Usefulness of positron emission tomography in diagnosis and treatment follow-up of brain tumors

18F-FACBC and 18F-FDG PET/MRI in the evaluation of 3 patients with primary central nervous system lymphoma: a pilot study

BACKGROUND

This PET/MRI study compared contrast-enhanced MRI, 18F-FACBC-, and 18F-FDG-PET in the detection of primary central nervous system lymphomas (PCNSL) in patients before and after high-dose methotrexate chemotherapy. Three immunocompetent PCNSL patients with diffuse large B-cell lymphoma received dynamic 18F-FACBC- and 18F-FDG-PET/MRI at baseline and response assessment. Lesion detection was defined by clinical evaluation of contrast enhanced T1 MRI (ce-MRI) and visual PET tracer uptake. SUVs and tumor-to-background ratios (TBRs) (for 18F-FACBC and 18F-FDG) and time-activity curves (for 18F-FACBC) were assessed.

RESULTS

At baseline, seven ce-MRI detected lesions were also detected with 18F-FACBC with high SUVs and TBRs (SUVmax:mean, 4.73, TBRmax: mean, 9.32, SUVpeak: mean, 3.21, TBRpeak:mean: 6.30). High TBR values of 18F-FACBC detected lesions were attributed to low SUVbackground. Baseline 18F-FDG detected six lesions with high SUVs (SUVmax: mean, 13.88). In response scans, two lesions were detected with ce-MRI, while only one was detected with 18F-FACBC. The lesion not detected with 18F-FACBC was a small atypical MRI detected lesion, which may indicate no residual disease, as this patient was still in complete remission 12 months after initial diagnosis. No lesions were detected with 18F-FDG in the response scans.

CONCLUSIONS

18F-FACBC provided high tumor contrast, outperforming 18F-FDG in lesion detection at both baseline and in response assessment. 18F-FACBC may be a useful supplement to ce-MRI in PCNSL detection and response assessment, but further studies are required to validate these findings. Trial registration ClinicalTrials.gov. Registered 15th of June 2017 (Identifier: NCT03188354, https://clinicaltrials.gov/study/NCT03188354 ).

Usefulness of carbon-11-labeled methionine positron-emission tomography for assessing the treatment response of primary central nervous system lymphoma

BACKGROUND

Primary central nervous system lymphoma (PCNSL) responds relatively quickly to chemotherapy or radiotherapy. However, determination of a complete response after treatment is often difficult because of extremely light residual contrast enhancement on magnetic resonance images due to the effects of microhemorrhages and scar tissue formation. These small enhancing lesions define an unconfirmed complete response. The aim of this study was to investigate the usefulness of carbon-11-labeled methionine (11C-Met) positron-emission tomography (PET) for determining the treatment response of PCNSL.

METHODS

Data for 36 patients who were treated for PCNSL between 2011 and 2015 and underwent magnetic resonance imaging and 11C-Met PET were reviewed. Magnetic resonance imaging findings were classified as complete response, unconfirmed complete response, and tumor mass (a composite of partial response, stable disease and progressive disease). PET images were evaluated, standardized uptake values were quantified, and the tumor-to-normal tissue count ratio (TNR) was calculated. Receiver operating characteristic curves were generated to determine the optimal cutoff TNRs.

RESULTS

The optimal TNRs for differentiating complete response and unconfirmed complete response from tumor mass were 1.83 (area under the curve, 0.951) and 1.80 (area under the curve, 0.932), respectively. The corresponding sensitivity and specificity values for the diagnosis of tumor mass were 82.4 and 100%, respectively, in the complete response group and 85.3 and 85%, respectively, in the unconfirmed complete response group.

CONCLUSIONS

A TNR of ≥1.80 can aid in the detection of active PCNSL using 11C-Met PET. Thus, 11C-Met-PET may be a useful tool for accurate evaluation of the treatment efficacy in PCNSL.

Diagnostic accuracy of 13N-ammonia PET, 11C-methionine PET and 18F-fluorodeoxyglucose PET: a comparative study in patients with suspected cerebral glioma

Background

The treatment of patients with glioma depended on the nature of the lesion and on histological grade of the tumor. Positron emission tomography (PET) using ¹³N-ammonia (NH₃), ¹¹C-methionine (MET) and ¹⁸F-fluorodeoxyglucose (FDG) have been used to assess brain tumors. Our aim was to compare their diagnostic accuracies in patients with suspected cerebral glioma.

Methods

Ninety patients with suspicion of glioma based on previous CT/MRI, who underwent NH₃ PET, MET PET and FDG PET, were prospectively enrolled in the study. The reference standard was established by histology or clinical and radiological follow-up. Images were interpreted by visual evaluation and semi-quantitative analysis using the lesion-to-normal white matter uptake ratio (L/WM ratio).

