Individual differences in cerebral blood flow in area 17 predict the time to evaluate visualized letters

Sixteen subjects closed their eyes and visualized uppercase letters of the alphabet at two sizes, as small as possible or as large as possible while remaining "visible." Subjects evaluated a shape characteristic of each letter (e.g., whether it has any curved lines), and responded as quickly as possible. Cerebral blood flow was normalized to the same value for each subject, and relative blood flow was computed for a set of regions of interest. The mean response time for each subject in the task was regressed onto the blood flow values. Blood flow in area 17 was negatively correlated with response time (r = -0.65), as was blood flow in area 19 (r = -0.66), whereas blood flow in the inferior parietal lobe was positively correlated with response time (r = 0.54). The first two effects persisted even when variance due to the other correlations was removed. These findings suggest that individual differences in the activation of specific brain loci are directly related to performance of tasks that rely on processing in those loci.

Decreased regional cerebral blood flow in medial prefrontal cortex during trauma-unrelated stressful imagery in Vietnam veterans with post-traumatic stress disorder

BACKGROUND

Neuroimaging research has demonstrated medial prefrontal cortex (mPFC) hyporesponsivity and amygdala hyperresponsivity to trauma-related or emotional stimuli in post-traumatic stress disorder (PTSD). Relatively few studies have examined brain responses to the recollection of stressful, but trauma-unrelated, personal events in PTSD. In the current study, we sought to determine whether regional cerebral blood flow (rCBF) abnormalities in mPFC and amygdala in PTSD could be observed during the recollection of trauma-unrelated stressful personal events.

METHOD

Participants were 35 right-handed male combat veterans (MCVs) and female nurse veterans (FNVs) who served in Vietnam: 17 (seven male, 10 female) with current military-related PTSD and 18 (nine male, nine female) with no current or lifetime PTSD. We used positron emission tomography (PET) and script-driven imagery to study rCBF during the recollection of trauma-unrelated stressful versus neutral and traumatic events.

RESULTS

Voxelwise tests revealed significant between-group differences for the trauma-unrelated stressful versus neutral comparison in mPFC, specifically in the anterior cingulate cortex (ACC). Functional region of interest (ROI) analyses demonstrated that this interaction in mPFC represented greater rCBF decreases in the PTSD group during trauma-unrelated stressful imagery relative to neutral imagery compared to the non-PTSD group. No differential amygdala activation was observed between groups or in either group separately.

CONCLUSIONS

Veterans with PTSD, compared to those without PTSD, exhibited decreased rCBF in mPFC during mental imagery of trauma-unrelated stressful personal experiences. Functional neuroanatomical models of PTSD must account for diminished mPFC responses that extend to emotional stimuli, including stressful personal experiences that are not directly related to PTSD.

Nonrigid PET motion compensation in the lower abdomen using simultaneous tagged-MRI and PET imaging

PURPOSE

We propose a novel approach for PET respiratory motion correction using tagged-MRI and simultaneous PET-MRI acquisitions.

METHODS

We use a tagged-MRI acquisition followed by motion tracking in the phase domain to estimate the nonrigid deformation of biological tissues during breathing. In order to accurately estimate motion even in the presence of noise and susceptibility artifacts, we regularize the traditional HARP tracking strategy using a quadratic roughness penalty on neighboring displacement vectors (R-HARP). We then incorporate the motion fields estimated with R-HARP in the system matrix of an MLEM PET reconstruction algorithm formulated both for sinogram and list-mode data representations. This approach allows reconstruction of all detected coincidences in a single image while modeling the effect of motion both in the emission and the attenuation maps. At present, tagged-MRI does not allow estimation of motion in the lungs and our approach is therefore limited to motion correction in soft tissues. Since it is difficult to assess the accuracy of motion correction approaches in vivo, we evaluated the proposed approach in numerical simulations of simultaneous PET-MRI acquisitions using the NCAT phantom. We also assessed its practical feasibility in PET-MRI acquisitions of a small deformable phantom that mimics the complex deformation pattern of a lung that we imaged on a combined PET-MRI brain scanner.

RESULTS

Simulations showed that the R-HARP tracking strategy accurately estimated realistic respiratory motion fields for different levels of noise in the tagged-MRI simulation. In simulations of tumors exhibiting increased uptake, contrast estimation was 20% more accurate with motion correction than without. Signal-to-noise ratio (SNR) was more than 100% greater when performing motion-corrected reconstruction which included all counts, compared to when reconstructing only coincidences detected in the first of eight gated frames. These results were confirmed in our proof-of-principle PET-MRI acquisitions, indicating that our motion correction strategy is accurate, practically feasible, and is therefore ready to be tested in vivo.

CONCLUSIONS

This work shows that PET motion correction using motion fields measured with tagged-MRI in simultaneous PET-MRI acquisitions can be made practical for clinical application and that doing so has the potential to remove motion blur in whole-body PET studies of the torso.

Fast formation of statistically reliable FDG parametric images based on clustering and principal components

Formation of parametric images requires voxel-by-voxel estimation of rate constants, a process sensitive to noise and computationally demanding. A model-based clustering method for a two-parameter model (CAKS) was extended to the FDG three-parameter model. The concept was to average voxels with similar kinetic signatures to reduce noise. Voxel kinetics were categorized by the first two principal components of the tissue time-activity curves for all voxels. k2 and k3 were estimated cluster-by-cluster, and K1 was estimated voxel-by-voxel within clusters. When CAKS was applied to simulated images with noise levels similar to brain FDG scans, estimation bias was well suppressed, and estimation errors were substantially smaller--1.3 times for Ki and 1.5 times for k3-than those of conventional voxel-based estimation. The statistical reliability of voxel-level estimation by CAKS was comparable with ROI analysis including 100 voxels. CAKS was applied to clinical cases with Alzheimer's disease (ALZ) and cortico basal degeneration (CBD). In ALZ, the affected regions had low Ki (K1k3/(k2 +k3)) and k3. In CBD, Ki was low, but k3 was preserved. These results were consistent with ROI-based kinetic analysis. Because CAKS decreased the number of invoked estimations, the calculation time was reduced substantially. In conclusion, CAKS has been extended to allow parametric imaging of a three-compartment model. The method is computationally efficient. with low bias and excellent noise properties.

Cerebral metabolic correlates as potential predictors of response to anterior cingulotomy for obsessive compulsive disorder

BACKGROUND

As interventions for severe, treatment-refractory obsessive compulsive disorder (OCD), neurosurgical procedures are associated with only modest efficacy. The purpose of this study was to identify cerebral metabolic correlates as potential predictors of treatment response to anterior cingulotomy for OCD.

METHODS

Clinical data were analyzed in the context of a retrospective design. Subjects were 11 patients who underwent stereotactic anterior cingulotomy for OCD. Symptom severity was measured using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) before and at approximately 6 months postoperative. Preoperative F-18-fluorodeoxyglucose-positron emission tomography (FDG-PET) data were available. Statistical parametric mapping methods were used to identify loci of significant correlation between preoperative regional cerebral metabolism and postoperative reduction in Y-BOCS scores.

RESULTS

One locus within right posterior cingulate cortex was identified, where preoperative metabolism was significantly correlated with improvement in OCD symptom severity following cingulotomy. Specifically, higher preoperative rates of metabolism at that locus were associated with better postoperative outcome.

CONCLUSIONS

A possible predictor of treatment response was identified for patients with OCD undergoing anterior cingulotomy. Further research, utilizing a prospective design, is indicated to determine the validity and reliability of this finding. If confirmed, an index for noninvasively predicting response to cingulotomy for OCD would be of great value.

Performance evaluation of an automated system for registration and postprocessing of CT scans

A prototype system optimized for automatic registration of CT scans and applications such as subtraction enhancement and CT angiography was evaluated. Co-registration was performed on 50 studies of various types, including CT angiograms. Mean registration speed was 109 s; accuracy was 2.0 mm. Examples of subtraction enhancement and automatic extraction of the vascular tree are provided. Unattended registration was demonstrated in routine application. Subtraction-enhanced images and extraction of the vascular tree may be useful in clinical practice.

