Perfusion MRI: the five most frequently asked technical questions. AJR Am J Roentgenol. 2013;200:24-34. [PMID: 23255738 DOI: 10.2214/ajr.12.9543]

Prediction of Hemorrhagic Transformation Severity in Acute Stroke From Source Perfusion MRI

OBJECTIVE

Hemorrhagic transformation (HT) is the most severe complication of reperfusion therapy in acute ischemic stroke (AIS) patients. Management of AIS patients could benefit from accurate prediction of upcoming HT. While prediction of HT occurrence has recently provided encouraging results, the prediction of the severity and territory of the HT could bring valuable insights that are beyond current methods.

METHODS

This study tackles these issues and aims to predict the spatial occurrence of HT in AIS from perfusion-weighted magnetic resonance imaging (PWI) combined with diffusion weighted imaging. In all, 165 patients were included in this study and analyzed retrospectively from a cohort of AIS patients treated with reperfusion therapy in a single stroke center.

RESULTS

Machine learning models are compared within our framework; support vector machines, linear regression, decision trees, neural networks, and kernel spectral regression were applied to the dataset. Kernel spectral regression performed best with an accuracy of $\text{83.7} \pm \text{2.6}\%$.

CONCLUSION

The key contribution of our framework formalize HT prediction as a machine learning problem. Specifically, the model learns to extract imaging markers of HT directly from source PWI images rather than from pre-established metrics.

SIGNIFICANCE

Predictions visualized in terms of spatial likelihood of HT in various territories of the brain were evaluated against follow-up gradient recalled echo and provide novel insights for neurointerventionalists prior to endovascular therapy.

Magnetic resonance imaging of rectal cancer

Magnetic resonance imaging (MRI) is still the most commonly used imaging technique for the diagnosis of rectal cancer with the highest degree of accuracy, and it is also recommended by the National Comprehensive Cancer Network, European Society for Medical Oncology, and Chinese guidelines for diagnosis and treatment of colorectal cancer. The application of diffusion weighted imaging, apparent diffusion coefficient, diffusion weighted imaging with background signal suppression, intravoxel incoherent motion, perfusion imaging, magnetic resonance spectroscopy, and molecular imaging has provided many choices for tumor detection and preoperative staging, differential diagnosis of benign and malignant rectum lesions, postoperative follow-up, recurrence monitoring, and efficacy evaluation. We believe that with the development of basic theory and related technology, MRI for rectal cancer assessment will become more efficient.

The impact of injector-based contrast agent administration in time-resolved MRA

OBJECTIVES

Time-resolved contrast-enhanced MR angiography (4D-MRA), which allows the simultaneous visualization of the vasculature and blood-flow dynamics, is widely used in clinical routine. In this study, the impact of two different contrast agent injection methods on 4D-MRA was examined in a controlled, standardized setting in an animal model.

METHODS

Six anesthetized Goettingen minipigs underwent two identical 4D-MRA examinations at 1.5 T in a single session. The contrast agent (0.1 mmol/kg body weight gadobutrol, followed by 20 ml saline) was injected using either manual injection or an automated injection system. A quantitative comparison of vascular signal enhancement and quantitative renal perfusion analyses were performed.

RESULTS

Analysis of signal enhancement revealed higher peak enhancements and shorter time to peak intervals for the automated injection. Significantly different bolus shapes were found: automated injection resulted in a compact first-pass bolus shape clearly separated from the recirculation while manual injection resulted in a disrupted first-pass bolus with two peaks. In the quantitative perfusion analyses, statistically significant differences in plasma flow values were found between the injection methods.

CONCLUSIONS

The results of both qualitative and quantitative 4D-MRA depend on the contrast agent injection method, with automated injection providing more defined bolus shapes and more standardized examination protocols.

KEY POINTS

• Automated and manual contrast agent injection result in different bolus shapes in 4D-MRA. • Manual injection results in an undefined and interrupted bolus with two peaks. • Automated injection provides more defined bolus shapes. • Automated injection can lead to more standardized examination protocols.

Angiographic perfusion imaging of intracranial stenting

Two-dimensional angiographic perfusion imaging (2DAP) is a new technique permitting perfusion imaging during angiography, and has been used to study cerebral vasospasm. Here we report our experience with this technique following angioplasty and stent placement in a patient with symptomatic and medically refractory stenosis of the right supraclinoid internal carotid artery. We found that intraprocedural angiographic perfusion imaging provided real-time and objective evidence of improved cerebral perfusion during intervention. Following treatment, the patient remains symptom-free at last follow-up.

Dynamic Susceptibility Contrast Perfusion Magnetic Resonance Imaging Demonstrates Reduced Periventricular Cerebral Blood Flow in Dogs with Ventriculomegaly

The nature of ventriculomegaly in dogs is still a matter of debate. Signs of increased intraventricular pressure and atrophy of the cerebral white matter have been found in dogs with ventriculomegaly, which would imply increased intraventricular pressure and, therefore, a pathological condition, i.e., to some extent. Reduced periventricular blood flow was found in people with high elevated intraventricular pressure. The aim of this study was to compare periventricular brain perfusion in dogs with and without ventriculomegaly using perfusion weighted-magnetic-resonance-imaging to clarify as to whether ventriculomegaly might be associated with an increase in intraventricular pressure. Perfusion was measured in 32 Cavalier King Charles spaniels (CKCS) with ventriculomegaly, 10 CKCSs were examined as a control group. Cerebral blood flow (CBF) was measured using free-hand regions of interest (ROI) in five brain regions: periventricular white matter, caudate nucleus, parietal cortex, hippocampus, and thalamus. CBF was significantly lower in the periventricular white matter of the dogs with ventriculomegaly (p = 0.0029) but not in the other ROIs. Reduction of periventricular CBF might imply increase of intraventricular pressure in ventriculomegaly.

Perfusion Imaging in Neuro-Oncology: Basic Techniques and Clinical Applications

Perfusion imaging is a method for assessing the flow of blood occurring at the tissue level and can be accomplished by both CT and MR perfusion techniques. The use of perfusion imaging has increased substantially in the past decade, particularly in neuro-oncologic imaging, where it is has been used for brain tumor grading and directing biopsies or targeted therapy, as well as for the evaluation of treatment response and disease progression. This article discusses the basic principles and techniques of perfusion imaging, as well as its applications in neuro-oncology.

