Ultra-High-Field MR Neuroimaging

Clinical applications of ultra-high field magnetic resonance imaging in multiple sclerosis

INTRODUCTION

Magnetic resonance imaging (MRI) is of paramount importance for the early diagnosis of multiple sclerosis (MS) and MRI findings are part of the MS diagnostic criteria. There is a growing interest in the use of ultra-high-field strength -7 Tesla- (7T) MRI to investigate, in vivo, the pathological substrate of the disease. Areas covered: An overview of 7T MRI applications in MS focusing on increased sensitivity for lesion detection, specificity of the central vein sign and better understanding of MS pathophysiology. Implications for disease diagnosis, monitoring and treatment planning are discussed. Expert commentary: 7T MRI provides increased signal-to-noise and contrast-to-noise-ratio that allow higher spatial resolution and better detection of anatomical and pathological features. The high spatial resolution reachable at 7T has been a game changer for neuroimaging applications not only in MS but also in epilepsy, brain tumors, dementia, and neuro-psychiatric disorders. Furthermore, the first 7T device has recently been cleared for clinical use by the food and drug administration.

Clinical Neuroimaging Using 7 T MRI: Challenges and Prospects

The aim of this article is to illustrate the principal challenges, from the medical and technical point of view, associated with the use of ultrahigh field (UHF) scanners in the clinical setting and to present available solutions to circumvent these limitations. We would like to show the differences between UHF scanners and those used routinely in clinical practice, the principal advantages, and disadvantages, the different UHFs that are ready be applied to routine clinical practice such as susceptibility-weighted imaging, fluid-attenuated inversion recovery, 3-dimensional time of flight, magnetization-prepared rapid acquisition gradient echo, magnetization-prepared 2 rapid acquisition gradient echo, and diffusion-weighted imaging, the technical principles of these sequences, and the particularities of advanced techniques such as diffusion tensor imaging, spectroscopy, and functional imaging at 7TMR. Finally, the main clinical applications in the field of the neuroradiology are discussed and the side effects are reported.

Nuclear magnetic relaxation dispersion of murine tissue for development of T1 (R1 ) dispersion contrast imaging

This study quantified the spin-lattice relaxation rate (R₁ ) dispersion of murine tissues from 0.24 mT to 3 T. A combination of ex vivo and in vivo spin-lattice relaxation rate measurements were acquired for murine tissue. Selected brain, liver, kidney, muscle, and fat tissues were excised and R₁ dispersion profiles were acquired from 0.24 mT to 1.0 T at 37 °C, using a fast field-cycling MR (FFC-MR) relaxometer. In vivo R₁ dispersion profiles of mice were acquired from 1.26 T to 1.74 T at 37 °C, using FFC-MRI on a 1.5 T scanner outfitted with a field-cycling insert electromagnet to dynamically control B₀ prior to imaging. Images at five field strengths (1.26, 1.39, 1.5, 1.61, 1.74 T) were acquired using a field-cycling pulse sequence, where B₀ was modulated for varying relaxation durations prior to imaging. R₁ maps and R₁ dispersion (ΔR₁ /ΔB₀ ) were calculated at 1.5 T on a pixel-by-pixel basis. In addition, in vivo R₁ maps of mice were acquired at 3 T. At fields less than 1 T, a large R₁ magnetic field dependence was observed for tissues. ROI analysis of the tissues showed little relaxation dispersion for magnetic fields from 1.26 T to 3 T. Our tissue measurements show strong R₁ dispersion at field strengths less than 1 T and limited R₁ dispersion at field strengths greater than 1 T. These findings emphasize the inherent weak R₁ magnetic field dependence of healthy tissues at clinical field strengths. This characteristic of tissues can be exploited by a combination of FFC-MRI and T₁ contrast agents that exhibit strong relaxivity magnetic field dependences (inherent or by binding to a protein), thereby increasing the agents' specificity and sensitivity. This development can provide potential insights into protein-based biomarkers using FFC-MRI to assess early changes in tumour development, which are not easily measureable with conventional MRI.

