Texture analysis of ultrahigh field T2*-weighted MR images of the brain: Application to Huntington's disease

Study protocol of IMAGINE-HD: Imaging iron accumulation and neuroinflammation with 7T-MRI + CSF in Huntington's disease

INTRODUCTION

Strong evidence suggests a significant role for iron accumulation in the brain in addition to the well-documented neurodegenerative aspects of Huntington's disease (HD). The putative mechanisms by which iron is linked to the HD pathogenesis are multiple, including oxidative stress, ferroptosis and neuroinflammation. However, no previous study in a neurodegenerative disease has linked the observed increase of brain iron accumulation as measured by MRI with well-established cerebrospinal fluid (CSF) and blood biomarkers for iron accumulation, or with associated processes such as neuroinflammation. This study is designed to link quantitative data from iron levels and neuroinflammation metabolites obtained from 7T MRI of HD patients, with specific and well-known clinical biofluid markers for iron accumulation, neurodegeneration and neuroinflammation. Biofluid markers will provide quantitative measures of overall iron accumulation, neurodegeneration and neuroinflammation, while MRI measurements on the other hand will provide quantitative spatial information on brain pathology, neuroinflammation and brain iron accumulation, which will be linked to clinical outcome measures.

METHODS

This is an observational cross-sectional study, IMAGINE-HD, in HD gene expansion carriers and healthy controls. We include premanifest HD gene expansion carriers and patients with manifest HD in an early or moderate stage. The study includes a 7T MRI scan of the brain, clinical evaluation, motor, functional, and neuropsychological assessments, and sampling of CSF and blood for the detection of iron, neurodegenerative and inflammatory markers. Quantitative Susceptibility Maps will be reconstructed using T2* weighted images to quantify brain iron levels and Magnetic Resonance Spectroscopy will be used to obtain information about neuroinflammation by measuring cell-specific intracellular metabolites' level and diffusion. Age and sex matched healthy subjects are included as a control group.

DISCUSSION

Results from this study will provide an important basis for the evaluation of brain iron levels and neuroinflammation metabolites as an imaging biomarker for disease stage in HD and their relationship with the salient pathomechanisms of the disease on the one hand, and with clinical outcome on the other.

Real-time shimming with FID navigators

PURPOSE

To implement a method for real-time field control using rapid FID navigator (FIDnav) measurements and evaluate the efficacy of the proposed approach for mitigating dynamic field perturbations and improvingT 2 * $$ {\mathrm{T}}_2^{\ast } $$ -weighted image quality.

METHODS

FIDnavs were embedded in a gradient echo sequence and a subject-specific linear calibration model was generated on the scanner to facilitate rapid shim updates in response to measured FIDnav signals. To confirm the accuracy of FID-navigated field updates, phantom and volunteer scans were performed with online updates of the scanner B0 shim settings. To evaluate improvement inT 2 * $$ {\mathrm{T}}_2^{\ast } $$ -weighted image quality with real-time shimming, 10 volunteers were scanned at 3T while performing deep-breathing and nose-touching tasks designed to modulate the B0 field. Quantitative image quality metrics were compared with and without FID-navigated field control. An additional volunteer was scanned at 7T to evaluate performance at ultra-high field.

RESULTS

Applying measured FIDnav shim updates successfully compensated for applied global and linear field offsets in phantoms and across all volunteers. FID-navigated real-time shimming led to a substantial reduction in field fluctuations and a consequent improvement inT 2 * $$ {\mathrm{T}}_2^{\ast } $$ -weighted image quality in volunteers performing deep-breathing and nose-touching tasks, with 7.57% ± 6.01% and 8.21% ± 10.90% improvement in peak SNR and structural similarity, respectively.

CONCLUSION

FIDnavs facilitate rapid measurement and application of field coefficients for slice-wise B0 shimming. The proposed approach can successfully counteract spatiotemporal field perturbations and substantially improvesT 2 * $$ {\mathrm{T}}_2^{\ast } $$ -weighted image quality, which is important for a variety of clinical and research applications, particularly at ultra-high field.

The Key Role of Magnetic Resonance Imaging in the Detection of Neurodegenerative Diseases-Associated Biomarkers: A Review

Neurodegenerative diseases (NDs), including chronic disease such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis, and acute diseases like traumatic brain injury and ischemic stroke are characterized by progressive degeneration, brain tissue damage and loss of neurons, accompanied by behavioral and cognitive dysfunctions. So far, there are no complete cures for NDs; thus, early and timely diagnoses are essential and beneficial to patients' treatment. Magnetic resonance imaging (MRI) has become one of the advanced medical imaging techniques widely used in the clinical examination of NDs due to its non-invasive diagnostic value. In this review, research published in English in current decade from PubMed electronic database on the use of MRI to detect specific biomarkers of NDs was collected, summarized, and discussed, which provides valuable suggestions for the early diagnosis, prevention, and treatment of NDs in the clinic.

Rapid measurement and correction of spatiotemporal B0 field changes using FID navigators and a multi-channel reference image

PURPOSE

To measure spatiotemporal B₀ field changes in real time using FID navigators (FIDnavs) and to demonstrate the efficacy of retrospectively correcting high-resolution T 2 * -weighted images using a novel FIDnav framework.

METHODS

A forward model of the complex FIDnav signals was generated by simulating the effect of changes in the underlying B₀ inhomogeneity coefficients, with spatial encoding provided by a multi-channel reference image. Experiments were performed at 3T to assess the accuracy of B₀ field estimates from FIDnavs acquired from a 64-channel head coil under different shim settings and in 5 volunteers performing deep-breathing and nose-touching tasks designed to modulate the B₀ field. Second-order, in-plane spherical harmonic (SH) inhomogeneity coefficients estimated from FIDnavs were incorporated into an iterative reconstruction to retrospectively correct 2D gradient-echo images acquired in both axial and sagittal planes.