Quantification of Tumor Vascular Permeability and Blood Volume by Positron Emission Tomography

Purpose: Evans Blue (EB) is an azo dye that binds quantitatively with serum albumin. With an albumin binding, NOTA conjugated truncated Evan's blue (NEB) dye derived PET tracer, we aimed to establish a strategy for evaluating vascular permeability in malignant tumors via non-invasive PET. Experimental design: Sixty-minute dynamic PET using [¹⁸F]FAl-NEB was performed in three xenograft tumor models including INS-1 rat insulinoma, UM-SCC-22B human head and neck carcinoma and U-87 MG human glioblastoma. Tumor vascular permeability was quantified by the difference of the slopes between tumor and blood time-activity curve (TACs, expressed as P_s ). The method was further substantiated by EB extraction and colorimetric assay and correlates with that calculated from dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). The changes in tumor vasculature at different time points were assessed with NEB PET in U-87 MG and UM-SCC-22B tumor models after treatment with bevacizumab or doxorubicin. Result: The P_s values calculated from tumor and blood TACs from multiple time-point static images are consistent with those from dynamic images. Moreover, the P_s showed a positive and significant correlation with extracted EB concentration and K_PS-MRI generated from DCE-MRI, which further confirmed the soundness of this methodology. The antiangiogenic effect of bevacizumab could be revealed by NEB PET in U-87 MG tumors as early as 8 hrs after therapy, demonstrated by a substantial decrease of P_s. On the contrary, there was no significant change of P_s in bevacizumab treated UM-SCC-22B tumors, compared with control group. However, the significant changes of P_s were overestimated in doxorubicin treated UM-SCC-22B tumors. Conclusions: We successfully developed a relatively convenient and novel strategy to evaluate vascular permeability and blood volume using NEB PET. This method will be advantageous in evaluating vascular permeability, promoting drug delivery, and monitoring tumor response to therapeutics that affect tumor angiogenesis.

Bone marrow perfusion measured with dynamic contrast enhanced magnetic resonance imaging is correlated to body mass index in adults

Bone marrow metabolism is complex and far from being fully understood. Novel aspects, such as the roles of bone marrow adiposity and vascularisation in bone metabolism currently attract attention. There is also a growing interest in the influence obesity might have on bone metabolism. Our objective was to determine the effect of BMI on bone marrow perfusion parameters using dynamic contrast-enhanced magnetic resonance imaging. This prospective monocentric study was approved by our local Ethics committee. Written consent was obtained. The right hip of 59 adults under 60years old (mean age 37.5) was imaged with a dynamic 3D T1 spoiled gradient echo magnetic resonance imaging sequence. Mean BMI was 24.8 (+/-4.4). Perfusion parameters were measured in the acetabulum and femoral neck, in the greater trochanter, in the femoral head epiphysis and in the subcutaneous adipose tissue. Associations between perfusion parameters and BMI were studied using a linear mixed model adjusted for age and sex effects. Our results showed that as the BMI increased, the exchanges between blood and bone marrow appeared more important (increased K_trans and K_ep values, p=0.018 and p=0.002 respectively) and the intramedullary blood flow appeared increased (lower time to peak values, p=0.0002). In the subcutaneous fat, as the BMI increased, the vascularization decreased (lower area under the curve and initial slope values, p=0.019 and p=0.013 respectively). These results suggest that there is a relation between bone marrow perfusion and BMI, and that subcutaneous fat and bone marrow fat have different microvascular behaviours. Researchers must be aware of the effect of BMI on bone marrow perfusion parameters when they build a MR research protocol and analyse their data. A better understanding of these findings may provide the basis for the management of obesity-related bone changes.

Comparison of Power Versus Manual Injection in Bolus Shape and Image Quality on Contrast-Enhanced Magnetic Resonance Angiography: An Experimental Study in a Swine Model

OBJECTIVE

The aim of this study was to compare power versus manual injection in bolus shape and image quality on contrast-enhanced magnetic resonance angiography (CE-MRA).

MATERIALS AND METHODS

Three types of CE-MRA (head-neck 3-dimensional [3D] MRA with a test-bolus technique, thoracic-abdominal 3D MRA with a bolus-tracking technique, and thoracic-abdominal time-resolved 4-dimensional [4D] MRA) were performed after power and manual injection of gadobutrol (0.1 mmol/kg) at 2 mL/s in 12 pigs (6 sets of power and manual injections for each type of CE-MRA). For the quantitative analysis, the signal-to-noise ratio was measured on ascending aorta, descending aorta, brachiocephalic trunk, common carotid artery, and external carotid artery on the 6 sets of head-neck 3D MRA, and on ascending aorta, descending aorta, brachiocephalic trunk, abdominal aorta, celiac trunk, and renal artery on the 6 sets of thoracic-abdominal 3D MRA. Bolus shapes were evaluated on the 6 sets each of test-bolus scans and 4D MRA. For the qualitative analysis, arterial enhancement, superimposition of nontargeted enhancement, and overall image quality were evaluated on 3D MRA. Visibility of bolus transition was assessed on 4D MRA. Intraindividual comparison between power and manual injection was made by paired t test, Wilcoxon rank sum test, and analysis of variance by ranks.

RESULTS

Signal-to-noise ratio on 3D MRA was statistically higher with power injection than with manual injection (P < 0.001). Bolus shapes (test-bolus, 4D MRA) were represented by a characteristic standard bolus curve (sharp first-pass peak followed by a gentle recirculation peak) in all the 12 scans with power injection, but only in 1 of the 12 scans with manual injection. Standard deviations of time-to-peak enhancement were smaller in power injection than in manual injection. Qualitatively, although both injection methods achieved diagnostic quality on 3D MRA, power injection exhibited significantly higher image quality than manual injection (P = 0.001) due to significantly higher arterial enhancement (P = 0.031) and less superimposition of nontargeted enhancement (P = 0.001). Visibility of bolus transition on 4D MRA was significantly better with power injection than with manual injection (P = 0.031).

CONCLUSIONS

Compared with manual injection, power injection provides more standardized bolus shapes and higher image quality due to higher arterial enhancement and less superimposition of nontargeted vessels.

Dynamic contrast enhanced MRI detects changes in vascular transport rate constants following treatment with thermally-sensitive liposomal doxorubicin

Temperature-sensitive liposomal formulations of chemotherapeutics, such as doxorubicin, can achieve locally high drug concentrations within a tumor and tumor vasculature while maintaining low systemic toxicity. Further, doxorubicin delivery by temperature-sensitive liposomes can reliably cure local cancer in mouse models. Histological sections of treated tumors have detected red blood cell extravasation within tumors treated with temperature-sensitive doxorubicin and ultrasound hyperthermia. We hypothesize that the local release of drug into the tumor vasculature and resulting high drug concentration can alter vascular transport rate constants along with having direct tumoricidal effects. Dynamic contrast enhanced MRI (DCE-MRI) coupled with a pharmacokinetic model can detect and quantify changes in such vascular transport rate constants. Here, we set out to determine whether changes in rate constants resulting from intravascular drug release were detectable by MRI. We found that the accumulation of gadoteridol was enhanced in tumors treated with temperature-sensitive liposomal doxorubicin and ultrasound hyperthermia. While the initial uptake rate of the small molecule tracer was slower (k₁=0.0478±0.011s^-1 versus 0.116±0.047s^-1) in treated compared to untreated tumors, the tracer was retained after treatment due to a larger reduction in the rate of clearance (k₂=0.291±0.030s^-1 versus 0.747±0.24s^-1). While DCE-MRI assesses a combination of blood flow and permeability, ultrasound imaging of microvascular flow rate is sensitive only to changes in vascular flow rate; based on this technique, blood flow was not significantly altered 30min after treatment. In summary, DCE-MRI provides a means to detect changes that are associated with treatment by thermally-activated particles and such changes can be exploited to enhance local delivery.

