Value of dynamic susceptibility contrast magnetic resonance imaging in the evaluation of intracranial tumors

Perfusion MRI in the evaluation of brain metastases: current practice review and rationale for study of baseline MR perfusion imaging prior to stereotactic radiosurgery (STARBEAM-X)

Stereotactic radiosurgery is an established focal treatment for brain metastases with high local control rates. An important side-effect of stereotactic radiosurgery is the development of radionecrosis. On conventional MR imaging, radionecrosis and tumour progression often have similar appearances, but have contrasting management approaches. Perfusion MR imaging is often used in the post-treatment setting in order to help distinguish between the two, but image interpretation can be fraught with challenges.Perfusion MR plays an established role in the baseline and post-treatment evaluation of primary brain tumours and a number of studies have concentrated on the value of perfusion imaging in brain metastases. Of the parameters generated, relative cerebral blood volume is the most widely used variable in terms of its clinical value in differentiating between radionecrosis and tumour progression. Although it has been suggested that the relative cerebral blood volume tends to be elevated in active metastatic disease following treatment with radiosurgery, but not with treatment-related changes, the literature available on interpretation of the ratios provided in the context of defining tumour progression is not consistent.This article aims to provide an overview of the role perfusion MRI plays in the assessment of brain metastases and introduces the rationale for the STARBEAM-X study (Study of assessment of radionecrosis in brain metastases using MR perfusion extra imaging), which will prospectively evaluate baseline perfusion imaging in brain metastases. We hope this will allow insight into the vascular appearance of metastases from different primary sites, and aid in the interpretation of post-treatment perfusion imaging.

Optimization of Acquisition and Analysis Methods for Clinical Dynamic Susceptibility Contrast MRI Using a Population-Based Digital Reference Object

BACKGROUND AND PURPOSE

The accuracy of DSC-MR imaging CBV maps in glioblastoma depends on acquisition and analysis protocols. Multisite protocol heterogeneity has challenged standardization initiatives due to the difficulties of in vivo validation. This study sought to compare the accuracy of routinely used protocols using a digital reference object.

MATERIALS AND METHODS

The digital reference object consisted of approximately 10,000 simulated voxels recapitulating typical signal heterogeneity encountered in vivo. The influence of acquisition and postprocessing methods on CBV reliability was evaluated across 6912 parameter combinations, including contrast agent dosing schemes, pulse sequence parameters, field strengths, and postprocessing methods. Accuracy and precision were assessed using the concordance correlation coefficient and coefficient of variation.

RESULTS

Across all parameter space, the optimal protocol included full-dose contrast agent preload and bolus, intermediate (60°) flip angle, 30-ms TE, and postprocessing with a leakage-correction algorithm (concordance correlation coefficient = 0.97, coefficient of variation = 6.6%). Protocols with no preload or fractional dose preload and bolus using these acquisition parameters were generally less robust. However, a protocol with no preload, full-dose bolus, and low (30°) flip angle performed very well (concordance correlation coefficient = 0.93, coefficient of variation = 8.7% at 1.5T and concordance correlation coefficient = 0.92, coefficient of variation = 8.2% at 3T).

CONCLUSIONS

Schemes with full-dose preload and bolus maximize CBV accuracy and reduce variability, which could enable smaller sample sizes and more reliable detection of CBV changes in clinical trials. When a lower total contrast agent dose is desired, use of a low flip angle, no preload, and full-dose bolus protocol may provide an attractive alternative.

A Population-Based Digital Reference Object (DRO) for Optimizing Dynamic Susceptibility Contrast (DSC)-MRI Methods for Clinical Trials

The standardization and broad-scale integration of dynamic susceptibility contrast (DSC)-magnetic resonance imaging (MRI) have been confounded by a lack of consensus on DSC-MRI methodology for preventing potential relative cerebral blood volume inaccuracies, including the choice of acquisition protocols and postprocessing algorithms. Therefore, we developed a digital reference object (DRO), using physiological and kinetic parameters derived from in vivo data, unique voxel-wise 3-dimensional tissue structures, and a validated MRI signal computational approach, aimed at validating image acquisition and analysis methods for accurately measuring relative cerebral blood volume in glioblastomas. To achieve DSC-MRI signals representative of the temporal characteristics, magnitude, and distribution of contrast agent-induced T₁ and T₂* changes observed across multiple glioblastomas, the DRO's input parameters were trained using DSC-MRI data from 23 glioblastomas (>40 000 voxels). The DRO's ability to produce reliable signals for combinations of pulse sequence parameters and contrast agent dosing schemes unlike those in the training data set was validated by comparison with in vivo dual-echo DSC-MRI data acquired in a separate cohort of patients with glioblastomas. Representative applications of the DRO are presented, including the selection of DSC-MRI acquisition and postprocessing methods that optimize CBV accuracy, determination of the impact of DSC-MRI methodology choices on sample size requirements, and the assessment of treatment response in clinical glioblastoma trials.

