Intracranial meningeomas: time- and dose-dependent effects of irradiation on tumor microcirculation monitored by dynamic MR imaging

Tumour status prediction by means of carbon-ion beam irradiation: comparison of washout rates between in-beam PET and DCE-MRI in rats

Objective.Tumour response to radiation therapy appears as changes in tumour vascular condition. There are several methods for analysing tumour blood circulatory changes one of which is dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), but there is no method that can observe the tumour vascular condition and physiological changes at the site of radiation therapy. Positron emission tomography (PET) has been applied for treatment verification in charged particle therapy, which is based on the detection of positron emitters produced through nuclear fragmentation reactions in a patient's body. However, the produced positron emitters are washed out biologically depending on the tumour vascular condition. This means that measuring the biological washout rate may allow evaluation of the tumour radiation response, in a similar manner to DCE-MRI. Therefore, this study compared the washout rates in rats between in-beam PET during12C ion beam irradiation and DCE-MRI.Approach.Different vascular conditions of the tumour model were prepared for six nude rats. The tumour of each nude rat was irradiated by a12C ion beam with simultaneous in-beam PET measurement. In 10-12 h, the DCE-MRI experiment was performed for the same six nude rats. The biological washout rate of the produced positron emitters (k2,1st) and the MRI contrast agent (k2a) were derived using the single tissue compartment model.Main results.A linear correlation was observed betweenk2,1standk2a, and they were inversely related to fractional necrotic volume.Significance.This is the first animal study which confirmed the biological washout rate of in-beam PET correlates closely with tumour vascular condition measured with the MRI contrast agent administrated intravenously.

Grading Trigone Meningiomas Using Conventional Magnetic Resonance Imaging With Susceptibility-Weighted Imaging and Perfusion-Weighted Imaging

OBJECTIVE

To compare conventional magnetic resonance imaging (MRI), susceptibility-weighted imaging (SWI), and perfusion-weighted imaging (PWI) characteristics in different grades of trigone meningiomas.

METHODS

Thirty patients with trigone meningiomas were enrolled in this retrospective study. Conventional MRI was performed in all patients; SWI (17 cases), dynamic contrast-enhanced PWI (10 cases), and dynamic susceptibility contrast PWI (6 cases) were performed. Demographics, conventional MRI features, SWI- and PWI-derived parameters were compared between different grades of trigone meningiomas.

RESULTS

On conventional MRI, the irregularity of tumor shape (ρ = 0.497, P = 0.005) and the extent of peritumoral edema (ρ = 0.187, P = 0.022) might help distinguish low-grade and high-grade trigone meningiomas. On multiparametric functional MRI, rTTPmax (1.17 ± 0.06 vs 1.30 ± 0.05, P = 0.048), Kep, Ve, and iAUC demonstrated their potentiality to predict World Health Organization grades I, II, and III trigone meningiomas.

CONCLUSIONS

Conventional MRI combined with dynamic susceptibility contrast and dynamic contrast-enhanced can help predict the World Health Organization grade of trigone meningiomas.

Role of gamma knife radiosurgery in the management of intracranial gliomas

Gamma knife for gliomas is a relatively obscure treatment modality with few reports and small series available on the same. An extensive search of English Language literature yields no comprehensive reviews of the same. We here, attempt to review the available literature on gamma knife for all types of gliomas: Low grade, High grade, recurrent, and also for pediatric populations. We used keywords such as "Gamma Knife Glioma," "Stereotactic Radiosurgery Glioma," "Gamma Knife," "Adjuvant therapy Glioma" "Recurrent Glioma" on PubMed search engine, and articles were selected with respect to their use of gamma Knife for Gliomas and outcome for the same. These were then analyzed and salient findings were elucidated. This was combined with National Comprehensive Cancer Network guidelines for the same and also included our own initial experience with these tumors. Gamma-knife improved long term survival and quality of life in patients with low grade gliomas. In pediatric low grade gliomas, it may be considered as a treatment modality with a marginal dose of 12-14 Gy, especially in eloquent structures such as brain stem glioma, anterior optic pathway hypothalamic glioma. However, in newly diagnosed high-grade glioma gamma knife radiosurgery (GKRS) is not recommended because of a lack of definitive evidence in tumor control and quality of life. GKRS may find its role in palliative care of recurrent gliomas irrespective of type and grade. Inspite of growing experience with GKRS for gliomas, there is no Level I evidence in support of GKRS, hence better designed randomized controlled trials with long term outcomes are warranted. Although this modality is not a "one size fits all' therapy, it has its moments when chosen correctly and applied wisely. Gliomas being the most common tumors operated in any neurosurgical setting, knowledge about this modality and its application is essential and useful.

Technical Note: Quantitative dynamic contrast-enhanced MRI of a 3-dimensional artificial capillary network

PURPOSE

Variability across devices, patients, and time still hinders widespread recognition of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) as quantitative biomarker. The purpose of this work was to introduce and characterize a dedicated microchannel phantom as a model for quantitative DCE-MRI measurements.

METHODS

A perfusable, MR-compatible microchannel network was constructed on the basis of sacrificial melt-spun sugar fibers embedded in a block of epoxy resin. Structural analysis was performed on the basis of light microscopy images before DCE-MRI experiments. During dynamic acquisition the capillary network was perfused with a standard contrast agent injection system. Flow-dependency, as well as inter- and intrascanner reproducibility of the computed DCE parameters were evaluated using a 3.0 T whole-body MRI.

RESULTS

Semi-quantitative and quantitative flow-related parameters exhibited the expected proportionality to the set flow rate (mean Pearson correlation coefficient: 0.991, P < 2.5e-5). The volume fraction was approximately independent from changes of the applied flow rate through the phantom. Repeatability and reproducibility experiments yielded maximum intrascanner coefficients of variation (CV) of 4.6% for quantitative parameters. All evaluated parameters were well in the range of known in vivo results for the applied flow rates.

