Impact of a Categorical AI System for Digital Breast Tomosynthesis on Breast Cancer Interpretation by Both General Radiologists and Breast Imaging Specialists

Purpose To evaluate performance improvements of general radiologists and breast imaging specialists when interpreting a set of diverse digital breast tomosynthesis (DBT) examinations with the aid of a custom-built categorical artificial intelligence (AI) system. Materials and Methods A fully balanced multireader, multicase reader study was conducted to compare the performance of 18 radiologists (nine general radiologists and nine breast imaging specialists) reading 240 retrospectively collected screening DBT mammograms (mean patient age, 59.8 years ± 11.3 [SD]; 100% women), acquired between August 2016 and March 2019, with and without the aid of a custom-built categorical AI system. The area under the receiver operating characteristic curve (AUC), sensitivity, and specificity across general radiologists and breast imaging specialists reading with versus without AI were assessed. Reader performance was also analyzed as a function of breast cancer characteristics and patient subgroups. Results Every radiologist demonstrated improved interpretation performance when reading with versus without AI, with an average AUC of 0.93 versus 0.87, demonstrating a difference in AUC of 0.06 (95% CI: 0.04, 0.08; P < .001). Improvement in AUC was observed for both general radiologists (difference of 0.08; P < .001) and breast imaging specialists (difference of 0.04; P < .001) and across all cancer characteristics (lesion type, lesion size, and pathology) and patient subgroups (race and ethnicity, age, and breast density) examined. Conclusion A categorical AI system helped improve overall radiologist interpretation performance of DBT screening mammograms for both general radiologists and breast imaging specialists and across various patient subgroups and breast cancer characteristics. Keywords: Computer-aided Diagnosis, Screening Mammography, Digital Breast Tomosynthesis, Breast Cancer, Screening, Convolutional Neural Network (CNN), Artificial Intelligence Supplemental material is available for this article. © RSNA, 2024.

External Validation of an Ensemble Model for Automated Mammography Interpretation by Artificial Intelligence

Importance

With a shortfall in fellowship-trained breast radiologists, mammography screening programs are looking toward artificial intelligence (AI) to increase efficiency and diagnostic accuracy. External validation studies provide an initial assessment of how promising AI algorithms perform in different practice settings.

Objective

To externally validate an ensemble deep-learning model using data from a high-volume, distributed screening program of an academic health system with a diverse patient population.

Design, Setting, and Participants

In this diagnostic study, an ensemble learning method, which reweights outputs of the 11 highest-performing individual AI models from the Digital Mammography Dialogue on Reverse Engineering Assessment and Methods (DREAM) Mammography Challenge, was used to predict the cancer status of an individual using a standard set of screening mammography images. This study was conducted using retrospective patient data collected between 2010 and 2020 from women aged 40 years and older who underwent a routine breast screening examination and participated in the Athena Breast Health Network at the University of California, Los Angeles (UCLA).

Main Outcomes and Measures

Performance of the challenge ensemble method (CEM) and the CEM combined with radiologist assessment (CEM+R) were compared with diagnosed ductal carcinoma in situ and invasive cancers within a year of the screening examination using performance metrics, such as sensitivity, specificity, and area under the receiver operating characteristic curve (AUROC).

Results

Evaluated on 37 317 examinations from 26 817 women (mean [SD] age, 58.4 [11.5] years), individual model AUROC estimates ranged from 0.77 (95% CI, 0.75-0.79) to 0.83 (95% CI, 0.81-0.85). The CEM model achieved an AUROC of 0.85 (95% CI, 0.84-0.87) in the UCLA cohort, lower than the performance achieved in the Kaiser Permanente Washington (AUROC, 0.90) and Karolinska Institute (AUROC, 0.92) cohorts. The CEM+R model achieved a sensitivity (0.813 [95% CI, 0.781-0.843] vs 0.826 [95% CI, 0.795-0.856]; P = .20) and specificity (0.925 [95% CI, 0.916-0.934] vs 0.930 [95% CI, 0.929-0.932]; P = .18) similar to the radiologist performance. The CEM+R model had significantly lower sensitivity (0.596 [95% CI, 0.466-0.717] vs 0.850 [95% CI, 0.766-0.923]; P < .001) and specificity (0.803 [95% CI, 0.734-0.861] vs 0.945 [95% CI, 0.936-0.954]; P < .001) than the radiologist in women with a prior history of breast cancer and Hispanic women (0.894 [95% CI, 0.873-0.910] vs 0.926 [95% CI, 0.919-0.933]; P = .004).

Conclusions and Relevance

This study found that the high performance of an ensemble deep-learning model for automated screening mammography interpretation did not generalize to a more diverse screening cohort, suggesting that the model experienced underspecification. This study suggests the need for model transparency and fine-tuning of AI models for specific target populations prior to their clinical adoption.

Deep learning-based detection and segmentation of diffusion abnormalities in acute ischemic stroke

Background

Accessible tools to efficiently detect and segment diffusion abnormalities in acute strokes are highly anticipated by the clinical and research communities.

Methods

We developed a tool with deep learning networks trained and tested on a large dataset of 2,348 clinical diffusion weighted MRIs of patients with acute and sub-acute ischemic strokes, and further tested for generalization on 280 MRIs of an external dataset (STIR).

Results

Our proposed model outperforms generic networks and DeepMedic, particularly in small lesions, with lower false positive rate, balanced precision and sensitivity, and robustness to data perturbs (e.g., artefacts, low resolution, technical heterogeneity). The agreement with human delineation rivals the inter-evaluator agreement; the automated lesion quantification of volume and contrast has virtually total agreement with human quantification.

Conclusion

Our tool is fast, public, accessible to non-experts, with minimal computational requirements, to detect and segment lesions via a single command line. Therefore, it fulfills the conditions to perform large scale, reliable and reproducible clinical and translational research.

Robust breast cancer detection in mammography and digital breast tomosynthesis using an annotation-efficient deep learning approach

Breast cancer remains a global challenge, causing over 600,000 deaths in 2018 (ref. ¹). To achieve earlier cancer detection, health organizations worldwide recommend screening mammography, which is estimated to decrease breast cancer mortality by 20-40% (refs. ^2,3). Despite the clear value of screening mammography, significant false positive and false negative rates along with non-uniformities in expert reader availability leave opportunities for improving quality and access^4,5. To address these limitations, there has been much recent interest in applying deep learning to mammography^6-18, and these efforts have highlighted two key difficulties: obtaining large amounts of annotated training data and ensuring generalization across populations, acquisition equipment and modalities. Here we present an annotation-efficient deep learning approach that (1) achieves state-of-the-art performance in mammogram classification, (2) successfully extends to digital breast tomosynthesis (DBT; '3D mammography'), (3) detects cancers in clinically negative prior mammograms of patients with cancer, (4) generalizes well to a population with low screening rates and (5) outperforms five out of five full-time breast-imaging specialists with an average increase in sensitivity of 14%. By creating new 'maximum suspicion projection' (MSP) images from DBT data, our progressively trained, multiple-instance learning approach effectively trains on DBT exams using only breast-level labels while maintaining localization-based interpretability. Altogether, our results demonstrate promise towards software that can improve the accuracy of and access to screening mammography worldwide.

Phase II trial of carboplatin and bevacizumab in patients with breast cancer brain metastases

BACKGROUND

We aimed to examine the safety and efficacy of bevacizumab and carboplatin in patients with breast cancer brain metastases.

METHODS

We enrolled patients with breast cancer and > 1 measurable new or progressive brain metastasis. Patients received bevacizumab 15 mg/kg intravenously (IV) on cycle 1 day 1 and carboplatin IV AUC = 5 on cycle 1 day 8. Patients with HER2-positive disease also received trastuzumab. In subsequent cycles, all drugs were administered on day 1 of each cycle. Contrast-enhanced brain MRI was performed at baseline, 24-96 h after the first bevacizumab dose (day + 1), and every 2 cycles. The primary endpoint was objective response rate in the central nervous system (CNS ORR) by composite criteria. Associations between germline VEGF single nucleotide polymorphisms (rs699947, rs2019063, rs1570360, rs833061) and progression-free survival (PFS) and overall survival (OS) were explored, as were associations between early (day + 1) MRI changes and outcomes.

RESULTS

Thirty-eight patients were enrolled (29 HER2-positive, 9 HER2-negative); all were evaluable for response. The CNS ORR was 63% (95% CI, 46-78). Median PFS was 5.62 months and median OS was 14.10 months. As compared with an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0, patients with ECOG PS 1-2 had significantly worse PFS and OS (all P < 0.01). No significant associations between VEGF genotypes or early MRI changes and clinical outcomes were observed.

CONCLUSIONS

The combination of bevacizumab and carboplatin results in a high rate of durable objective response in patients with brain metastases from breast cancer. This regimen warrants further investigation.

TRIAL REGISTRATION

NCT01004172 . Registered 28 October 2009.

