Velocity-Selective Arterial Spin Labeling Perfusion in Monitoring High Grade Gliomas Following Therapy: Clinical Feasibility at 1.5T and Comparison with Dynamic Susceptibility Contrast Perfusion

MR perfusion imaging is important in the clinical evaluation of primary brain tumors, particularly in differentiating between true progression and treatment-induced change. The utility of velocity-selective ASL (VSASL) compared to the more commonly utilized DSC perfusion technique was assessed in routine clinical surveillance MR exams of 28 patients with high-grade gliomas at 1.5T. Using RANO criteria, patients were assigned to two groups, one with detectable residual/recurrent tumor ("RT", n = 9), and the other with no detectable residual/recurrent tumor ("NRT", n = 19). An ROI was drawn to encompass the largest dimension of the lesion with measures normalized against normal gray matter to yield rCBF and tSNR from VSASL, as well as rCBF and leakage-corrected relative CBV (lc-rCBV) from DSC. VSASL (rCBF and tSNR) and DSC (rCBF and lc-rCBV) metrics were significantly higher in the RT group than the NRT group allowing adequate discrimination (p < 0.05, Mann-Whitney test). Lin's concordance analyses showed moderate to excellent concordance between the two methods, with a stronger, moderate correlation between VSASL rCBF and DSC lc-rCBV (r = 0.57, p = 0.002; Pearson's correlation). These results suggest that VSASL is clinically feasible at 1.5T and has the potential to offer a noninvasive alternative to DSC perfusion in monitoring high-grade gliomas following therapy.

Disease Assessments in Patients with Glioblastoma

PURPOSE OF REVIEW

The neuro-oncology team faces a unique challenge when assessing treatment response in patients diagnosed with glioblastoma. Magnetic resonance imaging (MRI) remains the standard imaging modality for measuring therapeutic response in both clinical practice and clinical trials. However, even for the neuroradiologist, MRI interpretations are not straightforward because of tumor heterogeneity, as evidenced by varying degrees of enhancement, infiltrating tumor patterns, cellular densities, and vasogenic edema. The situation is even more perplexing following therapy since treatment-related changes can mimic viable tumor. Additionally, antiangiogenic therapies can dramatically decrease contrast enhancement giving the false impression of decreasing tumor burden. Over the past few decades, several approaches have emerged to augment and improve visual interpretation of glioblastoma response to therapeutics. Herein, we summarize the state of the art for evaluating the response of glioblastoma to standard therapies and investigational agents as well as challenges and future directions for assessing treatment response in neuro-oncology.

RECENT FINDINGS

Monitoring glioblastoma responses to standard therapy and novel agents has been fraught with many challenges and limitations over the past decade. Excitingly, new promising methods are emerging to help address these challenges. Recently, the Response Assessment in Neuro-Oncology (RANO) working group proposed an updated response criteria (RANO 2.0) for the evaluation of all grades of glial tumors regardless of IDH status or therapies being evaluated. In addition, advanced neuroimaging techniques, such as histogram analysis, parametric response maps, morphometric segmentation, radio pharmacodynamics approaches, and the integrating of amino acid radiotracers in the tumor evaluation algorithm may help resolve equivocal lesion interpretations without operative intervention. Moreover, the introduction of other techniques, such as liquid biopsy and artificial intelligence could complement conventional visual assessment of glioblastoma response to therapies. Neuro-oncology has evolved over the past decade and has achieved significant milestones, including the establishment of new standards of care, emerging therapeutic options, and novel clinical, translational, and basic research. More recently, the integration of histopathology with molecular features for tumor classification has marked an important paradigm shift in brain tumor diagnosis. In a similar manner, treatment response monitoring in neuro-oncology has made considerable progress. While most techniques are still in their inception, there is an emerging body of evidence for clinical application. Further research will be critically important for the development of impactful breakthroughs in this area of the field.

Downfield Proton MRSI at 3 Tesla: A Pilot Study in Human Brain Tumors

PURPOSE

To investigate the use of 3D downfield proton magnetic resonance spectroscopic imaging (DF-MRSI) for evaluation of tumor recurrence in patients with glioblastoma (GBM).

METHODS

Seven patients (4F, age range 44-65 and mean ± standard deviation 59.3 ± 7.5 years) with previously treated GBM were scanned using a recently developed 3D DF-MRSI sequence at 3T. Short TE 3D DF-MRSI and water reference 3D-MRSI scans were collected with a nominal spatial resolution of 0.7 cm3. DF volume data in eight slices covered 12 cm of brain in the cranio-caudal axis. Data were analyzed using the 'LCModel' program and a basis set containing nine peaks ranging in frequency between 6.83 to 8.49 ppm. The DF8.18 (assigned to amides) and DF7.90 peaks were selected for the creation of metabolic images and statistical analysis. Longitudinal MR images and clinical history were used to classify brain lesions as either recurrent tumor or treatment effect, which may include necrosis. DF-MRSI data were compared between lesion groups (recurrent tumor, treatment effect) and normal-appearing brain.

RESULTS

Of the seven brain tumor patients, two were classified as having recurrent tumor and the rest were classified as treatment effect. Amide metabolite levels from recurrent tumor regions were significantly (p < 0.05) higher compared to both normal-appearing brain and treatment effect regions. Amide levels in lesion voxels classified as treatment effect were significantly lower than normal brain.

CONCLUSIONS

3D DF-MRSI in human brain tumors at 3T is feasible and was well tolerated by all patients enrolled in this preliminary study. Amide levels measured by 3D DF-MRSI were significantly different between treatment effect and tumor regrowth.