CONCLUSION

The constructed phantom enables reproducible, flow-dependent, contrast-enhanced MR measurements with the potential to facilitate standardization and comparability of DCE-MRI examinations.

Models and methods for analyzing DCE-MRI: a review

PURPOSE

To present a review of most commonly used techniques to analyze dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), discusses their strengths and weaknesses, and outlines recent clinical applications of findings from these approaches.

METHODS

DCE-MRI allows for noninvasive quantitative analysis of contrast agent (CA) transient in soft tissues. Thus, it is an important and well-established tool to reveal microvasculature and perfusion in various clinical applications. In the last three decades, a host of nonparametric and parametric models and methods have been developed in order to quantify the CA's perfusion into tissue and estimate perfusion-related parameters (indexes) from signal- or concentration-time curves. These indexes are widely used in various clinical applications for the detection, characterization, and therapy monitoring of different diseases.

RESULTS

Promising theoretical findings and experimental results for the reviewed models and techniques in a variety of clinical applications suggest that DCE-MRI is a clinically relevant imaging modality, which can be used for early diagnosis of different diseases, such as breast and prostate cancer, renal rejection, and liver tumors.

CONCLUSIONS

Both nonparametric and parametric approaches for DCE-MRI analysis possess the ability to quantify tissue perfusion.

Comparison between magnetic resonance spectroscopy and diffusion weighted imaging in the evaluation of gliomas response after treatment

PURPOSE

To compare magnetic resonance spectroscopy (MRS) and diffusion weighted imaging (DWI) in the assessment of progression and regression of brain tumors in order to assess whether there is correlation between MRS and DWI in the monitoring of patients with primary tumors after therapy.

METHODS

Magnetic resonance imaging (MRI) has been performed in 80 patients, 48 affected by high grade gliomas (HGG) and 32 affected by low grade gliomas (LGG). The variation of apparent diffusion coefficient (ADC) value and metabolite ratios before and after treatment has been used to test DWI sequences and MRS as predictor to response to therapy. Comparison between post contrast-enhancement sequences, MRS and DWI has been done in terms of accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). Moreover statistical correlation of ADC deviations with MRS metabolites variations before and after therapy have been studied.

RESULTS

In the case of HGG, MRS shows better sensitivity, specificity, PPV, NPV and accuracy compared to DWI, especially when considering the Choline/N-acetylaspartate (Cho/NAA) ratio. Regarding the LGG, the technique that better evaluates the response to treatment appears to be the DWI. A moderate correlation between ADC deviations and Cho, Lipide (Lip) and Lactate (Lac) has been found in LGG; while NAA revealed to be weakly correlated to ADC variation. Considering HGG, a weak correlation has been found between ADC deviations and MRS metabolites.

CONCLUSION

Combination of DWI and MRS can help to characterize different changes related to treatment and to evaluate brain tumor response to treatment.

Prediction of radiosensitivity in primary central nervous system germ cell tumors using dynamic contrast-enhanced magnetic resonance imaging

OBJECTIVE

To evaluate the feasibility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) for predicting tumor response to radiotherapy in patients with suspected primary central nervous system (CNS) germ cell tumors (GCTs).

METHODS

DCE-MRI parameters of 35 patients with suspected primary CNS GCTs were obtained prior to diagnostic radiation, using the Tofts and Kermode model. Radiosensitivity was determined in tumors diagnosed 2 weeks after radiation by observing changes in tumor size and markers as a response to MRI. Taking radiosensitivity as the gold standard, the cut-off value of DCE-MRI parameters was measured by receiver operating characteristic (ROC) curve. Diagnostic accuracy of DCE-MRI parameters for predicting radiosensitivity was evaluated by ROC curve.

RESULTS

A significant elevation in transfer constant (K(trans)) and extravascular extracellular space (Ve) (P=0.000), as well as a significant reduction in rate constant (Kep) (P=0.000) was observed in tumors. K(trans), relative K(trans), and relative Kep of the responsive group were significantly higher than non-responsive groups. No significant difference was found in Kep, Ve, and relative Ve between the two groups. Relative K(trans) showed the best diagnostic value in predicting radiosensitivity with a sensitivity of 100%, specificity of 91.7%, positive predictive value (PPV) of 95.8%, and negative predictive value (NPV) of 100%.

CONCLUSIONS

Relative K(trans) appeared promising in predicting tumor response to radiation therapy (RT). It is implied that DCE-MRI pre-treatment is a requisite step in diagnostic procedures and a novel and reliable approach to guide clinical choice of RT.

Treatment monitoring in gliomas: comparison of dynamic susceptibility-weighted contrast-enhanced and spectroscopic MRI techniques for identifying treatment failure

OBJECTIVE

To evaluate whether dynamic susceptibility-weighted contrast-enhanced (DSC), dynamic contrast-enhanced (DCE), and proton spectroscopic imaging ((1)H-MRSI) can identify progression and predict treatment failure during follow-up before tumor size changes, contrast agent uptake, or when new lesions become obvious. The aim was also to find out which of the aforementioned techniques had the best diagnostic performance compared with each other and standard magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Thirty-seven patients with gliomas (21 women, 16 men; mean age at inclusion, 48 ± 14 years [standard deviation]) were assessed prospectively by (1)H-MRSI (point-resolved spectroscopy), DCE, and DSC perfusion MRI, each after a single dose of gadobenate dimeglumine during follow-up. Histology was available in all cases (resection, N = 18; biopsy, N = 19). All patients with low-grade gliomas (n = 20) did not receive any radio- or chemotherapy after partial resection (n = 7) or biopsy (n = 13), whereas 17 patients with high-grade gliomas had received adjuvant radiotherapy immediately after surgery. Tumor progression (progressive disease, PD) was defined as increase in longest glioma diameter by at least 20% (Response Evaluation Criteria in Solid Tumors), appearance of new lesions, or new contrast-enhancement. DSC, DCE, and MRSI image analyses comprised a detailed semiquantitative region of interest (ROI) analysis of the different parameters. Wilcoxon signed-rank test, Wilcoxon rank sum test, and Cox regression were used for statistical analysis.

