Enhanced Deep-Inspiration Breath Hold Superior to High-Frequency Percussive Ventilation for Respiratory Motion Mitigation: A Physiology-Driven, MRI-Guided Assessment Toward Optimized Lung Cancer Treatment With Proton Therapy

Background: To safely treat lung tumors using particle radiation therapy (PRT), motion-mitigation strategies are of critical importance to ensure precise irradiation. Therefore, we compared applicability, effectiveness, reproducibility, and subjects' acceptance of enhanced deep-inspiration breath hold (eDIBH) with high-frequency percussive ventilation (HFPV) by MRI assessment within 1 month.

Methods: Twenty-one healthy subjects (12 males/9 females; age: 49.5 ± 5.8 years; BMI: 24.7 ± 3.3 kg/m⁻²) performed two 1.5 T MRI scans in four visits at weekly intervals under eDIBH and HFPV conditions, accompanied by daily, home-based breath-hold training and spirometric assessments over a 3-week period. eDIBH consisted of 8-min 100% O₂ breathing (3 min resting ventilation, 5 min controlled hyperventilation) prior to breath hold. HFPV was set at 200–250 pulses min⁻¹ and 0.8–1.2 bar. Subjects' acceptance and preference were evaluated by questionnaire. To quantify inter- and intrafractional changes, a lung distance metric representing lung topography was computed for 10 reference points: a motion-invariant spinal cord and nine lung structure contours (LSCs: apex, carina, diaphragm, and six vessels as tumor surrogates distributed equally across the lung). To parameterize individual LSC localizability, measures of their spatial variabilities were introduced and lung volumes calculated by automated MRI analysis.

Results: eDIBH increased breath-hold duration by > 100% up to 173 ± 73 s at visit 1, and to 217 ± 67 s after 3 weeks of home-based training at visit 4 (p < 0.001). Measures of vital capacity and lung volume remained constant over the 3-week period. Two vessels in the lower lung segment and the diaphragm yielded a two- to threefold improved positional stability with eDIBH, whereby absolute distance variability was significantly smaller for five LSCs; ≥70% of subjects showed significantly better intrafractional lung motion mitigation under reproducible conditions with eDIBH compared with HFPV with smaller ranges most apparent in the anterior-posterior and cranial-caudal directions. Approximately 80% of subjects preferred eDIBH over HFPV, with “less discomfort” named as most frequent reason.

Conclusions: Both, eDIBH, and HFPV were well-tolerated. eDIBH duration was long enough to allow for potential PRT. Variability in lung volume was smaller and position of lung structures more precise with eDIBH. Subjects preferred eDIBH over HFPV. Thus, eDIBH is a very promising tool for lung tumor therapy with PRT, and further investigation of its applicability in patients is warranted.

The Human Centriolar Protein CEP135 Contains a Two-Stranded Coiled-Coil Domain Critical for Microtubule Binding

Centrioles are microtubule-based structures that play important roles notably in cell division and cilium biogenesis. CEP135/Bld10p family members are evolutionarily conserved microtubule-binding proteins important for centriole formation. Here, we analyzed in detail the microtubule-binding activity of human CEP135 (HsCEP135). X-ray crystallography and small-angle X-ray scattering in combination with molecular modeling revealed that the 158 N-terminal residues of HsCEP135 (HsCEP135-N) form a parallel two-stranded coiled-coil structure. Biochemical, cryo-electron, and fluorescence microscopy analyses revealed that in vitro HsCEP135-N interacts with tubulin, protofilaments, and microtubules and induces the formation of microtubule bundles. We further identified a 13 amino acid segment spanning residues 96-108, which represents a major microtubule-binding site in HsCEP135-N. Within this segment, we identified a cluster of three lysine residues that contribute to the microtubule bundling activity of HsCEP135-N. Our results provide the first structural information on CEP135/Bld10p proteins and offer insights into their microtubule-binding mechanism.

Interhemispheric cerebral blood flow balance during recovery of motor hand function after ischemic stroke--a longitudinal MRI study using arterial spin labeling perfusion

BACKGROUND

Unilateral ischemic stroke disrupts the well balanced interactions within bilateral cortical networks. Restitution of interhemispheric balance is thought to contribute to post-stroke recovery. Longitudinal measurements of cerebral blood flow (CBF) changes might act as surrogate marker for this process.

OBJECTIVE

To quantify longitudinal CBF changes using arterial spin labeling MRI (ASL) and interhemispheric balance within the cortical sensorimotor network and to assess their relationship with motor hand function recovery.

METHODS

Longitudinal CBF data were acquired in 23 patients at 3 and 9 months after cortical sensorimotor stroke and in 20 healthy controls using pulsed ASL. Recovery of grip force and manual dexterity was assessed with tasks requiring power and precision grips. Voxel-based analysis was performed to identify areas of significant CBF change. Region-of-interest analyses were used to quantify the interhemispheric balance across nodes of the cortical sensorimotor network.

RESULTS

Dexterity was more affected, and recovered at a slower pace than grip force. In patients with successful recovery of dexterous hand function, CBF decreased over time in the contralesional supplementary motor area, paralimbic anterior cingulate cortex and superior precuneus, and interhemispheric balance returned to healthy control levels. In contrast, patients with poor recovery presented with sustained hypoperfusion in the sensorimotor cortices encompassing the ischemic tissue, and CBF remained lateralized to the contralesional hemisphere.

CONCLUSIONS

Sustained perfusion imbalance within the cortical sensorimotor network, as measured with task-unrelated ASL, is associated with poor recovery of dexterous hand function after stroke. CBF at rest might be used to monitor recovery and gain prognostic information.