A semi-automated volumetric software for segmentation and perfusion parameter quantification of brain tumors using 320-row multidetector computed tomography: a validation study

PURPOSE

We developed a semi-automated volumetric software, NPerfusion, to segment brain tumors and quantify perfusion parameters on whole-brain CT perfusion (WBCTP) images. The purpose of this study was to assess the feasibility of the software and to validate its performance compared with manual segmentation.

METHODS

Twenty-nine patients with pathologically proven brain tumors who underwent preoperative WBCTP between August 2012 and February 2015 were included. Three perfusion parameters, arterial flow (AF), equivalent blood volume (EBV), and Patlak flow (PF, which is a measure of permeability of capillaries), of brain tumors were generated by a commercial software and then quantified volumetrically by NPerfusion, which also semi-automatically segmented tumor boundaries. The quantification was validated by comparison with that of manual segmentation in terms of the concordance correlation coefficient and Bland-Altman analysis.

RESULTS

With NPerfusion, we successfully performed segmentation and quantified whole volumetric perfusion parameters of all 29 brain tumors that showed consistent perfusion trends with previous studies. The validation of the perfusion parameter quantification exhibited almost perfect agreement with manual segmentation, with Lin concordance correlation coefficients (ρ _c) for AF, EBV, and PF of 0.9988, 0.9994, and 0.9976, respectively. On Bland-Altman analysis, most differences between this software and manual segmentation on the commercial software were within the limit of agreement.

CONCLUSIONS

NPerfusion successfully performs segmentation of brain tumors and calculates perfusion parameters of brain tumors. We validated this semi-automated segmentation software by comparing it with manual segmentation. NPerfusion can be used to calculate volumetric perfusion parameters of brain tumors from WBCTP.

Divergent regional patterns of cerebral hypoperfusion and gray matter atrophy in mild cognitive impairment patients

Reductions of cerebral blood flow and gray matter structure have been implicated in early pathogenesis of Alzheimer's disease, potentially providing complementary information. The present study evaluated regional patterns of cerebral hypoperfusion and atrophy in patients with mild cognitive impairment and healthy older adults. In each participant, cerebral perfusion and gray matter structure were extracted within selected brain regions vulnerable to Alzheimer's disease using magnetic resonance imaging. Measures were compared between diagnostic groups with/without adjustment for covariates. In mild cognitive impairment patients, cerebral blood flow was significantly reduced in comparison with healthy controls in temporo-parietal regions and the basal ganglia in the absence of local gray matter atrophy. By contrast, gray matter structure was significantly reduced in the hippocampus in the absence of local hypoperfusion. Both, cerebral perfusion and gray matter structure were significantly reduced in the entorhinal and isthmus cingulate cortex in mild cognitive impairment patients compared with healthy older adults. Our results demonstrated partly divergent patterns of temporo-parietal hypoperfusion and medial-temporal atrophy in mild cognitive impairment patients, potentially indicating biomarker sensitivity to dissociable pathological mechanisms. The findings support applicability of cerebral perfusion and gray matter structure as complementary magnetic resonance imaging-based biomarkers in early Alzheimer's disease detection, a hypothesis to be further evaluated in longitudinal studies.

Prostate magnetic resonance imaging for brachytherapists: Anatomy and technique

PURPOSE

To present an overview of mp MRI techniques necessary for high-resolution imaging of prostate.

METHODS

We summarize examples from our clinical experience and concepts from the current literature that illustrate normal prostate anatomy on multiparametric MRI (mp MRI).

RESULTS

Our experience regarding optimal mp MRI image acquisition is provided, as well as a summary of prostate and periprostatic anatomy and anatomical variants that pose challenges for BT.

CONCLUSIONS

mp MRI provides unparalleled assessment of the prostate and periprostatic anatomy, making it the most appropriate imaging modality to facilitate prostate BT treatment planning, implantation, and followup. This work provides an introduction to prostate mp MR imaging, anatomy, and anatomical variants essential for successful integration mp MRI into prostate brachytherapy practice.

Pyogenic brain abscess with atypical features resembling glioblastoma in advanced MRI imaging

Differentiation between infectious and neoplastic brain processes is crucial for treatment planning. Advanced magnetic resonance imaging techniques, such as diffusion, perfusion, susceptibility weighted imaging, and magnetic resonance spectroscopy, enhance the imaging differences between these two pathologies. However, despite the utilization of these advanced techniques, the pathologic process may be confound by atypical findings. Here, we report a case of an autistic patient with multiple brain lesions with diffusion weighted imaging, susceptibility weighted imaging, and perfusion patterns resembling features of a multicentric glioblastoma, which were confirmed surgically, neuropathologically, and bacteriologically as brain abscesses. We discuss the differentiation of these different entities in the light of advanced magnetic resonance imaging techniques.

Retooling Laser Speckle Contrast Analysis Algorithm to Enhance Non-Invasive High Resolution Laser Speckle Functional Imaging of Cutaneous Microcirculation

Cutaneous microvasculopathy complicates wound healing. Functional assessment of gated individual dermal microvessels is therefore of outstanding interest. Functional performance of laser speckle contrast imaging (LSCI) systems is compromised by motion artefacts. To address such weakness, post-processing of stacked images is reported. We report the first post-processing of binary raw data from a high-resolution LSCI camera. Sharp images of low-flowing microvessels were enabled by introducing inverse variance in conjunction with speckle contrast in Matlab-based program code. Extended moving window averaging enhanced signal-to-noise ratio. Functional quantitative study of blood flow kinetics was performed on single gated microvessels using a free hand tool. Based on detection of flow in low-flow microvessels, a new sharp contrast image was derived. Thus, this work presents the first distinct image with quantitative microperfusion data from gated human foot microvasculature. This versatile platform is applicable to study a wide range of tissue systems including fine vascular network in murine brain without craniotomy as well as that in the murine dorsal skin. Importantly, the algorithm reported herein is hardware agnostic and is capable of post-processing binary raw data from any camera source to improve the sensitivity of functional flow data above and beyond standard limits of the optical system.

Mapping the dynamics of brain perfusion using functional ultrasound in a rat model of transient middle cerebral artery occlusion

Following middle cerebral artery occlusion, tissue outcome ranges from normal to infarcted depending on depth and duration of hypoperfusion as well as occurrence and efficiency of reperfusion. However, the precise time course of these changes in relation to tissue and behavioral outcome remains unsettled. To address these issues, a three-dimensional wide field-of-view and real-time quantitative functional imaging technique able to map perfusion in the rodent brain would be desirable. Here, we applied functional ultrasound imaging, a novel approach to map relative cerebral blood volume without contrast agent, in a rat model of brief proximal transient middle cerebral artery occlusion to assess perfusion in penetrating arterioles and venules acutely and over six days thanks to a thinned-skull preparation. Functional ultrasound imaging efficiently mapped the acute changes in relative cerebral blood volume during occlusion and following reperfusion with high spatial resolution (100 µm), notably documenting marked focal decreases during occlusion, and was able to chart the fine dynamics of tissue reperfusion (rate: one frame/5 s) in the individual rat. No behavioral and only mild post-mortem immunofluorescence changes were observed. Our study suggests functional ultrasound is a particularly well-adapted imaging technique to study cerebral perfusion in acute experimental stroke longitudinally from the hyper-acute up to the chronic stage in the same subject.