Prognostic value of contrast enhancement and FLAIR for survival in newly diagnosed glioblastoma treated with and without bevacizumab: results from ACRIN 6686

Background

ACRIN 6686/RTOG 0825 was a phase III trial of conventional chemoradiation plus adjuvant temozolomide with bevacizumab or without (placebo) in newly diagnosed glioblastoma. This study investigated whether changes in contrast-enhancing and fluid attenuated inversion recovery (FLAIR)-hyperintense tumor assessed by central reading prognosticate overall survival (OS).

Methods

Two hundred eighty-four patients (171 men; median age 57 y, range 19-79; 159 on bevacizumab) had MRI at post-op (baseline) and pre-cycle 4 of adjuvant temozolomide (22 wk post chemoradiation initiation). Four central readers measured bidimensional lesion enhancement (2D-T1) and FLAIR hyperintensity at both time points. Changes from baseline to pre-cycle 4 for both markers were dichotomized (increasing vs non-increasing). Cox proportional hazards model and Kaplan-Meier survival estimates were used for inference.

Results

Adjusting for treatment, increasing 2D-T1 (n = 262, hazard ratio [HR] = 2.07, 95% CI: 1.48-2.91, P < 0.0001) and FLAIR (n = 273, HR = 1.75, 95% CI: 1.26-2.41, P = 0.0008) significantly predicted worse OS. Median OS (days) was significantly shorter for patients with increasing versus non-increasing 2D-T1 for both bevacizumab (443 vs 535, P = 0.004) and placebo (526 vs 887, P = 0.001). Median OS was significantly shorter for patients with increasing versus non-increasing FLAIR for placebo (595 vs 872, P = 0.001), and trended similarly for bevacizumab (499 vs 535, P = 0.0935). Adjusting for 2D-T1 and treatment, increasing FLAIR represented significantly higher risk for death (HR = 1.59 [1.11-2.26], P = 0.01).

Conclusion

Increased 2D-T1 significantly predicts worse OS in both treatment groups, implying absence of a substantial proportion of pseudoprogression 22 weeks after initiation of standard therapy. FLAIR adds value beyond 2D-T1 in predicting OS, potentially addressing the pseudoresponse effect by substratifying bevacizumab-treated patients with non-increasing 2D-T1.

Ensemble of Convolutional Neural Networks Improves Automated Segmentation of Acute Ischemic Lesions Using Multiparametric Diffusion-Weighted MRI

BACKGROUND AND PURPOSE

Accurate automated infarct segmentation is needed for acute ischemic stroke studies relying on infarct volumes as an imaging phenotype or biomarker that require large numbers of subjects. This study investigated whether an ensemble of convolutional neural networks trained on multiparametric DWI maps outperforms single networks trained on solo DWI parametric maps.

MATERIALS AND METHODS

Convolutional neural networks were trained on combinations of DWI, ADC, and low b-value-weighted images from 116 subjects. The performances of the networks (measured by the Dice score, sensitivity, and precision) were compared with one another and with ensembles of 5 networks. To assess the generalizability of the approach, we applied the best-performing model to an independent Evaluation Cohort of 151 subjects. Agreement between manual and automated segmentations for identifying patients with large lesion volumes was calculated across multiple thresholds (21, 31, 51, and 70 cm³).

RESULTS

An ensemble of convolutional neural networks trained on DWI, ADC, and low b-value-weighted images produced the most accurate acute infarct segmentation over individual networks (P < .001). Automated volumes correlated with manually measured volumes (Spearman ρ = 0.91, P < .001) for the independent cohort. For the task of identifying patients with large lesion volumes, agreement between manual outlines and automated outlines was high (Cohen κ, 0.86-0.90; P < .001).

CONCLUSIONS

Acute infarcts are more accurately segmented using ensembles of convolutional neural networks trained with multiparametric maps than by using a single model trained with a solo map. Automated lesion segmentation has high agreement with manual techniques for identifying patients with large lesion volumes.

Abstract WP318: Reduced Infarct Growth With IV Heparin in Acute Ischemic Stroke

Background: The role of IV heparin in acute ischemic stroke (AIS) is controversial. We investigated the effect of IV heparin on ischemic lesion growth.

Methods: We analyzed data on 274 consecutive AIS patients with non-lacunar stroke prospectively enrolled in a study where diffusion/perfusion MRI (DWI-PWI) was completed <12 hrs after last seen well and a follow-up MRI/CT completed after day 4. We excluded patients treated with tPA, and those with MTT-DWI mismatch <20% of the DWI volume or absolute mismatch volume <10 mL. Lesion growth was assessed by (a) Absolute Lesion Growth , i.e. final infarct volume - admission DWI lesion volume, and (b) Percentage mismatch lost (PML) , i.e. (final infarct volume - admission DWI volume)/(mismatch volume)x100%. Image analysis was blinded to clinical data. Univariable and multivariable analysis were performed to determine the effects of IV heparin on infarct growth.

Results: N=113 met inclusion/exclusion criteria; 52 received IV heparin shortly after admission. Results of the univariable analysis are shown in Table 1. Heparin use was associated with smaller PML (p<0.05); there was approximately 5-fold difference in PML between heparin users and non-users. Absolute lesion growth was significantly associated with admission glucose, blood pressure, NIHSS score, DWI volume and stroke etiological subtypes; and there was a trend for association with age and heparin use. Intravenous heparin use was an independent predictor of both PML and absolute lesion growth (Table 2), and was associated with better 3-month outcomes (modified Rankin scale score 0-2, 80% vs. 57%, p=0.04).

Conclusion: These data suggest that IV heparin administration early after stroke may attenuate the progression of ischemic brain injury in non-thrombolyzed patients with significant ischemic penumbra.

Abstract B12: Adding angiotensin-system inhibitors to anti-angiogenic therapy reduces vasogenic edema in newly diagnosed glioblastomas but not in recurrent disease

Introduction: Recent theoretical [1], pre-clinical [2] and human tumor data [3] suggest anti-hypertensives with an extracellular matrix-depleting effect improve vascular function by reducing the solid stress that can squeeze tumor vessels shut [4]. This work is contrasted by studies showing that certain matrix-depleting anti-hypertensives (angiotensin-II receptor blockers) are also associated with reduced peri-tumoral edema [5]. We here show that combined matrix-depleting and anti-angiogenic therapy does reduce vasogenic edema in newly diagnosed glioblastomas but not in recurrent disease and that the mechanisms of action are therefore not fully understood.

Methods: We retrospectively assessed data from 40 patients with newly diagnosed glioblastomas (nGBM) and 30 patients with recurrent glioblastomas (rGBM) receiving cediranib, an oral pan-VEGFR inhibitor, with- (NCT00662506) and without (NCT00305656) chemoradiation, respectively. Conventional, perfusion and vessel caliber MRI were performed at baseline and repeated weekly (nGBM) or monthly (rGBM) [6, 7]. Vasogenic edema was measured as the relative volume of peri-tumoral hyper T2-Fluid Attenuated Inversion Recovery (FLAIR) signal on the conventional MRIs. For nGBM, after cediranib onset, 12/40 patients received angiotensin II receptor blockers (Valsartan), β1 receptor antagonists (Atenolol) or angiotensin-converting enzyme inhibitors (Lisinopril), while 8/40 patients received calcium antagonists (Norvasc, Amlodipine) [3]. Similarly, for rGBM, 15/30 patients received Atenolol and 7/30 patients Norvasc.

Results: While angiotensin-system inhibitors (ASIs) significantly improved the perfused vessel fraction (% of tumor values &gt;½ the value of healthy tissue; Wilcoxon P&lt;0.05) and the relative small vessel fraction (&lt;½ the size of healthy tissue; Wilcoxon P&lt;0.01) for both cohorts, reduction of vasogenic edema was only observed in nGBM patients. Here, both cediranib alone and in combination with ASIs reduced the median relative vasogenic edema volume (82% and 54% over study period and compared to baseline values, respectively; Wilcoxon P&lt;0.05), but not for non-ASI calcium antagonists (96%). For rGBMs, cediranib alone reduced the median relative vasogenic edema volume (90%; P&lt;0.05), but not when adding ASIs. Instead, there was a trend towards reduced vasogenic edema with non-ASI calcium antagonists.

Conclusion: The potential anti-edema effect associated with ASI anti-hypertensives is an attractive feature for reduced administration of steroids in patients with glioblastoma. However, our data indicate that the matrix-depleting activity of some anti-hypertensives improves vascular function in both nGBMs and rGBMs [3], but only reduces vasogenic edema in the newly diagnosed setting [5]. Further studies to understand the mechanisms of benefit of ASIs in cancer are warranted.

References:

1: PNAS 2013;110:18632-37

2: Nat Commun 2013; 4, 2516

3: Proc AACR Annual Meeting 2016; p3975

4: PNAS 2012; 109, 15101-8

5: J Neurol. 2016; 263, 524-30

6: PNAS 2013; 110, 19059-64

7: Nat Med 2013; 19, 1178-83

Citation Format: Kyrre E. Emblem, Elizabeth R. Gerstner, A Gregory Sorensen, Bruce R. Rosen, Patrick Y. Wen, Tracy T. Batchelor, Rakesh K. Jain. Adding angiotensin-system inhibitors to anti-angiogenic therapy reduces vasogenic edema in newly diagnosed glioblastomas but not in recurrent disease. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr B12.