Structural analysis of vascular endothelial growth factor receptor-2/ligand complexes by small-angle X-ray solution scattering

Receptor tyrosine kinases play essential roles in tissue development and homeostasis, and aberrant signaling by these molecules is the basis of many diseases. Understanding the activation mechanism of these receptors is thus of high clinical relevance. We investigated vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs), which regulate blood and lymph vessel formation. We analyzed the structural changes in the extracellular receptor domain that were induced by ligand binding and that represent the initial step in transmembrane signaling, culminating in the activation of the intracellular receptor kinase domain. High-resolution structural information for the ligand binding domain became available recently, but the flexibility of the extracellular domain and inhomogeneous glycosylation of VEGFRs have prevented the production of highly diffracting crystals of the entire extracellular domain so far. Therefore, we chose to further investigate VEGFR structure by small-angle X-ray scattering in solution (SAXS). SAXS data were combined with independent distance restraint determination obtained by mass spectrometric analysis of chemically cross-linked ligand/receptor complexes. With these data, we constructed a structural model of the entire extracellular receptor domain in the unbound form and in complex with VEGF.

On the neural networks of empathy: A principal component analysis of an fMRI study

BACKGROUND

Human emotional expressions serve an important communicatory role allowing the rapid transmission of valence information among individuals. We aimed at exploring the neural networks mediating the recognition of and empathy with human facial expressions of emotion.

METHODS

A principal component analysis was applied to event-related functional magnetic imaging (fMRI) data of 14 right-handed healthy volunteers (29 +/- 6 years). During scanning, subjects viewed happy, sad and neutral face expressions in the following conditions: emotion recognition, empathizing with emotion, and a control condition of simple object detection. Functionally relevant principal components (PCs) were identified by planned comparisons at an alpha level of p < 0.001.

RESULTS

Four PCs revealed significant differences in variance patterns of the conditions, thereby revealing distinct neural networks: mediating facial identification (PC 1), identification of an expressed emotion (PC 2), attention to an expressed emotion (PC 12), and sense of an emotional state (PC 27).

CONCLUSION

Our findings further the notion that the appraisal of human facial expressions involves multiple neural circuits that process highly differentiated cognitive aspects of emotion.

Brain areas involved in medial temporal lobe seizures: a principal component analysis of ictal SPECT data

The study describes brain areas involved in medial temporal lobe (mTL) seizures of 12 patients. All patients showed so-called oro-alimentary behavior within the first 20 s of clinical seizure manifestation characteristic of mTL seizures. Single photon emission computed tomography (SPECT) images of regional cerebral blood flow (rCBF) were acquired from the patients in ictal and interictal phases and from normal volunteers. Image analysis employed categorical comparisons with statistical parametric mapping and principal component analysis (PCA) to assess functional connectivity. PCA supplemented the findings of the categorical analysis by decomposing the covariance matrix containing images of patients and healthy subjects into distinct component images of independent variance, including areas not identified by the categorical analysis. Two principal components (PCs) discriminated the subject groups: patients with right or left mTL seizures and normal volunteers, indicating distinct neuronal networks implicated by the seizure. Both PCs were correlated with seizure duration, one positively and the other negatively, confirming their physiological significance. The independence of the two PCs yielded a clear clustering of subject groups. The local pattern within the temporal lobe describes critical relay nodes which are the counterpart of oro-alimentary behavior: (1) right mesial temporal zone and ipsilateral anterior insula in right mTL seizures, and (2) temporal poles on both sides that are densely interconnected by the anterior commissure. Regions remote from the temporal lobe may be related to seizure propagation and include positively and negatively loaded areas. These patterns, the covarying areas of the temporal pole and occipito-basal visual association cortices, for example, are related to known anatomic paths.

Performance evaluation of the 16-module quad-HIDAC small animal PET camera

The quad-HIDAC small animal PET camera is a quadratic array of high-density avalanche chambers; the camera described in this publication consists of 16 modules. We present the system response using point and line sources and a mouse phantom. The quad-HIDAC camera exhibits a count rate stability of better than 1% and linearity of response to coincidences up to 2.2 x 10(5) cps at 16 MBq activity. Corrected for deadtime and random coincidences, the efficiency for the line source is 0.011, of which unscattered coincidences yield 0.009. The scatter fraction originating from the detectors is 0.22. Absorption within the mouse phantom was 20% and the scatter fraction increased to 0.29. Resolution is uniform within the entire field-of-view, which is 28 cm axially and 17 cm radially. Reconstruction of a point source yields a resolution of 1.1 mm FWHM for all three components. The performance of the camera demonstrates its excellent suitability for the functional imaging of small animals.

Dynamic imaging of striatal D2 receptors in mice using quad-HIDAC PET

The novel, dedicated small animal PET tomograph, quad-HIDAC, offers submillimeter resolution in instrumental characterization experiments. The aim of this study was to establish the tomograph's utility in a biologic application and to demonstrate the feasibility of rapid dynamic neuroreceptor imaging in mice.

METHODS

We used the well-established, high-affinity dopamine D(2) receptor PET ligand (18)F-fallypride for imaging striatal D(2) receptors in NMRI mice. Dynamic PET data were acquired using the quad-HIDAC tomograph and subject to 2 different kinetic modeling approaches. The cerebellum, a brain region devoid of D(2) receptors, was chosen as a reference region for kinetic modeling.

