Oxygen metabolism changes in patients with idiopathic normal pressure hydrocephalus before and after shunting operation

OBJECTIVE

The present study revealed the changes in cerebral oxygen metabolism before and after ventriculo-peritoneal shunt (VPS) using (15)O positron emission tomography ((15)O-PET).

METHODS

Eight patients with idiopathic normal pressure hydrocephalus (i-NPH) underwent VPS. A (15)O-PET study was undertaken before and approximately 3 months after VPS. In five patients, the symptoms improved based on the classification by Krauss et al. [Neurosurgery 1996;39:292] (good responders) after VPS. In three patients, the symptoms improved subjectively following VPS (poor responders). The changes in oxygen metabolism before and after VPS were analyzed.

RESULTS

The postoperative regional cerebral metabolic rate of oxygen (rCMRO(2)) of the good responders increased significantly. The postoperative regional oxygen extraction fraction (rOEF) is reduced in the poor responders.

CONCLUSION

The improvement of rCMRO(2) correlated with the response to VPS. Significant changes in rOEF might predict poor response to VPS.

Metabolism of phenolic compounds during loquat fruit development

Phenolic compounds in loquat fruit were identified as 5-caffeoylquinic acid (chlorogenic acid), neochlorogenic acid, hydroxybenzoic acid, 5-p-feruloylquinic acid, protocatechuic acid, 4-caffeoylquinic acid, epicatechin, o-coumaric acid, ferulic acid, and p-coumaric acid. Neochlorogenic acid was found to be dominant in the early stages of loquat fruit development. Both the concentrations and types of phenolic compounds were high in young fruit but then decreased steadily during growth. However, the concentration of chlorogenic acid increased during ripening and became predominant in ripe fruit. The large rise in chlorogenic acid concentration appears to be a characteristic of loquat fruit ripening. In all of the cultivars tested, the types of phenolic compounds were similar but the total phenolic content varied from 81.8 to 173.8 mg/100 g of fresh pulp. In the biosynthetic pathway of chlorogenic acid, the enzyme activities of phenylalanine ammonia-lyase (PAL), 4-coumarate:CoA ligase (CL), and hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase (CQT) were high at the early stage of growth, diminished to low levels approximately 3 weeks prior to harvest, but then rose to a peak at 1 week before harvest. The changes of these enzyme activities seemed to be associated with variations in chlorogenic acid concentration during development, maturation, and ripening of loquat fruit.

Visualization of myocardial phosphoinositide turnover with 1-[1-(11)C]-butyryl-2-palmitoyl-rac-glycerol in rats with myocardial infarction

Phosphoinositide turnover mediates the signaling of angiotensin II, which plays a pivotal role in ventricular remodeling after myocardial infarction (MI). We tested the hypothesis that phosphoinositide turnover can be visualized by 1-[1 -(11)C]butyryl-2-palmitoyl-rac-glycerol (11C-DAG) in both infarcted and noninfarcted myocardium after MI in rats.

METHODS

Rats received an injection of 11C-DAG 7 d after left coronary artery ligation, and myocardial lipids were extracted from both infarcted and noninfarcted areas of myocardium (n = 3). Metabolites of 11C-DAG were determined by thin-layer chromatography. Quantitative autoradiography of hearts was performed to visualize myocardial phosphoinositide turnover in rats that received an injection of 11C-DAG 1 d (n = 3) and 7 d (n = 5) after MI and 7 d after a sham operation (n = 3). Quantitative autoradiography with 201TlCl was also performed to evaluate myocardial blood flow in rats 7 d after MI (n = 3). Cells occupying the infarcted myocardium were identified by immunohistochemistry.

RESULTS

The radioactivity incorporated into the intermediates of phosphoinositide turnover was predominant in both the infarcted (67.1% +/- 5.2% of the total activity) and the noninfarcted (57.4% +/- 3.2%) myocardium. 11C-DAG radioactivity in the infarcted region normalized to that in the noninfarcted region was 1.09 +/- 0.04 in rats 7 d after MI, which was significantly higher than that in rats 1 d after MI (0.38 +/- 0.03, P < 0.001). 201Tl radioactivity in the infarcted region normalized to that in the noninfarcted region was only 0.19 +/- 0.01 7 d after MI. 11C-DAG radioactivity in the noninfarcted region normalized to that in the right ventricular free wall tended to be increased in rats 1 and 7 d after MI compared with the sham-operated rats; the differences, however, were not statistically significant (1.30 +/- 0.15, 1.20 +/- 0.07, and 1.13 +/- 0.02, respectively). Immunohistochemistry revealed that abundant fibroblasts, myofibroblasts, and macrophages occupied the infarcted myocardium 7 d after MI, but the cellularity was low during the first day after MI.

CONCLUSION

These data suggest that 11C-DAG may be useful for visualizing regions with activated phosphoinositide turnover after MI. Because wound healing and fibrogenic processes are important factors of ventricular remodeling, 11C-DAG and PET may offer new information benefiting patient management after MI.

Simplification for measuring input function of FDG PET: investigation of 1-point blood sampling method

The current method for quantitative FDG PET study requires application of multiple arterial blood sampling for measuring the input function, but the procedure is invasive and complicated. The purpose of this study was to establish a 1-point blood sampling technique that gives data comparable with the data of more elaborate serial arterial sampling.

METHODS

We established a time point for 1-point arterial sampling that exhibited the highest correlation between plasma radioactivity at the time point and the real integrated value (IV) of the measured input function obtained by multiple arterial sampling in 120 patients and the smallest coefficient of variation of the real IV divided by plasma radioactivity at the time point in 120 patients. Scaling factors for estimation at each sampling point were determined, and a reference table was established to make the supposed input function.

RESULTS

The optimal time for 1-point arterial sampling was 12 min after FDG injection. A good correlation was observed between the real IVs and those estimated from 1-point arterial blood sampling at 12 min using the supposed input function (n = 120; P < 0.001). The time point at which the difference between values of arterial and venous blood disappeared was 40 min after FDG injection. The percentage errors of IV estimation by 1-point sampling were 1.70% (n = 120) for arterial blood at 12 min and 3.64% (n = 10) for venous blood at 40 min.

CONCLUSION

We conclude that the simplified 1-point sample method works in a manner that is comparable with serial arterial sampling and should be useful for clinical PET.

