Analysis of metabolic indices in regions of abnormal perfusion in patients with high-grade glioma

Multi-parametric hyperpolarized 13C/1H imaging reveals Warburg-related metabolic dysfunction and associated regional heterogeneity in high-grade human gliomas

BACKGROUND

Dynamic hyperpolarized (HP)-13C MRI has enabled real-time, non-invasive assessment of Warburg-related metabolic dysregulation in glioma using a [1-13C]pyruvate tracer that undergoes conversion to [1-13C]lactate and [13C]bicarbonate. Using a multi-parametric 1H/HP-13C imaging approach, we investigated dynamic and steady-state metabolism, together with physiological parameters, in high-grade gliomas to characterize active tumor.

METHODS

Multi-parametric 1H/HP-13C MRI data were acquired from fifteen patients with progressive/treatment-naïve glioblastoma [prog/TN GBM, IDH-wildtype (n = 11)], progressive astrocytoma, IDH-mutant, grade 4 (G4AIDH+, n = 2) and GBM manifesting treatment effects (n = 2). Voxel-wise regional analysis of the cohort with prog/TN GBM assessed imaging heterogeneity across contrast-enhancing/non-enhancing lesions (CEL/NEL) and normal-appearing white matter (NAWM) using a mixed effects model. To enable cross-nucleus parameter association, normalized perfusion, diffusion, and dynamic/steady-state (HP-13C/spectroscopic) metabolic data were collectively examined at the 13C resolution. Prog/TN GBM were similarly compared against progressive G4AIDH+ and treatment effects.

RESULTS

Regional analysis of Prog/TN GBM metabolism revealed statistically significant heterogeneity in 1H choline-to-N-acetylaspartate index (CNI)max, [1-13C]lactate, modified [1-13C]lactate-to-[1-13C]pyruvate ratio (CELval > NELval > NAWMval); [1-13C]lactate-to-[13C]bicarbonate ratio (CELval > NELval/NAWMval); and 1H-lactate (CELval/NELval > NAWMundetected). Significant associations were found between normalized perfusion (cerebral blood volume, nCBV; peak height, nPH) and levels of [1-13C]pyruvate and [1-13C]lactate, as well as between CNImax and levels of [1-13C]pyruvate, [1-13C]lactate and modified ratio. GBM, by comparison to G4AIDH+, displayed lower perfusion %-recovery and modeled rate constants for [1-13C]pyruvate-to-[1-13C]lactate conversion (kPL), and higher 1H-lactate and [1-13C]pyruvate levels, while having higher nCBV, %-recovery, kPL, [1-13C]pyruvate-to-[1-13C]lactate and modified ratios relative to treatment effects.

CONCLUSIONS

GBM consistently displayed aberrant, Warburg-related metabolism and regional heterogeneity detectable by novel HP-13C/1H imaging techniques.

Longitudinal MR spectroscopy to detect progression in patients with lower-grade glioma in the surveillance phase

Background

Monitoring lower-grade gliomas (LrGGs) for disease progression is made difficult by the limits of anatomical MRI to distinguish treatment related tissue changes from tumor progression. MR spectroscopic imaging (MRSI) offers additional metabolic information that can help address these challenges. The goal of this study was to compare longitudinal changes in multiparametric MRI, including diffusion weighted imaging, perfusion imaging, and 3D MRSI, for LrGG patients who progressed at the final time-point and those who remained clinically stable.

Methods

Forty-one patients with LrGG who were clinically stable were longitudinally assessed for progression. Changes in anatomical, diffusion, perfusion and MRSI data were acquired and compared between patients who remained clinically stable and those who progressed.

Results

Thirty-one patients remained stable, and 10 patients progressed. Over the study period, progressed patients had a significantly greater increase in normalized choline, choline-to-N-acetylaspartic acid index (CNI), normalized creatine, and creatine-to-N-acetylaspartic acid index (CRNI), than stable patients. CRNI was significantly associated with progression status and WHO type. Progressed astrocytoma patients had greater increases in CRNI than stable astrocytoma patients.

Conclusions

LrGG patients in surveillance with tumors that progressed had significantly increasing choline and creatine metabolite signals on MRSI, with a trend of increasing T2 FLAIR volumes, compared to LrGG patients who remained stable. These data show that MRSI can be used in conjunction with anatomical imaging studies to gain a clearer picture of LrGG progression, especially in the setting of clinical ambiguity.

Grading of IDH-mutant astrocytoma using diffusion, susceptibility and perfusion-weighted imaging

Background

The accurate grading of IDH-mutant astrocytoma is essential to make therapeutic strategies and assess the prognosis of patients. The purpose of this study was to investigate the usefulness of DWI, SWI and DSC-PWI in grading IDH-mutant astrocytoma.

