Dopamine transporter imaging with [18F]FE-PE2I PET and [123I]FP-CIT SPECT-a clinical comparison

Clinical assessment and striatal dopaminergic activity in healthy controls and patients with Parkinson's disease: a Bayesian approach

OBJECTIVES

We aimed to evaluate correlations between striatal dopamine transporter (DAT) uptake and clinical assessments in both patients with Parkinson's disease (PD) and healthy controls.

METHODS

This study enrolled 193 healthy controls, and 581 patients with PD. They underwent various clinical assessments and 123I-FP-CIT SPECT scans. After reconstruction, attenuation correction, and normalization of SPECT images, counts were measured from the bilateral caudate and putamen, and the occipital cortex for reference. Count densities for each region were extracted and used to calculate striatal binding ratios (SBRs) for each striatal region. SBR is calculated as (target region/reference region)-1. After logarithmic transformation of striatal SBRs, we analyzed the effects of clinical assessments on striatal SBRs using Bayesian hierarchical modeling.

RESULTS

MDS-UPDRS total score, part I, part II, part III, Epworth Sleepiness Scale, REM sleep behavior disorder screening questionnaire, SCOPA-AUT total score were negatively associated with striatal SBR in patients with PD. Also, HVLT recognition discrimination was positively associated with striatal SBR in both healthy controls and patients with PD. In healthy control, MDS-UPDRS part II, MOCA, SCOPA-AUT total score were positively associated with striatal SBR.

CONCLUSION

We demonstrated that motor symptom, sleep disturbance, autonomic symptom, and cognition of patients with PD were associated with striatal dopaminergic activity. In healthy controls, motor symptoms, autonomic symptom, and cognition were associated with striatal dopaminergic activity, some of which showing the opposite direction with patients with PD. This result might provide new insight to underlying mechanism of dopamine system with motor and non-motor assessments.

Positron Emission Tomography Imaging of Synaptic Dysfunction in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases with a complex pathogenesis. Aggregations formed by abnormal deposition of alpha-synuclein (αSyn) lead to synapse dysfunction of the dopamine and non-dopamine systems. The loss of dopaminergic neurons and concomitant alterations in non-dopaminergic function in PD constitute its primary pathological manifestation. Positron emission tomography (PET), as a representative molecular imaging technique, enables the non-invasive visualization, characterization, and quantification of biological processes at cellular and molecular levels. Imaging synaptic function with PET would provide insights into the mechanisms underlying PD and facilitate the optimization of clinical management. In this review, we focus on the synaptic dysfunction associated with the αSyn pathology of PD, summarize various related targets and radiopharmaceuticals, and discuss applications and perspectives of PET imaging of synaptic dysfunction in PD.

GMP production of [18F]FE-PE2I on a TRACERLab FX2 N synthesis module, a radiotracer for in vivo PET imaging of the dopamine transport

BACKGROUND

Parkinson's disease is a neurodegenerative disorder that is characterized by a degeneration of the dopaminergic system. Dopamine transporter (DAT) positron emission tomography (PET) imaging has emerged as a powerful and non-invasive method to quantify dopaminergic function in the living brain. The PET radioligand, [18F]FE-PE2I, a cocaine chemical derivative, has shown promising properties for in vivo PET imaging of DAT, including high affinity and selectivity for DAT, excellent brain permeability, and favorable metabolism. The aim of the current study was to scale up the production of [18F]FE-PE2I to fulfil the increasing clinical demand for this tracer.

RESULTS

Thus, a fully automated and GMP-compliant production procedure has been developed using a commercially available radiosynthesis module GE TRACERLab FX2 N. [18F]FE-PE2I was produced with a radiochemical yield of 39 ± 8% (n = 4, relative [18F]F- delivered to the module). The synthesis time was 70 min, and the molar activity was 925.3 ± 763 GBq/µmol (250 ± 20 Ci/µmol). The produced [18F]FE-PE2I was stable over 6 h at room temperature.

CONCLUSION

The protocol reliably provides a sterile and pyrogen-free GMP-compliant product.

Towards a biological diagnosis of PD

Since the original description by James Parkinson, Parkinson's disease (PD) has intrigued us for over 200 years. PD is a progressive condition that is incurable so far, and affects millions of people worldwide. Over the years, our knowledge has expanded tremendously, and a range of criteria have been put forward and used to try to define PD. However, owing to the complexity of the problem, it is still not consensual how to diagnose and classify a disease that manifests with diverse features, and that responds differently to existing therapies and to those under development. We are now living a time when 'biological' information is becoming abundant, precise, and accessible enabling us to attempt to incorporate different sources of information to classify different forms of PD. These refinements are essential for basic science, as they will enable us to develop improved models for studying PD, and to implement new findings into clinical practice, as this will be the path towards effective personalized medicine.

Dynamic multi-pinhole collimated brain SPECT of Parkinson's disease by [123I]FP-CIT: a feasibility study of fSPECT

We investigated the feasibility of using a dopamine transporter (DaT) tracer ligand ([123I]FP-CIT) along with novel multi-pinhole brain collimators for dynamic brain single photon emission computed tomography (SPECT) in suspected Parkinson's disease patients. Thirteen patients underwent dynamic tracer acquisitions before standard imaging. Uptake values were corrected for partial volume effects. Specific binding ratio (SBRcalc) was calculated, reflecting binding potential relative to non-displaceable binding (BPND) in the cortex. Additional pharmacokinetic parameters (BPND, R1, k2) were estimated using the simplified reference tissue model, revealing differences between Kahraman low-score (LS) and high-score (HS) groups. Results showed increasing striatal tracer uptake until 100 min post-injection, with consistent values afterward. Uptake and SBRcalc ratios matched visual assessment. LS patients had lower putamen than caudate nucleus tracer uptake, decreased BPND values, while R1 and k2 values were comparable to HS patients. In conclusion, dynamic multi-pinhole SPECT using DaT tracer with the extraction of pharmacokinetic parameters is feasible and could help enable early differentiation of reduced and normal DaT values.

The Role of Dual-Phase 18 F-FP-CIT PET to Early Diagnosis of Corticobasal Syndrome

BACKGROUND

Corticobasal syndrome (CBS) is a neurodegeneration characterized by asymmetric parkinsonism, dystonia, myoclonus, and apraxia. In the early stage, CBS presents with asymmetric parkinsonism and cortical symptoms (apraxia and alien hand), and neuroimaging finding is often vague, making early clinical differentiation from idiopathic Parkinson disease (IPD) challenging. This study was performed to delineate the specific patterns of cortical hypoperfusion, dopamine transporter (DAT) uptake using dual-phase FP-CIT PET in discriminating between CBS and IPD at early stage.

PATIENTS AND METHODS

The study enrolled clinically diagnosed CBS (n = 11) and IPD (n = 22) patients (age and sex matched). All participants underwent dual-phase 18 F-FP-CIT PET, and regional SUV ratio (SUVR) was obtained by semiquantitative analysis. The early perfusion imaging and DAT imaging were compared between groups.

RESULTS

The regional SUVRs (early phase) of the frontal lobe, thalamus, cingulate, and caudate were significantly lower in patients with CBS, whereas the SUVR of occipital lobe was lower in the IPD group. The CBS group exhibited more prominent asymmetry than the IPD group, particularly in the perirolandic area, superior frontal gyrus, and anterior parietal lobe in early phase PET. Striatal DAT uptake (delayed phase) revealed that the caudate showed lower SUVR and prominent asymmetry in the CBS group, and the caudate-to-putamen ratio (CP ratio) was significantly lower in CBS patients ( P < 0.001). Among the parameters (early and delayed), the CP ratio in DAT exhibited the most powerful discriminative power from receiver operating characteristic curve comparison (area under curve = 0.983).

CONCLUSIONS

This study demonstrated that the dual-phase FP-CIT PET is useful in differentiating CBS and IPD in the early stage of the disease, and a lower CP ratio of DAT imaging is highly informative for distinguishing between corticobasal degeneration and IPD.

An overview: Radiotracers and nano-radiopharmaceuticals for diagnosis of Parkinson's disease

Parkinson's disease (PD) is a widespread progressive neurodegenerative disease. Clinical diagnosis approaches are insufficient to provide an early and accurate diagnosis before a substantial of loss of dopaminergic neurons. PET and SPECT can be used for accurate and early diagnosis of PD by using target-specific radiotracers. Additionally, the importance of BBB penetrating targeted nanosystems has increased in recent years. This article reviews targeted radiopharmaceuticals used in clinics and novel nanocarriers for research purposes of PD imaging.

Clinical biomarkers for Lewy body diseases

Synucleinopathies are a group of neurodegenerative disorders characterized by pathologic aggregates of neural and glial α-synuclein (α-syn) in the form of Lewy bodies (LBs), Lewy neurites, and cytoplasmic inclusions in both neurons and glia. Two major classes of synucleinopathies are LB disease and multiple system atrophy. LB diseases include Parkinson's disease (PD), PD with dementia, and dementia with LBs. All are increasing in prevalence. Effective diagnostics, disease-modifying therapies, and therapeutic monitoring are urgently needed. Diagnostics capable of differentiating LB diseases are based on signs and symptoms which might overlap. To date, no specific diagnostic test exists despite disease-specific pathologies. Diagnostics are aided by brain imaging and cerebrospinal fluid evaluations, but more accessible biomarkers remain in need. Mechanisms of α-syn evolution to pathologic oligomers and insoluble fibrils can provide one of a spectrum of biomarkers to link complex neural pathways to effective therapies. With these in mind, we review promising biomarkers linked to effective disease-modifying interventions.

