondria in neuronal homeostasis. This also extends to iron and neuromelanin metabolism, two biochemical processes highly relevant to individual disease manifestation and progression. Modern neuroimaging methods help to gain in vivo insights into these intertwined pathways and may pave the road to individualized medicine in this debilitating disorder. In this narrative review, we will highlight the biological rationale for studying these pathways, how distinct neuroimaging methods can be applied in patients, their respective limitations, and which challenges need to be overcome for successful implementation in clinical studies.

Nigrosome and Neuromelanin Imaging as Tools to Differentiate Parkinson's Disease and Parkinsonism

Parkinson's disease (PD) lacks a definitive diagnosis due to a lack of pathological validation of patients at antemortem. The risk of misdiagnosis is high in the early stages of PD, often eluded by atypical parkinsonian symptoms. Neuroimaging and laboratory biomarkers are being sought to aid in the clinical diagnosis of PD. Nigrosome imaging and neuromelanin (NM)-sensitive magnetic resonance imaging (MRI) are the new emerging tools, both technically simple plus cost-effective for studying nigral pathology, and have shown potential for authenticating the clinical diagnosis of PD. Visual assessment of the nigrosome-1 appearance, at 3 or 7 Tesla, yields excellent diagnostic accuracy for differentiating idiopathic PD from healthy controls. Moreover, midbrain atrophy and putaminal hypointensity in nigrosome-1 imaging are valid pointers in distinguishing PD from allied parkinsonian disorders. The majority of studies employed T2 and susceptibility-weighted imaging MRI sequences to visualize nigrosome abnormalities, whereas T1-weighted fast-spin echo sequences were used for NM imaging. The diagnostic performance of NM-sensitive MRI in discriminating PD from normal HC can be improved further. Longitudinal studies with adequate sampling of varied uncertain PD cases should be designed to accurately evaluate the sensitivity and diagnostic potential of nigrosome and NM imaging techniques. Equal weightage is to be given to uniformity and standardization of protocols, data analysis, and interpretation of results. There is tremendous scope for identifying disease-specific structural changes in varied forms of parkinsonism with these low-cost imaging tools. Nigrosome-1 and midbrain NM imaging may not only provide an accurate diagnosis of PD but could mature into tools for personally tailored treatment and prognosis.

Image-guided/improved diseases management: From immune-strategies and beyond

Timely and accurate assessment and diagnosis are extremely important and beneficial for all diseases, especially for some of the major human disease, such as cancers, cardiovascular diseases, infectious diseases, and neurodegenerative diseases. Limited by the variable disease microenvironment, early imperceptible symptoms, complex immune system interactions, and delayed clinical phenotypes, disease diagnosis and treatment are difficult in most cases. Molecular imaging (MI) techniques can track therapeutic drugs and disease sites in vivo and in vitro in a non-invasive, real-time and visible strategies. Comprehensive visual imaging and quantitative analysis based on different levels can help to clarify the disease process, pathogenesis, drug pharmacokinetics, and further evaluate the therapeutic effects. This review summarizes the application of different MI techniques in the diagnosis and treatment of these major human diseases. It is hoped to shed a light on the development of related technologies and fields.

An Updated Overview of the Magnetic Resonance Imaging of Brain Iron in Movement Disorders

Brain iron load is one of the most important neuropathological hallmarks in movement disorders. Specifically, the iron provides most of the paramagnetic metal signals in the brain and its accumulation seems to play a key role, although not completely explained, in the degeneration of the basal ganglia, as well as other brain structures. Moreover, iron distribution patterns have been implicated in depicting different movement disorders. This work reviewed current literature on Magnetic Resonance Imaging for Brain Iron Detection and Quantification (MRI-BIDQ) in neurodegenerative processes underlying movement disorders.