Methods

One hundred and seven patients with IDH-mutant astrocytoma who underwent DWI, SWI and DSC-PWI were retrospectively reviewed. Minimum apparent diffusion coefficient (ADC_min), intratumoral susceptibility signal intensity(ITSS) and maximum relative cerebral blood volume (rCBV_max) values were assessed. ADC_min, ITSS and rCBV_max values were compared between grade 2 vs. grade 3, grade 3 vs. grade 4 and grade 2 + 3 vs. grade 4 tumors. Logistic regression, tenfold cross-validation,and receiver operating characteristic (ROC) curve analyses were used to assess their diagnostic performances.

Results

Grade 4 IDH-mutant astrocytomas showed significantly lower ADC_min and higher rCBV_max as compared to grade 3 tumors (adjusted P < 0.001). IDH-mutant grade 3 astrocytomas showed significantly lower ITSS levels as compared with grade 4 tumors (adjusted P < 0.001). ITSS levels between IDH-mutant grade 2 and grade 3 astrocytomas were significantly different (adjusted P = 0.002). Combined the ADC_min, ITSS and rCBV_max resulted in the highest AUC for differentiation grade 2 and grade 3 tumors from grade 4 tumors.

Conclusion

ADC_min, rCBV_max and ITSS can be used for grading the IDH-mutant astrocytomas. The combination of ADC_min, ITSS and rCBV_max could improve the diagnostic performance in grading of IDH-mutant astrocytoma.

Cho/Cr ratio at MR spectroscopy as a biomarker for cellular proliferation activity and prognosis in glioma: correlation with the expression of minichromosome maintenance protein 2

BACKGROUND

Magnetic resonance (MR) spectroscopy (¹H-MRS) has been demonstrated to be useful in grading glioma, but the utility in assessing cellular proliferation activity and prognosis correlated with the expression of minichromosome maintenance protein 2 (MCM2) has not been reported.

PURPOSE

To explore the correlation between proton MR spectroscopy parameters (including choline [Cho]/creatine [Cr], N-acetyl aspartate [NAA]/Cr, and Cho/NAA ratios) and the expression of MCM2 and to further evaluate whether ¹H-MRS can predict cell proliferative activity and provide prognostic information in high-grade gliomas (HGGs).

MATERIAL AND METHODS

Forty-three patients with histopathologically confirmed gliomas were involved in this study. All patients underwent ¹H-MRS examination before surgery. Proliferative activity of gliomas was evaluated by MCM2 labeling index (LI). Pearson correlation analysis and empiric receiver operating characteristic (ROC) curves were performed. The Kaplan-Meier method and Cox regression were used for survival analysis.

RESULTS

Significant correlation was observed between the Cho/Cr ratio and MCM2 LI ( r = 0.522, P < 0.01); however, there was no correlation between MCM2 LI and the Cho/NAA or NAA/Cr ratios ( r = 0.295, P = 0.55 and r = -0.042, P = 0.788, respectively). According to ROC analysis, MCM2 LI of 50% and Cho/Cr ratio of 2.68 represented the optimized cut-off values, respectively, to distinguish longer or shorter survival than 15 months in HGGs patients. Multivariate analysis revealed that both the Cho/Cr ratio and MCM2 expression were independent prognostic markers.

CONCLUSION

Cho/Cr ratio has a potential in predicting the expression of MCM2 and can evaluate cell proliferative activity noninvasively. Both the Cho/Cr ratio and MCM2 expression are independent prognostic markers in patients with HGGs.

Magnetic Resonance (MR) Metabolic Imaging in Glioma

This review is focused on describing the use of magnetic resonance (MR) spectroscopy for metabolic imaging of brain tumors. We will first review the MR metabolic imaging findings generated from preclinical models, focusing primarily on in vivo studies, and will then describe the use of metabolic imaging in the clinical setting. We will address relatively well-established (1) H MRS approaches, as well as (31) P MRS, (13) C MRS and emerging hyperpolarized (13) C MRS methodologies, and will describe the use of metabolic imaging for understanding the basic biology of glioma as well as for improving the characterization and monitoring of brain tumors in the clinic.

Assessing and monitoring intratumor heterogeneity in glioblastoma: how far has multimodal imaging come?

