Radiosynthesis and evaluation of [11C]AG-488, a dual anti-angiogenetic and anti-tubulin PET ligand

Combinations of antiangiogenic and cytotoxic agents show promising results in the treatment of cancer. However, there is a lack of single agent with both antiangiogenic and cytotoxic activities for clinical application. AG-488 aka FLAG-003 is a novel ligand with established antiangiogenetic properties via activation of receptor thymidine kinase (RTK) and anti-tubulin properties in tumor cells. AG-488 is also reported to reduce tumor volume and prolong survival in preclinical animal models of glioblastoma multiforme, breast cancer and is in clinical stage. Higher expression of RTKs and tubulins is reported in various cancers. This study reveals the development of [¹¹C]AG-488, a high affinity dual target inhibitor binding to RTK and anti-tubulin activities. We rationale that antiangiogenic RTK and anti-tubulin activity of [¹¹C]AG-488 may enhance the tumor to tissue ratio, assisting in cancer drug development. [¹¹C]AG-488 was synthesized in 35 ± 5 % radiochemical yield by radiomethylating the corresponding phenolate using [¹¹C]CH₃I. MicroPET studies in mice indicated blood-brain barrier penetration of [¹¹C]AG-488 and retention in the brain. However, blocking studies with antitubulin and RTK agent HD-800 and microtubule depolymerizing agent MPC-6827 show increased binding of [¹¹C]AG-488 in brain. The pattern of tracer binding in blocking conditions is similar to the baseline conditions. The higher binding may be due to the increased plasma uptake of radiotracer or the formation of more free tubulins due to microtubule dynamic instability during the blocking conditions.

Mucocele mimicking a gallbladder in a transplanted liver: A case report and review of the literature

Biliary mucoceles after deceased donor liver transplantation are a rarity, and mucoceles mimicking a gallbladder from the recipient remnant cystic duct have not been described until this case. We describe a 48-year-old male who presented with right upper quadrant pain and was found to have a recipient cystic duct mucocele 3 mo after receiving a deceased donor liver transplant. We describe the clinical presentation, laboratory and imaging findings (including the appearance of a gallbladder), multidisciplinary approach and surgical resolution of this mucocele originating from the recipient cystic duct, and a review of the literature.

Levodopa-induced abnormal involuntary movements correlate with altered permeability of the blood-brain-barrier in the basal ganglia

Chronic levodopa treatment leads to the appearance of dyskinesia in the majority of Parkinson’s disease patients. Neurovascular dysregulation in putaminal and pallidal regions is thought to be an underlying feature of this complication of treatment. We used microPET to study unilaterally lesioned 6-hydroxydopamine rats that developed levodopa-induced abnormal involuntary movements (AIMs) after three weeks of drug treatment. Animals were scanned with [¹⁵O]-labeled water and [¹⁸F]-fluorodeoxyglucose, to map regional cerebral blood flow and glucose metabolism, and with [¹¹C]-isoaminobutyric acid (AIB), to assess blood-brain-barrier (BBB) permeability, following separate injections of levodopa or saline. Multitracer scan data were acquired in each animal before initiating levodopa treatment, and again following the period of daily drug administration. Significant dissociation of vasomotor and metabolic levodopa responses was seen in the striatum/globus pallidus (GP) of the lesioned hemisphere. These changes were accompanied by nearby increases in [¹¹C]-AIB uptake in the ipsilateral GP, which correlated with AIMs scores. Histopathological analysis revealed high levels of microvascular nestin immunoreactivity in the same region. The findings demonstrate that regional flow-metabolism dissociation and increased BBB permeability are simultaneously induced by levodopa within areas of active microvascular remodeling, and that such changes correlate with the severity of dyskinesia.

Fluorine-18-fluorodihydroxyphenylalanine Positron-emission Tomography Scans of Neuroendocrine Tumors (Carcinoids and Pheochromocytomas)

Objectives:

Conventional methods of imaging neuroendocrine tumors with computed tomography, magnetic resonance imaging, indium-111-octreotide, or radiolabeled metaiodobenzilguanidine scintigraphy have limitations. This pilot study tried to improve the localization of these tumors with fluorine-18-fluorodihydroxyphenylalanine (F-DOPA) positron-emission tomography (PET) scanning.

Materials and Methods:

We studied 22 patients, the majority of whom were referred with clinical diagnosis or suspicion of carcinoid (n = 11), neuroendocrine tumors (n = 7) or pheochromocytoma/paraganglioma (PGL) (n = 4). The comparison was made with the prior conventional imaging.

Results:

The F-DOPA findings were compared with the results of subsequent surgery (2), endoscopy (1), or a long-term follow-up (mean duration, 49 months) for 17 patients. Two patients were lost to follow-up. Foci of F-DOPA deposition were detected in eight patients (final diagnosis of carcinoid in six, of neuroendocrine tumors in one, and of PGL in another). Comparison with the final diagnoses revealed concordance in 16 of the 22 patients. F-DOPA results appeared superior to those obtained with conventional imaging. Despite the small number and diagnostic heterogeneity, in a substantial fraction of patients F-DOPA PET added information relevant to clinical management.

Conclusion:

F-DOPA scanning added prognostic value, particularly when multiple abnormal foci versus a negative examination were considered.

Early Results of Pilot Study Using Hepatitis C Virus (HCV) Positive Kidneys to Transplant HCV Infected Patients with End-Stage Renal Disease Allowing for Successful Interferon-Free Direct Acting Antiviral Therapy after Transplantation

Introduction: Hepatitis C virus (HCV) infection in kidney transplant (KTX) patients reduces long-term patient and graft survival. Direct-acting antivirals (DAA) are > 90% effective in achieving sustained viral response (SVR); however, DAAs are not routinely available to patients with end-stage renal disease (ESRD). The University of Utah Transplant Program developed a protocol to allow HCV-positive potential KTX recipients to accept HCV-positive donors' kidneys. Three months after successful KTX, they were eligible for DAA therapy.

Methods: HCV-positive patients approved for KTX by the University of Utah Transplant Selection Committee were eligible to be enrolled in this study. Patients consented for the use of HCV-positive donor organs. Three to six months after successful KTX, these patients were treated for HCV with interferon-free direct-acting antiviral regimens according to viral genotype and prior treatment experience.

Results: Between 2014-2015, 12 HCV-positive patients were listed for KTX. Eight patients were kidney only eligible, seven patients received HCV-positive deceased donor kidneys, and one received an HCV-negative organ. Currently, six patients have completed treatment, all have achieved sustained viral response (SVR), and one patient is currently awaiting treatment. All seven patients have functioning kidney grafts. Wait time for KTX was reduced amongst all blood groups from an average of 1,350 days to only 65 days.

Conclusions: HCV-positive patients with ESRD can successfully receive an HCV-positive donor's kidney. Once transplanted, these patients can receive DAA therapy and achieve SVR. Use of HCV-positive organs reduced time on the waitlist by greater than three years and expanded the donor organ pool.

Human Radiation Dosimetry for the N-Methyl-D-Aspartate Receptor Radioligand 11C-CNS5161

(11)C-CNS5161 (N-(2-chloro-5-methylthiophenyl)-N'-(3-methylthiophenyl)-N'-(11)C-methylguanidine) has been successfully used in PET imaging of N-methyl-d-aspartate (NMDA) receptors. However, no human dosimetry data have been published. We are planning to use this radiotracer for investigating NMDA receptor function in systemic lupus erythematosus, traumatic brain injury, and Parkinson disease. We have therefore undertaken (11)C-CNS5161 PET imaging to measure the whole-body distribution of this radionuclide and to estimate radiation dose to various organs.

METHODS

Dynamic PET studies of the whole body were performed on 5 healthy adults. Regions of interest were drawn over the visualized structures. Resultant time-activity curves were generated and used to determine residence times for dosimetry calculations. S factors were implemented within the OLINDA/EXM software for each structure or organ.