Results

Finally, 30 high-grade gliomas (HGG), 27 low-grade gliomas (LGG), 10 non-glioma tumors and 23 non-neoplastic lesions (NNL) were diagnosed. On visual evaluation, sensitivity and specificity for differentiating tumors from NNL were 62.7% (42/67) and 95.7% (22/23) for NH₃ PET, 94.0% (63/67) and 56.5% (13/23) for MET PET, and 35.8% (24/67) and 65.2% (15/23) for FDG PET. On semi-quantitative analysis, brain tumors showed significantly higher L/WM ratios than NNL both in NH₃ and MET PET (both P < 0.001). The sensitivity, specificity and the area under the curve (AUC) by receiver operating characteristic (ROC) analysis, respectively, were 64.2, 100% and 0.819 for NH₃; and 89.6, 69.6% and 0.840 for MET. Besides, the L/WM ratios of NH₃, MET and FDG PET in HGG all significantly higher than that in LGG (all P < 0.001). The predicted (by ROC) accuracy of the tracers (AUC shown in parentheses) were 86.0% (0.896) for NH₃, 87.7% (0.928) for MET and 93.0% (0.964) for FDG. While no significant differences in the AUC were seen between them.

Conclusion

NH₃ PET has remarkably high specificity for the differentiation of brain tumors from NNL, but low sensitivity for the detection of LGG. MET PET was found to be highly useful for detection of brain tumors. However, like FDG, high MET uptake is frequently observed in some NNL. NH₃, MET and FDG PET all appears to be valuable for evaluating the histological grade of gliomas.

Usefulness of positron emission tomographic studies for gliomas

Non-invasive positron emission tomography (PET) enables the measurement of metabolic and molecular processes with high sensitivity. PET plays a significant role in the diagnosis, prognosis, and treatment of brain tumors and predominantly detects brain tumors by detecting their metabolic alterations, including energy metabolism, amino acids, nucleic acids, and hypoxia. Glucose metabolic tracers are related to tumor cell energy and exhibit good sensitivity but poor specificity for malignant tumors. Amino acid metabolic tracers provide a better delineation of tumors and cellular proliferation. Nucleic acid metabolic tracers have a high sensitivity for malignant tumors and cellular proliferation. Hypoxic metabolism tracers are useful for detecting resistance to radiotherapy and chemotherapy. Therefore, PET imaging techniques are useful for detecting biopsy-targeting points, deciding on tumor resection, radiotherapy planning, monitoring therapy, and distinguishing brain tumor recurrence or progression from post-radiotherapy effects. However, it is not possible to use only one PET tracer to make all clinical decisions because each tracer has both advantages and disadvantages. This study focuses on the different kinds of PET tracers and summarizes their recent applications in patients with gliomas. Combinational uses of PET tracers are expected to contribute to differential diagnosis, prognosis, treatment targeting, and monitoring therapy.

Visualization of Uptake of Mineral Elements and the Dynamics of Photosynthates in Arabidopsis by a Newly Developed Real-Time Radioisotope Imaging System (RRIS)

Minerals and photosynthates are essential for many plant processes, but their imaging in live plants is difficult. We have developed a method for their live imaging in Arabidopsis using a real-time radioisotope imaging system. When each radioisotope,(22)Na,(28)Mg,(32)P-phosphate,(35)S-sulfate,(42)K,(45)Ca,(54)Mn and(137)Cs, was employed as an ion tracer, ion movement from root to shoot over 24 h was clearly observed. The movements of(22)Na,(42)K,(32)P,(35)S and(137)Cs were fast so that they spread to the tip of stems. In contrast, high accumulation of(28)Mg,(45)Ca and(54)Mn was found in the basal part of the main stem. Based on this time-course analysis, the velocity of ion movement in the main stem was calculated, and found to be fastest for S and K among the ions we tested in this study. Furthermore, application of a heat-girdling treatment allowed determination of individual ion movement via xylem flow alone, excluding phloem flow, within the main stem of 43-day-old Arabidopsis inflorescences. We also successfully developed a new system for visualizing photosynthates using labeled carbon dioxide,(14)CO2 Using this system, the switching of source/sink organs and phloem flow direction could be monitored in parts of whole shoots and over time. In roots,(14)C photosynthates accumulated intensively in the growing root tip area, 200-800 µm behind the meristem. These results show that this real-time radioisotope imaging system allows visualization of many nuclides over a long time-course and thus constitutes a powerful tool for the analysis of various physiological phenomena.

A Dual Tracer 18F-FCH/18F-FDG PET Imaging of an Orthotopic Brain Tumor Xenograft Model

Early diagnosis of low grade glioma has been a challenge to clinicians. Positron Emission Tomography (PET) using 18F-FDG as a radio-tracer has limited utility in this area because of the high background in normal brain tissue. Other radiotracers such as 18F-Fluorocholine (18F-FCH) could provide better contrast between tumor and normal brain tissue but with high incidence of false positives. In this study, the potential application of a dual tracer 18F-FCH/18F-FDG-PET is investigated in order to improve the sensitivity of PET imaging for low grade glioma diagnosis based on a mouse orthotopic xenograft model. BALB/c nude mice with and without orthotopic glioma xenografts from U87 MG-luc2 glioma cell line are used for the study. The animals are subjected to 18F-FCH and 18F-FDG PET imaging, and images acquired from two separate scans are superimposed for analysis. The 18F-FCH counts are subtracted from the merged images to identify the tumor. Micro-CT, bioluminescence imaging (BLI), histology and measurement of the tumor diameter are also conducted for comparison. Results show that there is a significant contrast in 18F-FCH uptake between tumor and normal brain tissue (2.65 ± 0.98), but with a high false positive rate of 28.6%. The difficulty of identifying the tumor by 18F-FDG only is also proved in this study. All the tumors can be detected based on the dual tracer technique of 18F-FCH/18F-FDG-PET imaging in this study, while the false-positive caused by 18F-FCH can be eliminated. Dual tracer 18F-FCH/18F-FDG PET imaging has the potential to improve the visualization of low grade glioma. 18F-FCH delineates tumor areas and the tumor can be identified by subtracting the 18F-FCH counts. The sensitivity was over 95%. Further studies are required to evaluate the possibility of applying this technique in clinical trials.