Glioblastoma demonstrates imaging features of intratumor heterogeneity that result from underlying heterogeneous biological properties. This stems from variations in cellular behavior that result from genetic mutations that either drive, or are driven by, heterogeneous microenvironment conditions. Among all imaging methods available, only T1-weighted contrast-enhancing and T2-weighted fluid-attenuated inversion recovery are used in standard clinical glioblastoma assessment and monitoring. Advanced imaging modalities are still considered emerging techniques as appropriate end points and robust methodologies are missing from clinical trials. Discovering how these images specifically relate to the underlying tumor biology may aid in improving quality of clinical trials and understanding the factors involved in regional responses to treatment, including variable drug uptake and effect of radiotherapy. Upon validation and standardization of emerging MR techniques, providing information based on the underlying tumor biology, these images may allow for clinical decision-making that is tailored to an individual's response to treatment.

Inhibition of Pediatric Glioblastoma Tumor Growth by the Anti-Cancer Agent OKN-007 in Orthotopic Mouse Xenografts

Pediatric glioblastomas (pGBM), although rare, are one of the leading causes of cancer-related deaths in children, with tumors essentially refractory to existing treatments. Here, we describe the use of conventional and advanced in vivo magnetic resonance imaging (MRI) techniques to assess a novel orthotopic xenograft pGBM mouse (IC-3752GBM patient-derived culture) model, and to monitor the effects of the anti-cancer agent OKN-007 as an inhibitor of pGBM tumor growth. Immunohistochemistry support data is also presented for cell proliferation and tumor growth signaling. OKN-007 was found to significantly decrease tumor volumes (p<0.05) and increase animal survival (p<0.05) in all OKN-007-treated mice compared to untreated animals. In a responsive cohort of treated animals, OKN-007 was able to significantly decrease tumor volumes (p<0.0001), increase survival (p<0.001), and increase diffusion (p<0.01) and perfusion rates (p<0.05). OKN-007 also significantly reduced lipid tumor metabolism in responsive animals [(Lip1.3 and Lip0.9)-to-creatine ratio (p<0.05)], as well as significantly decrease tumor cell proliferation (p<0.05) and microvessel density (p<0.05). Furthermore, in relationship to the PDGFRα pathway, OKN-007 was able to significantly decrease SULF2 (p<0.05) and PDGFR-α (platelet-derived growth factor receptor-α) (p<0.05) immunoexpression, and significantly increase decorin expression (p<0.05) in responsive mice. This study indicates that OKN-007 may be an effective anti-cancer agent for some patients with pGBMs by inhibiting cell proliferation and angiogenesis, possibly via the PDGFRα pathway, and could be considered as an additional therapy for pediatric brain tumor patients.

MODELING GLIOBLASTOMA RESPONSE TO RADIOTHERAPY BY COMBINING A TWO-COMPARTMENT KINETIC MODEL AND MULTIPARAMETRIC NMR DATA

Glioblastoma are the most common and malignant primary brain tumor, and actual treatments consist of surgery (when possible), radiotherapy and chemotherapy. Recent discoveries in biology revealed the important role of radioresistant cancer stem cell in the tumor proliferation and also showed that differentiated tumor cells can revert to a stem-like state because of radiation. These discoveries can be used to create mathematical models to study and plan new optimized radiotherapy schedules. In literature, some models have already been developed on murine population. The aim of this study was to reproduce these models, to perform a sensitivity analysis to find the most sensitive parameters and to adapt them to standard schedules used with human patients. We found that the most sensitive parameters are those involving tumor cell proliferation, radio-sensibility and quiescence times of both stem and tumor cells.

Data-driven grading of brain gliomas: a multiparametric MR imaging study

PURPOSE

To grade brain gliomas by using a data-driven analysis of multiparametric magnetic resonance (MR) imaging, taking into account the heterogeneity of the lesions at MR imaging, and to compare these results with the most widespread current radiologic reporting methods.

MATERIALS AND METHODS

One hundred eighteen patients with histologically confirmed brain gliomas were evaluated retrospectively. Conventional and advanced MR sequences (perfusion-weighted imaging, MR spectroscopy, and diffusion-tensor imaging) were performed. Three evaluations were conducted: semiquantitative (based on conventional and advanced sequences with reported cutoffs), qualitative (exclusively based on conventional MR imaging), and quantitative. For quantitative analysis, four volumes of interest were placed: regions with contrast material enhancement, regions with highest and lowest signal intensity on T2-weighted images, and regions of most restricted diffusivity. Statistical analysis included t test, receiver operating characteristic (ROC) analysis, discriminant function analysis (DFA), leave-one-out cross-validation, and Kendall coefficient of concordance.