RESULTS

Spatiotemporal B₀ field changes measured from rapidly acquired FIDnavs were in good agreement with the results of second-order SH fitting to the measured field maps. FIDnav field estimates accounted for a significant proportion of the ΔB₀ variance induced by deep breathing (64 ± 21%) and nose touching (67 ± 34%) across all volunteers. Ghosting, blurring, and intensity modulation artifacts in T 2 * -weighted images, induced by spatiotemporal field changes, were visibly reduced following retrospective correction with FIDnav inhomogeneity coefficients.

CONCLUSIONS

Spatially resolved B₀ inhomogeneity changes up to second order can be characterized in real time using the proposed approach. Retrospective FIDnav correction substantially improves T 2 * -weighted image quality in the presence of strong B₀ field modulations, with potential for real-time shimming.

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.

Pituitary stalk thickening: the role of an innovative MRI imaging analysis which may assist in determining clinical management

CONTEXT

Disease processes that affect the pituitary stalk are broad; the diagnosis and management of these lesions remains unclear.

OBJECTIVE

The aim was to assess the clinical, biochemical and histopathological characteristics of pituitary stalk lesions and their association with specific MRI features in order to provide diagnostic and prognostic guidance.

DESIGN AND METHODS

Retrospective observational study of 36 patients (mean age 37years, range: 4-83) with pituitary stalk thickening evaluated at a university hospital in Oxford, UK, 2007-2015. We reviewed morphology, signal intensity, enhancement and texture appearance at MRI (evaluated with the ImageJ programme), along with clinical, biochemical, histopathological and long-term follow-up data.

RESULTS

Diagnosis was considered certain for 22 patients: 46% neoplastic, 32% inflammatory and 22% congenital lesions. In the remaining 14 patients, a diagnosis of a non-neoplastic disorder was assumed on the basis of long-term follow-up (mean 41.3months, range: 12-84). Diabetes insipidus and headache were common features in 47 and 42% at presentation, with secondary hypogonadism the most frequent anterior pituitary defect. Neoplasia was suggested on size criteria or progression with 30% sensitivity. However, textural analysis of MRI scans revealed a significant correlation between the tumour pathology and pituitary stalk heterogeneity in pre- and post-gadolinium T1-weighted images (sensitivity: 88.9%, specificity: 91.7%).

CONCLUSIONS

New techniques of MRI imaging analysis may identify clinically significant neoplastic lesions, thus directing future therapy. We propose possible textural heterogeneity criteria of the pituitary stalk on pre- and post-gadolinium T1 images with the aim of differentiating between neoplastic and non-neoplastic lesions with a high degree of accuracy.

Support vector machine classification of brain metastasis and radiation necrosis based on texture analysis in MRI

PURPOSE

To develop a classification model using texture features and support vector machine in contrast-enhanced T1-weighted images to differentiate between brain metastasis and radiation necrosis.

METHODS

Texture features were extracted from 115 lesions: 32 of them previously diagnosed as radiation necrosis, 23 as radiation-treated metastasis and 60 untreated metastases; including a total of 179 features derived from six texture analysis methods. A feature selection technique based on support vector machine was used to obtain a subset of features that provide optimal performance.

RESULTS

The highest classification accuracy evaluated over test sets was achieved with a subset of ten features when the untreated metastases were not considered; and with a subset of seven features when the classifier was trained with untreated metastases and tested on treated ones. Receiver operating characteristic curves provided area-under-the-curve (mean ± standard deviation) of 0.94 ± 0.07 in the first case, and 0.93 ± 0.02 in the second.

CONCLUSION

High classification accuracy (AUC > 0.9) was obtained using texture features and a support vector machine classifier in an approach based on conventional MRI to differentiate between brain metastasis and radiation necrosis.

Quantitative 7T phase imaging in premanifest Huntington disease

BACKGROUND AND PURPOSE

In vivo MR imaging and postmortem neuropathologic studies have demonstrated elevated iron concentration and atrophy within the striatum of patients with Huntington disease, implicating neuronal loss and iron accumulation in the pathogenesis of this neurodegenerative disorder. We used 7T MR imaging to determine whether quantitative phase, a measurement that reflects both iron content and tissue microstructure, is altered in subjects with premanifest Huntington disease.

MATERIALS AND METHODS

Local field shift, calculated from 7T MR phase images, was quantified in 13 subjects with premanifest Huntington disease and 13 age- and sex-matched controls. All participants underwent 3T and 7T MR imaging, including volumetric T1 and 7T gradient recalled-echo sequences. Local field shift maps were created from 7T phase data and registered to caudate ROIs automatically parcellated from the 3T T1 images. Huntington disease-specific disease burden and neurocognitive and motor evaluations were also performed and compared with local field shift.

RESULTS

Subjects with premanifest Huntington disease had smaller caudate volume and higher local field shift than controls. A significant correlation between these measurements was not detected, and prediction accuracy for disease state improved with inclusion of both variables. A positive correlation between local field shift and genetic disease burden was also found, and there was a trend toward significant correlations between local field shift and neurocognitive tests of working memory and executive function.

CONCLUSIONS

Subjects with premanifest Huntington disease exhibit differences in 7T MR imaging phase within the caudate nuclei that correlate with genetic disease burden and trend with neurocognitive assessments. Ultra-high-field MR imaging of quantitative phase may be a useful approach for monitoring neurodegeneration in premanifest Huntington disease.