Putaminal necrosis presenting with hemidystonia

A 7-year-old female presented with putaminal necrosis associated with hemidystonia. Cranial magnetic resonance imaging revealed bilateral putaminal lesions appearing as hypointense signals on T(1)-weighted images and hyperintense signals on T(2)-weighted images. After a differential diagnosis of basal ganglial degeneration was made, putaminal necrosis was diagnosed. Low doses of levodopa (0.5 mg/kg daily) were administered, but her clinical signs worsened. Positron emission tomography scanning with [(18)F]-6-fluoro-L-dopa revealed asymmetric uptake and right-sided dominant decreases of [(18)F]-6-fluoro-L-dopa uptake of the putamen. On the basis of these findings, standard doses of levodopa (10 mg/kg daily) were administered, and her clinical signs improved. These results suggest that hemidystonia is associated with a disturbance of the dopamine system.

Evaluation of phosphoinositide turnover on ischemic human brain with 1-[1-11C]-butyryl-2-palmitoyl-rac-glycerol using PET

It is important to evaluate cerebral function from neural signal transduction in ischemic brain in judging morbid state and prognosis. We synthesized 1-[1-(11)C]-butyryl-2-palmitoyl-rac-glycerol (DAG) for the purpose of imaging the second messenger on PET and applied it to clinical cases of cerebral infarction.

METHODS

Five patients, who had ischemic stroke, were examined with PET. [15O]-CO2 and [15O]-O2 inhalation methods were applied to cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2). For the measurement of phosphoinositide turnover after intravenous injection of DAG, dynamic PET data were collected continuously for 46 min. Arterial blood samples were taken to evaluate changes in the serum concentration of DAG. To quantify the metabolic activity of inositol phospholipid, the incorporation constant k*(DAG) was calculated on the basis of the kinetics of DAG.

RESULTS

The plasma concentration of DAG increased rapidly and peaked 30 s after injection of DAG solution. In the normal cortex, DAG concentration increased gradually and reached a plateau between 15 and 20 min after injection. In the ischemic core (infarction), DAG concentration increased slowly, and its peak concentration was lower than that in normal tissue. In comparison with blood flow and metabolic parameters, k*(DAG) showed the best correlation with CMRO2, suggesting a reflection of neuronal activity. Locally, CBF and CMRO2 gradually decreased from the normal area toward the ischemic center (infarction), whereas k*(DAG) and OEF significantly decreased only in the ischemic center.

CONCLUSION

The k*(DAG) of ischemic brain, including that caused by infarction, significantly correlated with CMRO2, suggesting that metabolic activity of inositol phospholipid reflects neural viability. Maintained metabolic activity of inositol phospholipid in the region around the ischemic core indicated preservation of the signal transduction system through the metabotropic receptor.

Visualization of mRNA expression in CNS using 11C-labeled phosphorothioate oligodeoxynucleotide

Antisense phosphorothioate oligodeoxynucleotide for mRNA of glial fibrillary acidic protein (GFAP) was labeled with the positron emitter 11C and administered i.v. to rats bearing glioma, which were expected to exhibit active expression of GFAP. Antisense oligodeoxynucleotide was retained in tumor cells, yielding clear images of tumors, while the control 20% mismatch oligodeoxynucleotide and sense-strand oligodeoxynucleotide were not retained in tumor cells. Findings revealed sequence-specific binding of the antisense oligodeoxynucleotide to the GFAP mRNA. Our methods can be used directly for non-invasive imaging of human gene expression using PET, a frequently used method of clinical examination.

Aberrant plasticity in Alzheimer's disease

Alzheimer's disease (AD) is a region-specific degenerative disease that mainly impairs the temporal and parietal lobes, with preservation of the frontal lobes until advanced stages of disease. Since [11C]diacylglycerol PET facilitates examination of loci exhibiting plasticity, it was performed in eight patients with AD and six age-matched normal control subjects to evaluate frontal lobe function. [11C]Diacylglycerol tomograms obtained from patients with AD demonstrated strong spotty incorporation of [11C]diacylglycerol mainly in the frontal association areas. However, [18F]fluorodeoxyglucose tomograms exhibited region-specific findings such as decreased CMRGIc in the parietotemporal association areas, which are involved in impairment of cognitive function. The strong spotty incorporation of [11C]diacylglycerol suggested a compensatory plastic process in the frontal lobes in response to involvement by Alzheimer's disease of the posterior association areas.

Neural features of recovery from CNS injury revealed by PET in human brain

Dysfunction of the brain occurring after local brain injury often improves clinically; however, the reason for this improvement has not been scientifically clarified. We used a new technique for imaging phosphoinositide turnover, carbon-11-labeled diacylglycerol-positron emission tomography, to observe the process of recovery from injury in human brain. Patients with local brain injury exhibited radioactive spots located in the association areas distant from the lesion, while normal controls did not exhibit such spots. These findings indicated one of possible features of the neural recovery from the central nervous system injury, which appears to play a role in modulation of synaptic transmission in the intact brain. Conventionally, attention has been directed primarily to areas surrounding brain injury, such as the penumbra; however, the present study suggests that initiation of reorganization of neural connections occurs in remote cortex.

Clinical application of magnetoencephalography in a patient with corticobasal degeneration

Previous neuroimaging studies in corticobasal degeneration (CBD), such as MRI and positron emission tomography, showed lateralized cortical atrophy and a decrease in cortical oxygen metabolism, respectively. The advantage of magnetoencephalography in the research of the auditory system is that activity of both hemispheres can be detected separately. Auditory-evoked magnetic fields (AEFs) were then applied to a patient with corticobasal degeneration. The strength of N100m equivalent current dipoles (ECD) in left hemisphere was extremely smaller (20 nAm) than that in right hemisphere (48 nAm). This results implies that CBD patient might have a decrease in the number of neurons in the primary auditory cortex. This study suggests that AEF measurement is one of the most powerful tools for detecting latent impairment of auditory function in patients with corticobasal degeneration.

