Quantitative blood flow measurements in gliomas using arterial spin-labeling at 3T: intermodality agreement and inter- and intraobserver reproducibility study

Use of Radiomics Models in Preoperative Grading of Cerebral Gliomas and Comparison with Three-dimensional Arterial Spin Labelling

AIMS

To build machine learning-based radiomics models to discriminate between high- (HGGs) and low-grade gliomas (LGGs) and to compare the effectiveness of three-dimensional arterial spin labelling (3D-ASL) to evaluate which is a better method.

MATERIALS AND METHODS

We retrospectively analysed the magnetic resonance imaging T1WI-enhanced images of 105 patients with gliomas that were pathologically confirmed in our hospital. We divided the patients into a training group and a verification group at a ratio of 8:2; 200 patients from the Brain Tumour Segmentation Challenge 2020 were selected as the test group for image segmentation, feature extraction and screening. We constructed models using multilayer perceptron (MLP), support vector machine, random forest and logistic regression and evaluated their predictive performance. We obtained the mean maximum relative cerebral blood flow (rCBFmax) value from 3D-ASL of 105 patients from the hospital to evaluate its efficacy in discriminating between HGGs and LGGs.

RESULTS

In machine learning, the MLP classifier model exhibited the best performance in discriminating between HGGs and LGGs; the areas under the curve obtained by MLP and rCBFmax were 0.968 versus 0.815 (verification group) and 0.981 versus 0.815 (test group), respectively. The machine learning-based MLP classifier model performed better in discriminating between HGGs and LGGs than 3D-ASL.

CONCLUSION

In our study, we found that machine learning-based radiomics models and 3D-ASL were valuable in discriminating between HGGs and LGGs and between them, the machine learning-based MLP model had better diagnostic performance.

Insights Into Meningioma Visibility on Arterial Spin Labeling MRI: Location Outweighs Size

Background Arterial Spin Labeling (ASL) MRI is a non-invasive imaging technique with potential applications for assessing meningiomas. This retrospective study aimed to investigate the impact of tumor location, size, age, and sex on the ASL visibility of meningiomas. Methods We retrospectively analysed 40 patients with meningiomas, who underwent 3 Tesla MRI examinations using a three-dimensional (3D) pulsed ASL technique. Tumor location was categorized as around the skull base or elsewhere, and size was determined by the area in the transverse plane. Results Our findings revealed that meningiomas around the skull base were significantly more likely to be ASL-visible compared to those located elsewhere (p < 0.001), whereas tumor size, age, and sex did not show a significant correlation with ASL visibility. This observation suggests that tumor location is a critical factor in determining the visibility of meningiomas on ASL MRI. Conclusion The results contribute to a better understanding of ASL visibility in meningiomas, highlighting the importance of tumor location over size. Further research, including larger cohorts and additional factors, such as histological variants, is needed to expand upon these findings and explore their clinical implications.

Qualitative Assessment of Advanced MRI in Post-Treatment High Grade Gliomas Follow Up: Do We Agree?

PURPOSE

MRI is commonly used in follow up of high grade glioma. Our purpose is to assess the interrater agreement on the increasingly used visual qualitative assessment of various conventional and advanced MR techniques in the setting of treated high grade glioma in comparison to the well established quantitative measurements.

METHODS

We prospectively enrolled HGG patients who underwent reresection of a new enhancing lesion on post-treatment 3T MR examination including DWI, DCE and DSC sequences. Two neuroradiologists objectively assessed the diffusion and perfusion maps by placing ROI on representative post-processed maps. They subjectively assessed the post-contrast, perfusion and diffusion sequences. Interrater agreement and concordance correlation coefficient were calculated.

RESULTS

Twenty-eight lesions were included. The interrater agreement on the qualitative assessment was good for k-trans (k = 0.73), moderate for Vp (k = 0.52), fair for AUC and Ve maps (k = 0.37 and 0.21), fair for corrected CBV (k = 0.39) and poor for the enhancement pattern and presence of diffusion restriction (k = 0.02 and 0.07). The concordance between the quantitative measurements was substantial for AUC and Vp (ρc = 0.98 and 0.97), moderate for k-trans and corrected CBV (ρc = 0.94) and poor for Ve and ADC (ρc = 0.86 and 0.24).

CONCLUSION

While the quantitative measurements of DSC and DCE perfusion maps show satisfactory inter-rater agreement, the qualitative assessment has lower interobserver agreement and should not be relied upon solely in the interpretation. Similarly, the suboptimal inter-rater agreement on the interpretation of enhancement pattern and diffusion restriction potentially limits their usefulness in differentiating glioma recurrence from treatment related changes.

Perfusion Parameter Obtained on 3-Tesla Magnetic Resonance Imaging and the Ki-67 Labeling Index Predict the Overall Survival of Glioblastoma

BACKGROUND

Pulsed arterial spin-labeling, diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS) are useful for predicting glioma survival. We performed a comparative review of multiple parameters obtained using these pulse sequences on 3-Tesla magnetic resonance imaging (MRI) including the molecular status and Ki-67 labeling index in newly diagnosed supratentorial glioblastomas.

METHODS

A total of 35 patients with glioblastomas underwent pulsed arterial spin-labeling, DTI, and MRS studies using 3-Tesla MRI preoperatively. The isocitrate dehydrogenase (IDH) mutation status, methylguanine-DNA methyltransferase methylation status, and Ki-67 labeling index were calculated from the tumor specimen. Cutoff values were identified by analyzing a receiver operating characteristic curve, and the multivariate survival statistical technique was performed to determine the significant and independent parameters for predicting overall survival.

RESULTS

The multivariate Cox analysis showed that the maximum/mean relative cerebral blood flow (rCBF) ratio and the Ki-67 labeling index were significant and independent predictive parameters with a cutoff value of 1.589 for the maximum rCBF ratio, 1.286 for the mean rCBF ratio, and 19% for the Ki-67 labeling index and hazard ratios of 6.132 and 5.119, respectively. The Kaplan-Meier survival curves showed that patients with higher rCBF ratios and Ki-67 labeling indices had a shorter overall survival than others, with median overall survival durations of 479 (95% CI, 370-559) and 1243 (95% CI, 666-NA) days, respectively (P = 0.000167).

CONCLUSIONS

Our findings indicate that the preoperative rCBF ratio and Ki-67 labeling index are useful parameters for predicting the overall survival of cerebral glioblastomas.

Noninvasive Differentiation of Meningiomas and Dural Metastases Using Intratumoral Vascularity Obtained by Arterial Spin Labeling

PURPOSE

Using conventional magnetic resonance imaging (MRI) techniques, the imaging features of meningiomas and dural metastases overlap and a differentiation between these tumor entities therefore remains difficult, particularly in patients with a known primary neoplasm. The purpose of this study was to explore the potential role of normalized vascular intratumoral signal intensity values (nVITS) obtained from pulsed arterial spin labeling (PASL) to differentiate between meningiomas and dural metastases.

METHODS

In this study PASL was performed in 46 patients with meningiomas (n = 30) and dural metastases (n = 16) on a 3T scanner, in addition to the routine diagnostic imaging protocol. The ratio between the vascular signal intensity of the tumor and the contralateral normal white matter obtained by PASL images was defined as nVITS.

RESULTS

Meningiomas showed significantly higher nVITS values compared to dural metastases (p < 0.001). The optimal nVITS cut-off value to differentiate between the 2 tumor entities was 1.989, with 100% sensitivity and 81.2% specificity.

CONCLUSION

The nVITS values obtained by PASL provide a fast and noninvasive MRI technique with which to differentiate between meningiomas and dural metastases in a routine clinical setting based on tumor vascularity.

