Biomedical subjects

P T Meyer

Publications and source records attributed to P T Meyer.

10 recordsLinked to original sources

PubMed2003

Preoperative motor system brain mapping using positron emission tomography and statistical parametric mapping: hints on cortical reorganisation.

OBJECTIVES: This study investigated the applicability of statistical parametric mapping (SPM) for analysing individual preoperative brain mapping studies in patients with cerebral mass lesions for neurosurgical planning. The study further investigated if hints on functional reorganisation processes can be found. METHODS: Nine adult patients with cerebral mass lesions underwent activation [(15)O]water-PET under stimulation by finger (n=9) and foot (n=4) movement. Individual SPM-t-maps were computed without anatomical normalisation and coregistered to the individual magnetic resonance imaging. Relative cerebral blood flow change maps were calculated for comparison. RESULTS: The spatial relation between the sensorimotor cortex and the lesion could be determined in all cases. Additional activations covered the ipsilateral sensorimotor cortex and the bilateral cerebellum, premotor cortices and supplementary motor areas. Patients with motor symptoms of the stimulated hand (paresis, focal seizures) activated the ipsilateral premotor cortices and contralateral cerebellum more often than patients without motor symptoms. The SPM results for p<0.005 and cerebral blood flow change maps showed considerably overlapping motor area activations. For p<0.001, SPM missed three sensorimotor cortex activations depicted by cerebral blood flow change maps and by SPM for p<0.005 in typical localisation. SPM analyses showed less activations probably unrelated to task performance. CONCLUSION: It is concluded that SPM provides an efficient method for analysing individual preoperative PET activation studies. Activations of the ipsilateral premotor cortices and contralateral cerebellum may indicate an enhanced recruitment of ipsilateral motor pathways evoked by functional reorganisation processes. However, this changed activation pattern was not necessarily associated with a better neurological status.

Adult↗

PubMed2002

Functional MRI and 18F FDG-positron emission tomography for presurgical planning: comparison with electrical cortical stimulation.

BACKGROUND: In patients with mass lesions near "eloquent" cortical areas different preoperative mapping techniques can be used. Two of the most widely used approaches include positron emission tomography (PET) and functional MRI (fMRI). We employed both methods in the same patients undergoing presurgical evaluation and compared the results to those obtained by direct electrical cortical stimulation (DECS). METHOD: 22 patients with tumours of different aetiology near the central region were investigated. FMRI was performed using a T2(*)-weighted gradient-echo BOLD sequence at 1.5 T, PET was performed after injection of 122-301 MBq (18)F-Fluorodeoxyglucose (18-FDG) under rest and activation conditions. DECS was performed in all patients with recordings of muscles primarily involved in the investigated tasks. FINDINGS: In 19 patients all three modalities could be compared, 1 patient demonstrated discordance between fMRI and PET with DECS speaking in favour of fMRI, 6 patients had neighbouring results of PET and fMRI (between 1-2 cm distance), 12 patients had overlapping results. INTERPRETATION: The high incidence of neighbouring results is presumably related to fMRI specific artefacts. Advantages of fMRI are: Higher spatial and temporal resolution, more and different functional runs, shorter examination time, wider availability, longitudinal examinations, non-invasiveness and cost-effectiveness, easy registration to anatomical images. Advantages of PET are: higher signal-to-noise ratio, lesser susceptibility to artefacts (motion, draining veins), evaluation of tumour metabolism. It is our opinion that the neurosurgeon has to decide on a case-by-case basis which study suits his specific needs in the presurgical evaluation of his patient.

Adult↗

PubMed2001

Comparison of visual and ROI-based brain tumour grading using 18F-FDG PET: ROC analyses.