Positron emission tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: part I

Determination of tumor boron-10 (10B) levels is required for accurate neutron dosimetry during boron neutron capture therapy. We assessed a new method for quantitative measurement of boronated drug uptake in high-grade gliomas. This method uses positron emission tomography (PET) with fluorine-18-labeled L-fluoroborono-phenylalanine (L-18F-10B-FBPA), which was synthesized as an analogue of L-boronophenylalanine. We studied the accumulation of L-18F-10B-FBPA by PET in patients with high-grade gliomas. Dynamic PET studies of brain tumors revealed that L-18F-10B-FBPA accumulated gradually after bolus injection, and the value of PET activity divided by the integrated plasma activity reached a constant level 42 min after injection, which was defined as the incorporation constant (Ic*). This constant reflected the appropriate L-18F-10B-FBPA accumulation in tumor tissue. Based on the Ic* constant, the methods for estimating tumor 10B concentration were devised. With this method, the estimated values of 10B concentration in gliomas were very close to the 10B levels in surgical specimens. This method was based solely on PET and can potentially provide data that would assist in the selection of patients for future treatment with boron neutron capture therapy after surgical resection of their brain tumors.

Positron emission tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: part II

Based on pharmacokinetic findings of fluorine-18-labeled L-fluoroboronophenylalanine by positron emission tomography (PET), methods for estimating tumor 10B concentration were devised. In clinical practice of boron neutron capture therapy (BNCT) for high-grade gliomas, a large amount of L-boronophenylalanine (L-10B-BPA)-fructose solution is used. Under these conditions, a slow i.v. infusion of L-10B-BPA-fructose solution should be performed for BNCT; therefore, the changes over time in 10B concentration in the target tissue were estimated by convoluting the actual time course of changes in plasma 10B concentration with a PET-based weight function including the proper rate constants [K1 (ml/g/min), k2 (min(-1)), k3 (min(-1)), and k4 (min(-1))]. With this method, the estimated values of 10B concentration in gliomas were very close to the 10B levels in surgical specimens. This demonstrated the similarity in pharmacokinetics between fluorine-18-labeled L-fluoroboronophenylalanine and L-10B-BPA. This method, using the appropriate rate constant, permits the determination of tumor 10B concentration and is widely suitable for clinical BNCT, because the averaged PET data are enough to use in future patients without individual PET study.

Potentiation of phosphoinositide-derived signals during LTP in intact rat brain

In order to examine the relationship between long-term potentiation (LTP) and phosphoinositide (PI) turnover, we evaluated these throughout anesthetized rat brain using carbon-11-labeled diacylglycerol (11C-DAG). High-frequency tetanic stimulation (400 pulses at 400 Hz) to the perforant pathway induced LTP in rat dentate gyrus. In autoradiograms of rat brains, LTP was associated with the occurrence of multiple highly radioactive spots in many regions distant from the stimulated site. Following i.v. administration of an NMDA receptor antagonist prior to stimulation, however, no high-density spots were found. These findings directly demonstrate that potentiation of phosphoinositide-derived signaling was induced during LTP, and the finding of multiple location suggests the occurrence of polysynaptic neurotransmission through neural networks pertaining to learning and memory.

[A lateralized reduction of NAA in a case of corticobasal degeneration (CBD): application of proton magnetic resonance spectroscopy (1H-MRS)]

We studied the application of proton magnetic resonance spectroscopy (1H-MRS) in a case of corticobasal degeneration. A 73-year-old woman was referred to our hospital for dysarthria and clumsiness in right arm movement. Intelligence was normal and neither ideational apraxia or ideomotor apraxia were observed. Her speech was slurred and extremely slow. Neurological findings showed a limitation of ocular upward gaze movement, impaired smooth pursuit in the horizontal gaze, rigidity, limb kinetic apraxia and cortical sensory disturbance in the right arm. Magnetic resonance imaging (MRI) showed diffuse brain atrophy, especially in the left fronto-parietal cortex around the central sulcus. A positron emission tomography (PET) study showed diffuse decrement of cerebral blood flow, dominantly in the left hemisphere. The decrease in the uptake of 18F-Fluoro-deoxyglucose also revealed glucose hypo-metabolism, especially in the left frontal and parietal lobe. 1H-MRS by the multivoxel method showed a decrease in N-acetylaspartate (NAA)/Creatine to 1.0 in the left basal ganglia and temporal lobe, compared to the values between 1.4 and 1.7 in the right basal ganglia. These findings indicated that 1H-MRS might detect neuronal loss or degeneration when MRI showed minimal cortical atrophy. This study, the first application of 1H-MRS in a case of corticobasal degeneration, showed that this method was useful for the evaluation of pathophysiological changes in corticobasal degeneration.

Fluorine-18-labeled fluoroboronophenylalanine PET in patients with glioma

We synthesized fluorine-18-labeled fluoroboronophenylalanine (18F-10B-FBPA), an analog of boronophenylalanine (10B-BPA), and characterized its pharmacokinetics in patients with glioma. We conducted PET studies on three types of gliomas to clarify the relationship between tumor grade and each rate constant [K1 (ml/g/min), k2 (min[-1]) and k3 (min[-1])], and here, we discuss the metabolism of the 10B-BPA analog (18F-10B-FBPA).

METHODS

Thirty-three cases of primary gliomas were studied by dynamic PET using DL-18F-10B-FBPA or L-18F-10B-FBPA. Dynamic PET images of 18F-10B-FBPA incorporation into tumors were obtained, and the arterial blood samplings were performed in all cases.

RESULTS

When the dynamic PET data were represented as Gjedde-Patlak plots, there was a positive slope, suggesting the involvement of the putative metabolic pool of this tracer. A three-compartment model using rate constants (K1, k2 and k3) was used for the kinetic analysis. The accumulation of 18F-10B-FBPA was found to correlate with the degree of malignancy, and the L form of 18F-10B-FBPA was taken up better than was the DL form. The results of dynamic PET analysis suggested that K1 (measuring amino acid transport process) is a major factor determining the accumulation of 18F-10B-FBPA. A comparison of the rate constants revealed that k3 (metabolic process) did not correlate with the degree of malignancy. The absence of evident differences in k3 between DL and L forms suggests that k3 represents phenomena that are not dependent on the native form of L.

CONCLUSION

These PET data will be of practical use for diagnosis of malignancy and direct prediction of the effectiveness of boron neutron capture therapy using 10B-BPA.