RESULTS

For (11)C-CNS5161, organ doses ranged from 0.0002 to 0.0393 mGy/MBq (0.0006-0.1455 rad/mCi). The critical organ for radiation burden was the lungs, with a dose of 0.0393 mGy/MBq (0.1455 rad/mCi). Radiation doses to the reproductive and blood-forming organs were 0.0023, 0.0002, and 0.0020 mGy/MBq (0.0086, 0.0006, and 0.0074 rad/mCi) for the ovaries, testes, and red marrow, respectively. The effective dose equivalent was 0.0106 mSv/MBq (0.0392 rem/mCi).

CONCLUSION

The radiation dosimetry for (11)C-CNS5161 for a standard single injection of 555 MBq (15 mCi) will result in an effective dose equivalent of 5.9 mSv (0.59 rem) and a lung dose of 21.8 mGy (2.18 rad) in young, healthy subjects.

The relationship between fasting serum glucose and cerebral glucose metabolism in late-life depression and normal aging

Evidence exists for late-life depression (LLD) as both a prodrome of and risk factor for Alzheimer׳s disease (AD). The underlying neurobiological mechanisms are poorly understood. Impaired peripheral glucose metabolism may explain the association between depression and AD given the connection between type 2 diabetes mellitus with both depression and AD. Positron emission tomography (PET) measures of cerebral glucose metabolism are sensitive to detecting changes in neural circuitry in LLD and AD. Fasting serum glucose (FSG) in non-diabetic young (YC; n=20) and elderly controls (EC; n=12) and LLD patients (n=16) was correlated with PET scans of cerebral glucose metabolism on a voxel-wise basis. The negative correlations were more extensive in EC versus YC and in LLD patients versus EC. Increased FSG correlated with decreased cerebral glucose metabolism in LLD patients to a greater extent than in EC in heteromodal association cortices involved in mood symptoms and cognitive deficits observed in LLD and dementia. Negative correlations in YC were observed in sensory and motor regions. Understanding the neurobiological consequences of diabetes and associated conditions will have substantial public health significance given that this is a modifiable risk factor for which prevention strategies could have an important impact on lowering dementia risk.

Longitudinal studies of cerebral glucose metabolism in late-life depression and normal aging

OBJECTIVE

Late-life depression (LLD) has a substantial public health impact and is both a risk factor for and a prodrome of dementia. Positron emission tomography (PET) studies of cerebral glucose metabolism have demonstrated sensitivity in evaluating neural circuitry involved in depression, aging, incipient cognitive decline, and dementia. The present study evaluated the long term effects of a course of antidepressant treatment on glucose metabolism in LLD patients.

METHODS

Nine LLD patients and seven non-depressed control subjects underwent clinical and cognitive evaluations as well as brain magnetic resonance imaging and PET studies of cerebral glucose metabolism at baseline, after 8 weeks of treatment with citalopram for a major depressive episode (patients only), and at an approximately 2-year follow-up.

RESULTS

The majority of LLD patients were remitted at follow-up (7/9). Neither patients nor controls showed significant cognitive decline. The patients showed greater increases in glucose metabolism than the controls in regions associated with mood symptoms (anterior cingulate and insula). Both groups showed decreases in metabolism in posterior association cortices implicated in dementia.

CONCLUSIONS

Longitudinal changes in cerebral glucose metabolism are observed in controls and in LLD patients without significant cognitive decline that are more extensive than the decreases in brain volume. Longer duration follow-up studies and the integration of other molecular imaging methods will have implications for understanding the clinical and neurobiological significance of these metabolic changes.

Serotonin modulation of cerebral glucose metabolism: sex and age effects

The serotonin system is implicated in a variety of psychiatric disorders whose clinical presentation and response to treatment differ between males and females, as well as with aging. However, human neurobiological studies are limited. Sex differences in the cerebral metabolic response to an increase in serotonin concentrations were measured, as well as the effect of aging, in men compared to women. Thirty-three normal healthy individuals (14 men/19 women, age range 20-79 years) underwent two resting positron emission tomography studies with the radiotracer [18F]-2-deoxy-2-fluoro-D-glucose ([(18)F]-FDG) after placebo and selective serotonin reuptake inhibitor (SSRI, citalopram) infusions on two separate days. Results indicated that women demonstrated widespread areas of increased cortical glucose metabolism with fewer areas of decrease in metabolism in response to citalopram. Men, in contrast, demonstrated several regions of decreased cortical metabolism, but no regions of increased metabolism. Age was associated with greater increases in women and greater decreases in men in most brain regions. These results support prior studies indicating that serotonin function differs in men and women across the lifespan. Future studies aimed at characterizing the influences of age and sex on the serotonin system in patients with psychiatric disorders are needed to elucidate the relationship between sex and age differences in brain chemistry and associated differences in symptom presentation and treatment response.

Distinct functional networks associated with improvement of affective symptoms and cognitive function during citalopram treatment in geriatric depression

Variability in the affective and cognitive symptom response to antidepressant treatment has been observed in geriatric depression. The underlying neural circuitry is poorly understood. This study evaluated the cerebral glucose metabolic effects of citalopram treatment and applied multivariate, functional connectivity analyses to identify brain networks associated with improvements in affective symptoms and cognitive function. Sixteen geriatric depressed patients underwent resting positron emission tomography (PET) studies of cerebral glucose metabolism and assessment of affective symptoms and cognitive function before and after 8 weeks of selective serotonin reuptake inhibitor treatment (citalopram). Voxel-wise analyses of the normalized glucose metabolic data showed decreased cerebral metabolism during citalopram treatment in the anterior cingulate gyrus, middle temporal gyrus, precuneus, amygdala, and parahippocampal gyrus. Increased metabolism was observed in the putamen, occipital cortex, and cerebellum. Functional connectivity analyses revealed two networks which were uniquely associated with improvement of affective symptoms and cognitive function during treatment. A subcortical-limbic-frontal network was associated with improvement in affect (depression and anxiety), while a medial temporal-parietal-frontal network was associated with improvement in cognition (immediate verbal learning/memory and verbal fluency). The regions that comprise the cognitive network overlap with the regions that are affected in Alzheimer's dementia. Thus, alterations in specific brain networks associated with improvement of affective symptoms and cognitive function are observed during citalopram treatment in geriatric depression.

Dopamine cell implantation in Parkinson's disease: long-term clinical and (18)F-FDOPA PET outcomes

We have previously reported the results of a 1-y double-blind, placebo-controlled study of embryonic dopamine cell implantation for Parkinson's disease. At the end of the blinded phase, we found a significant increase in putamen uptake on (18)F-fluorodopa ((18)F-FDOPA) PET reflecting the viability of the grafts. Nonetheless, clinical improvement was significant only in younger (age < or = 60 y) transplant recipients, as indicated by a reduction in Unified Parkinson's Disease Rating Scale (UPDRS) motor scores.

METHODS

We now report long-term clinical and PET outcomes from 33 of the original trial participants who were followed for 2 y after transplantation and 15 of these subjects who were followed for 2 additional years. Longitudinal changes in UPDRS motor ratings and caudate and putamen (18)F-FDOPA uptake were assessed with repeated-measures ANOVA. Relationships between these changes over time were evaluated by the analysis of within-subject correlations.

RESULTS

We found that UPDRS motor ratings declined over time after transplantation (P < 0.001). Clinical improvement at 1 y was relatively better for the younger transplant recipients and for men, but these age and sex differences were not evident at longer-term follow-up. Significant increases in putamen (18)F-FDOPA uptake were evident at all posttransplantation time points (P < 0.001) and were not influenced by either age or sex. Posttransplantation changes in putamen PET signal and clinical outcome were significantly intercorrelated (P < 0.02) over the course of the study. Image analysis at the voxel level revealed significant bilateral increases in (18)F-FDOPA uptake at 1 y (P < 0.001) in the posterior putamen engraftment sites. PET signal in this region increased further at 2 and 4 y after engraftment. Concurrently, this analysis disclosed progressive declines in radiotracer uptake in the nonengrafted caudate and ventrorostral putamen. Clinical improvement after transplantation correlated with the retention of PET signal in this region at the preoperative baseline.