Imagining rotation by endogenous versus exogenous forces: distinct neural mechanisms

Previous neuroimaging studies of mental image transformations have sometimes implicated motor processes and sometimes not. In this study, prior to neuroimaging the subjects either viewed an electric motor rotating an angular object, or they rotated the object manually. Following this, they performed the identical mental rotation task in which they compared members of pairs of such figures, but were asked to imagine the figures rotating as they had just seen the model rotate. When results from the two rotation conditions were directly compared, motor cortex (including area M1) was found to be activated only when subjects imagined the rotations as a consequence of manual activity. Thus, there are at least two, qualitatively distinct, ways to imagine objects rotating in images, and these different strategies can be adopted voluntarily.

Mental imagery of high- and low-resolution gratings activates area 17

Some, but not all, previous neuroimaging studies of visual mental imagery have found that Area 17 (primary visual cortex) is activated when people visualize objects. The present study was designed to test the hypothesis that the necessary degree of resolution of the mental image is a determining factor in whether Area 17 is activated during imagery. Eight male subjects visualized and compared sets of stripes that required high or low resolution to resolve, while their brains were scanned using 15O(CO2) positron emission tomography (PET). When imagery in general (visualization of high- and low-resolution gratings stimuli combined) was compared to an auditory baseline condition where subjects did not visualize, Area 17 was activated. However, region of interest (ROI) and statistical parametric mapping (SPM) analyses revealed no difference between imagery conditions using high- and low-resolution stimuli. These results indicate that the resolution of the stimuli alone does not necessarily determine whether Area 17 will be activated during visual mental imagery.

Neural substrates of anorexia nervosa: a behavioral challenge study with positron emission tomography

OBJECTIVE

To delineate functional brain abnormalities associated with anorexia nervosa (AN).

STUDY DESIGN

Positron emission tomographic measurements of regional cerebral blood flow (rCBF) were performed on 8 female patients with AN and 8 healthy female control subjects during exposure to 3 types of stimuli: high-calorie foods, low-calorie foods, and non-food items. Heart rate and internal state analog scale scores were also obtained. Stereotactic transformation and statistical parametric mapping techniques were used to analyze imaging data.

RESULTS

During the high-calorie condition, control subjects reported a significant desire to eat, whereas subjects with AN reported elevated anxiety and exhibited increases in heart rate. Patients with AN had elevated bilateral medial temporal lobe rCBF compared with control subjects. Planned comparisons for group-by-condition interactions demonstrated greater activation within left occipital cortex and right temporo-occipital cortex for the high-calorie versus low-calorie contrast in patients with AN compared with control subjects.

CONCLUSIONS

Our finding of elevated rCBF within bilateral medial temporal lobes is similar to published results in patients with psychotic disorders and may be related to the body image distortion common to AN. The high-calorie food phobia exhibited by patients with AN appears to be associated with exaggerated responses in visual association cortex, as has been previously observed in studies of specific phobias.

[(11)C, (127)I] Altropane: a highly selective ligand for PET imaging of dopamine transporter sites

The E isomer of (123)I-2beta-carbomethoxy-3beta-(4-fluorophenyl)-N-(1-iodoprop-1-en-3-yl)nortropane (Altropane(R)) shows high affinity (IC(50) = 6.62 +/- 0.78 nmol) and selectivity (DA/5-HT = 25) for DAT sites in the striatum. Recently, dynamic SPECT studies in healthy volunteers and patients with Parkinson disease demonstrated that the kinetics of striatal accumulation followed a pattern that is characteristic of a reversible tracer with maximal accumulation within 30 min after injection. These findings suggested that radiolabeling Altropane with [(11)C] might provide an equivalent and complementary tracer for PET studies. [(127)I] Altropane was treated with HCl to hydrolyze the methyl ester bond and yield a precursor for [(11)C] labeling. Introduction of an [(11)C] methyl ester group was achieved by treatment with [(11)C] CH(3)I followed by HPLC purification. Five healthy rhesus monkeys were injected with approximately 10 mCi of [(127)I,(11)C] Altropane and dynamic PET images were acquired over 90 min. Arterial blood samples were collected in parallel with imaging and metabolite analysis was performed by HPLC. The PET and metabolite corrected arterial blood data were to calculate k(3)/k(4) by two methods: 1) nonlinear least-squares fitting, and 2) a linear graphical method for reversible ligands. The synthetic procedure yielded high specific activity tracer, >1,000 mCi/micro mole, with radiochemical purity >95%. Synthesis time was approximately 30 min. The PET images revealed excellent striatal definition, with clear separation of caudate nucleus and putamen and minimal accumulation in brain regions with high 5HT transporter density. Metabolite analysis demonstrated that at 60 min after injection, approximately 80% of circulating tracer was intact [(127)I,(11)C] Altropane and the remainder was converted to polar metabolites. Values for k(3)/k(4) calculated by two analysis methods were remarkably similar: Method 1, 3.48 +/- 0.41; Method 2, 3.77 +/- 0.45 (mean +/- SEM, t = 2.31, df = 8, P = 0.64). These results establish that Altropane has the important characteristics of: 1) rapid and specific striatal binding; 2) high selectivity for DA vs. 5-HT transporter sites; 3) reversible binding kinetics; 4) potential for multiple injection studies; 5) high efficiency labeling with either [(11)C] or [(123)I]; 6) applicability for both PET and SPECT. These properties make Altropane an important DAT ligand for both research and clinical applications.

Priming within and across modalities: exploring the nature of rCBF increases and decreases

Neuroimaging studies suggest that within-modality priming is associated with reduced regional cerebral blood flow (rCBF) in the extrastriate area, whereas cross-modality priming is associated with increased rCBF in prefrontal cortex. To characterize the nature of rCBF changes in within- and cross-modality priming, we conducted two neuroimaging experiments using positron emission tomography (PET). In experiment 1, rCBF changes in within-modality auditory priming on a word stem completion task were observed under same- and different-voice conditions. Both conditions were associated with decreased rCBF in extrastriate cortex. In the different-voice condition there were additional rCBF changes in the middle temporal gyrus and prefrontal cortex. Results suggest that the extrastriate involvement in within-modality priming is sensitive to a change in sensory modality of target stimuli between study and test, but not to a change in the feature of a stimulus within the same modality. In experiment 2, we studied cross-modality priming on a visual stem completion test after encoding under full- and divided-attention conditions. Increased rCBF in the anterior prefrontal cortex was observed in the full- but not in the divided-attention condition. Because explicit retrieval is compromised after encoding under the divided-attention condition, prefrontal involvement in cross-modality priming indicates recruitment of an aspect of explicit retrieval mechanism. The aspect of explicit retrieval that is most likely to be involved in cross-modality priming is the familiarity effect.

Prefrontal regions supporting spontaneous and directed application of verbal learning strategies: evidence from PET

The prefrontal cortex has been implicated in strategic memory processes, including the ability to use semantic organizational strategies to facilitate episodic learning. An important feature of these strategies is the way they are applied in novel or ambiguous situations-failure to initiate effective strategies spontaneously in unstructured settings is a central cognitive deficit in patients with frontal lobe disorders. The current study examined strategic memory with PET and a verbal encoding paradigm that manipulated semantic organization in three encoding conditions: spontaneous, directed and unrelated. During the spontaneous condition, subjects heard 24 words that were related in four categories but presented in mixed order, and they were not informed of this structure beforehand. Any semantic reorganization was, therefore, initiated spontaneously by the subject. In the directed condition, subjects were given a different list of 24 related words and explicitly instructed to notice relationships and mentally group related words together to improve memory. The unrelated list consisted of 24 unrelated words. Behavioural measures included semantic clustering, which assessed active regrouping of words into semantic categories during free recall. In graded PET contrasts (directed > spontaneous > unrelated), two distinct activations were found in left inferior prefrontal cortex (inferior frontal gyrus) and left dorsolateral prefrontal cortex (middle frontal gyrus), corresponding to levels of semantic clustering observed in the behavioural data. Additional covariate analyses in the first spontaneous condition indicated that blood flow in orbitofrontal cortex (OFC) was strongly correlated with semantic clustering scores during immediate free recall. Thus, blood flow in OFC during encoding predicted which subjects would spontaneously initiate effective strategies during free recall. Our findings indicate that OFC performs an important, and previously unappreciated, role in strategic memory by supporting the early mobilization of effective behavioural strategies in novel or ambiguous situations. Once initiated, lateral regions of left prefrontal cortex control verbal semantic organization.