[Fluorine-18 labeled 6-fluoro-L-dopa: systematization and evaluation of its usefulness]

6-[18F]Fluoro-L-dopa (L-3,4-dihydroxy-6-[18F]fluorophenylalanine; 6-[18F]FDPA) is useful to assess presynaptic dopamine metabolism in central nervous system. In this paper, we report on the usefulness of the 6-[18F]FDOPA synthesis system developed for the routine synthesis. This system consists of the 6-[18F]FOPA synthesis and the separation units in conjunction with controller using a personal computer. The synthesis time of 6-[18F]FDOPA was 73 minutes. The typical yield and specific activity were 1.4-2.4 GBq and 244-270 MBq/mumol at the end of synthesis, respectively, under the irradiation condition of 50 microA for 130 minutes. The radiochemical yields of 6-[18F]FDOPA were 31.3-38.7% based on the [18F]acetylhypofluorite, and the results were affected with the condition of potassium acetate (AcOK) to produce gaseous [18F]acetylhypofluorite. This system is useful for the routine production of 6-[18F]FDOPA because of its high yield and high specific activity while maintaining AcOK in good condition, and decreasing the radiation exposure for chemist.

Dopaminergic modulation of LTP induction in the dentate gyrus of intact brain

The effect of the dopamine system on the induction of long-term potentiation (LTP) in the dentate gyrus was studied in anesthetized rats. A subthreshold tetanic train (seven pulses at 100 Hz) given to the perforant pathway, which usually fails to elicit LTP, potentiated a slope of field excitatory postsynaptic potentiation (fEPSP) measured from the hilus of the dentate gyrus when a precursor for catecholamine, L-3,4-dihydroxyphenylalanine (L-DOPA), was administered orally to rats. The increase in the fEPSP slope persisted for at least 60 min. Intraventricular injection of a specific dopamine D1/D5 agonist, SKF38393, mimicked the effect of L-DOPA, suggesting an involvement of D1/D5 receptors in the induction of dentate gyrus LTP. Consistent with this, intraventricular administration of the D1/D5 antagonist SCH23390 resulted in complete inhibition of LTP induction by a longer tetanus (100 pulses at 100 Hz), which usually elicits a robust LTP. Thus, D1/D5 receptor activation appears to modulate LTP induction in vivo.

In vivo diagnosis of human malignant melanoma with positron emission tomography using specific melanoma-seeking 18F-DOPA analogue

Detection and diagnosis of human malignant melanoma by Positron Emission Tomography (PET) using 18F-10B-L-BPA, a specific melanogenesis-seeking compound synthesized for use in Boron Neutron Capture Therapy for malignant melanoma (NCT), has been developed. This resulted in a novel, highly effective methodology for the selective three dimensional imaging of metastatic malignant melanomas, and for accurate determination of 10B concentration in the tumor and surrounding tissue, providing almost all diagnostic information necessary for complete non-invasive radiation dose planning in the treatment of malignant melanoma both for NCT as well as other therapeutic modalities.

Spontaneous regression of intracranial arteriovenous malformation on PET

We report a case of spontaneous regression of intracranial arteriovenous malformation (AVM) detected by PET in a 57-yr-old woman who had suffered repeated ruptures of the AVM at 28, 30 and 31 yr of age associated with pregnancy. The rupture at this hospitalization was the most critical, and after repeated ruptures for 1 mo, the AVM regressed spontaneously. The decreased cerebral blood volume (CBV) in the AVM indicated regression. The flow-to-volume (CBF/ CBV) ratios surrounding the AVM increased. The metabolic rate for oxygen (CMRO2) did not correlate with her improved neurological status, and an imbalance between CBF and CMRO2 was recognized.

Cerebral hemodynamics and metabolism of severe diffuse brain injury measured by PET

Cerebral hemodynamics and metabolism in three patients with severe diffuse brain injury were measured 10 days after onset using PET. In this study, regional cerebral blood flow (rCBF), oxygen extraction fraction (rOEF), cerebral blood volume (rCBV), cerebral metabolic rate for oxygen (rCMRO2), cerebral metabolic rate for glucose (rCMRglc) and cerebral metabolic ratio (rCMRO2/rCMRglc) were measured. The Glasgow Coma Scale scores on admission were 4, 5 and 5, respectively, and CT on admission showed typical findings of diffuse brain injury. As a result, PET revealed misery perfusion and hyperglycolysis in Patient 1 and matching low perfusion and low glucose metabolism in Patients 2 and 3. Although Patient 1 died, Patients 2 and 3 had good recoveries. We speculate that a long-lasting anaerobic state, indicated by a high OEF value and low metabolic ratio, is an important undesirable factor related to the outcome.

Radioiodinated diacylglycerol analogue: a potential imaging agent for single-photon emission tomographic investigations of cerebral ischaemia

Phospholipid metabolism is closely related to membrane perturbation in cerebral ischaemia. We investigated in vivo topographical lipid metabolism using an iodine-123-labelled diacylglycerol analogue, (1-(15-(4-iodine-123-iodophenyl)-pentadecanoyl)-2-stearoyl-rac-gly cerol) (123I-labelled DAG), in a middle cerebral artery (MCA) occlusion model with the aim of positive imaging of ischaemic insult. Sprague-Dawley rats underwent coagulation of the MCA to induce permanent occlusion. MCA occlusion times prior to injection of 123I-labelled DAG ranged from 15 min to 14 days. Each rat was injected with 11-37 MBq of 123I-labelled DAG via a tail vein. After 30 min, in vivo autoradiographs were reconstructed. Scanning of the living rat brain in this MCA occlusion model was performed using a gamma camera with a pinhole collimator. Cerebral infarctions were recognized in the frontal cortex, the parietal cortex and the lateral portion of the caudate-putamen by 2,3,5-triphenyltetrazolium hydrochloride staining. In infarcted regions (region 1), 123I-labelled DAG incorporation showed a slight decrease up to 12 h; it then increased up to 6 days and decreased thereafter. In peri-infarcted regions (region 2), the incorporation showed almost no change up to 12 h, then increased up to 5-6 days and decreased thereafter. In other regions (region 3), the incorporation showed no change. Lipid analysis showed that 123I-labelled DAG was metabolized to 15-(4-iodine-123-iodophenyl)-pentadecanoic acid by DAG lipase and to 123I-labelled phosphatidylcholine. Scanning of the ischaemic region showed higher accumulation than on the non-lesioned side. We established a method to visualize ischaemic foci as positive images. The early changes in 123I-labelled DAG incorporation were closely related to DAG lipase, which degraded the accumulated intrinsic DAG, and increased 123I-labelled DAG incorporation in the chronic stage involves several aspects of neural destruction in the process of autolysis. It is concluded that the reported method could have a clinical future.