Quantification of perivascular spaces at 7T: A potential MRI biomarker for epilepsy

PURPOSE

7T (7T) magnetic resonance imaging (MRI) facilitates the visualization of the brain with resolution and contrast beyond what is available at conventional clinical field strengths, enabling improved detection and quantification of small structural features such as perivascular spaces (PVSs). The distribution of PVSs, detected in vivo at 7T, may act as a biomarker for the effects of epilepsy. In this work, we systematically quantify the PVSs in the brains of epilepsy patients and compare them to healthy controls.

METHODS

T₂-weighted turbo spin echo images were obtained at 7T on 21 epilepsy patients and 17 healthy controls. For all subjects, PVSs were manually marked on Osirix image analysis software. Marked PVSs with diameter≥0.5mm were then mapped by hemisphere and lobe. The asymmetry index (AI) was calculated for each region and the maximum asymmetry index (|AI_max|) was reported for each subject. The asymmetry in epilepsy subjects was compared to that of controls, and the region with highest asymmetry was compared to the suspected seizure onset zone.

RESULTS

There was a significant difference between the |AI_max| in epilepsy subjects and in controls (p=0.016). In 72% of patients, the region or lobe of the brain showing maximum PVS asymmetry was the same as the region containing the suspected seizure onset zone.

CONCLUSION

These findings suggest that epilepsy may be associated with significantly asymmetric distribution of PVSs in the brain. Furthermore, the region of maximal asymmetry of the PVSs may help provide localization or confirmation of the seizure onset zone.

Progress in neuro-imaging of brain tumors

PURPOSE OF REVIEW

Magnetic resonance imaging (MRI) is routinely employed in the diagnosis and clinical management of brain tumors. This review provides an overview of the advancements in the field of MRI, with a particular focus on the quantitative assessment by advanced physiological magnetic resonance techniques in light of the new molecular classification of brain tumor.

RECENT FINDINGS

Understanding how molecular phenotypes of brain tumors are reflected in noninvasive imaging is the goal of radiogenomics, which aims at determining the association between imaging features and molecular markers in neuro-oncology. Advanced MRI techniques such as diffusion magnetic resonance imaging and perfusion-weighted imaging add important structural, hemodynamic, and physiological information for tumor diagnosis and classification, as well as to stratify tumor response. Magnetic resonance spectroscopy is able to depict with unprecedented accuracy metabolic biomarkers, which are relevant for molecular subtyping. Ultra-high-field imaging enhances anatomical detail and enables to explore new horizon in tumor imaging.

SUMMARY

The noninvasive MRI-based assessment of tumor malignancy and molecular status may offer the opportunity to predict prognosis and to select patients who may be candidates for individualized targeted therapies, providing more sensitive tools for their follow-up.

7T MRI for neurodegenerative dementias in vivo: a systematic review of the literature

The spatial resolution of 7T MRI approaches the scale of pathologies of interest in degenerative brain diseases, such as amyloid plaques and changes in cortical layers and subcortical nuclei. It may reveal new information about neurodegenerative dementias, although challenges may include increased artefact production and more adverse effects. We performed a systematic review of papers investigating Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD) and Huntington's disease (HD) in vivo using 7T MRI. Of 19 studies identified, 15 investigated AD (the majority of which examined hippocampal subfield changes), and 4 investigated HD. Ultrahigh resolution revealed changes not visible using lower field strengths, such as hippocampal subfield atrophy in mild cognitive impairment. Increased sensitivity to susceptibility-enhanced iron imaging, facilitating amyloid and microbleed examination; for example, higher microbleed prevalence was found in AD than previously recognised. Theoretical difficulties regarding image acquisition and scan tolerance were not reported as problematic. Study limitations included small subject groups, a lack of studies investigating LBD and FTD and an absence of longitudinal data. In vivo 7T MRI may illuminate disease processes and reveal new biomarkers and therapeutic targets. Evidence from AD and HD studies suggest that other neurodegenerative dementias would also benefit from imaging at ultrahigh resolution.