RESULTS

Significant differences were noted in age, relative cerebral blood volume (rCBV) in contrast-enhanced regions (cutoff > 2.59; sensitivity, 80%; specificity, 91%; area under the ROC curve [AUC] = 0.937; P = .0001), areas of lowest signal intensity on T2-weighted images (>2.45, 57%, 97%, 0.852, and P = .0001, respectively), restricted diffusivity regions (>2.61, 54%, 97%, 0.808, and P = .0001, respectively), and choline/creatine ratio in regions with the lowest signal intensity on T2-weighted images (>2.07, 49%, 88%, 0.685, and P = .0007, respectively). DFA that included age; rCBV in contrast-enhanced regions, areas of lowest signal intensity on T2-weighted images, and areas of restricted diffusivity; and choline/creatine ratio in areas with lowest signal intensity on T2-weighted images was used to classify 95% of patients correctly. Quantitative analysis showed a higher concordance with histologic findings than qualitative and semiquantitative methods (P < .0001).

CONCLUSION

A quantitative multiparametric MR imaging evaluation that incorporated heterogeneity at MR imaging significantly improved discrimination between low- and high-grade brain gliomas with a very high AUC (ie, 0.95), thus reducing the risk of inappropriate or delayed surgery, respectively.

MR-based hypoxia measures in human glioma

Hypoxia plays a central role in tumor stem cell genesis and is related to a more malignant tumor phenotype, therapy resistance (e.g. in anti-angiogenic therapies) and radio-insensitivity. Reliable hypoxia imaging would provide crucial metabolic information in the diagnostic work-up of brain tumors. In this study, we applied a novel BOLD-based MRI method for the measurement of relative oxygen extraction fraction (rOEF) in glioma patients and investigated potential benefits and drawbacks. Forty-five glioma patients were examined preoperatively in a pilot study on a 3T MR scanner. rOEF was calculated from quantitative transverse relaxation rates (T2, T2*) and cerebral blood volume (CBV) using a quantitative BOLD approach. rOEF maps were assessed visually and by means of a volume of interest (VOI) analysis. In six cases, MRI-targeted biopsy samples were analyzed using HIF-1α-immunohistochemistry. rOEF maps could be obtained with a diagnostic quality. Focal spots with high rOEF values were observed in the majority of high-grade tumors but in none of the low-grade tumors. VOI analysis revealed potentially hypoxic tumor regions with high rOEF in contrast-enhancing tumor regions as well as in the non-enhancing infiltration zone. Systematic bias was found as a result of non-BOLD susceptibility effects (T2*) and contrast agent leakage affecting CBV. Histological samples demonstrated reasonable correspondence between MRI characteristics and HIF-1α-staining. The presented method of rOEF imaging is a promising tool for the metabolic characterization of human glioma. For the interpretation of rOEF maps, confounding factors must be considered, with a special focus on CBV measurements in the presence of contrast agent leakage. Further validation involving a bigger cohort and extended immuno-histochemical correlation is required.

Evaluation of perfusion CT in grading and prognostication of high-grade gliomas at diagnosis: a pilot study

OBJECTIVE

Differentiation of grade 3 astrocytoma from glioblastoma multiforme can be difficult with conventional structural imaging but is important for prognosis. The purpose of this study was to assess perfusion CT in differentiating high-grade gliomas (HGGs) and their role in prognosis in the care of patients with HGG.

SUBJECTS AND METHODS

Twenty patients with previously untreated HGG underwent prospective evaluation with perfusion CT. Permeability surface area product (PS) and cerebral blood volume (CBV) were calculated by the deconvolution method and were compared between HGGs with Student two-sample t tests. Receiver operating characteristic curves were generated for PS, CBV, and the conjoint factor PS + CBV. Cox regression analysis was used to correlate these parameters with patient survival over a follow-up period. Hazard ratios were calculated, and Kaplan-Meier survival curves were drawn.

RESULTS

There was a significant difference between grade 3 and grade 4 gliomas for PS (p = 0.022) and PS + CBV (p = 0.019) but not for CBV alone (p = 0.411). Receiver operating characteristic analyses showed that PS (area under the curve [AUC], 0.72) and CBV + PS (AUC, 0.73) can be used to differentiate grade 3 from grade 4 gliomas but that CBV alone cannot be so used (AUC, 0.54). There was a significant relation between patient outcome and age (p = 0.034) and CBV + PS (p = 0.048). Patients with HGG and a CBV + PS greater than 9 had a poor outcome (hazard ratio, 6.00).

CONCLUSION

PS and CBV + PS can be used to differentiate grade 3 from grade 4 gliomas. The outcome of patients with HGG depends on age and CBV + PS.