RESULTS

The median follow-up time was 607 days. Twenty patients showed PD (54%), 8 of 20 with low-grade (40%) and 12 of 17 with high-grade gliomas (71%). In PD, significant positive differences between log2-transformed ROI ratios at the last measurement in comparison to the first measurement (baseline) could be detected for tumor blood flow (P < 0.006) and volume (P < 0.001) derived from DSC and for maximum choline within tumor tissue (P = 0.0029) and Cho/Cr (P = 0.032) but not choline/N-acetyl-aspartate (P = 0.37) derived from MRSI. In contrast, these parameters were not significantly higher at last measurement in stable disease. Also, the differences between last value and baseline were significantly different between PD and stable disease for tumor blood flow (P < 0.004) and volume (P < 0.002) as well as for maximum choline within tumor tissue (P = 0.0011). The best prognostic parameter for PD at Cox analysis was time-dependent difference to baseline of log2 of relative regional cerebral blood flow normalized on gray matter (hazard ratio, 2.67; 95% confidence interval, 1.25-6.08; P = 0.01), while a prognostic value of MRS parameters could not be demonstrated.

CONCLUSION

DSC perfusion imaging can identify progression and can predict treatment failure during follow-up of gliomas with the best diagnostic performance.

Tracer kinetic modelling of tumour angiogenesis based on dynamic contrast-enhanced CT and MRI measurements

PURPOSE

Technical developments in both magnetic resonance imaging (MRI) and computed tomography (CT) have helped to reduce scan times and expedited the development of dynamic contrast-enhanced (DCE) imaging techniques. Since the temporal change of the image signal following the administration of a diffusible, extracellular contrast agent (CA) is related to the local blood supply and the extravasation of the CA into the interstitial space, DCE imaging can be used to assess tissue microvasculature and microcirculation. It is the aim of this review to summarize the biophysical and tracer kinetic principles underlying this emerging imaging technique offering great potential for non-invasive characterization of tumour angiogenesis.

METHODS

In the first part, the relevant contrast mechanisms are presented that form the basis to relate signal variations measured by serial CT and MRI to local tissue concentrations of the administered CA. In the second part, the concepts most widely used for tracer kinetic modelling of concentration-time courses derived from measured DCE image data sets are described in a consistent and unified manner to highlight their particular structure and assumptions as well as the relationships among them. Finally, the concepts presented are exemplified by the analysis of representative DCE data as well as discussed with respect to present and future applications in cancer diagnosis and therapy.

RESULTS

Depending on the specific protocol used for the acquisition of DCE image data and the particular model applied for tracer kinetic analysis of the derived concentration-time courses, different aspects of tumour angiogenesis can be quantified in terms of well-defined physiological tissue parameters.

CONCLUSIONS

DCE imaging offers promising prospects for improved tumour diagnosis, individualization of cancer treatment as well as the evaluation of novel therapeutic concepts in preclinical and early-stage clinical trials.

DCEMRI of spontaneous canine tumors during fractionated radiotherapy: a pharmacokinetic analysis

PURPOSE

To estimate pharmacokinetic parameters from dynamic contrast-enhanced magnetic resonance (DCEMR) images of spontaneous canine tumors taken during the course of fractionated radiotherapy, and to quantify treatment-induced changes in these parameters.

MATERIALS AND METHODS

Six dogs with tumors in the oral or nasal cavity received fractionated conformal radiotherapy with 54 Gy given in 18 fractions. T(1)-weighted DCEMR imaging was performed prior to each treatment fraction. Time-intensity curves in the tumor were extracted voxel-by-voxel, and were fitted to the Brix pharmacokinetic model. The dependence of the pharmacokinetic parameters on the accumulated radiation dose was calculated.

RESULTS

The Brix model reproduced the time-intensity curves well. A reduction in the k(ep) parameter with accumulated radiation dose was found for five (three significant) out of six cases, while the results for the A parameter were less consistent. Both pre-treatment k(ep) and the change in k(ep) with accumulated dose correlated significantly with tumor regression.

CONCLUSIONS

Pharmacokinetic parameters derived from DCEMR images taken during fractionated radiotherapy may predict response to radiotherapy. This may potentially impact on patient stratification and monitoring of treatment response for image-guided treatment strategies.

MRI for identification of progression in brain tumors: from morphology to function

For monitoring of brain tumors, it is crucial to identify progression or treatment failure early during follow-up to change treatment schemes and, thereby, optimize patient outcome. In the past years, several areas within the field of magnetic resonance (MR) have seen considerable advances: modern contrast media, advanced morphologic approaches and several functional techniques, for example, in the visualization of tumor perfusion or tumor cell metabolism. This review presents these recent advances by introducing the different techniques and outlining their benefit for identification of progression in brain tumors, with a focus on gliomas, metastases and meningiomas. After radiotherapy, MR spectroscopy helps to more accurately discriminate between radiation necrosis and glioma progression. In low-grade gliomas, perfusion MR techniques enable a more sensitive detection of anaplastic transformation than conventional MRI. Modern contrast media, as well as diffusion tensor imaging, allow for an improved tumor delineation and assessment of tumor extension. We will also highlight the biological background of these techniques, their applicability and current limitations. In conclusion, modern MRI techniques have been developed that are on the doorstep to be integrated in clinical routine.

Acute neurocognitive impairment during cranial radiation therapy in patients with intracranial tumors

BACKGROUND AND PURPOSE

The objective of the current study was to evaluate the acute effects of cranial radiation therapy (CNS-RT) using different radiation doses (0, 1.8, 2, 3, >or=20 Gy) on cognitive function with special emphasis on memory. We assessed patients with and without intracranial tumors to distinguish between direct and indirect radiation effects on brain tissue.

MATERIALS AND METHODS

Eighty-two patients were evaluated with neuropsychological testing before and acutely after radiotherapy (RT). Sixty-four patients received RT to the brain (55 with, 9 without intracranial tumor). Eighteen patients treated with RT to the breast served as controls.