CONCLUSION

These results suggest that clinical benefit and graft viability are sustained up to 4 y after transplantation. Moreover, the dependence of clinical (but not imaging) outcomes on subject age and sex at 1 y may not persist over the long term. Last, the imaging changes reliably correlate with clinical outcome over the entire posttransplantation time course.

The functional neuroanatomy of geriatric depression

OBJECTIVE

Positron Emission Tomography (PET) studies of cerebral glucose metabolism have demonstrated sensitivity in evaluating the functional neuroanatomy of treatment response variability in depression, as well as in the early detection of functional changes associated with incipient cognitive decline. The evaluation of cerebral glucose metabolism in late life depression may have implications for understanding treatment response variability, as well as evaluating the neurobiological basis of depression in late life as a risk factor for dementia.

METHODS

Sixteen patients with geriatric depression and 13 comparison subjects underwent resting PET studies of cerebral glucose metabolism, as well as magnetic resonance (MR) imaging scans to evaluate brain structure.

RESULTS

Cerebral glucose metabolism was elevated in geriatric depressed patients relative to comparison subjects in anterior (right and left superior frontal gyrus) and posterior (precuneus, inferior parietal lobule) cortical regions. Cerebral atrophy (increased cerebrospinal fluid [CSF] and decreased grey and white matter volumes) were observed in some of these regions, as well. Regional cerebral metabolism was positively correlated with severity of depression and anxiety symptoms.

CONCLUSIONS

In contrast to decreased metabolism observed in normal aging and neurodegenerative conditions such as Alzheimer's disease, cortical glucose metabolism was increased in geriatric depressed patients relative to demographically matched controls, particularly in brain regions in which cerebral atrophy was observed, which may represent a compensatory response.

Abnormal striatal and thalamic dopamine neurotransmission: Genotype-related features of dystonia

OBJECTIVE

To determine whether changes in D(2) receptor availability are present in carriers of genetic mutations for primary dystonia.

METHODS

Manifesting and nonmanifesting carriers of the DYT1 and DYT6 dystonia mutations were scanned with [(11)C] raclopride (RAC) and PET. Measures of D(2) receptor availability in the caudate nucleus and putamen were determined using an automated region-of-interest approach. Values from mutation carriers and healthy controls were compared using analysis of variance to assess the effects of genotype and phenotype. Additionally, voxel-based whole brain searches were conducted to detect group differences in extrastriatal regions.

RESULTS

Significant reductions in caudate and putamen D(2) receptor availability were evident in both groups of mutation carriers relative to healthy controls (p < 0.001). The changes were greater in DYT6 relative to DYT1 carriers (-38.0 +/- 3.0% vs -15.0 +/- 3.0%, p < 0.001). By contrast, there was no significant difference between manifesting and nonmanifesting carriers of either genotype. Voxel-based analysis confirmed these findings and additionally revealed reduced RAC binding in the ventrolateral thalamus of both groups of mutation carriers. As in the striatum, the thalamic binding reductions were more pronounced in DYT6 carriers and were not influenced by the presence of clinical manifestations.

CONCLUSIONS

Reduced D(2) receptor availability in carriers of dystonia genes is compatible with dysfunction or loss of D(2)-bearing neurons, increased synaptic dopamine levels, or both. These changes, which may be present to different degrees in the DYT1 and DYT6 genotypes, are likely to represent susceptibility factors for the development of clinical manifestations in mutation carriers.

Selective serotonin reuptake inhibitor (SSRI) modulation of striatal dopamine measured with [11C]-raclopride and positron emission tomography

The effect of a pharmacologic increase in serotonin concentrations on striatal dopamine (D2) receptor availability has been measured in several studies using positron emission tomography (PET) and the radiotracer [11C]-raclopride as a method for the in vivo imaging of serotonin modulation of striatal dopamine in human subjects. These studies have shown that an acute increase in serotonin concentrations produced a decrease in striatal D2 receptor availability. The current study was undertaken to measure the effects of a more pharmacologically selective serotonergic agent compared to previous studies, the serotonin reuptake inhibitor, citalopram, on striatal D2 receptor availability. Twelve healthy control subjects underwent two PET scans performed on the same day following i.v. administration of saline (Scan 1) and citalopram (Scan 2, 40 mg, i.v.). The [11C]-raclopride data were analyzed with a graphical analysis method using the cerebellum as the input function. Plasma levels of citalopram, cortisol, and prolactin were measured. The citalopram concentrations peaked at the end of infusion (EOI) and remained relatively consistent from 30 min to 3 h postinfusion. An increase in cortisol and prolactin concentrations was observed from the EOI until 60 min after the EOI. A significant decrease in striatal D2 receptor availability was observed after citalopram infusion (-5%), presumably due to an increase in endogenous dopamine concentrations. In summary, i.v. administration of the selective serotonin reuptake inhibitor, citalopram, produced modest reductions in striatal D2 receptor availability, consistent with other human [11C]-raclopride studies using less pharmacologically selective serotonergic agents.

Cholinergic modulation of the cerebral metabolic response to citalopram in Alzheimer's disease

Pre-clinical and human neuropharmacological evidence suggests a role of cholinergic modulation of monoamines as a pathophysiological and therapeutic mechanism in Alzheimer's disease. The present study measured the effects of treatment with the cholinesterase inhibitor and nicotinic receptor modulator, galantamine, on the cerebral metabolic response to the selective serotonin reuptake inhibitor, citalopram. Seven probable Alzheimer's disease patients and seven demographically comparable controls underwent two positron emission tomography (PET) glucose metabolism scans, after administration of a saline placebo infusion (Day 1) and after citalopram (40 mg, IV, Day 2). The scan protocol was repeated in the Alzheimer's disease patients 2 months after titration to a 24 mg galantamine dose. At baseline, cerebral glucose metabolism was reduced in Alzheimer's disease patients relative to controls in right middle temporal, left posterior cingulate and parietal cortices (precuneus and inferior parietal lobule), as expected. Both groups demonstrated acute decreases in cerebral glucose metabolism after citalopram to a greater extent in the Alzheimer's disease patients. In the patients, relative to the controls, citalopram decreased glucose metabolism to a greater extent in middle frontal gyrus (bilaterally), left middle temporal gyrus and right posterior cingulate prior to treatment. Galantamine treatment alone increased metabolism in the right precuneus, right inferior parietal lobule and right middle occipital gyrus. In contrast, during galantamine treatment, citalopram increased metabolism in the right middle frontal gyrus, right post-central gyrus, right superior and middle temporal gyrus and right cerebellum. The combined cerebral metabolic effects of galantamine and citalopram suggest, consistent with preclinical data, a synergistic interaction of cholinergic and serotonergic systems.

Cerebral glucose metabolism and D2/D3 receptor availability in young adults with cannabis dependence measured with positron emission tomography

INTRODUCTION

Cannabis users have been reported to have decreased regional cerebral glucose metabolism after short periods of abstinence. The purpose of this study was to measure striatal dopamine receptor (D2/D3) availability and cerebral glucose metabolism with positron emission tomography (PET) in young adults who had a prolonged exposure to cannabis and who had been abstinent for a period of at least 12 weeks.

MATERIALS AND METHODS

Six 18-21-year-old male subjects with cannabis dependence in early full remission and six age- and sex-matched healthy subjects underwent PET scans for D2/D3 receptor availability measured with [C11]-raclopride and glucose metabolism measured with [18F]-FDG. All subjects were sober for at least 12 weeks before PET scan procedures. PET data were analyzed with statistical parametric mapping software (SPM99; uncorrected p < 0.001, corrected p < 0.05 at the cluster level). Toxicology screening was performed prior to the PET scan to confirm the lack of drugs of abuse.

