Thomas J. Mangner

Imaging proliferation in vivo with [F-18]FLT and positron emission tomography

Positron emission tomography (PET) is now regularly used in the diagnosis and staging of cancer. These uses and its ability to monitor treatment response would be aided by the development of imaging agents that can be used to measure tissue and tumor proliferation. We have developed and tested [F-18]FLT (3-deoxy-3-fluorothymidine); it is resistant to degradation, is retained in proliferating tissues by the action of thymidine kinase 1 (TK), and produces high-contrast images of normal marrow and tumors in canine and human subjects.

Brain Mapping of Language and Auditory Perception in High-Functioning Autistic Adults: A PET Study

We examined the brain organization for language and auditory functions in five high-functioning autistic and five normal adults, using [15O]-water positron emission tomography (PET). Cerebral blood flow was studied for rest, listening to tones, and listening to, repeating, and generating sentences. The autism group (compared to the control group) showed (a) reversed hemispheric dominance during verbal auditory stimulation; (b) a trend towards reduced activation of auditory cortex during acoustic stimulation; and (c) reduced cerebellar activation during nonverbal auditory perception and possibly expressive language. These results are compatible with findings of cerebellar anomalies and may suggest a tendency towards atypical dominance for language in autism.

Significance of abnormalities in developmental trajectory and asymmetry of cortical serotonin synthesis in autism

The role of serotonin in prenatal and postnatal brain development is well documented in the animal literature. In earlier studies using positron emission tomography (PET) with the tracer alpha[11C]methyl‐l‐tryptophan (AMT), we reported global and focal abnormalities of serotonin synthesis in children with autism. In the present study, we measured brain serotonin synthesis in a large group of autistic children (n = 117) with AMT PET and related these neuroimaging data to handedness and language function. Cortical AMT uptake abnormalities were objectively derived from small homotopic cortical regions using a predefined cutoff asymmetry threshold (>2 S.D. of normal asymmetry). Autistic children demonstrated several patterns of abnormal cortical involvement, including right cortical, left cortical, and absence of abnormal asymmetry. Global brain values for serotonin synthesis capacity (unidirectional uptake rate constant, K‐complex) values were plotted as a function of age. K‐complex values of autistic children with asymmetry or no asymmetry in cortical AMT uptake followed different developmental patterns, compared to that of a control group of non‐autistic children. The autism groups, defined by presence or absence and side of cortical asymmetry, differed on a measure of language as well as handedness. Autistic children with left cortical AMT decreases showed a higher prevalence of severe language impairment, whereas those with right cortical decreases showed a higher prevalence of left and mixed handedness. Global as well as focal abnormally asymmetric development in the serotonergic system could lead to miswiring of the neural circuits specifying hemispheric specialization.

Autism in tuberous sclerosis complex is related to both cortical and subcortical dysfunction

Objective: To examine the relationship between autism and epilepsy in relation to structural and functional brain abnormalities in children with tuberous sclerosis complex (TSC). Methods: Children with TSC and intractable epilepsy underwent MRI as well as PET scans with 2-deoxy-2-[18F]fluoro-d-glucose (FDG) and α-[11C]methyl-l-tryptophan (AMT). Based on the results of Autism Diagnostic Interview–Revised, Gilliam Autism Rating Scale, and overall adaptive behavioral composite (OABC) from Vineland Adaptive Behavior Scale, subjects were divided into three groups: autistic (OABC < 70; n = 9), mentally-retarded nonautistic (OABC < 70; n = 9), and relatively normal intelligence (OABC ≥ 70; n = 8). Results: PET studies showed that the autistic group had decreased glucose metabolism in the lateral temporal gyri bilaterally, increased glucose metabolism in the deep cerebellar nuclei bilaterally, and increased AMT uptake in the caudate nuclei bilaterally, compared to the mentally-retarded nonautistic group. In addition, a history of infantile spasms and glucose hypometabolism in the lateral temporal gyri were both significantly associated with communication disturbance. Glucose hypermetabolism in the deep cerebellar nuclei and increased AMT uptake in the caudate nuclei were both related to stereotypical behaviors and impaired social interaction, as well as communication disturbance. Conclusions: These results suggest that generalized epilepsy in early life and functional deficits in the temporal neocortices may be associated with communication delays, and that functional imbalance in subcortical circuits may be associated with stereotypical behaviors and impaired social interaction in children with TSC.

