Hospitalpage :: Medicine :: Imaging :: Magnetic Resonance Imaging

pubmed: 0730-725X

Improvement of spectral density-based activation detection of event-related fMRI data.
Ngan SC, Hu X, Tan LH, Khong PL Related Articles Improvement of spectral density-based activation detection of event-related fMRI data. Magn Reson Imaging. 2009 Sep;27(7):879-94 Authors: Ngan SC, Hu X, Tan LH, Khong PL For event-related data obtained from an experimental paradigm with a periodic design, spectral density at the fundamental frequency of the paradigm has been used as a template-free activation detection measure. In this article, we build and expand upon this detection measure to create an improved, integrated measure. Such an integrated measure linearly combines information contained in the spectral densities at the fundamental frequency as well as the harmonics of the paradigm and in a spatial correlation function characterizing the degree of co-activation among neighboring voxels. Several figures of merit are described and used to find appropriate values for the coefficients in the linear combination. Using receiver-operating characteristic analysis on simulated functional magnetic resonance imaging (fMRI) data sets, we quantify and validate the improved performance of the integrated measure over the spectral density measure based on the fundamental frequency as well as over some other popular template-free data analysis methods. We then demonstrate the application of the new method on an experimental fMRI data set. Finally, several extensions to this work are suggested. PMID: 19535208 [PubMed - indexed for MEDLINE]
On MRI turbulence quantification.
Dyverfeldt P, GĂĄrdhagen R, Sigfridsson A, Karlsson M, Ebbers T Related Articles On MRI turbulence quantification. Magn Reson Imaging. 2009 Sep;27(7):913-22 Authors: Dyverfeldt P, Gårdhagen R, Sigfridsson A, Karlsson M, Ebbers T Turbulent flow, characterized by velocity fluctuations, accompanies many forms of cardiovascular disease and may contribute to their progression and hemodynamic consequences. Several studies have investigated the effects of turbulence on the magnetic resonance imaging (MRI) signal. Quantitative MRI turbulence measurements have recently been shown to have great potential for application both in human cardiovascular flow and in engineering flow. In this article, potential pitfalls and sources of error in MRI turbulence measurements are theoretically and numerically investigated. Data acquisition strategies suitable for turbulence quantification are outlined. The results show that the sensitivity of MRI turbulence measurements to intravoxel mean velocity variations is negligible, but that noise may degrade the estimates if the turbulence encoding parameter is set improperly. Different approaches for utilizing a given amount of scan time were shown to influence the dynamic range and the uncertainty in the turbulence estimates due to noise. The findings reported in this work may be valuable for both in vitro and in vivo studies employing MRI methods for turbulence quantification. PMID: 19525079 [PubMed - indexed for MEDLINE]
Relaxo-volumetric multispectral quantitative magnetic resonance imaging of the brain over the human lifespan: global and regional aging patterns.
Saito N, Sakai O, Ozonoff A, Jara H Related Articles Relaxo-volumetric multispectral quantitative magnetic resonance imaging of the brain over the human lifespan: global and regional aging patterns. Magn Reson Imaging. 2009 Sep;27(7):895-906 Authors: Saito N, Sakai O, Ozonoff A, Jara H The objective of this study was to determine the T1, T2 and secular-T2 relaxo-volumetric brain aging patterns using multispectral quantitative magnetic resonance imaging, both globally and regionally, and covering an age range approaching the full human lifespan. Fifty-one subjects (28 males, 23 females; age range: 0.5-87 years) were studied consisting of 18 healthy volunteers and 33 patients. Patients were selected after carefully reviewing their radiology reports to have either normal-by-MRI findings (25 patient subjects) or small focal pathology less than 6 mm in size (eight patient subjects). All subjects were MR imaged at 1.5 T with the mixed turbo spin echo pulse sequence. The soft tissues inside the cranial vault, termed intracranial matter (ICM), were segmented using a dual-clustering segmentation algorithm. ICM segments were further divided into six subsegments: bilateral anterior cerebral, posterior cerebral and cerebellar subsegments. T1, T2 and secular-T2 relaxation time histograms of all segments were generated and modeled with Gaussian functions. For each segment, the volumes of white matter, gray matter and cerebrospinal fluid were calculated from the T1 histograms. The age-related tendencies of three quantitative MRI parameters (T1, T2 and secular-T2) and the fractional tissue volumes showed four distinct periods of life, specifically a maturation period (0-2 years), a development period (2-20 years), an adulthood period (20-60 years) and a senescence period (60 years and older). For all ages, the anterior cerebral subsegment exhibited consistently longer gray matter T1s and shorter white matter T1s than the posterior cerebral and cerebellar subsegments. Volumetric age-related changes of the cerebellar subsegment were more gradual than in the cerebral subsegments. This study shows that relaxometric and volumetric age-related changes are synchronized and define the same four periods of brain evolution both globally and regionally. PMID: 19520539 [PubMed - indexed for MEDLINE]
Fast low-angle positive contrast steady-state free precession imaging of USPIO-labeled macrophages: theory and in vitro experiment.