Multimodal brain and retinal imaging of dopaminergic degeneration in Parkinson disease

Parkinson disease (PD) is a progressive disorder characterized by dopaminergic neurodegeneration in the brain. The development of parkinsonism is preceded by a long prodromal phase, and >50% of dopaminergic neurons can be lost from the substantia nigra by the time of the initial diagnosis. Therefore, validation of in vivo imaging biomarkers for early diagnosis and monitoring of disease progression is essential for future therapeutic developments. PET and single-photon emission CT targeting the presynaptic terminals of dopaminergic neurons can be used for early diagnosis by detecting axonal degeneration in the striatum. However, these techniques poorly differentiate atypical parkinsonian syndromes from PD, and their availability is limited in clinical settings. Advanced MRI in which pathological changes in the substantia nigra are visualized with diffusion, iron-sensitive susceptibility and neuromelanin-sensitive sequences potentially represents a more accessible imaging tool. Although these techniques can visualize the classic degenerative changes in PD, they might be insufficient for phenotyping or prognostication of heterogeneous aspects of PD resulting from extranigral pathologies. The retina is an emerging imaging target owing to its pathological involvement early in PD, which correlates with brain pathology. Retinal optical coherence tomography (OCT) is a non-invasive technique to visualize structural changes in the retina. Progressive parafoveal thinning and fovea avascular zone remodelling, as revealed by OCT, provide potential biomarkers for early diagnosis and prognostication in PD. As we discuss in this Review, multimodal imaging of the substantia nigra and retina is a promising tool to aid diagnosis and management of PD.

Visual analysis of nigrosome-1 in the differential diagnosis of Parkinson's disease and essential tremor

Differentiation between Parkinson’s disease, especially in its early stages, and essential tremor, which is a phenotypically similar movement disorder, still remains an unsolved challenge for neurology. The aim of this study was to assess the diagnostic significance of nigrosome imaging (nigrosomes are dopaminergic neuron clusters in the substantia nigra of the midbrain) using 3T high-resolution SW-MRI. The study was conducted in 20 patients with Parkinson’s disease and 10 patients with essential tremor. Visual analysis of the acquired nigrosome-1 images was performed using a 4-point ordinal rating scale. Differences in sex, age and duration of the disease were calculated using the Fisher exact test and the Mann–Whitney U test. The diagnostic value of the method was assessed using Pearson’s chisquared test. Nigrosome-1 was bilaterally or unilaterally absent in 70% of parkinsonian patients. Less specific changes to the substantia nigra (SN) were observed in two more parkinsonian patients (10%), whose nigrosome-1 appeared reduced in size. By contrast, nigrosome-1 was bilaterally intact in all patients (100%) with essential tremor (p < 0.001). Our preliminary findings demonstrate the high potential of noninvasive nigrosome-1 imaging in the differential diagnosis of Parkinson’s disease and essential tremor.

Imaging the Pathophysiology of Essential Tremor-A Systematic Review

Background: The pathophysiology underlying essential tremor (ET) still is poorly understood. Recent research suggests a pivotal role of the cerebellum in tremor genesis, and an ongoing controversy remains as to whether ET constitutes a neurodegenerative disorder. In addition, mounting evidence indicates that alterations in the gamma-aminobutyric acid neurotransmitter system are involved in ET pathophysiology. Here, we systematically review structural, functional, and metabolic neuroimaging studies and discuss current concepts of ET pathophysiology from an imaging perspective.

Methods: We conducted a PubMed and Scopus search from 1966 up to December 2020, entering essential tremor in combination with any of the following search terms and their corresponding abbreviations: positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and gamma-aminobutyric acid (GABA).

Results: Altered functional connectivity in the cerebellum and cerebello-thalamico-cortical circuitry is a prevalent finding in functional imaging studies. Reports from structural imaging studies are less consistent, and there is no clear evidence for cerebellar neurodegeneration. However, diffusion tensor imaging robustly points toward microstructural cerebellar changes. Radiotracer imaging suggests that the dopaminergic axis is largely preserved in ET. Similarly, measurements of nigral iron content and neuromelanin are unremarkable in most studies; this is in contrast to Parkinson's disease (PD). PET and MRS studies provide limited evidence for cerebellar and thalamic GABAergic dysfunction.

Conclusions: There is robust evidence indicating that the cerebellum plays a key role within a multiple oscillator tremor network which underlies tremor genesis. However, whether cerebellar dysfunction relies on a neurodegenerative process remains unclear. Dopaminergic and iron imaging do not suggest a substantial overlap of ET with PD pathophysiology. There is limited evidence for alterations of the GABAergic neurotransmitter system in ET. The clinical, demographical, and genetic heterogeneity of ET translates into neuroimaging and likely explains the various inconsistencies reported.

Measuring the iron content of dopaminergic neurons in substantia nigra with MRI relaxometry

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Dopaminergic neurons dominate effective transverse relaxation in nigrosome 1.