Benefits of dynamic susceptibility-weighted contrast-enhanced perfusion MRI for glioma diagnosis and therapy

Glioma are the most common supra-tentorial brain tumor in the USA with an estimated annual incidence of 17,000 new cases per year. Dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI noninvasively characterizes tumor biology allowing for the diagnosis and therapeutic monitoring of glioma. This MRI technique utilizes the rapid changes in signal intensity caused by a rapid intravascular bolus of paramagnetic contrast agent to calculate physiologic perfusion metrics. DSC perfusion MRI has increasingly become an integrated part of glioma imaging. The specific aim of this article is to review the benefits of DSC perfusion MRI in the therapy of glioma.

Glioma Angiogenesis and Perfusion Imaging: Understanding the Relationship between Tumor Blood Volume and Leakiness with Increasing Glioma Grade

BACKGROUND AND PURPOSE

The purpose of this study was to investigate imaging correlates to the changes occurring during angiogenesis in gliomas. This was accomplished through in vivo assessment of vascular parameters (relative CBV and permeability surface-area product) and their changing relationship with increasing glioma grade.

MATERIALS AND METHODS

Seventy-six patients with gliomas underwent preoperative perfusion CT and assessment of relative CBV and permeability surface-area product. Regression analyses were performed to assess the rate of change between relative CBV and permeability surface-area product and to test whether these differed for distinct glioma grades. The ratio of relative CBV to permeability surface-area product was also computed and compared among glioma grades by using analysis of variance methods.

RESULTS

The rate of change in relative CBV with respect to permeability surface-area product was highest for grade II gliomas followed by grade III and then grade IV (1.64 versus 0.91 versus 0.27, respectively). The difference in the rate of change was significant between grade III and IV (P = .003) and showed a trend for grades II and IV (P = .098). Relative CBV/permeability surface-area product ratios were the highest for grade II and lowest for grade IV. The pair-wise difference among all 3 groups was significant (P < .001).

CONCLUSIONS

There is an increase in relative CBV more than permeability surface-area product in lower grade gliomas, whereas in grade III and especially grade IV gliomas, permeability surface-area product increases much more than relative CBV. The rate of change of relative CBV with respect to permeability surface-area product and relative CBV/permeability surface-area product ratio can serve as an imaging correlate to changes occurring at the tumor microvasculature level.

Definition of K(trans) and FA thresholds for better assessment of experimental glioma using high-field MRI: a feasibility study

PURPOSE

To define K(trans) and fractional anisotropy (FA) thresholds in correlation to histology for improved magnetic resonance imaging (MRI) tumor assessment in an animal model of brain glioma.

METHODS

Twelve rats underwent 4.7 T MRI at day 10 after tumor implantation. Anatomical scans (T2, T1 at 8 min after double dose contrast application) as well as dynamic contrast-enhanced (DCE) imaging with calculation of K(trans) and diffusion tensor imaging (DTI) with calculation of FA were performed. T2- and T1-derived tumor volumes were calculated and thresholds for K(trans) and FA were defined for best MRI tumor assessment correlated to histology.

RESULTS

Tumor volumes were 159 ± 14 mm(3) (histology), 126 ± 26 mm(3) (T1 with contrast, r=0.76), and 153 ± 12 mm(3) (T2, r=0.84), respectively. K(trans)- and FA-derived tumor volumes were 160 ± 16 mm(3) (for K(trans ≥ 0.04 min(-1), r=0.94), and 159 ± 14 mm(3) (for FA £0.14, r=0.96), respectively.

CONCLUSIONS

DCE-MRI and DTI with calculation of K(trans) and FA maps allow very precise brain glioma assessment comparable to histology if established thresholds for the given tumor model are used.

Effect of contrast leakage on the detection of abnormal brain tumor vasculature in high-grade glioma

Abnormal brain tumor vasculature has recently been highlighted by a dynamic susceptibility contrast (DSC) MRI processing technique. The technique uses independent component analysis (ICA) to separate arterial and venous perfusion. The overlap of the two, i.e. arterio-venous overlap or AVOL, preferentially occurs in brain tumors and predicts response to anti-angiogenic therapy. The effects of contrast agent leakage on the AVOL biomarker have yet to be established. DSC was acquired during two separate contrast boluses in ten patients undergoing clinical imaging for brain tumor diagnosis. Three components were modeled with ICA, which included the arterial and venous components. The percentage of each component as well as a third component were determined within contrast enhancing tumor and compared. AVOL within enhancing tumor was also compared between doses. The percentage of enhancing tumor classified as not arterial or venous and instead into a third component with contrast agent leakage apparent in the time-series was significantly greater for the first contrast dose compared to the second. The amount of AVOL detected within enhancing tumor was also significantly greater with the second dose compared to the first. Contrast leakage results in large signal variance classified as a separate component by the ICA algorithm. The use of a second dose mitigates the effect and allows measurement of AVOL within enhancement.