Immediate post-operative MRI suggestive of the site and timing of glioblastoma recurrence after gross total resection: a retrospective longitudinal preliminary study

OBJECTIVES

To retrospectively identify morphological and physiological post-operative magnetic resonance imaging (MRI) characteristics predictive of glioblastoma recurrences after gross total resection (gross-TR).

METHODS

Resection margins of 24 glioblastoma were analysed immediately post-operatively (MRI ≤ 2 h) and early post-operatively (24 h ≤ MRI ≤ 48 h), and subdivided into areas with and without subtle contrast enhancement previously considered non-specific. On follow-up MRI, tumour regrowth areas were subdivided according to recurrence extent (focally/extended) and delay (≤6 and ≥12 months). Co-registration of pre-operative, immediately post-operative and early post-operative MRI with the first follow-up MRI demonstrating recurrence authorised their morphological (contrast enhancements) and physiological (rCBV) characterisation.

RESULTS

Morphologically, on immediately post-operative MRI, micro-nodular and frayed enhancements correlate significantly with early recurrences (≤6 months). After gross-TR the absence of these enhancements is associated with a significant increase in progression-free survival (61 vs 15 weeks respectively) and overall survival (125 vs 51 weeks respectively). Physiologically, areas with a future focal recurrence have a trend toward higher rCBV than other areas.

CONCLUSION

Immediately post-operative topography of micro-nodular and frayed enhancements is suggestive of recurrence location and delay. Absence of such enhancements is associated with a fourfold increase in progression-free survival and a 2.5-fold increase in overall survival.

KEY POINTS

• Immediately post-operative MRI reveals contrast enhancement after glioblastoma gross total resection. • Immediately post-operative micro-nodular and frayed enhancement correlate with early recurrence. • Absence of micro-nodular/frayed enhancement is associated with 61 weeks' progression-free survival. • Absence of micro-nodular/frayed enhancement is associated with 125 weeks' overall survival.

Comparison of DSC-MRI post-processing techniques in predicting microvascular histopathology in patients newly diagnosed with GBM

PURPOSE

To evaluate which common post-processing method applied to gradient-echo DSC-MRI data, acquired with a single gadolinium injection and low flip-angle, most accurately reflects microvascular histopathology for patients with de novo, treatment-naive glioblastoma multiforme (GBM).

MATERIALS AND METHODS

Seventy-two tissue samples were collected from 35 patients with treatment-naive GBM. Sample locations were co-registered to preoperative gradient-echo dynamic susceptibility contrast (DSC) MRI acquired with 35° flip-angle and 0.1 mmol/kg gadolinium. Estimates of blood volume and leakiness at each sample location were calculated using four common postprocessing methods (leakage-corrected nonlinear gamma-variate, non-parametric, scaled MR-signal, and unscaled MR-signal). Tissue sample microvascular morphology was characterized using Factor VIII immunohistochemical analysis. A random-effects regression model, adjusted for repeated measures and contrast-enhancement (CE), identified whether MR parameter estimates significantly predicted IHC findings.

RESULTS

Elevated blood volume estimates from nonlinear and non-parametric methods significantly predicted increased microvascular hyperplasia. Abnormal microvasculature existed beyond the CE-lesion and was significantly reflected by increased blood volume from nonlinear, non-parametric, and scaled MR-signal analysis.

CONCLUSION

This study provides histopathological support for both non-parametric and nonlinear post-processing of low flip-angle DSC-MRI for characterizing microvascular hyperplasia within GBM. Non-parametric analysis with a single gadolinium injection may be a particularly useful strategy clinically, as it requires less computational expense and limits gadolinium exposure.

Repeatability of edited lactate and other metabolites in astrocytoma at 3T

PURPOSE

To assess the repeatability of measurement of lactate and other metabolites in tumors using magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

MRS with spectral editing for lactate was performed on 10 patients with astrocytoma (two Grade III, eight Grade IV) using an 8-channel receive coil at 3T. Lactate, lipid, choline, creatine, and N-acetyl aspartate (NAA) signals were measured in regions of tumor and contralateral white matter. Metabolites were quantified relative to unsuppressed water using LCModel fitting software.

RESULTS

The within-patient coefficients of variation were ≈16% (tumor lactate), 6%-8% (tumor choline and contralateral choline, creatine, and NAA), and 22% (tumor lipid). As expected due to their low concentration in normal tissue, lactate and lipid were not reliably detected in white matter but were found at high levels in most tumors. NAA and creatine were lower in tumors than in normal white matter, and choline varied between above- and below-normal values. No consistent short-term variation in metabolite levels was observed, despite differences in the time elapsed since administration of contrast agent.