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Ion beam microscopy reveals highest iron concentrations in dopaminergic neurons.

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Developed biophysical model links MRI parameters to cellular iron content.

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Ferritin- and neuromelanin-bound iron impact MRI parameters differently.

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Quantitative MRI provides a potential biomarker of iron in dopaminergic neurons.

In Parkinson’s disease, the depletion of iron-rich dopaminergic neurons in nigrosome 1 of the substantia nigra precedes motor symptoms by two decades. Methods capable of monitoring this neuronal depletion, at an early disease stage, are needed for early diagnosis and treatment monitoring. Magnetic resonance imaging (MRI) is particularly suitable for this task due to its sensitivity to tissue microstructure and in particular, to iron. However, the exact mechanisms of MRI contrast in the substantia nigra are not well understood, hindering the development of powerful biomarkers. In the present report, we illuminate the contrast mechanisms in gradient and spin echo MR images in human nigrosome 1 by combining quantitative 3D iron histology and biophysical modeling with quantitative MRI on post mortem human brain tissue. We show that the dominant contribution to the effective transverse relaxation rate (R2*) in nigrosome 1 originates from iron accumulated in the neuromelanin of dopaminergic neurons. This contribution is appropriately described by a static dephasing approximation of the MRI signal. We demonstrate that the R2* contribution from dopaminergic neurons reflects the product of cell density and cellular iron concentration. These results demonstrate that the in vivo monitoring of neuronal density and iron in nigrosome 1 may be feasible with MRI and provide directions for the development of biomarkers for an early detection of dopaminergic neuron depletion in Parkinson’s disease.

Imaging the Substantia Nigra in Parkinson Disease and Other Parkinsonian Syndromes

Parkinson disease is characterized by dopaminergic cell loss in the substantia nigra of the midbrain. There are various imaging markers for Parkinson disease. Recent advances in MRI have enabled elucidation of the underlying pathophysiologic changes in the nigral structure. This has contributed to accurate and early diagnosis and has improved disease progression monitoring. This article aims to review recent developments in nigral imaging for Parkinson disease and other parkinsonian syndromes, including nigrosome imaging, neuromelanin imaging, quantitative iron mapping, and diffusion-tensor imaging. In particular, this article examines nigrosome imaging using 7-T MRI and 3-T susceptibility-weighted imaging. Finally, this article discusses volumetry and its clinical importance related to symptom manifestation. This review will improve understanding of recent advancements in nigral imaging of Parkinson disease. Published under a CC BY 4.0 license.

MRI Signs of Parkinson's Disease and Atypical Parkinsonism

BACKGROUND

 Diagnosis of Parkinson's disease and atypical parkinsonism is based on clinical evaluation of the patient's symptoms and on magnetic resonance imaging (MRI) of the brain, which can be supplemented by nuclear medicine techniques. MRI plays a leading role in the differentiation between Parkinson's disease and atypical parkinsonism. While atypical parkinsonism is characterized by relatively specific MRI signs, imaging of Parkinson's disease previously lacked such signs. However, high-field MRI and new optimized MRI sequences now make it possible to define specific MRI signs of Parkinson's disease and have significant potential regarding differentiated imaging, early diagnosis, and imaging of disease progression.

METHODS

 PubMed was selectively searched for literature regarding the definition and discussion of specific MRI signs of Parkinson's disease, as well as the most common types of atypical parkinsonism with a leading motor component. No time frame was set, but the search was particularly focused on current literature.

RESULTS

 This review article discusses the different MRI signs of Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy. The pathogenesis of the MRI signs is described, and imaging examples are given. The technical aspects of image acquisition are briefly defined, and the different signs are discussed and compared with regard to their diagnostic significance according to current literature.

CONCLUSION

 The MRI signs of Parkinson's disease, which can be defined with high-field MRI and new optimized MRI sequences, enable differentiated structural image interpretation and consecutive diagnostic workup. Despite the fact that the signs are in need of further validation by bigger studies, they have the potential to achieve significant diagnostic relevance regarding the imaging of Parkinson's disease and atypical parkinsonism.

KEY POINTS

  · High-field MRI and specialized sequences make it possible to define specific MRI signs for neurodegenerative disorders. · Cerebral alterations can be detected in prodromal stages of Parkinson's disease. · The combination of specific MRI signs makes it possible to differentiate between Parkinson's disease and atypical parkinsonism.

