Author name cluster

Philipp T. Meyer

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

8 papers

1 author row

YNICL Journal 2024 Journal Article

Disbalanced recruitment of crossed and uncrossed cerebello-thalamic pathways during deep brain stimulation is predictive of delayed therapy escape in essential tremor

Bastian E.A. Sajonz
Marvin L. Frommer
Marco Reisert
Ganna Blazhenets
Nils Schröter
Alexander Rau
Thomas Prokop
Peter C. Reinacher

BACKGROUND: Thalamic deep brain stimulation (DBS) is an efficacious treatment for drug-resistant essential tremor (ET) and the dentato-rubro-thalamic tract (DRT) constitutes an important target structure. However, up to 40% of patients habituate and lose treatment efficacy over time, frequently accompanied by a stimulation-induced cerebellar syndrome. The phenomenon termed delayed therapy escape (DTE) is insufficiently understood. Our previous work showed that DTE clinically is pronounced on the non-dominant side and suggested that differential involvement of crossed versus uncrossed DRT (DRTx/DRTu) might play a role in DTE development. METHODS: F]Fluorodeoxyglucose positron emission tomography were applied. RESULTS: = 0.2319, p < 0.01). Moreover, increasing VAT size on the right (non-dominant) side was associated at trend level with more asymmetric glucose metabolism shifting towards the right (dominant) dentate nucleus. CONCLUSION: Our results suggest that a disbalanced recruitment of DRTu in the non-dominant VAT induces detrimental stimulation effects on the dominant cerebellar outflow (together with contralateral stimulation) leading to DTE and thus hampering the overall treatment efficacy.

Details DOI

YNICL Journal 2022 Journal Article

Unravelling delayed therapy escape after thalamic deep brain stimulation for essential tremor? – Additional clinical and neuroimaging evidence

Bastian E.A. Sajonz
Marvin L. Frommer
Isabelle D. Walz
Marco Reisert
Christoph Maurer
Michel Rijntjes
Tobias Piroth
Nils Schröter

BACKGROUND: Delayed therapy escape after thalamic deep brain stimulation (DBS) for essential tremor is a serious yet frequent condition. It is often difficult to detect this process at onset due to its gradual evolution. OBJECTIVE: Here we aim to identify clinical and neuroimaging hallmarks of delayed therapy escape. METHODS: F]FDG PET of an age-matched control group was performed. Exploratory correlation analyses were conducted with operationalized and parametric clinical data. RESULTS: compared with the healthy controls. CONCLUSIONS: Rebound frequency of postural tremor seems to be a good diagnostic marker for delayed therapy escape. Regional glucose metabolism suggests that this phenomenon may be associated with increased metabolic activity in the thalamus and dentate nucleus possibly due to antidromic stimulation effects. We see reasons to interpret the delayed therapy escape phenomenon as being related to long term and chronic DBS.

Details DOI

YNICL Journal 2019 Journal Article

Hypercapnic BOLD MRI compared to H215O PET/CT for the hemodynamic evaluation of patients with Moyamoya Disease

Till-Karsten Hauser
Achim Seeger
Benjamin Bender
Uwe Klose
Johannes Thurow
Ulrike Ernemann
Marcos Tatagiba
Philipp T. Meyer

BACKGROUND AND PURPOSE: O PET/CT with ACZ challenge to assess comparability between both modalities. METHODS: O PET/CT with ACZ challenge in patients with angiographically proven MMD. Images of both modalities were analyzed retrospectively in a blinded, standardized fashion by visual inspection, as well as with a semi-quantitative analysis using stimuli-induced approximated regional perfusion-weighted data and BOLD-signal changes with reference to cerebellum. RESULTS: 20 consecutive patients fulfilled the inclusion criteria, a total of 160 vascular territories were analyzed retrospectively. Visual analysis (4-step visual rating system) of standardized, color-coded cerebrovascular reserve/reactivity maps showed a very strong correlation (Spearman's rho = 0.9, P < 0.001) between both modalities. Likewise, comparison of approximated regional perfusion changes across vascular territories (normalized to cerebellar change) reveal a highly significant correlation between both methods (Pearson's r = 0.71, P < 0.001). CONCLUSIONS: O PET/CT with ACZ challenge. It therefore holds future potential in becoming a routine examination in the pre- and postoperative evaluation of MMD patients after further prospective evaluation.