Magnetic resonance imaging and positron emission tomography in the diagnosis of neurodegenerative dementias

Neuroimaging, both with magnetic resonance imaging (MRI) and positron emission tomography (PET), has gained a pivotal role in the diagnosis of primary neurodegenerative diseases. These two techniques are used as biomarkers of both pathology and progression of Alzheimer's disease (AD) and to differentiate AD from other neurodegenerative diseases. MRI is able to identify structural changes including patterns of atrophy characterizing neurodegenerative diseases, and to distinguish these from other causes of cognitive impairment, e.g. infarcts, space-occupying lesions and hydrocephalus. PET is widely used to identify regional patterns of glucose utilization, since distinct patterns of distribution of cerebral glucose metabolism are related to different subtypes of neurodegenerative dementia. The use of PET in mild cognitive impairment, though controversial, is deemed helpful for predicting conversion to dementia and the dementia clinical subtype. Recently, new radiopharmaceuticals for the in vivo imaging of amyloid burden have been licensed and more tracers are being developed for the assessment of tauopathies and inflammatory processes, which may underlie the onset of the amyloid cascade. At present, the cerebral amyloid burden, imaged with PET, may help to exclude the presence of AD as well as forecast its possible onset. Finally PET imaging may be particularly useful in ongoing clinical trials for the development of dementia treatments. In the near future, the use of the above methods, in accordance with specific guidelines, along with the use of effective treatments will likely lead to more timely and successful treatment of neurodegenerative dementias.

Investigating resting-state functional connectivity in the cervical spinal cord at 3T

The study of spontaneous fluctuations in the blood-oxygen-level-dependent (BOLD) signal has recently been extended from the brain to the spinal cord. Two ultra-high field functional magnetic resonance imaging (fMRI) studies in humans have provided evidence for reproducible resting-state connectivity between the dorsal horns as well as between the ventral horns, and a study in non-human primates has shown that these resting-state signals are impacted by spinal cord injury. As these studies were carried out at ultra-high field strengths using region-of-interest (ROI) based analyses, we investigated whether such resting-state signals could also be observed at the clinically more prevalent field strength of 3 T. In a reanalysis of a sample of 20 healthy human participants who underwent a resting-state fMRI acquisition of the cervical spinal cord, we were able to observe significant dorsal horn connectivity as well as ventral horn connectivity, but no consistent effects for connectivity between dorsal and ventral horns, thus replicating the human 7 T results. These effects were not only observable when averaging along the acquired length of the spinal cord, but also when we examined each of the acquired spinal segments separately, which showed similar patterns of connectivity. Finally, we investigated the robustness of these resting-state signals against variations in the analysis pipeline by varying the type of ROI creation, temporal filtering, nuisance regression and connectivity metric. We observed that – apart from the effects of band-pass filtering – ventral horn connectivity showed excellent robustness, whereas dorsal horn connectivity showed moderate robustness. Together, our results provide evidence that spinal cord resting-state connectivity is a robust and spatially consistent phenomenon that could be a valuable tool for investigating the effects of pathology, disease progression, and treatment response in neurological conditions with a spinal component, such as spinal cord injury.

Is There a Magnetic Resonance Imaging-Discernible Cause for Trigeminal Neuralgia? A Structured Review

BACKGROUND

Trigeminal neuralgia (TN) is a chronic brain condition involving the trigeminal nerve and characterized by severe and recurrent facial pain. Although the cause of TN has been researched extensively, there is a lack of convergence on the physiologic processes leading to pain symptoms. This review seeks to better elucidate the underlying pathophysiology of TN by analyzing the outcomes of studies that use magnetic resonance structural imaging and diffusion-weighted imaging to examine nerve damage in patients with TN.

METHODS

Performing a structured review of the literature, the authors included human magnetic resonance anatomic and diffusion-weighted imaging studies aimed at visualizing the trigeminal nerve or measuring neural damage pertaining to TN. Studies that measured and compared nerve damage in the affected and unaffected sides in patients or patients and controls were analyzed for neural changes associated with TN.