OBSERVATION AND RESULTS

Striatal D2/D3 receptor availability did not differ significantly between groups. Compared to controls, subjects with cannabis dependence had lower normalized glucose metabolism in the right orbitofrontal cortex, putamen bilaterally, and precuneus. There were no significant correlations between striatal D2/D3 receptor availability and normalized glucose metabolism in any region of the frontal cortex or striatum.

CONCLUSION

These findings may reflect both cannabis exposure and adaptive changes that occur after a prolonged period of abstinence. Subsequent studies should address whether metabolic and dopamine receptor effects are associated with either active use or longer-term withdrawal in these relatively young subjects.

Decreased striatal D2 receptor binding in non-manifesting carriers of the DYT1 dystonia mutation

To determine whether reduced striatal D2 receptor binding reported in patients with idiopathic torsion dystonia is associated with the genotype, the authors used PET and [11C]-raclopride to assess non-manifesting carriers of the DYT1 mutation. D2 receptor binding was reduced by approximately 15% in caudate and putamen (p < 0.005). These results suggest that striatal D2 binding reductions are a trait feature of the DYT1 genotype.

Caudate nucleus: influence of dopaminergic input on sequence learning and brain activation in Parkinsonism

In this study, we tested the hypotheses that (1) the acquisition of sequential information is related to the integrity of dopaminergic input to the caudate nucleus; and (2) the integrity of dopaminergic input to the caudate nucleus correlates significantly with brain activation during sequence acquisition. Twelve early stage Parkinson's disease (PD) patients and six age-matched healthy volunteers were scanned using a dual tracer PET imaging design. All subjects were scanned with [(18)F]fluoropropyl-betaCIT (FPCIT) to measure striatal dopamine transporter (DAT) binding and with [(15)O]water to assess activation during a sequence learning task where movements were made to a repeating sequence of eight targets. Caudate and putamen DAT binding in the PD cohort was reduced by 15% and 43%, respectively. In PD, caudate DAT binding correlated with target acquisition (R = 0.57, P < 0.05), while putamen DAT binding did not correlate with performance. In volunteers, caudate DAT binding correlated with learning-related activation (P < 0.05, corrected for multiple comparisons) in the left dorsolateral and ventral prefrontal cortices, the anterior cingulate and premotor regions, and the right cerebellum. A significant correlation with caudate DAT binding was additionally detected in the right anteromedial thalamus, extending into the rostral midbrain. By contrast, in the PD cohort, most of these regional relationships were lost: Only ventral and dorsolateral prefrontal cortex activation correlated with caudate dopaminergic tone. Our findings suggest that sequence learning is normally associated with tight coupling between dopaminergic input to the caudate and thalamo-cortical functional activity. Despite minimal reductions in nigro-caudate input, PD patients demonstrate a loss of this coupling early in the disease.

Gene microarray analysis of human brain arteriovenous malformations

OBJECTIVE

Human brain arteriovenous malformations (BAVMs) display abnormal expression of various angiogenesis-related genes and their products. We examined gene expression patterns in BAVMs by the gene microarray technique.

METHODS

We analyzed BAVM and control brain samples obtained by temporal lobectomy for medically intractable seizure by Affymetrix Human Gene Set U95Av2 (Affymetrix, Inc., Santa Clara, CA). The gene microarray data were compared with new and previously published data that used conventional molecular biology techniques.

RESULTS

We analyzed six BAVM and five control brain samples. From 12,625 gene probes assayed, 1781 gene probes showed differential expression between BAVMs and controls. BAVM samples had a gene expression pattern that was distinct from those of control brain samples. Increased messenger ribonucleic acid expression of vascular endothelial growth factor A was accompanied by increased expression of its protein product. A majority of the gene data was in agreement with previously published data. The gene microarray data generated a new testable hypothesis regarding integrin, and we found increased expression of integrin alphavbeta3 protein in BAVMs.

CONCLUSION

The gene expression pattern of BAVMs was distinct from those of control brain samples. We verified the gene microarray data by demonstrating that increased gene expression levels for angiogenesis-related molecules were accompanied by increased levels of their protein product expression. The gene microarray technique may be a useful tool to study multiple pathways simultaneously in BAVM specimens.

Radiosynthesis of [18F] N-(3-Fluoropropyl)-2-β-Carbomethoxy-3-β-(4-Bromophenyl) Nortropane and the regional brain uptake in non human primate using PET

A synthetic procedure for the preparation of [18F]FPCBT, an imaging agent for the dopamine transporter (DAT), has been developed. The radiosynthesis was carried out in a two step procedure. Even though the yield was low, we were able to prepare 20 to 30 mCi of the product, which was enough for two or three studies. The radiochemical purity was greater than 96%. The in vivo properties of this radiotracer were evaluated using baboon and it showed highest uptake in the striatum. The studies also revealed that the maximum uptake was reached within 7 to 10 minutes post injection. Plasma metabolite analysis indicated that there is only one metabolite and it is less lipophilic than the parent compound. [18F]FPCBT displayed good brain uptake and its high target to non target ratio indicate that it is a potential candidate for DAT imaging.

Dosimetry of the dopamine transporter radioligand 18F-FPCIT in human subjects

This study was designed to evaluate the radiation dosimetry in human subjects for a new radiopharmaceutical, N-(3-(18)F-fluoropropyl)-2beta-carbomethoxy-3beta-(4-iodophenyl)nortropane ((18)F-FPCIT). The goal was to determine a limiting dose consistent with accepted guidelines for use in clinical studies and to compare the radiation burden with other agents such as (123)I-FPCIT, (18)F-fluorodopa, and (18)F-FDG.

METHODS

Dynamic PET scans of the urinary bladder were obtained in 6 subjects; 2 subjects had brain scans and 5 subjects had scans of the thorax or abdomen. Regions of interest were placed over composite images of each organ for which activity was visualized to generate time-activity curves. Doses were calculated from residence times using the MIRDOSE3 program.

RESULTS

The critical organ for dosimetry is the urinary bladder wall with a dose of 0.0586 +/- 0.0164 mGy/MBq. The dose comes primarily (97.2%) from activity in the urinary bladder contents. The dose is lower than any of the other agents used commonly in PET to assess dopaminergic function. The effective dose equivalent (0.0120 mGy/MBq) is also lower than comparable compounds.

CONCLUSION

(18)F-FPCIT has favorable dosimetry when compared with other agents used to study dopaminergic function. Doses as high as 853 MBq (23 mCi) may be given to adult patients and remain within accepted guidelines.

Induction of focal angiogenesis through adenoviral vector mediated vascular endothelial cell growth factor gene transfer in the mature mouse brain

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and morphogen, which stimulates angiogenesis in a wide variety of tissues and lesions in vivo. In this study, we applied adenoviral vector delivered human VEGF165 cDNA to develop focal non-tumor angiogenesis in the mature mouse brain. Seventy-two adult CD-1 mice underwent Ad h VEGF, Ad lacZ, and saline injection for up to fourweeks. An adenoviral suspension containing 1 x 10(9) particles was injected stereotactically into the right hemisphere of the brain. The results showed that VEGF expression was increased in the Ad h VEGF transduced mice compared to Ad lacZ or saline injected mice ( P < 0.05). VEGF-positive cells were mainly located in the injection hemisphere of Ad h VEGF transduced mice. Quantitative vessel counting showed that microvessels in the Ad h VEGF transduced mice increased following 2 weeks of Ad h VEGF gene transfer compared to the other two groups (Ad h VEGF:241 +/- 19 vs. Ad lacZ :148 +/- 17 and Saline:150 +/- 14 vessels/mm2, P < 0.05). Morphology showed typical angiogenic changes. PCNA-positive staining confirmed these microvessels were actively proliferating. Our study demonstrates that Ad h VEGF-induced VEGF hyper-stimulation causes focal angiogenesis in the mature mouse brain. This novel method of inducing in vivo brain focal angiogenesis provides an opportunity to study the molecular mechanisms independent of the confounding effects of upstream inciting stimuli such as ischemia or tumor.