RESULTS

The resolution of the quad-HIDAC camera allowed clear visualization of the left and right mouse striatum with high target-to-nontarget signal ratios. The sensitivity of the tomograph permitted the generation of time-activity curves with initial time frames of 120 s. PET experiments acquiring data for 150 min demonstrated that the binding potential of (18)F-fallypride could be fitted robustly with both reference tissue models for scan durations of >or=40 min. Voxel-wise modeling resulted in parametric maps of high quality. The values for the binding potential in the striatum reached approximately 14, consistent with striatum-to-cerebellum ratios extracted from regional time-activity curves. Comparison of in vivo PET imaging results with ex vivo postmortem tissue sampling analyses indicated discrepancies in signal intensity, possibly resulting from scatter and random background in the cerebellum region of interest and leading to an overestimation of cerebellar activity concentrations and degradation of striatum-to-cerebellum ratios in PET experiments. Intraperitoneal injection of the unlabeled D(2) receptor antagonist haloperidol 30 min before intravenous injection of (18)F-fallypride blocked tracer accumulation in the striatum by >95%.

CONCLUSION

The quad-HIDAC camera represents a powerful tool for future dynamic neuroreceptor PET studies in mice and rats under numerous pharmacologic or pathophysiologic conditions.

Measurement of the extracellular space in brain tumors using 76Br-bromide and PET

Brain edema significantly contributes to the clinical course of human brain tumor patients. There is evidence that an enlargement of the extracellular space (ECS) is involved in the development of brain edema. Although T2-weighted magnetic resonance (T2-MR) images represent brain edema by its increased water content, they do not differentiate ECS enlargement from increased intracellular water content.

METHODS

On the basis of the known distribution of bromide in the ECS, we used (76)Br-bromide and PET to measure the regional ECS in 9 brain tumor patients. Transport rate constants and the distribution volume (DV) of (76)Br-bromide in normal brain and tumor were derived from dynamic PET scans and the measured (76)Br-bromide concentration in arterial plasma. We evaluated different models regarding their reliability in estimating the ECS.

RESULTS

Assuming that the DV of (76)Br-bromide represents the ECS, robust estimates were possible for all investigated regions. In normal brain, ECS was within a narrow range-for example, occipital lobe, 19.9% +/- 3.1%-and was lower in 2 dexamethasone-treated patients compared with untreated patients. In 7 of 9 tumors, increased ECS ranged between 43.8% and 61.1%. ECS increases were confined to the tumor mass and did not extend into peritumoral edematous brain. Two patients with large hyperintense lesions according to T2-MR images showed normal ECS values within the lesion.

CONCLUSION

(76)Br-Bromide PET allows a quantitative measurement of the ECS in brain edema and in normal brain. The discrepancies between lesions shown by T2-MRI and regional ECS enlargement as measured with PET challenge the concept of tumor-induced brain edema.

Neural activity related to the processing of increasing monetary reward in smokers and nonsmokers

This study investigated the processing of increasing monetary reward in nonsmoking and smoking subjects. The choice of the subject populations has been motivated by the observation of differences between nonsmokers and smokers in response to rewarding stimuli in a previous study. Subjects performed a pattern recognition task with delayed response, while rCBF was measured with [H215O] PET. Correct responses to the task were reinforced with three different amounts of monetary reward. The subjects received the sum of the rewards at the end of the experiment. The results show that a cortico-subcortical loop, including the dorsolateral prefrontal cortex, the orbitofrontal cortex, the cingulate gyrus and the thalamus is involved in processing increasing monetary reward. Furthermore, the striatal response differentiates nonsmokers from smokers. Thus, we found significant correlations between rCBF increases in striatum and increasing monetary reward and between striatal rCBF increases and mood in nonsmokers, but not in smokers. Moreover, no significant mood changes among the different monetary rewards could be observed in smokers. We infer that the response of the striatum to reward is related to changes in subjective feelings. The differences between smokers and nonsmokers confirm our previous conclusions that the association between blood flow, performance, mood and amount of reward is more direct in nonsmokers.

PET imaging drug distribution after intratumoral injection: the case for (124)I-iododeoxyuridine in malignant gliomas

Locoregional administration may yield higher tumor drug concentrations compared with intravenous injection and may reduce the risk of systemic adverse effect. Furthermore, in the case of brain tumors, it may circumvent limited drug delivery imposed by the blood-brain barrier. We used PET to study the retention and spatial distribution of iododeoxyuridine (IUdR), which has been used as a DNA-targeting radiosensitizing drug and which can be charged with therapeutic nuclides.

METHODS

Locoregional (resection cavity, tumor) instillation of 5-19 MBq (124)I-IUdR was achieved in 7 postoperative patients with malignant gliomas through a reservoir implanted in the skull. Patients were scanned with PET during the first hour and at 2, 24, and 48 h after (124)I-IUdR instillation. (124)I-IUdR metabolism was measured in the reservoir fluid in the presence or absence of a degradation inhibitor (5'-butyryl-IUdR [butyryl-IUdR]). Region-of-interest analysis was applied to calculate intratumoral retention (K(local)) of (124)I-IUdR from the PET images after a 24-h washout phase using an autoradiographic method.

RESULTS

At 24 h, radioactivity concentration in the reservoir was approximately 1% of the concentration 5 min after tracer instillation. The major metabolite of (124)I-IUdR in the reservoir was (124)I-iodouracil. (124)I-IUdR degradation could be partially inhibited by butyryl-IUdR. In the plasma, radioactivity peaked between 2 and 6 h. The area of tissue radioactivity increased with time up to 3-fold compared with the initial distribution. Tumor (124)I-IUdR retention (K(local)) ranged from 0.006 to 0.017 micro L/g/min, which is substantially lower compared with the IUdR-DNA incorporation reported recently after intravenous injection of (124)I-IUdR (K(i), 3.9 +/- 2.3 micro L/g/min, where K(i) is the DNA incorporation rate of (124)I-IUdR after intravenous tracer injection).