Evidence of reduced resting blood flow in viable myocardial regions with chronic asynergy

OBJECTIVES

We tested the hypothesis in patients (n = 24) with ischemic heart disease that chronic contractile dysfunction occurs in myocardial regions with true reduction in rest blood flow.

BACKGROUND

Whether viable myocardial regions with chronic contractile dysfunction have true reduction in rest myocardial blood flow is controversial.

METHODS

Positron emission tomography (PET) 13N-ammonia was used to measure myocardial blood flow in combination with 18F-fluorodeoxyglucose (18FDG) to assess myocardial viability. Viability also was assessed by dobutamine echo and recovery of function after coronary artery bypass grafting (CABG). Segments (n = 252) were selected based on PET measured reduced resting blood flow and rest asynergy on echo.

RESULTS

Regional myocardial viability was present in 20 of 23 patients by PET, 13 of 23 by dobutamine echo and 10 of 11 by postrevascularization criteria. Rest blood flow in normal regions was 1.14+/-0.52 ml/min/g and by definition exceeded (p < 0.005) that in both viable (0.48+/-0.15; n = 8 patients) and nonviable (0.45+/-0.14; n = 8 patients) regions (post-CABG criteria), which did not differ. Correction of rest myocardial blood flow in viable asynergic segments, only, for fibrosis and incomplete tracer recovery raised the level to 0.67+/-0.21 (p < 0.005 vs. normal). Finally, evidence of both stunning (rest asynergy with normal flow) and hibernation was present in 15 of 23 (65%) patients.

CONCLUSIONS

Reduced rest blood flow in viable myocardial regions with chronic asynergy is common and cannot be accounted for by partial volume effect. Thus, hypotheses concerning physiologic mechanisms underlying chronic contractile dysfunction should consider the role played by chronic reduction of basal myocardial blood flow.

Abnormalities in the thalamus and prefrontal cortex during episodic object recognition in schizophrenia

BACKGROUND

Many patients with schizophrenia demonstrate memory deficits. We studied patterns of brain activity during episodic recognition of new and previously seen three-dimensional objects.

METHODS

We used (15)O positron emission tomography to study regional cerebral blood flow in eight normal subjects and nine patients with schizophrenia during a visual object recognition task.

RESULTS

In comparison with control subjects, patients with schizophrenia showed less regional cerebral blood flow increases in the pulvinar region of the right thalamus and the right prefrontal cortex during the recognition of new objects and significantly greater left prefrontal cortex regional cerebral blood flow increases during the recognition of previously seen objects. Patients with schizophrenia exhibited alarm rates to new objects similar to those of control subjects, but significantly lower recognition rates for previously seen objects.

CONCLUSIONS

Schizophrenia is associated with attenuated right thalamic and right prefrontal activation during the recognition of novel visual stimuli and with increased left prefrontal cortical activation during impaired episodic recognition of previously seen visual stimuli. This study provides further evidence for abnormal thalamic and prefrontal cortex function in schizophrenia.

Robot-aided functional imaging: application to a motor learning study

The purpose of this study was to examine the neural activity underlying an implicit motor learning task. In particular, our goals were to determine whether initial phases of procedural learning of a motor task involve areas of the brain distinct from those involved in later phases of learning the task, and what changes in neural activity coincide with performance improvement. We describe a novel integration of robotic technology with functional brain imaging and its use in this study of implicit motor learning. A portable robotic device was used to generate forces that disturbed the subjects' arm movements, thereby generating a "virtual mechanical environment" that the subjects learned to manipulate. Positron emission tomography (PET) was used to measure indices of neural activity underlying learning of the motor task. Eight health, right-handed male subjects participated in the study. Results support the hypothesis that different stages of implicit learning (early and late implicit learning) occur in an orderly fashion, and that distinct neural structures may be involved in these different stages. In particular, neuroimaging results indicate that the cortico-striatal loop may play a significant role during early learning, and that the cortico-cerebellar loop may play a significant role during late learning.

Hypnotic visual illusion alters color processing in the brain

OBJECTIVE

This study was designed to determine whether hypnosis can modulate color perception. Such evidence would provide insight into the nature of hypnosis and its underlying mechanisms.

METHOD

Eight highly hypnotizable subjects were asked to see a color pattern in color, a similar gray-scale pattern in color, the color pattern as gray scale, and the gray-scale pattern as gray scale during positron emission tomography scanning by means of [(15)O]CO(2). The classic color area in the fusiform or lingual region of the brain was first identified by analyzing the results when subjects were asked to perceive color as color versus when they were asked to perceive gray scale as gray scale.

RESULTS

When subjects were hypnotized, color areas of the left and right hemispheres were activated when they were asked to perceive color, whether they were actually shown the color or the gray-scale stimulus. These brain regions had decreased activation when subjects were told to see gray scale, whether they were actually shown the color or gray-scale stimuli. These results were obtained only during hypnosis in the left hemisphere, whereas blood flow changes reflected instructions to perceive color versus gray scale in the right hemisphere, whether or not subjects had been hypnotized.

CONCLUSIONS

Among highly hypnotizable subjects, observed changes in subjective experience achieved during hypnosis were reflected by changes in brain function similar to those that occur in perception. These findings support the claim that hypnosis is a psychological state with distinct neural correlates and is not just the result of adopting a role.

Activation of anterior paralimbic structures during guilt-related script-driven imagery

BACKGROUND

Several recent neuroimaging studies have examined the neuroanatomical correlates of normal emotional states, such as happiness, sadness, fear, anger, anxiety, and disgust; however, no previous study has examined the emotional state of guilt.

METHODS

In the current study, we used positron emission tomography and the script-driven imagery paradigm to study regional cerebral blood flow (rCBF) during the transient emotional experience of guilt in eight healthy male participants. In the Guilt condition, participants recalled and imagined participating in a personal event involving the most guilt they had ever experienced. In the Neutral condition, participants recalled and imagined participating in an emotionally neutral personal event.

RESULTS

In the Guilt versus Neutral comparison, rCBF increases occurred in anterior paralimbic regions of the brain: bilateral anterior temporal poles, anterior cingulate gyrus, and left anterior insular cortex/inferior frontal gyrus.

CONCLUSIONS

These results, along with those of previous studies, are consistent with the notion that anterior paralimbic regions of the brain mediate negative emotional states in healthy individuals.

Comparison of 4 methods for quantification of dopamine transporters by SPECT with [123I]IACFT

2Beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1-iodoprop-1-en -3-yl) nortropane (IACFT) is a highly selective ligand for dopamine transporter (DAT) sites in the striatum. Recent reports have described the basic kinetics, neurobiology, and imaging properties of [123I]IACFT. This report focuses on the structural (i.e., the ability to produce consistent binding estimates) validity of 4 methods to quantify striatal binding potential (BP) for IACFT.

METHODS

Seven healthy volunteers and 8 patients with Parkinson's disease were subjects for this study. Dynamic SPECT images and arterial blood samples were acquired during the 1.5-2 h after injection of 185-370 MBq [123I]IACFT. Plasma radioactivity was analyzed chromatographically to obtain metabolite-corrected arterial input functions. The k3/k4 ratio (BP) for striatal DAT sites was calculated by 4 methods. In the first method, tissue time-activity curves and metabolite-corrected arterial input functions were analyzed by a linear graphic method developed for reversible receptor ligands. The second method was also graphic; however, the occipital cortex time-activity curve was used as the input function. In the third method, the difference between the striatal and occipital cortex time-activity curves at secular equilibrium was taken to represent bound tracer, the occipital cortex time-activity curve was used to represent tracer in the free and nonspecifically bound state, and equilibrium receptor equations were used to determine BP. The fourth method used the occipital cortex time-activity curve to mathematically derive an input function for fitting the striatal time-activity curve and to determine BP.

RESULTS

Analysis of the dynamic SPECT data by methods 1 and 2 resulted in highly linear plots (after approximately 15 min), supporting the reversibility of the tracer. A high linear correlation was found for BP determined by all 4 methods. ANOVA showed that methods 1-3 were indistinguishable; method 4 yielded lower BPs than did methods 1-3.

CONCLUSION

These results show that BP can be estimated consistently using 4 different methods. This finding lends support to the modeling assumptions and provides methods suitable for clinical investigation.