Differential Implications of Cerebral Hypoperfusion and Hyperperfusion in Parkinson's Disease

BACKGROUND

Patients with Parkinson's disease (PD) exhibit widespread brain perfusion changes.

OBJECTIVE

This study investigated whether cerebral regions with hypoperfusion and hyperperfusion have differential effects on motor and cognitive symptoms in PD using early-phase 18 F-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (18 F-FP-CIT) positron emission tomography (PET) scans.

METHODS

We enrolled 394 patients with newly diagnosed PD who underwent dual-phase 18 F-FP-CIT PET scans. Indices reflecting associated changes in regional cerebral hypoperfusion and hyperperfusion on early-phase 18 F-FP-CIT PET scans were calculated as PD[hypo] and PD[hyper] , respectively. The associations of PD[hypo] and PD[hyper] on motor and cognitive symptoms at baseline were assessed using multivariate linear regression. Also, Cox regression and linear mixed models were performed to investigate the effects of baseline PD[hypo] and PD[hyper] on longitudinal outcomes.

RESULTS

There was a weak correlation between PD[hypo] and PD[hyper] (γ = -0.19, P < 0.001). PD[hypo] was associated with baseline Unified Parkinson's Disease Rating Scale Part III scores (β = -1.02, P = 0.045), rapid increases in dopaminergic medications (β = -18.02, P < 0.001), and a higher risk for developing freezing of gait (hazard ratio [HR] = 0.67, P = 0.019), whereas PD[hyper] was not associated. Regarding cognitive function, PD[hypo] was more relevant to the baseline cognitive performance levels of visuospatial, memory, and frontal/executive function than PD[hyper] . However, greater PD[hyper] was associated with future dementia conversion (HR = 1.43, P = 0.004), whereas PD[hypo] was not associated.

CONCLUSIONS

These findings suggest that PD[hypo] and PD[hyper] may differentially affect motor and cognitive functions in patients with PD. © 2023 International Parkinson and Movement Disorder Society.

Sertraline treatment influences [18F]FE-PE2I PET imaging for Parkinsonism

BACKGROUND

The dopamine transporter (DaT) PET ligand [¹⁸F]FE-PE2I is used to aid the diagnosis of Parkinson's disease. After encountering four patients with a history of daily sertraline use, who all showed atypical findings on [¹⁸F]FE-PE2I PET, we suspected that the selective serotonin reuptake inhibitor (SSRI), sertraline, might interfere with the results and lead to globally reduced striatal [¹⁸F]FE-PE2I binding due to sertraline's high affinity for DaT.

METHODS

We rescanned the four patients with [¹⁸F]FE-PE2I PET after a 5-day sertraline pause. Sertraline plasma concentration was estimated based on body weight and dose, and specific binding ratios (SBR) in caudate nucleus, known to be more preserved in Parkinson's, were used to estimate the effect on tracer binding. Comparison was made to a patient with [¹⁸F]FE-PE2I PET before and after a 7-day Modafinil pause.

RESULTS

We found a significant effect of sertraline on caudate nucleus SBR (p = 0.029). The effect showed a linear dose-dependent relationship that corresponds to a reduction in SBR by 0.32 or 0.44 for a 75 kg male or a 65 kg female, respectively, taking a daily dose of 50 mg sertraline.

CONCLUSION

Sertraline is one of the most commonly used antidepressants and in contrast to other SSRI's, sertraline show high affinity for DaT. We recommend that sertraline treatment is taken into account when patients are undergoing [¹⁸F]FE-PE2I PET especially in patients showing apparent globally reduced PE2I binding. If tolerable, pausing of the sertraline treatment should be considered, especially for doses above 50 mg/day.

Reliability and validity of visual analysis of [ 18 F]FE-PE2I PET/CT in early Parkinsonian disease

OBJECTIVE

[ 18 F]FE-PE2I (FE-PE2I) is a new radiotracer for dopamine transporter (DAT) imaging with PET. The aim of this study was to evaluate the visual interpretation of FE-PE2I images for the diagnosis of idiopathic Parkinsonian syndrome (IPS). The inter-rater variability, sensitivity, specificity, and diagnostic accuracy for visual interpretation of striatal FE-PE2I compared to [ 123 I]FP-CIT (FP-CIT) single-photon emission computed tomography (SPECT) was evaluated.

METHODS

Thirty patients with newly onset parkinsonism and 32 healthy controls with both an FE-PE2I and FP-CIT were included in the study. Four patients had normal DAT imaging, of which three did not fulfil the IPS criteria at the clinical reassessment after 2 years. Six raters evaluated the DAT images blinded to the clinical diagnosis, interpreting the image as being 'normal' or 'pathological', and assessed the degree of DAT-reduction in the caudate and putamen. The inter-rater agreement was assessed with intra-class correlation and Cronbach's α . For calculation of sensitivity and specificity, DAT images were defined as correctly classified if categorized as normal or pathological by ≥4/6 raters.

RESULTS

The overall agreement in visual evaluation of the FE-PE2I- and FP-CIT images was high for the IPS patients ( α  = 0.960 and 0.898, respectively), but lower in healthy controls (FE-PE2I: α  = 0.693, FP-CIT: α  = 0.657). Visual interpretation gave high sensitivity (both 0.96) but lower specificity (FE-PE2I: 0.86, FP-CIT: 0.63) with an accuracy of 90% for FE-PE2I and 77% for FP-CIT.

CONCLUSION

Visual evaluation of FE-PE2I PET imaging demonstrates high reliability and diagnostic accuracy for IPS.

The Titrated Mannitol Improved Central [99mTc] Tc TRODAT-1 Uptake in an Animal Model-A Clinically Feasible Application

[99mTc]Tc TRODAT-1 is a widely used single photon emission tomography (SPECT) radiopharmaceutical in Asian practice for early detection of central dopaminergic disorders. However, its imaging quality remains sub-optimal. To overcome this problem, mannitol, an osmotic agent was used to observe its effect on improving striatal [99mTc]Tc TRODAT-1 uptake in rat brain by titrated human dosages to investigate a clinically feasible way to improve human imaging quality. [99mTc]Tc TRODAT-1 synthesis and quality control were performed as described. Sprague-Dawley rats were used for this study. The animal in vivo nanoSPECT/CT and ex vivo autoradiography were employed to observe and verify the striatal [99mTc]Tc TRODAT-1 uptake in rat brains using clinically equivalent doses (i.e., 0, 1 and 2 mL groups, each n = 5) of mannitol (20% w/v, equivalent to 200 mg/mL) by an intravenous administration. Specific binding ratios (SBRs) were calculated to express the central striatal uptake in different experimental groups. In the NanoSPECT/CT imaging, the highest SBRs of striatal [99mTc]Tc TRODAT-1 were reached at 75-90 min post-injection. The averaged striatal SBRs were 0.85 ± 0.13 (2 mL normal saline, the control group), 0.94 ± 0.26 (1 mL mannitol group) and 1.36 ± 0.12 (2 mL mannitol group, p < 0.01 which were significantly different than the control as well as 1 mL mannitol groups (p < 0.05). The SBRs from ex vivo autoradiography also showed a comparable trend of the striatal [99mTc]Tc TRODAT-1 uptake in the 2 mL, 1 mL mannitol and the control groups (1.76 ± 0.52, 0.91 ± 0.29, and 0.21 ± 0.03, respectively, p < 0.05). No remarkable changes of vital signs were found in the mannitol groups and the controls. Pre-treated mannitol revealed a significant increase of the central striatal [99mTc]Tc TRODAT-1 uptake in a rat model which not only enabled us to perform pre-clinical studies of dopaminergic related disorders but also provided a potential way to further optimize image quality in clinical practice.

Dual-phase 18 F-FP-CIT positron emission tomography and cardiac 123 I-MIBG scintigraphy of Parkinson's disease patients with GBA mutations: evidence of the body-first type?

BACKGROUND AND PURPOSE

Parkinson's disease (PD) with glucocerebrosidase (GBA) gene mutation (GBA-PD) is known to show more rapid clinical progression than sporadic PD without GBA mutation (sPD). This study was performed to delineate the specific patterns of cortical hypoperfusion, dopamine transporter uptake and cardiac meta-iodobenzylguanidine (MIBG) uptake of GBA-PD in comparison to sPD.

METHODS

Through next-generation sequencing analysis targeting 41 genes, a total of 16 GBA-PD and 24 sPD patients (sex, age matched) were enrolled in the study, and the clinical, dual-phase [¹⁸ F]-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (^{1 8} F-FP-CIT) positron emission tomography (PET) and cardiac ¹²³ I-MIBG scintigraphy results were compared between the two groups.