Imaging biomarkers of angiogenesis and the microvascular environment in cerebral tumours

Conventional contrast-enhanced CT and MRI are now in routine clinical use for the diagnosis, treatment and monitoring of diseases in the brain. The presence of contrast enhancement is a proxy for the pathological changes that occur in the normally highly regulated brain vasculature and blood-brain barrier. With recognition of the limitations of these techniques, and a greater appreciation for the nuanced mechanisms of microvascular change in a variety of pathological processes, novel techniques are under investigation for their utility in further interrogating the microvasculature of the brain. This is particularly important in tumours, where the reliance on angiogenesis (new vessel formation) is crucial for tumour growth, and the resulting microvascular configuration and derangement has profound implications for diagnosis, treatment and monitoring. In addition, novel therapeutic approaches that seek to directly modify the microvasculature require more sensitive and specific biological markers of baseline tumour behaviour and response. The currently used imaging biomarkers of angiogenesis and brain tumour microvascular environment are reviewed.

Clinical applications of imaging biomarkers. Part 3. The neuro-oncologist's perspective

Radiation therapy is an important treatment modality in the management of brain tumours. Imaging biomarkers continue to be a focus of active investigation and there is increasing evidence of the utility of biomarkers in refining the overall management plan. This article briefly reviews the literature and outlines the possible clinical applications of imaging biomarkers in neuro-oncology.

MRI perfusion in determining pseudoprogression in patients with glioblastoma

We examine the role of dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) perfusion in differentiating pseudoprogression from progression in 20 consecutive patients with treated glioblastoma. MRI perfusion was performed, and relative cerebral blood volume (rCBV), relative peak height (rPH), and percent signal recovery (PSR) were measured. Pseudoprogression demonstrated lower median rCBV (P=.009) and rPH (P<.001), and higher PSR (P=.039) than progression. DSC MRI perfusion successfully identified pseudoprogression in patients who did not require a change in treatment despite radiographic worsening following chemoradiotherapy.

Multiparametric analysis of magnetic resonance images for glioma grading and patient survival time prediction

BACKGROUND

A systematic comparison of magnetic resonance imaging (MRI) options for glioma diagnosis is lacking.

PURPOSE

To investigate multiple MR-derived image features with respect to diagnostic accuracy in tumor grading and survival prediction in glioma patients.

MATERIAL AND METHODS

T1 pre- and post-contrast, T2 and dynamic susceptibility contrast scans of 74 glioma patients with histologically confirmed grade were acquired. For each patient, a set of statistical features was obtained from the parametric maps derived from the original images, in a region-of-interest encompassing the tumor volume. A forward stepwise selection procedure was used to find the best combinations of features for grade prediction with a cross-validated logistic model and survival time prediction with a cox proportional-hazards regression.

RESULTS

Presence/absence of enhancement paired with kurtosis of the FM (first moment of the first-pass curve) was the feature combination that best predicted tumor grade (grade II vs. grade III-IV; median AUC = 0.96), with the main contribution being due to the first of the features. A lower predictive value (median AUC = 0.82) was obtained when grade IV tumors were excluded. Presence/absence of enhancement alone was the best predictor for survival time, and the regression was significant (P < 0.0001).

CONCLUSION

Presence/absence of enhancement, reflecting transendothelial leakage, was the feature with highest predictive value for grade and survival time in glioma patients.

Standardization of relative cerebral blood volume (rCBV) image maps for ease of both inter- and intrapatient comparisons

Relative cerebral blood volume (rCBV) measured using dynamic susceptibility contrast MRI suffers from interpatient and interstudy variability for the same tissue type. Traditionally, when a more quantitative assessment of rCBV is required, as for comparison across studies and patients, the rCBV values are normalized to the rCBV in a reference region such as normal-appearing white matter. However, this technique of normalization is subjective and time consuming and introduces user-dependent variability. In this study, we demonstrate that a method called standardization, applied to rCBV maps, is an objective means of translating all rCBV values to a consistent scale. This approach reduces interpatient and interstudy variability for the same tissue type, thus enabling easy and accurate visual and quantitative comparison across studies. One caveat to this approach is that it is not appropriate for the evaluation of global changes in blood volume, since systematic differences are removed in the process of standardization.

Dynamic susceptibility contrast perfusion MR imaging in distinguishing malignant from benign head and neck tumors: a pilot study

PURPOSE

To preliminarily investigate the utility of dynamic susceptibility contrast perfusion MR imaging in distinguishing malignant from benign head and neck tumors.

MATERIAL AND METHODS

Seventy eight patients with head and neck masses underwent single shot dynamic susceptibility contrast T2*-weighted perfusion weighted MR imaging after bolus infusion of gadolinium-DTPA was administrated. The signal intensity time curve of the lesion was created. Dynamic susceptibility contrast percentage (DSC%) was calculated and correlated with pathological findings.

RESULTS

The mean DSC% of malignant tumor (n=40) was 39.3±9.6% and of benign lesions (n=38) was 24.3±10.3%. There was a statistically significant difference of the DSC% between benign and malignant tumors (P=0.001) and within benign tumors (P=0.001). When DSC% of 30.7% was used as a threshold for differentiating malignant from benign tumors, the best results were obtained: accuracy of 84.6%, sensitivity of 80% and specificity of 89.2%.

CONCLUSION

Dynamic susceptibility contrast perfusion weighted MR imaging is a non-invasive imaging technique that can play a role in differentiation between malignant and benign head and neck tumors.