Epidemiology and survival outcomes of synchronous and metachronous brain metastases: a retrospective population-based study

OBJECTIVE

Brain metastases (BMs) are the most common CNS tumors, yet their prevalence is difficult to determine. Most studies only report synchronous metastases, which make up a fraction of all BMs. The authors report the incidence and prognosis of patients with synchronous and metachronous BMs over a decade.

METHODS

Study data were obtained from the TriNetX Research Network. Patients were included if they had a primary cancer diagnosis and a BM diagnosis, with primary cancer occurring between January 1, 2013, and January 1, 2023. Metachronous BM was defined as BM diagnosed more than 2 months after the primary cancer. Cohorts were balanced by propensity score matching for age, extracranial metastasis, and antineoplastic or radiation therapy. Kaplan-Meier plots were used to evaluate survival differences between synchronous and metachronous BMs and associations with clinical conditions. A log-rank test was used to evaluate BM-free survival for metachronous BM and overall survival (OS) for all BMs. Hazard ratios and 95% CIs were calculated.

RESULTS

Of the 11,497,663 patients with 15 primary cancers identified, 300,863 (2.6%) developed BMs. BMs most commonly arose from lung and breast cancers and melanoma. Of all BMs, 113,827 (37.8%) presented synchronously and 187,036 (62.2%) presented metachronously. Lung and bronchial cancer had the highest metastasis rate (11.0%) and the highest synchronous presentation (51.0%). For metachronous presentations, the time from primary diagnosis to metastasis ranged from 1.3 to 2.5 years, averaging 1.8 years. Metachronous BM diagnosis was associated with longer survival over synchronous BM from primary diagnosis (11.54 vs 37.41 months, p < 0.0001), but shorter survival than extracranial metastases without BM (38.75 vs 69.18 months, p < 0.0001). Antineoplastic therapy prior to BM was associated with improved BM-free survival (4.46 vs 17.80 months, p < 0.0001) and OS (25.15 vs 42.26 months, p < 0.0001). Radiotherapy showed a similar effect that was statistically significant but modest for BM-free survival (5.25 vs 11.44 months, p < 0.0001) and OS (30.13 vs 32.82 months, p < 0.0001).

CONCLUSIONS

The majority of BMs present metachronously and arise within 2 years of primary cancer diagnosis. The substantial rate of BMs presenting within 6 months of primary cancer, especially liver, lung, and pancreatic cancer, may guide future recommendations on intracranial staging. Antineoplastic therapy prior to the development of BM may prolong the time before metastasis and improve survival. Further characterization of this population can better inform screening, prevention, and treatment efforts.

Abstract 4483: Distinct spatial distribution patterns of ALK-inhibitor naïve versus ALK-inhibitor treated ALK-positive NSCLC brain metastases

Background: Non-small cell lung cancer (NSCLC) with anaplastic lymphoma kinase rearrangement (ALK+) has a high affinity to form brain metastases (BrM). The cumulative incidence of BrMs in ALK+ lung cancer is over 50%, despite highly effective ALK tyrosine kinase inhibitors (TKIs) with CNS activity. Pharmacokinetic (PK) data from other CNS-active lung cancer TKIs (e.g., osimertinib) have revealed major brain white vs. gray matter drug concentration differences, raising the possibility of a PK-driven effect on BrM formation and response. This study aims to compare the size and distribution of ALK+ NSCLC BrMs at diagnosis in a TKI-naïve and TKI-exposed cohort.

Methods: We retrospectively reviewed brain MRIs from the date of BrM diagnosis for patients with ALK+ NSCLC at Johns Hopkins. Demographic and clinical information were collected by chart review. Each tumor was marked in a standard space brain model in the corresponding anatomic location represented by a sphere of corresponding diameter using 3D Slicer 4.11. FreeSurfer white-gray matter atlases were used to assess BrM distribution. The data for patients who were on TKI vs TKI-naïve at the time of BrM diagnosis were then analyzed separately. T-tests were used to compare the metastatic burden (sum of BrM diameters), mean BrM diameter per patient, number of BM per patient, per individual mean of white matter exclusive (defined as no overlap with gray matter) and deep white matter (≥5mm away from gray matter) BrMs between patient groups.

Results: 429 BrMs were identified in 39 patients, with 25 patients being TKI-naïve at the time of BrM diagnosis while 14 patients were on TKI therapy. TKI-exposed patients had significantly smaller BrM diameters than those in the TKI-naïve group (6.1±3.8 vs 10.2±5.5mm, p=0.02). While metastatic burden was very similar between the groups, the mean number of BrM per patient was numerically higher in the TKI-exposed group (10.6±11.9 vs 6.2±9.5; p=0.22). Notably, patients in the TKI-exposed group also had higher numbers of white matter exclusive (3.5±4.4 vs 1.4±2.0, p=0.05) and deep white matter metastases (3.2±4.3 vs 1.3±2.0, p=0.06) than those who were TKI-naïve.

Conclusion: Our data highlight the differences in BrM characteristics among ALK+ NSCLC exposed to ALK TKI. TKI therapy was associated with similar BrM burden but smaller individual lesions that were more likely to be exclusive to the white matter where drug concentrations might be significantly lower. These findings suggest that suboptimal drug CNS distribution in the white matter may underly brain progression of ALK+ NSCLC despite TKI therapy. Spatial analyses evaluating ALK TKIs of varying CNS penetrance and later disease time points in more granular anatomic regions are ongoing.

Citation Format: Tia Cheunkarndee, Paola Ganem, Kristen A. Marrone, Joseph C. Murray, Josephine L. Feliciano, Christine L. Hann, Susan C. Scott, David Ettinger, Valsamo Anagnostou, Patrick M. Forde, Julie R. Brahmer, Benjamin P. Levy, Vincent Lam, David O. Kamson. Distinct spatial distribution patterns of ALK-inhibitor naïve versus ALK-inhibitor treated ALK-positive NSCLC brain metastases. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4483.