ACRIN 6684: Assessment of Tumor Hypoxia in Newly Diagnosed Glioblastoma Using 18F-FMISO PET and MRI

PURPOSE

Structural and functional alterations in tumor vasculature are thought to contribute to tumor hypoxia which is a primary driver of malignancy through its negative impact on the efficacy of radiation, immune surveillance, apoptosis, genomic stability, and accelerated angiogenesis. We performed a prospective, multicenter study to test the hypothesis that abnormal tumor vasculature and hypoxia, as measured with MRI and PET, will negatively impact survival in patients with newly diagnosed glioblastoma.

EXPERIMENTAL DESIGN

Prior to the start of chemoradiation, patients with glioblastoma underwent MRI scans that included dynamic contrast enhanced and dynamic susceptibility contrast perfusion sequences to quantitate tumor cerebral blood volume/flow (CBV/CBF) and vascular permeability (k^trans) as well as ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) PET to quantitate tumor hypoxia. ROC analysis and Cox regression models were used to determine the association of imaging variables with progression-free and overall survival.

RESULTS

Fifty patients were enrolled of which 42 had evaluable imaging data. Higher pretreatment ¹⁸F-FMISO SUV_peak (P = 0.048), mean k^trans (P = 0.024), and median k^trans (P = 0.045) were significantly associated with shorter overall survival. Higher pretreatment median k^trans (P = 0.021), normalized RCBV (P = 0.0096), and nCBF (P = 0.038) were significantly associated with shorter progression-free survival. SUV_peak [AUC = 0.75; 95% confidence interval (CI), 0.59-0.91], nRCBV (AUC = 0.72; 95% CI, 0.56-0.89), and nCBF (AUC = 0.72; 95% CI, 0.56-0.89) were predictive of survival at 1 year.

CONCLUSIONS

Increased tumor perfusion, vascular volume, vascular permeability, and hypoxia are negative prognostic markers in newly diagnosed patients with gioblastoma, and these important physiologic markers can be measured safely and reliably using MRI and ¹⁸F-FMISO PET. Clin Cancer Res; 22(20); 5079-86. ©2016 AACR.

Emerging techniques and technologies in brain tumor imaging

The purpose of this report is to describe the state of imaging techniques and technologies for detecting response of brain tumors to treatment in the setting of multicenter clinical trials. Within currently used technologies, implementation of standardized image acquisition and the use of volumetric estimates and subtraction maps are likely to help to improve tumor visualization, delineation, and quantification. Upon further development, refinement, and standardization, imaging technologies such as diffusion and perfusion MRI and amino acid PET may contribute to the detection of tumor response to treatment, particularly in specific treatment settings. Over the next few years, new technologies such as 2(3)Na MRI and CEST imaging technologies will be explored for their use in expanding the ability to quantitatively image tumor response to therapies in a clinical trial setting.

Diffusion MRI quality control and functional diffusion map results in ACRIN 6677/RTOG 0625: a multicenter, randomized, phase II trial of bevacizumab and chemotherapy in recurrent glioblastoma

Functional diffusion mapping (fDM) is a cancer imaging technique that quantifies voxelwise changes in apparent diffusion coefficient (ADC). Previous studies have shown value of fDMs in bevacizumab therapy for recurrent glioblastoma multiforme (GBM). The aim of the present study was to implement explicit criteria for diffusion MRI quality control and independently evaluate fDM performance in a multicenter clinical trial (RTOG 0625/ACRIN 6677). A total of 123 patients were enrolled in the current multicenter trial and signed institutional review board-approved informed consent at their respective institutions. MRI was acquired prior to and 8 weeks following therapy. A 5-point QC scoring system was used to evaluate DWI quality. fDM performance was evaluated according to the correlation of these metrics with PFS and OS at the first follow-up time-point. Results showed ADC variability of 7.3% in NAWM and 10.5% in CSF. A total of 68% of patients had usable DWI data and 47% of patients had high quality DWI data when also excluding patients that progressed before the first follow-up. fDM performance was improved by using only the highest quality DWI. High pre-treatment contrast enhancing tumor volume was associated with shorter PFS and OS. A high volume fraction of increasing ADC after therapy was associated with shorter PFS, while a high volume fraction of decreasing ADC was associated with shorter OS. In summary, DWI in multicenter trials are currently of limited value due to image quality. Improvements in consistency of image quality in multicenter trials are necessary for further advancement of DWI biomarkers.

Dynamic susceptibility contrast MRI measures of relative cerebral blood volume as a prognostic marker for overall survival in recurrent glioblastoma: results from the ACRIN 6677/RTOG 0625 multicenter trial

BACKGROUND

The study goal was to determine whether changes in relative cerebral blood volume (rCBV) derived from dynamic susceptibility contrast (DSC) MRI are predictive of overall survival (OS) in patients with recurrent glioblastoma multiforme (GBM) when measured 2, 8, and 16 weeks after treatment initiation.

METHODS

Patients with recurrent GBM (37/123) enrolled in ACRIN 6677/RTOG 0625, a multicenter, randomized, phase II trial of bevacizumab with irinotecan or temozolomide, consented to DSC-MRI plus conventional MRI, 21 with DSC-MRI at baseline and at least 1 postbaseline scan. Contrast-enhancing regions of interest were determined semi-automatically using pre- and postcontrast T1-weighted images. Mean tumor rCBV normalized to white matter (nRCBV) and standardized rCBV (sRCBV) were determined for these regions of interest. The OS rates for patients with positive versus negative changes from baseline in nRCBV and sRCBV were compared using Wilcoxon rank-sum and Kaplan-Meier survival estimates with log-rank tests.

RESULTS

Patients surviving at least 1 year (OS-1) had significantly larger decreases in nRCBV at week 2 (P = .0451) and sRCBV at week 16 (P = .014). Receiver operating characteristic analysis found the percent changes of nRCBV and sRCBV at week 2 and sRCBV at week 16, but not rCBV data at week 8, to be good prognostic markers for OS-1. Patients with positive change from baseline rCBV had significantly shorter OS than those with negative change at both week 2 and week 16 (P = .0015 and P = .0067 for nRCBV and P = .0251 and P = .0004 for sRCBV, respectively).

CONCLUSIONS

Early decreases in rCBV are predictive of improved survival in patients with recurrent GBM treated with bevacizumab.

Vessel caliber--a potential MRI biomarker of tumour response in clinical trials

Our understanding of the importance of blood vessels and angiogenesis in cancer has increased considerably over the past decades, and the assessment of tumour vessel calibre and structure has become increasingly important for in vivo monitoring of therapeutic response. The preferred method for in vivo imaging of most solid cancers is MRI, and the concept of vessel-calibre MRI has evolved since its initial inception in the early 1990s. Almost a quarter of a century later, unlike traditional contrast-enhanced MRI techniques, vessel-calibre MRI remains widely inaccessible to the general clinical community. The narrow availability of the technique is, in part, attributable to limited awareness and a lack of imaging standardization. Thus, the role of vessel-calibre MRI in early phase clinical trials remains to be determined. By contrast, regulatory approvals of antiangiogenic agents that are not directly cytotoxic have created an urgent need for clinical trials incorporating advanced imaging analyses, going beyond traditional assessments of tumour volume. To this end, we review the field of vessel-calibre MRI and summarize the emerging evidence supporting the use of this technique to monitor response to anticancer therapy. We also discuss the potential use of this biomarker assessment in clinical imaging trials and highlight relevant avenues for future research.

Low incidence of pseudoprogression by imaging in newly diagnosed glioblastoma patients treated with cediranib in combination with chemoradiation

BACKGROUND

Chemoradiation (CRT) can significantly modify the radiographic appearance of malignant gliomas, especially within the immediate post-CRT period. Pseudoprogression (PsP) is an increasingly recognized phenomenon in this setting, and is thought to be secondary to increased permeability as a byproduct of the complex process of radiation-induced tissue injury, possibly enhanced by temozolomide. We sought to determine whether the addition of a vascular endothelial growth factor (VEGF) signaling inhibitor (cediranib) to conventional CRT had an impact on the frequency of PsP, by comparing two groups of patients with newly diagnosed glioblastoma before, during, and after CRT.

METHODS

All patients underwent serial magnetic resonance imaging as part of institutional review board-approved clinical studies. Eleven patients in the control group received only chemoradiation, whereas 29 patients in the study group received chemoradiation and cediranib until disease progression or toxicity. Response assessment was defined according to Response Assessment in Neuro-Oncology criteria, and patients with enlarging lesions were classified into true tumor progressions (TTP) or PsP, based on serial radiographic follow-up.