RESULTS

The GBA-PD group had higher rates of rapid eye movement sleep behavior disorder, orthostatic hypotension and neuropsychiatric symptoms than the sPD group. Early-phase ¹⁸ F-FP-CIT PET showed significantly lower standard uptake value ratio on bilateral posterior parietal cortex (0.94 ± 0.05 vs. 1.02 ± 0.04, p = 0.011) and part of the occipital cortex (p < 0.05) in the GBA-PD group than the sPD group. In striatal dopamine transporter uptake, the regional standard uptake value ratio, asymmetry index and caudate-to-putamen ratio were similar between the two groups. The GBA-PD group had a lower heart-to-mediastinum uptake ratio in ¹²³ I-MIBG scintigraphy than the sPD group.

CONCLUSIONS

The GBA-PD patients showed decreased regional perfusion in the bilateral posterior parietal and occipital cortex. Cardiac sympathetic denervation and non-motor symptoms (orthostatic hypotension, rapid eye movement sleep behavior disorder) were more common in GBA-PD than sPD. These findings suggest that GBA-PD patients have more widespread peripheral (extranigral) α-synuclein accumulation, representing a body-first PD subtype.

Validation of dynamic [18F]FE-PE2I PET for estimation of relative regional cerebral blood flow: a comparison with [15O]H2O PET

BACKGROUND

Dopamine transporter (DAT) imaging is used in the diagnostic work-up in suspected parkinsonian syndromes and dementia with Lewy bodies but cannot differentiate between these syndromes, and an extra brain imaging examination of the regional cerebral blood flow (rCBF) or glucose metabolism is often needed for differential diagnosis. The requirement of two different imaging examinations is resource-consuming and inconvenient for the patients. Therefore, imaging of both cortical blood flow and DAT imaging with the same radiotracer would be more convenient and cost-effective. The aim of this study was to test whether relative regional cerebral blood flow (rCBF_R) can be measured with the DAT-specific positron emission tomography (PET) tracer [¹⁸F]FE-PE2I (FE-PE2I), by validation with cerebral perfusion measured with [¹⁵O]H₂O PET (H₂O).

METHODS

The rCBF_R was quantified by kinetic modeling for FE-PE2I (R1) and H₂O (F). The R1 was calculated using the simplified reference tissue model, and F was calculated with a modified Koopman double-integration method. The linear relationship and intraclass correlation (ICC) between R1 and F were tested in image data derived from 29 patients with recent onset parkinsonism and 30 healthy controls.

RESULTS

There was a strong linear correlation across all subjects between R1 and F in the frontal, parietal, temporal, cingulate and occipital cortex as well as in the striatum (r  ≥  0.731-0.905, p  < 0.001) with a good-to-excellent ICC, ranging from 0.727 to 0.943 (p < 0.001).

CONCLUSIONS

Our results suggest that FE-PE2I may be used as a proxy for cerebral perfusion, thus potentially serving as a radiotracer for assessment of both DAT availability and rCBF_R in one single dynamic scan. This could be valuable in the differential diagnosis of parkinsonian syndromes.

TRIAL REGISTRATION

EUDRA-CT 2015-003045-26. Registered 23 October 2015 https://www.clinicaltrialsregister.eu/ctr-search/search?query=2015-003045-26.

[18F]FE-PE2I PET is a feasible alternative to [123I]FP-CIT SPECT for dopamine transporter imaging in clinically uncertain parkinsonism

BACKGROUND

Dopamine transporter (DAT) imaging of striatum is clinically used in Parkinson's disease (PD) and neurodegenerative parkinsonian syndromes (PS) especially in the early disease stages. The aim of the present study was to evaluate the diagnostic performance of the recently developed tracer for DAT imaging [¹⁸F]FE-PE2I PET/CT to the reference standard [¹²³I]FP-CIT SPECT.

METHODS

Ninety-eight unselected patients referred for DAT imaging were included prospectively and consecutively and evaluated with [¹⁸F]FE-PE2I PET/CT and [¹²³I]FP-CIT SPECT on two separate days. PET and SPECT scans were categorized independently by two blinded expert readers as either normal, vascular changes, or mixed. Semiquantitative values were obtained for each modality and compared regarding effect size using Glass' delta.

RESULTS

Fifty-six of the [¹²³I]FP-CIT SPECT scans were considered abnormal (52 caused by PS, 4 by infarctions). Using [¹⁸F]FE-PE2I PET/CT, 95 of the 98 patients were categorized identically to SPECT as PS or non-PS with a sensitivity of 0.94 [0.84-0.99] and a specificity of 1.00 [0.92-1.00]. Inter-reader agreement for [¹⁸F]FE-PE2I PET with a kappa of 0.97 [0.89-1.00] was comparable to the agreement for [¹²³I]FP-CIT SPECT of 0.96 [0.76-1.00]. Semiquantitative values for short 10-min reconstructions of [¹⁸F]FE-PE2I PET/CT were comparable to longer reconstructions. The effect size for putamen/caudate nucleus ratio was significantly increased using PET compared to SPECT.

CONCLUSIONS

The high correspondence of [¹⁸F]FE-PE2I PET compared to reference standard [¹²³I]FP-CIT SPECT establishes [¹⁸F]FE-PE2I PET as a feasible PET tracer for clinical use with favourable scan logistics.

Longitudinal Positron Emission Tomography Imaging of Presynaptic Terminals in Early Parkinson's Disease

BACKGROUND

Imaging tools that allow quantification of Parkinson's disease (PD) progression could facilitate the development of disease-modifying therapies. Cross-sectional studies have shown presynaptic terminal damage in PD patients, but longitudinal data are limited.

OBJECTIVES

The aim of this study was to longitudinally assess loss of presynaptic terminals in general and dopaminergic presynaptic terminals in particular as measures of disease progression in early PD.

METHODS

A total of 27 patients with early PD and 18 age- and sex-matched healthy controls underwent positron emission tomography (PET) with ¹¹ C-UCB-J, a ligand for the brain-wide presynaptic terminal marker SV2A, and with ¹⁸ F-FE-PE2I, a highly selective dopamine transporter ligand, in combination with a comprehensive motor and non-motor clinical assessment at baseline (BL) and after 26.5 ± 2.1 months (Y2). SUVR-1 images were calculated and volumes of interest were delineated based on individual 3D T1 magnetic resonance imaging (MRI).

RESULTS

PD patients showed significant 2-year worsening of Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS-III) (off medication) scores, but not of non-motor scores. Motor and non-motor scores in controls did not change significantly over 2 years. ¹⁸ F-FE-PE2I binding in caudate and putamen showed significant 2-year decline in the PD group and remained unchanged in controls. Longitudinal decline of striatal ¹⁸ F-FE-PE2I binding in PD did not correlate with longitudinal changes in MDS-UPDRS-III scores. ¹¹ C-UCB-J PET did not show any region with significant 2-year change in PD or controls.

CONCLUSIONS

¹⁸ F-FE-PE2I PET showed robust 2-year decline in early PD, but ¹¹ C-UCB-J PET did not. Longitudinal changes in ¹⁸ F-FE-PE2I binding did not correlate with clinical motor progression. © 2022 International Parkinson and Movement Disorder Society.

Future Directions in Molecular Imaging of Neurodegenerative Disorders

The improvement of existing techniques and the development of new molecular imaging methods are an exciting and rapidly developing field in clinical care and research of neurodegenerative disorders. In the clinic, molecular imaging has the potential to improve early and differential diagnosis and to stratify and monitor therapy in these disorders. Meanwhile, in research, these techniques improve our understanding of the underlying pathophysiology and pathobiochemistry of these disorders and allow for drug testing. This article is an overview on our perspective on future developments in neurodegeneration tracers and the associated imaging technologies. For example, we predict that the current portfolio of β-amyloid and tau aggregate tracers will be improved and supplemented by tracers allowing imaging of other protein aggregation pathologies, such as α-synuclein and transactive response DNA binding protein 43 kDa. Future developments will likely also be observed in imaging neurotransmitter systems. This refers to both offering imaging to a broader population in cases involving the dopaminergic, cholinergic, and serotonergic systems and making possible the imaging of systems not yet explored, such as the glutamate and opioid systems. Tracers will be complemented by improved tracers of neuroinflammation and synaptic density. Technologywise, the use of hybrid PET/MRI, dedicated brain PET, and total-body PET scanners, as well as advanced image acquisition and processing protocols, will open doors toward broader and more efficient clinical use and novel research applications. Molecular imaging has the potential of becoming a standard and essential clinical and research tool to diagnose and study neurodegenerative disorders and to guide treatments. On that road, we will need to redefine the role of molecular imaging in relation to that of emerging blood-based biomarkers. Taken together, the unique features of molecular imaging-that is, the potential to provide direct noninvasive information on the presence, extent, localization, and quantity of molecular pathologic processes in the living body-together with the predicted novel tracer and imaging technology developments, provide optimism about a bright future for this approach to improved care and research on neurodegenerative disorders.