Development of a novel imaging system for cell therapy in the brain

Introduction

Stem cells have been evaluated as a potential therapeutic approach for several neurological disorders of the central and peripheral nervous system as well as for traumatic brain and spinal cord injury. Currently, the lack of a reliable and safe method to accurately and non-invasively locate the site of implantation and track the migration of stem cells in vivo hampers the development of stem cell therapy and its clinical application.

In this report, we present data that demonstrate the feasibility of using the human sodium iodide symporter (hNIS) as a reporter gene for tracking neural stem cells (NSCs) after transplantation in the brain by using single-photon emission tomography/computed tomography (SPECT/CT) imaging.

Methods

NSCs were isolated from the hippocampus of adult rats (Hipp-NSCs) and transduced with a lentiviral vector containing the hNIS gene. Hipp-NSCs expressing the hNIS (NIS-Hipp-NSCs) were characterized in vitro and in vivo after transplantation in the rat brain and imaged by using technetium-99m (^99mTc) and a small rodent SPECT/CT apparatus. Comparisons were made between Hipp-NSCs and NIS-Hipp-NSCs, and statistical analysis was performed by using two-tailed Student’s t test.

Results

Our results show that the expression of the hNIS allows the repeated visualization of NSCs in vivo in the brain by using SPECT/CT imaging and does not affect the ability of Hipp-NSCs to generate neuronal and glial cells in vitro and in vivo.

Conclusions

These data support the use of the hNIS as a reporter gene for non-invasive imaging of NSCs in the brain. The repeated, non-invasive tracking of implanted cells will accelerate the development of effective stem cell therapies for traumatic brain injury and other types of central nervous system injury.

Relationship between apathy and tumor location, size, and brain edema in patients with intracranial meningioma

BACKGROUND

The purpose of this study is to assess the relationship between apathy and tumor location, size, and brain edema in patients with intracranial meningioma.

METHODS

We enrolled 65 consecutive patients with meningioma and 31 normal controls matched for age, gender, and education. The patients were divided into frontal or non-frontal (NF) meningioma groups based on magnetic resonance imaging; the frontal group was then subdivided to dorsolateral frontal (DLF), medial frontal (MF), and ventral frontal (VF) groups. Tumor size and brain edema were also recorded. Apathy was assessed by the Apathy Evaluation Scale (AES). Assessments were carried out 1 week before and 3 months after surgery, respectively. Logistic regression analysis was performed to identify the predictive effect of tumor size, location, and brain edema on apathy. Analysis of variance and chi-square analysis were applied to compare apathy scores and apathy rates among the frontal, NF, and normal control groups, and all subgroups within the frontal group.

RESULTS

Compared with the NF and control groups, the mean AES score was much higher in the frontal group (34.0±8.3 versus 28.63±6.0, P=0.008, and 26.8±4.2, P<0.001). Subgroup analysis showed that AES scores in the MF group (42.1±6.6) and VF group (34.7±8.0) were higher than in the DLF group (28.5±4.36), NF group, and control group (P<0.05). The apathy rate was 63.6% in the MF group and 25% in the VF group, and significantly higher than in the DLF (5.6%), NF (5.3%), and control (0%) groups (P<0.001). A moderate correlation was found between AES score and mean diameter of the meningioma in all patient groups. Further analysis demonstrated that the correlation existed in the DLF (r=0.52, P=0.032), MF (r=0.84, P<0.001), and VF (r=0.64, P=0.008) groups, but not in the NF group (r=0.19, P=0.448). The AES score was much higher in patients with brain edema than in those without brain edema (34.73±8.28 versus 28.77±4.20, t=3.545, P=0.001). In subgroups within frontal meningioma patients, the statistical significance above only existed in the MF group (43.50±5.26 versus 25.67±6.03, P=0.001). Also, we examined the effect of related factors, such as age, sex, education, tumor size, tumor location and edema on the occurrence of apathy. The binary logistic regression analysis showed that MF [P=0.023, Exp(B) =145.6] and size [P=0.012, Exp(B) =1.20] got into the regression equation. Thirty-two patients underwent follow-up post-surgery. A significant reduction in AES was found in the MF group (AES1 - AES2 =6.86±6.82, t=2.68, P=0.04), but not in any of the other groups.

CONCLUSION

Apathy occurs frequently in patients with frontal meningioma, and is more severe, especially in the MF region. Apathy is probably correlated with tumor location and size. Brain edema might increase the severity of apathy.