RESULTS

Two patients in the study group (7%) showed signs of apparent early tumor progression, and both were subsequently classified as TTP. Six patients in the control group (54%) showed signs of apparent early tumor progression, and three were subsequently classified as TTP and three as PsP. The frequency of PsP was significantly higher in the control group.

CONCLUSION

Administration of a VEGF inhibitor during and after CRT modifies the expression of PsP by imaging.

Detection of oncogenic IDH1 mutations using magnetic resonance spectroscopy of 2-hydroxyglutarate

The investigation of metabolic pathways disturbed in isocitrate dehydrogenase (IDH) mutant tumors revealed that the hallmark metabolic alteration is the production of D-2-hydroxyglutarate (D-2HG). The biological impact of D-2HG strongly suggests that high levels of this metabolite may play a central role in propagating downstream the effects of mutant IDH, leading to malignant transformation of cells. Hence, D-2HG may be an ideal biomarker for both diagnosing and monitoring treatment response targeting IDH mutations. Magnetic resonance spectroscopy (MRS) is well suited to the task of noninvasive D-2HG detection, and there has been much interest in developing such methods. Here, we review recent efforts to translate methodology using MRS to reliably measure in vivo D-2HG into clinical research.

Vessel architectural imaging identifies cancer patient responders to anti-angiogenic therapy

Measurement of vessel caliber by Magnetic Resonance Imaging (MRI) is a valuable technique for in vivo monitoring of hemodynamic status and vascular development, especially in the brain. Here, we introduce a new paradigm in MRI coined as Vessel Architectural Imaging (VAI) that exploits an intriguing and overlooked temporal shift in the MR signal forming the basis for vessel caliber estimation and show how this phenomenon can reveal new information on vessel type and function not assessed by any other non-invasive imaging technique. We also show how this biomarker can provide novel biological insights into the treatment of cancer patients. As an example, we demonstrate using VAI that anti-angiogenic therapy can improve microcirculation and oxygen saturation levels and reduce vessel calibers in patients with recurrent glioblastomas, and more crucially, that patients with these responses have prolonged survival. Thus, VAI has the potential to identify patients who would benefit from therapies.

Phase III randomized trial comparing the efficacy of cediranib as monotherapy, and in combination with lomustine, versus lomustine alone in patients with recurrent glioblastoma

PURPOSE

A randomized, phase III, placebo-controlled, partially blinded clinical trial (REGAL [Recent in in Glioblastoma Alone and With Lomustine]) was conducted to determine the efficacy of cediranib, an oral pan-vascular endothelial growth factor (VEGF) receptor tyrosine kinase inhibitor, either as monotherapy or in combination with lomustine versus lomustine in patients with recurrent glioblastoma.

PATIENTS AND METHODS

Patients (N = 325) with recurrent glioblastoma who previously received radiation and temozolomide were randomly assigned 2:2:1 to receive (1) cediranib (30 mg) monotherapy; (2) cediranib (20 mg) plus lomustine (110 mg/m(2)); (3) lomustine (110 mg/m(2)) plus a placebo. The primary end point was progression-free survival based on blinded, independent radiographic assessment of postcontrast T1-weighted and noncontrast T2-weighted magnetic resonance imaging (MRI) brain scans.

RESULTS

The primary end point of progression-free survival (PFS) was not significantly different for either cediranib alone (hazard ratio [HR] = 1.05; 95% CI, 0.74 to 1.50; two-sided P = .90) or cediranib in combination with lomustine (HR = 0.76; 95% CI, 0.53 to 1.08; two-sided P = .16) versus lomustine based on independent or local review of postcontrast T1-weighted MRI.

CONCLUSION

This study did not meet its primary end point of PFS prolongation with cediranib either as monotherapy or in combination with lomustine versus lomustine in patients with recurrent glioblastoma, although cediranib showed evidence of clinical activity on some secondary end points including time to deterioration in neurologic status and corticosteroid-sparing effects.

Early post-bevacizumab progression on contrast-enhanced MRI as a prognostic marker for overall survival in recurrent glioblastoma: results from the ACRIN 6677/RTOG 0625 Central Reader Study

BACKGROUND

RTOG 0625/ACRIN 6677 is a multicenter, randomized, phase II trial of bevacizumab with irinotecan or temozolomide in recurrent glioblastoma (GBM). This study investigated whether early posttreatment progression on FLAIR or postcontrast MRI assessed by central reading predicts overall survival (OS).

METHODS

Of 123 enrolled patients, 107 had baseline and at least 1 posttreatment MRI. Two central neuroradiologists serially measured bidimensional (2D) and volumetric (3D) enhancement on postcontrast T1-weighted images and volume of FLAIR hyperintensity. Progression status on all posttreatment MRIs was determined using Macdonald and RANO imaging threshold criteria, with a third neuroradiologist adjudicating discrepancies of both progression occurrence and timing. For each MRI pulse sequence, Kaplan-Meier survival estimates and log-rank test were used to compare OS between cases with or without radiologic progression.

RESULTS

Radiologic progression occurred after 2 chemotherapy cycles (8 weeks) in 9 of 97 (9%), 9 of 73 (12%), and 11 of 98 (11%) 2D-T1, 3D-T1, and FLAIR cases, respectively, and 34 of 80 (43%), 21 of 58 (36%), and 37 of 79 (47%) corresponding cases after 4 cycles (16 weeks). Median OS among patients progressing at 8 or 16 weeks was significantly less than that among nonprogressors, as determined on 2D-T1 (114 vs 278 days and 214 vs 426 days, respectively; P < .0001 for both) and 3D-T1 (117 vs 306 days [P < .0001] and 223 vs 448 days [P = .0003], respectively) but not on FLAIR (201 vs 276 days [P = .38] and 303 vs 321 days [P = .13], respectively).

CONCLUSION

Early progression on 2D-T1 and 3D-T1, but not FLAIR MRI, after 8 and 16 weeks of anti-vascular endothelial growth factor therapy has highly significant prognostic value for OS in recurrent GBM.

Phase II trial of carboplatin (C) and bevacizumab (BEV) in patients (pts) with breast cancer brain metastases (BCBM)

513

Background: The anti-tumor and anti-edema effects of BEV provide a rationale for testing in BCBM. Carboplatin (C) is associated with CNS responses across multiple tumor types. We evaluated BEV + C in pts with BCBM. Methods: Pts with progressive, measurable BCBM (>/= 1 cm in longest dimension) were eligible. Cycle 1: BEV 15 mg/kg on Day 1, followed on Day 8 by carboplatin AUC=5 (plus trastuzumab if HER2+). In subsequent cycles, pts received BEV + C on Day 1 (plus trastuzumab if HER2+) of a 3 week (wk) cycle. Standard brain MRI was obtained at baseline (BL) and every 2 cycles. Non-CNS scans (CT or MRI) were performed after 2 cycles, 4 cycles, then every 4 cycles. Correlative brain imaging was obtained at BL, 12-96 hours after the first dose of BEV, and after 2 cycles. Circulating tumor cells and blood for VEGF polymorphisms were also collected. The primary endpoint was composite CNS objective response rate (CNS ORR). CNS partial response required all of the following: >/= 50% reduction in volumetric sum of target CNS lesions compared to BL, no progression of non-target lesions, no new lesions, stable/decreasing steroid dose, no progressive neurologic signs or symptoms, and no progression of non-CNS disease by RECIST 1.0. The study used a 2-stage design to distinguish between ORR 5% vs 20% (responses in >/= 1/12 pts to enter 2ndstage; responses in >/= 4/37 pts needed to be promising). Results: 38 pts were enrolled between 11/3/09-8/24/12 (30 HER2+; 8 HER2-negative). Most (76%) pts had received >/=2 lines of metastatic chemotherapy. 97% of pts with HER2+ disease received prior trastuzumab; 73% had prior lapatinib. All but 5 pts progressed after WBRT and/or SRS. As of 1/15/13, 3 pts remain on protocol therapy; 22 patients have died. The composite CNS ORR was 63% (95% CI 46%-78%). CNS ORR by RECIST was 45%. CNS responses were observed in both HER2+ and HER2-negative pts. Of 34 pts with >/= 24 wks potential follow-up time, median number of cycles was 8 (range 1-19). One grade 2 CNS hemorrhage event was reported; there were no cases of grade 3/4 CNS hemorrhage. Conclusions: BEV + carboplatin is associated with a high rate of durable CNS response in pts with BCBM. Updated results, including progression-free and overall survival will be presented. Clinical trial information: NCT01004172.

Magnetic resonance spectroscopy as an early indicator of response to anti-angiogenic therapy in patients with recurrent glioblastoma: RTOG 0625/ACRIN 6677

BACKGROUND

The prognosis for patients with recurrent glioblastoma remains poor. The purpose of this study was to assess the potential role of MR spectroscopy as an early indicator of response to anti-angiogenic therapy.