Imaging Dopaminergic Neurotransmission in Neurodegenerative Disorders

Imaging of dopaminergic transmission in neurodegenerative disorders such as Parkinson disease (PD) or dementia with Lewy bodies plays a major role in clinical practice and in clinical research. We here review the role of imaging of the nigrostriatal pathway, as well as of striatal receptors and dopamine release, in common neurodegenerative disorders in clinical practice and research. Imaging of the nigrostriatal pathway has a high diagnostic accuracy to detect nigrostriatal degeneration in disorders characterized by nigrostriatal degeneration, such as PD and dementia with Lewy bodies, and disorders of more clinical importance, namely in patients with clinically uncertain parkinsonism. Imaging of striatal dopamine D2/3 receptors is not recommended for the differential diagnosis of parkinsonian disorders in clinical practice anymore. Regarding research, recently the European Medicines Agency has qualified dopamine transporter imaging as an enrichment biomarker for clinical trials in early PD, which underlines the high diagnostic accuracy of this imaging tool and will be implemented in future trials. Also, imaging of the presynaptic dopaminergic system plays a major role in, for example, examining the extent of nigrostriatal degeneration in preclinical and premotor phases of neurodegenerative disorders and to examine subtypes of PD. Also, imaging of postsynaptic dopamine D2/3 receptors plays a role in studying, for example, the neuronal substrate of impulse control disorders in PD, as well as in measuring endogenous dopamine release to examine, for example, motor complications in the treatment of PD. Finally, novel MRI sequences as neuromelanin-sensitive MRI are promising new tools to study nigrostriatal degeneration in vivo.

VNTR polymorphism in the SLC6A3 gene does not influence dopamine transporter availability measured by [18F]FE-PE2I PET or [123I]FP-Cit SPECT

OBJECTIVE

To investigate the potential impact of polymorphism in the 3'-untranslated region (3'UTR) of the SLC6A3 gene (DAT1) on normal variation in dopamine transporter (DAT) imaging with [18F]FE-PE2I PET and [123I]FP-Cit SPECT.

METHODS

Thirty-six individuals (mean age 70.4±5.4 years) with normal [18F]FE-PE2I PET and [123I]FP-Cit SPECT were genotyped for variable number of tandem repeats (VNTR) in the 3'UTR of the DAT1 gene. The DAT-availability in the caudate and putamen as measured with [18F]FE-PE2I PET and [123I]FP-Cit SPECT, as well as in the substantia nigra with [18F]FE-PE2I PET were compared between the participants carrying one or two 9-repeat alleles (i.e. 9R+10R or 9R+9R; 47%) and the participants without a 9R allele (i.e. 10R+10R or 10R+11R; 53%). Nonparametric tests, linear regression analysis and mixed model analysis were used to assess any statistical difference in measured DAT availability between the two allele groups.

RESULTS

The measured DAT-availability in PET- and SPECT-imaging tended to be slightly higher in the 9R-group; however, the difference did not reach statistical significance in either the caudate or the putamen or the substantia nigra. Instead, age did have a significant effect on the DAT level (P < 0.05) notwithstanding the genotype.

CONCLUSION

No significant effect of DAT1-genotype was detectable in imaging with [18F]FE-PE2I PET or [123I]FP-Cit, instead, age accounted for the normal variation in DAT-PET and DAT-SPECT.

Prospective Paired Comparison of 123I-FP-CIT SPECT Images Obtained With a 360°-CZT and a Conventional Camera

PURPOSE

This study aimed to compare 123I-FP-CIT SPECT imaging obtained from a 360° cadmium-zinc-telluride (CZT) camera with different focus configurations and from a conventional Anger camera.

METHODS

This prospective study (NCT03980418) included patients referred to 123I-FP-CIT SPECT imaging who consecutively underwent a 30-minute acquisition on a conventional camera immediately followed by two 15-minute acquisitions on the 360°-CZT camera with, respectively, striatum and brain focus and reconstruction parameters to give equivalent contrast ratios, albeit with higher spatial resolution for the CZT camera. Tomographic count sensitivities were calculated. The images were analyzed through visual, according to 5 independent physicians, and automatic semiquantitative analyses.

RESULTS

Ninety-two patients were included in this study. The 360°-CZT camera tomographic count sensitivities showed increases of +25% and +18% for striatum and brain focus, respectively, as well as significantly higher quality scores (P ≤ 0.04) in comparison to the conventional camera. The κ scores of consensual visual analysis were 0.80 and 0.85, and correlation coefficients of semiquantitative analysis for striatum uptakes were 0.75 and 0.76 for the comparisons of images obtained with the 2 cameras, with striatum and brain focus, respectively, for the CZT camera. Advanced age was the single predictor of discordant cases (10/92 [11%]) showing systematically abnormal scans with the conventional camera, potentially as a result of partial volume effect.

CONCLUSIONS

Irrespective of focus mode, this high-sensitivity 360°-CZT camera provides concordant 123I-FP-CIT SPECT results when compared with a conventional camera, but with shorter acquisition times, higher image quality, and few discordant cases possibly explained by its higher spatial resolution.

N-acetylcysteine decreases dopamine transporter availability in the non-lesioned striatum of the 6-OHDA hemiparkinsonian rat

This study aimed to explore the beneficial effects of the antioxidant N-acetylcysteine (NAC) on the degenerated dopamine system. The short- and long-term regulatory mechanisms of NAC on the 6-OHDA hemiparkinsonian rat model were longitudinally investigated by performing positron emission tomography (PET) imaging using the specific dopamine transporter (DAT) radioligand [¹⁸F]FE-PE2I. The results demonstrate that after a unilateral dopamine insult NAC has a strong influence on the non-lesioned hemisphere by decreasing the levels of DAT in the striatum early after the lesion. We interpret this early and short-term decrease of DAT in the healthy striatum of NAC-treated animals as a beneficial compensatory effect induced by NAC.

Evaluation of dopamine transporter density in healthy Brazilians using Tc-99m TRODAT-1 SPECT

The presynaptic dopamine transporter (DAT) modulates the uptake of dopamine by regulating its concentration in the central nervous system. We aimed to evaluate the DAT binding potential (DAT-BP) in a sample of healthy Brazilians through technetium-99 metastable TRODAT-1 single-photon emission computed tomography imaging.We selected 126 healthy individuals comprising 72 men and 54 women, aged 18 to 80 years. We conducted semi-quantitative evaluation in transaxial slices, following which we identified the regions of interest in the striatal region using the occipital lobe as a region of non-specific DAT-BP.We found a decrease in DAT-BP in healthy individuals aged over 30 years, culminating in a 42% mean reduction after 80 years. There was no difference in the decrease by age group between the right (linear regression test [R2] linear = 0.466) and left striatum (R2 linear = 0.510). Women presented a higher DAT-BP than men (women: R2 linear = 0.431; men: R2 linear = 0.457); nonetheless, their decrease by age group was equal to that in men.Our study sheds light on important DAT-BP findings in healthy Brazilian subjects. Our results will facilitate understanding of brain illnesses that involve the dopamine system, such as neuropsychiatric disorders.

The role of neuroimaging in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects millions of people worldwide. Two hallmarks of PD are the accumulation of alpha-synuclein and the loss of dopaminergic neurons in the brain. There is no cure for PD, and all existing treatments focus on alleviating the symptoms. PD diagnosis is also based on the symptoms, such as abnormalities of movement, mood, and cognition observed in the patients. Molecular imaging methods such as magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), and positron emission tomography (PET) can detect objective alterations in the neurochemical machinery of the brain and help diagnose and study neurodegenerative diseases. This review addresses the application of functional MRI, PET, and SPECT in PD patients. We provide an overview of the imaging targets, discuss the rationale behind target selection, the agents (tracers) with which the imaging can be performed, and the main findings regarding each target's state in PD. Molecular imaging has proven itself effective in supporting clinical diagnosis of PD and has helped reveal that PD is a heterogeneous disorder, which has important implications for the development of future therapies. However, the application of molecular imaging for early diagnosis of PD or for differentiation between PD and atypical parkinsonisms has remained challenging. The final section of the review is dedicated to new imaging targets with which one can detect the PD-related pathological changes upstream from dopaminergic degeneration. The foremost of those targets is alpha-synuclein. We discuss the progress of tracer development achieved so far and challenges on the path toward alpha-synuclein imaging in humans.