Acute and chronic effects of citalopram on cerebral glucose metabolism in geriatric depression

OBJECTIVE

In vivo studies of serotonin function have been limited by the lack of safe and selective pharmacologic agents and availability of suitable radiotracers. In the present study, the authors evaluated the cerebral metabolic effects of acute and continued administration of the selective serotonin reuptake inhibitor citalopram in patients with geriatric depression as a potential marker of serotonin dysfunction.

METHODS

Six patients with geriatric depression and five comparison subjects underwent two resting positron emission tomography (PET) studies, performed after administration of a placebo infusion (Day 1) and a citalopram infusion (40 mg, Day 2). The patients were re-scanned after 8 weeks of treatment with the oral medication.

RESULTS

The elderly comparison subjects demonstrated greater right-hemisphere cortical decreases than the patients. The depressed patients demonstrated greater left-hemisphere cortical decreases than comparison subjects. The depressed patients demonstrated greater increases in the right putamen and left occipital cortex. After 8 weeks of citalopram treatment, regional decreases and increases in metabolism were observed.

CONCLUSION

These findings suggest regional deficits and also compensatory responses in the acute metabolic response to citalopram in the patients. These preliminary results suggest that the cerebral metabolic response to citalopram may be a useful marker of the pathophysiology of serotonin function in geriatric depression.

Comparative analysis of striatal FDOPA uptake in Parkinson's disease: ratio method versus graphical approach

Striatal-to-occipital ratio (SOR) and influx constant K(i)(occ) are commonly used as analytic parameters in L-3,4-dihydroxy-6-(18)F-fluorophenylalanine (FDOPA) PET studies. Both have been shown to be useful in discriminating Parkinson's disease (PD) patients from healthy subjects. We evaluated the relative performance of SOR and influx constant (K(i)(occ)) in the clinical assessment of nigrostriatal dopaminergic function in PD.

METHODS

Twenty-one parkinsonian patients (Hoehn and Yahr scale I-IV; mean age +/- SD, 56 +/- 9.2 y) and 11 healthy subjects (mean age, 60 +/- 16 y) underwent 3-dimensional dynamic FDOPA scanning from 0 to 100 min. After spatial realignment, PET images at each frame were integrated by summing 4 central striatal slices, and time-activity curves (TACs) were generated after placing a standard set of elliptic regions of interest over striatal and occipital structures. SOR and K(i)(occ) values for each subject were then computed from TACs at different times using an input function from the occipital cortex.

RESULTS

Both SOR and K(i)(occ) showed significant bilateral decreases in striatal dopamine uptake in the PD group compared with the control group. SOR values estimated for 10-min frames between 65 and 95 min are statistically equivalent in group discrimination. In addition, SOR values in the caudate and putamen correlated strongly with K(i)(occ), especially toward the end of the scanning epoch. Both parameters correlated significantly and comparably with Unified Parkinson's Disease Rating Scale motor scores.

CONCLUSION

These results suggest that SOR determined from a single 10-min scan at 95 min is as accurate as K(i)(occ) in separating PD patients from healthy subjects and in predicting clinical measures of disease severity.

Parametric mapping of [18F]FPCIT binding in early stage Parkinson's disease: a PET study

We have shown that fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane ([(18)F]FPCIT) and PET offer a valuable means of quantifying regional abnormality in dopamine transporter (DAT) imaging associated with Parkinson's disease (PD). The objective of this study was to delineate the topographic distribution of DAT binding in early stage idiopathic PD using statistical parametric analysis of [(18)F]FPCIT PET data. We performed dynamic PET studies in 15 hemi-parkinsonian (Hoehn & Yahr I) patients and 10 age-matched normal volunteers over 100 min and calculated images of [(18)F]FPCIT binding ratios on a pixel-by-pixel basis. Statistical parametric mapping (SPM) was then used to localize binding reductions in PD and to compute the absolute change relative to normal. [(18)F]FPCIT binding decreased significantly in the contralateral posterior putamen of the PD group (P < 0.001, corrected). A significant reduction was also seen in the ipsilateral putamen, which was smaller in extent but localized more posteriorly. A quantitative comparison of DAT binding in the two clusters showed that the onset of motor symptoms in PD was associated with an approximate 70% loss relative to the normal mean in the contralateral posterior putamen. These results suggest that SPM analysis of [(18)F]FPCIT PET data can be used to quantify and map abnormalities in DAT activity within the human striatum. This method provides a useful tool to track the onset and progression of PD at its earliest stages.

Serotonin modulation of cerebral glucose metabolism measured with positron emission tomography (PET) in human subjects

To develop a method to measure the dynamic response of the serotonin system in vivo, the effects of intravenously administered citalopram (the most selective of the serotonin reuptake inhibitors) on cerebral glucose metabolism were evaluated. Cerebral glucose metabolism was measured with positron emission tomography (PET) in 14 normal subjects scanned after administration of saline placebo and citalopram administered on 2 separate days. Citalopram administration resulted in a decrease in metabolism in the right anterior cingulate gyrus (BA 24/32), right superior (BA 9) and right middle frontal gyrus (BA 6), right parietal cortex (precuneus), right superior occipital gyrus, left thalamus, and right cerebellum. Increased metabolism was observed in the left superior temporal gyrus and left occipital cortex. Alterations in metabolism by acute citalopram administration involved the heteromodal association cortices that also show metabolic alterations in patients with geriatric depression and overlap with the regions affected by antidepressant treatment. Future studies will evaluate how the acute metabolic response to citalopram relates to the metabolic response after chronic treatment in patients with geriatric depression.

Blinded positron emission tomography study of dopamine cell implantation for Parkinson's disease

We assessed nigrostriatal dopaminergic function in Parkinson's disease (PD) patients undergoing a double-blind, placebo-controlled surgical trial of embryonic dopamine cell implantation. Forty PD patients underwent positron emission tomography (PET) imaging with [18F]fluorodopa (FDOPA) prior to randomization to transplantation or placebo surgery. The 39 surviving patients were rescanned one year following surgery. Images were quantified by investigators blinded to treatment status and clinical outcome. Following unblinding, we determined the effects of treatment status and age on the interval changes in FDOPA/PET signal. Blinded observers detected a significant increase in FDOPA uptake in the putamen of the group receiving implants compared to the placebo surgery patients (40.3%). Increases in putamen FDOPA uptake were similar in both younger (age < or = 60 years) and older (age > 60 years) transplant recipients. Significant decrements in putamen uptake were evident in younger placebo-operated patients (-6.5%) but not in their older counterparts. Correlations between the PET changes and clinical outcome were significant only in the younger patient subgroup (r = 0.58). The findings suggest that patient age does not influence graft viability or development in the first postoperative year. However, host age may influence the time course of the downstream functional changes that are needed for clinical benefit to occur.

Hydrogen-ion binding of polycytidylic acid immobilized between Langmuir layers of dimethyldioctadecylammonium (DODA) in thin multilayer films

The report describes the study of hydrogen-ion binding of Langmuir-Blodgett films contained with polycytidylic acid. A variety of multilayer films are analyzed and their UV absorption spectra are recorded. Poly (C) molecules established between dimethyldioctadecylammonium (DODA) layers are shown to exist in double stranded and semiprotonated form, independent of the pH value of the solution from which the films were made. A large hysteresis was found between forward and back proton titration of poly(C) immobilized in the LB films. This hysteresis points to a marked transference of both types of molecules during the film titration. This behavior also depends upon the types of molecules from which the films were made.