In-vivo magnetic resonance spectroscopy of lactate as a non-invasive biomarker of dichloroacetate activity in cancer and non-cancer central nervous system disorders

The adverse effects of lactic acidosis in the cancer microenvironment have been increasingly recognized. Dichloroacetate (DCA) is an orally bioavailable, blood brain barrier penetrable drug that has been extensively studied in the treatment of mitochondrial neurologic conditions to reduce lactate production. Due to its effect reversing aerobic glycolysis (i.e., Warburg-effect) and thus lactic acidosis, DCA became a drug of interest in cancer as well. Magnetic resonance spectroscopy (MRS) is a well-established, non-invasive technique that allows detection of prominent metabolic changes, such as shifts in lactate or glutamate levels. Thus, MRS is a potential radiographic biomarker to allow spatial and temporal mapping of DCA treatment. In this systematic literature review, we gathered the available evidence on the use of various MRS techniques to track metabolic changes after DCA administration in neurologic and oncologic disorders. We included in vitro, animal, and human studies. Evidence confirms that DCA has substantial effects on lactate and glutamate levels in neurologic and oncologic disease, which are detectable by both experimental and routine clinical MRS approaches. Data from mitochondrial diseases show slower lactate changes in the central nervous system (CNS) that correlate better with clinical function compared to blood. This difference is most striking in focal impairments of lactate metabolism suggesting that MRS might provide data not captured by solely monitoring blood. In summary, our findings corroborate the feasibility of MRS as a pharmacokinetic/pharmacodynamic biomarker of DCA delivery in the CNS, that is ready to be integrated into currently ongoing and future human clinical trials using DCA.

Epidemiological trends, prognostic factors, and survival outcomes of synchronous brain metastases from 2015 to 2019: a population-based study

Background

Brain metastases (BM) constitute a significant cause of oncological mortality. Statistics on the incidence of BM are limited because of the lack of systematic nationwide reporting. We report the incidence of synchronous brain metastases (sBM), defined as BM identified at the time of primary cancer diagnosis from 2015-2019 using NCI’s Surveillance, Epidemiology, and End Results (SEER) Program database.

Methods

We identified 1,872,057 patients with malignancies between 2015-2019 from the SEER 17 Registries database, including 35,986 (1.9%) patients with sBM. Age-adjusted incidence rates were examined using the NCI Joinpoint software. Kaplan-Meier curves and a multivariate Cox regression model were used to investigate survival.

Results

The incidence rate of sBM from 2015 to 2019 was 7.1 persons per 100,000. Lung and bronchus cancers had the highest incidence of sBM (5.18 to 5.64 per 100,000), followed by melanoma (0.30 to 0.34 per 100,000) and breast cancers (0.24 to 0.30 per 100,000). In children, renal tumors had the highest sBM incidence. SBM were associated with poorer survival than extracranial metastases only (HR: 1.40 [95%CI: 1.39 – 1.42], P&lt;0.001). We observed better survival in white patients relative to non-white patients with sBM (HR: 0.91 [95%CI: 0.90 - 0.94], P&lt;0.001).

Conclusions

The incidence rate of sBM has remained similar to rates reported over the last 9 years, with the majority associated with primary lung and bronchus cancers. SBM represent a national healthcare burden with tremendous mortality in pediatric and adult populations. This population may benefit from improved screening and treatment strategies.

Label-Free Assessment of Mannitol Accumulation Following Osmotic Blood-Brain Barrier Opening Using Chemical Exchange Saturation Transfer Magnetic Resonance Imaging

PURPOSE

Mannitol is a hyperosmolar agent for reducing intracranial pressure and inducing osmotic blood-brain barrier opening (OBBBO). There is a great clinical need for a non-invasive method to optimize the safety of mannitol dosing. The aim of this study was to develop a label-free Chemical Exchange Saturation Transfer (CEST)-based MRI approach for detecting intracranial accumulation of mannitol following OBBBO.

METHODS

In vitro MRI was conducted to measure the CEST properties of D-mannitol of different concentrations and pH. In vivo MRI and MRS measurements were conducted on Sprague-Dawley rats using a Biospec 11.7T horizontal MRI scanner. Rats were catheterized at the internal carotid artery (ICA) and randomly grouped to receive either 1 mL or 3 mL D-mannitol. CEST MR images were acquired before and at 20 min after the infusion.

RESULTS

In vitro MRI showed that mannitol has a strong, broad CEST contrast at around 0.8 ppm with a mM CEST MRI detectability. In vivo studies showed that CEST MRI could effectively detect mannitol in the brain. The low dose mannitol treatment led to OBBBO but no significant mannitol accumulation, whereas the high dose regimen resulted in both OBBBO and mannitol accumulation. The CEST MRI findings were consistent with ¹H-MRS and Gd-enhanced MRI assessments.

CONCLUSION

We demonstrated that CEST MRI can be used for non-invasive, label-free detection of mannitol accumulation in the brain following BBBO treatment. This method may be useful as a rapid imaging tool to optimize the dosing of mannitol-based OBBBO and improve its safety and efficacy.