Single Photon Emission Computed Tomography/Positron Emission Tomography Molecular Imaging for Parkinsonism: A Fast-Developing Field

The early differential diagnosis of Parkinson disease and atypical parkinsonism is a major challenge. The use of single photon emission computed tomography (SPECT)/positron emission tomography (PET) molecular imaging to investigate parkinsonism is a fast‐developing field. Imaging biomarker research may potentially lead to more accurate disease detection, enabling earlier diagnosis and treatment. This review summarizes recent SPECT/PET advances in radiopharmaceuticals and imaging technologies/analyses that improve the diagnosis of neurodegenerative parkinsonism. We are currently witnessing a turning point in the field. Integrating molecular imaging as a diagnostic technique represents an opportunity to reassess the strategies for diagnosing neurodegenerative parkinsonism. ANN NEUROL 2021;90:711–719

Fully Automated GMP-Compliant Synthesis of [18F]FE-PE2I

In the struggle to understand and accurately diagnose Parkinson's disease, radiopharmaceuticals and medical imaging techniques have played a major role. By being able to image and quantify the dopamine transporter density, noninvasive diagnostic imaging has become the gold standard. In the shift from the first generation of SPECT tracers, the fluorine-18-labeled tracer [18F]FE-PE2I has emerged as the agent of choice for many physicians. However, implementing suitable synthesis for the production of [18F]FE-PE2I has proved more challenging than expected. Through a thorough analysis of the relevant factors affecting the final radiochemical yield, we were able to implement high-yielding fully automated GMP-compliant synthesis of [18F]FE-PE2I on a Synthera®+ platform. By reaching RCYs up to 62%, it allowed us to isolate 25 GBq of the formulated product, and an optimized formulation resulted in the shelf life of 6 h, satisfying the increased demand for this radiopharmaceutical.

Simplified quantification of [18F]FE-PE2I PET in Parkinson's disease: Discriminative power, test-retest reliability and longitudinal validity during early peak and late pseudo-equilibrium

Quantification of dopamine transporter (DAT) availability with [¹⁸F]FE-PE2I PET enables the detection of presynaptic dopamine deficiency and provides a potential progression marker for Parkinson`s disease (PD). Simplified quantification is feasible, but the time window of short acquisition protocols may have a substantial impact on the reliability of striatal binding estimates. Dynamic [¹⁸F]FE-PE2I PET data of cross-sectional (33 PD patients, 24 controls), test-retest (9 patients), and longitudinal (12 patients) cohorts were used to assess the variability and reliability of specific binding ratios (SBR) measured during early peak and late pseudo-equilibrium. Receiver operating characteristics area under the curve (PD vs. controls) was high for early (0.996) and late (0.991) SBR. Early SBR provided more favourable effect size, absolute variability, and standard error of measurement than late SBR (caudate: 1.29 vs. 1.23; 6.9% vs. 9.8%; 0.09 vs. 0.20; putamen: 1.75 vs. 1.67; 7.7% vs. 14.0%; 0.08 vs. 0.17). The annual percentage change was comparable for both time windows (-7.2%-8.5%), but decline was significant only for early SBR. Whereas early and late [¹⁸F]FE-PE2I PET acquisitions have similar discriminative power to separate PD patients and controls, the early peak equilibrium acquisition can be recommended if [¹⁸F]FE-PE2I is used to measure longitudinal changes of DAT availability.

Multi-Atlas MRI-Based Striatum Segmentation for 123I-FP-CIT SPECT (DAT-SPECT) Compared With the Bolt Method and SPECT-Atlas-Based Segmentation Method Toward the Accurate Diagnosis of Parkinson's Disease/Syndrome

Aims: This study aimed to analyze the performance of multi-atlas MRI-based parcellation for ¹²³I-FP-CIT SPECT (DAT-SPECT) in healthy volunteers. The proposed method was compared with the SPECT-atlas-based and Bolt methods. ¹⁸F-FE-PE2I-PET (DAT-PET) was used as a reference.

Methods: Thirty healthy subjects underwent DAT-SPECT, DAT-PET, and 3D-T1WI-MRI. We calculated the striatum uptake ratio (SUR/SBR), caudate uptake ratio (CUR), and putamen uptake ratio (PUR) for DAT-SPECT using the multi-atlas MRI-based method, SPECT-atlas-based method, and Bolt method. In the multi-atlas MRI-based method, the cerebellum, occipital cortex, and whole-brain were used as reference regions. The correlation of age with DAT-SPECT activity and the correlations of SUR/SBR, CUR, and PUR between DAT-SPECT and DAT-PET were calculated by each of the three methods.

Results: The correlation between age and SUR/SBR for DAT-SPECT based on the multi-atlas MRI-based method was comparable to that based on the SPECT-atlas-based method (r = −0.441 to −0.496 vs. −0.488). The highest correlation between DAT-SPECT and DAT-PET was observed using the multi-atlas MRI-based method with the occipital lobe defined as the reference region compared with the SPECT-atlas-based and Bolt methods (SUR, CUR, and PUR: 0.687, 0.723, and 0.676 vs. 0.698, 0.660, and 0.616 vs. 0.655).

Conclusion: Multi-atlas MRI-based parcellation with the occipital lobe defined as the reference region was at least comparable to the clinical methods.

[18F]PR04.MZ PET/CT Imaging for Evaluation of Nigrostriatal Neuron Integrity in Patients With Parkinson Disease

INTRODUCTION

Degeneration of dopaminergic, nigrostriatal neurons is the hallmark of Parkinson disease (PD), and PET quantification of dopamine transporters is a widely accepted method for differential diagnosis between idiopathic PD and essential tremor. [18F]PR04.MZ is a new PET tracer with excellent imaging properties allowing for precise quantification of striatal and extrastriatal dopamine transporter. Here we describe our initial experience with [18F]PR04.MZ PET/CT in a larger cohort of healthy controls and PD patients as a proof-of-concept study for this tracer.

METHODS

Eighteen healthy subjects, 19 early PD patients (Hoehn-Yahr I-II), and 13 moderate-advanced PD patients (Hoehn-Yahr III-IV) underwent static PET/CT scans 60 to 90 minutes after injection of 5.16 ± 1.03 mCi (191 ± 38 MBq) [18F]PR04.MZ. Specific binding ratios (SBRs) were calculated for caudate nucleus, anterior putamen, posterior putamen, substantia nigra (SNpc), compared between different groups and correlated with clinical ratings.

RESULTS

[18F]PR04.MZ showed very high and specific uptake in the putamen, caudate, and substantia nigra pars compacta and very low nonspecific binding in other brain regions, and SBR values for the control group were 22.3 ± 4.1, 19.1 ± 3.5, and 5.4 ± 1.2, respectively. A reduction of SBR values was observed in all regions and in both initial and moderate PD, ranging from 35% to 89% (P < 0.001). The observed pattern of reduction was posterior putamen > anterior putamen > substantia nigra pars compacta > caudate, with contralateral posterior putamen being the most affected region. Rostrocaudal depletion gradient was evident in all PD patients and progression correlated with motor manifestations.

CONCLUSIONS

[18F]PR04.MZ PET/CT is a highly sensitive imaging modality for the detection of dopaminergic deficit in nigrostriatal pathways in PD.

Molecular Imaging of Striatal Dopaminergic Neuronal Loss and the Neurovascular Unit in Parkinson Disease

Parkinson disease (PD) is the second most common neurodegenerative disorder, characterized by loss of nigrostriatal dopaminergic neurons. Impairment of the neurovascular unit (NVU) has been hypothesized to play a critical role in early PD pathophysiology, and to precede neurodegenerative mechanisms. [C-11]-PE2I (N-(3-iodoprop-2E-enyl)-2b-carbomethoxy-3b-(4-methyl-phenyl)nortropane) (PE2I) is a PET radiotracer targeting neuronal dopamine transporters (DaT) with high specificity, allowing for highly accurate and specific DaT quantification. We investigated NVU integrity using arterial spin labeling (ASL) MRI in a prospective cohort of 26 patients with PD, and correlated our findings with analysis of striatal DaT density using PE2I PET in a subcohort of 17 patients. Analysis was performed in FreeSurfer to obtain rCBF and mean standardized regional PET avidity. Pearson correlations and Mann-Whitney tests were performed. Significantly lower mean normalized striatal PE2I SUV values were seen in multiple regions in patients with greater disease duration (p < 0.05). PET uptake in the putamen correlated with disease duration independent of patient age. Stratifying patients based on Montreal Cognitive Assessment (MoCA) scores (stratified into ≥ 27 vs. < 27), there was statistically significantly lower PE2I PET avidity in the higher MoCA score group in both more and less affected sides of the caudate, putamen and pallidum (p < 0.05). A moderate negative correlation between MDS-UPDRS part 3 (motor) "off" and rCBF values was also seen in the L and R cerebellum WM (r = -0.43 and -0.47, p < 0.05). A statistically significant negative correlation was found between dominant hand pegboard test results and rCBF in the less affected pallidum (r = -0.41; p = 0.046). A statistically significant negative correlation of ASL MRI with [11C]-PE2I PET was also found (r = -0.53 to -0.58; p-value 0.017-0.033) between left cerebral WM rCBF and more and less affected striatal PET regions. Our ROI-based analyses suggest that longer disease duration is associated with lower rCBF and lower PE2I mean SUV, implying greater NVU dysfunction and dopaminergic neuronal loss, respectively. Combined ASL MRI and PE2I PET imaging could inform future prospective clinical trials providing an improved mechanistic understanding of the disease, laying the foundation for the development of early disease biomarkers and potential therapeutic targets.