Effect of image quality fluctuations on the repeatability of thickness measurements in swept-source optical coherence tomography

This study investigated the effect of image quality fluctuations on the repeatability of thickness measurements of the peripapillary retinal nerve fibre (PP-RNFL) and ganglion cell-inner plexiform (GC-IPL) layers using swept-source optical coherence tomography (SS-OCT). Three consecutive OCT scans each were performed on 56 healthy subject. Finally, 168 SS-OCT results were analysed. Based on the tertile values of the mean absolute difference of image quality score, all subjects were divided into the following three groups—low-(LIQD), moderate-(MIQD), and high-(HIQD) image quality score difference groups. A linear mixed model and intraclass correlation coefficients (ICCs) were used for analyses. Despite high ICC values (> 0.9), several sectors showed significant differences in the ICC values in intergroup comparisons. For LIQD-HIQD and MIQD-HIQD, most PP-RNFL sectors showed significant differences. For GC-IPL sectors, the LIQD-HIQD comparison showed significant differences in the temporosuperior (p = 0.012), inferior (p < .001), and temporoinferior (p = 0.042) sectors. Significant differences existed in the average GC-IPL (p = 0.009), nasoinferior (p = 0.035), and inferior GC-IPL sectors (p < .001) for MIQD-HIQD comparison. With higher image quality fluctuations, the repeatability of SS-OCT decreased in several sectors, which are considered clinically relevant in evaluating glaucoma status. Therefore, maintaining high-quality image status is essential to enhance the reliability of SS-OCT.

Pseudo-continuous arterial spin labelling shows high diagnostic performance in the detection of postoperative residual lesion in hyper-vascularised adult brain tumours

OBJECTIVES

Our aim was to evaluate the contribution of pseudo-continuous arterial spin labelling (pCASL) in the detection of a postoperative residual lesion in adult brain tumours.

METHODS

Seventy-five patients were prospectively included. Following the results of preoperative DSC-PWI assessment, intra-axial lesions, including high-grade gliomas (n = 43) and certain metastases (n = 14), were classified as hyper-vascular (HV+ group, n = 57); other lesions, including low-grade gliomas and certain metastases, were classified as non-hyper-vascular (HV- group, n = 18). To confirm the absence/presence of a residual lesion or disease progression, postoperative MRI including pCASL sequence and follow-up-MRI were performed within 72 h and 1-6 months after the resection, respectively. Two raters evaluated the images. Mean and maximal ASL cerebral blood flow (CBF) values were measured in the perioperative region and normalised to the contralateral tissue. The pCASL-CBF maps and post-contrast T1WI were visually assessed for residual lesion. Quantitative data were analysed with unpaired Student t and Mann-Whitney U tests and the visual diagnostic performance with the McNemar test.

RESULTS

In the HV+ group, the mean normalised CBF was 1.97 ± 0.59 and 0.97 ± 0.29 (p < 0.0001, AUC = 0.964, cut-off = 1.27) for patients with or without residual tumours, respectively. The mean normalised CBF was not discriminative for assessing residual tumours in the HV- group (p = 0.454). Visual CBF evaluation allowed 92.98% patients belonging to the HV+ group to be correctly classified (sensitivity 93.02%, specificity 92.86%, p < 0.001). Visual evaluation was correlated with contrast enhancement evaluation and with the mean normalised CBF values (r = 0.505, p < 0.0001 and 0.838, p < 0.0001, respectively).

CONCLUSION

Qualitative and quantitative ASL evaluation shows high diagnostic performance in postoperative assessment of hyper-perfused tumours. In this case, postoperative pCASL may be useful, especially if contrast injection cannot be performed or when contrast enhancement is doubtful.

KEY POINTS

• Evaluation of postoperative residual lesion in the case of brain tumours is an imaging challenge. • This prospective monocentric study showed that increased normalised cerebral blood flow assessed by pseudo-continuous arterial spin labelling (pCASL) correlates well with the presence of a residual tumour in the case of hyper-vascular tumour diagnosed on preoperative MRI. • Qualitative and quantitative pCASL is an informative sequence for hyper-vascular residual tumour, especially if acquired more than 48 h after brain tumour surgery, when contrast enhancement can give ambiguous results due to blood-brain barrier disruption.

Combination of three-dimensional arterial spin labeling and stretched-exponential model in grading of gliomas

To evaluate the diagnostic value of combining 3D arterial spin labeling (ASL) and stretched-exponential diffusion model in grading of gliomas.A total of 72 patients with histo-pathology proved gliomas (34 low-grade, 38 high-grade) were included in this study. 3D ASL and multi-b diffusion weighted imaging (DWI) images were retrospectively analyzed. The ASL and DWI parameters-tumor blood flow (TBF), distributed diffusion coefficient (DDC), and diffusion heterogeneity α were compared between high-grade and low-grade groups and P < .05 was regarded as statistically significant. TBF was also normalized to the corresponding values in contralateral mirror regions of interest (ROI) (M-TBF), normal grey matter (G-TBF), and white matter (W-TBF) and were compared between high and low-grade tumors.TBF values were significantly higher in high-grade gliomas (P < .001). In stretched-exponential model, the α value of low-grade gliomas showed significant higher than high-grade gliomas group (P < .001), but there was no difference of DDC (P > .05). When TBF values were normalized to contralateral mirror ROI, normal grey matter and white matter, G-TBF showed the highest sensitivity and specificity for differentiation high-grade and low-grade gliomas. The area under area under curve (AUC) of G-TBF and α for glioma grading were 0.926 and 0.892, respectively. The area under AUC of the G-TBF combination with α was 0.960 and corresponding sensitivity and specificity were 94.1% and 98.7%.The combination of 3D ASL and stretched-exponential model parameters can be used to differentiate high-grade and low-grade gliomas. Combination G-TBF and α value can obtain best diagnostic performance.

The value of arterial spin labelling in adults glioma grading: systematic review and meta-analysis

This study aimed to evaluate the diagnostic performance of arterial spin labelling (ASL) in grading of adult gliomas. Eighteen studies matched the inclusion criteria and were included after systematic searches through EMBASE and MEDLINE databases. The quality of the included studies was assessed utilizing Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). The quantitative values were extracted and a meta-analysis was subsequently based on a random-effect model with forest plot and joint sensitivity and specificity modelling. Hierarchical summary receiver operating characteristic (HROC) curve analysis was also conducted. The absolute tumour blood flow (TBF) values can differentiate high-grade gliomas (HGGs) from low-grade gliomas (LGGs) and grade II from grade IV tumours. However, it lacked the capacity to differentiate grade II from grade III tumours and grade III from grade IV tumours. In contrast, the relative TBF (rTBF) is effective in differentiating HGG from LGG and in glioma grading. The maximum rTBF (rTBFmax) demonstrated the best results in glioma grading. These results were also reflected in the sensitivity/specificity analysis in which the rTBFmax showed the highest discrimination performance in glioma grading. The estimated effect size for the rTBF was approximately similar between HGGs and LGGs, and grade II and grade III tumours, (-1.46 (-2.00, -0.91), p-value < 0.001), (-1.39 (-1.89, -0.89), p-value < 0.001), respectively; while it exhibited smaller effect size between grade III and grade IV (-1.05 (-1.82, -0.27)), p < 0.05). Sensitivity and specificity analysis replicate these results as well. This meta-analysis suggests that ASL is useful for glioma grading, especially when considering the rTBFmax parameter.

Arterial spin labelling and diffusion-weighted imaging in paediatric brain tumours

BACKGROUND

Diffusion- and perfusion-weighted MRI are valuable tools for measuring the cellular and vascular properties of brain tumours. This has been well studied in adult patients, however, the biological features of childhood brain tumours are unique, and paediatric-focused studies are less common. We aimed to assess the diagnostic utility of apparent diffusion coefficient (ADC) values derived from diffusion-weighted imaging (DWI) and cerebral blood flow (CBF) values derived from arterial spin labelling (ASL) in paediatric brain tumours.

METHODS

We performed a meta-analysis of published studies reporting ADC and ASL-derived CBF values in paediatric brain tumours. Data were combined using a random effects model in order to define typical parameter ranges for different histological tumour subtypes and WHO grades. New data were also acquired in a 'validation cohort' at our institution, in which ADC and CBF values in treatment naïve paediatric brain tumour patients were measured, in order to test the validity of the findings from the literature in an un-seen cohort. ADC and CBF quantification was performed by two radiologists via manual placement of tumour regions of interest (ROIs), in addition to an automated approach to tumour ROI placement.