Neuroanatomy of human appetitive function: A positron emission tomography investigation

OBJECTIVE

The mediating neuroanatomy of human appetitive function is poorly understood. A state induction paradigm was employed, in conjunction with positron emission tomography, to test the hypothesis that limbic/paralimbic regions respond to the desirability of food stimuli.

METHODS

Eight normal subjects were studied during each of three conditions, involving visual exposure to high-caloric food, low-caloric food, and nonfood stimuli. Subjective indices of hunger were measured via analog scales.

RESULTS

Planned contrasts demonstrated significant increases in desire to eat and decreases in left temporoinsular cortical blood flow during the high-caloric versus control conditions.

DISCUSSION

Results implicate the temporo-insular cortex in normal appetitive function, suggesting that activity within this region is associated with the desirability or valence of food stimuli, prior to ingestion. These data will provide a broad foundation for future studies of patients with eating disorders.

Functional imaging of memory retrieval in deficit vs nondeficit schizophrenia

BACKGROUND

Neuroimaging studies have provided evidence of abnormal frontal and temporal lobe function in schizophrenia. Frontal cortex abnormalities have been associated with negative symptoms and temporal lobe abnormalities with positive symptoms. The deficit and nondeficit forms of schizophrenia were predicted to differ in prefrontal cortical activity, but not in medial temporal lobe activity.

METHODS

Regional cerebral blood flow was studied using oxygen 15 positron emission tomography during 3 different memory retrieval conditions in 8 control subjects, 8 patients with the deficit syndrome, and 8 patients without the deficit syndrome. Behavioral and positron emission tomography data were analyzed using a mixed-effects model to test for population differences.

RESULTS

In all memory conditions, frontal cortex activity was higher in patients without the deficit syndrome than in patients with the deficit syndrome. During the attempt to retrieve poorly encoded words, patients without the deficit syndrome recruited the left frontal cortex to a significantly greater degree than did patients with the deficit syndrome. The 2 schizophrenia subtypes did not differ in the activity or recruitment of the hippocampus during memory retrieval.

CONCLUSION

Frontal cortex function during memory retrieval is differentially impaired in deficit and nondeficit schizophrenia, whereas hippocampal recruitment deficits are not significantly different between the 2 schizophrenia groups.

Anger in healthy men: a PET study using script-driven imagery

BACKGROUND

An understanding of the neurobiological basis of normal emotional processing is useful in formulating hypotheses regarding the pathophysiology of psychiatric illnesses.

METHODS

This study examined the mediating functional neuroanatomy of anger in eight healthy men. Narrative scripts were developed from autobiographical information to induce anger and neutral states. The subjects imagined the content of the narrative scripts to induce anger during positron emission tomography to measure normalized regional cerebral blood flow (rCBF). Psychophysiologic responses and subjective ratings of emotional state were measured for each condition. Statistical parametric maps were constructed to reflect the Anger versus Neutral state contrast.

RESULTS

Anger was associated with activation of the left orbitofrontal cortex, right anterior cingulate cortex affective division, and bilateral anterior temporal poles.

CONCLUSIONS

These results suggest that the subjective experience of anger is associated with rCBF increases in anterior paralimbic regions of the brain.

Measurement of muscle protein synthesis by positron emission tomography with L-[methyl-11C]methionine: effects of transamination and transmethylation

BACKGROUND

Positron emission tomography with L-[methyl-11C]methionine provides a measure of regional protein synthesis rate (PSR) in skeletal muscle. However, the validity of the method depends on incorporation of methionine into protein with minimal transamination, transmethylation, or both. To test directly these assumptions, uptake of L-[methyl-14C]methionine in skeletal muscle was measured in control and cycloheximide-treated rats.

METHODS

Normal and cycloheximide-treated rats (n = 8/group) were injected with 50 microCi of L-[methyl-14C]methionine and arterial blood sampled over 90 minutes. After killing, thigh muscle was homogenized, centrifuged, and treated with trichloroacetic acid. PSR from circulating methionine was estimated from trichloroacetic acid-precipitable radioactivity, arterial time-activity curves, and plasma methionine concentrations.

RESULTS

In normal rats, approximately 70% of the tissue radioactivity was precipitated with trichloroacetic acid. In normal animals, PSR was 0.22 nmoles x min(-1) x g(-1), in excellent agreement with previous results. In the cycloheximide-treated group, PSR was 0.0032 nmoles x min(-1) x g(-1); approximately 98% reduction compared with controls.

CONCLUSION

These studies support the hypothesis that L-[methyl-11(14C]methionine accumulates in skeletal muscle as 11(14)C-labeled protein.

Neural activation during sexual and competitive arousal in healthy men

To investigate the mediating neuroanatomy of positively valenced arousal, we used script-driven imagery in conjunction with positron emission tomography to measure relative regional cerebral blood flow (rCBF) during sexual and competitive arousal, as well as neutral comparison states. Subjects were eight healthy right-handed men. Psychophysiologic responses and subjective ratings confirmed that the desired state manipulations were achieved. Statistical parametric mapping revealed similar patterns of rCBF changes for both positively valenced arousal conditions: increases were found within anterior cingulate and anterior temporal cortex as well as the ventral globus pallidus; decreases were found within widespread heteromodal association areas. These results complement findings from studies of other normal and pathological emotional states, and provide new insights regarding the neural substrates of pleasurable arousal in healthy men.

Visual word stem completion priming within and across modalities: a PET study

Using positron emission tomography, we studied changes in the regional cerebral blood flow (rCBF) associated with cross modality (auditory to visual) and within modality visual priming in a word stem completion task. Compared to baseline completion performance and to within modality visual priming, cross modality priming was associated with increased rCBF in prefrontal cortex and decreased rCBF in the left angular gyrus. The results confirm and complement trends observed in a previous study concerning visual to auditory cross modality priming, and suggest that distinct cortical mechanisms may mediate within- and cross modality priming on the stem completion task. The findings are consistent with the neuropsychological data concerning auditory to visual cross modality priming, and indicate involvement of aspects of explicit retrieval and lexical processes in cross modality priming.

Auditory priming within and across modalities: evidence from positron emission tomography

Previous neuroimaging studies of perceptual priming have reported priming-related decreases in the extrastriate cortex. However, because these experiments have used visual stimuli, it is unclear whether the observed decreases are associated specifically with some aspect of visual perceptual processing or with more general aspects of priming. We studied within- and cross-modality priming using an auditory word stem completion paradigm. Positron emission tomography (PET) images were obtained during stem completion and a fixation task. Within-modality auditory priming was associated with blood flow decreases in the extrastriate cortex (bilateral), medial/right anterior prefrontal cortex, right angular gyrus, and precuneus. In cross-modality priming, the study list was presented visually, and subjects completed auditory word stems. Cross-modality priming was associated with trends for blood flow decreases in the left angular gyrus and increases in the medial/right anterior prefrontal cortex. Results thus indicate that reduced activity in the extrastriate cortex accompanies within-modality priming in both visual and auditory modalities.

Relation between coronary "steal" and contractile function at rest in collateral-dependent myocardium of humans with ischemic heart disease

BACKGROUND

We tested the hypothesis that rest asynergy in collateral-dependent myocardium correlates with coronary steal.

METHODS AND RESULTS

PET with [13N]ammonia measured myocardial blood flow and flow reserve in 15 patients with symptomatic chronic ischemic heart disease. Coronary angiography assessed stenosis severity and collateral blood supply. Echocardiography or contrast ventriculography evaluated regional wall motion. Collateral-dependent segments with normal flow at rest and supplied by coronary vessels having </=50% diameter stenosis were studied. Steal was defined as a decline in myocardial blood flow with adenosine >/=0.15 mL. min-1. g-1 versus rest. Blood flow at rest in asynergic, collateral-dependent segments with steal (1.15+/-0.35 mL. min-1. g-1) exceeded (P<0.0001) that of asynergic segments without steal (0.81+/-0.24) and those with normal contraction (0.77+/-0.18). Although the flow reserve ratio of segments with normal contraction (1.8+/-0.8) exceeded that of asynergic ones with (0.6+/-0.1) or without (1.3+/-0.4) steal, overlap was great. Correlation between basal contraction and flow reserve ratio in collateral-dependent myocardium was significant but weak (r=0.45, P<0.001). However, segments demonstrating "steal" with adenosine manifested asynergy in 22 of 23 collateral-dependent segments versus 24 of 39 nonsteal segments (chi2=7.10, P<0.01).