Diffusion Tensor Imaging in Parkinson's Disease and Parkinsonian Syndrome: A Systematic Review

Diffusion tensor imaging (DTI) allows measuring fractional anisotropy and similar microstructural indices of the brain white matter. Lower than normal fractional anisotropy as well as higher than normal diffusivity is associated with loss of microstructural integrity and neurodegeneration. Previous DTI studies in Parkinson's disease (PD) have demonstrated abnormal fractional anisotropy in multiple white matter regions, particularly in the dopaminergic nuclei and dopaminergic pathways. However, DTI is not considered a diagnostic marker for the earliest Parkinson's disease since anisotropic alterations present a temporally divergent pattern during the earliest Parkinson's course. This article reviews a majority of clinically employed DTI studies in PD, and it aims to prove the utilities of DTI as a marker of diagnosing PD, correlating clinical symptomatology, tracking disease progression, and treatment effects. To address the challenge of DTI being a diagnostic marker for early PD, this article also provides a comparison of the results from a longitudinal, early stage, multicenter clinical cohort of Parkinson's research with previous publications. This review provides evidences of DTI as a promising marker for monitoring PD progression and classifying atypical PD types, and it also interprets the possible pathophysiologic processes under the complex pattern of fractional anisotropic changes in the first few years of PD. Recent technical advantages, limitations, and further research strategies of clinical DTI in PD are additionally discussed.

Dopamine transporter imaging in neurodegenerative movement disorders: PET vs. SPECT

Purpose

The dopamine transporter (DAT) serves as biomarker for parkinsonian syndromes. DAT can be measured in vivo with single-photon emission computed tomography (SPECT) and positron emission tomography (PET). DAT-SPECT is the current clinical molecular imaging standard. However, PET has advantages over SPECT measurements, and PET radioligands with the necessary properties for clinical applications are on the rise. Therefore, it is time to review the role of DAT imaging with SPECT compared to PET.

Methods

PubMed and Web of Science were searched for relevant literature of the previous 10 years. Four topics for comparison were used: diagnostic accuracy, quantitative accuracy, logistics, and flexibility.

Results

There are a few studies directly comparing DAT-PET and DAT-SPECT. PET and SPECT both perform well in discriminating neurodegenerative from non-neurodegenerative parkinsonism. Clinical DAT-PET imaging seems feasible only recently, thanks to simplified DAT assessments and better availability of PET radioligands and systems. The higher resolution of PET makes more comprehensive assessments of disease progression in the basal ganglia possible. Additionally, it has the possibility of multimodal target assessment.

Conclusion

DAT-SPECT is established for differentiating degenerative from non-degenerative parkinsonism. For further differentiation within neurodegenerative Parkinsonian syndromes, DAT-PET has essential benefits. Nowadays, because of wider availability of PET systems and radioligand production centers, and the possibility to use simplified quantification methods, DAT-PET imaging is feasible for clinical use. Therefore, DAT-PET needs to be considered for a more active role in the clinic to take a step forward to a more comprehensive understanding and assessment of Parkinson’s disease.

Longitudinal functional connectivity changes related to dopaminergic decline in Parkinson's disease

BACKGROUND

Resting-state functional magnetic resonance imaging (fMRI) studies have demonstrated that basal ganglia functional connectivity is altered in Parkinson's disease (PD) as compared to healthy controls. However, such functional connectivity alterations have not been related to the dopaminergic deficits that occurs in PD over time.

OBJECTIVES

To examine whether functional connectivity impairments are correlated with dopaminergic deficits across basal ganglia subdivisions in patients with PD both cross-sectionally and longitudinally.

METHODS

We assessed resting-state functional connectivity of basal ganglia subdivisions and dopamine transporter density using 11C-PE2I PET in thirty-four PD patients at baseline. Of these, twenty PD patients were rescanned after 19.9 ± 3.8 months. A seed-based approach was used to analyze resting-state fMRI data. 11C-PE2I binding potential (BPND) was calculated for each participant. PD patients were assessed for disease severity.

RESULTS

At baseline, PD patients with greater dopaminergic deficits, as measured with 11C-PE2I PET, showed larger decreases in posterior putamen functional connectivity with the midbrain and pallidum. Reduced functional connectivity of the posterior putamen with the thalamus, midbrain, supplementary motor area and sensorimotor cortex over time were significantly associated with changes in DAT density over the same period. Furthermore, increased motor disability was associated with lower intraregional functional connectivity of the posterior putamen.

CONCLUSIONS

Our findings suggest that basal ganglia functional connectivity is related to integrity of dopaminergic system in patients with PD. Application of resting-state fMRI in a large cohort and longitudinal scanning may be a powerful tool for assessing underlying PD pathology and its progression.

Reliability of dopamine transporter PET measurements with [18F]FE-PE2I in patients with Parkinson's disease

Background

Reliable quantification of dopamine transporter (DAT), a biomarker for Parkinson’s disease (PD), is essential for diagnostic purposes as well as for evaluation of potential disease-modifying treatment. Due to degeneration of dopaminergic neurons and thus lower expected radioligand binding to DAT, higher measurement variability in PD patients might be expected than earlier reproducibility results in healthy controls. Therefore, we aimed to examine the test-retest properties of [¹⁸F]FE-PE2I-PET in PD patients.

Methods

Nine patients with PD (Hoehn and Yahr stage < 3) were included (men/women 6/3; mean age 65.2 ± 6.8 years). Each patient underwent two [¹⁸F]FE-PE2I-PET measurements within 7–28 days. The outcome measure was non-displaceable binding potential generated using wavelet-aided parametric imaging with cerebellum as reference region. We assessed test-retest performance using estimates of reliability and repeatability. Regions for primary analysis were caudate, putamen, ventral striatum, and substantia nigra. Exploratory analysis was performed for functional subdivisions of the striatum. We also compared the more vs. less affected side.

Results

[¹⁸F]FE-PE2I showed absolute variability estimates of 5.3–7.6% in striatal regions and 11% in substantia nigra and ICCs of 0.74–0.97 (median 0.91). The absolute variability for functional striatal subdivisions was 6.0–9.6% and ICCs of 0.76–0.91 (median 0.91). The less affected substantia nigra exhibited greater consistency than the more affected side. According to power calculations based on the current sample size, DAT changes of 5–11% in the striatum and 28% in the substantia nigra can be detected with a power of 0.8 (p < 0.0125).

Conclusion

DAT-PET measurements with [¹⁸F]FE-PE2I in PD patients showed good repeatability and reliability. The slightly lower reliability in the substantia nigra in patients may be explained by lower DAT density and smaller anatomical size. Power calculations suggest that [¹⁸F]FE-PE2I PET is a suitable marker for longitudinal DAT decline in PD.

Trial registration

EudraCT 2017-003327-29

Imaging of dopamine transporters in Parkinson disease: a meta-analysis of 18 F/123 I-FP-CIT studies

OBJECTIVE

¹⁸ F-FP-CIT and ¹²³ I-FP-CIT are widely used radiotracers in molecular imaging for Parkinson's disease (PD) diagnosis. Compared with ¹²³ I-FP-CIT, ¹⁸ F-FP-CIT has superior tracer kinetics. We aimed to conduct a meta-analysis to assess the efficacy of using ¹⁸ F-FP-CIT positron emission tomography (PET) and ¹²³ I-FP-CIT single-photon emission computed tomography (SPECT) of dopamine transporters in patients with PD in order to provide evidence for clinical decision-making.

METHODS

We searched the PubMed, Embase, Wanfang Data, and China National Knowledge Infrastructure databases to identify the relevant studies from the time of inception of the databases to 30 April 2020. We identified six PET studies, including 779 patients with PD and 124 healthy controls, which met the inclusion criteria. Twenty-seven SPECT studies with 1244 PD patients and 859 controls were also included in this meta-analysis.

RESULTS

Overall effect-size analysis indicated that patients with PD showed significantly reduced ¹⁸ F-FP-CIT uptake in three brain regions [caudate nucleus: standardized mean difference (SMD) = -1.71, Z = -3.31, P = 0.0009; anterior putamen: SMD = -3.71, Z = -6.26, P < 0.0001; and posterior putamen: SMD = -5.49, Z = -5.97, P < 0.0001]. Significant decreases of ¹²³ I-FP-CIT uptake were also observed in the caudate (SMD = -2.31, Z = -11.49, P < 0.0001) and putamen (SMD = -3.25, Z = -14.79, P < 0.0001).

INTERPRETATION

In conclusion, our findings indicate that both ¹⁸ F-FP-CIT PET and ¹²³ I-FP-CIT SPECT imaging of dopamine transporters can provide viable biomarkers for early PD diagnosis.

Efficiency of 123I-ioflupane SPECT as the marker of basal ganglia damage in acute methanol poisoning: 6-year prospective study

CONTEXT

Investigate whether ¹²³I-ioflupane SPECT (DaT SPECT) has the potential as a marker of basal ganglia damage in acute methanol poisoning.

METHODS

Prospective, single-centre, cohort study of patients with confirmed methanol poisoning was conducted. DaT SPECT was performed twice with semi-quantification using DaTQUANT^TM and MRI-based volumetry was calculated. Specific binding ratios (SBR) of striatum, caudate nucleus, and putamen were correlated with laboratory parameters of outcome, volumetric data, and retinal nerve fibres layer (RNFL) thickness measurements.