Radiosynthesis of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta (4' methylphenyl) nortropane (FPCMT)

A synthetic procedure for the routine preparation of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta-(4' methylphenyl) nortropane (18F FPCMT) has been developed. The synthesis is based on alkylation of nortropane with 18F labeled fluoropropyl tosylate. Purification of the final product was achieved by a preparative HPLC procedure using Alltech Econosil column. Separation of the desired compound was achieved and the product was clean. The radiochemical yield (without decay correction) is 4 to 5%, calculated at the end of the synthesis based on the total amount of fluorine recovered from the target. Radiochemical purity was in the range of 98 to 99%.

Quantitative brain FDG/PET studies using dynamic aortic imaging

Positron emission tomography (PET) measurements of cerebral glucose utilization using 18F-fluorodeoxyglucose (FDG) are a useful tool in the investigation of localized brain function in normal and disease states. A major impediment to the application of FDG/PET in clinical investigation has been the need for arterial blood sampling to quantify cerebral glucose metabolism (CMRGlc). Qualitative studies, though informative in a variety of clinical settings, are of limited value for research applications and do not utilize the inherent quantitative nature of PET. We present a novel PET technique employing a whole-body PET tomograph with abdominal aortic imaging from 0 to 30 min as an alternative to arterial blood sampling to obtain the input function for cerebral metabolic rate calculations. Two or three arterial samples taken during the 10-45 min period were used to scale and extend the blood curve and the brain was imaged from 35-55 min post-injection. We performed 12 studies in which both arterial blood sampling and aortic scans were obtained. We found the correlation of global metabolic rates (GMR) when comparing the two techniques to be extremely high (R2 = 0.99). This suggests that the use of dynamic aortic imaging is less invasive and a viable alternative to arterial blood sampling in quantitative FDG/PET imaging.

Dopamine transporter imaging with fluorine-18-FPCIT and PET

Fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane (FPCIT) has been synthesized as a dopamine transporter ligand for PET studies. We evaluated the regional brain uptake and the plasma metabolism of [18F]-FPCIT.

METHODS

PET studies were conducted on 7 normal subjects and on 10 patients with Parkinson's disease. After the [18F]-FPCIT injection (4.4+/-1.8 mCi), dynamic scans were acquired over 100 min. Plasma metabolite analysis was performed using high-performance liquid chromatography (HPLC).

RESULTS

Plasma HPLC revealed two peaks corresponding to unmetabolized [18F]-FPCIT and a polar metabolite. The fraction of the parent compound decreased rapidly to 25% at 25 min. Fluorine-18-FPCIT showed a striatum-to-occipital ratio (SOR) of 3.5 at 90 min postinjection. The ratio of striatal-to-occipital distribution volume (DVR) was calculated directly by using a mean tissue-to-plasma efflux constant for occipital cortex obtained in 10 subjects (ki=0.037 min(-1)). DVR measures determined with and without plasma input function were correlated (r=0.98, p < 0.0001). In normal subjects, a significant age-related decline of DVR was observed both for caudate and putamen, corresponding to a 7.7% and 6.4% decline per decade, respectively (r > 0.85, p < 0.01). Both DVR and SOR correctly classified early-stage Parkinson's disease patients with comparable accuracy (p < 0.0001). Age-corrected DVR values correlated negatively with the Uniform Parkinson's Disease Rating Scale composite motor ratings (r=0.66, p < 0.05).

CONCLUSION

The tracer characteristics are compatible with a high-affinity, reversible ligand. FPCIT/PET demonstrated age-related decline in dopamine transporter binding in normal subjects as well as significant reductions in patients with idiopathic Parkinson's disease, which correlates with the disease severity.

Quantitative Brain PET Comparison of 2D and 3D Acquisitions on the GE Advance Scanner

PURPOSE: Recent developments in the design of positron emission tomography (PET) scanners have made three-dimensional (3D) data acquisition attractive because of significantly higher sensitivity compared to the conventional 2D mode (with lead/tungsten septa extended). However, the increased count rate in 3D mode comes at the cost of increased scatter, randoms, and dead time. Several schemes to correct for these effects have been proposed and validated in phantom studies. In this study, we evaluated the overall improvement afforded by 3D imaging in quantitative human brain PET studies carried out at our institution.METHODS: Subjects were studied using sequential/interleaved 2D and 3D data acquisition with a GE Advance scanner. We calculated regional and global cerebral glucose metabolism with [(18)F]flourodeoxyglucose (FDG) and estimated rate constants for striatal [(18)F]fluorodopa (FDOPA) uptake.RESULTS: FDG: Global mean glucose metabolic rates were in almost complete agreement (within 1%) between the two modes whereas the regional differences ranged from -7.7% to +9% for all cortical structures. However, for small regions (<2 cm(2)) like caudate nuclei, the maximum difference was 14.7%. FDOPA: A significant improvement in image quality was evident in 3D mode and there was complete agreement between the estimated parameters in the two scanning modes for the same noise equivalent counts: Striatal-to-occipital ratio (SOR) and striatal FDOPA uptake (K(i)(FD)) had mean differences of less than 2% and 5%, respectively.CONCLUSIONS: 3D FDG studies can be done with either half the injected dose or half the scan duration to a comparable 2D study. 3D PET imaging has distinct advantages over 2D in the quantitative fluorodopa studies.

Radiosynthesis of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta-(4-iodophenyl) nortropane and the first human study with positron emission tomography

A procedure for the routine preparation of [18F]FP-CIT has been developed. Purification of the final product was achieved by preparative HPLC using phenethyl column without decomposition or epimerization. [18F] labeled-N-fluoropropyl-2 beta-carbomethoxy-3 beta-(4-iodophenyl) nortropane was prepared and PET imaging was performed on human subjects. A high uptake into striatal regions was observed. HPLC plasma analysis using [18F]FP-CIT indicated the presence of only one metabolite. By directly comparing the behavior of these three radiotracers ([18F]DOPA, [123I]FP-CIT, and [18F]FP-CIT) in the same subjects, we can enhance our understanding of the dopaminergic system as well as the relative potential of these techniques in a clinical research setting.

Bladder wall radiation dose in humans from fluorine-18-FDOPA

PET, in conjunction with 18F-fluorodopa (FDOPA), has become the standard technique to assess basal ganglia degeneration in patients with movement disorders. Based on published dosimetry data, the injected dose of FDOPA is limited to 111 Mbq (3 mCi) because of exposure to the bladder wall, which is the critical organ for such studies. These dosimetry studies are based on mathematical models for the bladder radioactivity accumulation and clearance when the subjects were asked to void approximately 2 hr after the intravenous injection of FDOPA. In this study, we improved the radiation dose estimate to the bladder wall using dynamic PET to image the bladder during the uptake phase as well as before and after voiding.

METHODS

The subjects were tested on a new protocol. They were hydrated preinjection and given a first bladder void break at 40 min postinjection and a second void at the end of study at 120 min.

RESULTS

The MIRD model, applied to the data collected from 10 adults of both sexes, yielded an average absorbed dose of 0.15 +/- 0.08 mGy/MBq (0.57 +/- 0.28 rad/mCi).

CONCLUSION

This absorbed dose is significantly lower than previous estimates and allows for FDOPA injections up to 333 Mbq (9 mCi).

Comparative nigrostriatal dopaminergic imaging with iodine-123-beta CIT-FP/SPECT and fluorine-18-FDOPA/PET

SPECT imaging of the dopamine transporter is now an alternative to PET in the quantification of nigrostriatal dopaminergic function. We compared [123I] beta CIT-FP/SPECT and [18F]FDOPA/PET in the assessment of nigrostriatal dopaminergic function in Parkinson's disease (PD) and normal aging.

METHODS

We studied 12 mildly affected PD patients (mean age: 61.0 +/- 13.2 yr; H&Y Stage I-II) with both [123I] beta CIT-FP and [18F]FDOPA. Fifteen normal volunteers (mean age: 45.5 +/- 22.1 yr) served as controls for both tracers. We measured the striato-occipital ratio (SOR) for both tracers at approximately 100 min postinjection.