RESULTS

Patients with intracranial tumor demonstrated attention (19-38th percentile) and verbal memory scores (34-46th percentile) below the population average at baseline. The average Verbal Memory score was significantly different between patients with intracranial tumor and controls both at baseline (38th vs. 58th percentile) and after irradiation (27th vs. 52th percentile). Patients with preexisting peritumoral edema performed worse than patients without edema and controls. Radiation dose-related deficits were seen for working memory performance in patients with intracranial tumor.

CONCLUSION

Our data indicate no measurable impairment of cognitive functioning acutely after prophylactic cranial irradiation. Patients with intracranial tumor show a deterioration of almost all memory functions with a dose-dependent impairment in working memory. Patients with preexisting peritumoral brain edema show the strongest deterioration.

Dynamic contrast-enhanced MRI as a predictor of tumour response to radiotherapy

A predictive technique in the management of patients with cancer could improve the therapeutic index by allowing better individualisation of treatment. The standard risk factors that are currently used do not adequately account for the unpredictable and substantial variation seen in the treatment response of patients with a similar risk profile. Dynamic contrast-enhanced (DCE) MRI is a non-invasive technique that can provide anatomical and physiological information on the tumour. The DCE-MRI data reflects the tumour microenvironment variables that are known to influence radiation response. The aim of this review is to describe the potential clinical application of DCE-MRI as a predictor of radiation response. We have reviewed the literature and identified 29 studies (total of 1194 patients) that correlate DCE-MRI with histopathological or clinical outcome data relevant to radiotherapy.

Contrast-enhanced magnetic resonance imaging of central nervous system tumors: agents, mechanisms, and applications

Brain tumors are one of the most common neoplasms in young adults and are associated with a high mortality and disability rate. Magnetic resonance imaging (MRI) is widely accepted to be the most sensitive imaging modality in the assessment of cerebral neoplasms. Because the detection, characterization, and exact delineation of brain tumors require a high lesion contrast that depends on the signal of the lesion in relation to the surrounding tissue, contrast media is given routinely. Anatomical and functional, contrast agent-based MRI techniques allow for a better differential diagnosis, grading, and especially therapy decision, planing, and follow-up. In this article, the basics of contrast enhancement of brain tumors will be reviewed. The underlying pathology of a disrupted blood-brain barrier and drug influences will be discussed. An overview of the currently available contrast media and the influences of dosage, field strength, and application on the tumor tissue contrast will be given. Challenging, contrast-enhanced, functional imaging techniques, such as perfusion MRI and dynamic contrast-enhanced MRI, are presented both from the technical side and the clinical experience in the assessment of brain tumors. The advantages over conventional, anatomical MRI techniques will be discussed as well as possible pitfalls and drawbacks.

Gamma knife surgery for glioblastoma multiforme

Despite the implementation of increasingly aggressive surgery, chemotherapy, and fractionated radiotherapy for the treatment of glioblastoma multiforme (GBM), most therapeutic regimens have resulted in only modest improvements in patient survival. Gamma knife surgery (GKS) has become an indispensable tool in the primary and adjuvant management of many intracranial pathologies, including meningiomas, pituitary tumors, and arteriovenous malformations. Although it would seem that radiosurgical techniques, which produce steep radiation dose fall-off around the target, would not be well suited to treat these infiltrative lesions, a limited number of institutional series suggest that GKS might provide a survival benefit when used as part of the comprehensive management of GBM. This may largely be attributed to the observation that tumors typically recur within a 2-cm margin of the tumor resection cavity. Despite these encouraging results, enthusiasm for radiosurgery as a primary treatment for GBM is significantly tempered by the failure of the only randomized trial that has been conducted to yield any benefit for patients with GBM who were treated with radiosurgery. In this paper, the authors review the pathophysiological mechanisms of GKS and its applications for GBM management.

[Perfusion measurement using the T2* contrast media dynamics in neuro-oncology. Physical basics and clinical applications]

Perfusion imaging in the central nervous system (CNS) is mostly performed using the first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) MRI. The first-pass of a contrast bolus in brain tissue is monitored by a series of T2*-weighted MR images. The susceptibility effect of the paramagnetic contrast agent leads to a signal loss that can be converted, using the principles of the indicator dilution theory, into an increase of the contrast agent concentration. From these data, parameter maps of cerebral blood volume (CBV) and flow (CBF) can be derived. Regional CBF and CBV values can be obtained by region-of-interest analysis. This review article describes physical basics of DSC MRI and summarizes the literature of DSC MRI in neurooncological issues.Studies, all with relatively limited patient numbers, report that DSC MRI is useful in the preoperative diagnosis of gliomas, CNS-lymphomas, and solitary metastases, as well as in the differentiation of these neoplastic lesions from infections and tumor-like manifestations of demyelinating disease. Additionally, DSC MRI is suitable for determining glioma grade and regions of active tumor growth which should be the target of stereotactic biopsy. After therapy, DSC MRI helps better assessing the tumor response to therapy, residual tumor after therapy, and possible treatment failure and therapy-related complications, such as radiation necrosis. The preliminary results show that DSC MRI is a diagnostic tool depicting regional variations in microvasculature of normal and diseased brains.

Dynamic contrast-enhanced magnetic resonance imaging in radiotherapeutic efficacy in the head and neck tumors

PURPOSE

The purpose to this study is to identify correlations between pathology and dynamic contrast-enhanced magnetic resonance imaging (MRI) and to assess the utility of this technique in the evaluation of radiation response for head and neck cancer.

MATERIALS AND METHODS

MRI was prospectively performed after radiotherapy in 27 patients with various head and neck tumors. After bolus injection of contrast material, a dynamic study was performed using a spoiled gradient-recalled imaging sequence. The maximum slope of increase (MSI) on the time-intensity curve was displayed as a color-coded image. The ratio of MSI (MSIR) was obtained for tumor and normal muscles. Pathological specimens were obtained after MRI in all cases. Histological grading of irradiation changes was classified into 5 grades (0-4). Correlations between MSIR and histological grade were examined.