Quantitative imaging biomarkers in neuro-oncology

Conventional structural imaging provides limited information on tumor characterization and prognosis. Advances in neurosurgical techniques, radiotherapy planning and novel drug treatments for brain tumors have generated increasing need for reproducible, noninvasive, quantitative imaging biomarkers. This Review considers the role of physiological MRI and PET molecular imaging in understanding metabolic processes associated with tumor growth, blood flow and ultrastructure. We address the utility of various techniques in distinguishing between tumors and non-neoplastic processes, in tumor grading, in defining anatomical relationships between tumor and eloquent brain regions and in determining the biological substrates of treatment response. Much of the evidence is derived from limited case series in individual centers. Despite their 'added value', the effect of these techniques as an adjunct to structural imaging in clinical research and practice remains limited.

Glioma grading: sensitivity, specificity, positive and negative predictive values of diffusion and perfusion imaging

PURPOSE

The purpose of our study was to determine the statistical significance of thresholds of relative cerebral blood volume (rCBV), apparent diffusion coefficient (ADC) and ADC ratios in grading cerebral gliomas.

MATERIALS AND METHODS

In this retrospective study, 51 patients with histopathologically confirmed primary cerebral gliomas who had undergone conventional MR imaging, dynamic contrast-enhanced T2*-weighted perfusion MR imaging and diffusion MR imaging were included. A retrospective blinded analysis of the imaging findings including the perfusion and diffusion parameters was done. The rCBV measurements were obtained from regions of maximum perfusion. Minimum ADC values were obtained from the region of maximum hypointensity within the tumor and from the corresponding opposite white matter. Tumor grade determined with the two methods were then compared with the histopathologic grade. Mann-Whitney tests were performed to compare the DWI and PWI between tumor types. Receiver operating characteristic analyses were performed to determine optimum thresholds for tumor grading and also to calculate the sensitivity, specificity, PPV, and NPV for identifying high-grade gliomas.

RESULTS

Statistical analysis demonstrated a threshold value of 2.91 for rCBV to provide sensitivity, specificity, PPV, and NPV of 94.7, 93.75, 90.0, and 96.8%, respectively, in determining high-grade gliomas. An ADC value of 98.50 mm(2)/s was defined as a threshold below which tumors were classified as high-grade gliomas and a sensitivity, specificity, PPV, and NPV of 90, 87.1, 81.81 and 93.10% respectively, were obtained. Significant differences were noted in the rCBV ratios, ADC and ADC ratios between low- and high-grade gliomas (P < 0.0001).

CONCLUSION

Combining PWI and DWI with conventional MR imaging increases the accuracy of pre-operative imaging grading of glial neoplasms. The rCBV measurements had the most superior diagnostic performance in predicting glioma grade. Absolute ADC values or ADC ratios were also helpful in preoperative grading of gliomas. Threshold values can be used in a clinical setting to evaluate tumors preoperatively for histologic grade and provide a means for guiding treatment and predicting postoperative patient outcome.

[Diffusion and perfusion magnetic resonance imaging in evaluation of primary glial brain tumors]

INTRODUCTION

Diffusion (DWI) and perfusion (PWI) imaging can give important data about physiological characteristics of tissue, which complete morphologic findings from conventional MRI. The aim of this study is to estimate the value of these MRI technics in evaluation of primary glial brain tumors.

MATERIALS AND METHODS

The significance of DWI and PWI in differentiation of histologically proven low- and high-grade gliomas was estimated in 48 patient with diagnosed brain gliomas. ADC and rCBV values were compared by aplication of Mann-Whitney test, and logistic regression analysis was used to determine which of these two parameters contributed the most in increasing the diagnostic accuracy, ia. its sensitivity, specificity and predictive velues. ROC curves were constructed to determine threshold values for differentiation of low- from high-grade lesions.

RESULTS

Statistical significance were showed between mean values of rCBV for low-grade (0.82) and high-grade (5.32) gliomas, which was not found for values of ADC parameters. Threshold rCBV value of 1.23 was determinated for discrimination between low- and high-grade gliomas with a sensitivity of 83.2% and a specificity of 77.5%.

CONCLUSION

Conventional MRI combined with PWI increases the accuracy in determination of glioma grade.

Magnetic resonance perfusion imaging in neuro-oncology

Recent advances in magnetic resonance imaging (MRI) have seen the development of techniques that allow quantitative imaging of a number of anatomical and physiological descriptors. These techniques have been increasingly applied to cancer imaging where they can provide some insight into tumour microvascular structure and physiology. This review details technical approaches and application of quantitative MRI, focusing particularly on perfusion imaging and its role in neuro-oncology.

[Value of relative cerebral blood volume measurement using perfusion MRI in glioma management]

INTRODUCTION

Neoangiogenesis is a critical feature that can differentiate high-grade from low-grade glioma. Conventional MR imaging does not assess this histological feature accurately. The goal of this study was to evaluate the gain in relative cerebral blood volume measurement using perfusion MRI in the management of cerebral gliomas.