CITATION FORMAT

· Aludin S, Schmill LA. MRI Signs of Parkinson's Disease and Atypical Parkinsonism. Fortschr Röntgenstr 2021; DOI: 10.1055/a-1460-8795.

Neuroimaging Assessment of Nigrosome 1 with a Multiecho Gre Magnetic Resonance Sequence in the Differentiation Between Parkinsons Disease from Essential Tremor and Healthy Individuals

Background and purpose

Parkinsonism is commonly seen in many clinical conditions, and the establishment of its etiology may take many years. The possible development of neuroprotective treatments for Parkinsons disease (PD) in the near future will require correct and early diagnosis. This study aims to analyze the accuracy of a low-cost MRI sequence to differentiate PD from patients with essential tremor (ET) and healthy control (HC) individuals.

Material and methods

We recruited 70 individuals with clinical diagnoses of PD (38 patients), ET (11 patients) and healthy volunteers (21 individuals), all of whom underwent 3T MRI multiecho GRE sequence. Two blinded neuroradiologists independently evaluated the presence or absence of nigrosome-1(N1). We considered the unilateral or bilateral absence of nigrosome 1 signal as indicative of PD.

Results

The absence of at least one N1 could differentiate with 98% accuracy patients with clinical established PD from healthy controls. The presence of both nigrosomes was 96% accurate as a sign to differentiate PD from ET patients.

Conclusion

The 3T MRI with multiecho GRE is a simple and universally available technique and it can be used as a good auxiliary tool to differentiate PD from ET patients and controls.

Imaging of the dopamine system with focus on pharmacological MRI and neuromelanin imaging

The dopamine system in the brain is involved in a variety of neurologic and psychiatric disorders, such as Parkinson's disease, attention-deficit/hyperactivity disorder and psychosis. Different aspects of the dopamine system can be visualized and measured with positron emission tomography (PET) and single photon emission computed tomography (SPECT), including dopamine receptors, dopamine transporters, and dopamine release. New developments in MR imaging also provide proxy measures of the dopamine system in the brain, offering alternatives with the advantages MR imaging, i.e. no radiation, lower costs, usually less invasive and time consuming. This review will give an overview of these developments with a focus on the most developed techniques: pharmacological MRI (phMRI) and neuromelanin sensitive MRI (NM-MRI). PhMRI is a collective term for functional MRI techniques that administer a pharmacological challenge to assess its effects on brain hemodynamics. By doing so, it indirectly assesses brain neurotransmitter function such as dopamine function. NM-MRI is an upcoming MRI technique that enables in vivo visualization and semi-quantification of neuromelanin in the substantia nigra. Neuromelanin is located in the cell bodies of dopaminergic neurons of the nigrostriatal pathway and can be used as a proxy measure for long term dopamine function or degeneration of dopaminergic neurons. Both techniques are still primarily used in clinical research, but there is promise for clinical application, in particular for NM-MRI in dopaminergic neurodegenerative diseases like Parkinson's disease.

Evaluation of the Swallow-Tail Sign and Correlations of Neuromelanin Signal with Susceptibility and Relaxations

The presence of a swallow-tail sign in the nigrosome-1 with hyperintense signal shown on the susceptibility-weighted imaging (SWI) has been shown to be sensitive in detecting the abnormal iron deposits in this area. A systematic evaluation in healthy subjects is required before this tool can be recommended in a widespread application. We evaluated a simple and practical SWI approach using a multiecho gradient-echo sequence with an improved contrast-to-noise ratio (CNR). We also evaluated the association of the neuromelanin imaging contrast behavior with the susceptibility and relaxation measurements. Twenty-five older and 23 young healthy adults were evaluated. The CNRs of the nigrosome-1 were compared along with method and group. Correlations of the nigrosome-1 neuromelanin signal in the neuromelanin-sensitive imaging with CNRs in the susceptibility, T1 and T2 mappings were examined. Two different coils were used to confirm the reproducibility. Compared with the single-echo, multiecho SWI can improve the CNR of the swallow-tail sign. We found significant correlations between neuromelanin signal and CNRs in the susceptibility and T2 mappings, and T1 value. The older subjects exhibited increased CNRs compared with the young adults. No significant difference was observed in the measurements between 20 and 64 channels. The multiecho technique allows the high-quality nigrosome-1 images in SWI and allows for a joint analysis of T2* and quantitative-susceptibility mapping at high spatial resolution. The correlations of neuromelanin-sensitive imaging with susceptibility and T2 imply that the iron content in the nigrosome-1 may have significant influences on the hyperintensity of neuromelanin in the magnetization transfer-related contrast.