CONCLUSION

MRS appears repeatable enough to provide longitudinal measures of metabolite content in tumors and contralateral tissue in the brain in vivo.

Advances in ultra-high field MRI for the clinical management of patients with brain tumors

PURPOSE OF REVIEW

The last 5 years have seen the number of ultra-high field (UHF; 7 T and beyond) MRI scanners nearly double. Benefits include improved specificity, better sensitivity for signal-starved compounds, and the ability to detect, quantify, and monitor tumor activity and treatment effects. This is especially important in the current climate in which new treatments alter established markers of tumor and the surrounding environment, confounding traditional response criteria.

RECENT FINDINGS

Intra-tumoral heterogeneity and dramatic improvement in spatial localization have been observed with 7 and 8 T high-resolution T2-weighted and T2*-weighted imaging. This depiction of lesions that were not readily detected at lower field improved the classification of glioma. Sub-millimeter visualization of microvasculature has facilitated the detection of microbleeds associated with long-term effects of radiation. New metabolic markers seen at UHF may also assist in distinguishing tumor progression from treatment effect.

SUMMARY

Although progress has been limited by technical challenges, initial experience has demonstrated the promise of 7-T MRI in advancing existing paradigms for diagnosing, monitoring, and managing patients with brain tumors. The success of these systems will depend upon what new information can be gained by UHF, rather than simply improving the quality of the current lower field standard.

Proton magnetic resonance spectroscopy predicts survival in children with diffuse intrinsic pontine glioma

Patients with diffuse intrinsic pontine glioma (DIPG) face a grim prognosis with limited treatment options. Many patients will enroll on investigational trials though the role of chemotherapy or immunotherapy is unclear. Radiographic changes on conventional MRI are used to evaluate tumor response and progression, but are not predictive of outcome in these patients. More sensitive measures of tumor biology are needed to improve patient management. We evaluated changes in magnetic resonance spectroscopy (MRS) biomarkers in patients with DIPG. Thirty-eight patients were enrolled prospectively on an IRB-approved protocol, which included standard MRI, single voxel spectroscopy (SVS) and multi-slice multi-voxel spectroscopy (MRSI). Scans were performed at multiple time points during each patient's clinical course, with a total of 142 scans. The prognostic values of Choline:N-acetylaspartate (Cho:NAA), Cho:Creatine (Cho:Cr) and the presence of lactate and lipids (+Lac/Lip) were evaluated. Cho:NAA and variance in Cho:NAA values among different voxels within a tumor were each predictive of shorter survival. This prospective study shows that MRS can be used to identify high-risk patients and monitor changes in tumor metabolism, which may reflect changes in tumor behavior.

Assessment of therapeutic response and treatment planning for brain tumors using metabolic and physiological MRI

MRI is routinely used for diagnosis, treatment planning and assessment of response to therapy for patients with glioma. Gliomas are spatially heterogeneous and infiltrative lesions that are quite variable in terms of their response to therapy. Patients classified as having low-grade histology have a median overall survival of 7 years or more, but need to be monitored carefully to make sure that their tumor does not upgrade to a more malignant phenotype. Patients with the most aggressive grade IV histology have a median overall survival of 12-15 months and often undergo multiple surgeries and adjuvant therapies in an attempt to control their disease. Despite improvements in the spatial resolution and sensitivity of anatomic images, there remain considerable ambiguities in the interpretation of changes in the size of the gadolinium-enhancing lesion on T(1) -weighted images as a measure of treatment response, and in differentiating between treatment effects and infiltrating tumor within the larger T(2) lesion. The planning of focal therapies, such as surgery, radiation and targeted drug delivery, as well as a more reliable assessment of the response to therapy, would benefit considerably from the integration of metabolic and physiological imaging techniques into routine clinical MR examinations. Advanced methods that have been shown to provide valuable data for patients with glioma are diffusion, perfusion and spectroscopic imaging. Multiparametric examinations that include the acquisition of such data are able to assess tumor cellularity, hypoxia, disruption of normal tissue architecture, changes in vascular density and vessel permeability, in addition to the standard measures of changes in the volume of enhancing and nonenhancing anatomic lesions. This is particularly critical for the interpretation of the results of Phase I and Phase II clinical trials of novel therapies, which are increasingly including agents that are designed to have anti-angiogenic and anti-proliferative properties as opposed to having a direct effect on tumor cell viability.