MATERIALS AND METHODS

Between 1998 and 2001, 32 histologically proven glial tumors were assessed by perfusion MRI using echoplanar imaging (EPI) and gradient-echo techniques. Relative cerebral blood volume (rCBV) was measured in all patients and compared to histological data.

RESULTS

rCBV values were significantly correlated to histological grading in all 32 patients (P<0.001). Mean rCBV values were 8.74 (+/-3.79) for glioblastomas, 7.37 (+/-2.83) for anaplastic gliomas and 0.84 (+/-0.61) for low-grade gliomas. Mean rCBV values were significantly different between low- and high-grade gliomas, making it possible to determine a threshold (2.5-3) that can separate these two types of lesion. In determining the histological grading, rCBV was shown to be significantly more accurate than conventional MRI (P<0.005).

CONCLUSION

Perfusion MRI using the EPI technique reliably assesses tumoral neoangiogenesis in gliomas preoperatively. The specificity and sensitivity of this technique make this radiological modality a valuable tool in the assessment of cerebral gliomas.

Gliomas: predicting time to progression or survival with cerebral blood volume measurements at dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging

PURPOSE

To retrospectively determine whether relative cerebral blood volume (CBV) measurements can be used to predict clinical outcome in patients with high-grade gliomas (HGGs) and low-grade gliomas (LGGs) and specifically whether patients who have gliomas with a high initial relative CBV have more rapid progression than those who have gliomas with a low relative CBV.

MATERIALS AND METHODS

Approval for this retrospective HIPAA-compliant study was obtained from the Institutional Board of Research Associates, with waiver of informed consent. One hundred eighty-nine patients (122 male and 67 female patients; median age, 43 years; range, 4-80 years) were examined with dynamic susceptibility-weighted contrast material-enhanced perfusion magnetic resonance (MR) imaging and were followed up clinically with MR imaging (median follow-up, 334 days). Log-rank tests were used to evaluate the association between relative CBV and time to progression by using Kaplan-Meier curves. Binary logistic regression was used to determine whether age, sex, and relative CBV were associated with an adverse event (progressive disease or death).

RESULTS

Values for the mean relative CBV for patients according to each clinical response were as follows: 1.41 +/- 0.13 (standard deviation) for complete response (n = 4), 2.36 +/- 1.78 for stable disease (n = 41), 4.84 +/- 3.32 for progressive disease (n = 130), and 3.82 +/- 1.93 for death (n = 14). Kaplan-Meier estimates of median time to progression in days indicated that patients with a relative CBV of less than 1.75 had a median time to progression of 3585 days, whereas patients with a relative CBV of more than 1.75 had a time to progression of 265 days. Age and relative CBV were also independent predictors for clinical outcome.

CONCLUSION

Dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging can be used to predict median time to progression in patients with gliomas, independent of pathologic findings. Patients who have HGGs and LGGs with a high relative CBV (>1.75) have a significantly more rapid time to progression than do patients who have gliomas with a low relative CBV.

Quantitative characterization of hemodynamic properties and vasculature dysfunction of high-grade gliomas

Aberrations in tumor and peritumoral vasculature may not be distinguishable by cerebral blood flow (CBF) or cerebral blood volume (CBV) alone. The relationships between CBF and CBV were examined to estimate vasculature-specific hemodynamic characteristics. Twenty glioma patients were studied with dynamic susceptibility T2*-weighted MRI [(dynamic contrast-enhanced magnetic resonance imaging (DSC-MRI)] before and during week 1 and 3 of radiotherapy (RT). CBF and CBV were calculated from DSC-MRI, and relationships between the two were evaluated: the physiological measure of mean transit time (MTT) = CBV/CBF; empirical fitting using the power law CBV = constant x (CBF)(beta). Three different tissue types were assessed: the Gd-enhancing tumor volume (GEV); non-enhanced abnormal tissue located beyond GEV but within the abnormal hyperintense region on FLAIR images (NEV); normal tissue in the hemisphere contralateral to the tumor (CNT). The effects of tissue types, CBV magnitudes (low, medium and high), before and during RT, on MTT and beta were analyzed by analysis of variance (ANOVA). The MTT and beta for the three tissue types were significantly different (p < 0.009). MTT increased from CNT (1.60 s) to NEV (1.93 s) to GEV (2.28 s) (p < 0.0005). beta was significantly greater in GEV (1.079) and NEV (1.070) than in CNT (1.025). Beta increased with increasing CBV magnitude while MTT was independent of CBV magnitude. There was a significant decrease in MTT of NEV and GEV during week 3 of RT compared with pre-RT values for all CBV magnitudes. There was a significant increase in beta during RT in the tumor and peritumor. Progressive abnormalities in vasculature and hemodynamic characteristics of the vascular bed were delineated, with significant disorder in the tumor but mild abnormality in peritumoral tissue.