Details DOI

YNICL Journal 2018 Journal Article

Voxel-wise deviations from healthy aging for the detection of region-specific atrophy

Stefan Klöppel
Shan Yang
Elias Kellner
Marco Reisert
Bernhard Heimbach
Horst Urbach
Jennifer Linn
Stefan Weidauer

The identification of pathological atrophy in MRI scans requires specialized training, which is scarce outside dedicated centers. We sought to investigate the clinical usefulness of computer-generated representations of local grey matter (GM) loss or increased volume of cerebral fluids (CSF) as normalized deviations (z-scores) from healthy aging to either aid human visual readings or directly detect pathological atrophy. Two experienced neuroradiologists rated atrophy in 30 patients with Alzheimer's disease (AD), 30 patients with frontotemporal dementia (FTD), 30 with dementia due to Lewy-body disease (LBD) and 30 healthy controls (HC) on a three-point scale in 10 anatomical regions as reference gold standard. Seven raters, varying in their experience with MRI diagnostics rated all cases on the same scale once with and once without computer-generated volume deviation maps that were overlaid on anatomical slices. In addition, we investigated the predictive value of the computer generated deviation maps on their own for the detection of atrophy as identified by the gold standard raters. Inter and intra-rater agreements of the two gold standard raters were substantial (Cohen's kappa κ > 0.62). The intra-rater agreement of the other raters ranged from fair (κ = 0.37) to substantial (κ = 0.72) and improved on average by 0.13 (0.57 < κ < 0.87) when volume deviation maps were displayed. The seven other raters showed good agreement with the gold standard in regions including the hippocampus but agreement was substantially lower in e.g. the parietal cortex and did not improve with the display of atrophy scores. Rating speed increased over the course of the study and irrespective of the presentation of voxel-wise deviations. Automatically detected large deviations of local volume were consistently associated with gold standard atrophy reading as shown by an area under the receiver operator characteristic of up to 0.95 for the hippocampus region. When applying these test characteristics to prevalences typically found in a memory clinic, we observed a positive or negative predictive value close to or above 0.9 in the hippocampus for almost all of the expected cases. The volume deviation maps derived from CSF volume increase were generally better in detecting atrophy. Our study demonstrates an agreement of visual ratings among non-experts not further increased by displaying, region-specific deviations of volume. The high predictive value of computer generated local deviations independent from human interaction and the consistent advantages of CSF-over GM-based estimations should be considered in the development of diagnostic tools and indicate clinical utility well beyond aiding visual assessments.

Details DOI

YNIMG Journal 2010 Journal Article

Simplified quantification of 5-HT2A receptors in the human brain with [11C]MDL 100,907 PET and non-invasive kinetic analyses

Philipp T. Meyer
Zubin Bhagwagar
Philip J. Cowen
Vincent J. Cunningham
Paul M. Grasby
Rainer Hinz

Background: [11C]MDL100, 907 is a promising positron emission tomography (PET) ligand for 5-HT2A receptor quantification in vivo. Studies suggest that [11C]MDL100, 907 PET may be quantified by non-invasive reference tissue analyses using cerebellum as reference region. We systematically investigated the validity of such analyses. Methods: Five healthy volunteers underwent [11C]MDL100, 907 PET at baseline and after mirtazapine pre-treatment. Regional time–activity curves of 10 regions of interest (ROI) were analyzed for binding potential (BP ND) and mirtazapine receptor occupancy (Occ) using: simplified reference tissue model (SRTM), multi-linear reference tissue model (MRTM), their two-parameter versions (SRTM2/MRTM2), non-invasive graphical analysis (NIGA) and a tissue activity concentration ratio. NIGA was also applied voxel-wise to generate BP ND maps. These methods were compared with a two-tissue compartment model with arterial input function (2TCM) Results: SRTM and MRTM frequently failed to yield reliable results. SRTM2 and MRTM2 gave virtually identical estimates of BP ND, which were highly correlated with 2TCM analyses (R 2 ≥0. 86) although with negative bias (−29±27% at baseline across all ROI). NIGA was less biased (−19±16%) and better correlated with 2TCM (R 2 ≥0. 93). Regarding Occ, NIGA and SRTM2/MRTM2 showed comparable mean biases (−11±27% vs. −7±47%) but correlation with 2TCM was higher for NIGA (R 2 =0. 90 vs. 0. 77). NIGA parametric maps (analysed using identical ROI) resulted in moderate bias in BP ND (−26±22%; R 2 ≥0. 88) and Occ (−17±36%; R 2 =0. 78). Estimates obtained from tissue ratios performed least favourably. Conclusions: NIGA is well suited for analysis of [11C]MDL100, 907 PET studies, yielding estimates of 5-HT2A receptor availability and changes that are highly correlated with results from invasive 2TCM analyses. This should greatly enhance the applicability of 5-HT2A receptor PET studies.

Details DOI

YNIMG Journal 2008 Journal Article

Kinetic analyses of [123I]IBZM SPECT for quantification of striatal dopamine D2 receptor binding: A critical evaluation of the single-scan approach

Philipp T. Meyer
Bernhard Sattler
Oliver H. Winz
Rico Fundke
Christian Oehlwein
Kai Kendziorra
Swen Hesse
Wolfgang M. Schaefer