RESULTS

Twenty-five studies met inclusion criteria. Overall, the data from the anatomic and diffusion studies showed decreased volume and cross-sectional area, decreased fractional anisotropy, and increased apparent diffusion coefficient and diffusivity associated with the affected side of patients compared with the unaffected side as well as in patients compared with controls.

CONCLUSIONS

A review of the studies included indicates that neural differences exist between the affected and unaffected sides in patients as well as between patients and controls in both structural and diffusion metrics. The amalgamated data suggest that damage of the trigeminal nerve tissue is commonly found in patients with TN and could be a primary factor in TN pathophysiology.

High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields

A well-known problem in ultra-high-field MRI is generation of high-resolution three-dimensional images for detailed characterization of white and gray matter anatomical structures. T₁-weighted imaging traditionally used for this purpose suffers from the loss of contrast between white and gray matter with an increase of magnetic field strength. Macromolecular proton fraction (MPF) mapping is a new method potentially capable to mitigate this problem due to strong myelin-based contrast and independence of this parameter of field strength. MPF is a key parameter determining the magnetization transfer effect in tissues and defined within the two-pool model as a relative amount of macromolecular protons involved into magnetization exchange with water protons. The objectives of this study were to characterize the two-pool model parameters in brain tissues in ultra-high magnetic fields and introduce fast high-field 3D MPF mapping as both anatomical and quantitative neuroimaging modality for small animal applications. In vivo imaging data were obtained from four adult male rats using an 11.7T animal MRI scanner. Comprehensive comparison of brain tissue contrast was performed for standard R₁ and T₂ maps and reconstructed from Z-spectroscopic images two-pool model parameter maps including MPF, cross-relaxation rate constant, and T₂ of pools. Additionally, high-resolution whole-brain 3D MPF maps were obtained with isotropic 170µm voxel size using the single-point synthetic-reference method. MPF maps showed 3-6-fold increase in contrast between white and gray matter compared to other parameters. MPF measurements by the single-point synthetic reference method were in excellent agreement with the Z-spectroscopic method. MPF values in rat brain structures at 11.7T were similar to those at lower field strengths, thus confirming field independence of MPF. 3D MPF mapping provides a useful tool for neuroimaging in ultra-high magnetic fields enabling both quantitative tissue characterization based on the myelin content and high-resolution neuroanatomical visualization with high contrast between white and gray matter.

Investigation of hippocampal substructures in focal temporal lobe epilepsy with and without hippocampal sclerosis at 7T

PURPOSE

To provide a more detailed investigation of hippocampal subfields using 7T magnetic resonance imaging (MRI) for the identification of hippocampal sclerosis in temporal lobe epilepsy (TLE).

MATERIALS AND METHODS

Patients (n = 13) with drug-resistant TLE previously identified by conventional imaging as having hippocampal sclerosis (HS) or not (nine without HS, four HS) and 20 age-matched healthy controls were scanned and compared using a 7T MRI protocol. Using a manual segmentation scheme to delineate hippocampal subfields, subfield-specific volume changes and apparent transverse relaxation rate ( R2*) were studied between the two groups. In addition, qualitative assessment at 7T and clinical outcomes were correlated with measured subfield changes.

RESULTS

Volumetry of the hippocampus at 7T in HS patients revealed significant ipsilateral subfield atrophy in CA1 (P = 0.001) and CA4+DG (P < 0.001). Volumetry also uncovered subfield atrophy in 33% of patients without HS, which had not been detected using conventional imaging. R2* was significantly lower in the CA4+DG subfields (P = 0.001) and the whole hippocampus (P = 0.029) of HS patients compared to controls but not significantly lower than the group without HS (P = 0.077, P = 0.109). No correlation was found between quantitative volumetry and qualitative assessment as well as surgical outcomes (Sub, P = 0.495, P = 0.567, P = 0.528; CA1, P = 0.104 ± 0.171, P = 0.273, P = 0.554; CA2+CA3, P = 0.517, P = 0.952, P = 0.130 ± 0.256; CA4+DG, P = 0.052 ± 0.173, P = 0.212, P = 0.124 ± 0.204; WholeHipp, P = 0.187, P = 0.132 ± 0.197, P = 0.628).