Dynamic contrast-enhanced CEST MRI using a low molecular weight dextran

Natural and synthetic sugars have great potential for developing highly biocompatible and translatable chemical exchange saturation transfer (CEST) MRI contrast agents. In this study, we aimed to develop the smallest clinically available form of dextran, Dex1 (molecular weight, MW ~ 1 kDa), as a new CEST agent. We first characterized the CEST properties of Dex1 in vitro at 11.7 T and showed that the Dex1 had a detectable CEST signal at ~1.2 ppm, attributed to hydroxyl protons. In vivo CEST MRI studies were then carried out on C57BL6 mice bearing orthotopic GL261 brain tumors (n = 5) using a Bruker BioSpec 11.7 T MRI scanner. Both steady-state full Z-spectral images and single offset (1.2 ppm) dynamic dextran-enhanced (DDE) images were acquired before and after the intravenous injection of Dex1 (2 g/kg). The steady-state Z-spectral analysis showed a significantly higher CEST contrast enhancement in the tumor than in contralateral brain (∆MTRasym1.2 ppm  = 0.010 ± 0.006 versus 0.002 ± 0.008, P = 0.0069) at 20 min after the injection of Dex1. Pharmacokinetic analyses of DDE were performed using the area under the curve (AUC) in the first 10 min after Dex1 injection, revealing a significantly higher uptake of Dex1 in the tumor than in brain tissue for tumor-bearing mice (AUC[0-10 min] = 21.9 ± 4.2 versus 5.3 ± 6.4%·min, P = 0.0294). In contrast, no Dex1 uptake was foundling in the brains of non-tumor-bearing mice (AUC[0-10 min] = -1.59 ± 2.43%·min). Importantly, the CEST MRI findings were consistent with the measurements obtained using DCE MRI and fluorescence microscopy, demonstrating the potential of Dex1 as a highly translatable CEST MRI contrast agent for assessing tumor hemodynamics.

Treatment of Déjerine-Roussy syndrome pain with scrambler therapy

Aim: Déjerine-Roussy syndrome or central thalamic pain can be devastating, and treatment with drugs and even deep brain stimulation can be unsatisfactory. Scrambler therapy is a form of neuromodulation that uses external skin electrodes to send a 'non-pain' signal to the brain, with some success in difficult-to-treat syndromes such as neuromyelitis optica spectrum disorder. We used scrambler therapy to treat a patient with 6 years of disabling Déjerine-Roussy syndrome pain. Methods: A 56-year-old man received multiple daily then monthly treatments with electrode pairs placed just above the area of distal pain. Each treatment was for 40 min. Results: His allodynia and hyperalgesia resolved within 10 min, and his pain score fell to almost zero after 30 min. Months later, he resumed normal activity and is off all his pain medications. No side effects were noted. Conclusion: Scrambler therapy appeared to reverse 6 years of disabling pain safely and economically, and continues to be effective. Further multi-institutional trials are warranted for this rare syndrome.

Occult teratoma in a case of N-methyl-D-aspartate receptor encephalitis

N-methyl-D-aspartate receptor encephalitis (NMDARe) is one of 13 autoimmune-mediated encephalitides that have been discovered over the last decade. This case report describes the course of a 26-year-old female who presented with new-onset seizures and insomnia, complicated by encephalitis. The initial workup ruled out common causes of encephalitis, while a transvaginal ultrasound (TVUS), and computed tomography (CT) scans of the chest, abdomen, and pelvis did not identify a mass. Based on the suspicion that she may have autoimmune encephalitis, the patient was treated with intravenous immunoglobulins and plasma exchange, but continued to deteriorate. Whole-body positron emission tomography (PET) scan identified a small hypermetabolic pelvic mass. Shortly thereafter serum and cerebral spinal fluid NMDAR antibody titers were reported as positive, prompting repetition of the TVUS, which confirmed the presence of an ovarian teratoma. The patient had a laparoscopic oophorectomy with subsequent resolution of her symptoms, further confirming the diagnosis. Despite the sensitivities of TVUS and CT of up to 94% and 98%, respectively, the teratoma was unusually small, necessitating the addition of a PET scan to identify the lesion. These neoplasms are thought to have low uptake on PET; however, it is possible that focal inflammation may have enhanced the detection. It is unlikely that the teratoma grew during hospitalization as the average growth rate is 1.8 mm per year. Regardless, the lesson that can be learned is that imaging modalities beyond CT and TVUS, such as PET, can be helpful, as identification of a resectable tumor may alter management and ultimately improve outcomes.

State-of-the-art considerations in small cell lung cancer brain metastases

BACKGROUND

Small cell lung cancer (SCLC) frequently leads to development of brain metastases. These unfortunately continue to be associated with short survival. Substantial advances have been made in our understanding of the underlying biology of disease. This understanding on the background of previously evaluated and currently utilized therapeutic treatments can help guide the next steps in investigations into this disease with the potential to influence future treatments.

DESIGN

A comprehensive review of the literature covering epidemiology, pathophysiology, imaging characteristics, prognosis, and therapeutic management of SCLC brain metastases was performed.

RESULTS

SCLC brain metastases continue to have a poor prognosis. Both unique aspects of SCLC brain metastases as well as features seen more universally across other solid tumor brain metastases are discussed. Systemic therapeutic studies and radiotherapeutic approaches are reviewed.

CONCLUSIONS

A clearer understanding of SCLC brain metastases will help lay the framework for studies which will hopefully translate into meaningful therapeutic options for these patients.

Prognostic Molecular and Imaging Biomarkers in Primary Glioblastoma

PURPOSE

Several molecular glioma markers (including isocitrate dehydrogenase 1 [IDH1] mutation, amplification of the epidermal growth factor receptor [EGFR], and methylation of the O6-methylguanine-DNA methyltransferase [MGMT] promoter) have been associated with glioblastoma survival. In this study, we examined the association between tumoral amino acid uptake, molecular markers, and overall survival in patients with IDH1 wild-type (primary) glioblastoma.