Cerebral proton magnetic resonance spectroscopy demonstrates reversibility of N-acetylaspartate/creatine in gray matter after delayed encephalopathy due to carbon monoxide intoxication: a case report

Introduction

Predictive markers for long-term outcome in carbon monoxide-intoxicated patients with late encephalopathy are desired. Here we present the first data demonstrating a full reversibility pattern of specific brain substances measured by cerebral proton magnetic resonance spectroscopy in a carbon monoxide-intoxicated victim. This may provide clinicians with important information when estimating patient outcome.

Case presentation

We report the case of a 40-year-old Caucasian woman with severe carbon monoxide poisoning who was treated with five repetitive sessions of hyperbaric oxygen therapy in a multiplace chamber (100 percent oxygen with a ventilator, 90 minutes exposure to 2.8 atmospheres absolute). Initially, our patient recovered completely after three days of hospitalization, but became encephalopathic after a lucid interval of four weeks. An examination of the brain with cerebral proton magnetic resonance spectroscopy showed a dramatically decrease in N-acetylaspartate to total creatine ratios and elevated lactate levels in the gray matter. Subsequently, our patient received six additional sessions of hyperbaric oxygen therapy with only minimal recovery. At six-month follow-up our patient showed significant improvement in cognition and neuromuscular coordination. Extraordinarily, the cerebral proton magnetic resonance spectroscopy measurements at relapse compared to measurements at follow-up (217 days post insult) revealed full reversal of the severe abnormalities in mid-occipital gray matter and partial reversal in white matter.

Conclusions

The present case indicates that cerebral proton magnetic spectroscopy provides valuable information on brain metabolism in patients presenting with delayed encephalopathy after acute carbon monoxide intoxication. The full reversal of N-acetylaspartate to total creatine ratios in gray matter has, to our knowledge, never been described before and shows that severe, initial measurements may not predict poor long-term patient outcome.

Molecular imaging and tracking stem cells in neurosciences

Stem cell transplantation is a promising new therapeutic option in different neurological diseases. However, it is not yet possible to translate its potential from animal models to clinical application. One of the main problems of applying stem cell transplantation in clinical medium is the difficulty of detection, localization, and examination of the stem cells in vivo at both cellular and molecular levels. State-of-the-art molecular imaging techniques provide new and better means for noninvasive, repeated, and quantitative tracking of stem cell implant or transplant. From initial deposition to the survival, migration, and differentiation of the transplant/implanted stem cells, current molecular imaging methods allow monitoring of the infused cells in the same live recipient over time. The present review briefly summarizes and compares these molecular imaging methods for cell labeling and imaging in animal models as well as in clinical application and sheds light on consecutive new therapeutic options if appropriate.

Molecular imaging for stem cell transplantation in neuroregenerative medicine

Stem cell transplantation is a promising new therapeutic option in different neurological diseases. However, it was not yet possible to translate its potential from animal models to clinical application. One of the main problems of applying stem cell transplantation in clinical medium is the difficulty of detection, localization, and examination of the stem cells in vivo at both cellular and molecular levels. State-of-the-art molecular imaging techniques provide new and better means for noninvasive, repeated, and quantitative tracking of stem cell implant or transplant. From initial deposition to the survival, migration, and differentiation of the transplant/implanted stem cells, current molecular imaging methods allow monitoring of the infused cells in the same live recipient over time. The present review briefly summarizes and compares these molecular imaging methods for cell labeling and imaging in animal models as well as in clinical application and sheds light on consecutive new therapeutic options if appropriate.

Molecular imaging of potential bone metastasis from differentiated thyroid cancer: a case report

INTRODUCTION

Molecular imaging of the spine is a rarely used diagnostic method for which only a few case reports exist in the literature. Here, to the best of our knowledge we present the first case of a combination of molecular imaging by single photon emission computer tomography and positron emission tomography used in post-operative spinal diagnostic assessment.

CASE PRESENTATION

We present the case of a 50-year-old Caucasian woman experiencing progressive spinal cord compression caused by a vertebral metastasis of a less well differentiated thyroid cancer. Following tumor resection and vertebral stabilization, total thyroidectomy was performed revealing follicular thyroid carcinoma pT2 pNxM1 (lung, bone). During follow-up our patient underwent five radioiodine therapy procedures (5.3 to 5.7 GBq each) over a two-year period. Post-therapeutic I-131 scans showed decreasing uptake in multiple Pulmonary metastases. However, following an initial decrease, stimulated thyroglobulin remained at pathologically increased levels, indicating further neoplastic activity. F18 Fludeoxyglucose positron emission tomography, which was performed in parallel, showed remaining hypermetabolism in the lungs but no hypermetabolism of the spinal lesions correlating with the stable neurological examinations. While on single photon emission computer tomography images Pulmonary hyperfixation of I-131 disappeared (most likely indicating dedifferentiation), there was persistent spinal hyperfixation at the operated level and even higher fixation at the spinal process of L3. Based on the negative results of the spinal F18 fludeoxyglucose positron emission tomography, a decision was made not to operate again on the spine since our patient was completely asymptomatic and the neurological risk seemed to be too high. During further follow-up our patient remained neurologically stable.

CONCLUSIONS

Molecular imaging by F18 fludeoxyglucose positron emission tomography helps to exclude metabolically active spinal metastases and to spare further risky surgery.