RESULTS

Histologically, 18 tumors were classified as grade 2 (presence of viable tumor cells), 4 were grade 3 (nonviable tumor cells), and 5 were grade 4 (no tumor cells). Although the mean +/- SD of MSIR in patients with histological grade 2 or 3 was 7.4 +/- 7.9, MSIR in patients with grade 4 was 1.8 +/- 0.73, representing a significant difference ( P < .05). Every patient with grade 4 displayed an MSIR of 2.5 or less, although 5 of 22 patients with grade 2 or 3 had an MSIR of 2.5 or less.

CONCLUSIONS

MSI quantitatively reflects response to radiotherapy for head and neck cancer. Color-coded MSI display is feasible for depicting permeability changes after radiotherapy.

New criteria for assessing fit quality in dynamic contrast-enhancedT1-weighted MRI for perfusion and permeability imaging

Contrast-enhanced (CE) MRI provides in vivo physiological information that cannot be obtained by conventional imaging methods. This information is generally extracted by using models to represent the circulation of contrast agent in the body. However, the results depend on the quality of the fit obtained with the chosen model. Therefore, one must check the fit quality to avoid working on physiologically irrelevant parameters. In this study two dimensionless criteria-the fraction of modeling information (FMI) and the fraction of residual information (FRI)-are proposed to identify errors caused by poor fit. These are compared with more conventional criteria, namely the quadratic error and the correlation coefficient, both theoretically and with the use of simulated and real CE-MRI data. The results indicate the superiority of the new criteria. It is also shown that these new criteria can be used to detect oversimplified models.

BOLD MRI response to hypercapnic hyperoxia in patients with meningiomas: correlation with Gadolinium-DTPA uptake rate

Because meningiomas tend to recur after (partial) surgical resection, radiotherapy is increasingly being applied for the treatment of these tumors. Radiation dose levels are limited, however, to avoid radiation damage to the surrounding normal tissue. The radiosensitivity of tumors can be improved by increasing tumor oxygen levels. The aim of this study was to investigate if breathing a hyperoxic hypercapnic gas mixture could improve the oxygenation of meningiomas. Blood oxygen level-dependent magnetic resonance imaging and dynamic Gadolinium (Gd)-DTPA contrast-enhanced MRI were used to assess changes in tumor blood oxygenation and vascularity, respectively. Ten meningioma patients were each studied twice; without and with breathing a gas mixture consisting of 2% CO(2) and 98% O(2). Values of T(2)* and the Gd-DTPA uptake rate k(ep) were calculated under both conditions. In six tumors a significant increase in the value of T(2)* in the tumor was found, suggesting an improved tumor blood oxygenation, which exceeded the effect in normal brain tissue. Contrarily, two tumors showed a significant T(2)* decrease. The change in T(2)* was found to correlate with both k(ep) and with the change in k(ep). The presence of both vascular effects and oxygenation effects and the heterogeneous response to hypercapnic hyperoxia necessitates individual assessment of the effects of breathing a hyperoxic hypercapnic gas mixture on meningiomas. Thus, the current MRI protocol may assist in radiation treatment selection for patients with meningiomas.

Assessment of Irradiated Brain Metastases by Means of Arterial Spin-Labeling and Dynamic Susceptibility-Weighted Contrast-Enhanced Perfusion MRI

RATIONALE AND OBJECTIVES

To assess if preradiation and early follow-up measurements of relative regional cerebral blood flow (rrCBF) can predict treatment outcome in patients with cerebral metastases and to evaluate rrCBF changes in tumor and normal tissue after stereotactic radiosurgery using arterial spin-labeling (ASL) and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI.

METHODS

In 25 patients with a total of 28 brain metastases, DSC MRI and ASL perfusion MRI using the Q2TIPS sequence were performed with a 1.5-T unit. Measurements were performed prior to and at 6 weeks, 12 weeks, and 24 weeks after stereotactic radiosurgery. Follow-up examinations were completely available in 25 patients for Q2TIPS and 17 patients with 18 metastases for DSC MRI. The rrCBF of the metastases and the normal brain tissue was determined by a region-of-interest analysis. rrCBF values were correlated with the treatment outcome that was classified according to tumor volume changes at 6 months.

RESULTS

The alteration of the rrCBF at the 6-week follow-up was highly predictive for treatment outcome. A decrease of the rrCBF value predicted tumor response correctly in all metastases for Q2TIPS and in 13 of 16 metastases for DSC MRI. The pretherapeutic rrCBF was not able to predict treatment outcome. The rrCBF values in normal brain tissue affected by radiation doses less than 0.5 Gy remained unchanged after therapy.

CONCLUSION

These preliminary results suggest that ASL and DSC MRI techniques determining rrCBF changes in brain metastases after stereotactic radiosurgery allow the prediction of treatment outcome.

Neuropsychological outcome after fractionated stereotactic radiotherapy (FSRT) for base of skull meningiomas: a prospective 1-year follow-up

PURPOSE

The purpose of this study was to evaluate the cognitive outcome after fractionated stereotactic radiotherapy (FSRT) in patients with base of skull meningiomas.

METHODS AND MATERIAL

A total of 40 patients with base of skull meningiomas were neuropsychologically evaluated before, after the first fraction (1.8 Gy), at the end of FSRT (n=37), 6 weeks (n=24), 6 (n=18) and 12 months (n=14) after FSRT. A comprehensive test battery including assessment of general intelligence, attention and memory functions was used. Alternate forms were used and current mood state was controlled.

RESULTS

After the first fraction a transient decline in memory function and simultaneous improvements in attention functions were observed. No cognitive deteriorations were seen during further follow-up, but increases in attention and memory functions were observed. Mood state improved after the first fraction, at the end of radiotherapy and 6 weeks after radiotherapy.