No evidence of iron deposition in essential tremor: a susceptibility-weighted imaging study

OBJECTIVE

To evaluate the role of iron deposition in subcortical nuclei of patients with essential tremor (ET).

METHODS

Twenty-three patients with ET underwent a standardized 3T-MRI protocol. We specifically assessed iron deposition using susceptibility-weighted angiography (SWAN) images in seven specific regions of interest (ROIs): the thalamus, putamen, globus pallidus, caudate nucleus, substantia nigra, red nucleus, and dentate nucleus. Tremor in ET patients was clinically assessed using the Fahn-Tolosa-Marin Tremor Rating Scale (FTM-TRS). ET patient data were compared with data obtained from 23 Parkinson's disease (PD) patients and 14 healthy subjects (HS).

RESULTS

No differences in iron deposition in the seven ROIs were found between ET patients and HS. Conversely, PD patients showed increased iron deposition in the substantia nigra in comparison with both ET patients and HS.

CONCLUSIONS

Our results indicate the absence of iron deposition in subcortical nuclei of ET patients, which is generally considered a marker of neurodegeneration.

Quick MR Neuromelanin Imaging Using a Chemical Shift Selective Pulse

Not only magnetization transfer contrast (MTC) pulse, but also chemical shift selective (CHESS) pulse would be a useful additional one for shortening the scan time of neuromelanin imaging. We compared three sequences among turbo-spin echo (TSE) images with CHESS, MTC, and without an additional pulse in the same short time, 3 min 20 s. The TSE with CHESS image was the most useful for the diagnosis of neuromelanin within the limited time.

Swallow tail sign on susceptibility map-weighted imaging (SMWI) for disease diagnosing and severity evaluating in parkinsonism

BACKGROUND

Loss of swallow tail sign (STS) on iron-sensitive magnetic resonance imaging (MRI) has been recognized as an imaging feature in parkinsonism (PS).

PURPOSE

To investigate the diagnostic and differential diagnostic value of STS scale on susceptibility map-weighted imaging (SMWI) in PS, including Parkinson's disease (PD), progressive supranuclear palsy syndrome (PSP), and multiple system atrophy (MSA), and to evaluate its correlation with disease severity.

MATERIAL AND METHODS

Ninety-nine patients (55 PD, 29 PSP, and 15 MSA) and 47 healthy controls (HC) were prospectively recruited and scanned using quantitative susceptibility mapping (QSM). STS was visually assessed on SMWI derived from QSM. STS scale in the range of 0-4 at participant level was calculated by summing bilateral STS scores (0-2). We used receiver operating characteristic analysis of STS scale for evaluating the diagnostic power of parkinsonism and Spearman's correlation for assessing disease severity.

RESULTS

Frequency distribution of STS scale was significantly different in parkinsonism and HC groups, and among PD, PSP, and MSA subgroups. STS scale ≤3 could distinguish parkinsonism from HC with high accuracy (91.78%), PD from HC (91.18%), and MSA from HC (88.71%). STS scale ≤2 could distinguish PSP from HC (96.05%). STS scale = 0 could distinguish PSP from PD (70.24%) and PSP from MSA (72.73%). STS scale was negatively correlated with H-Y stage (P = 0.007, r = -0.359) and duration of disease (P = 0.006, r = -0.367) in PD patients.

CONCLUSION

STS scale on SMWI may serve as a useful imaging biomarker for diagnosis of parkinsonism and disease progression evaluation in PD.

Diagnostic performance of loss of nigral hyperintensity on susceptibility-weighted imaging in parkinsonism: an updated meta-analysis

OBJECTIVES

To evaluate diagnostic performance of loss of nigral hyperintensity on SWI in differentiating idiopathic Parkinson's disease (IPD) or primary parkinsonism (including IPD and Parkinson-plus syndrome) from healthy/disease controls.