RESULTS

A total of 14 studies met the inclusion criteria for the meta-analysis, constituting data acquired in 542 paediatric patients. Parameters of interest were based on measurements from ROIs placed within the tumour, including mean and minimum ADC values (ADC_ROI-mean, ADC_ROI-min) and the maximum CBF value normalised to grey matter (nCBF_ROI-max). After combination of the literature data, a number of histological tumour subtype groups showed significant differences in ADC values, which were confirmed, where possible, in our validation cohort of 32 patients. In both the meta-analysis and our cohort, diffuse midline glioma was found to be an outlier among high-grade tumour subtypes, with ADC and CBF values more similar to the low-grade tumours. After grouping patients by WHO grade, significant differences in grade groups were found in ADC_ROI-mean, ADC_ROI-min, and nCBF_ROI-max, in both the meta-analysis and our validation cohort. After excluding diffuse midline glioma, optimum thresholds (derived from ROC analysis) for separating low/high-grade tumours were 0.95 × 10^-3 mm²/s (ADC_ROI-mean), 0.82 × 10^-3 mm²/s (ADC_ROI-min) and 1.45 (nCBF_ROI-max). These thresholds were able to identify low/high-grade tumours with 96%, 83%, and 83% accuracy respectively in our validation cohort, and agreed well with the results from the meta-analysis. Diagnostic power was improved by combining ADC and CBF measurements from the same tumour, after which 100% of tumours in our cohort were correctly classified as either low- or high-grade (excluding diffuse midline glioma).

CONCLUSION

ADC and CBF values are useful for differentiating certain histological subtypes, and separating low- and high-grade paediatric brain tumours. The threshold values presented here are in agreement with previously published studies, as well as a new patient cohort. If ADC and CBF values acquired in the same tumour are combined, the diagnostic accuracy is optimised.

Overview and Critical Appraisal of Arterial Spin Labelling Technique in Brain Perfusion Imaging

Arterial spin labelling (ASL) allows absolute quantification of CBF via a diffusible intrinsic tracer (magnetically labelled blood water) that disperses from the vascular system into neighbouring tissue. Thus, it can provide absolute CBF quantification, which eliminates the need for the contrast agent, and can be performed repeatedly. This review will focus on the common ASL acquisition techniques (continuous, pulsed, and pseudocontinuous ASL) and how ASL image quality might be affected by intrinsic factors that may bias the CBF measurements. We also provide suggestions to mitigate these risks, model appropriately the acquired signal, increase the image quality, and hence estimate the reliability of the CBF, which consists an important noninvasive biomarker. Emerging methodologies for extraction of new ASL-based biomarkers, such as arterial arrival time (AAT) and arterial blood volume (aBV), will be also briefly discussed.

Pseudoprogression of brain tumors

This review describes the definition, incidence, clinical implications, and magnetic resonance imaging (MRI) findings of pseudoprogression of brain tumors, in particular, but not limited to, high-grade glioma. Pseudoprogression is an important clinical problem after brain tumor treatment, interfering not only with day-to-day patient care but also the execution and interpretation of clinical trials. Radiologically, pseudoprogression is defined as a new or enlarging area(s) of contrast agent enhancement, in the absence of true tumor growth, which subsides or stabilizes without a change in therapy. The clinical definitions of pseudoprogression have been quite variable, which may explain some of the differences in reported incidences, which range from 9-30%. Conventional structural MRI is insufficient for distinguishing pseudoprogression from true progressive disease, and advanced imaging is needed to obtain higher levels of diagnostic certainty. Perfusion MRI is the most widely used imaging technique to diagnose pseudoprogression and has high reported diagnostic accuracy. Diagnostic performance of MR spectroscopy (MRS) appears to be somewhat higher, but MRS is less suitable for the routine and universal application in brain tumor follow-up. The combination of MRS and diffusion-weighted imaging and/or perfusion MRI seems to be particularly powerful, with diagnostic accuracy reaching up to or even greater than 90%. While diagnostic performance can be high with appropriate implementation and interpretation, even a combination of techniques, however, does not provide 100% accuracy. It should also be noted that most studies to date are small, heterogeneous, and retrospective in nature. Future improvements in diagnostic accuracy can be expected with harmonization of acquisition and postprocessing, quantitative MRI and computer-aided diagnostic technology, and meticulous evaluation with clinical and pathological data.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

The role of cerebral blood flow gradient in peritumoral edema for differentiation of glioblastomas from solitary metastatic lesions

OBJECTIVE

Differentiation of glioblastomas from solitary brain metastases using conventional MRI remains an important unsolved problem. In this study, we introduced the conception of the cerebral blood flow (CBF) gradient in peritumoral edema-the difference in CBF values from the proximity of the enhancing tumor to the normal-appearing white matter, and investigated the contribution of perfusion metrics on the discrimination of glioblastoma from a metastatic lesion.

MATERIALS AND METHODS

Fifty-two consecutive patients with glioblastoma or a solitary metastatic lesion underwent three-dimensional arterial spin labeling (3D-ASL) before surgical resection. The CBF values were measured in the peritumoral edema (near: G1; Intermediate: G2; Far: G3). The CBF gradient was calculated as the subtractions CBFG1 -CBFG3, CBFG1 - CBFG2 and CBFG2 - CBFG3. A receiver operating characteristic (ROC) curve analysis was used to seek for the best cutoff value permitting discrimination between these two tumors.

RESULTS

The absolute/related CBF values and the CBF gradient in the peritumoral regions of glioblastomas were significantly higher than those in metastases(P < 0.038). ROC curve analysis reveals, a cutoff value of 1.92 ml/100g for the CBF gradient of CBFG1 -CBFG3 generated the best combination of sensitivity (92.86%) and specificity (100.00%) for distinguishing between a glioblastoma and metastasis.

CONCLUSION

The CBF gradient in peritumoral edema appears to be a more promising ASL perfusion metrics in differentiating high grade glioma from a solitary metastasis.

[Non-contrast ASL perfusion in preoperative diagnosis of supratentorial gliomas]

The purpose of this study was to investigate the potential of pseudocontinuous arterial spin labeling perfusion (pCASL) in assessing the degree of malignancy of brain gliomas at the preoperative stage. MATERIAL AND METHODS: The study included 126 patients aged 12-75 years with supratentorial gliomas of different malignancy (35 low-grade gliomas and 91 high-grade gliomas). The maximum tumor blood flow (TBF) was measured, and the normalized tumor blood flow (nTBF) was calculated relative to the intact semiovale white matter of the contralateral hemisphere. The TBF and nTBF indicators differed significantly between low-grade and high-grade glioma groups (p<0.001). When using TBF and nTBF in the differential diagnosis of low-grade and high-grade gliomas, the area under the ROC curve was 0.96 in both cases. Our findings suggest that 3D pCASL perfusion is an effective technique for preoperative differential diagnosis of low-grade and high-grade gliomas. The study was supported by the Russian Foundation for Basic Research (grant #18-315-00384).

Diagnostic Performance of Arterial Spin Labeling for Grading Nonenhancing Astrocytic Tumors

Purpose:

We evaluated the utility of arterial spin labeling (ASL) imaging of tumor blood flow (TBF) for grading non-enhancing astrocytic tumors.

Materials and Methods:

Thirteen non-enhancing astrocytomas were divided into high-grade (n = 7) and low-grade (n = 6) groups. Both ASL and conventional sequences were acquired using the same magnetic resonance machine. Intratumoral absolute maximum TBF (TBF_max), absolute mean TBF (TBF_mean), and corresponding values normalized to cerebral blood flow (TBF_max and TBF_mean ratios) were measured. The Mann-Whitney U test and receiver operating characteristic (ROC) curve analysis were used to assess the accuracy of TBF variables for tumor grading.

Results:

Compared with low-grade astrocytoma, high-grade astrocytoma exhibited significantly greater absolute TBF_max (90.93 ± 24.96 vs 46.94 ± 20.97 ml/100 g/min, P < 0.001), TBF_mean (58.75 ± 19.89 vs 31.16 ± 17.63 ml/100 g/min, P < 0.001), TBF_max ratio (3.34 ± 1.22 vs 1.35 ± 0.5, P < 0.001), and TBF_mean ratio (2.15 ± 0.94 vs 0.88 ± 0.41, P < 0.001). The TBF_max ratio yielded the highest diagnostic accuracy (sensitivity 100%, specificity 86.3%), while absolute TBF_mean yielded the lowest accuracy (sensitivity 85.7%, specificity 70.1%) by ROC analysis.