Diagnostic Accuracy of T1-Weighted Dynamic Contrast-Enhanced-MRI and DWI-ADC for Differentiation of Glioblastoma and Primary CNS Lymphoma

BACKGROUND AND PURPOSE

Glioblastoma and primary CNS lymphoma dictate different neurosurgical strategies; it is critical to distinguish them preoperatively. However, current imaging modalities do not effectively differentiate them. We aimed to examine the use of DWI and T1-weighted dynamic contrast-enhanced-MR imaging as potential discriminative tools.

MATERIALS AND METHODS

We retrospectively reviewed 18 patients with primary CNS lymphoma and 36 matched patients with glioblastoma with pretreatment DWI and dynamic contrast-enhanced-MR imaging. VOIs were drawn around the tumor on contrast-enhanced T1WI and FLAIR images; these images were transferred onto coregistered ADC maps to obtain the ADC and onto dynamic contrast-enhanced perfusion maps to obtain the plasma volume and permeability transfer constant. Histogram analysis was performed to determine the mean and relative ADC_mean and relative 90th percentile values for plasma volume and the permeability transfer constant. Nonparametric tests were used to assess differences, and receiver operating characteristic analysis was performed for optimal threshold calculations.

RESULTS

The enhancing component of primary CNS lymphoma was found to have significantly lower ADC_mean (1.1 × 10^-3 versus 1.4 × 10^-3; P < .001) and relative ADC_mean (1.5 versus 1.9; P < .001) and relative 90th percentile values for plasma volume (3.7 versus 5.0; P < .05) than the enhancing component of glioblastoma, but not significantly different relative 90th percentile values for the permeability transfer constant (5.4 versus 4.4; P = .83). The nonenhancing portions of glioblastoma and primary CNS lymphoma did not differ in these parameters. On the basis of receiver operating characteristic analysis, mean ADC provided the best threshold (area under the curve = 0.83) to distinguish primary CNS lymphoma from glioblastoma, which was not improved with normalized ADC or the addition of perfusion parameters.

CONCLUSIONS

ADC was superior to dynamic contrast-enhanced-MR imaging perfusion, alone or in combination, in differentiating primary CNS lymphoma from glioblastoma.

Artificial Neural Networks approach to pharmacokinetic model selection in DCE-MRI studies

PURPOSE

In pharmacokinetic analysis of Dynamic Contrast Enhanced MRI data, a descriptive physiological model should be selected properly out of a set of candidate models. Classical techniques suggested for this purpose suffer from issues like computation time and general fitting problems. This article proposes an approach based on Artificial Neural Networks (ANNs) for solving these problems.

METHODS

A set of three physiologically and mathematically nested models generated from the Tofts model were assumed: Model I, II and III. These models cover three possible tissue types from normal to malignant. Using 21 experimental arterial input functions and 12 levels of noise, a set of 27,216 time traces were generated. ANN was validated and optimized by the k-fold cross validation technique. An experimental dataset of 20 patients with glioblastoma was applied to ANN and the results were compared to outputs of F-test using Dice index.

RESULTS

Optimum neuronal architecture ([6:7:1]) and number of training epochs (50) of the ANN were determined. ANN correctly classified more than 99% of the dataset. Confusion matrices for both ANN and F-test results showed the superior performance of the ANN classifier. The average Dice index (over 20 patients) indicated a 75% similarity between model selection maps of ANN and F-test.

CONCLUSIONS

ANN improves the model selection process by removing the need for time-consuming, problematic fitting algorithms; as well as the need for hypothesis testing.

Kinetic Analysis of Benign and Malignant Breast Lesions With Ultrafast Dynamic Contrast-Enhanced MRI: Comparison With Standard Kinetic Assessment

OBJECTIVE

The purposes of this study were to evaluate diagnostic parameters measured with ultrafast MRI acquisition and with standard acquisition and to compare diagnostic utility for differentiating benign from malignant lesions.

MATERIALS AND METHODS

Ultrafast acquisition is a high-temporal-resolution (7 seconds) imaging technique for obtaining 3D whole-breast images. The dynamic contrast-enhanced 3-T MRI protocol consists of an unenhanced standard and an ultrafast acquisition that includes eight contrast-enhanced ultrafast images and four standard images. Retrospective assessment was performed for 60 patients with 33 malignant and 29 benign lesions. A computer-aided detection system was used to obtain initial enhancement rate and signal enhancement ratio (SER) by means of identification of a voxel showing the highest signal intensity in the first phase of standard imaging. From the same voxel, the enhancement rate at each time point of the ultrafast acquisition and the AUC of the kinetic curve from zero to each time point of ultrafast imaging were obtained.

RESULTS

There was a statistically significant difference between benign and malignant lesions in enhancement rate and kinetic AUC for ultrafast imaging and also in initial enhancement rate and SER for standard imaging. ROC analysis showed no significant differences between enhancement rate in ultrafast imaging and SER or initial enhancement rate in standard imaging.

CONCLUSION

Ultrafast imaging is useful for discriminating benign from malignant lesions. The differential utility of ultrafast imaging is comparable to that of standard kinetic assessment in a shorter study time.

Detecting tumor progression in glioma: current standards and new techniques

INTRODUCTION

The post-treatment monitoring of glioma patients remains an area of active research and development. Conventional imaging with MRI is a highly sensitive modality for detecting and monitoring primary and secondary brain tumors and includes multi-parametric sequences to better characterize the disease. Standardized schemes for measuring response to treatment are in wide clinical use; however, the introduction of new therapeutics have introduced new patterns of response that can confound interpretation of conventional MRI and can cause uncertainty in the proper management following therapy. Areas covered: A summary of current and evolving techniques for assessing glioma response in this era of new therapies that address these challenges are presented in this review. While this review focuses more on clinical and early clinical methodologies for MRI and nuclear medicine techniques some promising pre-clinical techniques are also presented. Expert commentary: While successful single institution results have been widely reported in the literature, any new methodologies must be undertaken in multi-center settings. Additionally, the need for standardization of protocols in quantitative measured are an important area that must be addressed for new and promising techniques to be implemented to a wide array of patients.