Principles and Application of PET in Brain Tumors

For tumors of the central nervous system (CNS), the ability to accurately delineate the extent of tumor has implications for diagnosis, prognosis, and treatment. PET, mainly with (18)F-fluorodeoxyglucose (FDG), has become commonplace in the work-up of many extracranial tumors. However, the relative high background of FDG-PET activity of normal brain tissue has limited the applicability of this modality in CNS tumors to date. More recently, novel PET tracers for imaging of CNS tumors have been developed. This article outlines recent advances in PET as a complementary imaging modality with implications for diagnosis, prognosis, surgical and radiation treatment planning, and post-therapy surveillance in malignancies of the CNS. Pharmacokinetic properties of the radiotracers and the influence of blood-brain-barrier integrity are also incorporated into the discussion.

Current molecular imaging of spinal tumors in clinical practice

Energy metabolism measurements in spinal cord tumors, as well as in osseous spinal tumors/metastasis in vivo, are rarely performed only with molecular imaging (MI) by positron emission tomography (PET). This imaging modality developed from a small number of basic clinical science investigations followed by subsequent work that influenced and enhanced the research of others. Apart from precise anatomical localization by coregistration of morphological imaging and quantification, the most intriguing advantage of this imaging is the opportunity to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Most importantly, MI represents one of the key technologies in translational molecular neuroscience research, helping to develop experimental protocols that may later be applied to human patients. PET may help monitor a patient at the vertebral level after surgery and during adjuvant treatment for recurrent or progressive disease. Common clinical indications for MI of primary or secondary CNS spinal tumors are: (i) tumor diagnosis, (ii) identification of the metabolically active tumor compartments (differentiation of viable tumor tissue from necrosis) and (iii) prediction of treatment response by measurement of tumor perfusion or ischemia. While spinal PET has been used under specific circumstances, a question remains as to whether the magnitude of biochemical alterations observed by MI in CNS tumors in general (specifically spinal tumors) can reveal any prognostic value with respect to survival. MI may be able to better identify early disease and to differentiate benign from malignant lesions than more traditional methods. Moreover, an adequate identification of treatment effectiveness may influence patient management. MI probes could be developed to image the function of targets without disturbing them or as treatment to modify the target's function. MI therefore closes the gap between in vitro and in vivo integrative biology of disease. At the spinal level, MI may help to detect progression or recurrence of metastatic disease after surgical treatment. In cases of nonsurgical treatments such as chemo-, hormone- or radiotherapy, it may better assess biological efficiency than conventional imaging modalities coupled with blood tumor markers. In fact, PET provides a unique possibility to correlate topography and specific metabolic activity, but it requires additional clinical and experimental experience and research to find new indications for primary or secondary spinal tumors.

Stem cell transplantation in brain tumors: a new field for molecular imaging?

Neural stem cells have been proposed as a new and promising treatment modality in various pathologies of the central nervous system, including malignant brain tumors. However, the underlying mechanism by which neural stem cells target tumor areas remains elusive. Monitoring of these cells is currently done by use of various modes of molecular imaging, such as optical imaging, magnetic resonance imaging and positron emission tomography, which is a novel technology for visualizing metabolism and signal transduction to gene expression. In this new context, the microenvironment of (malignant) brain tumors and the blood-brain barrier gains increased interest. The authors of this review give a unique overview of the current molecular-imaging techniques used in different therapeutic experimental brain tumor models in relation to neural stem cells. Such methods for molecular imaging of gene-engineered neural stem/progenitor cells are currently used to trace the location and temporal level of expression of therapeutic and endogenous genes in malignant brain tumors, closing the gap between in vitro and in vivo integrative biology of disease in neural stem cell transplantation.

Strategies for molecular imaging dementia and neurodegenerative diseases

Dementia represents a heterogeneous term that has evolved to describe the behavioral syndromes associated with a variety of clinical and neuropathological changes during continuing degenerative disease of the brain. As such, there lacks a clear consensus regarding the neuropsychological and other constituent characteristics associated with various cerebrovascular changes in this disease process. But increasing this knowledge has given more insights into memory deterioration in patients suffering from Alzheimer's disease and other subtypes of dementia. The author reviews current knowledge of the physiological coupling between cerebral blood flow and metabolism in the light of state-of-the-art-imaging methods and its changes in dementia with special reference to Alzheimer's disease. Different imaging techniques are discussed with respect to their visualizing effect of biochemical, cellular, and/or structural changes in dementia. The pathophysiology of dementia in advanced age is becoming increasingly understood by revealing the underlying basis of neuropsychological changes with current imaging techniques, genetic and pathological features, which suggests that alterations of (neuro) vascular regulatory mechanisms may lead to brain dysfunction and disease. The current view is that cerebrovascular deregulation is seen as a contributor to cerebrovascular pathologies, such as stroke, but also to neurodegenerative conditions, such as Alzheimer's disease. The better understanding of these (patho) physiological mechanisms may open an approach to new interventional strategies in dementia to enhance neurovascular repair and to protect neurovascular coupling.