CONCLUSION

Although a single injection of (124)I-IUdR resulted in radioactivity distribution over the tumor, retention at 24 h was substantially lower compared with intravenous injection of (124)I-IUdR. Slow diffusion after locoregional administration, in contrast to fast delivery via tumor capillaries after intravenous injection, may account for our findings, resulting in a low amount of drug incorporation into DNA before degradation and washout from tissue.

Metabolic network abnormalities in early Huntington's disease: an [(18)F]FDG PET study

The identification of discrete patterns of altered functional brain circuitry in preclinical Huntington's disease (HD) gene carriers is important to understanding the pathophysiology of this disorder and could be useful as a biologic disease marker. The purpose of this study was to use PET imaging of regional cerebral glucose metabolism to identify abnormal networks of brain regions that are specifically related to the preclinical phase of HD.

METHODS

Eighteen presymptomatic HD gene carriers, 13 early-stage HD patients, and 8 age-matched gene-negative relatives were scanned using PET with [(18)F]FDG to quantify regional glucose utilization. A network modeling strategy was applied to the FDG PET data to identify disease-related regional metabolic covariance patterns in the preclinical HD cohort. The outcome measures were the region weights defining the metabolic topography of the HD gene carriers and the subject scores quantifying the expression of the pattern in individual subjects.

RESULTS

Network analysis of the presymptomatic carriers and the gene-negative control subjects revealed a significant metabolic covariance pattern characterized by caudate and putamenal hypometabolism but also included mediotemporal metabolic reductions as well as relative metabolic increases in the occipital cortex. Subject scores for this pattern were abnormally elevated in the preclinical group compared with those of the control group (P < 0.005) and in the early symptomatic group compared with those of the presymptomatic group (P < 0.005).

CONCLUSION

These findings show that FDG PET with network analysis can be used to identify specific patterns of abnormal brain function in preclinical HD. The presence of discrete patterns of metabolic abnormality in preclinical HD carriers may provide a useful means of quantifying the rate of disease progression during the earliest phases of this illness.

Reward mechanisms in the brain and their role in dependence: evidence from neurophysiological and neuroimaging studies

This article reviews neuronal activity related to reward processing in primate and human brains. In the primate brain, neurophysiological methods provide a differentiated view of reward processing in a limited number of brain structures. Dopamine neurons respond to unpredictable rewards and produce a global reinforcement signal. Some neurons in the striatum also react to the expectation and detection of reward. Other striatal neurons show reward-related activities related to the preparation, initiation and execution of movement. Orbitofrontal neurons discriminate among different rewards and code reward preferences. In the human brain, regions belonging to a meso-striatal and meso-corticolimbic loop respond to reinforcement stimuli in control subjects. These observations corroborate results obtained in primates. Additionally, reward induces activation in regions specific to task performance. Our results also show a similar pattern of reward-related activation in nicotine and opiate addicts. Thus, in contrast to healthy subjects, typical reward-related regions respond in addicts to monetary reward but not to nonmonetary reinforcement. Reduced activation in performance-related regions is also observed in both groups of dependent subjects. The results of animal and human studies suggest that dopamine and dopamine-related regions are associated with the integration of motivational information and movement execution. Dopamine-related pathological disorders can be associated with movement disorders, such as Parkinson's disease or with false motivational attributions such as drug dependence.

Changes in reward-induced brain activation in opiate addicts

Many studies indicate a role of the cerebral dopaminergic reward system in addiction. Motivated by these findings, we examined in opiate addicts whether brain regions involved in the reward circuitry also react to human prototypical rewards. We measured regional cerebral blood flow (rCBF) with H(2)(15)O positron emission tomography (PET) during a visuo-spatial recognition task with delayed response in control subjects and in opiate addicts participating in a methadone program. Three conditions were defined by the types of feedback: nonsense feedback; nonmonetary reinforcement; or monetary reward, received by the subjects for a correct response. We found in the control subjects rCBF increases in regions associated with the meso-striatal and meso-corticolimbic circuits in response to both monetary reward and nonmonetary reinforcement. In opiate addicts, these regions were activated only in response to monetary reward. Furthermore, nonmonetary reinforcement elicited rCBF increases in limbic regions of the opiate addicts that were not activated in the control subjects. Because psychoactive drugs serve as rewards and directly affect regions of the dopaminergic system like the striatum, we conclude that the differences in rCBF increases between controls and addicts can be attributed to an adaptive consequence of the addiction process.

Changes in brain activation associated with reward processing in smokers and nonsmokers. A positron emission tomography study

Tobacco smoking is the most frequent form of substance abuse. Several studies have shown that the addictive action of nicotine is mediated by the mesolimbic dopamine system. This system is implicated in reward processing. In order to better understand the relationship between nicotine addiction and reward in humans, we investigated differences between smokers and nonsmokers in the activation of brain regions involved in processing reward information. Using [H2(15O)] positron emission tomography (PET), we measured regional cerebral blood flow (rCBF) in healthy smokers and nonsmokers while they performed a prelearned, pattern-recognition task. We compared two conditions involving nonmonetary reinforcement or monetary reward with a baseline condition in which nonsense feedback was presented. With monetary reward, we found activation in the frontal and orbitofrontal cortex, occipital cortex, cingulate gyrus, cerebellum, and midbrain in both groups. Additionally, monetary reward activated typical dopaminergic regions such as the striatum in nonsmokers but not in smokers. We found a similar pattern of activation associated with nonmonetary reinforcement in nonsmokers, whereas activation was found in smokers only in the cerebellum. The different patterns of activation suggest that the brains of smokers react in a different way to reward than those of nonsmokers. This difference involves in particular the regions of the dopaminergic system including the striatum. In principle these observations could be interpreted either as a consequence of tobacco use or as a primitive condition of the brain that led people to smoke. Supported by related nonimaging studies, we interpret these differences as a consequence of tobacco smoking, even if a short-term effect of smoking prior to the experiment cannot be excluded.