Conclusion:

Parameters from ASL perfusion imaging, particularly TBF_max ratio, may be useful for distinguishing high-grade from low-grade astrocytoma in cases with equivocal conventional MRI findings.

Reduced regional cerebral blood flow in patients with heart failure

AIMS

Heart failure (HF) patients show significant lateralized neural injury, accompanied by autonomic, mood and cognitive deficits. Both gray and white matter damage occurs and probably develops from altered cerebral blood flow (CBF), a consequence of impaired cardiac output. However, the distribution of regional CBF changes in HF patients is unknown, but is an issue in determining mechanisms of neural injury. Our aim was to compare regional CBF changes in HF with CBF in control subjects using non-invasive pseudo-continuous arterial spin labelling (ASL) procedures.

METHODS AND RESULTS

We collected pseudo-continuous ASL data from 19 HF patients [mean age 55.5 ± 9.1 years; mean body mass index 27.7 ± 5.3 kg/m² ; 13 male) and 29 control subjects (mean age 51.4 ± 5.3 years; mean body mass index 25.7 ± 3.6 kg/m² ; 18 male), using a 3.0-Tesla magnetic resonance imaging (MRI) scanner. Whole-brain CBF maps were calculated, normalized to a common space, smoothed and compared between groups using ANCOVA (covariates; age, gender and gray matter volume). Reduced CBF appeared in multiple sites in HF patients in comparison with controls, with principally lateralized lower flow in temporal, parietal and occipital regions. Areas with decreased CBF included the bilateral prefrontal, frontal, temporal and occipital cortex, thalamus, cerebellum, corona radiate, corpus callosum, hippocampus and amygdala.

CONCLUSIONS

Heart failure patients showed lower, and largely lateralized, CBF in multiple autonomic, mood and cognitive regulatory sites. The reduced CBF is likely to contribute to the lateralized brain injury, leading to the autonomic and neuropsychological deficits found in the condition.

Three-dimensional arterial spin labeling imaging and dynamic susceptibility contrast perfusion-weighted imaging value in diagnosing glioma grade prior to surgery

The current study aimed to investigate whole-brain three-dimensional arterial spin labeling imaging (3D ASL) and dynamic susceptibility contrast perfusion-weighted imaging (DSC-PWI), in regards to their diagnostic value of preoperative glioma grade. The parameter values obtained after correction will be correlated with the diagnostic value of 3D ASL and DSC-PWI perfusion. In the current study, 50 patients with gliomas confirmed by pathology were used, including 27 low-grade gliomas (LGGs) and 23 high-grade gliomas (HGGs). Prior to surgery all patients underwent 3 Tesla magnetic resonance imaging (MRI), 3D ASL, DSC-PWI and conventional enhanced MRI scans to obtain original 3D ASL and DSC-PWI images, and the tumor regions with the most obvious parenchyma perfusion and contralateral normal white matter were selected. In these areas, the ASL-relative cerebral blood flow (ASL-rCBF), DSC-relative cerebral blood flow (DSC-rCBF) and DSC-relative cerebral blood volume (DSC-rCBV) parameter values were then obtained after correction for individual differences. The results of the present study show that ASL-CBF, DSC-CBF, DSC-CBV values and ASL-rCBF, DSC-rCBF, DSC-rCBV values increased as the grade of the glioma being imaged increased, and there was a marked difference between the HGGs and the LGGs. ASL-rCBF was significantly positively correlated with DSC-rCBF (r=0.580, P<0.01). In addition, ASL-rCBF was significantly positively correlated with DSC-rCBV (r=0.431, P<0.01). Receiver operating characteristic (ROC) curves were applied to compare the two perfusion parameters of DSC-PWI and 3D ASL in the diagnosis of glioma grade. ASL-rCBF had the highest area value under the ROC curve (0.836). The areas under the ROC curve of DSC-rCBF and DSC-rCBV were analyzed using the Z test, but the difference was not statistically significant. When ASL-rCBF, DSC-rCBF and DSC-rCBV were cutoff at 2.24, 1.85 and 1.68, the sensitivity of HGG diagnosis was 83.2, 91.3 and 91.3%, and the specificity was 77.7, 63.9 and 66.7%, respectively.

Magnetic resonance imaging based functional imaging in paediatric oncology

Imaging is central to management of solid tumours in children. Conventional magnetic resonance imaging (MRI) is the standard imaging modality for tumours of the central nervous system (CNS) and limbs and is increasingly used in the abdomen. It provides excellent structural detail, but imparts limited information about tumour type, aggressiveness, metastatic potential or early treatment response. MRI based functional imaging techniques, such as magnetic resonance spectroscopy, diffusion and perfusion weighted imaging, probe tissue properties to provide clinically important information about metabolites, structure and blood flow. This review describes the role of and evidence behind these functional imaging techniques in paediatric oncology and implications for integrating them into routine clinical practice.

A meta-analysis of arterial spin labelling perfusion values for the prediction of glioma grade

AIM

To investigate the ability of arterial spin labelling (ASL) perfusion parameters to distinguish high-grade from low-grade gliomas.

MATERIALS AND METHODS

The PubMed and EMBASE databases were systematically searched for relevant articles published up to September 2015. Studies that evaluated both high- and low-grade gliomas using ASL were included. The random effect model was used to calculate the standardised mean difference (SMD) of maximum mean absolute tumour blood flow values (aTBF_max, aTBF_mean) and maximum mean relative tumour blood flow (rTBF_max, rTBF_mean) between high- and low-grade gliomas.

RESULTS

Nine studies encompassing 305 patients with high- and low-grade gliomas, met all inclusion and exclusion criteria and were included in the study. Compared with low-grade gliomas, high-grade gliomas had a significant increase in all ASL perfusion values: aTBF_max (SMD=0.70, 95% confidence interval [CI]: 0.22-1.19, p=0.0046); aTBF_mean (SMD=0.86, 95% CI: 0.2-1.52, p=0.01); rTBF_max (SMD=1.08, 95% CI: 0.54-1.63, p=0.0001) and rTBF_mean (SMD=0.88, 95% CI: 0.35-1.4, p=0.0011).

CONCLUSIONS

The current study results indicate that tumour blood flow from ASL differs significantly with respect to the glioma grade. Despite some limitations, there is evidence that ASL may be useful to distinguish high- and low-grade gliomas. Further larger-scale studies are necessary to examine the utility of ASL to distinguish tumour grade.

Improving the Grading Accuracy of Astrocytic Neoplasms Noninvasively by Combining Timing Information with Cerebral Blood Flow: A Multi-TI Arterial Spin-Labeling MR Imaging Study

BACKGROUND AND PURPOSE

Systematic and accurate glioma grading has clinical significance. We present the utility of multi-TI arterial spin-labeling imaging and provide the bolus arrival time maps for grading astrocytomas.

MATERIALS AND METHODS

Forty-three patients with astrocytomas (21 men; mean age, 51 years) were recruited. The classification abilities of conventional MR imaging features, normalized CBF value derived from multi-TI arterial spin-labeling imaging, normalized bolus arrival time, and normalized CBF derived from single-TI arterial spin-labeling were compared in patients with World Health Organization (WHO) grade II, III, and IV astrocytomas.

RESULTS

The normalized CBF value derived from multi-TI arterial spin-labeling imaging was higher in patients with higher grade astrocytoma malignancies compared with patients with lower grade astrocytomas, while the normalized bolus arrival time showed the opposite tendency. The normalized CBF value derived from the multi-TI arterial spin-labeling imaging showed excellent performance with areas under the receiver operating characteristic curve of 0.813 (WHO II versus III), 0.964 (WHO II versus IV), 0.872 (WHO III versus IV), and 0.883 (low-grade-versus-high-grade gliomas). The normalized CBF value derived from single-TI arterial spin-labeling imaging could statistically differentiate the WHO II and IV groups (area under the receiver operating characteristic curve = 0.826). The normalized bolus arrival time effectively identified the WHO grades II and III with an area under the receiver operating characteristic curve of 0.836. Combining the normalized CBF value derived from multi-TI arterial spin-labeling imaging and normalized bolus arrival time improved the diagnostic accuracy from 65.10% to 72.10% compared with the normalized CBF value derived from multi-TI arterial spin-labeling imaging being applied independently. The combination of multi-TI arterial spin-labeling imaging and conventional MR imaging had the best performance, with a diagnostic accuracy of 81.40%.