Dynamic small-animal PET imaging of tumor proliferation with 3'-deoxy-3'-18F-fluorothymidine in a genetically engineered mouse model of high-grade gliomas

3'-Deoxy-3'-(18)F-fluorothymidine ((18)F-FLT), a partially metabolized thymidine analog, has been used in preclinical and clinical settings for the diagnostic evaluation and therapeutic monitoring of tumor proliferation status. We investigated the use of (18)F-FLT for detecting and characterizing genetically engineered mouse (GEM) high-grade gliomas and evaluating the pharmacokinetics in GEM gliomas and normal brain tissue. Our goal was to develop a robust and reproducible method of kinetic analysis for the quantitative evaluation of tumor proliferation.

METHODS

Dynamic (18)F-FLT PET imaging was performed for 60 min in glioma-bearing mice (n = 10) and in non-tumor-bearing control mice (n = 4) by use of a dedicated small-animal PET scanner. A 3-compartment, 4-parameter model was used to characterize (18)F-FLT kinetics in vivo. For compartmental analysis, the arterial input was measured by placing a region of interest over the left ventricular blood pool and was corrected for partial-volume averaging. The (18)F-FLT "trapping" and tissue flux model parameters were correlated with measured uptake (percentage injected dose per gram [%ID/g]) values at 60 min.

RESULTS

(18)F-FLT uptake values (%ID/g) at 1 h in brain tumors were significantly greater than those in control brains (mean +/- SD: 4.33 +/- 0.58 and 0.86 +/- 0.22, respectively; P < 0.0004). Kinetic analyses of the measured time-activity curves yielded independent, robust estimates of tracer transport and metabolism, with compartmental model-derived time-activity data closely fitting the measured data. Except for tracer transport, statistically significant differences were found between the applicable model parameters for tumors and normal brains. The tracer retention rate constant strongly correlated with measured (18)F-FLT uptake values (r = 0.85, P < 0.0025), whereas a more moderate correlation was found between net (18)F-FLT flux and (18)F-FLT uptake values (r = 0.61, P < 0.02).

CONCLUSION

A clinically relevant mouse glioma model was characterized by both static and dynamic small-animal PET imaging of (18)F-FLT uptake. Time-activity curves were kinetically modeled to distinguish early transport from a subsequent tracer retention phase. Estimated (18)F-FLT rate constants correlated positively with %ID/g measurements. Dynamic evaluation of (18)F-FLT uptake offers a promising approach for noninvasively assessing cellular proliferation in vivo and for quantitatively monitoring new antiproliferation therapies.

Molecular Imaging of Brain Tumors: A Bridge Between Clinical and Molecular Medicine?

As the research on cellular changes has shed invaluable light on the pathophysiology and biochemistry of brain tumors, clinical and experimental use of molecular imaging methods is expanding and allows quantitative assessment. The term molecular imaging is defined as the in vivo characterization and measurement of biologic processes at the cellular and molecular level. Molecular imaging sets forth to probe the molecular abnormalities that are the basis of disease rather than to visualize the end effects of these molecular alterations and, therefore, provides different additional biochemical or molecular information about primary brain tumors compared to histological methods "classical" neuroradiological diagnostic studies. Common clinical indications for molecular imaging contain primary brain tumor diagnosis and identification of the metabolically most active brain tumor reactions (differentiation of viable tumor tissue from necrosis), prediction of treatment response by measurement of tumor perfusion, or ischemia. The interesting key question remains not only whether the magnitude of biochemical alterations demonstrated by molecular imaging reveals prognostic value with respect to survival, but also whether it identifies early disease and differentiates benign from malignant lesions. Moreover, an early identification of treatment success or failure by molecular imaging could significantly influence patient management by providing more objective decision criteria for evaluation of specific therapeutic strategies. Specially, as molecular imaging represents a novel technology for visualizing metabolism and signal transduction to gene expression, reporter gene assays are used to trace the location and temporal level of expression of therapeutic and endogenous genes. Molecular imaging probes and drugs are being developed to image the function of targets without disturbing them and in mass amounts to modify the target's function as a drug. Molecular imaging helps to close the gap between in vitro and in vivo integrative biology of disease.

Resection of Gliomas Using Positron Emission Tomography/Computed Tomography Neuronavigation

Two patients presented with provisional diagnoses of glioma. Computed tomography (CT) and magnetic resonance imaging failed to show the boundaries of the tumor clearly. Positron emission tomography (PET)/CT with [(18)F]fluorodeoxyglucose and (11)C-methionine clearly showed the location, extent, and heterogeneity of the tumors. The tumors were resected under PET/CT neuronavigation guidance. Histological examination of the specimens showed that PET/CT neuronavigation provided reliable distinction between normal brain and glioma, and that the uptake of PET tracers can indicate the degree of proliferation.