Advanced MR imaging in hemispheric low-grade gliomas before surgery; the indications and limits in the pediatric age

INTRODUCTION

Advanced magnetic resonance imaging (MRI) techniques is an umbrella term that includes diffusion (DWI) and diffusion tensor (DTI), perfusion (PWI), spectroscopy (MRS), and functional (fMRI) imaging. These advanced modalities have improved the imaging of brain tumors and provided valuable additional information for treatment planning. Despite abundant literature on advanced MRI techniques in adult brain tumors, few reports exist for pediatric brain ones, potentially because of technical challenges.

REVIEW OF THE LITERATURE

The authors review techniques and clinical applications of DWI, PWI, MRS, and fMRI, in the setting of pediatric hemispheric low-grade gliomas.

PERSONAL EXPERIENCE

The authors propose their personal experience to highlight benefits and limits of advanced MR imaging in diagnosis, grading, and presurgical planning of pediatric hemispheric low-grade gliomas.

DISCUSSION

Advanced techniques should be used as complementary tools to conventional MRI, and in theory, the combined use of the three techniques should ensure achieving the best results in the diagnosis of hemispheric low-grade glioma and in presurgical planning to maximize tumor resection and preserve brain function.

FUTURE PERSPECTIVES

In the setting of pediatric neurooncology, these techniques can be used to distinguish low-grade from high-grade tumor. However, these methods have to be applied on a large scale to understand their real potential and clinical relapse, and further technical development is required to reduce the excessive scan times and other technical limitations.

Antiangiogenic Effect of Bevacizumab: Application of Arterial Spin-Labeling Perfusion MR Imaging in a Rat Glioblastoma Model

BACKGROUND AND PURPOSE

The usefulness of arterial spin-labeling for the evaluation of the effect of the antiangiogenic therapy has not been elucidated. Our aim was to evaluate the antiangiogenic effect of bevacizumab in a rat glioblastoma model based on arterial spin-labeling perfusion MR imaging.

MATERIALS AND METHODS

DSC and arterial spin-labeling perfusion MR imaging were performed by using a 9.4T MR imaging scanner in nude rats with glioblastoma. Rats were randomly assigned to the following 3 groups: control, 3-day treatment, and 10-day treatment after bevacizumab injection. One-way analysis of variance with a post hoc test was used to compare perfusion parameters (eg, normalized CBV and normalized CBF from DSC MR imaging and normalized CBF based on arterial spin-labeling) with microvessel area on histology. The Pearson correlations between perfusion parameters and microvessel area were also determined.

RESULTS

All of the normalized CBV from DSC, normalized CBF from DSC, normalized CBF from arterial spin-labeling, and microvessel area values showed significant decrease after treatment (P < .001, P < .001, P = .005, and P < .001, respectively). In addition, normalized CBV and normalized CBF from DSC and normalized CBF from arterial spin-labeling strongly correlated with microvessel area (correlation coefficient, r = 0.911, 0.869, and 0.860, respectively; P < .001 for all).

CONCLUSIONS

Normalized CBF based on arterial spin-labeling and normalized CBV and normalized CBF based on DSC have the potential for evaluating the effect of antiangiogenic therapy on glioblastomas treated with bevacizumab, with a strong correlation with microvessel area.

Detecting Tumor Metastases: The Road to Therapy Starts Here

Metastasis is the complex process by which primary tumor cells migrate and establish secondary tumors in an adjacent or distant location in the body. Early detection of metastatic disease and effective therapeutic options for targeting these detected metastases remain impediments to effectively treating patients with advanced cancers. If metastatic lesions are identified early, patients might maximally benefit from effective early therapeutic interventions. Further, monitoring patients whose primary tumors are effectively treated for potential metastatic disease onset is also highly valuable. Finally, patients with metastatic disease can be monitored for efficacy of specific therapeutic interventions through effective metastatic detection techniques. Thus, being able to detect and visualize metastatic lesions is key and provides potential to greatly improve overall patient outcomes. In order to achieve these objectives, researchers have endeavored to mechanistically define the steps involved in the metastatic process as well as ways to effectively detect metastatic progression. We presently overview various preclinical and clinical in vitro and in vivo assays developed to more efficiently detect tumor metastases, which provides the foundation for developing more effective therapies for this invariably fatal component of the cancerous process.

Functional magnetic resonance imaging techniques and their development for radiation therapy planning and monitoring in the head and neck cancers

Radiation therapy (RT), in particular intensity-modulated radiation therapy (IMRT), is becoming a more important nonsurgical treatment strategy in head and neck cancer (HNC). The further development of IMRT imposes more critical requirements on clinical imaging, and these requirements cannot be fully fulfilled by the existing radiotherapeutic imaging workhorse of X-ray based imaging methods. Magnetic resonance imaging (MRI) has increasingly gained more interests from radiation oncology community and holds great potential for RT applications, mainly due to its non-ionizing radiation nature and superior soft tissue image contrast. Beyond anatomical imaging, MRI provides a variety of functional imaging techniques to investigate the functionality and metabolism of living tissue. The major purpose of this paper is to give a concise and timely review of some advanced functional MRI techniques that may potentially benefit conformal, tailored and adaptive RT in the HNC. The basic principle of each functional MRI technique is briefly introduced and their use in RT of HNC is described. Limitation and future development of these functional MRI techniques for HNC radiotherapeutic applications are discussed. More rigorous studies are warranted to translate the hypotheses into credible evidences in order to establish the role of functional MRI in the clinical practice of head and neck radiation oncology.

Quantitative Perfusion and Permeability Biomarkers in Brain Cancer from Tomographic CT and MR Images

Dynamic contrast-enhanced perfusion and permeability imaging, using computed tomography and magnetic resonance systems, are important techniques for assessing the vascular supply and hemodynamics of healthy brain parenchyma and tumors. These techniques can measure blood flow, blood volume, and blood-brain barrier permeability surface area product and, thus, may provide information complementary to clinical and pathological assessments. These have been used as biomarkers to enhance the treatment planning process, to optimize treatment decision-making, and to enable monitoring of the treatment noninvasively. In this review, the principles of magnetic resonance and computed tomography dynamic contrast-enhanced perfusion and permeability imaging are described (with an emphasis on their commonalities), and the potential values of these techniques for differentiating high-grade gliomas from other brain lesions, distinguishing true progression from posttreatment effects, and predicting survival after radiotherapy, chemotherapy, and antiangiogenic treatments are presented.

Cerebral blood flow and autoregulation: current measurement techniques and prospects for noninvasive optical methods

Cerebral blood flow (CBF) and cerebral autoregulation (CA) are critically important to maintain proper brain perfusion and supply the brain with the necessary oxygen and energy substrates. Adequate brain perfusion is required to support normal brain function, to achieve successful aging, and to navigate acute and chronic medical conditions. We review the general principles of CBF measurements and the current techniques to measure CBF based on direct intravascular measurements, nuclear medicine, X-ray imaging, magnetic resonance imaging, ultrasound techniques, thermal diffusion, and optical methods. We also review techniques for arterial blood pressure measurements as well as theoretical and experimental methods for the assessment of CA, including recent approaches based on optical techniques. The assessment of cerebral perfusion in the clinical practice is also presented. The comprehensive description of principles, methods, and clinical requirements of CBF and CA measurements highlights the potentially important role that noninvasive optical methods can play in the assessment of neurovascular health. In fact, optical techniques have the ability to provide a noninvasive, quantitative, and continuous monitor of CBF and autoregulation.