METHODS

MEDLINE/PubMed and EMBASE databases were searched to identify original articles investigating the diagnostic performance of loss of nigral hyperintensity for differentiating IPD or primary parkinsonism from healthy/disease control, up to April 3, 2020. Pooled sensitivity and specificity were calculated using a bivariate random-effects model. The proportion of nondiagnostic scan, inter- and intrareader agreement, and the proportion of concordance between clinical laterality and imaging asymmetry were also pooled.

RESULTS

Nineteen articles covering 2125 patients (1097 with primary parkinsonism, 1028 healthy/disease controls) were included. For discrimination between IPD and healthy/disease controls, pooled sensitivity and specificity were 0.96 (95% CI, 0.91-0.98) and 0.95 (95% CI, 0.92-0.97). For discrimination between primary parkinsonism and healthy/disease controls, pooled sensitivity and specificity were 0.87 (95% CI, 0.75-0.94) and 0.93 (95% CI, 0.85-0.97). The pooled proportion of non-diagnostic scans on random-effects modeling was 4.2% (95% CI, 2.5-6.9%). The inter- and intrareader agreements were almost perfect, with the pooled coefficients being 0.84 (95% CI, 0.78-0.89) and 0.96 (95% CI, 0.89-0.99), respectively. The pooled proportion of concordant cases was 69.3% (95% CI, 58.4-78.4%).

CONCLUSIONS

Loss of nigral hyperintensity on SWI can differentiate IPD or primary parkinsonism from a healthy/disease control group with high accuracy. However, the proportion of non-diagnostic scans is not negligible and must be taken into account.

KEY POINTS

• For discrimination between idiopathic Parkinson's disease and healthy/disease controls, pooled sensitivity and specificity of loss of nigral hyperintensity were 0.96 and 0.95. • For discrimination between primary parkinsonism and healthy/disease controls, pooled sensitivity and specificity of loss of nigral hyperintensity were 0.87 and 0.93. • The pooled proportion of non-diagnostic scans on random-effects modeling was 4.2%.

Fast 3 T nigral hyperintensity magnetic resonance imaging in Parkinson's disease

The absence of nigral hyperintensity is a promising MR marker for Parkinson’s disease (PD), but its small size imposes limitations on its routine use. Our aim was to compare Multi Echo Data Image Combination (MEDIC), segmented echo-planar imaging (EPISEG) and fluid-attenuated inversion recovery (FLAIR) sequences, as well as both magnitude (MAG) and susceptibility-weighted imaging (SWI) reconstructions of single-echo gradient echo for nigral hyperintensity imaging. Twenty-five healthy and twenty PD subjects were included. Sensitivity to motion artefacts, confidence of the radiologist in interpretation, rate of nondiagnostic scans and diagnostic accuracy were assessed. EPISEG was less motion-sensitive than MEDIC, MAG, and SWI, while FLAIR was less motion-sensitive than MAG and SWI. The reviewers were more confident when using EPISEG compared to any other techniques and MEDIC was superior to FLAIR. The proportions of nondiagnostic scans were lower for EPISEG than for other sequences. The best diagnostic performance was achieved for EPISEG (sensitivity = 65%, specificity = 96%). Using EPISEG, the absence of nigral hyperintensity in PD was associated with higher Hoehn-Yahr stage and MDS-UPDRS II + III. Nigral hyperintensity may be intact at the very early stages of PD. The promising properties of EPISEG may help the transfer of nigral hyperintensity imaging into daily clinical practice.

Advances in multimodal data fusion in neuroimaging: Overview, challenges, and novel orientation

Multimodal fusion in neuroimaging combines data from multiple imaging modalities to overcome the fundamental limitations of individual modalities. Neuroimaging fusion can achieve higher temporal and spatial resolution, enhance contrast, correct imaging distortions, and bridge physiological and cognitive information. In this study, we analyzed over 450 references from PubMed, Google Scholar, IEEE, ScienceDirect, Web of Science, and various sources published from 1978 to 2020. We provide a review that encompasses (1) an overview of current challenges in multimodal fusion (2) the current medical applications of fusion for specific neurological diseases, (3) strengths and limitations of available imaging modalities, (4) fundamental fusion rules, (5) fusion quality assessment methods, and (6) the applications of fusion for atlas-based segmentation and quantification. Overall, multimodal fusion shows significant benefits in clinical diagnosis and neuroscience research. Widespread education and further research amongst engineers, researchers and clinicians will benefit the field of multimodal neuroimaging.