RESULTS

We found a highly significant correlation between SOR measures obtained for both tracers (r = 0.79, p < 0.0001). In normal volunteers a significant age-related decline in striatal uptake was noted with [123I] beta CIT-FP (r = -0.56, p < 0.04) but not with [18F]FDOPA. SOR values for both tracers discriminated PD patients from controls with comparable accuracy (F[1,25] = 52.1 and 53.0, p < 0.0001 for [123I] beta CIT-FP and [18F]FDOPA, respectively). UPDRS motor ratings correlated with SOR values obtained by both imaging techniques (r = -0.69 and -0.60, p < 0.04 for [123I] beta CIT-FP and [18F]FDOPA, respectively).

CONCLUSION

These results indicate that [123I] beta CIT-FP/SPECT can provide quantitative descriptors of presynaptic dopaminergic function comparable to those obtained with [18F]FDOPA/PET.

Fluorodopa positron emission tomography with an inhibitor of catechol-O-methyltransferase: effect of the plasma 3-O-methyldopa fraction on data analysis

Flurodopa (FDOPA) is an analogue of L-di-hydroxyphenylalanine (L-dopa) used to assess the nigrostriatal dopamine system in vivo with positron emission tomography (PET). However, FDOPA/PET quantitation is complicated by the presence of the 3-O-methyl-FDOPA (3OMFD) fraction in brain and plasma. Pretreatment with entacapone (OR-611), a peripheral catechol O-methyl-transferase (COMT) inhibitor, greatly reduces the plasma 3OMFD fraction and provides an ideal situation to evaluate the contribution of the plasma 3OMFD fraction in several kinetic models of FDOPA uptake. We performed FDOPA/PET with and without the OR-611 preadministration in six Parkinson's disease (PD) patients. We measured the time-course of the plasma FDOPA and 3OMFD fractions using high-pressure liquid chromatography (HPLC). We calculated striato-occipital ratios (SOR), and estimated the striatal FDOPA uptake rate constant graphically using the plasma FDOPA and occipital tissue time activity curves (KiFD and KiOCC, respectively). We also estimated striatal dopa decarboxylase (DDC) activity (k3D) using a model incorporating independent measurements of 3OMFD transport kinetic rate constants. With the preadministration of OR-611, the pharmacological efficiency in plasma was prolonged significantly (21.1-37.7%; p < 0.01). We also observed significant mean elevations in SOR and KiOCC by 21.8 and 53.5%, respectively (p < 0.05). KiFD and k3D did not show significant change. We conclude that OR-611 prolongs the circulation time of FDOPA in the plasma but does not alter rate constants for striatal FDOPA uptake or decarboxylation.

Combined FDOPA and 3OMFD PET studies in Parkinson's disease

PET has been used to quantify striatal 6-[18F]fluoro-L-dopa (FDOPA) uptake as a measure of presynaptic dopaminergic function. It has been suggested that the estimation of dopa-decarboxylation (DDC) rate, kD3, using a compartmental approach to dynamic FDOPA/PET data, can provide a better objective marker of parkinsonism. This modeling process, however, requires many assumptions to estimate DDC activity with acceptable errors.

METHODS

We combined FDOPA 3-O-methyl-fluorodopa PET studies on three normal subjects and five Parkinson's disease patients.

RESULTS

The contradicted modeling assumptions are: (a) the rate constants across the blood-brain barrier, KD1 and kD2, for 3OMFD and FDOPA were in similar range (ratio approximately equal to 1) and thus not equal to assumed values of KM1/KD1 of 2.3 derived from rat studies and applied to human FDOPA studies and (b) the KD1/kD2 ratio for frontal cortex was not equal to that for the striatum (0.70 +/- 0.15 versus 1.07 +/- 0.3; p < 0.002). Discriminant analyses indicate that simple estimates like the striatum-to-occipital ratio, or the graphically derived unidirectional transport rate constant (KiFD) separate normals from Parkinson's disease patients at least as accurately as estimates of striatal DDC activity (kD3).

CONCLUSION

Measurements of striatal DDC activity with dynamic FDOPA/PET and compartmental modeling may be based on incorrect assumptions. Even though such complex models yield microparameters that may be applicable to certain clinical research demands, they may produce misleading results in other experimental settings.

Clinical significance of striatal DOPA decarboxylase activity in Parkinson's disease

We performed dynamic PET studies with fluorodopa (FDOPA) in 9 normal volunteers and 16 patients with Parkinson's disease to investigate the applicability of dopa decarboxylase (DDC) activity measurements as useful markers of the parkinsonian disease process.

METHODS

From the 3-O-methyl-FDOPA (3OMFD)/PET studies, we obtained mean population values of the kinetic rate constants for 3OMFD (K1M = 0.0400 and k2M = 0.0420). We applied these values to calculate striatal DDC activity using the FDOPA compartmental model. We estimated k3D in this group using dynamic FDOPA-PET and population mean K1M and k2M values. We then applied the mean population K1M and k2M values to estimate k3D(pop) to a new group (6 normal volunteers and 11 patients) studied only with dynamic FDOPA-PET. In all FDOPA/PET studies, we calculated striatal uptake rate constants (KiFD) using a graphical method and also measured the striato-occipital ratio (SOR).

RESULTS

Although DDC activity has been postulated as a precise indicator of presynaptic nigrostriatal dopaminergic function, KiFD and SOR provided better between-group discrimination than did estimates of striatal DDC activity. KiFD and k3D(pop) both correlated significantly with quantitative disease severity ratings, with a similar degree of accuracy (r = 0.69 and 0.63 for k3D(pop) and KiFD, respectively; p < 0.01).

CONCLUSION

Although estimated striatal DDC activity correlates with clinical disability, this measure is comparably less effective for early diagnosis. We conclude that a simple estimate such as striatal KiFD is superior to k3D measurements for most clinical and research applications.

Early differential diagnosis of Parkinson's disease with 18F-fluorodeoxyglucose and positron emission tomography

Early-stage Parkinson's disease (EPD) is often clinically asymmetric. We used 18F-fluorodeoxyglucose (FDG) and PET to assess whether EPD can be detected by a characteristic pattern of regional metabolic asymmetry. To identify this pattern, we studied 10 EPD (Hoehn and Yahr stage I) patients (mean age 61.1 +/- 11.1 years) using 18F-FDG and PET to calculate regional metabolic rates for glucose. The scaled subprofile model (SSM) was applied to metabolic asymmetry measurements for the combined group of EPD patients and normal subjects to identify a specific covariation pattern that discriminated EPD patients from normal subjects. To determine whether this pattern could be used diagnostically, we studied a subsequent group of five presumptive EPD patients (mean age 50.9 +/- 18.3), five normal subjects (mean age 44.6 +/- 15.3), and nine patients with atypical drug-resistant early-stage parkinsonism (APD) (mean age 44.6 +/- 14.0). In each member of this prospective cohort, we calculated the expression of the EPD-related covariation pattern (subject scores) on a case-by-case basis. We also studied 11 of the EPD patients, five patients with APD, and 10 normal subjects with 18F-fluorodopa (FDOPA) and PET to measure presynaptic nigrostriatal dopaminergic function, and we assessed the accuracy of differential diagnosis with both PET methods using discrimination analysis. SSM analysis disclosed a significant topographic contrast profile characterized by covariate basal ganglia and thalamic asymmetries. Subject scores for this profile accurately discriminated EPD patients from normal subjects and APD patients (p < 0.0001). Group assignments into the normal or parkinsonian categories with FDG/PET were comparable to those achieved with FDOPA/PET, although APD and EPD patients were not differentiable by the latter method. Metabolic brain imaging with FDG/PET may be useful in the differential diagnosis of EPD.