CONCLUSIONS

Although myocardial flow reserve in collateral-dependent segments with normal contraction exceeded that of asynergic segments, overlap was great. However, in patients with angina or congestive heart failure, left ventricular segments demonstrating steal with adenosine almost always exhibit asynergy at rest. Thus, coronary steal may play an important role in the pathogenesis of chronic contractile impairment at rest, whereas simple reduction of flow reserve may be less important in selected patients.

Effects of nifedipine on myocardial blood flow and systolic function in humans with ischemic heart disease

OBJECTIVE

To test the hypothesis that, in humans with ischemic heart disease, nifedipine is a primary dilator of the coronary circulation and in general exerts a net positive effect on the balance of myocardial oxygen supply and demand.

METHODS

Positron-emission tomography with [13N]-ammonia was used to measure myocardial blood flow in patients at rest, and during infusion of adenosine and ingestion of nifedipine (10 mg capsule, a bite-and-chew technique). Myocardial segments were defined physiologically on the basis of blood flow to adenosine as being normal or having mild, moderate, or severe impairment of dilator reserve. Myocardial systolic function was assessed under comparable physiologic conditions using gated single-photon-emission computed tomography radionuclide ventriculography.

RESULTS

Our study population consisted of 13 male patients and one female patient. Ingestion of nifedipine increased heart rate (from 63 +/- 11 to 80 +/- 16 beats/min, P < 0.001) and, as intended, lowered systolic arterial pressure (from 148 +/- 20 to 123 +/- 14 mmHg, P < 0.001) but had no effect on heart rate-pressure product (which changed from 9283 +/- 1576 to 9942 +/- 2162 mmHg/min). Myocardial blood flow in patients at rest in segments with mild, moderate, and severe reductions of dilator capacity (0.63 +/- 0.20, 0.67 +/- 0.25, and 0.58 +/- 0.27 ml/min per g, respectively) was less (P < 0.01) than normal (0.91 +/- 0.29 ml/min per g). Nevertheless, flow of blood was increased versus that at rest (P < 0.01) by infusion of adenosine (to 1.78 +/- 0.13, 1.29 +/- 0.16, and 0.75 +/- 0.22 ml/min per g) and ingestion of nifedipine (to 1.17 +/- 0.51, 1.06 +/- 0.36, 0.85 +/- 0.42 ml/min per g) in segments with mild, moderate, and severe reduction of dilator capacity as well as in normal segments (to 3.18 +/- 0.85 ml/min per g with adenosine and 1.68 +/- 0.65 ml/min per g with nifedipine). Global left ventricular systolic function remained unchanged versus baseline (ejection fraction 0.74 +/- 0.09) with nifedipine (0.76 +/- 0.10). Regional contraction expressed in normalized amplitude units also remained unchanged versus baseline in response to nifedipine.

CONCLUSION

Nifedipine increases myocardial blood flow in humans with ischemic heart disease in normal segments as well as in segments with mild, moderate, and severe reductions of dilator capacity, albeit to a lesser extent with increasing impairment of dilator capacity. Both global and regional left ventricular contractile function also are not adversely affected by nifedipine. These improvements in myocardial blood flow in face of no change or a decrease in myocardial demand for oxygen reflect an overall favorable effect on the balance between the supply of and demand for myocardial oxygen.

Improved signal-to-noise ratio in parametric images by cluster analysis

Parametric images are formed by analyzing the concentration history of every voxel in PET data sets. Because PET concentration data at the voxel level are rather noisy, noise propagation into the parametric image is often quite noticeable. To address this problem, a model-based clustering method has been developed to generate parametric images. The basic idea of the clustering method is to average over voxels whose concentration histories have the same shape. We applied the method to a two-parameter (K1, k2) compartment model of local cerebral blood flow. The statistic R = integral tC(t) dt/integral C(t) dt= integral te-k2t multiply sign in circle Ca(t) dt/integral e-k2t multiply sign in circle Ca(t) dt classifies curves in terms of k2, where C(t) and Ca(t) denote the tissue and blood concentration histories, respectively, and multiply sign in circle is the convolution operator. Simulation studies of noise propagation in the clustering statistic showed that 30% voxel noise yielded a 2% standard deviation in R. Parametric images of blood flow and partition coefficient were computed for an O15 study, with and without clustering. Cluster size affected bias, statistical precision, and computation time. With clusters of 400 voxels, the variance of the flow parameter was around 1/50 smaller with clustering, with negligible bias and a computation time of 30 s on a 64-MHz workstation for 15 x 128 x 128 images with MATLAB 5.1.

The role of area 17 in visual imagery: convergent evidence from PET and rTMS

Visual imagery is used in a wide range of mental activities, ranging from memory to reasoning, and also plays a role in perception proper. The contribution of early visual cortex, specifically Area 17, to visual mental imagery was examined by the use of two convergent techniques. In one, subjects closed their eyes during positron emission tomography (PET) while they visualized and compared properties (for example, relative length) of sets of stripes. The results showed that when people perform this task, Area 17 is activated. In the other, repetitive transcranial magnetic stimulation (rTMS) was applied to medial occipital cortex before presentation of the same task. Performance was impaired after rTMS compared with a sham control condition; similar results were obtained when the subjects performed the task by actually looking at the stimuli. In sum, the PET results showed that when patterns of stripes are visualized, Area 17 is activated, and the rTMS results showed that such activation underlies information processing.

Regional cerebral blood flow during script-driven imagery in childhood sexual abuse-related PTSD: A PET investigation

OBJECTIVE

The purpose of this study was to determine whether anterior limbic and paralimbic regions of the brain are differentially activated during the recollection and imagery of traumatic events in trauma-exposed individuals with and without posttraumatic stress disorder (PTSD).

METHOD

Positron emission tomography (PET) was used to measure normalized regional cerebral blood flow (CBF) in 16 women with histories of childhood sexual abuse: eight with current PTSD and eight without current PTSD. In separate script-driven imagery conditions, participants recalled and imagined traumatic and neutral autobiographical events. Psychophysiologic responses and subjective ratings of emotional state were measured for each condition.

RESULTS

In the traumatic condition versus the neutral control conditions, both groups exhibited regional CBF increases in orbitofrontal cortex and anterior temporal poles; however, these increases were greater in the PTSD group than in the comparison group. The comparison group exhibited regional CBF increases in insular cortex and anterior cingulate gyrus; increases in anterior cingulate gyrus were greater in the comparison group than in the PTSD group. Regional CBF decreases in bilateral anterior frontal regions were greater in the PTSD group than in the comparison group, and only the PTSD group exhibited regional CBF decreases in left inferior frontal gyrus.

CONCLUSIONS

The recollection and imagery of traumatic events versus neutral events was accompanied by regional CBF increases in anterior paralimbic regions of the brain in trauma-exposed individuals with and without PTSD. However, the PTSD group had greater increases in orbitofrontal cortex and anterior temporal pole, whereas the comparison group had greater increases in anterior cingulate gyrus.

A method for assessing the accuracy of intersubject registration of the human brain using anatomic landmarks

Several groups have developed methods for registering an individual's 3D MRI by deforming a standard template. This achievement leads to many possibilities for segmentation and morphology that will impact nuclear medical research in areas such as activation and receptor studies. Accordingly, there is a need for methods that can assess the accuracy of intersubject registration. We have developed a method based on a set of 128 anatomic landmarks per hemisphere, both cortical and subcortical, that allows assessment of both global and local transformation accuracy. We applied our method to compare the accuracy of two standard methods of intersubject registration, AIR 3.0 with fifth-order polynomial warping and the Talairach stereotaxic transformation (Talairach and Tournoux, 1988). SPGR MRI's (256 x 256 x 160) of six normal subjects (age 18-24 years) were derformed to match a standard template volume. To assess registration accuracy the landmarks were located on both the template volume and the transformed volumes by an experienced neuroanatomist. The resulting list of coordinates was analyzed graphically and by ANOVA to compare the accuracy of the two methods and the results of the manual analysis. ANOVA performed over all 128 landmarks showed that the Woods method was more accurate than Talairach (left hemisphere F = 2.8, P < 0.001 and right hemisphere F =2.4, P < 0.006). The Woods method provided a better brain surface transformation than did Talairach (F = 18.0, P < 0.0001), but as expected there was a smaller difference for subcortical structures and both had an accuracy <1 mm for the majority of subcortical landmarks. Overall, both the Woods and Talairach method located about 70% of landmarks with an error of 3 mm or less. More striking differences were noted for landmark accuracy </=1 mm, where the Woods method located about 40% and Talairach about 23%. These results demonstrate that this anatomically based assessment method can help evaluate new methods of intersubject registration and should be a helpful tool in appreciating regional differences in accuracy. Consistent with expectation, we confirmed that the Woods nonlinear registration method was more accurate than Talairach. Landmark-based anatomic analyses of intersubject registration accuracy offer opportunities to explore the relationship among structure, function and architectonic boundaries in the human brain.