Comparison of susceptibility-weighted imaging and susceptibility map-weighted imaging for the diagnosis of Parkinsonism with nigral hyperintensity

OBJECTIVE

To determine whether susceptibility map-weighted imaging (SMWI) was superior to conventional susceptibility-weighted imaging (SWI) in the diagnosis of Parkinson's disease (PD) and in its correlation with ¹²³I-2bcarbomethoxy-3b-(4-iodophenyl)-N-(3-fluoropropyl)-nortropane single photon emission computerized tomography (¹²³I-FP-CIT SPECT).

METHODS

Between May 2017 and February 2018, 125 consecutive patients diagnosed with idiopathic PD, vascular pseudoparkinsonism, essential tremor, or drug-induced parkinsonism and who underwent ¹²³I-FP-CIT SPECT imaging and 3 T SWI on the same day or within 3 months were included in this retrospective study. In all patients, SMWI images were generated from SWI images. On both MRIs, two neuroradiologists independently evaluated the status of nigral hyperintensity on each side of substantia nigra. Inter-observer agreements for the nigral hyperintensity were tested. Using consensus reading, concordance between SWI, SMWI, and ¹²³I-FP-CIT SPECT were evaluated, and the diagnostic performance between SWI and SMWI for PD was compared.

RESULTS

Inter-observer agreement for the nigral hyperintensity was higher for SMWI (right, κ = 0.919; left, κ = 0.984) than for SWI (right, κ = 0.918; left, κ = 0.902). SMWI (right 67.2 %, left 68.0 %) showed a higher concordance rate with the results of ¹²³I-FP-CIT SPECT than SWI (right 60.0 %, left 59.2 %). SMWI (area under curve [AUC], 0.791) provided significantly higher diagnostic performance for PD than SWI (AUC, 0.720; P = 0.0005).

CONCLUSION

SMWI may be a superior assessment tool for nigral hyperintensity than SWI and may be an improved diagnostic imaging modality for patients with suspected PD.

Diagnostic performance of neuromelanin-sensitive magnetic resonance imaging for patients with Parkinson's disease and factor analysis for its heterogeneity: a systematic review and meta-analysis

OBJECTIVE

To determine the diagnostic performance of neuromelanin-sensitive magnetic resonance imaging discriminating between patients with Parkinson's disease and normal healthy controls and to identify factors causing heterogeneity influencing the diagnostic performance.

METHODS

A systematic literature search in the Ovid-MEDLINE and EMBASE databases was performed for studies reporting the relevant topic before February 17, 2020. The pooled sensitivity and specificity values with their 95% confidence intervals were calculated using bivariate random-effects modeling. Subgroup and meta-regression analyses were also performed to determine factors influencing heterogeneity.

RESULTS

Twelve articles including 403 patients with Parkinson's disease and 298 control participants were included in this systematic review and meta-analysis. Neuromelanin-sensitive magnetic resonance imaging showed a pooled sensitivity of 89% (95% confidence interval, 86-92%) and a pooled specificity of 83% (95% confidence interval, 76-88%). In the subgroup and meta-regression analysis, a disease duration longer than 5 and 10 years, comparisons using measured volumes instead of signal intensities, a slice thickness in terms of magnetic resonance imaging parameters of more than 2 mm, and semi-/automated segmentation methods instead of manual segmentation improved the diagnostic performance.

CONCLUSION

Neuromelanin-sensitive magnetic resonance imaging had a favorable diagnostic performance in discriminating patients with Parkinson's disease from healthy controls. To improve diagnostic accuracy, further investigations directly comparing these heterogeneity-affecting factors and optimizing these parameters are necessary.

KEY POINTS

• Neuromelanin-sensitive MRI favorably discriminates patients with Parkinson's disease from healthy controls. • Disease duration, parameters used for comparison, magnetic resonance imaging slice thickness, and segmentation methods affected heterogeneity across the studies.