Assessment of disease severity in parkinsonism with fluorine-18-fluorodeoxyglucose and PET

Fluorine-18-fluorodeoxyglucose (FDG) and PET have been used to identify an abnormal regional metabolic covariance pattern in Parkinson's disease (PD). To examine the potential use of this covariance pattern as a metabolic imaging marker for PD, we describe the Topographic Profile Rating (TPR), which is a method for calculating subject scores for this pattern in individual PD patients. We then assess the relationship between these metabolic measures and objective independent disease severity ratings.

METHODS

Two independent groups of PD patients were studied with FDG-PET. Group A consisted of 23 patients (mean age 60.2 +/- 12.2; mean Hoehn and Yahr stages 2.4 +/- 1.3) and Group B had 14 patients (mean age 49.0 +/- 12.1; mean Hoehn and Yahr stage 3.2 +/- 1.2). The regional cerebral metabolic rates for glucose (rCMRGlc) in all patients in each group were measured. TPR was used to calculate subject scores for the disease-related covariance pattern on a patient-by-patient basis.

RESULTS

In both PD patient groups, subject scores correlated with Hoehn and Yahr disease severity ratings (Group A: r = 0.59, p < 0.004; Group B: 0.57, p < 0.04), quantitative ratings for bradykinesia (Group A: r = 0.63, p < 0.002; Group B: r = 0.61, p < 0.03), rigidity (Group A: r = 0.59, p < 0.004; Group B: r = 0.59, p < 0.04), but not with tremor.

CONCLUSION

These findings indicate that regional metabolic covariance patterns are robust imaging markers of disease severity. FDG-PET may be useful clinically in assessing parkinsonian disability and disease progression.

Metabolic topography of the hemiparkinsonism-hemiatrophy syndrome

We estimated regional and global metabolic rates for glucose using 18F-fluorodeoxyglucose (FDG) and PET in six patients with hemiparkinsonism-hemiatrophy syndrome (HPHA; mean age, 41.0 +/- 12.4 years). We used 18F-fluorodopa (FDOPA) and PET in two patients to quantify presynaptic nigrostriatal dopaminergic function. We compared measures of brain glucose metabolism and striatal FDOPA uptake with those calculated for 10 age-matched normal volunteers (mean age, 35.1 +/- 8.0 years) and 10 patients with typical unilateral Parkinson's disease (unilat-PD; mean age, 58.2 +/- 13.8 years). All six HPHA patients demonstrated significant metabolic reductions (> 3 SD) in the contralateral basal ganglia or frontal cortex as compared with normal control values. Mean normalized glucose metabolism was reduced in the contralateral caudate and lentiform nuclei (p < 0.005) as compared with that in unilat-PD and normal controls. In both patients studied with FDOPA, contralateral striatal uptake was significantly reduced (> 3 SD) as compared with normal control values. These results suggest that the clinical manifestations of HPHA arise through a combination of pre- and postsynaptic nigrostriatal dopaminergic dysfunction. FDG and PET may be useful in differentiating this disorder from typical unilat-PD.

The metabolic topography of parkinsonism

We used [18F]fluorodeoxyglucose/positron emission tomography (18F-FDG/PET) and a statistical model of regional covariation to study brain topographic organization in parkinsonism. We studied 22 patients with Parkinson's disease (PD), 20 age-matched normal volunteers, and 10 age- and severity-matched patients with presumed striatonigral degeneration (SND). We used FDG/PET to calculate global, regional, and normalized metabolic rates for glucose (GMR, rCMRglc, rCMRglc/GMR). Metabolic parameters in the three groups were compared using an analysis of variance, with a correction for multiple comparisons, and discriminant analysis. The scaled subprofile model (SSM) was applied to the combined rCMRglc dataset to identify topographic covariance profiles that distinguish PD patients from SND patients and normals. GMR, rCMRglc, and rCMRglc/GMR were normal in PD; caudate and lentiform rCMRglc/GMR was reduced in the SND group (p < 0.01). SSM analysis of the combined group of patients and normals revealed a significant topographic profile characterized by increased metabolic activity in the lentiform nucleus and thalamus associated with decreased activity in the lateral frontal, paracentral, inferior parietal, and parietooccipital areas. Individual subject scores for this profile were significantly elevated in PD patients compared with normals and SND patients (p < 0.001) and discriminated the three groups. In the PD group, subject scores for this factor correlated with individual subject Hoehn and Yahr (H & Y) scores (p < 0.02), and with quantitative rigidity (p < 0.01) and bradykinesia (p < 0.03) ratings, but not with tremor ratings. SSM analysis of right-left metabolic asymmetries yielded a topographic contrast profile that accurately discriminated mildly affected PD patients (H & Y Stage I) from normals. Our findings demonstrate that abnormal topographic covariance profiles exist in parkinsonism. These profiles have potential clinical application as neuroimaging markers in parkinsonism.

Input functions for 6-[fluorine-18]fluorodopa quantitation in parkinsonism: comparative studies and clinical correlations

PET has been used to quantify striatal 6-[18F]fluoro-L-dopa (FDOPA) uptake as a measure of presynaptic dopaminergic function. Striatal FDOPA uptake rate constants (Ki) can be calculated using dynamic PET imaging with measurements of the plasma FDOPA input function determined either directly or by several estimation procedures.

METHODS

We assessed the comparative clinical utility of these methods by calculating the striato-occipital ratio (SOR) and striatal Ki values in 12 patients with mild to moderate PD and 12 age-matched normal volunteers. The plasma FDOPA time-activity curve (KiFD); the plasma 18F time-activity curve (KiP); the occipital time-activity curve (KiOCC); and a simplified population-derived FDOPA input function (KiEFD) were used to calculate striatal Ki.

RESULTS

Mean values for all striatal Ki estimates and SOR were significantly lower in the PD group. Although all measured parameters discriminated PD patients from normals, KiFD and KiEFD provided the best between-group separation. KiFD, KiEFD and KiOCC measures correlated significantly with quantitative disease severity ratings, although KiFD predicted quantitative clinical disability most accurately.

CONCLUSION

These results suggest that KiFD may be an optimal marker of the parkinsonian disease process. KiEFD may be a useful alternative to KiFD for most clinical research applications.

Striatal 18F-dopa uptake: absence of an aging effect

L-[18F]6-Fluoro-DOPA (L-[18F]6-fluoro-3,4-dihydroxyphenylalanine; FDOPA) has been used with quantitative positron emission tomography (PET) to assess presynaptic nigrostriatal dopaminergic function in life. The relationship of estimated kinetic rate constants for striatal FDOPA uptake [Ki(FDOPA)] to the normal aging process has been the subject of conflicting reports. Resolution of this issue has been hampered by methodological differences in previous FDOPA/PET investigations. We studied 19 healthy normal subjects (aged 27-77 years) and measured striatal Ki-(FDOPA) according to each of the earlier methods. While significant correlations (p < 0.005) existed between Ki(FDOPA) values estimated by the various techniques, none correlated with normal aging. We conclude that normal striatal Ki(FDOPA) values estimated using quantitative FDOPA/PET are uncorrelated with the aging process.

Positron emission tomographic findings in Filipino X-linked dystonia-parkinsonism

Regional and global metabolic rates for glucose (rCMRGlc and GMR) were estimated using [18F]fluorodeoxyglucose and positron emission tomography in 3 patients with Filipino X-linked dystonia-parkinsonism (lubag). In all 3 patients a selective reduction in normalized striatal glucose metabolism (rCMRGlc/GMR) was observed compared with 15 normal volunteer subjects. Presynaptic nigrostriatal function was assessed in these patients using [18F]fluorodopa and positron emission tomography. Striatal rate constants for [18F]flurodopa uptake were found to be in the normal range in all 3 patients with lubag. These findings suggest that the extrapyramidal manifestations of lubag are metabolically localized to the striatum and that clinical parkinsonism in these patients may be secondary to extranigral factors.