METHODS

Thirteen patients with recurrent glioblastoma were enrolled in RTOG 0625/ACRIN 6677, a prospective multicenter trial in which bevacizumab was used in combination with either temozolomide or irinotecan. Patients were scanned prior to treatment and at specific timepoints during the treatment regimen. Postcontrast T1-weighted MRI was used to assess 6-month progression-free survival. Spectra from the enhancing tumor and peritumoral regions were defined on the postcontrast T1-weighted images. Changes in the concentration ratios of n-acetylaspartate/creatine (NAA/Cr), choline-containing compounds (Cho)/Cr, and NAA/Cho were quantified in comparison with pretreatment values.

RESULTS

NAA/Cho levels increased and Cho/Cr levels decreased within enhancing tumor at 2 weeks relative to pretreatment levels (P = .048 and P = .016, respectively), suggesting a possible antitumor effect of bevacizumab with cytotoxic chemotherapy. Nine of the 13 patients were alive and progression free at 6 months. Analysis of receiver operating characteristic curves for NAA/Cho changes in tumor at 8 weeks revealed higher levels in patients progression free at 6 months (area under the curve = 0.85), suggesting that NAA/Cho is associated with treatment response. Similar results were observed for receiver operating characteristic curve analyses against 1-year survival. In addition, decreased Cho/Cr and increased NAA/Cr and NAA/Cho in tumor periphery at 16 weeks posttreatment were associated with both 6-month progression-free survival and 1-year survival.

CONCLUSION

Changes in NAA and Cho by MR spectroscopy may potentially be useful as imaging biomarkers in assessing response to anti-angiogenic treatment.

Abstract LB-297: Vessel architectural imaging identifies cancer patient responders to anti-angiogenic therapy

Purpose: Traditional magnetic resonance imaging (MRI) of cancer in vivo is confounded by heterogeneous vessel architecture with stochastic perfusion. Here, we present a new imaging method coined as vessel architectural imaging (VAI), exploiting an overlooked temporal shift in the MRI signal used in vessel caliber estimation. We show that VAI identifies glioblastoma patients who respond to anti-VEGF therapy by improved microcirculation and prolonged survival [1].

Materials & Methods: In this IRB-approved phase II study of cediranib (NCT00305656), an oral pan-VEGF receptor kinase inhibitor [2], 30 patients with recurrent glioblastoma were imaged monthly during therapy, using a simultaneously acquired gradient-echo and spin-echo contrast enhanced perfusion MRI sequence for VAI [1]. When visualized in a scatter plot, the resulting point-by-point temporal gradient-echo and spin-echo tissue-concentration curves will form a vortex of a certain shape and traverse in a clockwise or counter-clockwise direction depending on tissue type. Typically, a clockwise vortex direction reflects the presence of smaller-caliber, fast-inflow arteriole vessels and capillaries only, whereas a counter-clockwise vortex direction is observed if the tissue also includes a larger-caliber, slow-inflow venule component. The vortex direction effect is attributed to the level of deoxygenated blood in the tissue and the corresponding size of the vortex area is proportional to the relative arteriole-to-venule oxygen saturation (SO2) levels of the tissue [1].

Results: Collectively, patients showed a significant increase in tumoral image voxels with a clockwise vortex direction during therapy (pair-wise Wilcoxons; P &lt; 0.05), mimicking the direction ratios and vessel branching architecture of healthy tissue [1]. Ten responding patients, showing the biggest relative increase in image voxels with a clockwise vortex direction during therapy, also had reduced vessel calibers, improved SO2 levels and prolonged overall survival compared to 12 non-responders (341 days versus 146 days, Cox regression with time dependent covariates; P &lt; 0.01) [1].

Discussion: Using VAI we were able to obtain novel information not provided by traditional MRI, including vessel architecture and SO2 levels. Our results indicate that VAI is a different and potentially more sensitive biomarker for anti-VEGF therapy response.

[1] Emblem KE et al. Nature Med. 2013; In press.

[2] Batchelor TT et al. J Clin Oncol. 2010; 28(17):2817-23.

Citation Format: Kyrre E. Emblem, Kim Mouridsen, Atle Bjornerud, Christian T. Farrar, Dominique Jennings, Ronald J.H Borra, Patrick Y. Wen, Percy Ivy, Tracy T. Batchelor, Bruce R. Rosen, Rakesh K. Jain, A. Gregory Sorensen. Vessel architectural imaging identifies cancer patient responders to anti-angiogenic therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-297. doi:10.1158/1538-7445.AM2013-LB-297

Impact of adjuvant anti-VEGF therapy on treatment-related pseudoprogression in patients with newly diagnosed glioblastoma receiving chemoradiation with or without anti-VEGF therapy

2025

Background: Chemoradiation (CRT) can significantly modify the appearance of glioblastoma (GBM) on MRI, especially within the 3-month window after CRT. Pseudoprogression (PsP) is an increasingly recognized phenomenon in this scenario, and is thought to be secondary to increased permeability of the tumor vessels from irradiation, possibly enhanced by temozolomide (TMZ). We sought to determine if the addition of a VEGF signaling inhibitor (cediranib) during and after CRT had an impact on the frequency of PsP, by comparing two groups of patients with newly diagnosed GBMs. Methods: Two groups of patients enrolled in IRB-approved trials underwent serial MRIs at baseline, weekly during CRT and monthly thereafter. The control group received radiation plus TMZ, while the other group (CED) also received cediranib until progression (which was defined by RANO criteria) or toxicity. Patients that progressed up to 3 months after CRT were considered to have apparent progression (AP) and kept on treatment. Lesions that subsequently stabilized/regressed were classified as PsP, while those that maintained growth despite treatment were classified as true early progression (EP). Results: Forty patients were enrolled in CED and 11 as controls. Ten patients from CED and three controls were excluded due to treatment discontinuation before 3 months (drug-related toxicity and enrollment in post-CRT trials respectively). Three patients in CED (6%) had AP (all confirmed as EP) and no patients fulfilled criteria for PsP. Six patients from control (54%) had AP; 3 (27%) were eventually classified as EP and 3 (27%) as PsP. The frequency of PsP was significantly higher in the control group (p=0.0086). Conclusions: The addition of a VEGF inhibitor as part of adjuvant treatment in this cohort of glioblastoma patients prevented the development of early treatment-related effects (PsP). Suppressing the edema and mass effect that accompanies PsP may improve the tolerability of treatment. Additionally, this effect may be exploited as a strategy to make chemoradiation feasible in patients with large, unresectable tumors and/or poor baseline performance status.

Response of nonenhancing regions in glioblastoma to VEGF-signaling inhibitor cediranib correlates with tumor infiltration

3036

Background: Antiangiogenic therapy has limited direct antitumor effect in glioblastoma (GBM). Mainly its benefits may derive from anti-permeability and anti edema effects. In GBMs treated with cediranib we found that regions on MRI that are suggestive of being vasogenic edema, according to Diffusion Tensor Imaging (DTI) data, experience a greater decrease in volume than non-enhancing regions suggestive of being tumor infiltrated. Methods: Thirty-four newly diagnosed GBM patients were scanned on 3Tesla Siemens at two pre-therapy time points (2 days apart). Patients were treated with cediranib, standard radiation and temozolomide. Due to technical difficulties, 4 patients were left out of the analysis. Diffusion images were acquired with TR=7500ms, TE=84ms and b-values 0 and 700s/mm2 in 42 directions. A board certified radiologist determined the extent of abnormality on FLAIR and T1-weighted post contrast images. Non-enhancing regions (NER) were determined by subtracting the T1 enhancing area and any necrosis from the FLAIR abnormality. Volume of NERs was observed at baseline and day 47 of treatment. Mean Apparent Diffusion Coefficient (ADC) and mean Fractional Anisotropy (FA) of the NER were used to represent extent of tumor burden. Tumor Infiltration Index (TII), a measure based on comparing DTI metrics in metastatic tumors to GBM, was also derived. Twelve patients with metastatic cancer to the brain who underwent the same imaging and analysis pretreatment were used. High FA and low ADC and TII represent areas with more tumor burden. Results: There was a significant correlation between mean FA in the NERs at baseline and the percent volume reduction of the NER at day 47 (rho=0.45, p<0.02). Similarly, ADC and TII were correlated with percent volume reduction in the NER. Conclusions: DTI metrics have been used in GBMs to measure tumor infiltration. We found volume reduction of NERs to be inversely correlated to tumor burden. Thus, glioma patients with greater vasogenic edema may benefit from a different treatment paradigm than patients with lower vasogenic edema. [Table: see text]

Effects of cediranib (VEGF signaling inhibitor) on edema in newly diagnosed glioblastoma patients during initial chemoradiation