CONCLUSION

The present data support the conclusion that the probability for the development of permanent cognitive dysfunctions appears to be very low after FSRT. The transient memory impairments on day 1 are interpreted as most likely related to an increase of a preexisting peritumoral edema, whereas the significant acute improvements in attention functions are interpreted as practice effects. An analysis of localization specific effects of radiation failed to show clear hemisphere specific cognitive changes.

Comparison of Arterial Spin-Labeling Techniques and Dynamic Susceptibility-Weighted Contrast-Enhanced MRI in Perfusion Imaging of Normal Brain Tissue

OBJECTIVES

To evaluate relative cerebral blood flow (rCBF) in normal brain tissue using arterial spin-labeling (ASL) methods and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) magnetic resonance imaging (MRI).

METHODS

Sixty-two patients with brain metastases were examined on a 1.5 T-system up to 6 times during routine follow-up after stereotactic radiosurgery. Perfusion values in normal gray and white matter were measured using the ASL techniques ITS-FAIR in 38 patients, Q2TIPS in 62 patients, and the first-pass DSC echo-planar (EPI) MRI after bolus administration of gadopentetate dimeglumine in 42 patients. Precision of the ASL sequences was tested in follow-up examinations in 10 healthy volunteers.

RESULTS

Perfusion values in normal brain tissue obtained by all sequences correlated well by calculating Pearson's correlation coefficients (P < 0.0001) and remained unchanged after stereotactic radiosurgery as shown by analysis of variance (P > 0.05).

CONCLUSION

Both ASL and DSC EPI MRI yield highly comparable perfusion values in normal brain tissue.

Combretastatin A4 phosphate has tumor antivascular activity in rat and man as demonstrated by dynamic magnetic resonance imaging

PURPOSE

Combretastatin A4 phosphate (CA4P) is a novel vascular targeting agent. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) studies were performed to examine changes in parameters related to blood flow and vascular permeability in tumor and normal tissue after CA4P treatment.

MATERIALS AND METHODS

Changes in kinetic DCE-MRI parameters (transfer constant [Ktrans] and area under contrast medium-time curve [AUC]) over 24 hours after treatment with CA4P were measured in 18 patients in a phase I trial and compared with those obtained in the rat P22 carcinosarcoma model, using the same imaging technique. Rats were treated with 30 mg/kg of CA4P; patients received escalating doses from 5 to 114 mg/m2.

RESULTS

A similar pattern and time course of change in tumor and normal tissue parameters was seen in rats and humans. Rat tumor Ktrans was reduced by 64% 6 hours after treatment with CA4P (30 mg/kg). No significant reductions in kidney or muscle parameters were seen. Significant reductions were seen in tumor Ktrans in six of 16 patients treated at >or= 52 mg/m2, with a significant group mean reduction of 37% and 29% at 4 and 24 hours, respectively, after treatment. The mean reduction in tumor initial area under the gadolinium-diethylenetriamine pentaacetic acid concentration-time curve (AUC) was 33% and 18%, respectively, at these times. No reduction was seen in muscle Ktrans or in kidney AUC in group analysis of the clinical data.

CONCLUSION

CA4P acutely reduces Ktrans in human as well as rat tumors at well-tolerated doses, with no significant changes in kidney or muscle, providing proof of principle that this drug has tumor antivascular activity in rats and humans.

Reproducibility of quantitative dynamic contrast-enhanced MRI in newly presenting glioma

We have investigated the reproducibility of dynamic contrast enhanced imaging techniques in nine patients with cerebral glioma. Patients were imaged twice with a 2 day interval between scans. Maps were produced of the time taken to achieve 90% enhancement (T90), the maximal intensity change per time interval ratio (MITR), the volume transfer coefficient between plasma and the extravascular extracellular space (K(trans)) and the extravascular extracellular contrast distribution volume, v(e). Measurements of K(trans) greater than 1.2 min(-1) were used to exclude pixels where first pass perfusion effects dominated the measurement. Measures of the test-retest coefficient of variation (CoV) and intraclass correlation coefficients were used to assess reproducibility for measurements from a volume of interest containing enhancing tissue from the whole tumour. MITR showed poor reproducibility (mean CoV 17.9%, 95% confidence limits for group comparisons 20.2%). T90 showed good reproducibility (mean CoV 7.1%, 95% confidence limits for group comparisons 5.2%). Calculated values of K(trans) and v(e) also showed good reproducibility (mean CoV 7.7% and 6.2% respectively, 95% confidence limits for group comparisons 6.2% and 4.8%, respectively). We conclude that the measurements of K(trans) and v(e) derived from pharmacokinetic analysis are sufficiently reproducible to support their use as a biological markers in therapeutic trials.

Measurement of volumetric and vascular changes with dynamic contrast enhanced MRI for cancer therapy monitoring

Longitudinal dynamic contrast enhanced MRI studies were undertaken to monitor therapy induced volumetric and vascular changes. Three study components are presented in this work: one animal tumor chemotherapy study (R3230 AC adenocarcinoma treated with Taxotere), one patient with invasive lobular breast cancer undergoing neoadjuvant chemotherapy (AC regimen), and one patient with brain metastasis of primary breast cancer undergoing radiation therapy (40 Gray whole brain irradiation). In the animal study two contrast media with different molecular weights, Gadodiamide and Gadomer-17, were used. Only Gadomer-17 revealed significant changes in vascular properties. The responders showed decreased V(b) (vascular volume index) and K(2) (out-flux transport rate), which preceded tumor regression. The control tumors showed increased V(b) and K(2), before tumor growth became much faster. In the patient undergoing neoadjuvant therapy, the tumor was shrinking by 45% after 2 cycles of treatment, then again by 45% after 2 additional cycles. K(2) was decreasing over time with treatment. In the patient with brain metastasis, the 2 follow-up studies were much longer apart to monitor the regression and relapse of lesions. The pre-treatment volumes of lesions in the group without recurrence were significantly smaller compared to those with recurrence. In summary, the tumor volume was more sensitive than the vascular parameters measured by the small extracellular contrast medium for the assessment of therapy response and prediction of recurrence. The vascular properties measured by macromolecular contrast medium may have the potential to serve as early therapeutic efficacy indicators.