Biodistribution of polysorbate 80-coated doxorubicin-loaded [14C]-poly(butyl cyanoacrylate) nanoparticles after intravenous administration to glioblastoma-bearing rats

It was recently shown that doxorubicin (DOX) bound to polysorbate-coated nanoparticles (NP) crossed the intact blood-brain barrier (BBB), and thus reached therapeutic concentrations in the brain. Here, we investigated the biodistribution in the brain and in the body of poly(butyl-2-cyano[3-(14)C]acrylate) NP ([(14)C]-PBCA NP), polysorbate 80 (PS 80)-coated [(14)C]-PBCA NP, DOX-loaded [(14)C]-PBCA NP in glioblastoma 101/8-bearing rats after i.v. injection. The biodistribution profiles and brain concentrations of radiolabeled NP were determined by radioactivity counting after i.v. administration in rats. Changes in BBB permeability after tumour inoculation were assessed by i.v. injection of Evans Blue solution. The accumulation of NP in the tumour site and in the contralateral hemisphere in glioblastoma bearing-rats probably was augmented by the enhanced permeability and retention effect (EPR effect) that may have been becoming instrumental due to the impaired BBB on the NP delivery into the brain. The uptake of the NP by the organs of the reticuloendothelial system (RES) was reduced after PS 80-coating, but the addition of DOX increased again the concentration of NP in the RES.

Neuroprotection in primary brain tumors: sense or nonsense?

Primary brain tumors are generally difficult to treat because of the unique location of the lesions. In addition, normal brain structures are often destroyed by the growing neoplasm. Even with effective therapy to surgically resect and destroy the neoplastic tissues, the brain is sometimes still injured, which can leave the patient in a debilitated state. The hemodynamic and metabolic state of such peritumoral brain tissue is not yet well understood, and there are only a small number of experimental hypotheses of its reaction and changes to the growing primary brain tumor. In addition, primary brain tumors may be influenced by certain anticancer drugs, which cause oxidative stress and consecutive cell death, or by gamma-irradiation. Currently, no established diagnostic methods exist to demonstrate and/or quantify the metabolic condition of the peritumoral tissue. The therapeutic strategy for possible pharmacological neuroprotection should, in the future, still be related to metabolic parameters, as well as in the peritumor tissue to treat primary brain tumors without risk to sensitive normal tissue. To achieve this aim, there has been particular emphasis on the biological behavior of primary brain tumors and peritumor tissue, as well as the potential correlation among them. Thus, priority should be given to identifying more target antigens in primary brain tumors and defining those cells present in the brain parenchyma that are essential to maintain a neuroprotective effect. However, at this time, the postinjury enhancement of neurogenesis appears to offer the best hope for long-lasting functional recovery following surgery of primary brain tumors.

Serial O-(2-[(18)F]fluoroethyl)-L: -tyrosine PET for monitoring the effects of intracavitary radioimmunotherapy in patients with malignant glioma

Purpose

Intracavitary radioimmunotherapy (RIT) offers an effective adjuvant therapeutic approach in patients with malignant gliomas. Since differentiation between recurrence and reactive changes following RIT has a critical impact on patient management, the aim of this study was to analyse the value of serial O-(2-[¹⁸F]fluoroethyl)-l-tyrosine (FET) PET scans in monitoring the effects of this locoregional treatment.

Methods

Following conventional therapy, 24 glioma patients (5 WHO III, 19 WHO IV) underwent one to five RIT cycles with either ¹³¹I-labelled (n=19) or ¹⁸⁸Re-labelled (n=5) anti-tenascin antibodies. Patients were monitored with serial FET PET scans (2–12 scans). For semiquantitative evaluation, maximal tumoural uptake (TU_max) was evaluated and the ratio to background (BG) was calculated. Results of PET were correlated with histopathological findings (n=9) and long-term clinical follow-up for up to 87 months.

Results

In seven tumour-free patients, PET revealed slightly increasing but homogeneous FET uptake surrounding the resection cavity with a peak up to 18 months following RIT (TU_max/BG 2.07±0.25) but stable or decreasing values during further follow-up (last follow-up: TU_max/BG 1.63±0.22). Seventeen patients developed regrowth of residual tumour/tumour recurrence showing additional nodular FET uptake (TU_max/BG 2.79±0.53). A threshold value of 2.4 (TU_max/BG) allowed best differentiation between recurrence and reactive changes (sensitivity 82%, specificity 100%).

Conclusion

FET PET is a sensitive tool for monitoring the effects of locoregional RIT. Homogeneous, slightly increasing FET uptake around the tumour cavity with a peak up to 18 months after RIT, followed by stable or decreasing uptake, points to benign, therapy-related changes. In contrast, nodular uptake is a reliable indicator of recurrence.

Optimization of semi-quantification in metabolic PET studies with 18F-fluorodeoxyglucose and 11C-methionine in the determination of malignancy of gliomas