Neuronal-astrocyte metabolic interactions: understanding the transition into abnormal astrocytoma metabolism

Brain function depends on complex metabolic interactions among only a few different cell types, with astrocytes providing critical support for neurons. Astrocyte functions include buffering the extracellular space, providing substrates to neurons, interchanging glutamate and glutamine for synaptic transmission with neurons, and facilitating access to blood vessels. Whereas neurons possess highly oxidative metabolism and easily succumb to ischemia, astrocytes rely more on glycolytic metabolism and hence are less susceptible tolack of oxygen. Astrocytoma cells seem to retain basic metabolic mechanisms of astrocytes; for example, they show a high glycolytic rate, lactate extrusion, ability to flourish under hypoxia, and opportunistic use of mechanisms to enhance cell division and maintain growth. Differences in metabolism between neurons and astrocytes may also extend to astrocytoma cells, providing therapeutic opportunities against astrocytomas, including sensitivity to acetate, a high rate of glycolysis and lactate extrusion, glutamate uptake transporters, differential sensitivities of monocarboxylate transporters, presence of glycogen, high interlinking with gap junctions, use of nicotinamide adenine dinucleotide phosphate for lipid synthesis, using different isoforms of synthetic enzymes (e.g. isocitrate dehydrogenase, pyruvate carboxylase, pyruvate kinase, lactate dehydrogenase), and different glucose uptake mechanisms. These unique metabolic susceptibilities may augment conventional therapeutic attacks based on cell division differences and surface receptors alone.

Signal intensity in T2' magnetic resonance imaging is related to brain glioma grade

OBJECTIVES

T2' values reflect the presence of deoxyhaemoglobin related to high local oxygen extraction. We assessed the feasibility of T2' imaging to display regions with high metabolic activity in brain gliomas.

METHODS

MRI was performed in 25 patients (12 female; median age 46 years; range 2-69) with brain gliomas with additional T2 and T2* sequences. T2' maps were derived from T2 and T2*. Dynamic susceptibility weighted contrast (DSC) perfusion was performed in 12/25 patients. Images were visually assessed by two readers and five ROIs were evaluated for each patient. Pearson correlation, Mann-Whitney and Kruskal-Wallis tests were applied for statistical analysis.

RESULTS

Three patients were not further evaluated because of artefacts. Mean values of high-grade (III-IV) gliomas showed significantly lower T2' values than low-grade (II) gliomas (p < 0.001). An inverse relationship was observed between rCBV and sqr (T2') (r = -0.463, p < 0.001). No correlation was observed between T2' and rCBV for grade II tumours (r = 0.038; p = 0.875).

CONCLUSIONS

High-grade tumours revealed lower T2' values, presumably because of higher oxygen consumption in proliferating tissue. Our results indicate that T2' imaging can be used as an alternative to DSC perfusion in the detection of subtle deviations in tumour metabolism.

Stripe-like increase of rCBV beyond the visible border of glioblastomas: site of tumor infiltration growing after neurosurgery

We observed a stripe-like pattern of regional cerebral blood volume (rCBV) increase in a defined region adjacent to the contrast enhancement (CE) on MRI of glioblastomas (GBM) that we defined as the "striate sign" (SS). We hypothesized that the SS marks infiltration of GBM outside the CE volume transforming into future CE tumor in the follow-up. T2*-weighted dynamic susceptibility-weighted CE (DSC)-MRI, and T1 and T2-weighted images (WI) of 16 patients with GBM were retrospectively evaluated in a baseline MRI performed before neurosurgery. In seven of these patients we also performed a (1)H MR spectroscopic imaging ((1)H MRSI). The regions of interest (ROI) delineating the SS were defined on rCBV maps for each patient. ROIs were overlaid on follow-up T1-WI and T2-WI MRI performed 3, 6, and 9 months after neurosurgery. Size and maximum signal intensity (max SI) of de novo CE within the area of the SS were analyzed. Statistical analysis was performed with the Friedman test (P < 0.05). In 15/16 patients de novo CE completely covered the area of the SS within nine months. Normalized max SI of de-novo CE of the 3, 6, and 9-months follow-up MR examinations were significantly higher than in the baseline MRI (P < 0.001). Normalized choline was increased within the SS in all patients with de novo CE (n = 6). De-novo CE appeared within the SS in all patients (96% of all slices). This implies that the SS might indicate the site of future CE tumor, which represents the area of tumor growth after neurosurgery.

In vivo 13C magnetic resonance spectroscopy of a human brain tumor after application of 13C-1-enriched glucose

OBJECTIVES

As a unique tool to assess metabolic fluxes noninvasively, (13)C magnetic resonance spectroscopy (MRS) could help to characterize and understand malignancy in human tumors. However, its low sensitivity has hampered applications in patients. The aim of this study was to demonstrate that with sensitivity-optimized localized (13)C MRS and intravenous infusion of [1-(13)C]glucose under euglycemia, it is possible to assess the dynamic conversion of glucose into its metabolic products in vivo in human glioma tissue.