PATIENTS AND METHODS

Twenty-one patients with newly diagnosed IDH1 wild-type glioblastomas underwent presurgical MRI and PET scanning with alpha[C-11]-L-methyl-tryptophan (AMT). MRI characteristics (T2- and T1-contrast volume), tumoral tryptophan uptake, PET-based metabolic tumor volume, and kinetic variables were correlated with prognostic molecular markers (EGFR and MGMT) and overall survival.

RESULTS

EGFR amplification was associated with lower T1-contrast volume (P = 0.04) as well as lower T1-contrast/T2 volume (P = 0.04) and T1-contrast/PET volume ratios (P = 0.02). Tumors with MGMT promoter methylation showed lower metabolic volume (P = 0.045) and lower tumor/cortex AMT unidirectional uptake ratios than those with unmethylated MGMT promoter (P = 0.009). While neither EGFR amplification nor MGMT promoter methylation was significantly associated with survival, high AMT tumor/cortex uptake ratios on PET were strongly prognostic for longer survival (hazards ratio, 30; P = 0.002). Estimated mean overall survival was 26 months in patients with high versus 8 months in those with low tumoral AMT uptake ratios.

CONCLUSIONS

The results demonstrate specific MRI and amino acid PET imaging characteristics associated with EGFR amplification and MGMT promoter methylation in patients with primary glioblastoma. High tryptophan uptake on PET may identify a subgroup with prolonged survival.

Cortical thickness asymmetries and surgical outcome in neocortical epilepsy

PURPOSE

We evaluated if cortical thickness measures were associated with surgical outcome in patients with non-lesional neocortical epilepsy.

METHODS

Twenty-one young patients (age: 2.4-19.7years) with epilepsy of neocortical origin and normal MRI underwent two-stage epilepsy surgery with subdural EEG monitoring. Cortical thickness was measured on presurgical volumetric MRI using the FreeSurfer software. The prognostic value of hemispheric and lobar/regional cortical thickness measures for 1-year and 2-year post-surgical seizure outcome has been analyzed.

RESULTS

At one-year follow-up, 14 patients (67%) were seizure-free. Hemispheric and frontal lobe cortical thickness showed no/minimal asymmetry in seizure-free patients but thinner cortex ipsilateral to the seizure focus in those with recurrent seizures (p=0.02). More robust differences were found in patients≥6years of age (p=0.006 for frontal asymmetries), whose cortical thickness asymmetries remained prognostic for 2-year post-surgical outcome (p=0.007). By using an optimal cutoff threshold based on a receiver operating characteristic analysis, mean hemispheric asymmetry predicted one-year seizure freedom with 93% sensitivity and 71% specificity in the whole group, and with 100% sensitivity and 92% specificity in patients≥6years of age.

CONCLUSION

In patients with neocortical epilepsy and normal MRI, neocortical thinning in the epileptic hemisphere, particularly in frontal cortex, is associated with poor surgical outcome. Although these results require validation in a larger cohort prospectively, these data suggest that presurgical evaluation of cortical thickness may assist in identification of patients at high risk for surgical failure.

Imaging cerebral tryptophan metabolism in brain tumor-associated depression

BACKGROUND

Depression in patients with brain tumors is associated with impaired quality of life and shorter survival. Altered metabolism of tryptophan to serotonin and kynurenine metabolites may play a role in tumor-associated depression. Our recent studies with alpha[(11)C]methyl-L-tryptophan (AMT)-PET in brain tumor patients indicated abnormal tryptophan metabolism not only in the tumor mass but also in normal-appearing contralateral brain. In the present study, we explored if tryptophan metabolism in such brain regions is associated with depression.

METHODS

Twenty-one patients (mean age: 57 years) with a brain tumor (10 meningiomas, 8 gliomas, and 3 brain metastases) underwent AMT-PET scanning. MRI and AMT-PET images were co-registered, and AMT kinetic parameters, including volume of distribution (VD', an estimate of net tryptophan transport) and K (unidirectional uptake, related to tryptophan metabolism), were measured in the tumor mass and in unaffected cortical and subcortical regions contralateral to the tumor. Depression scores (based on the Beck Depression Inventory-II [BDI-II]) were correlated with tumor size, grade, type, and AMT-PET variables.

RESULTS

The mean BDI-II score was 12 ± 10 (range: 2-33); clinical levels of depression were identified in seven patients (33 %). High BDI-II scores were most strongly associated with high thalamic AMT K values both in the whole group (Spearman's rho = 0.63, p = 0.004) and in the subgroup of 18 primary brain tumors (r = 0.68, p = 0.004). Frontal and striatal VD' values were higher in the depressed subgroup than in non-depressed patients (p < 0.05); the group difference was even more robust when moderately/severely depressed patients were compared to patients with no/mild depression (frontal: p = 0.005; striatal: p < 0.001). Tumor size, grade, and tumor type were not related to depression scores.

CONCLUSIONS

Abnormalities of tryptophan transport and metabolism in the thalamus, striatum, and frontal cortex, measured by PET, are associated with depression in patients with brain tumor. These changes may indicate an imbalance between the serotonin and kynurenine pathways and serve as a molecular imaging marker of brain tumor-associated depression.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02367469.

Multi-modal imaging of tumor cellularity and Tryptophan metabolism in human Gliomas

Background

To assess gliomas using image-based estimation of cellularity, we utilized isotropic diffusion spectrum imaging (IDSI) on clinically feasible diffusion tensor imaging (DTI) and compared it with amino acid uptake measured by α[¹¹C]methyl-L-tryptophan positron emission tomography (AMT-PET).