2012

Background: A significant benefit of antiangiogenic therapy is control of brain edema. We evaluated the impact of adding cediranib to standard chemoradiation (CRT) on peritumoral edema in patients with newly diagnosed glioblastoma(GBM) during the initial 6 weeks of CRT. Methods: Two cohorts of patients were enrolled in two clinical trials. The control group (N=13) received radiation for 6 weeks plus temozolomide. The cediranib (CED) group received standard CRT plus daily cediranib (N=34). MRIs were performed at baseline and weekly during CRT. Volumes of interest (VOIs) were drawn outlining the enhancing tumor on T1-weighted post contrast images and the abnormal FLAIR hyperintensity. ADC (apparent diffusion coefficient) maps were calculated from diffusion-weighted images and histograms of the distribution of ADC values created for each visit using the baseline FLAIR VOI to characterize the peritumoraledema. Patients were on stable or decreasing doses of steroids. Results: In the CED group, T1 and FLAIR VOI decreased during CRT vs controls where T1 VOI did not change and FLAIR VOI increased. By the end of CRT, the mode of the ADC histogram in the CED group shifted to the left while the mode of the controls shifted to the right. The skewness, a measure of asymmetry of the distribution, increased in the CED group and decreased in controls. Conclusions: In patients with newly diagnosed GBM treated with CRT and cediranib, tumor volume decreased on T1 and FLAIR images whereas the FLAIR volume significantly increased in the control group suggesting increased edema. The shift of mode to the right and decreasing skewness in controls (indicating an increase in the proportion of very high ADC values) suggests that adding cediranibprevented the development of edema and contributed to the resolution of existing edema. Preventing the edema by adding anti-VEGF treatment may improve the tolerability of CRT for GBM patients. [Table: see text]

Effects of cediranib, a VEGF signaling inhibitor, in combination with chemoradiation on tumor blood flow and survival in newly diagnosed glioblastoma

2009

Background: Anti-angiogenic therapy is hypothesized to synergize with radiation and chemotherapy by improving tumor blood flow. We evaluated the tolerability, efficacy and potential mechanism of action of radiation, temozolomide, and cediranib in newly diagnosed glioblastoma patients. Methods: Newly diagnosed glioblastoma patients were treated with radiation, temozolomide, and cediranib followed by monthly temozolomide for 6 cycles and daily cediranib until tumor progression or toxicity as part of an IRB-approved, Phase Ib/II clinical trial. MRI scans including measurement of cerebral blood flow were performed at baseline, weekly during the 6 weeks of chemoradiation and then monthly. Radiographic response was determined by RANO criteria. Results: Six patients were enrolled in the phase Ib part of the study with cediranib 30 mg daily in combination with temozolomide and radiation. No dose-limiting toxicities were identified. Forty patients were enrolled in the phase II part of the study. Among the entire cohort of 46 patients, median age was 57 (range 35-74), median KPS was 90% (60-100), 36 patients underwent a subtotal resection and 10 underwent biopsy. 26/30 patients taking corticosteroids were able to taper corticosteroids during chemoradiation. Off study reasons included toxicity (14), disease progression (18), and patient preference (2). Five patients remain on study without disease progression and 20 patients have died. Median duration on study was 158 days. Median progression free survival was 288 days (95%CI 240,∞) and median overall survival was 786 days (95%CI 411 ,∞). Best radiographic response in patients who completed chemoradiation was CR in 2 patients, PR in 20 patients, and SD in 15 patients. Patients with increased tumor perfusion during chemoradiation survived nearly 1 year longer (mean OS=611 days) than patients with decreased perfusion (mean OS=269 days). Conclusions: Cediranib was well tolerated and led to improved PFS and OS compared to historical controls, particularly in those with improved perfusion. This combination is being evaluated in an ongoing randomized trial (RTOG 0837).

Diffusion tensor imaging shows structural remodeling of stroke mirror region: results from a pilot study

BACKGROUND

The role of the non-injured hemisphere in stroke recovery is poorly understood. In this pilot study, we sought to explore the presence of structural changes detectable by diffusion tensor imaging (DTI) in the contralesional hemispheres of patients who recovered well from ischemic stroke.

METHODS

We analyzed serial DTI data from 16 stroke patients who had moderate initial neurological deficits (NIHSS scores 3-12) and good functional outcome at 3-6 months (NIHSS score 0 or modified Rankin Score ≤1). We segmented the brain tissue in gray and white matter (GM and WM) and measured the apparent diffusion coefficient (ADC) and fractional anisotropy in the infarct, in the contralesional infarct mirror region as well as in concentrically expanding regions around them.

RESULTS

We found that GM and WM ADC significantly increased in the infarct region (p < 0.01) from acute to chronic time points, whereas in the infarct mirror region, GM and WM ADC increased (p < 0.01) and WM fractional anisotropy decreased (p < 0.05). No significant changes were detected in other regions.

CONCLUSION

DTI-based metrics are sensitive to regional structural changes in the contralesional hemisphere during stroke recovery. Prospective studies in larger cohorts with varying levels of recovery are needed to confirm our findings.

Incidental findings in brain MRI research: what do we owe our subjects?

Concern regarding incidental findings on brain MRI studies has been increasing with the growing use of MRI as tool for scientific investigation. In this article, the authors provide an overview of possible approaches to address incidental findings. Incidental findings are surprisingly common (5%-20% of all examinations), although the percentage of clinically serious abnormalities is low (0.3%-3.4%). At present, there is no consensus concerning the optimal strategy on how to deal with incidental findings, in particular how to fulfill ethical responsibilities appropriately within the constraints of available resources. There are a variety of responses possible, and currently, reasonable guidelines exist for formulating a plan tailored to the needs of each institution that will meet the reasonable expectations of subjects participating in brain research studies.

Fast radio-frequency enforced steady state (FRESS) spin echo MRI for quantitative T2 mapping: minimizing the apparent repetition time (TR) dependence for fast T2 measurement

Transverse relaxation time (T(2)) is a basic but very informative MRI parameter, widely used in imaging to examine a host of diseases, including multiple sclerosis, stroke, and tumor. However, short repetition time (TR) is often used to minimize scan time, which may introduce non-negligible errors in T(2) measurement. Specifically, due to the use of refocusing pulse, the steady state magnetization depends not only on TR but also on the TE. Hence, if the TE dependence is not properly accounted for, it may be mistaken as T(2)-induced signal attenuation, leading to non-negligible T(2) underestimation. Our study proposed a fast radio-frequency enforced steady state (FRESS) spin echo (SE) MRI sequence, which saturates the magnetization after the echo and ensures a TE-independent steady state. The proposed FRESS-SE MRI was evaluated with numerical simulation, implemented with echo planar imaging readout, and validated by both phantom and in vivo experiments. In summary, FRESS-SE T(2) MRI technique was developed for fast and accurate T(2) imaging, suitable for in vivo applications.

Real-time motion and B0 correction for localized adiabatic selective refocusing (LASER) MRSI using echo planar imaging volumetric navigators

A method is presented to correct the effects of motion and motion-related B(0) perturbations on spectroscopic imaging in real time through the use of a volumetric navigator. It is demonstrated that, for an axial slice, lifting the chin significantly disrupts the B(0) homogeneity in the zero-order (frequency), first-order Y (coronal) axis and second-order ZY term. This volumetric navigator is able to measure and correct in real time both head pose and zero- to first-order B(0) inhomogeneities. The volumetric navigator was validated in six volunteers who deliberately lifted and then dropped their chin during the scan. These scans show that motion correction alone is not sufficient to recover the spectral quality. By applying real-time shim adjustments, spectral quality was fully recovered to linewidths below 0.08 ppm and the signal-to-noise ratio to within acceptable limits in five of six subjects. In the sixth subject, 83% of the spectra within the volume of interest were recovered, compared with the worst case nonshim-corrected scan, where none of the voxels fell within these quality bounds. It is shown that the use of a volumetric navigator comes at no additional cost to the scan time or spectral signal-to-noise ratio.

Correlation chemical shift imaging with low-power adiabatic pulses and constant-density spiral trajectories

In this work we introduce the concept of correlation chemical shift imaging (CCSI). Novel CCSI pulse sequences are demonstrated on clinical scanners for two-dimensional Correlation Spectroscopy (COSY) and Total Correlation Spectroscopy (TOCSY) imaging experiments. To date there has been limited progress reported towards a feasible and robust multivoxel 2D COSY. Localized 2D TOCSY imaging is shown for the first time in this work. Excitation with adiabatic GOIA-W(16,4) pulses (Gradient Offset Independent Adiabaticity Wurst modulation) provides minimal chemical shift displacement error, reduced lipid contamination from subcutaneous fat, uniform optimal flip angles, and efficient mixing for coupled spins, while enabling short repetition times due to low power requirements. Constant-density spiral readout trajectories are used to acquire simultaneously two spatial dimensions and f(2) frequency dimension in (k(x),k(y),t(2)) space in order to speed up data collection, while f(1) frequency dimension is encoded by consecutive time increments of t(1) in (k(x),k(y),t(1),t(2)) space. The efficient spiral sampling of the k-space enables the acquisition of a single-slice 2D COSY dataset with an 8 × 8 matrix in 8:32  min on 3 T clinical scanners, which makes it feasible for in vivo studies on human subjects. Here we present the first results obtained on phantoms, human volunteers and patients with brain tumors. The patient data obtained by us represent the first clinical demonstration of a feasible and robust multivoxel 2D COSY. Compared to the 2D J-resolved method, 2D COSY and TOCSY provide increased spectral dispersion which scales up with increasing main magnetic field strength and may have improved ability to unambiguously identify overlapping metabolites. It is expected that the new developments presented in this work will facilitate in vivo application of 2D chemical shift correlation MRS in basic science and clinical studies.