Reduced reward processing in the brains of Parkinsonian patients

Regional cerebral blood flow (rCBF) in healthy controls and non-demented, non-depressed Parkinsonian patients was measured using H2(15)O PET while subjects performed a prelearned pattern recognition task with delayed response. To investigate differences between the two groups in response to reward, the experimental design consisted of three reinforcement conditions: no reinforcement consisting of nonsense feedback, positive symbolic reinforcement and monetary reward. In the controls, monetary reward activated bilaterally the striatum and anterior cingulate gyrus, as well as unilaterally the left cerebellum, midbrain and medial frontal gyrus. Symbolic reinforcement revealed a similar pattern of activation, except that the striatum and left midbrain showed no activation. The Parkinsonian patients responded to monetary reward with increased activation bilaterally in the cerebellum, medial frontal gyrus, and anterior cingulate gyrus as well as unilaterally in the right fusiform gyrus and midbrain and left caudate nucleus and precentral gyrus. Symbolic reinforcement induced significantly increased rCBF in the right cerebellum only. Compared with symbolic reinforcement, monetary reward produced extended activation of temporoparietal association cortex. The pattern observed in the controls demonstrates the role in reward processing of dopaminergic mesolimbic pathways in the healthy human brain, whereas the pattern in the Parkinsonian patients suggests the involvement of compensatory cortical loops in the diseased brain.

Imaging brain tumor proliferative activity with [124I]iododeoxyuridine

Iododeoxyuridine (IUdR) uptake and retention was imaged by positron emission tomography (PET) at 0-48 min and 24 h after administration of 28.0-64.4 MBq (0.76-1.74 mCi) of [124I]IUdR in 20 patients with brain tumors, including meningiomas and gliomas. The PET images were directly compared with gadolinium contrast-enhanced or T2-weighted magnetic resonance images. Estimates for IUdR-DNA incorporation in tumor tissue (Ki) required pharmacokinetic modeling and fitting of the 0-48 min dynamically acquired data to correct the 24-h image data for residual, nonincorporated radioactivity that did not clear from the tissue during the 24-h period after IUdR injection. Standard uptake values (SUVs) and tumor:brain activity ratios (Tm:Br) were also calculated from the 24-h image data. The Ki, SUV, and Tm/Br values were related to tumor type and grade, tumor labeling index, and survival after the PET scan. The plasma half-life of [124I]IUdR was short (2-3 min), and the arterial plasma input function was similar between patients (48 +/- 12 SUV*min). Plasma clearance of the major radiolabeled metabolite ([124I]iodide) varied somewhat between patients and was markedly prolonged in one patient with renal insufficiency. It was apparent from our analysis that a sizable fraction (15-93%) of residual nonincorporated radioactivity (largely [124I]iodide) remained in the tumors after the 24-h washout period, and this fraction varied between the different tumor groups. Because the SUV and Tm:Br ratio values reflect both IUdR-DNA incorporated and exchangeable nonincorporated radioactivity, any residual nonincorporated radioactivity will amplify their values and distort their significance and interpretation. This was particularly apparent in the meningioma and glioblastoma multiforme groups of tumors. Mean tumor Ki values ranged between 0.5 +/- 0.9 (meningiomas) and 3.9 +/- 2.3 microl/min/g (peak value for glioblastoma multiforme, GBM). Comparable SUV and Tm:Br values at 24 h ranged from 0.13 +/- 0.03 to 0.29 +/- 0.19 and from 2.0 +/- 0.6 to 6.1 +/- 1.5 for meningiomas and peak GBMs, respectively. Thus, the range of values was much greater for Ki (approximately 8-fold) compared with that for SUV (approximately 2.2-fold) and Tm:Br (approximately 3-fold). The expected relationships between Ki, SUV, and Tm:Br and other measures of tumor proliferation (tumor type and grade, labeling index, and patient survival) were observed. However, greater image specificity and significance of the SUV and Tm:Br values would be obtained by achieving greater washout and clearance of the exchangeable fraction of residual (background) radioactivity in the tumors, i.e., by increased hydration and urinary clearance and possibly by imaging later than 24 h after [124I]IUdR administration.

On two methods of statistical image analysis

The computerized brain atlas (CBA) and statistical parametric mapping (SPM) are two procedures for voxel-based statistical evaluation of PET activation studies. Each includes spatial standardization of image volumes, computation of a statistic, and evaluation of its significance. In addition, smoothing and correcting for differences of global means are commonly performed in SPM before statistical analysis. We report a comparison of methods in an analysis of regional cerebral blood flow (rCBF) in 10 human volunteers and 10 simulated activations. For the human studies, CBA or linear SPM standarization methods were followed by smoothing and computation of a statistic with the paired t-test of CBA or general linear model of SPM. No standardization, linear, and nonlinear SPM standardization were applied to the simulations. Significance of the statistic was evaluated using the cluster-size method common to SPM and CBA. SPM employs the theory of Gaussian random fields to estimate the cluster size distributions; simulations described in the Appendix provided empirical distributions derived from t-maps. The quantities evaluated were number and size of functional regions (FRs), maximum statistic, average resting rCBF, and percentage change. For the simulations, the efficiency of signal detection and rate of false positives could be evaluated as well as the distributions of statistics and cluster size in the absence of signal. The similarity of the results yielded by similar methods of analysis for the human studies and the simulated activations substantiates the robustness of the methods for selecting functional regions. However, the analysis of simulated activations demonstrated that quantitative evaluation of significance of a functional region encounters important obstacles at every stage of the analysis.