Methods

In 10 patients with a newly-diagnosed glioma, metabolically active tumor regions were defined in both FLAIR hyperintense areas and based on increased uptake on AMT-PET. A recently developed independent component analysis with a ball and stick model was extended to perform IDSI in clinical DTI data. In tumor regions, IDSI was used to define tumor cellularity which was compared between low and high grade glioma and correlated with the glioma proliferative index.

Results

The IDSI-derived cellularity values were elevated in both FLAIR and AMT-PET-derived regions of high-grade gliomas. ROC curve analysis found that the IDSI-derived cellularity can provide good differentiation of low-grade from high-grade gliomas (accuracy/sensitivity/specificity of 0.80/0.80/0.80). . Both apparent diffusion coefficient (ADC) and IDSI-derived cellularity showed a significant correlation with the glioma proliferative index (based on Ki-67 labeling; R = 0.95, p < 0.001), which was particularly strong when the tumor regions were confined to areas with high tryptophan uptake excluding areas with peritumoral edema.

Conclusion

IDSI-MRI combined with AMT-PET may provide a multi-modal imaging tool to enhance pretreatment assessment of human gliomas by evaluating tumor cellularity and differentiate low-grade form high-grade gliomas.

Electronic supplementary material

The online version of this article (doi:10.1186/s40644-015-0045-1) contains supplementary material, which is available to authorized users.

Molecular imaging correlates of tryptophan metabolism via the kynurenine pathway in human meningiomas

BACKGROUND

Increased tryptophan metabolism via the kynurenine pathway (KP) is a key mechanism of tumoral immune suppression in gliomas. However, details of tryptophan metabolism in meningiomas have not been elucidated. In this study, we evaluated in vivo tryptophan metabolism in meningiomas and compared it with gliomas using α-[(11)C]-methyl-L-tryptophan (AMT)-PET. We also explored expression patterns of KP enzymes in resected meningiomas.

METHODS

Forty-seven patients with MRI-detected meningioma (n = 16) and glioma (n = 31) underwent presurgical AMT-PET scanning. Tumoral AMT uptake and tracer kinetic parameters (including K and k3' evaluating unidirectional uptake and trapping, respectively) were measured, correlated with meningioma grade, and compared between meningiomas and gliomas. Patterns of KP enzyme expression were assessed by immunohistochemistry in all meningiomas.

RESULTS

Meningioma grade showed a positive correlation with AMT k3' tumor/cortex ratio (r = 0.75, P = .003), and this PET parameter distinguished grade I from grade II/III meningiomas with 92% accuracy. Kinetic AMT parameters could differentiate meningiomas from both low-grade gliomas (97% accuracy by k3' ratios) and high-grade gliomas (83% accuracy by K ratios). Among 3 initial KP enzymes (indoleamine 2,3-dioxygenase 1/2, and tryptophan 2,3-dioxygenase 2 [TDO2]), TDO2 showed the strongest immunostaining, particularly in grade I meningiomas. TDO2 also showed a strong negative correlation with AMT k3' ratios (P = .001).

CONCLUSIONS

PET imaging of tryptophan metabolism can provide quantitative imaging markers for differentiating grade I from grade II/III meningiomas. TDO2 may be an important driver of in vivo tryptophan metabolism in these tumors. These results can have implications for pharmacological targeting of the KP in meningiomas.

Detection of hand and leg motor tract injury using novel diffusion tensor MRI tractography in children with central motor dysfunction

PURPOSE

To examine whether an objective segmenation of corticospinal tract (CST) associated with hand and leg movements can be used to detect central motor weakness in the corresponding extremities in a pediatric population.

MATERIAL AND METHODS

This retrospective study included diffusion tensor imaging (DTI) of 25 children with central paresis affecting at least one limb (age: 9.0±4.2years, 15 boys, 5/13/7 children with left/right/both hemispheric lesions including ischemia, cyst, and gliosis), as well as 42 pediatric control subjects with no motor dysfunction (age: 9.0±5.5years, 21 boys, 31 healthy/11 non-lesional epilepsy children). Leg- and hand-related CST pathways were segmented using DTI-maximum a posteriori (DTI-MAP) classification. The resulting CST volumes were then divided by total supratentorial white matter volume, resulting in a marker called "normalized streamline volume ratio (NSVR)" to quantify the degree of axonal loss in separate CST pathways associated with leg and hand motor functions. A receiver operating characteristic curve was applied to measure the accuracy of this marker to identify extremities with motor weakness.

RESULTS

NSVR values of hand/leg CST selectively achieved the following values of accuracy/sensitivity/specificity: 0.84/0.84/0.57, 0.82/0.81/0.55, 0.78/0.75/0.55, 0.79/0.81/0.54 at a cut-off of 0.03/0.03/0.03/0.02 for right hand CST, left hand CST, right leg CST, and left leg CST, respectively. Motor weakness of hand and leg was most likely present at the cut-off values of hand and leg NSVR (i.e., 0.029/0.028/0.025/0.020 for left-hand/right-hand/left-leg/right-leg). The control group showed a moderate age-related increase in absolute CST volumes and a biphasic age-related variation of the normalized CST volumes, which were lacking in the paretic children.

CONCLUSIONS

This study demonstrates that DTI-MAP classification may provide a new imaging tool to quantify axonal loss in children with central motor dysfunction. Using this technique, we found that early-life brain lesions affect the maturational trajectory of the primary motor pathway which may be used as an effective marker to facilitate evidence-based treatment of paretic children.

Novel diffusion tensor imaging technique reveals developmental streamline volume changes in the corticospinal tract associated with leg motor control

BACKGROUND

Diffusion tensor imaging (DTI) has expanded our knowledge of corticospinal tract (CST) anatomy and development. However, previous developmental DTI studies assessed the CST as a whole, overlooking potential differences in development of its components related to control of the upper and lower extremities. The present cross-sectional study investigated age-related changes, side and gender differences in streamline volume of the leg- and hand-related segments of the CST in children.