Several studies have suggested that the use of simple visual interpretation criteria for the investigation of brain tumours by positron emission tomography with fluorine-18 fluorodeoxyglucose (FDG-PET) might be similarly or even more accurate than quantitative or semi-quantitative approaches. We investigated this hypothesis by comparing the accuracy of FDG-PET brain tumour grading using a proposed six-step visual grading scale (VGS; applied by three independent observers unaware of the clinical history and the results of histopathology) and three different region of interest (ROI) ratios (maximal tumour uptake compared with contralateral tissue [Tu/Tis], grey matter [Tu/GM] and white matter [Tu/WM]). The patient population comprised 47 patients suffering from 17 benign (7 gliomas of grade II, 10 non-gliomatous tumours) and 30 malignant (23 gliomas of grade III-IV, 7 non-gliomatous tumours) tumours. The VGS results were highly correlated with the different ROI ratios (R=0.91 for Tu/GM, R=0.82 for Tu/WM, and R=0.79 for Tu/Tis), and high inter-observer agreement was achieved (kappa=0.63, 0.76 and 0.81 for the three observers). The mean ROI ratios and VGS readings of gliomatous and non-gliomatous lesions were not significantly different. For all measures, high-grade lesions showed significantly higher FDG uptake than low-grade lesions (P<0.005 to P<0.0001, depending on the measure used). Nominal logistic regressions and receiver operating characteristic (ROC) analyses were used to calculate cut-off values to differentiate low- from high-grade lesions. The predicted (by ROC) diagnostic sensitivity/specificity of the different tests (cut-off ratios shown in parentheses) were: Tu/GM: 0.87/0.85 (0.7), Tu/WM: 0.93/0.80 (1.3). Tu/Tis: 0.80/0.80 (0.8) and VGS: 0.84/0.95 (uptake < GM, but >> WM). The VGS yielded the highest Az (+/-SE) value (i.e. area under the ROC curve as a measure of predicted accuracy), 0.97+/-0.03, which showed a strong tendency towards being significantly greater than the Az of Tu/Tis (0.88+/-0.06; P=0.06). Tu/GM (0.92+/-0.04) and Tu/WM (0.91+/-0.05) reached intermediate Az values (not significantly different from any other value). We conclude that the VGS represents a measure at least as accurate as the Tu/GM and Tu/WM ratios. The Tu/Tis ratio is less valid owing to the high dependence on the location of the lesion. Depending on the investigator's experience and the structure of the lesions, the easily used VGS might be the most favourable grading criterion.

Adolescent↗

PubMed2001

Localisation of motor areas in brain tumour patients: a comparison of preoperative [18F]FDG-PET and intraoperative cortical electrostimulation.

Assessment of the exact spatial relation between tumour and adjacent functionally relevant brain areas is a primary tool in the presurgical planning in brain tumour patients. The purpose of this study was to compare a preoperative fluorine-18 fluorodeoxyglucose positron emission tomography ([18F]FDG PET) activation protocol in patients with tumours near the central area with the results of intraoperative direct cortical electrostimulation, and to determine whether non-invasive preoperative PET imaging can provide results equivalent to those achieved with the invasive neurosurgical "gold standard". In this prospective study, we examined 20 patients with various tumours of the central area, performing two PET scans (each 30 min after i.v. injection of 134-341 MBq [18F]FDG) in each patient: (1) a resting baseline scan and (2) an activation scan using a standardised motor task (finger tapping, foot stretching). Following PET/MRI realignment and normalisation to the whole brain counts, parametric images of the activation versus the rest study were calculated and pixels above categorical threshold values were projected to the individual MRI for bimodal assessment of morphology and function (PET/MRI overlay). Intraoperative direct cortical electrostimulation was performed using a Viking IV probe (5 pulses, each of 100 micros) and documented using a dedicated neuro navigation system. Results were compared with the preoperative PET findings. PET revealed significant activation of the contralateral primary motor cortex in 95% (19/20) of the brain tumour patients (hand activation 13/13, foot activation 6/7), showing a mean increase in normalised [18F]FDG uptake of 20.5% +/- 5.2% (hand activation task) and 17.2% +/- 2.5% (foot activation task). Additionally detected activation of the ipsilateral primary motor cortex was interpreted as a metabolic indication for interhemispheric compensational processes. Evaluation of the PET findings by cortical stimulation yielded a 94% sensitivity and a 95% specificity for identification of motor-associated brain areas. In conclusion, the findings indicate that a relatively simple and clinically available [18F]FDG PET activation protocol enables a sufficiently precise assessment of the local relation between the intracranial tumour and the adjacent motor cortex areas and may facilitate the presurgical planning of tumour resection.