Comparison of cerebral blood volume maps generated fromT2* andT1weighted MRI data in intra-axial cerebral tumours

We compared parametric maps, measured values and value distributions of cerebral blood volume (CBV) derived from (1) first pass T1 weighted dynamic contrast-enhanced (DCE) data (T1-CBV) using the recently described leakage profile model and (2) conventional T2* weighted DCE data (T2*-CBV) using a conventional curve fitting technique, in nine patients with intraaxial tumours. Regions of interest were defined around enhancing tumour tissue on matched slices. Median tumour values and conspicuity indexes of CBV from the two techniques were compared, demonstrating good correlation (r = 0.667,p<0.05) in enhancing tumour and no significant difference in conspicuity. Pixel-by-pixel scattergrams of values in normal brain in a representative matched slice were produced for each case, which showed excellent correlation (r = 0.96,p<0.001). Distortion of blood vessels around susceptibility interfaces was evident on T2* CBV but not on T1 CBV maps. Leakage-free T1 CBV maps do not suffer from the susceptibility artifacts seen in T2* CBV maps, although they present comparable biological information.

Comparison of region-of-interest analysis with three different histogram analysis methods in the determination of perfusion metrics in patients with brain gliomas

PURPOSE

To compare routine ROI analysis and three different histogram analyses in the grading of glial neoplasms. The hypothesis is that histogram methods can provide a robust and objective technique for quantifying perfusion data in brain gliomas. Current region-of-interest (ROI)-based methods for the analysis of dynamic susceptibility contrast perfusion magnetic resonance imaging (DSC MRI) data are operator-dependent.

MATERIALS AND METHODS

A total of 92 patients underwent conventional and DSC MRI. Multiple histogram metrics were obtained for cerebral blood flow (CBF), cerebral blood volume (CBV), and relative CBV (rCBV) maps using tumoral (T), peritumoral (P), and total tumoral (TT) analysis. Results were compared to histopathologic grades. Statistical analysis included Mann-Whitney (MW) tests, Spearman rank correlation coefficients, logistic regression, and McNemar tests.

RESULTS

The maximum value of rCBV (rCBV(max)) showed highly significant correlation with glioma grade (r = 0.734, P < 0.001). The strongest histogram correlations (P < 0.0001) occurred with rCBV(T) SD (r = 0.718), rCBV(P) SD(25) (r = 0.724) and rCBV(TT) SD(50) (r = 0.685). Multiple rCBV(T), rCBV(P), and rCBV(TT) histogram metrics showed significant correlations. CBF and CBV histogram metrics were less strongly correlated with glioma grade than rCBV histogram metrics.

CONCLUSION

Histogram analysis of perfusion MR provides prediction of glioma grade, with peritumoral metrics outperforming tumoral and total tumoral metrics. Further refinement may lead to automated methods for perfusion data analysis.

IRM de diffusion-perfusion dans l’évaluation des lymphomes cérébraux

Because of the increasing incidence of cerebral lymphoma, it is critical for patient management to recognize the MR features of this disease. We present the characteristic morphological and functional MRI features of this tumor. The findings on MRI studies, including morphological, diffusion and perfusion imaging, performed in 9 biopsy-proven cases of cerebral lymphoma with 13 lesions are presented and analyzed, and are discussed in comparison with published literature data. All patients underwent diffusion-weighted imaging with a single shot echo-planar pulse sequence. Dynamic susceptibility-contrast MRI was performed using a T2*-weighted gradient-echo echo-planar sequence after intravenous injection of chelates of gadolinium at the rate of 6 ml/s and a temporal resolution of 1 second. All cases of cerebral lymphoma appeared hypointense or isointense on T1-weighted images and in 75% of cases iso- or hypointense on T2-weighted images. All lesions enhanced except one in a patient receiving steroid therapy. On diffusion-weighted images, tumours were hyperintense with normal or decreased ADC values (0.717+/-0.152.10-3 mm2/sec, range: 0.550-1.014) and an ADC ratio tumour/normal white matter of 0.974+/-0.190 (range: 0.768-1.410). On perfusion, the signal intensity-time curve of each tumour showed a characteristic type of curve with a significant increase of the signal intensity above the baseline and a low maximum relative cerebral blood volume ratio (rCVBmax) of 1.43+/-0.64 (0.55-2.62). Due to their higher cellularity, the lack of neoangiogenesis, and the increased permeability of the blood-brain barrier related to the infiltration of blood vessels wall by lymphomatous cells, cerebral lymphoma presents characteristic diffusion and perfusion MRI features that should be useful for diagnosis and patient follow-up.

Advanced MR Imaging Techniques in the Diagnosis of Intraaxial Brain Tumors in Adults

Intraaxial brain masses are a significant health problem and present several imaging challenges. The role of imaging is no longer limited to merely providing anatomic details. Sophisticated magnetic resonance (MR) imaging techniques allow insight into such processes as the freedom of water molecule movement, the microvascular integrity and hemodynamic characteristics, and the chemical makeup of certain compounds of masses. The role of the most commonly used advanced MR imaging techniques-perfusion imaging, diffusion-weighted imaging, and MR spectroscopy-in the diagnosis and classification of the most common intraaxial brain tumors in adults is explored. These lesions include primary neoplasms (high- and low-grade), secondary (meta-static) neoplasms, lymphoma, tumefactive demyelinating lesions, abscesses, and encephalitis. Application of a diagnostic algorithm that integrates advanced MR imaging features with conventional MR imaging findings may help the practicing radiologist make a more specific diagnosis for an intraaxial tumor.

Dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging in pediatric patients

Dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MR (pMR) imaging provides hemodynamic information that complements traditional structural MR imaging and is becoming increasingly used in clinical practice to diagnose, manage, and understand brain tumors in the pediatric patient group. pMR imaging-derived regional cerebral blood volume (rCBV) maps provide quantitative estimates of rCBV that can be used to grade gliomas, differentiate between different brain tumor types, and distinguish tumor from nonneoplastic lesions. There are a few minor limitations of the DSC pMR imaging technique, such as susceptibility artifacts, relative rather than absolute quantification of cerebral blood volume (CBV), and inaccurate estimation of CBV in situations of severe disruption or absence of the blood-brain barrier. Recognizing its strengths and potential pitfalls, pMR imaging can be used as part of the routine evaluation of brain tumors to improve the diagnostic accuracy, understand tumor pathophysiology, detect and quantify tumor angiogenesis, and, with further work, serve as an arbiter to assess existing and novel cancer therapies that target blood vessels.

Place de l’imagerie de perfusion par irm dans la prise en charge des tumeurs cérébrales, gliales en particulier

OBJECT

To discuss the pertinency of perfusion MR imaging for initial diagnosis and follow up of brain tumors.

METHODOLOGY

Dynamic susceptibility contrast MR imaging was applied. Images were thus obtained with intensities proportional to the cerebral blood volume (CBV). Relative cerebral blood volume (rCBV) maps were then generated by normalizing the signal intensities with respect to measurements made in healthy tissue.

RESULTS

The method provided interesting data for establishing the differential diagnosis between different kinds of lesions, in particular between lymphoma and pilocytic astrocytoma, and for grading gliomas.

DISCUSSION AND CONCLUSION

Limits of the approach are discussed, in particular with respect to quantification aspects and interpretation of the results. The approach could be particularly useful for grading oligodendrogliomas, for which histological diagnosis on biopsy is sometimes difficult.

Correlation of MR perfusion imaging and vessel tortuosity parameters in assessment of intracranial neoplasms

Advances in noninvasive imaging techniques such as magnetic resonance perfusion imaging have been found useful in grading cerebral neoplasms and have potential for significant clinical benefit. The purpose of this study was to determine the correlation between tumor vessel tortuosity as measured from vessels extracted from magnetic resonance angiograms (MRA) and perfusion parameters of cerebral blood flow (CBF) and cerebral blood volume (CBV) in intracranial neoplasms. We hypothesized that tumor blood vessel tortuosity measures and perfusion measures would be correlated, since both are increased by tumor angiogenesis. 18 patients with 19 cerebral neoplasms were evaluated with conventional MR imaging and dynamic contrast-enhanced T2-weighted perfusion MR imaging (PWI). Both benign and malignant lesions were included, as were hyper- and hypovascular tumors. Regions of interest were plotted within the tumor area to locate foci of maximum CBV and CBF. CBV and CBF measurements were also recorded in contralateral normal appearing white matter to calculate relative CBV (rCBV) and relative CBF (rCBF). Vessel tortuosity analyses were conducted upon vessels segmented from MRA images of the same patients using two tortuosity descriptors (SOAM and ICM), which have previously been demonstrated to have efficacy in separating benign from malignant disease. Linear regression analyses were conducted to determine if correlations exist between CBV or CBF and the two tortuosity measurements. For the overall set of tumors, no significant correlations were found between flow or volume measures and the tortuosity measures. However, when the 7 glioblastoma multiforme tumors were examined as a subgroup, the following significant correlations were found: rCBV and SOAM (R2=0.799), rCBV and ICM (R2=0.214). Our results demonstrate that MR perfusion imaging data do not correlate significantly with vessel tortuosity parameters as determined from the larger vessels seen by MRA. However, for subgroups of a particular tumor type such as GBM, there may be significant correlations. It appears that perfusion and tortuosity data may provide independently useful data in the assessment of cerebral neoplasms.

MRI for assessing antivascular cancer treatments

Selective antiangiogenesis and vascular targeting drugs hold out the promise of improved efficacy and tolerability for anticancer treatments. Early phase 1 drug trials have shown good tolerability for antiangiogenesis agents with biological activity below the maximum tolerated dose. Advanced clinical trials have demonstrated that morphological assessments of tumour response are of limited value in gauging the efficacy of treatment. MRI is a versatile technique which is sensitive to contrast mechanisms that can be affected by antivascular treatments; this use for MRI has been validated in xenografts and humans. Dynamic contrast-enhanced MRI (DCE-MRI), which demonstrates tissue perfusion and permeability, is being used clinically as a pharmacodynamic indicator of biological activity for antivascular cancer drugs. Early data show that DCE-MRI studies can define the biologically active dose and predict the efficacy of treatment on the basis of changes observed. MRI with macromolecular contrast media (MMCM) depicts microvessel permeability and fractional plasma volume. Xenograft studies with MMCM have shown great promise for evaluating antivascular treatments but this has not been used clinically. Intrinsic susceptibility-weighted MRI, which is sensitive to blood oxygenation and flow, is emerging as a technique that may be able to monitor vascular targeting therapies.