Irradiation effects on the metabolism of metastatic brain tumors: analysis by positron emission tomography and 1H-magnetic resonance spectroscopy

To evaluate irradiation effects on the metabolism of metastatic brain tumors treated by Gamma Knife radiosurgery, positron emission tomography (PET) and 1H-magnetic resonance spectroscopy (MRS) studies were performed on five patients. The tumor origins were lung cancer in three patients and breast cancer in two. Treatment volume was 0.4-10.1 cm3 (mean: 5.5 cm3). The marginal dose to the tumor was 24-30 Gy (mean: 26.2 Gy). The follow-up period was 5-19 months (mean: 13.4 months). No patients had conventional whole-brain radiation therapy. 18F-fluoroboronophenylalanine (18FBPA) or 18F-fluorodeoxyglucose (18FDG) were used as tracers for the PET study. Using 1H-MRS, several metabolites were simultaneously measured in metastatic brain tumor and adjacent brain. In the PET study of the representative case, the uptake rate of 18FBPA that is actively transported to the tumor decreased markedly 15 days after radiosurgery and continued to decrease thereafter. In the 1H-MRS study, choline, which is characteristically high in metastatic brain tumors, also decreased over time. In two cases with suspected radiation injury, the enhanced region, which was decreased in size in early follow-up, enlarged progressively and was accompanied by edema. However, 18FBPA and 18FDG were not transported to the enhanced region. The peak of free lipid, which might show destruction of the cell membrane, was recognized in the enhanced region and adjacent brain in these cases. This study revealed that radiation effects on the metabolism of metastatic brain tumors occur at an early stage after radiosurgery and continue over several months. In particular, in the case of radiation injury, PET and 1H-MRS studies made it possible to distinguish between regrowth of the tumor and radiation injury.

Chronological positron emission tomographic study of severe diffuse brain injury in the chronic stage

Cerebral blood flow and metabolism were investigated in five patients with severe diffuse brain injury in the chronic stage, using positron emission tomography (PET). Regional cerebral blood flow, regional oxygen extraction fraction, regional cerebral blood volume, regional cerebral metabolic rate for oxygen, and regional cerebral metabolic rate for glucose were measured bilaterally in the frontal, temporal, occipital, and parietal gray matter, as well as the white matter of the centrum semiovale. In 4 of 5 patients, a follow-up PET study was also performed. In three cases, below-normal regional cerebral blood flow and regional cerebral metabolic rate for oxygen values accompanied by above-normal regional oxygen extraction fraction values, as well as low metabolism, were demonstrated in the initial PET studies. In two of three cases, clinical improvements were observed, and follow-up PET data also improved. These findings suggest that chronological PET studies may be able to assess quantitatively clinical improvements in patients with diffuse brain injury.

Rapid incorporation of carbon-11-labeled diacylglycerol as a probe of signal transduction in glioma

We have synthesized and characterized a positron-emitting carbon-11-labeled 1,2-diacylglycerol to study phosphoinositide turnover in tumor cells. Rapid incorporation of the 1,2-diacylglycerol was observed in the C6 glioma cell line. The incorporated lipid fraction consisted chiefly of phosphoinositide pool and another phospholipid pool in the proliferative state. When the state was inhibited by (-)-3D-3-deoxy-3-fluoro-myo-inositol, incorporation into the phosphoinositide pool decreased selectively. This suggested that phosphoinositide turnover is the leading regulator of tumor proliferation potential. On the basis of the concept of carbon-11-labeled 1,2-diacylglycerol as a specific probe for visualizing the tumor signal transduction in vivo, we obtained proliferating images of implanted C6 glioma cells in the rat brain by autoradiography and visualized the proliferation signal in human glioma by positron emission tomography.

[Carbon-11 labeled diacylglycerol for signal transduction imaging by positron CT: evaluation of the quality and safety for clinical use]

To elucidate the synaptic transmission in the neural system, we have been developing fundamental studies for intracellular signaling. For clinical application of carbon-11 labeled diacylglycerol (1-[1-11C]butyryl-2-palmitoyl-rac-glycerol: 11C-DAG) using positron emission computed tomography (PET), we evaluated the quality and the safety of 11C-DAG as the solution for injection. As a result, 11C-DAG was synthesized within 50 minutes, including the preparation step for injection. The half life time and energy spectrum of 11C-DAG were the same as the physical character of carbon-11, and other radioisotopes were not detected. In the quality control, 11C-DAG solution was negative in the examination of bacterial contamination and the pyrogen test in three successive synthesis procedures. In the acute toxicity test by administration of 11C-DAG and 100 mumol/kg of non-radioactive DAG to the rat intravenously, the systemic condition of the rat was not changed and no abnormalities were found in any organ 24 hours after administration. These findings indicated the safety of 11C-DAG solution. Clinical application of 11C-DAG using positron emission tomography may be useful to elucidate the dysfunction of intracellular signaling in disorders of higher cortical function such as Alzheimer disease.

[Carbon-11 labeled diacylglycerol for signal transduction imaging: effect of the solubilizer on the distribution and radiation dosimetry]

Carbon-11 labeled diacylglycerol (11C-DAG) has been developed as a signal transduction imaging agent for the CNS, and it can visualize the second messenger. For clinical application by positron CT (PET), the 11C-DAG solution must be prepared for intravenous injection. However, the 11C-DAG does not dissolve in water because of its lipophilicity and requires a solubilizer such as human serum albumin (HSA) and Tween 80 (TW-80). We examined the influence of these solubilizers on the tissue distribution of 11C-DAG, and estimated the radiation dosimetry. In the brain, uptake of 11C-DAG dissolved with HSA was 1.3-1.8 times higher than that of dissolved with TW-80. On the other hand, the lung and spleen showed a higher uptake of 11C-DAG using TW-80 than when using HSA. Especially, the lungs showed 20-40 times higher uptake than when using HSA. Also, the washout of radioactivity from tissue was slower, and the dose of radiation exposure was estimated to be higher, with TW-80 than with HSA. Therefore, between TW-80 and HSA with different solubilizing mechanisms, the later was suggested to be a better solubilizer of 11C-DAG.