MATERIALS AND METHODS

Measurements were done at 3 T with a broadband single RF channel and a quadrature (13)C surface coil inserted in a (1)H volume coil. A (1)H/(13)C polarization transfer sequence was applied, modified for localized acquisition, alternatively in two (50 ml) voxels, one encompassing the tumor and the other normal brain tissue.

RESULTS

After about 20 min of [1-(13)C]glucose infusion, a [3-(13)C]lactate signal appeared among several resonances of metabolic products of glucose in MR spectra of the tumor voxel. The resonance of [3-(13)C]lactate was absent in MR spectra from contralateral tissue. In addition, the intensity of [1-(13)C]glucose signals in the tumor area was about 50% higher than that in normal tissue, likely reflecting more glucose in extracellular space due to a defective blood-brain barrier. The signal intensity for metabolites produced in or via the tricarboxylic acid (TCA) cycle was lower in the tumor than in the contralateral area, albeit that the ratios of isotopomer signals were comparable.

CONCLUSION

With an improved (13)C MRS approach, the uptake of glucose and its conversion into metabolites such as lactate can be monitored noninvasively in vivo in human brain tumors. This opens the way to assessing metabolic activity in human tumor tissue.

Investigation of blood perfusion and metabolic activity of brain tumours in adults by using 99mTc-methoxyisobutylisonitrile

OBJECTIVES

(i) To examine blood perfusion and metabolic activity of various brain tumours using radionuclide cerebral angiography (RCA) and single-photon emission tomography (SPET) after a single dose of Tc-methoxyisobutylisonitrile (MIBI). (ii) To examine if the inclusion of RCA can improve insight into the relative contribution of tumour perfusion to the uptake of MIBI shown by SPET, and to improve evaluation of tumour biology. (iii) To determine the value and the roles of MIBI in the management of brain tumour patients.

METHODS

Fifty adult patients (38 male, 12 female) with a total of 56 intracranial space-occupying lesions have been included prospectively, 37 of which were newly diagnosed and the remaining with signs of recurrence/rest of earlier resected and irradiated brain tumours. The control group consisted of nine volunteers with no evidence of organic cerebral disease. Scintigraphic examination consisted of a dynamic first-pass study lasting 60 s (3 s/frame) and two SPET studies (60 projections each, 25 s/projection), starting 15 min and 2 h after intravenous injection of MIBI. Regions of interest of the tumour and normal brain tissue were drawn on RCA and both early and delayed SPET slices. The following tumour/brain activity ratios have been calculated: (i) tumour perfusion index (P); (ii) early uptake index (E); (iii) delayed uptake index (D); and(iv) retention index (R). Analogous indices have been calculated from the same examinations performed in controls, reflecting maximal physiologic regional variations of perfusion and uptake in brain tissue.

RESULTS

Mean P of various brain tumours (low-grade gliomas 0.98, anaplastic gliomas 1.14, glioblastoma multiforme 1.20, metastases 1.09, lymphomas 1.08) differ little from each other and do not exceed maximal physiologic regional variations of cerebral perfusion (1.33), with the exception of meningioma (1.87, F=2.83, P=0.015). The receiver operating characteristics curve analysis of P showed that for the cut-off value of 1.45 the sensitivity for distinguishing meningioma from other tumours is 75%, specificity 87%, positive predictive value 33% and negative predictive value 97%. Mean E of malignant brain tumours (8.3, n=31, 23 primary, eight secondary), except anaplastic gliomas (3.5, n=5), differed significantly (P=0.02) from those of benign gliomas (3, n=9) but not from that of meningioma (11.9, n=4). The cut-off value for distinguishing malignant from benign lesions on the basis of E set at 4.8 resulted in sensitivity 67%, specificity 75%, accuracy 70%, positive predictive value 80% and negative predictive value 60%. D and R showed tendency of wash-out of MIBI from meningiomas, but otherwise did not improve the results substantially.

CONCLUSION

Integrated results of RCA and SPET with Tc-MIBI indicate that blood perfusion, blood-tumour barrier permeability and metabolic activity of the tumour are all very important for the resultant uptake shown by SPET. If the perfusion index is less than 1.45, then meningioma can be ruled out. Early SPET is recommendable for distinguishing glioblastoma from low-grade gliomas, as a complement to standard magnetic resonance imaging and/or computed tomography.