CONCLUSIONS

Multi-TI arterial spin-labeling imaging can evaluate perfusion dynamics by combining normalized bolus arrival time and normalized CBF values derived from multiple TIs. It is superior to single-TI arterial spin-labeling imaging and conventional MR imaging features when applied independently and can improve the diagnostic accuracy when combined with conventional MR imaging for grading astrocytomas.

Differentiation of Glioblastoma from Brain Metastasis: Qualitative and Quantitative Analysis Using Arterial Spin Labeling MR Imaging

PURPOSE

To evaluate the diagnostic performance of cerebral blood flow (CBF) by using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging to differentiate glioblastoma (GBM) from brain metastasis.

MATERIALS AND METHODS

The institutional review board of our hospital approved this retrospective study. The study population consisted of 128 consecutive patients who underwent surgical resection and were diagnosed as either GBM (n = 89) or brain metastasis (n = 39). All participants underwent preoperative MR imaging including ASL. For qualitative analysis, the tumors were visually graded into five categories based on ASL-CBF maps by two blinded reviewers. For quantitative analysis, the reviewers drew regions of interest (ROIs) on ASL-CBF maps upon the most hyperperfused portion within the tumor and upon peritumoral T2 hyperintensity area. Signal intensities of intratumoral and peritumoral ROIs for each subject were normalized by dividing the values by those of contralateral normal gray matter (nCBFintratumoral and nCBFperitumoral, respectively). Visual grading scales and quantitative parameters between GBM and brain metastasis were compared. In addition, the area under the receiver-operating characteristic curve was used to evaluate the diagnostic performance of ASL-driven CBF to differentiate GBM from brain metastasis.

RESULTS

For qualitative analysis, GBM group showed significantly higher grade compared to metastasis group (p = 0.001). For quantitative analysis, both nCBFintratumoral and nCBFperitumoral in GBM were significantly higher than those in metastasis (both p < 0.001). The areas under the curve were 0.677, 0.714, and 0.835 for visual grading, nCBFintratumoral, and nCBFperitumoral, respectively (all p < 0.001).

CONCLUSION

ASL perfusion MR imaging can aid in the differentiation of GBM from brain metastasis.

Arterial spin labeling: Pathologically proven superiority over conventional MRI for detection of high-grade glioma progression after treatment

BACKGROUND

Standard of care for high-grade gliomas (HGGs) includes surgical debulking and adjuvant chemotherapy and radiation. Patients under treatment require frequent clinical and imaging monitoring for therapy modulation. Differentiating tumor progression from treatment-related changes can be challenging on conventional MRI, resulting in delayed recognition of tumor progression. Arterial spin labeling (ASL) may be more sensitive for tumor progression.

MATERIALS AND METHODS

ASL and associated conventional MR images obtained in patients previously treated for HGGs and before biopsy or re-resection were reviewed by three neuroradiologists who were blinded to the histopathologic results. Regions of interest (ROIs) of greatest perfusion were chosen by consensus, and mirror-image contralateral ROIs were also placed. Sensitivity of ASL for tumor progression was compared with those of contrast-enhanced T1-weighted (T1W-CE) and fluid-attenuated inversion recovery (FLAIR) images using McNemar's test. We tested for an association between cerebral blood flow (CBF) and apparent diffusion correlation (ADC) using a Hotelling-Lawley trace. Finally, we used a Pearson's analysis to test for a correlation between CBF and percentage of tumor within each resection.

RESULTS

Twenty-two patients were studied. ASL demonstrated hyperperfusion in all cases with mean CBF ratio 3.37 (±1.71). T1W-CE and FLAIR images were positive in 15 (p = 0.0233) and 16 (p = 0.0412) cases, respectively. There was no association between ADC and CBF (p = 0.687). There was a correlation between CBF and percentage of tumor (p = 0.048).

CONCLUSION

ASL may be more sensitive than conventional MR sequences for the detection of tumor progression in patients treated for HGGs.

Assessment of glioma response to radiotherapy using 3D pulsed-continuous arterial spin labeling and 3D segmented volume

BACKGROUND

Gliomas are the most common primary brain tumors in adults, in some cases, radiotherapy may be the preferred treatment option especially for elderly people who cannot endure surgery. Therefore, it is necessary to evaluate the effects of radiotherapy on glioma. Arterial spin labeling (ASL) is an MR imaging technique that allows for a quantitative determination of cerebral blood flow (CBF) noninvasively. Tumor volume is still an important determinant for evaluating treatment response. The purpose of this study was to investigate the relationship between the tumor perfusion parameters and tumor volume and assess the effects of radiotherapy on glioma using pulsed-continuous arterial spin labeling (pcASL) technique.

METHODS

35 patients with gliomas, histologically classified as low-grade group (n=16) and high-grade group (n=19), treated with radiotherapy only or before using other therapies were included in this study. MR examinations, including T1 weighted image and pcASL, were performed before and 4, 8, 12, 16 weeks after radiotherapy. Regional CBF of normal tissue, mean tumor blood flow (TBF_mean), maximum tumor blood flow (TBF_max), and tumor volume were evaluated at each time point. Both the percentage change in CBF (CBF ratio), TBF_mean (TBF_mean ratio), TBF_max (TBF_max ratio) and the percentage change in tumor volume (volume ratio) were calculated using values obtained before and after radiotherapy. The correlation between the volume ratio and CBF ratio, TBF_mean ratio, TBF_max ratio was assessed using linear regression analysis and Pearson's correlation.

RESULTS

The TBF_mean and TBF_max of high-grade gliomas were significantly higher than that of low-grade group. In high-grade group, a strong correlation was demonstrated between the tumor volume and the TBF_max before radiotherapy (R²=0.35, r_s=0.59, p<0.05). There was also a significant correlation between the TBF_max before radiotherapy and the tumor volume ratio before and 8 weeks after radiotherapy (R²=0.56, r_s=-0.74, p<0.05).

CONCLUSION

The TBF_max measured using pcASL could assess tumoral grade and also could become a potential tool for evaluating the therapeutic effects of radiation.

Comparison between dynamic susceptibility contrast magnetic resonance imaging and arterial spin labeling techniques in distinguishing malignant from benign brain tumors

OBJECTIVES

The purpose of this study was to preliminarily compare unenhanced arterial spin-labeled (ASL) imaging, dynamic susceptibility contrast-enhanced cerebral blood volume (DSCE-CBV) magnetic resonance imaging (MRI) for evaluation of tumor perfusion in patients with brain tumors.

MATERIALS AND METHODS

A total of 27 patients with brain tumors were examined in 1,5T MRI. Single phase and multiphase ASL, DSCE-CBV examinations were assessed by both qualitative and quantitative analysis for the detection of malignancy. Imaging results were correlated with a histopathology or follow-up.

RESULTS

Based on 31 studies in 27 patients with brain tumors, the visual inspection sensitivities for ASL and dynamic DSC perfusion imaging were 88% and 94%, respectively, with 100% specificity for both. On qualitative evaluation, sensitivities for ASL and DSC perfusion imaging perfusions were 88% and 94%, respectively, with 100% specificity for both. The highest sensitivity values for quantitative ASL imaging were obtained using a normalized cut-off ratio of 1.65, resulting in sensitivity of 94% for ASL imaging and cut-off ratio of 1.95 and sensitivity 94% for DSCE-CBV imaging.

CONCLUSION

The present study revealed similar sensitivity and specificity for both multhiphase ASL and DSC MRI. Thus, we suggest that ASL perfusion can be used in daily clinical practice.

Arterial Spin Labeling Techniques 2009-2014

PURPOSE

Arterial spin labeling (ASL) techniques have been implemented across a diverse range of clinical and experimental applications. This review aims to evaluate the current feasibility of ASL in clinical neuroradiology based on recent improvements to ASL sequences and highlight areas for potential clinical applications.