Phosphoinositide turnover imaging linked to muscarinic cholinergic receptor in the central nervous system by positron emission tomography

Receptor-mediated membrane processing plays an essential role in neural function in the synapses. In such neurotransmission process, the phosphoinositide (PI) response, an effector in the production of second-messengers, can be used to assess in vivo signal transduction. Using in vivo autoradiography and positron emission tomography (PET), we attempted to visualize the PI response to muscarinic cholinergic receptor (mAChR)-stimulation in rats and monkeys, which were administered 1,2-[11C]diacylglycerol (DAG) intravenously. Enhancement of 1,2-[11C]DAG incorporation was observed in the rat ipsilateral hippocampus and cortex in which mAChR-agonist was administered by local injection, but this was in contrast to spreading cortical depression in the ipsilateral cortex using KCl. In monkey PET studies, dynamic brain scanning revealed increase in activity over time for about 15 min after a bolus injection of 1,2-[11C]DAG in an awake state. The activity then remained at a constant level. This finding documented the theoretical "membrane-trapping" mechanism. The systemic mAChR-stimulation accelerated incorporation in the cerebral cortices of the same monkey brain. Radioactivity uptake did not differ significantly between the mAChR-stimulated and nonstimulated early scan images. This suggested that cerebral blood flow does not greatly affect DAG incorporation. In sequential membrane processes of PI turnover, diacylglycerol kinase rapidly metabolizes DAG, included in PI turnover. In conclusion 1,2-[11C]DAG incorporation was limited by receptor-mediated PI turnover, which can represent real synaptic transmission in neural networks.

Hemodynamic disturbances in cerebral ischemia: correlation between positron emission tomographic and angiographic findings

Proper treatment of ischemic stroke requires better understanding of cerebral hemodynamic changes. The hemodynamic changes associated with ischemia were measured using positron emission tomography and related to angiographic findings in the subacute and chronic stages of 17 ischemia patients who showed symptoms of main trunk stenosis of the internal carotid artery system. The hemodynamic factors, cerebral blood flow, cerebral blood volume, cerebral metabolic rate for oxygen, oxygen extraction fraction, and flow/volume ratio, were measured in regions of interest determined from the angiographic stenosis (over 50%) and compared in each stage. The cerebral blood flow and flow/volume ratio in the territory downstream of the main trunk stenosis and cerebral metabolic rate for oxygen in the whole cortex were decreased in the subacute stage. In the chronic stage, cerebral blood flow and flow/volume ratio decreased mainly in borderzone areas.

Protein kinase C imaging using carbon-11-labeled phorbol esters: 12-deoxyphorbol 13-isobutyrate-20-[1-11C]butyrate as the potential ligand for positron emission tomography

Protein kinase C plays a crucial role in signal transduction for a variety of biologically active substances which activates cellular functions and their proliferation. The actions are closely related to both normal and abnormal functions in the nervous system. Tumor-promoting phorbol esters can substitute for diacylglycerols which are important ligands that bind to protein kinase C. Three typical phorbol esters, phorbol 13-[1-11C]butyrate, phorbol 12,13-[1-11C]dibutyrate and 12-deoxyphorbol 13-isobutyrate-20-[1-11C]butyrate, were synthesized by using [11C]ethylketene with a high specific activity (186GBq/mumol). Their in vivo autoradiograms demonstrated a heterogenous distribution in rat brain. 12-deoxyphorbol 13-isobutyrate-20-[1-11C]butyrate was particularly suited for in vivo use due to its nontumor-promoting activity and its ready permeability to the blood-brain barrier. High optical density was observed in the cortex, amygdala and hippocampus. The in vivo binding properties of this compound to protein kinase C were confirmed by in vivo displacement studies with unlabeled 12-deoxyphorbol 13-isobutyrate-20-butyrate and unlabeled phorbol 12,13-dibutyrate. This suggests that 12-deoxyphorbol 13-isobutyrate-20-[1-11C] butyrate has a specific binding affinity for protein kinase C.

Positron emission tomographic measurement of acute hemodynamic changes in primate middle cerebral artery occlusion

Specific hemodynamic changes in acute ischemia were investigated using a middle cerebral artery occlusion primate model and positron emission tomography. The cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate for oxygen were measured 1, 3, and 9 hours after occlusion. OEF showed an increase in ischemic areas, and especially where CBF was below 18 ml/100 gm/min 1 hour after occlusion the OEF increased significantly (0.69 +/- 0.20, p < 0.05). Nine hours after occlusion, the OEF values were lower compared to those 1 and 3 hours after occlusion. Areas where CBF ranged from 18 to 31 ml/100 gm/min showed an increase in OEF at all times (p < 0.05). Clearly, OEF changes remarkably in the acute stage.

Effect of hemodilution on cerebral hemodynamics and oxygen metabolism

BACKGROUND AND PURPOSE

To evaluate the effects of hemodilution on cerebral hemodynamics and oxygen metabolism in the normal human brain, we measured regional cerebral blood flow, oxygen extraction fraction, oxygen metabolic rate, and regional cerebral blood volume in eight normal volunteers before and after hemodilution using positron emission tomography and oxygen-15-labeled gas inhalation technique.

SUMMARY OF REPORT

Hemodilution was accomplished by phlebotomy of 400 ml and drip infusion of 500 ml low molecular weight dextran, which reduced hematocrit from 42.5% to 37.2% and arterial oxygen content from 19.1 to 16.9 ml/dl (both p less than 0.005). It also increased mean cerebral blood flow from 45.2 to 47.7 ml/100 ml/min (p less than 0.025), but decreased tissue oxygen delivery from 8.7 to 8.0 ml/100 ml/min (p less than 0.05) and cerebral blood volume from 4.9% to 4.6% (p less than 0.025) in the overall cortical gray matter.

CONCLUSIONS

Our results indicate that hemodilution in the tested range does not improve oxygen transport or tissue oxygenation in the normal human brain, although it increases cerebral blood flow.