Pharmacokinetic modeling of Gd-DTPA extravasation in brain tumors

RATIONALE AND OBJECTIVES

The endothelial permeability of brain tumors affecting the blood-brain barrier can be quantified using dynamic contrast enhanced MR imaging.

MATERIALS AND METHODS

The dynamics of contrast medium (CM) exchange was investigated in 31 brain tumors (intra- and extra-axial) by fast repeated T1-weighted imaging in order to determine the exchange rates and saturation concentrations.

RESULTS

The analysis of CM exchange reveals two different transport processes from the blood into two separate interstitial subcompartments for intra- and extra-axial tumors, a rapid one with a transfer constant of 1/ =7.0 seconds and a slow one with 1/ =133.7 seconds. Highly significant differences exhibit gliomas and meningiomas with respect to the saturation concentrations of fast and slowly enhancing compartments.

CONCLUSIONS

The fast component is probably caused by extravasation into viable tissue (enhanced in meningiomas) while the slow one probably reflects increased diffusion distances into poorly perfused tissue such as necrotic areas in glioblastomas.

Reproducibility of dynamic contrast-enhanced MRI in human muscle and tumours: comparison of quantitative and semi-quantitative analysis

The purpose of this study was to determine the reproducibility of dynamic contrast-enhanced (DCE)-MRI and compare quantitative kinetic parameters with semi-quantitative methods, and whole region-of-interest (ROI) with pixel analysis. Twenty-one patients with a range of tumour types underwent paired MRI examinations within a week, of which 16 pairs were evaluable. A proton density-weighted image was obtained prior to a dynamic series of 30 T(1)-weighted spoiled gradient echo images every 11.9 s with an intravenous bolus of gadopentetate dimeglumine given after the third baseline data point. Identical ROIs around the whole tumour and in skeletal muscle were drawn by the same observer on each pair of examinations and used for the reproducibility analysis. Semi-quantitative parameters, gradient, enhancement and AUC (area under the curve) were derived from tissue enhancement curves. Quantitative parameters (K(trans), k(ep), v(e)) were obtained by the application of the Tofts' model. Analysis was performed on data averaged across the whole ROI and on the median value from individual pixels within the ROI. No parameter showed a significant change between examinations. For all parameters except K(trans), the variability was not dependent on the parameter value, so the absolute values for the size of changes needed for significance should be used for future reference rather than percentages. The size of change needed for significance in a group of 16 in tumours for K(trans), k(ep) and v(e) was -14 to +16%, -0.20 ml/ml/min (15%) and -1.9[?]ml/ml (6%), respectively (pixel analysis), and -16 to +19%, -0.23 ml/ml/min (16%) and +/- 1.9[?]ml/ml (6%) (whole ROI analysis). For a single tumour, changes greater than -45 to +83%, +/- 0.78 ml/ml/min (60%) and +/- 7.6 ml/ml (24%), respectively, would be significant (pixel analysis). For gradient, enhancement and AUC the size of change needed for significance in tumours was -0.24 (17%), -0.05 (6%) and -0.06 (8%), respectively for a group of 16 (pixel analysis), and +/- 0.96 (68%), +/- 0.20 (25%) and +/- 0.22 (32%) for individuals. In muscle, the size of change needed for significance in a group of 16 for K(trans), k(ep) and v(e) was -30 to +44%, +/- 0.81 ml/ml/min (61%) and +/- 1.7 ml/ml (13%). For gradient, enhancement and AUC it was +/- 0.09 (20%), +/- 0.02 (8%) and +/- 0.03 (12%). v(e), enhancement and AUC are highly reproducible DCE-MRI parameters. K(trans), k(ep) and gradient have greater variability, with larger changes in individuals required to be statistically significant, but are nevertheless sufficiently reproducible to detect changes greater than 14-17% in a cohort of 16 patients. Pixel analyses slightly improve reproducibility estimates and retain information about spatial heterogeneity. Reproducibility studies are recommended when treatment effects are being monitored.

Dynamic MR Imaging and Radiotherapy

Dynamic MRI has been used to improve the detection of tumors and to make differential diagnosis. Most malignant lesions show early enhancement and early washout of contrast media on dynamic MRI, but the characterization of the tumor remains unclear. Pharmacokinetic analysis of dynamic MRI can provide information about the permeability of contrast media in the tumor that may reflect the oxygen concentration of the tumor. This information may be useful in the prediction of a tumor's response to radiation therapy.

Reproducibility of T2* blood volume and vascular tortuosity maps in cerebral gliomas

The development of anti-angiogenic therapies for tumors has led to a demand for imaging-based surrogate markers of the angiogenic process. The utility of such markers is highly dependent on their test-retest reproducibility. This paper presents a formal assessment of the reproducibility of measurements of relative blood volume (rBV), normalized rBV (rBVnorm), and vascular tortuosity as estimated by measurement of relative recirculation (rR). The study was conducted in 11 patients with glioma who were scanned on two occasions 36-56 hours apart. The observed reliability estimates were used to calculate 95% confidence limits for detection of differences between groups and for changes in individual cases. The results show that measurement of rBV or rBVnorm in consecutive studies is statistically capable of reliably detecting changes in excess of 15% in between group studies and 25% in individual patients. Measurement of vascular tortuosity using is less reproducible but is able to confidently identify changes in excess of 30% in group studies and 35% in individuals.

[Role of radiotherapy in the treatment of cerebral meningiomas]

Cerebral meningiomas account for 15-20% of all cerebral tumours. Although seldom malignant, they frequently recur in spite of complete surgery, which remains the cornerstone of the treatment. In order to decrease the probability of local recurrence, radiotherapy has often been recommended in atypical or malignant meningioma as well as in benign meningioma which was incompletely resected. However, this treatment never was the subject of prospective studies, randomized or not. The purpose of this review of the literature was to give a progress report on the results of different published series in the field of methodology as well as in the techniques of radiotherapy. Proposals for a therapeutic choice are made according to this analysis. For grade I or grade II-III meningiomas, limits of gross tumor volume (GTV) include the tumour in place or the residual tumour after surgery; clinical target volume (CTV) limits include gross tumour volume before surgery with a GTV-CTV distance of 1 and 2 cm respectively. Delivered doses are 55 Gy into CTV and 55-60 Gy and 70 Gy into GTV for grade I and grade II-III meningiomas respectively.