Epilepsy Surgery Outcome in Children With Tuberous Sclerosis Complex Evaluated With α-[11C]Methyl-L-Tryptophan Positron Emission Tomography (PET):

Tuberous sclerosis complex is commonly associated with medically intractable seizures. We previously demonstrated that high uptake of α-[11C]methyl-L-tryptophan (AMT) on positron emission tomography (PET) occurs in a subset of epileptogenic tubers consistent with the location of seizure focus. In the present study, we analyzed the surgical outcome of children with tuberous sclerosis complex in relation to AMT PET results. Seventeen children (mean age 4.7 years) underwent epilepsy surgery, guided by long-term videoelectroencephalography (EEG) (including intracranial EEG in 14 cases), magnetic resonance imaging (MRI), and AMT PET. AMT uptake values of cortical tubers were measured using regions of interest delineated on coregistered MRI and were divided by the value for normal-appearing cortex to obtain an AMT uptake ratio. Based on surgical outcome data, tubers showing increased AMT uptake (uptake ratio greater than 1.00) were classified into three categories: (1) epileptogenic (tubers within an EEG-defined epileptic focus whose resection resulted in seizure-free outcome), (2) nonepileptogenic (tubers that were not resected but the patient became seizure free), or (3) uncertain (all other tubers). Increased AMT uptake was found in 30 tubers of 16 children, and 23 of these tubers (77%) were located in an EEG-defined epileptic focus. The tuber with the highest uptake was located in an ictal EEG onset region in each patient. Increased AMT uptake indicated an epileptic region not suspected by scalp EEG in four cases. Twelve children (71%) achieved seizure-free outcome (median follow-up 15 months). Based on outcome criteria, 19 of 30 tubers (63%) with increased AMT uptake were epileptogenic, and these tubers had significantly higher AMT uptake than the nonepileptogenic ones (P = .009). Tubers with at least 10% increase of AMT uptake (in nine patients) were all epileptogenic. Using a cutoff threshold of 1.02 for AMT uptake ratio provided an optimal accuracy of 83% for detecting tubers that needed to be resected to achieve a seizure-free outcome. The findings suggest that resection of tubers with increased AMT uptake is highly desirable to achieve seizure-free surgical outcome in children with tuberous sclerosis complex and intractable epilepsy. AMT PET can provide independent complementary information regarding the localization of epileptogenic regions in tuberous sclerosis complex and enhance the confidence of patient selection for successful epilepsy surgery. (J Child Neurol 2005;20:429—438).

Human brain serotonin synthesis capacity measured in vivo with α-[C-11]methyl-L-tryptophan

Local cerebral serotonin synthesis capacity was measured with α‐[C‐11]methyl‐L‐tryptophan ([C‐11]AMT) in normal adult human brain (n = 10; five males, five females; age range, 18–38 years, mean 28.3 years) by using positron emission tomography (PET). [C‐11]AMT is an analog of tryptophan, the precursor for serotonin synthesis, and is converted to α‐[C‐11]methyl‐serotonin ([C‐11]AM‐5HT), which is trapped in serotonergic neurons because [C‐11]AM‐5HT is not degraded by monoamine oxidase. Kinetic analysis of [C‐11] activity in brain after injection of [C‐11]AMT confirmed the presence of a compartment with unidirectional uptake that represented approximately 40% of the activity in the brain at 50 min after tracer administration. The undirectional rate constant K, which represents the uptake of [C‐11]AMT from the plasma to brain tissue followed by the synthesis and physiologic trapping of [C‐11]AM‐5HT, was calculated using the Patlak graphic approach on a pixel‐by‐pixel basis, thus creating parametric images. The rank order of K values for different brain regions corresponded well to the regional concentrations of serotonin in human brain (P < .0001). High serotonin synthesis capacity values were measured in putamen, caudate, thalamus, and hippocampus. Among cortical regions, the highest values were measured in the rectal gyrus of the inferior frontal lobe, followed by transverse temporal gyrus; anterior and posterior cingulate gyrus; middle, superior, and inferior temporal gyri; parietal cortex; occipital cortex, in descending order. Values in women were 10–20% higher (P < .05, MANOVA) throughout the brain than those measured in men. Differences in the serotonin synthesis capacity between men and women measured in this study may reflect gender differences of importance to both normal and pathologic behavior. This study demonstrates the suitability of [C‐11]AMT as a tracer for PET scanning of serotonin synthesis capacity in human brain and provides normal adult values for future comparison with patient groups. Synapse 28:33–43, 1998.