Muscle protein synthesis by positron-emission tomography with L-[methyl-11C]methionine in adult humans

Existing methods for assessing protein synthetic rates (PSRs) in human skeletal muscle are invasive and do not readily provide information about individual muscle groups. Recent studies in canine skeletal muscle yielded PSRs similar to results of simultaneous stable isotope measurements using L-[1-13C, methyl-2H3]methionine, suggesting that positron-emission tomography (PET) with L-[methyl-11C]methionine could be used along with blood sampling and a kinetic model to provide a less invasive, regional assessment of PSR. We have extended and refined this method in an investigation with healthy volunteers studied in the postabsorptive state. They received approximately 25 mCi of L-[methyl-11C]methionine with serial PET imaging of the thighs and arterial blood sampling for a period of 90 min. Tissue and metabolite-corrected arterial blood time activity curves were fitted to a three-compartment model. PSR (nmol methionine.min-1.g muscle tissue-1) was calculated from the fitted parameter values and the plasma methionine concentrations, assuming equal rates of protein synthesis and degradation. Pooled mean PSR for the anterior and posterior sites was 0.50 +/- 0.040. When converted to a fractional synthesis rate for mixed proteins in muscle, assuming a protein-bound methionine content of muscle tissue, the value of 0.125 +/- 0.01%.h-1 compares well with estimates from direct tracer incorporation studies, which generally range from approximately 0.05 to 0.09%.h-1. We conclude that PET can be used to estimate skeletal muscle PSR in healthy human subjects and that it holds promise for future in vivo, noninvasive studies of the influences of physiological factors, pharmacological manipulations, and disease states on this important component of muscle protein turnover and balance.

Differences in cerebral activation during smooth pursuit and saccadic eye movements using positron-emission tomography

BACKGROUND

Abnormalities of smooth pursuit eye movements occur commonly in schizophrenia, but the pathophysiological significance of these abnormalities is unknown. To address this, the authors conducted a pilot study in which we examined differences in regional cerebral activation using positron-emission tomography (PET) in normal volunteers as they performed two types of eye movements.

METHODS

Cerebral activation in 10 normal volunteers was studied using C15O2 PET while subjects tracked a visual target using smooth pursuit and saccadic eye movements. A left-hand movement comparison task provided a physiologic landmark for verification of the location of the frontal eye fields (FEFs).

RESULTS

Subjects exhibited FEF activation during both smooth pursuit and saccadic eye movements, which was greater in the latter. During smooth pursuit, subjects also exhibited increased cerebral activation in the left temporal-occipital border and left superior frontal cortex and decreased activation in medial superior parietal and insular regions relative to saccades. Other cortical visual and eye-movement brain regions also demonstrated differences in activation between the two visual tasks.

CONCLUSIONS

Significant fEF activation appears to underlie both smooth pursuit and saccadic eye movements but may be more critical in the former. Dysfunction of the frontal lobe, and possibly of other areas in the pursuit pathway such as the temporo-occipital motion area, may contribute to observed eye-movement abnormalities in patients with schizophrenia.

Effects of short-term treatment of hyperlipidemia on coronary vasodilator function and myocardial perfusion in regions having substantial impairment of baseline dilator reverse

BACKGROUND

We tested the hypothesis that correction of hyperlipidemia improves coronary vasodilator response and maximal perfusion in myocardial regions having substantial impairment of pretreatment vasodilator capacity.

METHODS AND RESULTS

Measurements of myocardial blood flow were made with PET [13N]ammonia in 12 patients with ischemic heart disease (11 men; age, 65+/-8 years [mean+/-SD]) at rest and during adenosine at 70 and then 140 microg . kg-1 . min-1 for 5 minutes each before and approximately 4 months after simvastatin treatment (40 mg daily). Simvastatin reduced LDL (171+/-13 before versus 99+/-18 mg/dL after simvastatin, P<0.001) and increased HDL (39+/-8 versus 45+/-9 mg/dL, P<0.05). Myocardial segments were classified on the basis of pretreatment blood flow response to 140 microg . kg-1 . min-1 adenosine as normal (flow >/=2 mL . min-1 . g-1) or abnormal (flow <2 mL . min-1 . g-1). In normal segments, baseline myocardial blood flow (0.95+/-0.32) increased (P<0.001) at both low- (1.62+/-0.81) and high- (2.63+/-0.41) dose adenosine and was unchanged both at rest and with adenosine after simvastatin. In abnormal segments, myocardial blood flow at rest (0. 73+/-0.19) increased at low- (1.06+/-0.59, P<0.02) and high- (1. 29+/-0.33, P<0.01) dose adenosine. After simvastatin, myocardial blood flow increased more compared with pretreatment at both low- (1. 37+/-0.66, P<0.05 versus pretreatment) and high- (1.89+/-0.79, P<0. 01 versus pretreatment) dose adenosine.

CONCLUSIONS

Short-term lipid-lowering therapy increases stenotic segment maximal myocardial blood flow by approximately 45%. The mechanism involves enhanced, flow-mediated dilation of stenotic epicardial conduit vessels and may account at least in part for the efficacy of lipid lowering in secondary prevention trials and in reducing ischemic episodes in ambulatory patients.

Impaired recruitment of the hippocampus during conscious recollection in schizophrenia

Poor attention and impaired memory are enduring and core features of schizophrenia. These impairments have been attributed either to global cortical dysfunction or to perturbations of specific components associated with the dorsolateral prefrontal cortex (DLPFC), hippocampus and cerebellum. Here, we used positron emission tomography (PET) to dissociate activations in DLPFC and hippocampus during verbal episodic memory retrieval. We found reduced hippocampal activation during conscious recollection of studied words, but robust activation of the DLPFC during the effort to retrieve poorly encoded material in schizophrenic patients. This finding provides the first evidence of hippocampal dysfunction during episodic memory retrieval in schizophrenia.

Pharmacokinetics of [18F]trovafloxacin in healthy human subjects studied with positron emission tomography

Tissue pharmacokinetics of trovafloxacin, a new broad-spectrum fluoroquinolone antimicrobial agent, were measured by positron emission tomography (PET) with [18F]trovafloxacin in 16 healthy volunteers (12 men and 4 women). Each subject received a single oral dose of trovafloxacin (200 mg) daily beginning 5 to 8 days before the PET measurements. Approximately 2 h after the final oral dose, the subject was positioned in the gantry of the PET camera, and 1 h later 10 to 20 mCi of [18F]trovafloxacin was infused intravenously over 1 to 2 min. Serial PET images and blood samples were collected for 6 to 8 h, starting at the initiation of the infusion. Drug concentrations were expressed as the percentage of injected dose per gram, and absolute concentrations were estimated by assuming complete absorption of the final oral dose. In most tissues, there was rapid accumulation of the radiolabeled drug, with high levels achieved within 10 min after tracer infusion. Peak concentrations of more than five times the MIC at which 90% of the isolates are inhibited (MIC90) for most members of Enterobacteriaceae and anaerobes (>10-fold for most organisms) were achieved in virtually all tissues, and the concentrations remained above this level for more than 6 to 8 h. Particularly high peak concentrations (micrograms per gram; mean +/- standard error of the mean [SEM]) were achieved in the liver (35.06 +/- 5.89), pancreas (32.36 +/- 20. 18), kidney (27.20 +/- 10.68), lung (22.51 +/- 7.11), and spleen (21. 77 +/- 11.33). Plateau concentrations (measured at 2 to 8 h; micrograms per gram; mean +/- SEM) were 3.25 +/- 0.43 in the myocardium, 7.23 +/- 0.95 in the lung, 11.29 +/- 0.75 in the liver, 9.50 +/- 2.72 in the pancreas, 4.74 +/- 0.54 in the spleen, 1.32 +/- 0.09 in the bowel, 4.42 +/- 0.32 in the kidney, 1.51 +/- 0.15 in the bone, 2.46 +/- 0.17 in the muscle, 4.94 +/- 1.17 in the prostate, and 3.27 +/- 0.49 in the uterus. In the brain, the concentrations (peak, approximately 2.63 +/- 1.49 microg/g; plateau, approximately 0.91 +/- 0.15 microg/g) exceeded the MIC90s for such common causes of central nervous system infections as Streptococcus pneumoniae (MIC90, <0.2 microg/ml), Neisseria meningitidis (MIC90, <0.008 microg/ml), and Haemophilus influenzae (MIC90, <0.03 microg/ml). These PET results suggest that trovafloxacin will be useful in the treatment of a broad range of infections at diverse anatomic sites.