METHODS AND MATERIALS

In December 2014, a literature search was conducted on PubMed Central, EMBASE, and Scopus using the search terms: "arterial spin labeling, neuroradiology," for studies published between 2009 and 2014 (inclusive). Of 483 studies matching the inclusion criteria, the number of studies using continuous, pseudocontinuous, pulsed, and velocity-selective ASL sequences was 42, 209, 226, and 3, respectively. Studies were classified based on several common clinical applications according to the type of ASL sequence used. Studies using pulsed ASL and pseudo-continuous ASL were grouped based on common sequences.

RESULTS

The number of clinical studies was 264. Numerous studies applied ASL to stroke management (43 studies), drug testing (21 studies), neurodegenerative diseases (40 studies), and psychiatric disorders (26 studies).

CONCLUSIONS

This review discusses several factors hindering the implementation of clinical ASL and ASL-related radiofrequency safety issues encountered in clinical practice. However, a limited number of search terms were used. Further development of robust sequences with multislice imaging capabilities and reduced radiofrequency energy deposition will hopefully improve the clinical acceptance of ASL.

Intravoxel incoherent motion diffusion-weighted imaging analysis of diffusion and microperfusion in grading gliomas and comparison with arterial spin labeling for evaluation of tumor perfusion

PURPOSE

To determine the utility of intravoxel incoherent motion (IVIM) imaging in grading gliomas and compare IVIM perfusion metrics with arterial spin labeling (ASL)-derived cerebral blood flow (CBF).

MATERIALS AND METHODS

Fifty-two patients with pathologically confirmed gliomas underwent IVIM and ASL imaging at 3.0T. IVIM perfusion-related diffusivity (D*), perfusion fraction (f), product of f and D*(f×D*), true diffusivity (D), and apparent diffusion coefficient (ADC) were obtained to distinguish glioma grades. The CBF derived from pseudocontinuous ASL within the solid tumor was compared and correlated with IVIM perfusion metrics for grading of gliomas. Values were also normalized to the contralateral normal-appearing white matter. Receiver-operating characteristic was performed to determine diagnostic efficiency. The reliability was estimated with intraclass coefficient, coefficient of variance, and Bland-Altman plots.

RESULTS

IVIM perfusion metrics and CBF were significantly higher in the high-grade than the low-grade gliomas (P < 0.001), ADC and D were significantly lower in the high-grade than the low-grade gliomas (P < 0.001). f×D* differed significantly between grades II through IV (P < 0.05 for all). The other metrics showed significant difference between grade II and grade III (P < 0.05 for all). Area under the curve (AUC) was largest for f×D* in distinguishing high-grade from low-grade gliomas (AUC = 0.979, P < 0.001) and between grade II and grade III (AUC = 0.957, P < 0.001). f×D* improved diagnostic performance of CBF in grading gliomas and showed strong correlation with CBF (r = 0.696, P < 0.001).

CONCLUSION

IVIM-derived metrics are promising biomarkers in preoperative grading gliomas. IVIM imaging may be an additive method to ASL and ADC for evaluating tumor perfusion and diffusion. J. Magn. Reson. Imaging 2016;44:620-632.

Application of Ultrahigh Field Magnetic Resonance Imaging in the Treatment of Brain Tumors: A Meta-Analysis

BACKGROUND

Magnetic resonance imaging (MRI) is the imaging modality of choice for the clinical management of brain tumors, and the majority of scanners operate with static magnetic field strengths of 1.5 or 3.0 Tesla (T). During the past decade, ultrahigh field (UHF) MRI has been investigated for its clinical applicability. This meta-analysis evaluates studies pertaining to the application of UHF MRI to patients with brain tumors.

METHODS

The authors performed a systematic review of the literature. Articles relating to application of UHF MRI to brain anatomy and brain tumors with living subjects were included. Studies were grouped into 1 of 3 categories based on area of focus: "Anatomical Structures Involved with Brain Tumors," "Tumor characterization," and "Treatment Monitoring." Comparison studies with extractable outcomes measure data were analyzed for performance of UHF MRI versus clinical field strengths (1.5 T and 3 T).

RESULTS

Twenty-four studies (361 subjects) met inclusion criteria. The field of study was heterogeneous and rigorous statistical analysis was not possible. Overall, 279 patients with brain tumors scanned at UHF MRI have been reported. Of these, glioma and glioblastoma multiforme are the most commonly studied lesions (38.9% and 24.4%, respectively). In comparison studies between UHF MRI and clinical field strengths, 24 of 51 patients had outcome measures that were better with UHF MRI, 17 of 24 were equivalent at both field strengths, and 9 were worse at UHF MRI. The most common causes of a worse performance were susceptibility artifacts and magnetic field inhomogeneities (3 of 9). Imaging of the pituitary gland, pineal gland veins, cranial nerves, and tumor microvasculature were all shown to be feasible.

CONCLUSIONS

UHF MRI shows promise to improve detection and characterization of brain tumors, preoperative planning for neurosurgical resection, and longitudinal monitoring of the effects of radiation and antibody-based therapies. Technical innovations are needed to overcome field inhomogeneity and susceptibility artifacts in certain regions of the skull. Finally, larger studies comparing 1.5 T, 3.0 T, and 7.0 T or greater will determine whether UHF MRI gains acceptance as a clinical standard.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.

Optimization of arterial spin labeling MRI for quantitative tumor perfusion in a mouse xenograft model

Perfusion is an important biomarker of tissue function and has been associated with tumor pathophysiology such as angiogenesis and hypoxia. Arterial spin labeling (ASL) MRI allows noninvasive and quantitative imaging of perfusion; however, the application in mouse xenograft tumor models has been challenging due to the low sensitivity and high perfusion heterogeneity. In this study, flow-sensitive alternating inversion recovery (FAIR) ASL was optimized for a mouse xenograft tumor. To assess the sensitivity and reliability for measuring low perfusion, the lumbar muscle was used as a reference region. By optimizing the number of averages and inversion times, muscle perfusion as low as 32.4 ± 4.8 (mean ± standard deviation) ml/100 g/min could be measured in 20 min at 7 T with a quantification error of 14.4 ± 9.1%. Applying the optimized protocol, heterogeneous perfusion ranging from 49.5 to 211.2 ml/100 g/min in a renal carcinoma was observed. To understand the relationship with tumor pathology, global and regional tumor perfusion was compared with histological staining of blood vessels (CD34), hypoxia (CAIX) and apoptosis (TUNEL). No correlation was observed when the global tumor perfusion was compared with these pathological parameters. Regional analysis shows that areas of high perfusion had low microvessel density, which was due to larger vessel area compared with areas of low perfusion. Nonetheless, these were not correlated with hypoxia or apoptosis. The results suggest that tumor perfusion may reflect certain aspect of angiogenesis, but its relationship with other pathologies needs further investigation.

Comparison of Intravoxel Incoherent Motion Diffusion-Weighted MR Imaging and Arterial Spin Labeling MR Imaging in Gliomas

Gliomas grading is important for treatment plan; we aimed to investigate the application of intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) in gliomas grading, by comparing with the three-dimensional pseudocontinuous arterial spin labeling (3D pCASL). 24 patients (13 high grade gliomas and 11 low grade gliomas) underwent IVIM DWI and 3D pCASL imaging before operation; maps of fast diffusion coefficient (D^∗), slow diffusion coefficient (D), fractional perfusion-related volume (f), and apparent diffusion coefficient (ADC) as well as cerebral blood flow (CBF) were calculated and then coregistered to generate the corresponding parameter values. We found CBF and D^∗ were higher in the high grade gliomas, whereas ADC, D, and f were lower (all P < 0.05). In differentiating the high from low grade gliomas, the maximum areas under the curves (AUC) of D^∗, CBF, and ADC were 0.857, 0.85, and 0.902, respectively. CBF was negatively correlated with f in tumor (r = −0.619, P = 0.001). ADC was positively correlated with D in both tumor and white matter (r = 0.887, P = 0.000 and r = 0.824, P = 0.000, resp.). There was no correlation between CBF and D^∗ in both tumor and white matter (P > 0.05). IVIM DWI showed more efficiency than 3D pCASL but less validity than conventional DWI in differentiating the high from low grade gliomas.