Detection of 2-hydroxyglutarate in IDH-mutated glioma patients by in vivo spectral-editing and 2D correlation magnetic resonance spectroscopy

Mutations in the gene isocitrate dehydrogenase 1 (IDH1) are present in up to 86% of grade II and III gliomas and secondary glioblastoma. Arginine 132 (R132) mutations in the enzyme IDH1 result in excess production of the metabolite 2-hydroxyglutarate (2HG), which could be used as a biomarker for this subset of gliomas. Here, we use optimized in vivo spectral-editing and two-dimensional (2D) correlation magnetic resonance spectroscopy (MRS) methods to unambiguously detect 2HG noninvasively in glioma patients with IDH1 mutations. By comparison, fitting of conventional 1D MR spectra can provide false-positive readouts owing to spectral overlap of 2HG and chemically similar brain metabolites, such as glutamate and glutamine. 2HG was also detected using 2D high-resolution magic angle spinning MRS performed ex vivo on a separate set of glioma biopsy samples. 2HG detection by in vivo or ex vivo MRS enabled detailed molecular characterization of a clinically important subset of human gliomas. This has implications for diagnosis as well as monitoring of treatments targeting mutated IDH1.

Neurologic 3D MR spectroscopic imaging with low-power adiabatic pulses and fast spiral acquisition

PURPOSE

To improve clinical three-dimensional (3D) MR spectroscopic imaging with more accurate localization and faster acquisition schemes.

MATERIALS AND METHODS

Institutional review board approval and patient informed consent were obtained. Data were acquired with a 3-T MR imager and a 32-channel head coil in phantoms, five healthy volunteers, and five patients with glioblastoma. Excitation was performed with localized adiabatic spin-echo refocusing (LASER) by using adiabatic gradient-offset independent adiabaticity wideband uniform rate and smooth truncation (GOIA-W[16,4]) pulses with 3.5-msec duration, 20-kHz bandwidth, 0.81-kHz amplitude, and 45-msec echo time. Interleaved constant-density spirals simultaneously encoded one frequency and two spatial dimensions. Conventional phase encoding (PE) (1-cm3 voxels) was performed after LASER excitation and was the reference standard. Spectra acquired with spiral encoding at similar and higher spatial resolution and with shorter imaging time were compared with those acquired with PE. Metabolite levels were fitted with software, and Bland-Altman analysis was performed.

RESULTS

Clinical 3D MR spectroscopic images were acquired four times faster with spiral protocols than with the elliptical PE protocol at low spatial resolution (1 cm3). Higher-spatial-resolution images (0.39 cm3) were acquired twice as fast with spiral protocols compared with the low-spatial-resolution elliptical PE protocol. A minimum signal-to-noise ratio (SNR) of 5 was obtained with spiral protocols under these conditions and was considered clinically adequate to reliably distinguish metabolites from noise. The apparent SNR loss was not linear with decreasing voxel sizes because of longer local T2* times. Improvement of spectral line width from 4.8 Hz to 3.5 Hz was observed at high spatial resolution. The Bland-Altman agreement between spiral and PE data is characterized by narrow 95% confidence intervals for their differences (0.12, 0.18 of their means). GOIA-W(16,4) pulses minimize chemical-shift displacement error to 2.1%, reduce nonuniformity of excitation to 5%, and eliminate the need for outer volume suppression.

CONCLUSION

The proposed adiabatic spiral 3D MR spectroscopic imaging sequence can be performed in a standard clinical MR environment. Improvements in image quality and imaging time could enable more routine acquisition of spectroscopic data than is possible with current pulse sequences.

Increased survival of glioblastoma patients who respond to antiangiogenic therapy with elevated blood perfusion

The abnormal vasculature of the tumor microenvironment supports progression and resistance to treatment. Judicious application of antiangiogenic therapy may normalize the structure and function of the tumor vasculature, promoting improved blood perfusion. However, direct clinical evidence is lacking for improvements in blood perfusion after antiangiogenic therapy. In this study, we used MRI to assess tumor blood perfusion in 30 recurrent glioblastoma patients who were undergoing treatment with cediranib, a pan-VEGF receptor tyrosine kinase inhibitor. Tumor blood perfusion increased durably for more than 1 month in 7 of 30 patients, in whom it was associated with longer survival. Together, our findings offer direct clinical evidence in support of the hypothesis that vascular normalization can increase tumor perfusion and help improve patient survival.

DWI-FLAIR mismatch for the identification of patients with acute ischaemic stroke within 4·5 h of symptom onset (PRE-FLAIR): a multicentre observational study

BACKGROUND

Many patients with stroke are precluded from thrombolysis treatment because the time from onset of their symptoms is unknown. We aimed to test whether a mismatch in visibility of an acute ischaemic lesion between diffusion-weighted MRI (DWI) and fluid-attenuated inversion recovery (FLAIR) MRI (DWI-FLAIR mismatch) can be used to detect patients within the recommended time window for thrombolysis.

METHODS

In this multicentre observational study, we analysed clinical and MRI data from patients presenting between Jan 1, 2001, and May 31, 2009, with acute stroke for whom DWI and FLAIR were done within 12 h of observed symptom onset. Two neurologists masked to clinical data judged the visibility of acute ischaemic lesions on DWI and FLAIR imaging, and DWI-FLAIR mismatch was diagnosed by consensus. We calculated predictive values of DWI-FLAIR mismatch for the identification of patients with symptom onset within 4·5 h and within 6 h and did multivariate regression analysis to identify potential confounding covariates. This study is registered with ClinicalTrials.gov, number NCT01021319.

FINDINGS

The final analysis included 543 patients. Mean age was 66·0 years (95% CI 64·7-67·3) and median National Institutes of Health Stroke Scale score was 8 (IQR 4-15). Acute ischaemic lesions were identified on DWI in 516 patients (95%) and on FLAIR in 271 patients (50%). Interobserver agreement for acute ischaemic lesion visibility on FLAIR imaging was moderate (κ=0·569, 95% CI 0·504-0·634). DWI-FLAIR mismatch identified patients within 4·5 h of symptom onset with 62% (95% CI 57-67) sensitivity, 78% (72-84) specificity, 83% (79-88) positive predictive value, and 54% (48-60) negative predictive value. Multivariate regression analysis identified a longer time to MRI (p<0·0001), a lower age (p=0·0009), and a larger DWI lesion volume (p=0·0226) as independent predictors of lesion visibility on FLAIR imaging.

INTERPRETATION

Patients with an acute ischaemic lesion detected with DWI but not with FLAIR imaging are likely to be within a time window for which thrombolysis is safe and effective. These findings lend support to the use of DWI-FLAIR mismatch for selection of patients in a future randomised trial of thrombolysis in patients with unknown time of symptom onset.

FUNDING

Else Kröner-Fresenius-Stiftung, National Institutes of Health.

Diffusion imaging with prospective motion correction and reacquisition

A major source of artifacts in diffusion-weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion-weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion-weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion-weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time.

Severity of leukoaraiosis determines clinical phenotype after brain infarction

OBJECTIVE

To determine whether the extent of leukoaraiosis, a composite marker of baseline brain integrity, differed between patients with TIA with diffusion-weighted imaging (DWI) evidence of infarction (transient symptoms with infarction [TSI]) and patients with ischemic stroke.

METHODS

Leukoaraiosis volume on MRI was quantified in a consecutive series of 153 TSI and 354 ischemic stroke patients with comparable infarct volumes on DWI. We explored the relationship between leukoaraiosis volume and clinical phenotype (TIA or ischemic stroke) using a logistic regression model.

RESULTS

Patients with TSI tended to be younger (median age 66 vs 69 years, p = 0.062) and had smaller median normalized leukoaraiosis volume (1.2 mL, interquartile range [IQR] 0.2-4.7 mL vs 3.5 mL, IQR 1.2-8.6 mL, p < 0.001). In multivariable analysis controlling for age, stroke risk factors, etiologic stroke mechanism, infarct volume, and infarct location, increasing leukoaraiosis volume remained associated with ischemic stroke (odds ratio 1.05 per mL, 95%confidence interval 1.02-1.09, p = 0.004), along with infarct volume and infarct location.

CONCLUSION

The probability of ischemic stroke rather than TSI increases with increasing leukoaraiosis volume, independent of infarct size and location. Our findings support the concept that the integrity of white matter tracts connecting different parts of the brain could contribute to whether or not patients develop TSI or ischemic stroke in an event of brain infarction.