Clinical parameters outweigh diffusion- and perfusion-derived MRI parameters in predicting survival in newly diagnosed glioblastoma

BACKGROUND

The purpose of this study was to determine the relevance of clinical data, apparent diffusion coefficient (ADC), and relative cerebral blood volume (rCBV) from dynamic susceptibility contrast (DSC) perfusion and the volume transfer constant (k^trans) from dynamic contrast-enhanced (DCE) perfusion for predicting overall survival (OS) and progression-free survival (PFS) in newly diagnosed treatment-naïve glioblastoma patients.

METHODS

Preoperative MR scans including standardized contrast-enhanced T1 (cT1), T2 - fluid-attenuated inversion recovery (FLAIR), ADC, DSC, and DCE of 125 patients with subsequent histopathologically confirmed glioblastoma were performed on a 3 Tesla MRI scanner. ADC, DSC, and DCE parameters were analyzed in semiautomatically segmented tumor volumes on contrast-enhanced (CE) cT1 and hyperintense signal changes on T2 FLAIR (ED). Univariate and multivariable Cox regression analyses including age, sex, extent of resection (EOR), and KPS were performed to assess the influence of each parameter on OS and PFS.

RESULTS

Univariate Cox regression analysis demonstrated a significant association of age, KPS, and EOR with PFS and age, KPS, EOR, lower ADC, and higher rCBV with OS. Multivariable analysis showed independent significance of male sex, KPS, EOR, and increased rCBV_CE for PFS, and age, sex, KPS, and EOR for OS.

CONCLUSIONS

MRI parameters help to predict OS in a univariate Cox regression analysis, and increased rCBV_CE is associated with shorter PFS in the multivariable model. In summary, however, our findings suggest that the relevance of MRI parameters is outperformed by clinical parameters in a multivariable analysis, which limits their prognostic value for survival prediction at the time of initial diagnosis.

Dynamic Susceptibility Contrast-Enhanced MR Perfusion Imaging in Assessing Recurrent Glioblastoma Response to Superselective Intra-Arterial Bevacizumab Therapy

BACKGROUND AND PURPOSE

Recurrent glioblastoma currently has no established standard of care. We evaluated the response of recurrent glioblastoma to superselective intra-arterial cerebral infusion of bevacizumab by using dynamic susceptibility contrast-enhanced MR perfusion imaging. We hypothesized that treatment response would be associated with decreased relative CBV and relative CBF.

MATERIALS AND METHODS

Patients were accrued for this study from larger ongoing serial Phase I/II trials. Twenty-five patients (14 men, 11 women; median age, 55 years) were analyzed. Four distinct ROIs were chosen: 1) normal-appearing white matter on the contralateral side, 2) the location of the highest T1 enhancement in the lesion (maximum enhancing), 3) the location of highest relative CBV in the lesion (maximum relative CBV), and 4) nonenhancing T2 hyperintense signal abnormality surrounding the tumor (nonenhancing T2 hyperintensity).

RESULTS

There was a statistically significant median percentage change of -32.34% (P = .001) in relative CBV in areas of maximum relative CBV following intra-arterial bevacizumab therapy. There was also a statistically significant median percentage decrease in relative CBF of -30.67 (P = .001) and -27.25 (P = .037) in areas of maximum relative CBV and maximum tumor enhancement, respectively. Last, a trend toward statistical significance for increasing relative CBV in nonenhancing T2 hyperintense areas (median percent change, 30.04; P = .069) was noted.

CONCLUSIONS

Dynamic susceptibility contrast-enhanced MR perfusion imaging demonstrated a significant decrease in tumor perfusion metrics within recurrent glioblastomas in response to superselective intra-arterial cerebral infusion of bevacizumab; however, these changes did not correlate with time to progression or overall survival.

Multicenter Survey of Current Practice Patterns in Perfusion MRI in Neuroradiology: Why, When, and How Is It Performed?

OBJECTIVE

Perfusion MRI is an advanced imaging technique with a number of potential neuroradiologic applications. However, there are few guidelines about the application of perfusion MRI in clinical practice. The purpose of this study was to assess when and how perfusion MRI is performed across national and international practices.

MATERIALS AND METHODS

An international survey was conducted through the American Society of Neuroradiology e-mail list. The survey included questions relating to demographics, whether perfusion MRI was offered, technical details, reporting, and reimbursement.

RESULTS

Most (81.0%) of the practices responding offered perfusion MRI; this proportion increases to 94.3% among academic and 95.3% among large practices. Intraaxial tumor, stroke, and arterial stenosis are the most frequent reasons for offering perfusion imaging. Most practices offer perfusion imaging on the basis of the judgment of the referring physician or person writing the protocol for the study, or they offer it for all intraaxial tumors. The most frequent method is dynamic susceptibility contrast-enhanced MRI (86.8%) followed by dynamic contrast-enhanced MRI (40.7%) and arterial spin-labeling MRI (34.8%). A minority (22.7%) of practices seek reimbursement for perfusion MRI. Most of the practices provide quantitative findings in radiology reports, most frequently cerebral blood volume (92.7%), cerebral blood (62.9%), and mean transit time (51.0%).

CONCLUSION

Despite the paucity of high-quality trials and guidelines for specific clinical applications, perfusion MRI is widely used by both academic and private practices. A minority of practices attempt to obtain reimbursement. This widespread adoption of perfusion imaging beyond its apparent financial footprint suggests that practicing radiologists and referring clinicians find value in the technique and underscores the need for more high-quality trials to solidify understanding of the role of perfusion MRI.

Assessment of Glioma Response to Radiotherapy Using Multiple MRI Biomarkers with Manual and Semiautomated Segmentation Algorithms

BACKGROUND AND PURPOSE

Multimodality magnetic resonance imaging (MRI) can provide complementary information in the assessment of brain tumors. We aimed to segment tumor in amide proton transfer-weighted (APTw) images and to investigate multiparametric MRI biomarkers for the assessment of glioma response to radiotherapy. For tumor extraction, we evaluated a semiautomated segmentation method based on region of interest (ROI) results by comparing it with the manual segmentation method.

METHODS

Thirteen nude rats injected with U87 tumor cells were irradiated by an 8-Gy radiation dose. All MRI scans were performed on a 4.7-T animal scanner preradiation, and at day 1, day 4, and day 8 postradiation. Two experts performed manual and semiautomated methods to extract tumor ROIs on APTw images. Multimodality MRI signals of the tumors, including structural (T₂ and T₁ ), functional (apparent diffusion coefficient and blood flow), and molecular (APTw and magnetization transfer ratio or MTR), were calculated and compared quantitatively.

RESULTS

The semiautomated method provided more reliable tumor extraction results on APTw images than the manual segmentation, in less time. A considerable increase in the ADC intensities of the tumor was observed during the postradiation. A steady decrease in the blood flow values and in the APTw signal intensities were found after radiotherapy.