Adult↗

PubMed2001

Inter-modality comparisons of seizure focus lateralization in complex partial seizures.

Anterior temporal lobectomy offers a high chance of seizure-free outcome in patients suffering from drug-refractory complex partial seizure (CPS) originating from the temporal lobe. Other than EEG, several functional and morphologic imaging methods are used to define the spatial seizure origin. The present study was undertaken to compare the merits of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET), magnetic resonance imaging (MRI) and single-voxel proton MR spectroscopy (MRS) for the lateralization of temporal lobe seizure foci. The clinical charts and imaging data of 43 consecutive CPS patients were reviewed. Based on surface EEG, 31 patients were classified with temporal lobe epilepsy (TLE; 25 lateralized, 6 not lateralized) and 12 with non-temporal lobe epilepsy. All were examined by FDG-PET, MRS and MRI within 6 weeks. FDG-PET and MRI were interpreted visually, while the N-acetyl-aspartate to creatine ratio was used for MRS interpretation. One FDG-PET scan was invalid due to seizure activity post injection. The MR spectra could not be evaluated in five cases bilaterally and three cases unilaterally for technical reasons. A total of 15 patients underwent anterior temporal lobectomy. All showed a beneficial postoperative outcome. When the proportions of agreement between FDG-PET (0.77), MRI (0.58) and MRS (0.56) and surface EEG in TLE cases were compared, there were no significant differences (P>0.10). However, FDG-PET showed a significantly higher agreement (0.93) than MRI (0.60; P=0.03) with the side of successful temporal lobectomy. The concordance of MRS with the side of successful temporal lobectomy was intermediate (0.75). When the results of functional and morphologic imaging were combined, no significant differences were found between the rates of agreement of FDG-PET/MRI and MRS/MRI with EEG (0.80 vs 0.68; P=0.50) and with the side of successful temporal lobectomy (0.87 vs 0.92; P=0.50) in TLE cases. However, MRS/MRI showed significantly more lateralized temporal lobe abnormalities in non-temporal lobe epilepsy cases than FDG-PET/MRI (0.90 vs. 0.17; P<0.01). Although FDG-PET seems to be the most reliable and stable method for this purpose, we conclude that in TLE cases it may be justified to perform MRS, which is less expensive, faster and has no radiation exposure, in combination with MRI before FDG-PET, since FDG-PET offers little additional diagnostic information if MRS and MRI indicate the same seizure focus lateralization.

Adolescent↗

PubMed2001

Metabolic and electrophysiological validation of functional MRI.

OBJECTIVES: Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neuronal activity is not exactly known. Experience with methods that may validate fMRI data and the results obtained when coregistering fMRI with different preoperative and intraoperative mapping modalities including metabolically based (18)F-fluorodeoxyglucose PET, electrophysiologcally based transcranial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described. METHODS: Fifty patients were included. PET was performed in 30, TMS in 10, and DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouring (<2 cm), or contradictory (>2 cm). RESULTS: Comparing fMRI with PET, 18 overlapping, seven neighbouring, and one contradictory result were obtained. In four patients no comparison was possible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and fMRI showed seven overlapping and three neighbouring results. In three patients no DECS results could be obtained. Of the remaining 38 patients, fMRI hand motor tasks were compared with DECS results of the upper limb muscles in 36 patients, and fMRI foot motor tasks were compared with DECS results of the lower limb on 13 occasions. Of those 49 studies, overlapping results were obtained in 31 patients, and neighbouring in 14. On four occasions fMRI did not show functional information (because of motion artefacts and low signal to noise). CONCLUSIONS: All validation techniques have intrinsic limitations that restrict their spatial resolution. However, of 50 investigated patients, there was only one in whom results contradictory to fMRI were obtained. Although it is not thought that fMRI can replace the intraoperatively updated functional information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.