The treatment of the glioma patient depends on the nature of the lesion and on the aggressiveness of the tumor. The management of gliomas continues to be a challenging task, because morphological neuroimaging techniques do not always differentiate them from nontumoral lesions or high grade tumors from low grade lesions. Positron Emission Tomography (PET) offers the possibility of the in vivo quantitative characterization of brain tumors. Despite decades of useful application of PET in the clinical monitoring of gliomas, no consensus has been reached on the most effective image analysis approach for providing the best diagnostic performance under heavy-duty clinical diagnostic circumstances. The main objective of the present study was to find and validate optimal semi-quantitative search strategies for metabolic PET studies on gliomas, with special regard to the optimization of those metabolic tracer uptake ratios most sensitive in predicting histologic grade and prognosis. 11C-Methionine (11C-Met, n = 50) and/or 18F-Fluorodeoxyglucose (18F-FDG, n = 33) PET measurements were performed in 59 patients with primary and recurrent brain gliomas (22 high grade and 37 low grade tumors) in order to correlate the biological behavior and 11C-Met/18F-FDG uptake of tumors. Data were analyzed by region-of-interests (ROI) methods using standard uptake value calculation. Different ROI defining strategies were then compared with each other for two of the most commonly used metabolic radiotracers, 18F-FDG and 11C-Met, in order to determine their usefulness in grading gliomas. The results were compared to histological data in all patients. Both ANOVA and receiver operating characteristic (ROC) analysis indicated that the performance of 18F-FDG was superior to that of 11C-Met for most of the ratios. 18F-FDG is therefore suggested as the tracer of choice for noninvasive semi-quantitative indicator of histologic grade of gliomas. 11C-Methionine has been suggested as a complimentary tracer, useful in delineating the extent of the tumor. The best diagnostic performance was obtained by calculating the ratio of the peak 18F-FDG uptake of the tumor to that of white matter (p < 0.001; ANOVA). This metabolic tracer uptake ratio is therefore suggested as an easily obtained semi-quantitative PET indicator of malignancy and histological grade in gliomas.

Evaluation of tumor FDG transport and metabolism in primary central nervous system lymphoma using [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) kinetic analysis

OBJECTIVE

Although 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has been used as a promising tool to diagnose primary central nervous system lymphoma (PCNSL) because the tumor shows very high FDG accumulation, no data exist evaluating the extent of tumor FDG transport and metabolism. The aim of this study was to evaluate the feasibility of FDG-PET kinetic analysis in measurement of uptake parameters of FDG in the lymphoma tissues and in the assessment of treatment effects in patients with PCNSL.

METHODS

Dynamic FDG-PET examination was performed in 7 histologically proven PCNSL patients before and after methotrexate-based chemotherapy.

RESULTS

Before the chemotherapy, the highest CMRglc in the tumor for all 7 patients was 79.4 +/- 27.2 micromol/100 g/min. This value was significantly higher than that observed in the normal cortex in 14 control patients (44.3 +/- 6.0 micromol/100 g/min, p < 0.001). The phosphorylation (k3) activity was also significantly higher in the tumor (0.093 +/- 0.026 min(-1)) compared with the normal cortex (0.064 +/- 0.014 min(-1), p < 0.05). On the other hand, the transporter (K1) activity in the tumor (0.079 +/- 0.016 ml/min) was similar to that observed in the normal cortex (0.082 +/- 0.012 ml/min). The chemotherapy significantly reduced the volume of the tumor in 6 of 7 patients and the highest CMRglc in the tumor examined 18.0 +/- 5.5 days after the chemotherapy (34.0 +/- 21.8 micromol/100 g/min) was significantly lower than that observed before the chemotherapy (p < 0.01). This reduction in FDG uptake was concomitant with a significant reduction in both the K1 and k3 values (p < 0.05). The reduction in the k3 value after the chemotherapy was marked in 6 of 7 patients in whom the tumor responded to the first chemotherapy.

CONCLUSIONS

Dynamic image acquisition can separate regional FDG uptake into FDG transport and phosphorylation activity in the lymphoma tissues. Tumor FDG uptake was significantly higher with accelerated phosphorylation activity compared with that observed in the normal cortex.

Lessons from brain mapping in surgery for low-grade glioma: insights into associations between tumour and brain plasticity

Surgical treatment of low-grade gliomas (LGGs) aims to maximise the amount of tumour tissue resected, while minimising the risk of functional sequelae. In this review I address the issue of how to reconcile these two conflicting goals. First, I review the natural history of LGG-growth, invasion, and anaplastic transformation. Second, I discuss the contribution of new techniques, such as functional mapping, to our understanding of brain reorganisation in response to progressive growth of LGG. Third, I consider the clinical implications of interactions between tumour progression and brain plasticity. In particular, I show how longitudinal studies (preoperative, intraoperative, and postoperative) could allow us to optimise the surgical risk-to-benefit ratios. I will also discuss controversial issues such as defining surgical indications for LGGs, predicting the risk of postoperative deficit, aspects of operative surgical neuro-oncology (eg, preoperative planning and preservation of functional areas and tracts), and postoperative functional recovery.

Influences of brain tumor-associated pH changes and hypoxia on epileptogenesis

OBJECTIVE

The pathophysiological changes related to epileptic activity in peri- and intra-tumoral tissue are complex and have been only partly understood until now; possible mechanisms involve different structural, biochemical and histological tumor-related alterations.

METHODS

Medical databases were searched for evidence on influence of brain tumor-associated pH changes and hypoxia on epileptogenesis.

RESULTS

During the perioperative period, tumor-related hypoxia and acidity related to tumor neovascularization by vascular endothelial growth factor (VEGF) in combination with angiopoietins 1/2 (ang 1/2), may be a major factor contributing to outcomes involving epileptic activity after surgical tumor removal. Because anaerobic fermentation produces far less ATP than oxidative phosphorlyation per molecule of glucose, increased activity of the glycolytic pathway is necessary to maintain free ATP levels in the hypoxic cell. In mammalian cells, this metabolic switch is regulated by the transcription factor hypoxia-inducible factor-1.

CONCLUSIONS

From the molecular point of view, therapeutic implications for the perioperative period may have relevance for the future.