Membrane trapping of carbon-11-labeled 1,2-diacylglycerols as a basic concept for assessing phosphatidylinositol turnover in neurotransmission process

The uptake mechanism of 1,2-[11C]diacylglycerols (DAG) was studied and its use as a probe for the measurement of phosphatidylinositol (PI) turnover was verified. A method of synthesis for producing rac-1,2-[11C]DAG using [11C]ethylketene was developed to label the 1- or 3-hydroxyl group of 2-monoacylglycerol. After intravenous injection, these tracers were metabolized rapidly in the rat brain cortex to phosphatidic acids, phosphatidylinositols and phosphatidylinositol phosphates. The brain cortex anesthetized by barbiturate, which represents inhibited state of synaptic transmission, did not produce differences in uptake values between sn-1,2-[11C]DAG and rac-1,2-[11C]DAG. However, in the liver, lung, and pancreas under the same conditions, the uptake values of rac-1,2-[11C]DAG were higher than those of sn-1,2-[11C] DAG, in which the labeling position was on the 2-hydroxyl group in the sn type. These findings suggest that the lipase activity in the brain should be disregarded because lipase predominantly hydrolyzes the 1- or 3-position of rac-1,2-[11C] DAG, which should be the main factor producing the differences in uptake values in other organs. Cholinergic stimulation prompted accumulation of 1,2-[11C]DAG in the conscious rat brain. In conclusion, sn-1,2-[11C]DAG, administered even in the racemic mixture, could serve as a tracer that becomes mixed with receptor-linked PI turnover and could accumulate in the brain based on the membrane trapping mechanism.

[An evaluation of cerebral blood flow and metabolism of reconstructive vascular surgery using positron emission tomography--a report of 4 cases]

Changes in cerebral hemodynamics due to reconstructive cerebral vascular surgery were evaluated using positron emission tomography (PET). Three minor stroke cases and 1 TIA case, brought on by main trunk stenosis, were included. STA-MCA anastomoses was performed in two of the cases and carotid endarterectomy was performed in the remaining two cases. CBF, CBV, OEF, CMRO2 and CBF/CBV were investigated using PET with the ROIs fixed in both normal and stenosis areas. On the two cases of STA - MCA anastomosis, clear hemodynamic improvement was not demonstrated. On the two carotid endarterectomy cases, the hemodynamic factors showed improvement.

No-carrier-added carbon-11-labeled sn-1,2- and sn-1,3-diacylglycerols by [11C]propyl ketene method

This article describes the preparation of sn-1,2-[11C]diacylglycerols and sn-1,3-[11C]diacylglycerols by a no-carrier-added reaction based on a labeling method using [1-11C]propyl ketene, which is one of the most potent acylating agents. [1-11C]Propyl ketene was produced by pyrolytic decomposition of [1-11C]butyric acid and was trapped in pyridine containing L-alpha-palmitoyl-lysophosphatidylcholine, producing L-alpha-palmitoyl-2-[1-11C]butyryl-sn-glycero-3-phosphorylcholine. We adopted an enzymatic reaction to remove the phosphorylcholine, in which L-alpha-palmitoyl-2-[1-11C]butyryl-sn-glycero-3-phosphorylcholine was incubated with phospholipase C, hydrolyzing to produce 1-palmitoyl-sn-2-[1-11C]butyrylglycerol. Total synthesis time was about 50 minutes and the specific activity was estimated at 93 GBq/mumol (2.5 Ci/mumol) at end of synthesis. Radiochemical yield was 3.8% based on the trapped 11CO2. sn-1,3-[11C]Diacylglycerol was also synthesized by [1-11C]propyl ketene reaction with 1-palmitoyl-sn-glycerol in a single procedure. The regional brain tissue radioactivities obtained in sn-1,2-[11C]diacylglycerol were higher than those of sn-1,3-[11C]diacylglycerol, and the regional values varied widely. In autoradiography of brain slices from conscious rats, sn-1,2-[11C]diacylglycerol incorporation sites were discretely localized, especially in the amygdala, cerebral cortex, and hippocampus, suggesting that intensive neuronal processing occurred in these areas on the basis of phosphatidylinositol turnover.

6-[18F]fluoro-L-fucose: a possible tracer for assessing glycoconjugate synthesis in tumors with positron emission tomography

The potential of 6-[18F]fluoro-L-fucose (6-[18F]FFuc) for assessing glycoconjugate synthesis in tumors with positron emission tomography (PET) was investigated. Using the tissue sampling method with five tumor models, different time-radioactivity profiles were found: a nearly constant level in Lewis lung carcinoma (3LL) and different clearance patterns in others. Rapid clearance in normal tissues resulted in preferable uptake ratios for tumor imaging of brain and pancreas. Metabolic studies and the L-fucose loading effects on the tissue uptake proved the tracer to be a biochemically active L-fucose analog. Imaging of the intracranial rat glioma and 3LL in lungs or hepatomas in mice by autoradiography (ARG) and intramuscular VX-2 carcinoma in rabbits by PET was demonstrated. Using double-radionuclide ARG, similar distribution images of 6-[18F]FFuc and 14C-L-fucose but different tumor-to-liver uptake ratios were found. A metastasis model seemed to show a higher uptake of both tracers as compared to a primary tumor model.

Positron emission tomographic studies on cerebral hemodynamics in patients with cerebral contusion

Positron emission tomography is currently one of the most useful methods for measurements of cerebral hemodynamics and oxygen metabolism, because it facilitates accurate analysis of the local cerebral circulation in three-dimensional quantitative images. In this study, we performed positron emission tomography studies to measure cerebral circulation in a total of 11 patients who sustained head injuries with contusion. Several parameters were measured including regional cerebral blood flow, regional cerebral blood volume, permeability, and regional cerebral metabolic rate for oxygen. Data from brains both with and without contusion were analyzed for chronological changes, in the subacute stage from the 8th to 29th day and in the chronic stage until 360 days after the injury and compared with similar data in a group of normal subjects. It was concluded that in the subacute stage, regional cerebral blood flow decreased (26 +/- 7 and 39 +/- 10 ml/100 g/min) and regional cerebral blood volume increased (5.6 +/- 1.8 and 5.4 +/- 0.9 ml/100 g) both in areas of cerebral contusion and in areas remote from cerebral contusion and that permeability increased in areas of contusion but not in remote brain areas. In the chronic stage, these parameters showed a tendency for recovery.