15O PET Measurement of Blood Flow and Oxygen Consumption in Cold-Activated Human Brown Fat

Although it has been believed that brown adipose tissue (BAT) depots disappear shortly after the perinatal period in humans, PET imaging using the glucose analog 18F-FDG has shown unequivocally the existence of functional BAT in adult humans, suggesting that many humans retain some functional BAT past infancy. The objective of this study was to determine to what extent BAT thermogenesis is activated in adults during cold stress and to establish the relationship between BAT oxidative metabolism and 18F-FDG tracer uptake. Methods: Twenty-five healthy adults (15 women and 10 men; mean age ± SD, 30 ± 7 y) underwent triple-oxygen scans (H215O, C15O, and 15O2) as well as measurements of daily energy expenditure (DEE; kcal/d) both at rest and after exposure to mild cold (15.5°C [60°F]) using indirect calorimetry. The subjects were divided into 2 groups (high BAT and low BAT) based on the presence or absence of 18F-FDG tracer uptake (standardized uptake value [SUV] > 2) in cervical–supraclavicular BAT. Blood flow and oxygen extraction fraction (OEF) were calculated from dynamic PET scans at the location of BAT, muscle, and white adipose tissue. Regional blood oxygen saturation was determined by near-infrared spectroscopy. The total energy expenditure during rest and mild cold stress was measured by indirect calorimetry. Tissue-level metabolic rate of oxygen (MRO2) in BAT was determined and used to calculate the contribution of activated BAT to DEE. Results: The mass of activated BAT was 59.1 ± 17.5 g (range, 32–85 g) in the high-BAT group (8 women and 1 man; mean age, 29.6 ± 5.5 y) and 2.2 ± 3.6 g (range, 0–9.3 g) in the low-BAT group (9 men and 7 women; mean age, 31.4 ± 10 y). Corresponding maximal SUVs were significantly higher in the high-BAT group than in the low-BAT group (10.7 ± 3.9 vs. 2.1 ± 0.7, P = 0.01). Blood flow values were significantly higher in the high-BAT group than in the low-BAT group for BAT (12.9 ± 4.1 vs. 5.9 ± 2.2 mL/100 g/min, P = 0.03) and white adipose tissue (7.2 ± 3.4 vs. 5.7 ± 2.3 mL/100 g/min, P = 0.03) but were similar for muscle (4.4 ± 1.9 vs. 3.9 ± 1.7 mL/100 g/min). Moreover, OEF in BAT was similar in the 2 groups (0.51 ± 0.17 in high-BAT group vs. 0.47 ± 0.18 in low-BAT group, P = 0.39). During mild cold stress, calculated MRO2 values in BAT increased from 0.97 ± 0.53 to 1.42 ± 0.68 mL/100 g/min (P = 0.04) in the high-BAT group and were significantly higher than those determined in the low-BAT group (0.40 ± 0.28 vs. 0.51 ± 0.23, P = 0.67). The increase in DEE associated with BAT oxidative metabolism was highly variable in the high-BAT group, with an average of 3.2 ± 2.4 kcal/d (range, 1.9–4.6 kcal/d) at rest, and increased to 6.3 ± 3.5 kcal/d (range, 4.0–9.9 kcal/d) during exposure to mild cold. Although BAT accounted for only a small fraction of the cold-induced increase in DEE, such increases were not observed in subjects lacking BAT. Conclusion: Mild cold-induced thermogenesis in BAT accounts for 15–25 kcal/d in subjects with relatively large BAT depots. Thus, although the presence of active BAT is correlated with cold-induced energy expenditure, direct measurement of MRO2 indicates that BAT is a minor source of thermogenesis in humans.