Background Dopamine-D2 receptor imaging with single-photon emission computed tomography (SPECT) and [123I]IBZM is of great interest for basic and applied neurosciences. However, the use of kinetic analyses for quantification of dynamic [123I]IBZM SPECT and the validity of the commonly employed single-scan pseudo-equilibrium analysis (PsEA) have not been appropriately investigated. The present study addresses these shortcomings. Methods Ten movement disorder patients underwent dynamic SPECT (142 min) after single-bolus [123I]IBZM injection. Kinetic analyses comprise: simplified reference tissue model (SRTM), multi-linear reference tissue model (MRTM), their two-parameter versions (SRTM2/MRTM2) and non-invasive graphical analysis (NIGA). Simplified single-scan analyses were performed at peak time of specific binding (peak-equilibrium analysis, PEA) and during pseudo-equilibrium (PsEA). Results SRTM and MRTM are compromised by the high noise level of dynamic SPECT. SRTM2 and MRTM2 yielded reliable binding potential estimates that agreed excellently (mean difference=−0. 1±1. 0%, R 2 >0. 99). Concordance between SRTM/MRTM and SRTM2/MRTM2 was high in cases in which SRTM/MRTM provided reliable results (SRTM2 or MRTM2 vs. SRTM: 3. 7±5. 0%, R 2 =0. 88). NIGA was affected by a negative bias (−9. 1±6. 3%, R 2 =0. 75; MRTM2 as reference) or high variability (−1. 2±7. 4%, R 2 =0. 71) for analyses without and with inclusion of the k 2′-term, respectively. PsEA showed a positive bias and low correlation in comparison with SRTM2/MRTM2 (7. 6±10. 8%, R 2 =0. 59), which was considerably improved for PEA (−2. 7±7. 6%, R 2 =0. 72). MRTM2 provided parametric images with minimal bias suited for voxel-wise statistical analyses. Conclusions MRTM2 and SRTM2 can be reliably applied to dynamic [123I]IBZM SPECT. PEA is a suitable method for clinical routine, while our results discourage the use of PsEA (current clinical standard).

Details DOI

YNIMG Journal 2006 Journal Article

A1 adenosine receptor PET using [18F]CPFPX: Displacement studies in humans

Philipp T. Meyer
David Elmenhorst
Andreas Matusch
Oliver Winz
Karl Zilles
Andreas Bauer

Background. Imaging of cerebral A1 adenosine receptors (A1AR) with positron emission tomography (PET) has recently become available for neurological research. To date, it has still not been unraveled if there is a valid reference region without specific radioligand binding that may be used to improve image quantification. We conducted in vivo displacement studies in humans to elucidate this important question using the A1AR ligand [18F]CPFPX. Methods. Five healthy male volunteers underwent [18F]CPFPX bolus/infusion PET with short infusion of unlabelled CPFPX as competitor (n = 4; 0. 9 to 4. 0 mg) or vehicle (n = 1; control condition) after equilibrium of [18F]CPFPX distribution was attained. Results. Infusion of CPFPX induced a rapid displacement of [18F]CPFPX binding in all regions, including the cerebellum (region with lowest binding). Even at the highest competitor dose, no full displacement was reached. Displacement was dose-dependent in all regions except the cerebellum where floor effects and/or noise might have obscured dose dependency. Specific binding was estimated to account for about one third and two thirds of total equilibrium uptake in cerebellum and cortex, respectively. Conclusions. Although the cerebellum is the region with lowest in vivo [18F]CPFPX binding, it is not an ideal reference region devoid of specific binding. Nevertheless, as will be discussed, the use of a reference region analysis may be a useful, non-invasive alternative analysis method in carefully selected applications.

Details DOI

YNIMG Journal 2005 Journal Article

Quantification of cerebral A1 adenosine receptors in humans using [18F]CPFPX and PET: an equilibrium approach

Philipp T. Meyer
David Elmenhorst
Dirk Bier
Marcus H. Holschbach
Andreas Matusch
Heinz H. Coenen
Karl Zilles
Andreas Bauer

The cerebral A1 adenosine receptor (A1AR) has recently become accessible for in vivo imaging using the selective A1AR ligand [18F]CPFPX and PET. For broad application in neurosciences, imaging at distribution equilibrium is advantageous to quantify stimulus-dependent changes in receptor availability and to avoid arterial blood sampling. Here we propose a bolus/infusion (B/I) protocol to assess the total distribution volume (DVt) of [18F]CPFPX under equilibrium conditions. Employing a bolus-to-infusion ratio of 0. 8 h, (near) equilibrium conditions were attained within 60 min. The regional DVt′ given by arterial and venous equilibrium analyses agreed well with conventional two-tissue compartment model analyses (r 2 > 0. 94 and r 2 > 0. 84, respectively) and Logan's graphical analyses (r 2 = 1. 0 and r 2 > 0. 93, respectively) (n = 4 healthy volunteers). The mean regional DVt′ values of these equilibrium analyses and of venous equilibrium analyses in additional seven volunteers demonstrated excellent agreement with the results of earlier bolus studies (r 2 > 0. 98). Error simulations show that minor deviations from true equilibrium are associated with negligible to small DVt errors. In conclusion, [18F]CPFPX shows suitable characteristics for A1AR quantification by B/I PET scanning. Carefully standardized venous equilibrium analyses may substitute arterial analyses and thus considerably enhance applicability of A1AR PET in clinical routine.

Details DOI