Adult↗

PubMed2001

Detection of mesial temporal lobe hypoperfusion in patients with temporal lobe epilepsy by use of arterial spin labeled perfusion MR imaging.

BACKGROUND AND PURPOSE: Interictal hypometabolism has lateralizing value in cases of temporal lobe epilepsy and positive predictive value for seizure-free outcome after surgery to treat epilepsy. Alterations in regional cerebral metabolism can also be inferred from measurements of regional cerebral perfusion. The purpose of this study was to determine the feasibility of detecting cerebral blood flow (CBF) asymmetries in the mesial temporal lobes using continuous arterial spin labeling perfusion MR imaging, which is a noninvasive method for calculating regional CBF. METHODS: Twelve patients with medically refractory temporal lobe epilepsy who underwent preoperative evaluation for temporal lobectomy and 12 normal control participants were studied retrospectively. Absolute and normalized mesial temporal CBF measurements were compared between the patient and control groups. Lateralization based on a perfusion asymmetry index was compared with metabolic ((18)[F]-fluorodeoxyglucose positron emission tomography) and hippocampal volumetric asymmetry indices and with clinical lateralization. RESULTS: Mesial temporal CBF was more asymmetric in patients with temporal lobe epilepsy than in normal control participants, although asymmetric mesial temporal CBF was also found in normal participants, with the left side dominant. Ipsilateral mesial temporal CBF was significantly decreased compared with contralateral mesial temporal CBF in patients with temporal lobe epilepsy. Global CBF measurements were significantly decreased in patients compared with control participants. Asymmetry in mesial temporal blood flow in patients persisted after normalization to global CBF. Lateralization using continuous arterial spin labeling perfusion MR imaging asymmetry index significantly correlated with lateralization based on (18)[F]-fluorodeoxyglucose positron emission tomography hypometabolism, hippocampal volumes, and clinical evaluation. CONCLUSION: Continuous arterial spin labeling perfusion MR imaging can detect interictal asymmetries in mesial temporal lobe perfusion in patients with temporal lobe epilepsy. This technique is readily combined with routine structural assessment and potentially offers an inexpensive and noninvasive means of screening for asymmetries in interictal mesial temporal lobe function.

Adult↗

PubMed2000

Simplified quantification of dopamine transporters in humans using [99mTc]TRODAT-1 and single-photon emission tomography.

Quantification of dopamine transporters (DAT) using [99mTc]TRODAT-1 and single-photon emission tomography (SPET) requires full kinetic modeling of the data, using complex and invasive arterial blood sampling to provide an input function to the model. We have shown previously that a simpler reference tissue model provides accurate quantitative results, using a reference region devoid of DAT as the input to the model and thereby obviating the need for blood sampling. We now extend this work into humans, and develop further simplifications to make the imaging protocol much more practical as a routine procedure. Fourteen healthy subjects (age 29.8 +/- 8.4 years, range 18.7-45.5 years) underwent dynamic SPET for 6 h following injection of 752 +/- 28 MBq [99mTc]TRODAT-1. The kinetic data were analyzed using nonlinear regression analysis (NLRA) and Logan-Patlak graphical analysis. In addition, simple average ratios of striatal-to-background counts were obtained for three 1-h periods (3-4 h, 4-5 h, 5-6 h), and compared against the kinetic models. All methods gave an index of specific binding, proportional to the binding potential, known as the distribution volume ratio (DVR). The reference tissue NLRA gave mean values of k3=0.013 +/- 0.003 min(-1), k4=0.011 +/- 0.002 min(-1), and DVR=2.29 +/- 0.17. Graphical analysis gave a value of DVR=2.28 +/- 0. 16, and the three ratio values of DVR were: 3-4 h, 2.18 +/- 0.15; 4-5 h, 2.34 +/- 0.13; and 5-6 h, 2.46 +/- 0.19. Graphical analysis was highly correlated with NLRA (R2=0.91, slope=0.90 +/- 0.08). The ratio methods correlated well with NLRA (3-4 h, R2=0.71, slope= 0.73 +/- 0.13; 4-5 h, R2=0.86, slope=0.73 +/- 0.09; 5-6 h, R2=0.80, slope=1.00 +/- 0.15), and also with graphical analysis (3-4 h, R2=0.65, slope=0.74 +/- 0.16; 4-5 h, R2=0.85, slope=0.78 +/- 0.09; 5-6 h, R2=0.88, slope=1.11 +/- 0.12). The optimum equilibrium time point for obtaining a simple ratio was approximately 4.5-5.5 h. In conclusion, the simple ratio techniques for obtaining a quantitative measure of specific binding correlated well with the reference tissue kinetic models, using both NLRA and graphical analysis. The optimum time for obtaining a ratio appeared to be in the range 4.5-5.5 h. Earlier time points, while still relatively accurate, had a lower sensitivity and may not be optimized for measuring small changes in DAT concentrations.