CONCLUSION

These preliminary findings indicate that hippocampal subfield volumetry assessed at 7T is capable of identifying characteristic patterns of hippocampal atrophy in HS patients; however, difficulty remains in using imaging to identify hippocampal pathologies in cases without HS.

LEVEL OF EVIDENCE

2 J. MAGN. RESON. IMAGING 2017;45:1359-1370.

Usage of SWI (susceptibility weighted imaging) acquired at 7T for qualitative evaluation of temporal lobe epilepsy patients with histopathological and clinical correlation: An initial pilot study

OBJECTIVES

Ultra high field MRI at 7T is able to provide much improved spatial and contrast resolution which may aid in the diagnosis of hippocampal abnormalities. This paper presents a preliminary experience on qualitative evaluation of 7T MRI in temporal lobe epilepsy patients with a focus on comparison to histopathology.

METHODS

7T ultra high field MRI data, using T1-weighted, T2*-weighted and susceptibility-weighted images (SWI), were acquired for 13 patients with drug resistant temporal lobe epilepsy (TLE) during evaluation for potential epilepsy surgery. Qualitative evaluation of the imaging data for scan quality and presence of hippocampal and temporal lobe abnormalities were scored while blinded to the clinical data. Correlation of imaging findings with the clinical data was performed. Blinded evaluation of 1.5T scans was also performed.

RESULTS

On the 7T MRI findings, eight out of 13 cases demonstrated concordance with the clinically suspected TLE. Among these concordant cases, three exhibited supportive abnormal 7T MRI findings which were not detected by the clinical 1.5T MRI. Of the ten cases that progressed to epilepsy surgery, seven showed concordance between 7T MRI findings and histopathology; of these, four cases had hippocampal sclerosis. SWI had the highest concordance with the clinical and histopathological findings. Similar clinical and histopathological concordance was found with 1.5T MRI.

CONCLUSIONS

There was moderate and high concordance between the 7T imaging findings with the clinical data and histopathology respectively.

Surgical Accuracy of 3-Tesla Versus 7-Tesla Magnetic Resonance Imaging in Deep Brain Stimulation for Parkinson Disease

BACKGROUND

In deep brain stimulation (DBS), accurate placement of the lead is critical. Target definition is highly dependent on visual recognition on magnetic resonance imaging (MRI). We prospectively investigated whether the 7-T MRI enabled better visualization of targets and led to better placement of leads compared with the 1.5-T and the 3-T MRI.

METHODS

Three patients with PD (mean, 55 years) were scanned on 1.5-, 3-, and 7-T MRI before surgery. Tissue contrast and signal-to-noise ratio were measured. Target coordinates were noted on MRI and during surgery. Differences were analyzed with post-hoc analysis of variance.

RESULTS

The 7-T MRI demonstrated a significant improvement in tissue visualization (P < 0.005) and signal-to-noise ratio (P < 0.005). However, no difference in the target coordinates was found between the 7-T and the 3-T MRI.

CONCLUSIONS

Although the 7-T MRI enables a significant better visualization of the DBS target in patients with PD, we found no clinical benefit for the placement of the DBS leads.

Susceptibility Sensitive Magnetic Resonance Imaging Displays Pallidofugal and Striatonigral Fiber Tracts

BACKGROUND

The pallidofugal and striatonigral fiber tracts form a functional part of the basal ganglionic neuronal networks. For deep brain stimulation, a surgical procedure applied in the treatment of Parkinson disease and dystonia, precise localization of pallidofugal pathways may be of particular clinical relevance for correct electrode positioning.

OBJECTIVE

To investigate whether the pallidofugal and striatonigral pathways can be visualized with magnetic resonance imaging in vivo by exploiting their intrinsic magnetic susceptibility.