RESULTS

Forty-two patients (mean age 46.3 ± 4.2 years; 8 females), including 15 with MRI-detected putamen lesions (group I) and 27 patients with intact putamen (group II), underwent DaT SPECT. Volumetry was calculated in 35 of the patients assessed. SBR values for the left putamen correlated with putamen volume (r = 0.665; p < 0.001). Decreased bilateral SBR values were determined for the striatum and the putamen, but not for the nucleus caudate, in group I (p < 0.05). Significant correlation was observed between the SBR of the posterior putamen and arterial blood pH (r = 0.574; p < 0.001) and other toxicological parameters of severity of poisoning/outcome including serum lactate, glucose, and creatinine concentrations (p < 0.05). The SBR of the posterior putamen positively correlated with the global RNFL thickness (p < 0.05). ROC analysis demonstrated a significant discriminatory ability of SBR of the posterior putamen with AUC = 0.753 (95%CI 0.604-0.902; p = 0.007). The multivariate regression model demonstrated that arterial blood pH, age, and gender were the most significant factors associated with SBR of the posterior putamen.

CONCLUSION

DaT SPECT demonstrates significant potential for the diagnosis of methanol-induced basal ganglia damage.

Loss of Presynaptic Terminal Integrity in the Substantia Nigra in Early Parkinson's Disease

BACKGROUND

It has been hypothesized that the pathology of Parkinson's disease (PD) primarily affects presynaptic terminals and spreads trans-synaptically.

OBJECTIVES

The main objective of this study was to assess the magnitude and anatomical extent of presynaptic terminal loss across the brain in early PD. A second objective was to compare loss of presynaptic terminals and cell bodies within the nigrostriatal tract.

METHODS

A total of 30 patients with early PD and 20 age- and gender-matched healthy controls underwent positron emission tomography with ¹¹ C-UCB-J, a ligand for the universal presynaptic terminal marker synaptic vesicle protein 2A (SV2A), and with the dopamine transporter ligand ¹⁸ F-FE-PE2I, as well as a detailed clinical assessment. Volumes of interest were delineated based on individual 3-dimensional T1 magnetic resonance imaging. BP_ND images were calculated.

RESULTS

Patients with PD showed significant loss of SV2A binding in the substantia nigra only. Loss of dopamine transporter binding in the PD group was much greater in the putamen than in the substantia nigra. We found no correlations between SV2A or dopamine transporter binding and any of the clinical motor or nonmotor scores. Homologous voxel-based analysis in the PD group showed significant correlations between SV2A and dopamine transporter binding in the caudate and substantia nigra.

CONCLUSIONS

Presynaptic terminals appear to be the most heavily affected subcellular compartment of nigrostriatal neurons in early PD. Moreover, early PD causes loss of presynaptic terminals that innervate the nigrostriatal neurons. This loss of presynaptic boutons in the substantia nigra may reflect an axonal response to target deprivation or could possibly point to a trans-synaptic mode of propagation of the disease process. © 2020 International Parkinson and Movement Disorder Society.

Low dopamine transporter binding in the nucleus accumbens in geriatric patients with severe depression

AIM

Dysfunction of dopaminergic neurons in the central nervous system is considered to be related to major depressive disorder (MDD). Especially, MDD in geriatric patients is characterized by anhedonia, which is assumed to be associated with reduced dopamine neurotransmission in the reward system. Dopamine transporter (DAT) is considered to reflect the function of the dopamine nerve system. However, previous DAT imaging studies using single photon emission computed tomography or positron emission tomography (PET) have shown inconsistent results. The radioligand [¹⁸ F]FE-PE2I for PET enables more precise evaluation of DAT availability. Hence, we aimed to evaluate the DAT availability in geriatric patients with MDD using [¹⁸ F]FE-PE2I.

METHODS

Eleven geriatric patients with severe MDD and 27 healthy controls underwent PET with [¹⁸ F]FE-PE2I, which has high affinity and selectivity for DAT. Binding potentials (BP_ND ) in the striatum (caudate and putamen), nucleus accumbens (NAc), and substantia nigra were calculated. BP_ND values were compared between MDD patients and healthy controls.

RESULTS

MDD patients showed significantly lower DAT BP_ND in the NAc (P = 0.009), and there was a trend of lower BP_ND in the putamen (P = 0.032) compared to controls.

CONCLUSION

We found low DAT in the NAc and putamen in geriatric patients with severe MDD, which could be related to dysregulation of the reward system.

Nuclear Imaging in the Diagnosis of Clinically Uncertain Parkinsonian Syndromes

BACKGROUND

Parkinsonian syndromes are classified by etiology mainly on clinical grounds, that is, on the basis of the clinical manifestations and with the aid of conventional ancillary studies. In most cases, the clinical diagnosis is clear. In up to 30% of cases, however, the etiological classification remains uncertain after completion of the basic clinical diagnostic evaluation, and additional investigation with nuclear imaging may be indicated. In particular, cerebral single-photon emission computed tomography (SPECT) with dopamine transporter (DAT) ligands may be helpful. DAT-SPECT can be used to demonstrate or rule out nigrostriatal degeneration and thereby differentiate neurodegenerative parkinsonian syndromes from symptomatic parkinsonian syndromes and other differential diagnoses. Positron emission tomography (PET) with the glucose analogue [18F]fluorodeoxyglucose (FDG) can be used to identify disease-specific patterns of neuronal dysfunction/degeneration in order to differentiate the various neurodegenerative parkinsonian syndromes from one another.

METHODS

In this review, we summarize the current state of the evidence on DAT-SPECT and FDG-PET for the indications mentioned above on the basis of a selective review of the literature.

RESULTS

DAT-SPECT has been adequately validated as an in vivo marker for nigrostriatal degeneration. Studies using the clinical diagnosis of a movement disorders specialist over the course of the disease as a reference have shown that DAT- SPECT is 78-100% sensitive (median, 93%) and 70-100% specific (median, 89%) for the differentiation of neurodegenerative parkinsonian syndromes from symptomatic parkinsonism and other differential diagnoses in clinically unclear cases. DAT- SPECT scanning led to a change of diagnosis in 27-56% of patients (median, 43%) and to a change of treatment in 33-72% (median, 43%). FDG-PET enables the differentiation of atypical neurodegenerative parkinsonian syndromes from the idiopathic parkinsonian syndrome (i.e., Parkinson's disease proper) with high sensitivity and specificity (both approximately 90%), when the clinical diagnosis by a movement disorders specialist over the course of the disease is used as a reference.

CONCLUSION

DAT-SPECT has been well documented to be highly diagnostically accurate and to have a relevant influence on the diagnosis and treatment of patients with clinically uncertain parkinsonian or tremor syndrome. It has not yet been shown to improve patient-relevant endpoints such as mortality, morbidity, and health-related quality of life; proof of this will probably have to await the introduction of neuroprotective treatments. The current evidence for the high differential diagnostic accuracy of FDG-PET in neurodegenerative parkinsonian syndromes needs to be reinforced by prospective studies with neuropathological verification of the diagnosis.

EANM practice guideline/SNMMI procedure standard for dopaminergic imaging in Parkinsonian syndromes 1.0

Purpose

This joint practice guideline or procedure standard was developed collaboratively by the European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI). The goal of this guideline is to assist nuclear medicine practitioners in recommending, performing, interpreting, and reporting the results of dopaminergic imaging in parkinsonian syndromes.

Methods

Currently nuclear medicine investigations can assess both presynaptic and postsynaptic function of dopaminergic synapses. To date both EANM and SNMMI have published procedural guidelines for dopamine transporter imaging with single photon emission computed tomography (SPECT) (in 2009 and 2011, respectively). An EANM guideline for D2 SPECT imaging is also available (2009). Since the publication of these previous guidelines, new lines of evidence have been made available on semiquantification, harmonization, comparison with normal datasets, and longitudinal analyses of dopamine transporter imaging with SPECT. Similarly, details on acquisition protocols and simplified quantification methods are now available for dopamine transporter imaging with PET, including recently developed fluorinated tracers. Finally, [¹⁸F]fluorodopa PET is now used in some centers for the differential diagnosis of parkinsonism, although procedural guidelines aiming to define standard procedures for [¹⁸F]fluorodopa imaging in this setting are still lacking.

Conclusion

All these emerging issues are addressed in the present procedural guidelines for dopaminergic imaging in parkinsonian syndromes.