3D GRASE pulsed arterial spin labeling at multiple inflow times in patients with long arterial transit times: comparison with dynamic susceptibility-weighted contrast-enhanced MRI at 3 Tesla

Pulsed arterial spin labeling (PASL) at multiple inflow times (multi-TIs) is advantageous for the measurement of brain perfusion in patients with long arterial transit times (ATTs) as in steno-occlusive disease, because bolus-arrival-time can be measured and blood flow measurements can be corrected accordingly. Owing to its increased signal-to-noise ratio, a combination with a three-dimensional gradient and spin echo (GRASE) readout allows acquiring a sufficient number of multi-TIs within a clinically feasible acquisition time of 5 minutes. We compared this technique with the clinical standard dynamic susceptibility-weighted contrast-enhanced imaging-magnetic resonance imaging in patients with unilateral stenosis >70% of the internal carotid or middle cerebral artery (MCA) at 3 Tesla. We performed qualitative (assessment by three expert raters) and quantitative (region of interest (ROI)/volume of interest (VOI) based) comparisons. In 43 patients, multi-TI PASL-GRASE showed perfusion alterations with moderate accuracy in the qualitative analysis. Quantitatively, moderate correlation coefficients were found for the MCA territory (ROI based: r=0.52, VOI based: r=0.48). In the anterior cerebral artery (ACA) territory, a readout related right-sided susceptibility artifact impaired correlation (ROI based: r=0.29, VOI based: r=0.34). Arterial transit delay artifacts were found only in 12% of patients. In conclusion, multi-TI PASL-GRASE can correct for arterial transit delay in patients with long ATTs. These results are promising for the transfer of ASL to the clinical practice.

Assesment of perfusion in glial tumors with arterial spin labeling; comparison with dynamic susceptibility contrast method

PURPOSE

Arterial spin labeling perfusion imaging (ASL-PI) is a non-invasive perfusion imaging method that can be used for evaluation and quantification of cerebral blood flow (CBF). Aim of our study was to evaluating the efficiency of ASL in histopathological grade estimation of glial tumors and comparing findings with dynamic susceptibility contrast perfusion imaging (DSC-PI) method.

METHODS

This study involved 33 patients (20 high-grade and 13 low-grade gliomas). Multiphase multislice pulsed ASL MRI sequence and a first-passage gadopentetate dimeglumine T2*-weighted gradient-echo single-shot echo-planar sequence were acquired for all the patients. For each patient, perfusion relative signal intensity (rSI), CBF and relative CBF (rCBF) on ASL-PI and relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) values on DSC-PI were determined. The relative signal intensity of each tumor was determined as the maximal SI within the tumor divided by SI within symetric region in the contralateral hemisphere on ASL-PI. rCBV and rCBF were calculated by deconvolution of an arterial input function. Relative values of the lesions were obtained by dividing the values to the normal appearing symmetric region on the contralateral hemisphere. For statistical analysis, Mann-Whitney ranksum test was carried out. Receiver operating characteristic curve (ROC) analysis was performed to assess the relationship between the rCBF-ASL, rSI-ASL, rCBV and rCBF ratios and grade of gliomas. Their cut-off values permitting best discrimination was calculated. The correlation between rCBV, rCBF, rSI-ASL and rCBF-ASL and glioma grade was assessed using Spearman correlation analysis.

RESULTS

There was a statistically significant difference between low and high-grade tumors for all parameters. Correlation analyses revealed significant positive correlations between rCBV and rCBF-ASL (r=0.81, p<0.001). However correlation between rCBF and rCBF-ASL was weaker (r=0.64, p<0.001).

CONCLUSION

Arterial spin labeling is an employable imaging technique for evaluating tumor perfusion non-invasively and may be useful in differentiating high and low grade gliomas.

Comparison of multiple parameters obtained on 3T pulsed arterial spin-labeling, diffusion tensor imaging, and MRS and the Ki-67 labeling index in evaluating glioma grading

BACKGROUND AND PURPOSE

Pulsed arterial spin-labeling, DTI, and MR spectroscopy provide useful data for tumor evaluation. We evaluated multiple parameters by using these pulse sequences and the Ki-67 labeling index in newly diagnosed supratentorial gliomas.

MATERIALS AND METHODS

All 32 patients, with grade II (3 each of diffuse astrocytoma, oligodendroglioma, and oligoastrocytoma), grade III (3 anaplastic astrocytomas, 4 anaplastic oligodendrogliomas, and 1 anaplastic oligoastrocytoma), and grade IV (14 glioblastomas and 1 glioblastoma with an oligodendroglioma component) cases underwent pulsed arterial spin-labeling, DTI, and MR spectroscopy studies by using 3T MR imaging. The following variables were used to compare the tumors: relative cerebral blood flow, fractional anisotropy; ADC tumor/normal ratios; and the Cho/Cr, NAA/Cho, NAA/Cr, and lactate/Cr ratios. A logistic regression and receiver operating characteristic analysis were used to assess parameters with a high sensitivity and specificity to identify the threshold values for separate grading. We compared the Ki-67 index with various MR imaging parameters in tumor specimens.

RESULTS

Significant correlations were observed between the Ki-67 index and the mean, maximum, and minimum ADC, Cho/Cr, and lactate/Cr ratios. The receiver operating characteristic analysis showed that the combination of the minimum ADC and Cho/Cr ratios could differentiate low-grade and high-grade gliomas, with a sensitivity and specificity of 87.0% and 88.9%, respectively. The mean and maximum relative cerebral blood flow ratios were used to classify glioblastomas from other-grade astrocytomas, with a sensitivity and specificity of 92.9% and 83.3%, respectively.

CONCLUSIONS

Our findings indicate that pulsed arterial spin-labeling, DTI, and MR spectroscopy are useful for predicting glioma grade. Additionally, the parameters obtained on DTI and MR spectroscopy closely correlated with the proliferative potential of gliomas.

Prognostic value of blood flow measurements using arterial spin labeling in gliomas

The period of event-free survival (EFS) within the same histopathological glioma grades may have high variability, mainly without a known cause. The purpose of this study was to reveal the prognostic value of quantified tumor blood flow (TBF) values obtained by arterial spin labeling (ASL) for EFS in patients with histopathologically proven astrocytomas independent of WHO (World Health Organization) grade. Twenty-four patients with untreated gliomas underwent tumor perfusion quantification by means of pulsed ASL in 3T. The clinical history of the patients was retrospectively extracted from the local database. Six patients had to be excluded due to insufficent follow-up data for further evaluation or histopathologically verified oligodendroglioma tumor components. Receiver operating characteristic (ROC) curves were used to define an optimal cut-off value of maximum TBF (mTBF) values for subgrouping in low-perfused and high-perfused gliomas. Kaplan-Meier curves and Cox proportional hazard regression model were used to determine the prognostic value of mTBF for EFS. An optimal mTBF cut-off value of 182 ml/100 g/min (sensitivity  = 83%, specificity  = 100%) was determined. Patients with low-perfused gliomas had significantly longer EFS compared to patients with high-perfused gliomas (p = 0.0012) independent of the WHO glioma grade. Quantified mTBF values obtained by ASL offer a new and totally non-invasive marker to prognosticate the EFS, independently on histopathological tumor grading, in patients with gliomas.

Comparative analysis of arterial spin labeling and dynamic susceptibility contrast perfusion imaging for quantitative perfusion measurements of brain tumors

We comparatively analyzed the difference between three-dimensional arterial spin labeling (3D-ASL) and the conventional dynamic susceptibility contrast (DSC) perfusion imaging in the setting of assessing brain tumor perfusion in 28 patients with proved brain tumors. All patients were scheduled with standard MRI, 3D-ASL and DSC scannings on a GE DISCOVERY MR 750 system. Maximal relative tumor perfusion was obtained based on the region of interest (ROI) method. A close correlation between 3D-ASL and DSC perfusion imaging was noted as manifested by the absence of significant differences between ASL nTBF and DSC nTBF when normalized to M (mirror region) and GM (contralateral gray matter). However, ASL nTBF was found to be highly correlated with DSC nTBF and DSC nTBV when normalized to M, GM and WM (contralateral normal white matter). Together, our data support that 3D-ASL possesses the potential to be a noninvasive alternate for DSC-MRI in assessing brain tumor perfusion in the setting of treatment prognosis and metastasis, particularly for those patients with renal failure and patients required for collection of follow up information.

