Ryan Sangill

Experimentally and computationally fast method for estimation of a mean kurtosis.

Results from several recent studies suggest the magnetic resonance diffusion‐derived metric mean kurtosis (MK) to be a sensitive marker for tissue pathology; however, lengthy acquisition and postprocessing time hamper further exploration. The purpose of this study is to introduce and evaluate a new MK metric and a rapid protocol for its estimation.

Mean Diffusional Kurtosis in Patients with Glioma: Initial Results with a Fast Imaging Method in a Clinical Setting

BACKGROUND AND PURPOSE: Diffusional kurtosis imaging is an MR imaging technique that provides microstructural information in biologic systems. Its application in clinical studies, however, is hampered by long acquisition and postprocessing times. We evaluated a new and fast (2 minutes 46 seconds) diffusional kurtosis imaging method with regard to glioma grading, compared it with conventional diffusional kurtosis imaging, and compared the diagnostic accuracy of fast mean kurtosis (MK′) to that of the widely used mean diffusivity. MATERIALS AND METHODS: MK′ and mean diffusivity were measured in the contrast-enhancing tumor core, the perifocal hyperintensity (indicated on T2 FLAIR images), and the contralateral normal-appearing white and gray matter of 34 patients (22 with high-grade and 12 with low-grade gliomas). MK′ and mean diffusivity in the different tumor grades were compared by using a Wilcoxon rank sum test. Receiver operating characteristic curves and the areas under the curve were calculated to determine the diagnostic accuracy of MK′ and mean diffusivity. RESULTS: MK′ in the tumor core, but not mean diffusivity, differentiated high-grade from low-grade gliomas, and MK′ differentiated glioblastomas from the remaining gliomas with high accuracy (area under the curveMK′ = 0.842; PMK′ < .001). MK′ and mean diffusivity identified glioblastomas in the group of high-grade gliomas with similar significance and accuracy (area under the curveMK′ = 0.886; area under the curvemean diffusivity = 0.876; PMK′ = .003; Pmean diffusivity = .004). The mean MK′ in all tissue types was comparable to that obtained by conventional diffusional kurtosis imaging. CONCLUSIONS: The diffusional kurtosis imaging approach used here is considerably faster than conventional diffusional kurtosis imaging methods but yields comparable results. It can be accommodated in clinical protocols and enables exploration of the role of MK′ as a biomarker in determining glioma subtypes or response evaluation.

Experimental considerations for fast kurtosis imaging

The clinical use of kurtosis imaging is impeded by long acquisitions and postprocessing. Recently, estimation of mean kurtosis tensor W¯ and mean diffusivity ( D¯ ) was made possible from 13 distinct diffusion weighted MRI acquisitions (the 1‐3‐9 protocol) with simple postprocessing. Here, we analyze the effects of noise and nonideal diffusion encoding, and propose a new correction strategy. We also present a 1‐9‐9 protocol with increased robustness to experimental imperfections and minimal additional scan time. This refinement does not affect computation time and also provides a fast estimate of fractional anisotropy (FA).

Noninvasive assessment of isocitrate dehydrogenase mutation status in cerebral gliomas by magnetic resonance spectroscopy in a clinical setting

OBJECTIVE Mutations in the isocitrate dehydrogenase (IDH) genes are of proven diagnostic and prognostic significance for cerebral gliomas. The objective of this study was to evaluate the clinical feasibility of using a recently described method for determining IDH mutation status by using magnetic resonance spectroscopy (MRS) to detect the presence of 2-hydroxyglutarate (2HG), the metabolic product of the mutant IDH enzyme. METHODS By extending imaging time by 6 minutes, the authors were able to include a point-resolved spectroscopy (PRESS) MRS sequence in their routine glioma imaging protocol. In 30 of 35 patients for whom this revised protocol was used the lesions were subsequently diagnosed histologically as gliomas. Of the remaining 5 patients, 1 had a gangliocytoma, 1 had a primary CNS lymphoma, and 3 had nonneoplastic lesions. Immunohistochemistry and/or polymerase chain reaction were used to detect the presence of IDH mutations in the glioma tissue resected. RESULTS In vivo MRS for 2HG correctly identified the IDH mutational status in 88.6% of patients. The sensitivity and specificity was 89.5% and 81.3%, respectively, when using 2 mM 2HG as threshold to discriminate IDH-mutated from wildtype tumors. Two glioblastomas that had elevated 2HG levels did not have detectable IDH mutations, and in 2 IDH-mutated gliomas 2HG was not reliably detectable. CONCLUSIONS The noninvasive determination of the IDH mutation status of a presumed glioma by means of MRS may be incorporated into a routine diagnostic imaging protocol and can be used to obtain additional information for patient care.