Rapid detection of Parkinson's disease by SPECT with altropane: a selective ligand for dopamine transporters

Increasing evidence indicates that dopamine (DA) transporter density declines in Parkinson's disease (PD). 2Beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1-iodoprop-1-en -3-yl) nortropane (IACFT, Altropane) is a cocaine analog with high affinity and selectivity for dopamine transporter (DAT) sites in the striatum. In this study, single photon emission computed tomography (SPECT) with [123I]altropane was used to measure DAT density in seven healthy volunteers (five males, age 37-75, and two females, ages 26 and 39) and eight male patients with Parkinson's disease (age 14-79, Hoehn and Yahr stage: 1.5-3 (n = 5) and 4-5 (n = 3)). Dynamic SPECT images and arterial blood samples were acquired over 1.5-2 hr and plasma radioactivity was analyzed chromatographically to obtain metabolite corrected arterial input functions. Binding potential (BP, B'max/KD) for striatal (Str) DAT sites was calculated by two methods using occipital cortex (Occ) as a reference. In the first method, tissue time-activity curves (TAC) and metabolite corrected arterial input functions were analyzed by a linear graphical method developed for reversible receptor ligands. In the second method, the expression (Str(TAC) - Occ(TAC)) was fitted to a gamma variate function and the maximum divided by Occ(TAC) at the same time was used to estimate BP. In five of the PD patients, the SPECT data were compared with the results of PET with [18F] 6-fluoro DOPA (FD-PET). Plasma analysis indicated that [123I]altropane is rapidly converted to polar metabolites. SPECT images in healthy volunteers showed that [123I] altropane accumulated rapidly and selectively in the striatum and yielded excellent quality images within 1 h after injection. Both methods of analysis revealed a 7.6%/decade reduction in BP and average striatal values (corrected to age 25) were 1.83 +/- 0.22 and 2.09 +/- 0.20 by methods 1 and 2. In all the PD patients, striatal accumulation was markedly reduced and the pattern of loss was similar to that reported for DA; most profound in the posterior putamen with relative sparing of the caudate nuclei. A comparable pattern was observed with FD-PET. For total striatum, age-corrected BP was significantly (P < 0.001) reduced; 0.83 +/- 0.06 (method 1), 0.84 +/- 0.07 (method 2). BPs measured by the two methods were remarkably similar and highly correlated r2 = 0.88, (P < 0.001). These results indicate that [123I]altropane is an excellent SPECT ligand for imaging the DAT/DA neurons in human brain. The high selectivity and rapid striatal accumulation of the ligand allows for accurate quantitation of DAT sites in less than 2 hr. The results further demonstrate that [123I]altropane is an effective marker for PD.

Mental rotation of objects versus hands: neural mechanisms revealed by positron emission tomography

Twelve right-handed men participated in two mental rotation tasks as their regional cerebral blood flow (rCBF) was monitored using positron emission tomography. In one task, participants mentally rotated and compared figures composed of angular branching forms; in the other task, participants mentally rotated and compared drawings of human hands. In both cases, rCBF was compared with a baseline condition that used identical stimuli and required the same comparison, but in which rotation was not required. Mental rotation of branching objects engendered activation in the parietal lobe and Area 19. In contrast, mental rotation of hands engendered activation in the precentral gyrus (M1), superior and inferior parietal lobes, primary visual cortex, insula, and frontal Areas 6 and 9. The results suggest that at least two different mechanisms can be used in mental rotation, one mechanism that recruits processes that prepare motor movements and another mechanism that does not.

Probing striatal function in obsessive-compulsive disorder: a PET study of implicit sequence learning

Positron emission tomography was employed to contrast the brain activation pattern in patients with obsessive-compulsive disorder (OCD) to that of matched control subjects while they performed an implicit learning task. Although patients and control subjects evidenced comparable learning, imaging data from control subjects indicated bilateral inferior striatal activation, whereas OCD patients did not activate right or left inferior striatum and instead showed bilateral medial temporal activation. The findings further implicate corticostriatal dysfunction in obsessive-compulsive disorder. Furthermore, when OCD patients are confronted with stimuli that call for recruitment of corticostriatal systems, they instead appear to access brain regions normally associated with explicit (conscious) information processing.

Dehydrogenase regulation of metabolite oxidation and efflux from mitochondria in intact hearts

To test how alpha-ketoglutarate dehydrogenase (alpha-KGDH) activity influences the balance between oxidative flux and transmitochondrial metabolite exchange, we monitored these rates in isolated mitochondria and in perfused rabbit hearts at an altered kinetics (Km) of alpha-KGDH for alpha-ketoglutarate (alpha-KG). In isolated mitochondria, relative Km dropped from 0.23 mM at pH = 7.2 to 0.10 mM at pH 6.8 (P < 0.05), and alpha-KG efflux decreased from 126 to 95 nmol.min-1.mg-1. In intact hearts, Km was reduced with low intracellular pH, while matching control workload and respiratory rate with increased Ca2+ (pHi = 7.20, perfusate CaCl2 = 1.5 mM; pHi = 6.89, perfusate CaCl2 = 3 +/- 1 mM). Sequential 13C nuclear magnetic resonance spectra from hearts oxidizing [2-13C]acetate provided tricarboxylic acid cycle flux and the exchange rate between alpha-KG and cytosolic glutamate (F1). Tricarboxylic acid cycle flux was 10 mumol.min-1.g-1 in both groups, but F1 fell from a control of 9.3 +/- 0.6 to 2.8 +/- 0.4 mumol.min-1.g-1 at low Km. The results indicate that increased activity of alpha-KGDH occurs at the expense of alpha-KG efflux during support of normal workloads.

Positron emission tomographic analysis of central dopamine D1 receptor binding in normal subjects treated with the atypical neuroleptic, SDZ MAR 327

SDZ MAR 327 is a new neuroleptic agent with high in vitro affinity for dopamine D1 and D2 receptors. The goal of this study was to determine the effect of time after SDZ MAR 327 administration on central dopamine D1 receptor occupancy in healthy humans. Positron emission tomography (PET) with the dopamine D1 receptor ligand, [11C] SCH 23390, was performed in 6 male volunteers (age 22-34), in both the drug naive state and at 1, 2 and 4 h after a single oral dose of SDZ MAR 327 (9 mg). The pre and post drug treatment [11C] SCH 23390 dynamic data were analyzed using two different methods, each yielding a parameter proportional to the receptor density: i) a simple regional comparison approximating the specifically bound to free fraction, B/F; and ii) a two compartment, two parameter model yielding the apparent distribution volume DV". With both methods, a metabolite corrected arterial input function was used and the vascular fraction of tissue (Vb) was fixed at a previously determined value of 4%. Method I served as a qualitative comparison of the paired studies and demonstrated little difference between the pre and post drug conditions, method II also confirmed that there was no significant change in binding of [11C] SCH 23390 in the striatum. These data indicate that SDZ MAR 327 produces little if any effect on dopamine D1 receptor binding at the dose used.

Effects of dobutamine at maximally tolerated dose on myocardial blood flow in humans with ischemic heart disease

BACKGROUND

This study tests the hypothesis in humans with ischemic heart disease that myocardial blood flow response to dobutamine is linearly correlated with blood flow response to adenosine.