Early detection of antiangiogenic treatment responses in a mouse xenograft tumor model using quantitative perfusion MRI

Angiogenesis plays a major role in tumor growth and metastasis, with tumor perfusion regarded as a marker for angiogenesis. To evaluate antiangiogenic treatment response in vivo, we investigated arterial spin labeling (ASL) magnetic resonance imaging (MRI) to measure tumor perfusion quantitatively. Chronic and 24-h acute treatment responses to bevacizumab were assessed by ASL and dynamic-contrast-enhanced (DCE) MRI in the A498 xenograft mouse model. After the MRI, tumor vasculature was assessed by CD34 staining. After 39 days of chronic treatment, tumor perfusion decreased to 44.8 ± 16.1 mL/100 g/min (P < 0.05), compared to 92.6 ± 42.9 mL/100 g/min in the control group. In the acute treatment study, tumor perfusion in the treated group decreased from 107.2 ± 32.7 to 73.7 ± 27.8 mL/100 g/min (P < 0.01; two-way analysis of variance), as well as compared with control group post dosing. A significant reduction in vessel density and vessel size was observed after the chronic treatment, while only vessel size was reduced 24 h after acute treatment. The tumor perfusion correlated with vessel size (r = 0.66; P < 0.005) after chronic, but not after acute treatment. The results from DCE-MRI also detected a significant change between treated and control groups in both chronic and acute treatment studies, but not between 0 and 24 h in the acute treatment group. These results indicate that tumor perfusion measured by MRI can detect early vascular responses to antiangiogenic treatment. With its noninvasive and quantitative nature, ASL MRI would be valuable for longitudinal assessment of tumor perfusion and in translation from animal models to human.

Arterial spin-labeling assessment of normalized vascular intratumoral signal intensity as a predictor of histologic grade of astrocytic neoplasms

BACKGROUND AND PURPOSE

Pulsed arterial spin-labeling is a noninvasive MR imaging perfusion method performed with the use of water in the arterial blood as an endogenous contrast agent. The purpose of this study was to determine the inversion time with the largest difference in normalized intratumoral signal intensity between high-grade and low-grade astrocytomas.

MATERIALS AND METHODS

Thirty-three patients with gliomas, histologically classified as low-grade (n = 7) or high-grade astrocytomas (n = 26) according to the World Health Organization brain tumor classification, were included. A 3T MR scanner was used to perform pulsed arterial spin-labeling measurements at 8 different inversion times (370 ms, 614 ms, 864 ms, 1114 ms, 1364 ms, 1614 ms, 1864 ms, and 2114 ms). Normalized intratumoral signal intensity was calculated, which was defined by the signal intensity ratio of the tumor and the contralateral normal brain tissue for all fixed inversion times. A 3-way mixed ANOVA was used to reveal potential differences in the normalized vascular intratumoral signal intensity between high-grade and low-grade astrocytomas.

RESULTS

The difference in normalized vascular intratumoral signal intensity between high-grade and low-grade astrocytomas obtained the most statistically significant results at 370 ms (P = .003, other P values ranged from .012-.955).

CONCLUSIONS

The inversion time by which to differentiate high-grade and low-grade astrocytomas by use of normalized vascular intratumoral signal intensity was 370 ms in our study. The normalized vascular intratumoral signal intensity values at this inversion time mainly reflect the labeled intra-arterial blood bolus and therefore could be referred to as normalized vascular intratumoral signal intensity. Our data indicate that the use of normalized vascular intratumoral signal intensity values allows differentiation between low-grade and high-grade astrocytomas and thus may serve as a new, noninvasive marker for astrocytoma grading.

Clinical applications of arterial spin labeling

MR arterial spin labeling is primarily applied as a neuroimaging method to measure cerebral blood flow. As this technique becomes more widely available, a basic understanding of the clinical applications is necessary for optimal utilization in the setting of patient care. This review focuses on the use of arterial spin labeling imaging for the evaluation of cerebrovascular disease, brain tumors and neuropsychiatric illness.

Arterial spin-labeled perfusion of pediatric brain tumors

BACKGROUND AND PURPOSE

Pediatric brain tumors have diverse pathologic features, which poses diagnostic challenges. Although perfusion evaluation of adult tumors is well established, hemodynamic properties are not well characterized in children. Our goal was to apply arterial spin-labeling perfusion for various pathologic types of pediatric brain tumors and evaluate the role of arterial spin-labeling in the prediction of tumor grade.

MATERIALS AND METHODS

Arterial spin-labeling perfusion of 54 children (mean age, 7.5 years; 33 boys and 21 girls) with treatment-naive brain tumors was retrospectively evaluated. The 3D pseudocontinuous spin-echo arterial spin-labeling technique was acquired at 3T MR imaging. Maximal relative tumor blood flow was obtained by use of the ROI method and was compared with tumor histologic features and grade.

RESULTS

Tumors consisted of astrocytic (20), embryonal (11), ependymal (3), mixed neuronal-glial (8), choroid plexus (5), craniopharyngioma (4), and other pathologic types (3). The maximal relative tumor blood flow of high-grade tumors (grades III and IV) was significantly higher than that of low-grade tumors (grades I and II) (P < .001). There was a wider relative tumor blood flow range among high-grade tumors (2.14 ± 1.78) compared with low-grade tumors (0.60 ± 0.29) (P < .001). Across the cohort, relative tumor blood flow did not distinguish individual histology; however, among posterior fossa tumors, relative tumor blood flow was significantly higher for medulloblastoma compared with pilocytic astrocytoma (P = .014).

CONCLUSIONS

Characteristic arterial spin-labeling perfusion patterns were seen among diverse pathologic types of brain tumors in children. Arterial spin-labeling perfusion can be used to distinguish high-grade and low-grade tumors.

Comparison of three-dimensional pseudo-continuous arterial spin labeling perfusion imaging with gradient-echo and spin-echo dynamic susceptibility contrast MRI

PURPOSE

To compare the relative cerebral blood flow (CBF) obtained by pseudo-continuous arterial spin labeling sequence incorporated with volumetric fast spin-echo readout (3D-PCASL) with those by gradient-echo (GE) and spin-echo (SE) dynamic susceptibility contrast (DSC) MRI.

MATERIALS AND METHODS

Thirty patients with various neurological diseases participated in this study. In addition to 3D-PCASL, 15 patients received GE-DSC and the others received SE-DSC imaging on a 3 Tesla scanner. A cortical gray matter (GM) to white matter (WM) and a thalamus (TM) to WM CBF ratio were determined from each perfusion scan. In addition, histograms of relative CBF distributions were obtained from each method for comparison.

RESULTS

Significant correlations of CBF ratios were found between 3D-PCASL and the two DSC methods (P < 0.05). The 3D-PCASL resulted in GM/WM CBF ratios similar to SE-DSC but significantly smaller than GE-DSC (P = 2.3 × 10(-7) ). TM/WM CBF ratio obtained by 3D-PCASL was significantly smaller than those by GE- and SE-DSC (P = 4.1 × 10(-7) and 1.2 × 10(-6) , respectively). The histogram of relative CBF maps obtained from SE-DSC, after applied spatial smoothing, agreed well with that from 3D-PCASL.

CONCLUSION

This study suggested that perfusion images obtained from 3D-PCASL exhibited significant correlations with DSC-MRI, with greater microvascular weighting like SE-DSC.

Heterogeneity of cortical lesions in multiple sclerosis: an MRI perfusion study

In this study, dynamic susceptibility contrast-magnetic resonance imaging (DSC-MRI) was used to quantify the cerebral blood flow (CBF), the cerebral blood volume (CBV), and the mean transit time (MTT) and to analyze the changes in cerebral perfusion associated with the cortical lesions in 44 patients with relapsing-remitting multiple sclerosis. The cortical lesions showed a statistically significant reduction in CBF and CBV compared with the normal-appearing gray matter, whereas there were no significant changes in the MTT. The reduced perfusion suggests a reduction of metabolism because of the loss of cortical neurons. A small population of outliers showing an increased CBF and/or CBV has also been detected. The presence of hyperperfused outliers may imply that perfusion could evolve during inflammation. These findings show that perfusion is altered in cortical lesions and that DSC-MRI can be a useful tool to investigate more deeply the evolution of cortical lesions in multiple sclerosis.