Time evolution of cerebral perfusion and apparent diffusion coefficient measured by magnetic resonance imaging in a porcine stroke model

To demonstrate the feasibility of sequential diffusion‐weighted (DW) and perfusion‐weighted (PW) magnetic resonance imaging (MRI) of a recently developed porcine stroke model and to evaluate the evolution of cerebral perfusion and the apparent diffusion coefficient (ADC) over time.

Structural brain abnormalities in unselected in-patients with major depression

Objective: Several studies have indicated an increased frequency of cerebral atrophy and white matter lesions in patients with major depression, especially in older age groups.

Erratum: Hansen, Lund, Sangill, and Jespersen. Experimentally and Computationally Fast Method for Estimation of a Mean Kurtosis. Magnetic Resonance in Medicine 69:1754–1760 (2013)

Department of Physics and Astronomy, Aarhus University, Aarhus,Denmark.*Correspondence to: Sune Jespersen, Ph.D., CFIN/Department of Physics,Aarhus University, Building 10G, 5th Floor, N rrebrogade 44, DK-8000A˚rhus C, Denmark. E-mail: sune@cfin.au.dkReceived 29 November 2013; accepted 2 December 2013DOI 10.1002/mrm.25090Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).

White matter biomarkers from fast protocols using axially symmetric diffusion kurtosis imaging

White matter tract integrity (WMTI) can characterize brain microstructure in areas with highly aligned fiber bundles. Several WMTI biomarkers have now been validated against microscopy and provided promising results in studies of brain development and aging, as well as in a number of brain disorders. Currently, WMTI is mostly used in dedicated animal studies and clinical studies of slowly progressing diseases, and has not yet emerged as a routine clinical tool. To this end, a less data intensive experimental method would be beneficial by enabling high resolution validation studies, and ease clinical applications by speeding up data acquisition compared with typical diffusion kurtosis imaging (DKI) protocols utilized as part of WMTI imaging.

MRI protocol for in vivo visualization of the Göttingen minipig brain improves targeting in experimental functional neurosurgery

BACKGROUND The Göttingen minipig is increasingly used as an animal model in experimental neuroscience as a much needed alternative to non-human primates. Accurate spatial targeting in this species in vivo is challenging, and most clinically available magnetic resonance imaging (MRI) protocols do not provide sufficient spatial resolution for this purpose. Thus, the aim of this study was to develop an in vivo pre-operative MRI protocol allowing direct visualization of individual nuclei of major interest in the minipig brain. MATERIALS AND METHODS Three Göttingen minipigs underwent MRI using an inversion-recovery fast spin-echo sequence that was optimized with regards to the following parameters: inversion time, relaxation time, echo time and spatial and temporal resolution, giving a scan duration acceptable for the tight schedule usually employed in a neurosurgical procedure. The most optimal pulse sequence was applied in 8 Göttingen minipigs and the anatomical structures were identified. RESULTS AND CONCLUSION High-resolution images with excellent contrast were acquired, presenting negligible geometric distortions. Minor flow artifacts from the large neck vessels generated the most prominent artifact. Determination of coordinates necessary in experimental neurosurgery in the Göttingen minipig was considerably improved with this MRI protocol.

New surgical technique reduces the susceptibility artefact at air–tissue interfaces on in vivo cerebral MRI in the Göttingen minipig

Advanced and exclusive software solutions are offered to reduce susceptibility artefacts on MRI echo-planar sequences. We present a straightforward surgical technique to reduce the cortical distortion and signal loss that normally occur using diffusion tensor imaging (DTI) of the Göttingen minipig brain. Pronounced pneumatisation of the minipig cranium causes considerable susceptibility artefacts at the air/tissue interface around the frontal sinuses. Five Göttingen minipigs had burr holes drilled through the outer lamina of the skull bilaterally at the level of bregma. The underlying frontal sinuses were filled with a suspension of an MRI-compatible alginate. DTI was obtained before and after placing the medium in the sinus, quantifying the change using mutual information and Wilcoxons rank-sum test. Fibertracking algorithms were applied to visualize the effect of treatment. We showed that the susceptibility artefacts were reduced at the air, bone and brain interfaces and that major cortical fiberbundles could be reliably visualized. This study demonstrated that DTI fibertracking of cortical bundles in experimental animals with extensive skull pneumatisation is feasible even when advanced software is unavailable.