CONCLUSIONS

The semiautomated method of tumor extraction showed greater efficiency and stability than the manual method. Apparent diffusion coefficient, blood flow, and APTw are all useful biomarkers in assessing glioma response to radiotherapy.

A review of heart chamber segmentation for structural and functional analysis using cardiac magnetic resonance imaging

Cardiovascular magnetic resonance (CMR) has become a key imaging modality in clinical cardiology practice due to its unique capabilities for non-invasive imaging of the cardiac chambers and great vessels. A wide range of CMR sequences have been developed to assess various aspects of cardiac structure and function, and significant advances have also been made in terms of imaging quality and acquisition times. A lot of research has been dedicated to the development of global and regional quantitative CMR indices that help the distinction between health and pathology. The goal of this review paper is to discuss the structural and functional CMR indices that have been proposed thus far for clinical assessment of the cardiac chambers. We include indices definitions, the requirements for the calculations, exemplar applications in cardiovascular diseases, and the corresponding normal ranges. Furthermore, we review the most recent state-of-the art techniques for the automatic segmentation of the cardiac boundaries, which are necessary for the calculation of the CMR indices. Finally, we provide a detailed discussion of the existing literature and of the future challenges that need to be addressed to enable a more robust and comprehensive assessment of the cardiac chambers in clinical practice.

Safety of gadobutrol in over 23,000 patients: the GARDIAN study, a global multicentre, prospective, non-interventional study

OBJECTIVES

To investigate the safety and tolerability of gadobutrol at the recommended dose in patients requiring contrast-enhanced magnetic resonance imaging/angiography (MRI/MRA) in the routine setting.

METHODS

GARDIAN prospectively enrolled 23,708 patients undergoing routine gadobutrol-enhanced MRI/MRA for approved indications at 272 study centres in Europe, Asia, North America, and Africa and monitored for adverse events.

RESULTS

Median gadobutrol dose was 0.11 mmol/kg body weight. The overall incidence of adverse drug reactions (ADRs) was 0.7 % (n = 170 patients), with similar incidences in patients with renal impairment or cardiac disease, from different geographic regions and in different gadobutrol dose groups. Patients at risk for contrast media reaction had an ADR incidence of 2.5 %. Five patients (0.02 %) experienced serious adverse events, four were drug-related. One patient experienced a fatal anaphylactoid shock, assessed to be related to injection of gadobutrol. The contrast quality of gadobutrol-enhanced images was rated by treating physicians as good or excellent in 97 % cases, with similar ratings in all patient subgroups and indications.

CONCLUSIONS

The GARDIAN study shows that gadobutrol at the recommended dose is well tolerated across a large, diverse patient population.

KEY POINTS

• Gadobutrol at recommended dose shows low rates of adverse drug reactions • Gadobutrol demonstrates a uniform safety profile across diverse patient groups • Gadobutrol provides excellent contrast quality in routine practice.

Imaging of the Posttherapeutic Brain

This review covers important topics relating to the imaging evaluation of glioblastoma multiforme after therapy. An overview of the Macdonald and Response Assessment in Neuro-Oncology criteria as well as important questions and limitations regarding their use are provided. Pseudoprogression and pseudoresponse as well as the use of advanced magnetic resonance imaging techniques such as perfusion, diffusion, and spectroscopy in the evaluation of the posttherapeutic brain are also reviewed.

Advanced Imaging of Intracranial Meningiomas

Although typically not necessary for the diagnosis of intracranial meningiomas, advanced imaging techniques, including perfusion and diffusion imaging, spectroscopy, and nuclear medicine imaging, can help confirm the diagnosis of intracranial meningiomas, especially for meningiomas that do not exhibit the typical anatomic imaging findings. Advanced imaging techniques also have the potential to be able to differentiate between the subtypes of meningiomas, predict clinical aggressiveness of the tumor, and better characterize response to treatment. Although no advanced imaging technique has been able to definitively subclassify meningiomas, current results are encouraging and may be helpful in surgical planning.

Neuroradiology of the Brain

A variety of imaging modalities are currently used to evaluate the brain. Prior to the 1970s, neurologic imaging involved radiographs, invasive procedures for spinal and carotid artery air and contrast injection, and painful patient manipulation. The brain was considered inaccessible to imaging and referred to as "the dark continent." Since then, advances in neuroradiology have moved the brain from being a dark continent to evaluation techniques that illuminate brain contents and pathology. These advances enable quick acquisition of images for prompt diagnosis and treatment. This article reviews anatomy, diagnostic principles, and clinical application of brain imaging beyond plain radiographs.

Safety of gadobutrol in more than 1,000 pediatric patients: subanalysis of the GARDIAN study, a global multicenter prospective non-interventional study

BACKGROUND

Gadobutrol is a gadolinium-based contrast agent, uniquely formulated at 1.0 mmol/ml. Although there is extensive safety evidence on the use of gadobutrol in adults, few studies have addressed the safety and tolerability of gadobutrol in pediatric patients.

OBJECTIVE

This subanalysis of data from the GARDIAN study evaluated the safety and use of gadobutrol in pediatric patients (age <18 years).

MATERIALS AND METHODS

The GARDIAN study was a large phase IV non-interventional prospective multicenter post-authorization safety study performed in Europe, Asia, North America and Africa. A total of 23,708 patients were included who were scheduled to undergo cranial or spinal MRI, liver or kidney MRI, or MR angiography with gadobutrol enhancement. The primary study endpoint was the overall incidence of adverse drug reactions (ADRs) and serious adverse events (SAEs) following gadobutrol administration.

RESULTS

The GARDIAN study included 1,142 children (age <18 years) who received gadobutrol at a mean dose of 0.13 (range 0.04-0.50) mmol/kg body weight. Gadobutrol was well tolerated in these children, with low rates of ADRs (0.5%) and no SAEs, consistent with results in adults enrolled in the GARDIAN study. Rates of adverse events and ADRs were unrelated to pediatric age or gadobutrol weight-adjusted dose. There were no symptoms suggestive of nephrogenic systemic fibrosis. Investigators rated the contrast quality of gadobutrol-enhanced images as good or excellent in 97.8% of pediatric patients, similar to the main study population.

CONCLUSION

Gadobutrol is very well tolerated and provides excellent contrast quality at the recommended weight-adjusted dose in children (age <18 years), similar to the profile in adults.

Brain perfusion evaluated by perfusion-weighted magnetic resonance imaging before and after stenting internal carotid artery stenosis in asymptomatic and symptomatic patients

PURPOSE

To evaluate the brain perfusion with MRI perfusion weighted imaging (PWI) before and after ICA stenting in asymptomatic and symptomatic patients.