Reproducibility of regional metabolic covariance patterns: comparison of four populations

In a previous [18F]fluorodeoxyglucose (FDG) PET study we analyzed regional metabolic data from a combined group of Parkinson's disease (PD) patients and healthy volunteers (N), using network analysis. By this method, we identified a unique pattern of regional metabolic covariation with an expression which accurately discriminated patients from healthy volunteers. To assess the reproducibility of this pattern as a potential marker for PD, we compared the pattern's topography with that of the disease-related covariance patterns identified in three other independent populations of patients with PD and healthy individuals studied in different PET laboratories.

METHODS

The following patient populations were studied: group A (original cohort: 22 PD, 20 N; resolution: 7.5 mm full width at half maximum [FWHM]); group B (18 PD, 12 N; resolution: 4.2 mm FWHM); group C (25 PD, 15 N; resolution: 8.0 mm FWHM); and group D (14 PD, 10 N; resolution: 10 mm FWHM). Region weights for the PD-related covariance pattern (PDRP) identified in the group A analysis were correlated with those for the disease-related patterns identified in the analyses of groups B, C and D. In addition, subject scores for the group A PDRP were computed prospectively for every individual in each of the study populations. PDRP scores for PD and N within each cohort were compared.

RESULTS

The PDRP topography identified in group A was highly correlated with each of the corresponding topographies identified in the other populations (r2 approximately 0.60, P < 0.0001). Prospectively computed subject scores for the group A PDRP significantly discriminated PD from N in each population (P < 0.004).

CONCLUSION

The PDRP topography identified previously in Group A is highly reproducible across patient populations and tomographs. Prospectively computed PDRP scores can accurately discriminate patients from controls in multiple populations studied with different tomographs. Brain network imaging with FDG PET can provide robust metabolic markers for the diagnosis of PD.

How does the human brain deal with a spinal cord injury?

The primary sensorimotor cortex of the adult brain is capable of significant reorganization of topographic maps after deafferentation and de-efferentation. Here we show that patients with spinal cord injury exhibit extensive changes in the activation of cortical and subcortical brain areas during hand movements, irrespective of normal (paraplegic) or impaired (tetraplegic patients) hand function. Positron emission tomography ([15O]-H2O-PET) revealed not only an expansion of the cortical 'hand area' towards the cortical 'leg area', but also an enhanced bilateral activation of the thalamus and cerebellum. The areas of the brain which were activated were qualitatively the same in both paraplegic and tetraplegic patients, but differed quantitatively as a function of the level of their spinal cord injury. We postulate that the changes in brain activation following spinal cord injury may reflect an adaptation of hand movement to a new body reference scheme secondary to a reduced and altered spino-thalamic and spino-cerebellar input.

Crossed cerebellar diaschisis and brain tumor biochemistry studied with positron emission tomography, [18F]fluorodeoxyglucose and [11C]methionine

Cerebral gliomas may cause a reduction of glucose metabolism in the cerebellum contralateral to the tumor side (crossed cerebellar diaschisis, CCD). We investigated whether CCD is related to tumor localization, histological grade, size and tumor biochemistry. Cerebellar glucose metabolism was measured in 44 glioma patients and 15 healthy subjects using positron emission tomography and [18F]fluorodeoxyglucose (FDG). CCD was determined by calculating an asymmetry index of cerebellar glucose metabolism. Further, the tumor uptake of FDG and [11C]methionine (MET) was also assessed, and was expressed as ratio of normalized tracer uptake in tumor over contralateral cortex (T/C). Frontal lobe tumors were associated with highest CCD values. For these tumors, CCD was higher in malignant (-11.8+/-9.9%) than in low-grade (-4.3+/-4.1%) gliomas (P=0.010). In addition, frontal lobe tumors showed increasing CCD values with increasing size. In tumors of the parietal or temporal lobe, CCD was less marked or absent. T/C ratios of tumor tracer uptake were higher in malignant than in low-grade gliomas, but were not correlated with CCD. Our data indicate that the magnitude of CCD is mainly determined by tumor localization and size, the latter being associated with tumor grade. These findings raise the question whether CCD provides a measure of expansion or progression particularly in low-grade tumors of the frontal lobe.

Complementary PET studies of striatal neuronal function in the differential diagnosis between multiple system atrophy and Parkinson's disease

We used PET with the tracers [18F]fluorodeoxyglucose (FDG), [18F]fluorodopa (FDOPA) and [11C]raclopride (RACLO) to study striatal glucose and dopa metabolism, and dopamine D2 receptor binding, respectively, in nine patients with multiple system atrophy. Ten patients with classical Parkinson's disease were investigated with the same three PET tracers' and three separate groups, each of 10 healthy subjects, served as control populations. We found that striatal FDOPA values separated all healthy subjects from patients with parkinsonism but they were not useful in distinguishing multiple system atrophy from Parkinson's disease. Conversely, striatal RACLO as well as FDG values discriminated all multiple system atrophy from Parkinson's disease patients as well as from healthy control subjects. Metabolic and receptor binding decrements in the putamen of multiple system atrophy patients were significantly correlated. Stepwise regression analysis revealed that a linear combination of putamen RACLO and FDOPA values accurately predicted clinical measures of disease severity in the multiple system atrophy group. Our findings suggest that striatal FDG and particularly RACLO are sensitive and effective measures of striatal function and may help characterizing patients with multiple system atrophy. In contrast, FDOPA measurements are accurate in detecting abnormalities of the nigrostriatal dopaminergic system but may not distinguish among different forms of parkinsonism.