METHODS AND RESULTS

PET with [13N]ammonia was used to measure myocardial blood flow at rest and during adenosine and dobutamine at the maximally tolerated dose. Myocardial segments were defined physiologically on the basis of blood flow response to adenosine: normal, > or = 2 mL x min(-1) x g(-1); abnormal, < 2 mL x min(-1) x g(-1); and "steal," decline versus baseline > or = 0.15 mL x min(-1) x g(-1). The patient population consisted of 11 men and 2 women. Dobutamine increased heart rate (79+/-22 to 115+/-28 bpm) and rate-pressure product (9748+/-2862 to 15,157+/-3433 mm Hg/min) significantly (both P<.01). Myocardial blood flow at rest in abnormal segments (0.50+/-0.23 mL x min(-1) x g(-1)) was reduced (P<.001) versus normal (0.90+/-0.45) and steal (0.92+/-0.60). Nevertheless, in abnormal segments, blood flow increased versus rest (P<.001) with dobutamine (0.83+/-0.43) and adenosine (0.90+/-0.49). In steal segments, myocardial blood flow declined versus baseline (P<.001) with dobutamine (0.68+/-0.46) and adenosine (0.50+/-0.45). In normal segments, myocardial blood flow increased (P<.001) with dobutamine (2.16+/-0.99) and adenosine (3.10+/-0.90). Over the range of flows, the correlation between adenosine and dobutamine was good (r=.78, P<.0001). Although flow with dobutamine in normal segments correlated with rate-pressure product (r=.81, P<.05), the slope of the line was 2.7+/-0.8 (P<.02), and normalized blood flow (3.3+/-2.5 x rest) exceeded normalized rate-pressure product (1.9+/-0.8 x rest; P<.05).

CONCLUSIONS

In humans with ischemic heart disease, myocardial blood flow responses to dobutamine and adenosine are linearly correlated over a wide range. The hyperemic response to dobutamine is in excess of that predicted by rate-pressure product and reflects the unmeasured inotropic, oxygen-wasting, and beta2-agonist effects of the drug. Dobutamine induces coronary steal with a frequency approaching that of adenosine.

Neural systems shared by visual imagery and visual perception: a positron emission tomography study

Subjects participated in perceptual and imagery tasks while their brains were scanned using positron emission tomography. In the perceptual conditions, subjects judged whether names were appropriate for pictures. In one condition, the objects were pictured from canonical perspectives and could be recognized at first glance; in the other, the objects were pictured from noncanonical perspectives and were not immediately recognizable. In this second condition, we assume that top-down processing is used to evaluate the names. In the imagery conditions, subjects saw a grid with a single X mark; a lowercase letter was presented before the grid. In the baseline condition, they simply responded when they saw the stimulus, whereas in the imagery condition they visualized the corresponding block letter in the grid and decided whether it would have covered the X if it were physically present. Fourteen areas were activated in common by both tasks, only 1 of which may not be involved in visual processing (the precentral gyrus); in addition, 2 were activated in perception but not imagery, and 5 were activated in imagery but not perception. Thus, two-thirds of the activated areas were activated in common.

The role of positron emission tomography in pharmacokinetic analysis

The physiological and biochemical measurements that can be performed noninvasively in humans with modern imaging techniques offer great promise for defining the precise state of a patient's disease and its response to therapy. In general, there are two critical points in drug development when PET measurements are likely to be particularly useful: (1) In preclinical studies, a new drug can be precisely compared to standard therapies or a series of analogs can be screened for further development on the basis of performance in appropriate animal models. (2) In phase I-II human studies, classic pharmacokinetic measurements can be coupled with imaging measurements (a) to define optimal dosing schedule; (b) to define the potential utility of interventions in particular clinical situations; and (c) to formulate the design of phase III studies that are crucial for drug licensure. In general, the types of measurements that are possible can be grouped into the following categories: 1. In those situations in which the drug can be radiolabeled, the time course of tissue delivery can be determined noninvasively in vivo in health and disease. Such information should be useful for determining dosing schedules, establishing efficacy, and predicting possible toxicity. 2. Ligand-receptor binding can be assessed in vivo in two ways. The ability of the drug to displace standard radiolabeled ligands from their receptors can be determined; alternatively, labeled drug can be used to more directly assess the distribution and time course of binding. These measurements are particularly useful for studying drugs that are active in the central nervous and cardiovascular systems. 3. Measurements of tissue metabolism will be useful in determining the effects of therapies aimed at particular metabolic abnormalities. In addition, these measurements may be useful in defining viability and function of tissues in such widely disparate clinical situations as cancer chemotherapy and cardiology. For example, effects of CNS or cardiovascular drugs can be monitored by observing 18FDG metabolism in brain and heart. We suggest that the joining of classic clinical pharmacology to exquisite imaging measurements will help form the basis for 21st-century clinical drug development.

The functional neuroanatomy of anxiety: a study of three disorders using positron emission tomography and symptom provocation

Previous neuroimaging research has contributed insights regarding the neural substrates of specific psychiatric disorders. The purpose of this study was to determine the shared mediating neuroanatomy of anxiety symptoms across three different anxiety disorders. Data were pooled from 23 right-handed adult outpatients meeting criteria for obsessive-compulsive disorder, simple phobia, or posttraumatic stress disorder. Relative regional cerebral blood flow (rCBF) was measured using positron emission tomography in the context of symptom provocation paradigms. Symptom severity was measured via self-reports. The analysis of pooled imaging data indicated activation in right inferior frontal cortex, right posterior medial orbitofrontal cortex, bilateral insular cortex, bilateral lenticulate nuclei, and bilateral brain stem foci during the symptomatic versus control conditions. A positive correlation was found between rCBF at one brain stem locus and subjective anxiety scores (r = .744, p < .001). These findings suggest that elements of the paralimbic belt together with right inferior frontal cortex and subcortical nuclei mediate symptoms across different anxiety disorders. In addition, activation at one brain stem locus appears to be associated with the subjective severity of anxiety. Further studies are warranted to determine whether these same brain systems mediate normal anxiety states as well.

FDG hypermetabolism associated with inflammatory necrotic changes following radiation of meningioma

PET with 18F-fluoro-2-deoxy-D-glucose (FDG) is currently the noninvasive gold standard for distinguishing brain tumor recurrence from radiation necrosis. We present a case report that appears to contradict this doctrine. The patient had a history of atypical meningioma and was treated with surgical resection and postoperative proton-beam radiation therapy. Approximately 16 mo after completion of therapy, MRI demonstrated two new regions of enhancement, and an FDG-PET study was performed to further characterize these lesions. FDG-PET demonstrated an area of intense hypermetabolism, and wide surgical resection was performed. Histological examination of the surgical specimen revealed reactive changes and areas of necrosis. There was no evidence of either recurrent or radiation-induced tumor.

Modeling enrichment kinetics from dynamic 13C-NMR spectra: theoretical analysis and practical considerations

Measurements of oxidative metabolism in the heart from dynamic 13C nuclear magnetic resonance (NMR) spectroscopy rely on 13C turnover in the NMR-detectable glutamate pool. A kinetic model was developed for the analysis of isotope turnover to determine tricarboxylic acid cycle flux (VTCA) and the interconversion rate between alpha-ketoglutarate and glutamate (F1) by fitting the model to NMR data of glutamate enrichment. The results of data fitting are highly reproducible when the noise level is within 10%, making this model applicable to single or grouped experiments. The values for VTCA and F1 were unchanged whether obtained from least-squares fitting of the model to mean experimental enrichment data with standard deviations in the cost function (VTCA = 10.52 mumol.min-1.g dry wt-1, F1 = 10.67 mumol.min-1.g dry wt-1) or to the individual enrichment values for each heart with the NMR noise level in the cost function (VTCA = 10.67 mumol.min-1.g dry wt-1, F1 = 10.18 mumol.min-1.g dry wt-1). Computer simulation and theoretical analysis indicate that glutamate enrichment kinetics are insensitive to the fractional enrichment of acetyl-CoA and changes in small intermediate pools (< 1 mumol/g dry wt). Therefore, high-resolution NMR analysis of tissue extracts and biochemical assays for intermediates at low concentrations are unnecessary. However, a high correlation between VTCA and F1 exists, as anticipated from competition for alpha-ketoglutarate, which indicates the utility of introducing independent experimental constraints into the data fitting for accurate quantification.