Les méningiomes rachidiens extraduraux : Données IRM à propos de deux observations

Spinal extradural meningiomas are rare and may be easily confused with malignant neoplasms. We report two unusual cases of epidural spinal meningioma one within the left C6-C7 foramen and the other within the left posterolateral epidural space at the T3-T4 level. Low signal intensity of the tumor on T2-wi, thickening and enhancement of the dura with only the possibility of bone erosion are the most characteristic MR findings.

Perfusion MR imaging: basic principles and clinical applications

Dynamic contrast-enhanced perfusion MR imaging provides hemodynamic information that complements traditional structural imaging and is increasingly used in clinical practice to diagnose, manage, and understand brain tumors. Relative cerebral blood volume maps derived from perfusion MR imaging data provide quantifiable estimates of regional blood volume that can be used to grade gliomas, differentiate different brain tumor types, and distinguish tumors from non-neoplastic lesions. There are a few minor limitations of the dynamic contrastenhanced perfusion MR imaging technique-susceptibility artifacts, relative rather than absolute quantification of cerebral blood volume, and the inaccurate estimation of cerebral blood volume in patients in whom the blood-brain barrier has been severely disrupted or destroyed. Despite the minor potential pitfalls of the technique, inclusion of perfusion MR imaging as part of a routine evaluation of brain tumors can lead to improved diagnostic accuracy, understanding of tumor pathophysiology, and detection and quantification of tumor angiogenesis. With further work, perfusion MR imaging could be used to assess existing and novel cancer therapies that target blood vessels.

Blood oxygenation level-dependent MRI of cerebral gliomas during breath holding

PURPOSE

To assess the cerebrovascular responses to short breath holding of cerebral gliomas using blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Six patients with a low-grade glioma and one patient with a high-grade glioma were studied using T2*-weighted echo planar imaging (EPI) during repeated periods of 15-second or 20-second breath-holding. Tumor vascularity was evaluated using dynamic susceptibility contrast perfusion MRI.

RESULTS

Increases in BOLD signal intensity during repeated breath-holding were consistently identified in patients' normal appearing gray matter, comparable with those in healthy adults. Absence of significant BOLD signal enhancement was noted both in low-grade and high-grade gliomas, which is either due to overwhelming hypoxia in a tumor, inadequacy or absence of hypercapnia-induced vasodilatation of tumor vessels, or both. Breath-hold regulated decreases in BOLD signals occurred only in the high-grade glioma, which is most likely due to the hypercapnia-induced steal effect that redistributes blood flow from tumor regions with unresponsive neovasculature to surrounding normal tissue.

CONCLUSION

BOLD MRI during short breath holding can disclose differential cerebrovascular response between normal tissue and cerebral glioma.

Dynamic contrast-enhanced MRI in clinical oncology: current status and future directions

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is performed after the administration of intravenous contrast medium to noninvasively access tumor vascular characteristics. DCE-MRI techniques utilizing low-molecular-weight contrast media have successfully made the transition from methodological development to preclinical and clinical validation and are now rapidly becoming mainstream clinical tools. DCE-MRI using macromolecular contrast medium (MMCM) can also assay microvascular characteristics of human tumor xenografts. MMCM approval for human use will occur soon. The success of both techniques depends on their ability to demonstrate quantitative differences of contrast medium behavior in a variety of tissues. Evidence is mounting that kinetic parameters correlate with immunohistochemical surrogates of tumor angiogenesis, including microvessel density, and with pathologic tumor grade. DCE-MRI is being applied to monitor the clinical effectiveness of a variety of treatments, including antiangiogenic drugs. Kinetic parameter changes following treatment have correlated with histopathological outcome and patient survival. This article reviews the current clinical status of low-molecular-weight DCE-MRI and reviews the potential of MMCM techniques for evaluating human tumors. Ongoing challenges faced by DCE-MRI as clinical and research tools will be explored.

Intracranial mass lesions: dynamic contrast-enhanced susceptibility-weighted echo-planar perfusion MR imaging

Dynamic contrast agent-enhanced perfusion magnetic resonance (MR) imaging provides physiologic information that complements the anatomic information available with conventional MR imaging. Analysis of dynamic data from perfusion MR imaging, based on tracer kinetic theory, yields quantitative estimates of cerebral blood volume that reflect the underlying microvasculature and angiogenesis. Perfusion MR imaging is a fast and robust imaging technique that is increasingly used as a research tool to help evaluate and understand intracranial disease processes and as a clinical tool to help diagnose, manage, and understand intracranial mass lesions. With the increasing number of applications of perfusion MR imaging, it is important to understand the principles underlying the technique. In this review, the essential underlying physics and methods of dynamic contrast-enhanced susceptibility-weighted echo-planar perfusion MR imaging are described. The clinical applications of cerebral blood volume maps obtained with perfusion MR imaging in the differential diagnosis of intracranial mass lesions, as well as the pitfalls and limitations of the technique, are discussed. Emphasis is on the clinical role of perfusion MR imaging in providing insight into the underlying pathophysiology of cerebral microcirculation.