METHODS

Three-dimensional gradient-echo imaging of 5 volunteers was performed on a 7 T magnetic resonance imaging system. To demonstrate that the displayed tubular structures in the vicinity of the subthalamic nucleus and substantia nigra truly represent fiber tracts rather than veins, gradient-echo data of a formalin-fixated brain and a volunteer during inhalation of ambient air and carbogen were collected at 3 T. Susceptibility weighted images, quantitative susceptibility maps, and effective transverse relaxation maps were reconstructed and the depiction of fiber tracts was qualitatively assessed.

RESULTS

High-resolution susceptibility-based magnetic resonance imaging contrasts enabled visualization of pallidofugal and striatonigral fiber tracts noninvasively at 3 T and 7 T. We verified that the stripe-like pattern observed on susceptibility-sensitive images is not caused by veins crossing the internal capsule but by fiber tracts traversing the internal capsule.

CONCLUSION

Pallidofugal and striatonigral fiber tracts have been visualized in vivo for the first time by using susceptibility-sensitive image contrasts. Considering the course of pallidofugal pathways, in particular for deep brain stimulation procedures in the vicinity of the subthalamic nucleus, could provide landmarks for optimal targeting during stereotactic planning.

The traveling heads: multicenter brain imaging at 7 Tesla

OBJECTIVE

This study evaluates the inter-site and intra-site reproducibility of 7 Tesla brain imaging and compares it to literature values for other field strengths.

MATERIALS AND METHODS

The same two subjects were imaged at eight different 7 T sites. MP2RAGE, TSE, TOF, SWI, EPI as well as B1 and B0 field maps were analyzed quantitatively to assess inter-site reproducibility. Intra-site reproducibility was measured with rescans at three sites.

RESULTS

Quantitative measures of MP2RAGE scans showed high agreement. Inter-site and intra-site reproducibility errors were comparable to 1.5 and 3 T. Other sequences also showed high reproducibility between the sites, but differences were also revealed. The different RF coils used were the main source for systematic differences between the sites.

CONCLUSION

Our results show for the first time that multi-center brain imaging studies of the supratentorial brain can be performed at 7 T with high reproducibility and similar reliability as at 3T. This study develops the basis for future large-scale 7 T multi-site studies.

7T MRI in focal epilepsy with unrevealing conventional field strength imaging

OBJECTIVE

To assess the diagnostic yield of 7T magnetic resonance imaging (MRI) in detecting and characterizing structural lesions in patients with intractable focal epilepsy and unrevealing conventional (1.5 or 3T) MRI.

METHODS

We conducted an observational clinical imaging study on 21 patients (17 adults and 4 children) with intractable focal epilepsy, exhibiting clinical and electroencephalographic features consistent with a single seizure-onset zone (SOZ) and unrevealing conventional MRI. Patients were enrolled at two tertiary epilepsy surgery centers and imaged at 7T, including whole brain (three-dimensional [3D] T1 -weighted [T1W] fast-spoiled gradient echo (FSPGR), 3D susceptibility-weighted angiography [SWAN], 3D fluid-attenuated inversion recovery [FLAIR]) and targeted imaging (2D T2*-weighted dual-echo gradient-recalled echo [GRE] and 2D gray-white matter tissue border enhancement [TBE] fast spin echo inversion recovery [FSE-IR]). MRI studies at 1.5 or 3T deemed unrevealing at the referral center were reviewed by three experts in epilepsy imaging. Reviewers were provided information regarding the suspected localization of the SOZ. The same team subsequently reviewed 7T images. Agreement in imaging interpretation was reached through consensus-based discussions based on visual identification of structural abnormalities and their likely correlation with clinical and electrographic data.

RESULTS

7T MRI revealed structural lesions in 6 (29%) of 21 patients. The diagnostic gain in detection was obtained using GRE and FLAIR images. Four of the six patients with abnormal 7T underwent epilepsy surgery. Histopathology revealed focal cortical dysplasia (FCD) in all. In the remaining 15 patients (71%), 7T MRI remained unrevealing; 4 of the patients underwent epilepsy surgery and histopathologic evaluation revealed gliosis.