Prediction of early stroke risk in transient symptoms with infarction: relevance to the new tissue-based definition

BACKGROUND AND PURPOSE

The risk of stroke shortly after transient ischemic attack with infarction on diffusion-weighted images, also known as transient symptoms with infarction (TSI), is substantially higher than is the risk after imaging-normal transient ischemic attack. We sought to assess the utility of a Web-based recurrence risk estimator (RRE; http://www.nmr.mgh.harvard.edu/RRE/) originally developed for use in patients with ischemic stroke for predicting 7-day risk of stroke in patients with TSI.

METHODS

We calculated RRE and ABCD² scores in a retrospective series of 257 consecutive patients with TSI diagnosed by diffusion-weighted images within 24 hours of symptom onset. We defined subsequent stroke as clinical deterioration associated with new infarction spatially distinct from the index lesion. We assessed the predictive performance of each model by computing the area under receiver-operating characteristics curve.

RESULTS

Over 7-day follow-up, 16 patients developed a recurrent stroke (6.2%). The sensitivity and specificity of an RRE score of ≥ 2 for predicting 7-day stroke risk were 87% and 73%, respectively. The area under the receiver-operating characteristics curve was 0.85 (95% CI, 0.78-0.92) for RRE and 0.57 (95% CI, 0.45-0.69) for ABCD² score (z-test; P<0.001).

CONCLUSIONS

The RRE score seems to predict 7-day risk of stroke after a TSI. If further validated in larger data sets, the RRE score could be useful in identifying high-risk patients with TSI who may benefit from early intervention with targeted stroke prevention strategies.

QUantitative Imaging of eXtraction of oxygen and TIssue consumption (QUIXOTIC) using venular-targeted velocity-selective spin labeling

While oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO(2)) are fundamental parameters of brain health and function, a robust MRI-based mapping of OEF and CMRO(2) amenable to functional MRI (fMRI) has not been established. To address this issue, a novel method called QUantitative Imaging of eXtraction of Oxygen and TIssue Consumption, or QUIXOTIC, is introduced. The key innovation in QUIXOTIC is the use of velocity-selective spin labeling to isolate MR signal exclusively from postcapillary venular blood on a voxel-by-voxel basis. Measuring the T(2) of this venular-targeted blood allows calibration to venular oxygen saturation (Y(v)) via theoretical and experimental T(2) versus blood oxygen saturation relationships. Y(v) is converted to OEF, and baseline CMRO(2) is subsequently estimated from OEF and additional cerebral blood flow and hematocrit measurements. Theory behind the QUIXOTIC technique is presented, and implications of cutoff velocity (V(CUTOFF)) and outflow time parameters are discussed. Cortical gray matter values obtained with QUIXOTIC in 10 healthy volunteers are Y(v) = 0.73 ± 0.02, OEF = 0.26 ± 0.02, and CMRO(2) = 125 ± 15 μmol/100 g min. Results are compared to global measures obtained with the T(2) relaxation under spin tagging (TRUST) technique. The preliminary data presented suggest that QUIXOTIC will be useful for mapping Y(v), OEF, and CMRO(2), in both clinical and functional MRI settings.

Lower hemoglobin correlates with larger stroke volumes in acute ischemic stroke

Background

Hemoglobin tetramers are the major oxygen-carrying molecules within the blood. We hypothesized that a lower hemoglobin level and its reduced oxygen-carrying capacity would associate with larger infarction in acute ischemic stroke patients.

Methods

We studied 135 consecutive patients with acute ischemic stroke and perfusion brain MRI. We explored the association of admission hemoglobin with initial infarct volumes on acute images and the volume of infarct expansion on follow-up images. Multivariable linear regression was performed to analyze the independent effect of hemoglobin on imaging outcomes.

Results

Bivariate analyses showed a significant inverse correlation between hemoglobin and initial volume in diffusion-weighted imaging (r = −0.20, p = 0.02) and absolute infarct growth (r = −0.20, p = 0.02). Multivariable linear regression modeling revealed that hemoglobin remained independently predictive of larger infarct volumes acutely (p < 0.005) and with greater infarct expansion (p < 0.01) after adjusting for known covariates.

Conclusions

Hemoglobin level at the time of acute ischemic stroke associates with larger infarcts and increased infarct growth. Clarification of the mechanism of this effect may yield novel insights for therapy.

Imaging stroke patients with unclear onset times

Stroke is a leading cause of death and adult morbidity worldwide. By defining stroke symptom onset by the time the patient was last known to be well, many patients whose onsets are unwitnessed are automatically ineligible for thrombolytic therapy. Advanced brain imaging may serve as a substitute witness to estimate stroke onset and duration in those patients who do not have a human witness. This article reviews and compares some of these imaging-based approaches to thrombolysis eligibility, which can potentially expand the use of thrombolytic therapy to a broader population of acute stroke patients.

Serial magnetic resonance spectroscopy reveals a direct metabolic effect of cediranib in glioblastoma

Proton magnetic resonance spectroscopy is increasingly used in clinical studies of brain tumor to provide information about tissue metabolic profiles. In this study, we evaluated changes in the levels of metabolites predominant in recurrent glioblastoma multiforme (rGBM) to characterize the response of rGBM to antiangiogenic therapy. We examined 31 rGBM patients treated with daily doses of cediranib, acquiring serial chemical shift imaging data at specific time points during the treatment regimen. We defined spectra from three regions of interest (ROI)--enhancing tumor (ET), peritumoral tissue, and normal tissue on the contralateral side (cNT)--in post-contrast T1-weighted images, and normalized the concentrations of N-acetylaspartate (NAA) and choline (Cho) in each ROI to the concentration of creatine in cNT (norCre). We analyzed the ratios of these normalized metabolites (i.e., NAA/Cho, NAA/norCre, and Cho/norCre) by averaging all patients and categorizing two different survival groups. Relative to pretreatment values, NAA/Cho in ET was unchanged through day 28. However, after day 28, NAA/Cho significantly increased in relation to a significant increase in NAA/norCre and a decrease in Cho/norCre; interestingly, the observed trend was reversed after day 56, consistent with the clinical course of GBM recurrence. Notably, receiver operating characteristic analysis indicated that NAA/Cho in tumor shows a high prediction to 6-month overall survival. These metabolic changes in these rGBM patients strongly suggest a direct metabolic effect of cediranib and might also reflect an antitumor response to antiangiogenic treatment during the first 2 months of treatment. Further study is needed to confirm these findings.

Vagus nerve stimulation reduces infarct size in rat focal cerebral ischemia: an unlikely role for cerebral blood flow

We sought to investigate the effect of cervical vagus nerve stimulation (VNS) on cerebral blood flow (CBF), infarct volume, and clinical outcome in a model of middle cerebral artery occlusion in rats. Electrical stimulation of the right and left vagus nerves was initiated 30min after the induction of the right-sided ischemia and lasted for 1h. Infarct size measurement revealed that the volume of ischemic damage was 41-45% smaller in animals receiving stimulation as compared with control animals. Both the right and left VNS caused subtle reduction in CBF during each 30-s stimulation period that quickly returned back to the baseline level at the end of each stimulation cycle. There was no significant effect of VNS on CBF during the entire 1-h stimulation period. The effect of VNS on tissue outcome was associated with better neurological outcome at both 1- and 3-day time points after the induction of ischemia. These findings suggest that VNS-induced protection against acute ischemic brain injury is not primarily mediated by changes in CBF, stimulation of both the right and left nerve have comparable effects, and VNS is effective after ipsilateral and contralateral focal ischemia.

In vivo 31P spectroscopy by fully adiabatic extended image selected in vivo spectroscopy: a comparison between 3 T and 7 T

An improved image selected in vivo spectroscopy (ISIS) sequence for localized (31)P magnetic resonance spectroscopy at 7 T was developed. To reduce errors in localization accuracy, adiabatic excitation, gradient offset independent adiabatic inversion pulses, and a special extended ISIS ordering scheme were used. The localization accuracy of extended ISIS was investigated in phantoms. The possible spectral quality and reproducibility in vivo was explored in a volunteer (brain, muscle, and liver). A comparison between 3 T and 7 T was performed in five volunteers. Adiabatic extended ISIS provided high spectral quality and accurate localization. The contamination in phantom experiments was only ∼5%, even if a pulse repetition time ∼ 1.2·T(1) was chosen to maximize the signal-to-noise ratio per unit time. High reproducibility was found in the calf muscle for 2.5 cm isotropic voxels at 7 T. When compared with 3 T, localized (31)P magnetic resonance spectroscopy in the human calf muscle at 7 T provided ∼3.2 times higher signal-to-noise ratio (as judged from phosphocreatine peak amplitude in frequency domain after matched filtering). At 7 T, extended ISIS allowed the performance of high-quality localized (31)P magnetic resonance spectroscopy in a short measurement time (∼3 to 4 min) and isotropic voxel sizes of ∼2.5 to 3 cm. With such short measurement times, localized (31)P magnetic resonance spectroscopy has the potential to be applied not only for clinical research but also for routine clinical practice.