Synthesis of 2′-deoxy-2′-[18F]fluoro-β-D-arabinofuranosyl nucleosides, [18F]FAU, [18F]FMAU, [18F]FBAU and [18F]FIAU, as potential PET agents for imaging cellular proliferation: synthesis of [18F]labelled FAU, FMAU, FBAU, FIAU

An efficient and reliable synthesis of 2-deoxy-2-[(18)F]fluoro-beta-D-arabinofuranosyl nucleosides is presented. Overall decay-corrected radiochemical yields of 35-45% of 4 analogs, FAU, FMAU, FBAU and FIAU are routinely obtained in >98% radiochemical purity and with specific activities of greater than 3 Ci/micromol (110 MBq/micromol) in a synthesis time of approximately 3 hours. When approximately 220 mCi (8.15 GBq) of starting [(18)F]fluoride is used, 25 -30 mCi (0.93 -1.11 GBq) of product (enough to image two patients sequentially) is typically obtained.

Analysis of [C-11]Alpha-Methyl-Tryptophan Kinetics for the Estimation of Serotonin Synthesis Rate In Vivo

We describe the tracer kinetic analysis of [C-11]-labeled alpha-methyl-tryptophan (AMT), an analogue of tryptophan, which has been developed as a tracer for serotonin synthesis using positron emission tomography (PET) in human brain. Dynamic PET data were acquired from young healthy volunteers (n = 10) as a series of 22 scans covering a total of 60 minutes and analyzed by means of a three-compartment, four-parameter model. In addition, functional images of the K-complex were created using the Patlak-plot approach. The application of a three-compartment model resulted in low identifiability of individual k-values, especially that of k3. Model identifiability analysis using a singular value decomposition of the final sensitivity matrix showed parameter identifiability to increase by 50% when the Patlak-plot approach was used. K-complex values derived by the Patlak-plot approach overestimated the compartmental values by 10 to 20%, because of the violation of the dynamic equilibrium assumption. However, this bias was fairly constant in all structures of the brain. The rank order of K-complex values from different brain regions corresponded well to the regional concentrations of serotonin in human brain (P < 0.0001). These results indicate that the Patlak-plot method can be readily applied to [C-11]AMT data in order to create functional images of the K-complex, reflecting serotonin synthesis rate, within an acceptable error margin.

Imaging DNA synthesis with [18F]FMAU and positron emission tomography in patients with cancer

PurposeFMAU (1-(2′-deoxy-2′-fluoro-β-D-arabinofuranosyl)thymine) is a thymidine analog that can be phosphorylated by thymidine kinase and incorporated into DNA. This first-in-human study of [18F]FMAU was conducted as a pilot in patients to determine its biodistribution and suitability for imaging DNA synthesis in tumors using positron emission tomography (PET).MethodsFourteen patients with diverse cancers (brain, prostate, colorectal, lung, and breast) were imaged with [18F]FMAU. We obtained dynamic PET images for 60xa0min and a whole-body image. Blood and urine samples were analyzed by high-performance liquid chromatography to measure metabolites and clearance.ResultsActive tumors in the breast, brain, lung and prostate were clearly visualized with standardized uptake values (SUVs) of 2.19, 1.28, 2.21, and 2.27–4.42, respectively. Unlike with other tracers of proliferation, low uptake of [18F]FMAU was seen in the normal bone marrow (SUVmean 0.7), allowing visualization of metastatic prostate cancer (SUV 3.07). Low background was also observed in the brain, pelvis, and thorax, aside from heart uptake (SUV 3.36–8.78). In the abdomen, increased physiological uptake was seen in the liver (SUV 10.07–20.88) and kidneys (SUV 7.18–15.66) due to metabolism and/or excretion, but the urinary bladder was barely visible (SUVmean 2.03). On average, 95% of the activity in the blood was cleared within 10xa0min post injection and an average of 70% of the activity in the urine was intact FMAU at 60xa0min post injection.ConclusionTumors in the brain, prostate, thorax, and bone can be clearly visualized with FMAU. In the upper abdomen, visualization is limited by the physiological uptake by the liver and kidneys.