Adolescent↗

PubMed2000

High F-18 FDG uptake in a low-grade supratentorial ganglioma: a positron emission tomography case report.

PURPOSE: Positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose (F-18 FDG) is used for the noninvasive monitoring and grading of primary brain tumors. Here the FDG uptake is positively correlated with the malignant extent of the lesion and thereby negatively correlated with patient survival. Little is known about the FDG PET features of primary brain tumors in children, such as mixed neuronal-glial tumors. METHODS: The authors describe a 13-year-old boy who had partial complex seizures since early childhood caused by a brain tumor in the left temporal lobe. RESULTS: Magnetic resonance and computed tomographic examinations yielded uncharacteristic results: mixed density, marked calcifications, little contrast enhancement, a nearly absent mass effect, and no edema. The FDG PET scan revealed a large hypermetabolic tumor, with a tumor: contralateral gray matter FDG uptake ratio of 1.45. In contrast to this intense hypermetabolism, the pathologic analysis after gross total resection revealed a low-grade ganglioglioma (WHO grade 1), which is usually associated with an excellent prognosis. CONCLUSIONS: Mixed neuronal-glial tumors such as gangliogliomas must be considered in making differential diagnoses by judging hypermetabolic FDG PET scans in young patients with brain tumors in the presence of uncharacteristic imaging features.

Adolescent↗

PubMed2000

[Comparison of different methods for attenuation correction in brain PET: effect on the calculation of the metabolic rate of glucose].

AIM: There are several approaches for correcting the effects of photon scatter or absorption by body tissues on positron emission tomography (PET). We examined the influence of cold, hot and segmented transmission as well as of a mathematical procedure on attenuation correction using regional cerebral glucose metabolism (rMRGlu). METHODS: 6 patients with different cerebral diseases were examined under resting conditions using an ECAT Exact 922/47. The attenuation-corrected data (corrected by means of cold, hot and segmented transmission as well as a mathematical procedure) were then quantified absolutely for assessment of regional glucose metabolism in 16 regions of interest (ROIs). RESULTS: Using absolutely quantified glucose metabolism in 16 ROIs, no significant differences were found between cold transmission and the mathematical procedure except for three regions (left and right temporal occipital and right parietal occipital). Unlike the mathematical procedure, both hot and segmented transmission showed a significantly lower value for regional glucose utilization in all 16 ROIs than did cold transmission. The left and the right hemisphere both showed metabolic values (rMRGlu) in the same decreasing order: cold transmission, the mathematical procedure, hot or segmented transmission. There was no significant difference between global cerebral glucose metabolism values for cold transmission and the mathematical procedure (p = 0.25) while those for hot (p = 0.03) and segmented transmission (p = 0.03) did show a significant difference. CONCLUSIONS: Except for 3 regions (temporo-occipital left, temporo-occipital right and parieto-occipital right) attenuation correction procedures used for brain PET studies on patients show no significant quantitative differences between cold transmission and the mathematical procedure. rMRGlu of images corrected for attenuation using hot and segmented transmission is significantly lower than of attenuation corrected images where cold transmission was employed. For clinical routine examinations, the mathematical procedure seems the best alternative to cold transmission for a faster brain PET acquisition.

Adult↗