Intermanual transfer of training: blood flow correlates in the human brain

In a previous study, we found that relearning of a task with one hand might negatively be influenced by previous, opposite hand training of the analogue task, Thut G., et al., Exp. Brain Res., 108 (1996) 321-327. Drawing of a figure with the right hand, following left hand training, was slower than right hand drawing of an unknown figure. These conditions were termed right hand transfer learning (rTL) and right hand original learning (rOL). The present study aimed to identify the cerebral areas associated with these influences by measuring regional cerebral blood flow (rCBF) in 16 right-handed, healthy subjects during rTL and rOL. Positron emission tomography and statistical parametric mapping were used. Compared with rOL, rTL was associated with increased rCBF in the left medial prefrontal cortex and the right prefrontal convexity. Individual rCBF changes in the area homotopic to the right prefrontal convexity furthermore correlated with individual changes in rTL performance. While the smallest rCBF increases were found in subjects with weakest slowing of rTL relative to rOL, highest rCBF increases were present when rTL slowing dominated. Comparisons between rTL and rOL, however, revealed on average no performance differences. Our data suggest that relearning after previous opposite hand training activates neural mechanisms within the prefrontal convexity which might have an inhibitory function but that inhibition does not have to be the net final behavioral result.

Thalamic glucose metabolism in temporal lobe epilepsy measured with 18F-FDG positron emission tomography (PET)

Thalamic glucose metabolism has been studied in 24 patients suffering from temporal lobe epilepsy (TLE) using interictal 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). A total of 17 patients had a unilateral TL seizure onset, 11 of these patients had a mesial temporal lobe epilepsy syndrome (MTLE), with mesial gliosis and a mesial TL seizure origin. Three patients had a lateral TL seizure origin, and 3 patients had mesial TL tumors. Bilateral TLE was assumed in 7 patients. Only in the patient group with MTLE (n = 11), the ipsilateral thalamic glucose uptake showed a statistically significant lower value when compared to the thalamus of the contralateral side (Wilcoxon paired sign test, P = 0.012). There was a more pronounced hypometabolism in right TLE compared to left TLE. A 'hypersynchronous seizure onset pattern' in ictal EEG was only seen in 6 (26%) patients (1 patient with bilateral, 5 with unilateral TLE). No correlation existed between the thalamic, temporal glucose metabolism and the 'hypersynchronous seizure onset pattern'.

Cerebral glucose metabolism in patients with spasmodic torticollis

The pathophysiology of spasmodic torticollis is not clear. Basal ganglia dysfunction has been suggested to underlie this clinical syndrome. We studied resting cerebral glucose metabolism in 10 spasmodic torticollis patients and 10 healthy controls by using positron-emission tomography and [18F]2-fluoro-2-deoxy-D-glucose. Statistical parametric mapping (SPM95) was used to compare both groups on a pixel-by-pixel basis. Torticollis patients showed a significantly higher glucose metabolism bilaterally in the lentiform nucleus (p < 0.005). Analyses performed using normalization of regional to global glucose metabolism confirmed this finding (controls, 1.26 +/- 0.06, and patients, 1.35 +/- 0.06; p < 0.01). The torticollis score did not correlate with glucose metabolism, nor did disease duration or side of chin direction. Our results indicate that the lentiform nucleus plays a predominant role in the pathophysiology of idiopathic spasmodic torticollis.

Reduced glucose metabolism in the frontal cortex and basal ganglia of multiple sclerosis patients with fatigue: a 18F-fluorodeoxyglucose positron emission tomography study

To investigate the pathophysiology of fatigue in MS, we assessed cerebral glucose metabolism (CMR-Glu) in 47 MS patients using PET and 18F-fluorodeoxyglucose. Applying the Fatigue Severity Scale (FSS), we first compared MS patients with severe fatigue (MS-FAT, n = 19, FSS > 4.9) and MS patients without fatigue (MS-NOF, n = 16, FSS < 3.7) on a pixel-by-pixel basis using Statistical Parametric Mapping (SPM95). Second, we compared FSS values of all 47 patients covering the whole range of this scale with CMRGlu using an analysis of covariance (SPM95). In addition, we determined global CMRGlu by region-of-interest analysis. Sixteen healthy subjects served as control subjects (CON). Global CMRGlu was significantly lower in both MS groups compared with CON (CON 43.3 +/- 6.9 mumol/100 mL/min, MS-FAT 34.7 +/- 4.4, MS-NOF 35.4 +/- 4.5) but was not related to fatigue severity. Comparing the two MS groups, SPM95 analysis revealed predominant CMRGlu reductions bilaterally in a prefrontal area involving the lateral and medial prefrontal cortex and adjacent white matter, in the premotor cortex, putamen, and in the right supplementary motor area of MS-FAT. In addition, there were CMRGlu reductions in the white matter extending from the rostral putamen toward the lateral head of the caudate nucleus. FSS values were inversely related to CMRGlu in the right prefrontal cortex. CMRGlu in the cerebellar vermis and anterior cingulate was relatively higher in MS-FAT than in MS-NOF patients. CMRGlu of both regions showed positive correlations with FSS values. Our data suggest that fatigue in MS is associated with frontal cortex and basal ganglia dysfunction that could result from demyelination of the frontal white matter.