MATERIALS AND METHODS

PWI was performed 3-21 days before and 3 days after ICA stenting in 31 asymptomatic patients with ICA >70% stenosis - Group I, and in 14 symptomatic patients with ICA >50% stenosis - Group II. PWI was evaluated qualitatively and quantitatively in 5 cerebral territories with: mean transit time (MTT), cerebral blood volume (CBV) and cerebral blood flow (CBF). Mean values of perfusion parameters were measured before and after stenting ΔMTT, ΔCBV, ΔCBF were calculated as subtraction of after-treatment values from those before treatment.

RESULTS

In qualitative evaluation after ICA stenting perfusion was normalized in 21 patients (80.8%) in Group I and in 8 patients (80%) in Group II. In quantitative estimation MTT decreased significantly after CAS on stented side vs. non-stented side in all examined patients regardless of the group, p<0.05. MTT decreased more in Group II than in Group I in all territories (p<0.05) with the exception of temporal lobe. CBV and CBF have shown insignificant differences.

Two-Dimensional Perfusion Angiography of the Foot

Purpose: To report the feasibility, technical considerations, and initial results of 2-dimensional (2D) perfusion angiography of the foot before and after endovascular interventions. Methods: A retrospective single-center study involved 21 patients (mean age 73.4±10.5 years; 14 men) with severe peripheral vascular disease [Fontaine stage III (n=10) or IV (n=14)] who underwent lower limb digital subtraction angiography (DSA) prior to and following endovascular treatment of above- and/or below-knee lesions. A standardized contrast administration protocol (15 mL iodixanol 320 mg I/mL at 3 mL/s via a 5/6-F antegrade sheath) was applied during DSA using a 2D perfusion–enabled image intensifier. Representative hindfoot and forefoot regions of interest were analyzed, and representative numeric density values [time to peak (TTP), peak density value (PDV), and area under the (time-density) curve (AUC)] were calculated using 2D perfusion–enabled angiographic software to assess foot perfusion. Values were compared before and after angioplasty and by level of treatment (above or below knee). The parameters were correlated with disease severity (stenosis vs occlusion) and symptom level (Fontaine stage). Results: A clinically significant improvement (29.4%) in the AUC was noted following angioplasty, reaching statistical significance within the hindfoot (p=0.03). No significant change in TTP or PDV was detected following angioplasty. Foot movement remained problematic when measuring time-density values. No statistical difference in perfusion values was appreciable between above- and below-knee angioplasty. Conclusion: Two-dimensional perfusion angiography of the foot allows quantitative evaluation using various density values with potential benefit for treatment planning and technical outcome analysis. Methodical restrictions currently remain, mainly regarding patient movement.

Accuracy of percentage of signal intensity recovery and relative cerebral blood volume derived from dynamic susceptibility-weighted, contrast-enhanced MRI in the preoperative diagnosis of cerebral tumours

Conventional magnetic resonance imaging (MRI) is the technique of choice for diagnosis of cerebral tumours, and has become an increasingly powerful tool for their evaluation; however, the diagnosis of common contrast-enhancing lesions can be challenging, as it is sometimes impossible to differentiate them using conventional imaging. Histopathological analysis of biopsy specimens is the gold standard for diagnosis; however, there are significant risks associated with the invasive procedure and definitive diagnosis is not always achieved. Early accurate diagnosis is important, as management differs accordingly. Advanced MRI techniques have increasing utility for aiding diagnosis in a variety of clinical scenarios. Dynamic susceptibility-weighted contrast-enhanced (DSC) MRI is a perfusion imaging technique and a potentially important tool for the characterisation of cerebral tumours. The percentage of signal intensity recovery (PSR) and relative cerebral blood volume (rCBV) derived from DSC MRI provide information about tumour capillary permeability and neoangiogenesis, which can be used to characterise tumour type and grade, and distinguish tumour recurrence from treatment-related effects. Therefore, PSR and rCBV potentially represent a non-invasive means of diagnosis; however, the clinical utility of these parameters has yet to be established. We present a review of the literature to date.

Physiologic MRI for assessment of response to therapy and prognosis in glioblastoma

Aside from bidimensional measurements from conventional contrast-enhanced MRI, there are no validated or FDA-qualified imaging biomarkers for high-grade gliomas. However, advanced functional MRI techniques, including perfusion- and diffusion-weighted MRI, have demonstrated much potential for determining prognosis, predicting therapeutic response, and assessing early treatment response. They may also prove useful for differentiating pseudoprogression from true progression after temozolomide chemoradiation and pseudoresponse from true response after anti-angiogenic therapy. This review will highlight recent developments using these techniques and emphasize the need for technical standardization and validation in prospective studies in order for these methods to become incorporated into standard-of-care imaging for brain tumor patients.

Impact of Software Modeling on the Accuracy of Perfusion MRI in Glioma

BACKGROUND AND PURPOSE

Relative cerebral blood volume, as measured by T2*-weighted dynamic susceptibility-weighted contrast-enhanced MRI, represents the most robust and widely used perfusion MR imaging metric in neuro-oncology. Our aim was to determine whether differences in modeling implementation will impact the correction of leakage effects (from blood-brain barrier disruption) and the accuracy of relative CBV calculations as measured on T2*-weighted dynamic susceptibility-weighted contrast-enhanced MR imaging at 3T field strength.

MATERIALS AND METHODS

This study included 52 patients with glioma undergoing DSC MR imaging. Thirty-six patients underwent both non-preload dose- and preload dose-corrected DSC acquisitions, with 16 patients undergoing preload dose-corrected acquisitions only. For each acquisition, we generated 2 sets of relative CBV metrics by using 2 separate, widely published, FDA-approved commercial software packages: IB Neuro and nordicICE. We calculated 4 relative CBV metrics within tumor volumes: mean relative CBV, mode relative CBV, percentage of voxels with relative CBV > 1.75, and percentage of voxels with relative CBV > 1.0 (fractional tumor burden). We determined Pearson (r) and Spearman (ρ) correlations between non-preload dose- and preload dose-corrected metrics. In a subset of patients with recurrent glioblastoma (n = 25), we determined receiver operating characteristic area under the curve for fractional tumor burden accuracy to predict the tissue diagnosis of tumor recurrence versus posttreatment effect. We also determined correlations between rCBV and microvessel area from stereotactic biopsies (n = 29) in 12 patients.

RESULTS

With IB Neuro, relative CBV metrics correlated highly between non-preload dose- and preload dose-corrected conditions for fractional tumor burden (r = 0.96, ρ = 0.94), percentage > 1.75 (r = 0.93, ρ = 0.91), mean (r = 0.87, ρ = 0.86), and mode (r = 0.78, ρ = 0.76). These correlations dropped substantially with nordicICE. With fractional tumor burden, IB Neuro was more accurate than nordicICE in diagnosing tumor versus posttreatment effect (area under the curve = 0.85 versus 0.67) (P < .01). The highest relative CBV-microvessel area correlations required preload dose and IB Neuro (r = 0.64, ρ = 0.58, P = .001).

CONCLUSIONS

Different implementations of perfusion MR imaging software modeling can impact the accuracy of leakage correction, relative CBV calculation, and correlations with histologic benchmarks.