Metabolic and hemodynamic aspects of peritumoral low-density areas in human brain tumor

With the use of positron emission tomography, regional cerebral blood flow, oxygen utilization, and glucose utilization were measured in the peritumoral low-density areas on x-ray computed tomographic images in 23 patients with supratentorial brain tumors: 7 meningiomas, 11 malignant gliomas, and 5 metastatic brain tumors. Findings on positron emission tomography in these areas revealed characteristic patterns associated with the types of tumor and the degree of mass effect. It is likely that two different types of pathophysiological states exist in "peritumoral edema": 1) primary ischemia caused by mechanical compression by the tumor mass in meningiomas; and 2) primary metabolic suppression (mainly in oxygen metabolism) in malignant brain tumors.

[The Chronological changes in the cerebral blood flow and cerebral metabolic rate for glucose in the ischemic rabbit brain]

Chronological changes in regional cerebral blood flow (rCBF) and in the regional cerebral metabolic rate for glucose (rCMRGlu) were studied by a double tracer autoradiographic method in regions of local ischemia in rabbit brains. Local ischemia was produced by cautery of the bilateral vertebral artery, followed several days later by cautery of the left middle cerebral artery through a transorbital approach and ligation of the left common carotid artery. Autoradiography was performed, 2 hours, 6 hours, and 4 days after occlusion, by a double tracer method involving the use of 14C-iodo-antipyrine and 18F-fluoro-deoxyglucose. Absolute rCBF values were estimated by Sakurada's method and rCMRGlu values by Hutchins' formula. Histological examination was performed concurrently with the rCBF and rCMRGlu study. Mildly ischemic lesions (rCBF of 25 to 40 ml/100 g/min) were detected in the superior portion of the left frontal lobe, the left parietal lobe, and the left occipital lobe. Severely ischemic lesions (rCBF below 25 ml/100 g/min) were found in the lateral part of the left frontal lobe, the left temporal lobe, and the left caudate nucleus. In the mildly ischemic regions, rCMRGlu decreased in proportion to the decrease in rCBF. That is, matched low perfusion was observed, but there were no histological abnormalities. In severe ischemia the situation was quite different. Two hours after occlusion, most areas showed a decrease in rCMRGlu in proportion to the decrease in rCBF. However, 6 hours after occlusion, rCMRGlu decreased nonuniformly: in some places the decrease was dramatic and in others, rCMRGlu residue was found. Four days after occlusion, the reduction in rCMRGlu was again proportional to the rCBF decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative hemodynamic and metabolic changes in patients with subarachnoid hemorrhage

Positron emission tomography was performed using an oxygen-15 gas inhalation technique to measure regional cerebral blood flow, metabolic rate for oxygen, oxygen extraction fraction, and cerebral blood volume in 13 patients with subarachnoid hemorrhage during the period of delayed vasospasm after surgery as well as in 10 volunteers as controls. Compared with the controls, the patients showed decreased hemoglobin concentration and decreased total arterial oxygen content due to postoperative hemodilution. Global reductions in the metabolic rate for oxygen and in the tissue oxygen supply were noted even in the apparently normal cortex of the patients in spite of adequate blood flow and adequate oxygen extraction fraction. In addition, regional reductions in blood flow and in perfusion reserve were seen in the cortical territory corresponding to cerebral vasospasm. Our results indicate that two processes are involved in the pathophysiology of cerebral vasospasm: 1) generalized impairment of oxygen metabolism with a reduced tissue oxygen supply, even in the apparently normal cortex, and 2) additional impairment of regional perfusion in the territory of vasospasm.

[Positron emission tomographic evaluations on hemodynamics and glucose metabolism of brain tumors and perifocal edematous tissues]

Blood flow and glucose metabolism of the tumors and perifocal edematous tissues were evaluated using positron emission tomography (PET). Thirty-one brain tumor cases were investigated 12 non glial tumors (9 meningiomas and 3 metastatic tumors) and 19 gliomas (these were classified in 5 astrocytomas, 7 anaplastic astrocytomas and 7 glioblastomas, according to the malignancy). The diagnosis were confirmed pathologically in 30 cases. Cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), oxygen extraction fraction (OEF) and cerebral blood volume (CBV) were measured by O-15 labeled gases inhalation methods. Cerebral metabolic rate for glucose (CMFglu) were measured by F-18 Deoxyglucose intravenous injection method and calculated by Hutchins's formula. The rate constant (ks) and lumped constant (LC) used in this study were the same as those published by Phelps et al. in 1979. The blood flow and glucose metabolic rates of tumors were measured by the same methods. The results were as follows: 1) Meningiomas showed very high blood flow and blood volume with a wide range. The OEF and metabolic rate for glucose (MRglu) values were very low. 2) Metastatic tumors showed the low values of blood flow, metabolic rate for oxygen (MRO2) and OEF. 3) The blood flow and MRglu values on gliomas were varied with no significant differences between the three subgroups. On the other hands, as the malignancy of the glioma increased, a statistically significant increase in blood volume and a decrease in OEF were noted. 4) The OEF values from the various types of tumors studied were significantly lower than those obtained from the normal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of 2-deoxy-2-[18F]fluoro-D-galactose in the liver by phosphate and uridylate trapping

To investigate the highest accumulation of 2-deoxy-2-[18F]fluoro-D-galactose ([18F]FdGal) in the liver, metabolic studies with [18F]FdGal were carried out in Wistar rats for 120 min after i.v. injection. As main metabolites 2-deoxy-2-[18F]fluoro-D-galactose 1-phosphate ([18F]FdGal-1-P) and UDP-2-deoxy-2-[18F]-fluoro-D-galactose (UDP-[18F]FdGal) were identified in the liver and other tissues. The [18F]FdGal was phosphorylated by galactokinase. The phosphorylation rate was very rapid in the liver, in which at 5 min after injection 81% of 18F was detected as [18F]FdGal-1-P. After this time the phosphate form decreased with time, which was explained by conversion of [18F]FdGal-1-P to UDP-[18F]FdGal by UDP-glucose: galactose-1-phosphate uridyltransferase. At 120 min after injection 77% of the 18F was measured in the UDP-[18F]FdGal. In the brain both reaction rates were slower than in the liver. Both phosphate and uridylate derivates were also observed as main metabolites in the heart, lung, spleen and small intestine. On the other hand, a small amount of [18F]FdGal-1-P was detected in the plasma, in which the percentage of phosphate increased gradually and was 6% at 120 min. These results show that the [18F]FdGal metabolism in tissue results in phosphate and uridylate trapping and that the [18F]FdGal has potential for measuring in vivo galactose metabolism with positron emission tomography.