Clinical and Imaging Markers of Prodromal Parkinson's Disease

The diagnosis of Parkinson's disease (PD) relies on the clinical effects of dopamine deficiency, including bradykinesia, rigidity and tremor, usually manifesting asymmetrically. Misdiagnosis is common, due to overlap of symptoms with other neurodegenerative disorders such as multiple system atrophy and progressive supranuclear palsy, and only autopsy can definitively confirm the disease. Motor deficits generally appear when 50–60% of dopaminergic neurons in the substantia nigra are already lost, limiting the effectiveness of potential neuroprotective therapies. Today, we consider PD to be not just a movement disorder, but rather a complex syndrome non-motor symptoms (NMS) including disorders of sleep-wake cycle regulation, cognitive impairment, disorders of mood and affect, autonomic dysfunction, sensory symptoms and pain. Symptomatic LRRK2 mutation carriers share non-motor features with individuals with sporadic PD, including hyposmia, constipation, impaired color discrimination, depression, and sleep disturbance. Following the assumption that the pre-symptomatic gene mutation carriers will eventually exhibit clinical symptoms, their neuroimaging results can be extended to the pre-symptomatic stage of PD. The long latent phase of PD, termed prodromal-PD, represents an opportunity for early recognition of incipient PD. Early recognition could allow initiation of possible neuroprotective therapies at a stage when therapies might be most effective. The number of markers with the sufficient level of evidence to be included in the MDS research criteria for prodromal PD have increased during the last 10 years. Here, we review the approach to prodromal PD, with an emphasis on clinical and imaging markers and report results from our neuroimaging study, a retrospective evaluation of a cohort of 39 participants who underwent DAT-SPECT scan as part of their follow up. The study was carried out to see if it was possible to detect subclinical signs in the preclinical (neurodegenerative processes have commenced, but there are no evident symptoms or signs) and prodromal (symptoms and signs are present, but are yet insufficient to define disease) stages of PD.

Olfactory dysfunction correlates with putaminal dopamine turnover in early de novo Parkinson's disease

Although olfactory dysfunction is one of the most well-established prodromal symptoms in Parkinson's disease (PD), its correlation with clinical disease progression or dopaminergic dysfunction still remains unclear. We here evaluated the association of striatal dopamine metabolism and olfactory function in a homogenous cohort of 30 patients with early untreated de novo PD. Striatal dopamine metabolism was assessed by the extended ¹⁸Fluorodopa PET scanning protocol to measure ¹⁸Fluorodopa uptake (K_occ) and the effective dopamine distribution volume ratio (EDVR) as the inverse of dopamine turnover. Olfactory function was estimated by the "Sniffin' Sticks" test including odor threshold (T), discrimination (D) and identification (I) assessment. We detected moderate correlations of the EDVR in the posterior putamen with the TDI composite score (r = 0.412; p = 0.024; Pearson's correlation test) and the odor identification score (r = 0.444; p = 0.014). These correlations were confirmed by multivariate regression analyses using age, sex, symptom duration and disease severity as measured by UPDRSIII motor score as candidate covariates. No other associations were observed between olfaction measures and K_occ and EDVR in all striatal regions. Together, olfactory dysfunction in early PD is not correlated with striatal ¹⁸Fluorodopa uptake as a measure for dopaminergic degeneration, but with putaminal dopamine turnover as a marker for dopaminergic presynaptic compensatory processes in early PD. These results should be treated as hypothesis generating and require confirmation by larger multicenter studies.

Delayed Dopamine Dysfunction and Motor Deficits in Female Parkinson Model Mice

This study analyzed gender differences in the progressive dopamine (DA) deficiency phenotype in the MitoPark (MP) mouse model of Parkinson’s disease (PD) with progressive loss of DA release and reuptake in midbrain DA pathways. We found that the progressive loss of these DA presynaptic parameters begins significantly earlier in male than female MP mice. This was correlated with behavioral gender differences of both forced and spontaneous motor behavior. The degeneration of the nigrostriatal DA system in MP mice is earlier and more marked than that of the mesolimbic DA system, with male MP mice again being more strongly affected than female MP mice. After ovariectomy, DA presynaptic and behavioral changes in female mice become very similar to those of male animals. Our results suggest that estrogen, either directly or indirectly, is neuroprotective in the midbrain DA system. Our results are compatible with epidemiological data on incidence and symptom progression in PD, showing that men are more strongly affected than women at early ages.

Quantification and discriminative power of 18F-FE-PE2I PET in patients with Parkinson's disease

RATIONALE

Dopamine transporter (DAT) imaging is an important adjunct in the diagnostic workup of patients with Parkinsonism. ¹⁸F-FE-PE2I is a suitable PET radioligand for DAT quantification and imaging with good pharmacokinetics. The aim of this study was to determine a clinical optimal simplified reference tissue-based image acquisition protocol and to compare the discriminatory value and effect size for ¹⁸F-FE-PE2I to that for ¹²³I-FP-CIT scan currently used in clinical practice.

METHODS

Nine patients with early Parkinson's disease (PD, 64.3 ± 6.8 years, 3M), who had previously undergone a ¹²³I-FP-CIT scan as part of their diagnostic workup, and 34 healthy volunteers (HV, 47.7 ± 16.8 years, 13M) underwent a 60-min dynamic ¹⁸F-FE-PE2I PET-MR scan on a GE Signa 3T PET-MR. Based on dynamic data and MR-based VOI delineation, BP_ND, semi-quantitative uptake ratio and SUVR_[t1-t2] images were calculated using either occipital cortex or cerebellum as reference region. For start-and-end time of the SUVR interval, three time frames [t₁-t₂] were investigated: [15-40] min, [40-60] min, and [50-60] min postinjection. Data for putamen (PUT) and caudate nucleus-putamen ratio (CPR) were compared in terms of quantification bias versus BP_ND and discriminative power.

RESULTS

Using occipital cortex as reference region resulted in smaller bias of SUVR with respect to BP_ND + 1 and higher correlation between SUVR and BP_ND + 1 compared with using cerebellum, irrespective of SUVR [t₁-t₂] interval. Smallest bias was observed with the [15-40]-min time window, in accordance with previous literature. The correlation between BP_ND + 1 and SUVR was slightly better for the late time windows. Discriminant analysis between PD and HV using both PUT and CPR SUVRs showed an accuracy of ≥ 90%, for both reference regions and all studied time windows. Semi-quantitative ¹²³I-FP-CIT and ¹⁸F-FE-PE2I values and relative decrease in the striatum for patients were highly correlated, with a higher effect size for ¹⁸F-FE-PE2I for PUT and CPR SUVR.

CONCLUSION

¹⁸F-FE-PE2I is a suitable radioligand for in vivo DAT imaging with high discriminative power between early PD and healthy controls. Whereas a [15-40]-min window has lowest bias with respect to BP_ND, a [50-60]-min time window at pseudoequilibrium can be advocated in terms of clinical feasibility with optimal discriminative power. The occipital cortex may be slightly preferable as reference region because of the higher time stability, stronger correlation of SUVR with BP_ND + 1, and lower bias. Moreover, the data suggest that the diagnostic accuracy of a 10-min static ¹⁸F-FE-PE2I scan is non-inferior compared with ¹²³I-FP-CIT scan used in standard clinical practice.

Design and Challenges of Radiopharmaceuticals

This review describes general concepts with regard to radiopharmaceuticals for diagnostic or therapeutic applications that help to understand the specific challenges encountered during the design, (radio)synthesis, in vitro and in vivo evaluation and clinical translation of novel radiopharmaceuticals. The design of a radiopharmaceutical requires upfront decisions with regard to combining a suitable vector molecule with an appropriate radionuclide, considering the type and location of the molecular target, the desired application, and the time constraints imposed by the relatively short half-life of radionuclides. Well-designed in vitro and in vivo experiments allow nonclinical validation of radiotracers. Ultimately, in combination with a limited toxicology package, the radiotracer becomes a radiopharmaceutical for clinical evaluation, produced in compliance with regulatory requirements for medicines for intravenous (IV) injection.

The Story of the Dopamine Transporter PET Tracer LBT-999: From Conception to Clinical Use

The membrane dopamine transporter (DAT) is involved in a number of brain disorders and its exploration by positron emission tomography (PET) imaging is highly relevant for the early and differential diagnosis, follow-up and treatment assessment of these diseases. A number of carbon-11 and fluor-18 labeled tracers are to date available for this aim, the majority of them being derived from the chemical structure of cocaine. The development of such a tracer, from its conception to its use, is a long process, the expected result being to obtain the best radiopharmaceutical adapted for clinical protocols. In this context, the cocaine derivative (E)-N-(4-fluorobut-2-enyl)2β-carbomethoxy-3β-(4′-tolyl)nortropane, or LBT-999, has passed all the required stages of the development that makes it now a highly relevant imaging tool, particularly in the context of Parkinson's disease. This review describes the different steps of the development of LBT-999 which initially came from its non-fluorinated derivative (E)-N-(3-iodoprop-2-enyl)-2-carbomethoxy-3-(4-methylphenyl) nortropane, or PE2I, because of its high promising properties. [¹⁸F]LBT-999 has been extensively characterized in rodent and non-human primate models, in which it demonstrated its capability to explore in vivo the DAT localized at the dopaminergic nerve endings as well as at the mesencephalic cell bodies, in physiological conditions. In lesion-induced rat models of Parkinson's disease, [¹⁸F]LBT-999 was able to precisely quantify in vivo the dopaminergic neuron loss, and to assess the beneficial effects of therapeutic approaches such as pharmacological treatment and cell transplantation. Finally recent clinical data demonstrated the efficiency of [¹⁸F]LBT-999 in the diagnosis of Parkinson's disease.