Parkinson's Disease: Available Clinical and Promising Omics Tests for Diagnostics, Disease Risk Assessment, and Pharmacotherapy Personalization

Parkinson's disease is the second most frequent neurodegenerative disease, representing a significant medical and socio-economic problem. Modern medicine still has no answer to the question of why Parkinson's disease develops and whether it is possible to develop an effective system of prevention. Therefore, active work is currently underway to find ways to assess the risks of the disease, as well as a means to extend the life of patients and improve its quality. Modern studies aim to create a method of assessing the risk of occurrence of Parkinson's disease (PD), to search for the specific ways of correction of biochemical disorders occurring in the prodromal stage of Parkinson's disease, and to personalize approaches to antiparkinsonian pharmacotherapy. In this review, we summarized all available clinically approved tests and techniques for PD diagnostics. Then, we reviewed major improvements and recent advancements in genomics, transcriptomics, and proteomics studies and application of metabolomics in PD research, and discussed the major metabolomics findings for diagnostics and therapy of the disease.

Essential tremor: New advances

Background

Essential Tremor (ET) is one of the most common movement disorders but many controversies still exist in regards to its definition and pathophysiology. In view of the recent published criteria by the Tremor Task Force of the International Parkinson's and Movement Disorders Society (IPMDS), we intended to analyze if this has changed our view of ET and if new developments have arisen since.

Methods

A Medline search for English-written articles was done on June 15, 2019 using the keyword "Essential Tremor". Publications from November 2017 (publication date of the new tremor classification) were taken into account. Reviews, letters and original studies relevant to the subject were selected and reviewed according to the following themes: clinical characteristics, epidemiology, genetics, pathology, biomarkers and treatment.

Results

Out of 132 publications the most relevant articles were selected and reviewed (total of 65 articles). The great majority of these studies focused on surgical treatments (new targets, new technologies) while relatively few articles addressed epidemiology, pathology and pathophysiology.

Conclusions

The use of the new classification is not commonly used still, excepting more recent studies on therapeutics. This is in keeping with diverse opinions and criticisms reported by the IPMDS task force members themselves. One important change has been validating ET as a heterogeneous condition and defining the ET-plus category. We propose a further sub-group classification derived from the new definition of ET-plus.

Biomarkers for Parkinson's Disease: How Good Are They?

Parkinson's disease (PD) is a complex neurodegenerative disorder with no cure in sight. Clinical challenges of the disease include the inability to make a definitive diagnosis at the early stages and difficulties in predicting the disease progression. The unmet demand to identify reliable biomarkers for early diagnosis and management of the disease course of PD has attracted a lot of attention. However, only a few reported candidate biomarkers have been tried in clinical practice at the present time. Studies on PD biomarkers have often overemphasized the discovery of novel identity, whereas efforts to further evaluate such candidates are rare. Therefore, we update the new development of biomarker discovery in PD and discuss the standard process in the evaluation and assessment of the diagnostic or prognostic value of the identified potential PD biomarkers in this review article. Recent developments in combined biomarkers and the current status of clinical trials of biomarkers as outcome measures are also discussed. We believe that the combination of different biomarkers might enhance the specificity and sensitivity over a single measure that might not be sufficient for such a multiplex disease.

Crosstalk between Nrf2 signaling and mitochondrial function in Parkinson's disease

Search for a definitive cure for neurodegenerative disorders like Parkinson's disease (PD) has met with little success. Mitochondrial dysfunction and elevated oxidative stress precede characteristic loss of dopamine-producing neurons from the midbrain in PD. The majority of PD cases are classified as sporadic (sPD) with an unknown etiology, whereas mutations in a handful of genes cause monogenic form called familial (fPD). Both sPD and fPD is characterized by proteinopathy and mitochondrial dysfunction leading to increased oxidative stress. These pathophysiological mechanisms create a vicious cycle feeding into each other, ultimately tipping the neurons to its demise. Effect of iron accumulation and dopamine oxidation adds an additional dimension to mitochondrial oxidative stress and apoptotic pathways affected. Nrf2 is a redox-sensitive transcription factor which regulates basal as well as inducible expression of antioxidant enzymes and proteins involved in xenobiotic detoxification. Recent advances, however, shows a multifaceted role for Nrf2 in the regulation of genes connected with inflammatory response, metabolic pathways, protein homeostasis, iron management, and mitochondrial bioenergetics. Here we review the role of mitochondria and oxidative stress in the PD etiology and the potential crosstalk between Nrf2 signaling and mitochondrial function in PD. We also make a case for the development of therapeutics that safely activates Nrf2 pathway in halting the progression of neurodegeneration in PD patients.