Pharmacokinetic analysis of glioma compartments with dynamic Gd-DTPA-enhanced magnetic resonance imaging

Dynamic contrast-enhanced magnetic resonance imaging (MRI) is widely used for measuring perfusion and blood volume, especially cerebral blood volume (CBV). In case of blood-brain barrier (BBB) disruption, the conventional techniques only partially determine the pharmacokinetic parameters of contrast medium (CM) exchange between different compartments. Here a modified pharmacokinetic model is applied, which is based on the bidirectional CM exchange between blood and two interstitial compartments in terms of the fractional volumes of the compartments and the vessel permeabilities between them. The evaluation technique using this model allows one to quantify the fractional volumes of the different compartments (blood, cells, slowly and fast enhancing interstitium) as well as the vessel permeabilities and cerebral blood flow (CBF) with a single T1-weighted dynamic MRI measurement. The method has been successfully applied in 25 glioma patients for generating maps of all of these parameters. The fractional volume maps allow for the differentiation of glioma vascularization types. The maps show a good correlation with the histological grading of these tumors. Furthermore, regions with enhanced interstitial volumes are found in high-grade gliomas. Differences in permeability maps of Gd-DTPA apart from BBB disruption do not exist between different tissue types. CBF measured in high-grade glioma is less pronounced than it would be expected from their blood volume. Therefore pharmacokinetic imaging provides an additional tool for glioma characterization.

Evolution from empirical dynamic contrast-enhanced magnetic resonance imaging to pharmacokinetic MRI

For chemotherapy to be effective against cancers which grow as solid tumors, agents must reach all tumor cells in effective quantities. Although many clinical trials include studies of the pharmacokinetics of the agents in body fluids such as blood or cerebrospinal fluid (CSF), there is presently no widely applicable way to determine access of chemotherapeutic agents to all regions of a solid tumor in an individual patient. This review discusses a relatively new methodology in MR imaging - dynamic contrast-enhanced imaging for exploring tumor microcirculation and drug access by imaging the uptake, or leakage, of contrast agent into tumor interstitial (extracellular and extravascular) space. The aims and methods of dynamic contrast-enhanced MRI evaluations to measure contrast uptake are distinguished from dynamic contrast-enhanced MRI to measure blood volume or flow, by MR imaging of the first-pass effects of a contrast bolus. Measures of contrast uptake by dynamic MRI have demonstrated a convincing ability to aid in diagnosing the presence of viable tumor and to measure response for a range of human tumors. This body of clinical results will be summarized. While questions remain to be answered about how to extract non-invasive pharmacokinetic measures of drug access from these novel dynamic imaging methods, we are optimistic that these methods can provide important new clinical measures that reflect the range of biological variation within and between naturally-occurring solid tumors.

MR microcirculation assessment in cervical cancer: correlations with histomorphological tumor markers and clinical outcome

This article reviews the experience available to date on microcirculation assessment in cancer of the cervix including correlation studies of magnetic resonance (MR) microcirculatory parameters with histo-morphometric predictors and direct correlation with patient outcome. The data suggest that MR microcirculation parameters do not always correlate with histo-morphometric parameters, while there is evidence that MR parameters predict patients' treatment outcome. These observations raise the issue that perhaps the histo-morphometric parameters, accepted gold standards for tumor angiogenesis and prognostic factors, reflect anatomical information at a "static" single time point and may not always provide sufficient information on the "dynamic" microcirculation function of the tumor. MR microcirculation assessment reflects both anatomical and functional information and may provide this additional information on the "dynamic" angiogenic and metabolic status of a tumor. Therefore, assessment of tumor microcirculation may augment the individual risk profile in cervical cancer patients and has the potential to impact on therapy selection and treatment outcome.

Pharmacokinetic MRI for assessment of malignant glioma response to stereotactic radiotherapy: initial results

The purpose of this study was to assess the value of dynamic, contrast-enhanced MRI in patients with malignant glioma (a) to predict before stereotactic radiotherapy local tumor control, (b) to investigate temporal changes in tumor microcirculation after stereotactic radiotherapy, and (c) to analyze whether malignant glioma response may be predicted earlier by alterations in the tissue pharmacokinetics rather than in terms of tumor volume. Ninety MRI studies were performed of 18 patients with malignant glioma before and 6, 18, 26, 52, and 72 weeks after the end of stereotactic radiotherapy. The signal time courses of the contrast-enhanced tumors were analyzed using a pharmacokinetic two-compartment model that calculates for the parameter A, reflecting the degree of MRI signal enhancement [no units] and the exchange rate constant k21 [min(-1)]. Before radiotherapy, the amplitude A was significantly (P < .05) lower in patients with subsequent local tumor control (n = 8; mean A = .34 +/- .15) compared to patients without subsequent local tumor control (n = 10; mean A = .94 +/- .71). In the local tumor control group, early after stereotactic radiotherapy (at 6-18 weeks), there was a significant (P < .05) time-dependent decrease in the parameter k21, whereas there was still no alteration in the tumor volume. A low amplitude A before radiotherapy, combined with an early drop of k21 after stereotactic radiotherapy, reliably characterized the group of patients with subsequent tumor volume decrease. Our preliminary results suggest that two contrast-enhanced dynamic MR studies, one before and one early after stereotactic radiotherapy, offer important information on local tumor control within the first 6 to 18 weeks after stereotactic radiotherapy. Moreover, this response may be evidenced before tumor volume changes and provides a therapeutic window to broaden treatment options and to improve treatment outcome.