Activation of the human brain by monetary reward

With the purpose of studying neural activation associated with reward processing in humans, we measured regional cerebral blood flow in 10 right-handed healthy subjects performing a delayed go-no go task in two different reinforcement conditions. Correct responses were either rewarded by money or a simple "ok' reinforcer. Behaviour rewarded by money, as compared with the "ok' reinforcement, was most significantly associated with activation of dorsolateral and orbital frontal cortex and also involved the midbrain and thalamus. These results may reflect the processing of reward information, although arousal effects cannot be completely excluded. It is suggested that the observed foci are implicated in the assessment of consequences in goal-directed behaviour which agrees with research in non-human primates.

Metabolic hyperfrontality and psychopathology in the ketamine model of psychosis using positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG)

To date, the ketamine/PCP model of psychosis has been proposed to be one of the best pharmacological models to mimic schizophrenic psychosis in healthy volunteers, since ketamine can induce both positive and negative symptoms of schizophrenia. At subanesthetic doses, ketamine has been reported to primarily block N-methyl-D-aspartate (NMDA) receptor complex giving support to a glutamate deficiency hypothesis in schizophrenia. Positron emission tomography was used to study ketamine-induced psychotic symptom formation in relation to cerebral metabolic alterations in healthy volunteers. Our study shows that NMDA receptor blockade results in a hyperfrontal metabolic pattern. Increased metabolic activity in the frontomedial and anterior cingulate cortex correlated positively with psychotic symptom formation, in particular with ego pathology. Analysis of correlations between syndrome scores and metabolic rate of glucose (CMRglu) or metabolic gradients (ratios) revealed that each psychopathological syndrome was associated with a number of metabolic alterations in cortical and subcortical brain regions, suggesting that not a single brain region, but distributed neuronal networks are involved in acute psychotic symptom formation.

Influence of spinal cord injury on cerebral sensorimotor systems: a PET study

OBJECTIVES

To assess the effect of a transverse spinal cord lesion on cerebral energy metabolism in view of sensorimotor reorganisation.

METHODS

PET and 18F-fluorodeoxyglucose were used to study resting cerebral glucose metabolism in 11 patients with complete paraplegia or tetraplegia after spinal cord injury and 12 healthy subjects. Regions of interest analysis was performed to determine global glucose metabolism (CMRGlu). Statistical parametric mapping was applied to compare both groups on a pixel by pixel basis (significance level P = 0.001).

RESULTS

Global absolute CMRGlu was lower in spinal cord injury (33.6 (6.6) mumol/100 ml/min (mean (SD)) than in controls (45.6 (6.2), Mann-Whitney P = 0.0026). Statistical parametric mapping analysis disclosed relatively increased glucose metabolism particularly in the supplementary motor area, anterior cingulate, and putamen. Relatively reduced glucose metabolism in patients with spinal cord injury was found in the midbrain, cerebellar hemispheres, and temporal cortex.

CONCLUSIONS

It is assumed that cerebral deafferentiation due to reduction or loss of sensorimotor function results in the low level of absolute global CMRGlu found in patients with spinal cord injury. Relatively increased glucose metabolism in brain regions involved in attention and initiation of movement may be related to secondary disinhibition of these regions.

Complementary positron emission tomographic studies of the striatal dopaminergic system in Parkinson's disease

OBJECTIVE

To assess the relationship between striatal dopa decarboxylase capacity, D2 dopamine receptor binding, and energy metabolism in Parkinson's disease (PD).

DESIGN

Positron emission tomographic (PET) studies of glucose and dopa metabolism and D2 dopamine receptor binding in the caudate nucleus and putamen of patients with PD at different Hoehn and Yahr (HY) stages using PET and the tracers 18F-fluorodeoxyglucose (FDG), 6-18F-fluoro-L-dopa (FDOPA), and 11C-raclopride (RACLO).

SETTING

Positron emission tomography research program at the Paul Scherrer Institute.

SUBJECTS

Twenty patients with PD at different stages of the disease (HY stages I through IV; five patients for each stage) compared with separate groups of age-matched healthy subjects.

MAIN OUTCOME MEASURES

Influx constant (Ki) for specific FDOPA uptake; uptake index ratio for RACLO binding to D2 dopamine receptors; normalized to global FDG metabolic rate for glucose consumption; and semiquantitative score for assessment of tremor, rigidity, and bradykinesia in PD.

RESULTS

Patients with PD at HY stages I to II (hereafter HY-I-II PD) revealed reduced FDOPA metabolism, particularly in the putamen. The FDOPA uptake in the putamen and caudate nucleus declined with increasing HY staging and scoring for bradykinesia and rigidity. Putamen RACLO binding to D2 dopamine receptors was up-regulated in patients with HY-I-II PD but declined toward control values, with increasing disease severity. Putamen side-to-side asymmetries of FDOPA metabolism and RACLO binding revealed a significant correlation. Putamen FDG metabolism showed a relative increase in all patients with PD.

CONCLUSIONS

Our results show that FDOPA, RACLO, and FDG PET measurements provide complementary information to characterize metabolic and receptor changes in the striatum of PD with different degrees of motor disability. The FDOPA uptake reflects the best motor-related pathologic features, as indicated by the significant correlation between Ki values and clinical scores. The significant association between RACLO and FDOPA in the putamen suggests that D2 dopamine receptor changes are related to the reduction of presynaptic dopaminergic nerve terminals. Putamen FDG increase is probably the result of more complex feedback mechanisms that are primarily induced by striatal dopamine deficiency.