SIGNIFICANCE

7T MRI improves detection of epileptogenic FCD that is not visible at conventional field strengths. A dedicated protocol including whole brain FLAIR and GRE images at 7T targeted at the suspected SOZ increases the diagnostic yield.

Cortical abnormalities and association with symptom dimensions across the depressive spectrum

BACKGROUND

Few studies have investigated the relationship between structural brain abnormalities and dimensions of depressive symptomatology.

METHODS

In the current study, we examined the relationship between cortical structural abnormalities and specific behavioral dimensions relevant to depression in a sample of unmedicated patients with major depressive disorder (MDD, n=57) and demographically similar healthy control volunteers (HC, n=29). All subjects underwent diagnostic assessment with the SCID, MRI at 3T, and dimensional assessments using the visual analog scales (VAS). Cortical regions were extracted for each subject, and group comparisons of cortical volume (CV), surface area (SA), and cortical thickness (CT) were performed controlling for multiple comparisons using a bootstrapping technique. Regions demonstrating group differences were analyzed for correlation with specific dimensions assessments.

RESULTS

As compared with HC, MDD subjects exhibited reduced CV within the left supramarginal gyrus, right ventrolateral prefrontal cortex (VLPFC), entorhinal cortex, parahippocampal gyrus, fusiform gyrus and pericalcarine; reduced SA in the right VLPFC, cuneus, and left temporal pole; and reduced CT in the right rostral anterior cingulate cortex (rACC) (all p's<0.05, corrected). The largest effect occurred within the right VLPFC for CV and SA (MDD<HC; effect sizes: 0.60). CV in the right VLPFC inversely correlated with sadness, fatigue and worry; CT in the right rACC inversely correlated with irritability and fatigue.

LIMITATIONS

Future studies will be required to further map the anatomical changes in depression to behavioral dimensions.

CONCLUSIONS

Our results indicate that specific cortical abnormalities are associated with specific behavioral components linked to depression.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

MRI safety: a report of current practice and advancements in patient preparation and screening

MRI offers detailed diagnostic images without ionizing radiation; however, there are considerable safety concerns associated with high electromagnetic field strength. With increasing use of high and ultra high (7T) magnetic field strength, adequate patient preparation and screening for ferrous material is increasingly important. We review current safety standards for patient screening and preparation and how they are implemented at our institution. In addition, we describe a novel supplemental screening technique wherein the lights are dimmed in response to detected ferrous metal at the threshold of Zone IV.

Perspectives of Ultra-High-Field MRI in Neuroradiology

PURPOSE

Magnetic resonance imaging (MRI) is one of the most important methods for the diagnosis and therapy monitoring of various diseases. Today, magnets up to 3 T are standard. This review will give an overview of the clinical perspectives of ultra-high field MRI, meaning mainly 7 T.

METHODS

Literature review with focus on clinical applications of 7 T imaging in neuroscience combined with examples of own studies and perspectives.

RESULTS

This high-resolution technique offers the potential to improve certain tissue contrasts and signal in functional (fMRI) and metabolic (MRS) imaging. This overview demonstrates already existing potentials and advantages of the ultra-high magnetic field for central nervous system (CNS) diseases.

CONCLUSIONS

Although there are still some technical challenges for brain and spine imaging at 7 T, the method has clear benefit in selected structural, functional, and metabolic imaging.

[Towards more precision in the therapy of brain tumors. Possibilities and limits of MRI]

Due to the introduction of advanced functional and spectroscopic magnetic resonance (MR) sequences, MR imaging has gained significant importance in neuro-oncology. In contrast to recent years when neuro-oncological imaging was mostly limited to contrast-enhanced T1-weighted images, advanced MR methods provide direct visualization and assessment of tumor pathophysiology. This article summarizes the most relevant MR methods for neuro-oncological imaging and highlights the pathophysiological background as well as potential clinical applications. Ultimately, this article gives a glimpse into the future and introduces potential applications of ultra-high field MRI.