SUBJECTS AND METHODS

DTI data of 31 children (1-14 years; mean age: 6±4 years; 17 girls) with normal conventional MRI were analyzed. Leg- and hand-related CST streamline volumes were quantified separately, using a recently validated novel tractography approach. CST streamline volumes on both sides were compared between genders and correlated with age.

RESULTS

Higher absolute streamline volumes were found in the left leg-related CST compared to the right (p=0.001) without a gender effect (p=0.4), whereas no differences were found in the absolute hand-related CST volumes (p>0.4). CST leg-related streamline volumes, normalized to hemispheric white matter volumes, declined with age in the right hemisphere only (R=-.51; p=0.004). Absolute leg-related CST streamline volumes showed similar, but slightly weaker correlations. Hand-related absolute or normalized CST streamline volumes showed no age-related variations on either side.

CONCLUSION

These results suggest differential development of CST segments controlling hand vs. leg movements. Asymmetric volume changes in the lower limb motor pathway may be secondary to gradually strengthening left hemispheric dominance and is consistent with previous data suggesting that footedness is a better predictor of hemispheric lateralization than handedness.

Comparison of amino acid positron emission tomographic radiotracers for molecular imaging of primary and metastatic brain tumors

Positron emission tomography (PET) is an imaging technology that can detect and characterize tumors based on their molecular and biochemical properties, such as altered glucose, nucleoside, or amino acid metabolism. PET plays a significant role in the diagnosis, prognostication, and treatment of various cancers, including brain tumors. In this article, we compare uptake mechanisms and the clinical performance of the amino acid PET radiotracers (l-[methyl-11C]methionine [MET], 18F-fluoroethyl-tyrosine [FET], 18F-fluoro-l-dihydroxy-phenylalanine [FDOPA], and 11C-alpha-methyl-l-tryptophan [AMT]) most commonly used for brain tumor imaging. First, we discuss and compare the mechanisms of tumoral transport and accumulation, the basis of differential performance of these radioligands in clinical studies. Then we summarize studies that provided direct comparisons among these amino acid tracers and to clinically used 2-deoxy-2[18F]fluoro-d-glucose [FDG] PET imaging. We also discuss how tracer kinetic analysis can enhance the clinical information obtained from amino acid PET images. We discuss both similarities and differences in potential clinical value for each radioligand. This comparative review can guide which radiotracer to favor in future clinical trials aimed at defining the role of these molecular imaging modalities in the clinical management of brain tumor patients.

Clinical significance of tryptophan metabolism in the nontumoral hemisphere in patients with malignant glioma

α-(11)C-methyl-L-tryptophan (AMT) PET allows evaluation of brain serotonin synthesis and can also track upregulation of the immunosuppressive kynurenine pathway in tumor tissue. Increased AMT uptake is a hallmark of World Health Organization grade III-IV gliomas. Our recent study also suggested decreased frontal cortical AMT uptake in glioma patients contralateral to the tumor. The clinical significance of extratumoral tryptophan metabolism has not been established. In the present study, we investigated clinical correlates of tryptophan metabolic abnormalities in the nontumoral hemisphere of glioma patients.

METHODS

Standardized AMT uptake values (SUVs) and the uptake rate constant of AMT (K [mL/g/min], a measure proportional to serotonin synthesis in nontumoral gray matter) were quantified in the frontal and temporal cortex and thalamus in the nontumoral hemisphere in 77 AMT PET scans of 66 patients (41 men, 25 women; mean age ± SD, 55 ± 15 y) with grade III-IV gliomas. These AMT values were determined before treatment in 35 and after treatment in 42 patients and were correlated with clinical variables and survival.

RESULTS

AMT uptake in the thalamus showed a moderate age-related increase before treatment (SUV, r = 0.39, P = 0.02) but decrease after treatment (K, r = -0.33, P = 0.057). Women had higher thalamic SUVs before treatment (P = 0.037) and higher thalamic (P = 0.013) and frontal cortical K values (P = 0.023) after treatment. In the posttreatment glioma group, high thalamic SUVs and high thalamocortical SUV ratios were associated with short survival in Cox regression analysis. The thalamocortical ratio remained strongly prognostic (P < 0.01) when clinical predictors, including age, glioma grade, and time since radiotherapy, were entered in the regression model. Long interval between radiotherapy and posttreatment AMT PET as well as high radiation dose affecting the thalamus were associated with lower contralateral thalamic or cortical AMT uptake values.

CONCLUSION

These observations provide evidence for altered tryptophan uptake in contralateral cortical and thalamic brain regions in glioma patients after initial therapy, suggesting treatment effects on the serotonergic system. Low thalamic tryptophan uptake appears to be a strong, independent predictor of long survival in patients with previous glioma treatment.

Patterns of structural reorganization of the corticospinal tract in children with Sturge-Weber syndrome

BACKGROUND

Reorganization of the corticospinal tract after early damage can limit motor deficit. In this study, we explored patterns of structural corticospinal tract reorganization in children with Sturge-Weber syndrome.

METHODS

Five children (age 1.5-7 years) with motor deficit resulting from unilateral Sturge-Weber syndrome were studied prospectively and longitudinally (1-2 years follow-up). Corticospinal tract segments belonging to hand and leg movements were separated and their volume was measured by diffusion tensor imaging tractography using a recently validated method. Corticospinal tract segmental volumes were normalized and compared between the Sturge-Weber syndrome children and age-matched healthy controls. Volume changes during follow-up were also compared with clinical motor symptoms.

RESULTS

In the Sturge-Weber syndrome children, hand-related (but not leg-related) corticospinal tract volumes were consistently decreased in the affected cerebral hemisphere at baseline. At follow-up, two distinct patterns of hand corticospinal tract volume changes emerged. (1) Two children with extensive frontal lobe damage showed a corticospinal tract volume decrease in the lesional hemisphere and a concomitant increase in the nonlesional (contralateral) hemisphere. These children developed good hand grasp but no fine motor skills. (2) The three other children, with relative sparing of the frontal lobe, showed an interval increase of the normalized hand corticospinal tract volume in the affected hemisphere; these children showed no gross motor deficit at follow-up.

CONCLUSIONS

Diffusion tensor imaging tractography can detect differential abnormalities in the hand corticospinal tract segment both ipsi- and contralateral to the lesion. Interval increase in the corticospinal tract hand segment suggests structural reorganization, whose pattern may determine clinical motor outcome and could guide strategies for early motor intervention.

Increased tryptophan uptake on PET has strong independent prognostic value in patients with a previously treated high-grade glioma

BACKGROUND

Previously, we demonstrated the high accuracy of alpha-[(11)C]methyl-L-tryptophan (AMT) PET for differentiating recurrent gliomas from radiation injury. The present study evaluated the prognostic value of increased AMT uptake in patients with previously treated high-grade glioma.

METHODS

AMT-PET was performed in 39 patients with suspected recurrence of World Health Organization grades III-IV glioma following surgical resection, radiation, and chemotherapy. Mean and maximum standardized uptake values (SUVs) and unidirectional AMT uptake (K) were measured in brain regions suspicious for tumor and compared with the contralateral cortex (ie, background). Optimal cutoff thresholds for 1-year survival prediction were determined for each AMT parameter and used for calculating the prognostic value of high (above threshold) versus low (below threshold) values for post-PET overall survival (OS).

RESULTS

In univariate analyses, 1-year survival was strongly associated with 3 AMT parameters (SUVmax, SUVmean, and tumor-to-background K-ratio; odds ratios: 21.3-25.6; P ≤ .001) and with recent change in MRI contrast enhancement (odds ratio: 14.7; P = .02). Median OS was 876 days in the low- versus 177 days in the high-AMT groups (log-rank P < .001). In multivariate analyses, all 3 AMT parameters remained strong predictors of survival: high AMT values were associated with unfavorable 1-year survival (binary regression P ≤ .003) and shorter overall survival in the whole group (Cox regression hazard ratios: 5.3-10.0) and in patients with recent enhancement change on MRI as well (hazard ratios: 7.0-9.3; P ≤ .001).

CONCLUSION

Increased AMT uptake on PET is highly prognostic for 1-year and overall survival, independent of MRI contrast enhancement and other prognostic factors in patients with a previously treated high-grade glioma.

Differentiation of glioblastomas from metastatic brain tumors by tryptophan uptake and kinetic analysis: a positron emission tomographic study with magnetic resonance imaging comparison

Differentiating high-grade gliomas from solitary brain metastases is often difficult by conventional magnetic resonance imaging (MRI); molecular imaging may facilitate such discrimination. We tested the accuracy of α[11C]methyl-l-tryptophan (AMT)-positron emission tomography (PET) to differentiate newly diagnosed glioblastomas from brain metastases. AMT-PET was performed in 36 adults with suspected brain malignancy. Tumoral AMT accumulation was measured by standardized uptake values (SUVs). Tracer kinetic analysis was also performed to separate tumoral net tryptophan transport (by AMT volume of distribution [VD]) from unidirectional uptake rates using dynamic PET and blood input function. Differentiating the accuracy of these PET variables was evaluated and compared to conventional MRI. For glioblastoma/metastasis differentiation, tumoral AMT SUV showed the highest accuracy (74%) and the tumor/cortex VD ratio had the highest positive predictive value (82%). The combined accuracy of MRI (size of contrast-enhancing lesion) and AMT-PET reached up to 93%. For ring-enhancing lesions, tumor/cortex SUV ratios were higher in glioblastomas than in metastatic tumors and could differentiate these two tumor types with > 90% accuracy. These results demonstrate that evaluation of tryptophan accumulation by PET can enhance pretreatment differentiation of glioblastomas and metastatic brain tumors. This approach may be particularly useful in patients with a newly diagnosed solitary ring-enhancing mass.

In vivo metabolism of tryptophan in meningiomas is mediated by indoleamine 2,3-dioxygenase 1

Expression and activity of indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting step of the kynurenine pathway of tryptophan catabolism, can enable tumor cells to effectively evade the host's immune response. The potential role of this system was investigated in meningiomas. Surgical specimens from 22 patients with meningiomas were used for cellular, immunological and molecular techniques (immunofluorescence, western blotting, RT-PCR and biochemical assay of enzyme activity) to investigate the expression and activity of IDO. In addition, PET imaging was obtained preoperatively in 10 patients using the tracer α-[ ( 11) C]methyl-L-tryptophan (AMT) which interrogates the uptake and metabolism of tryptophan. Strong AMT accumulation was noted in all meningiomas by PET imaging indicating in vivo tryptophan uptake. Freshly-resected meningiomas expressed both LAT1, the tryptophan transporter system and IDO, demonstrating an active kynurenine pathway. Dissociated meningioma cells lost IDO expression. Following exposure to interferon-γ (IFNγ), IDO expression was reinduced and could be blocked by a selective IDO1 inhibitor. IDO activity may represent an element of local self-protection by meningiomas and could be targeted by emerging IDO1 inhibitors.