Mascheri N, Dharmakumar R, Zhang Z, Paunesku T, Woloschak G, Li D Related Articles Fast low-angle positive contrast steady-state free precession imaging of USPIO-labeled macrophages: theory and in vitro experiment. Magn Reson Imaging. 2009 Sep;27(7):961-9 Authors: Mascheri N, Dharmakumar R, Zhang Z, Paunesku T, Woloschak G, Li D The feasibility of imaging macrophages labeled with ultrasmall superparamagnetic iron-oxide nanoparticles (USPIO) with fast low-angle positive contrast steady-state free precession (FLAPS) was investigated through theory and in vitro experiment. Human macrophage cells were labeled with USPIO and imaged at 1.5 T. The metric "visibility," which combines magnitude and spatial extent of positive contrast, was used to evaluate the images. Negative contrast steady-state free precession (SSFP) and gradient-echo (GRE) imaging were also evaluated. Positive contrast was observed for relatively high concentrations of labeled cells for flip angles less than alpha=25 degrees . Theoretical and experimental results indicate that positive visibility (VIS(POS)) was maximized at alpha=10 degrees and 15 degrees. Low flip angle SSFP also provided negative contrast comparable to standard SSFP and GRE imaging. Results suggest that USPIO-labeled macrophages are capable of producing the conditions necessary for positive contrast with FLAPS at clinical field strength (1.5 T) and resolution (0.8x0.8x3 mm(3)). PMID: 19520536 [PubMed - indexed for MEDLINE]
A fully automated algorithm under modified FCM framework for improved brain MR image segmentation.
Sikka K, Sinha N, Singh PK, Mishra AK Related Articles A fully automated algorithm under modified FCM framework for improved brain MR image segmentation. Magn Reson Imaging. 2009 Sep;27(7):994-1004 Authors: Sikka K, Sinha N, Singh PK, Mishra AK Automated brain magnetic resonance image (MRI) segmentation is a complex problem especially if accompanied by quality depreciating factors such as intensity inhomogeneity and noise. This article presents a new algorithm for automated segmentation of both normal and diseased brain MRI. An entropy driven homomorphic filtering technique has been employed in this work to remove the bias field. The initial cluster centers are estimated using a proposed algorithm called histogram-based local peak merger using adaptive window. Subsequently, a modified fuzzy c-mean (MFCM) technique using the neighborhood pixel considerations is applied. Finally, a new technique called neighborhood-based membership ambiguity correction (NMAC) has been used for smoothing the boundaries between different tissue classes as well as to remove small pixel level noise, which appear as misclassified pixels even after the MFCM approach. NMAC leads to much sharper boundaries between tissues and, hence, has been found to be highly effective in prominently estimating the tissue and tumor areas in a brain MR scan. The algorithm has been validated against MFCM and FMRIB software library using MRI scans from BrainWeb. Superior results to those achieved with MFCM technique have been observed along with the collateral advantages of fully automatic segmentation, faster computation and faster convergence of the objective function. PMID: 19395212 [PubMed - indexed for MEDLINE]
Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation.
Li J, Wang Y, Jiang Y, Xie H, Li G Related Articles Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation. Magn Reson Imaging. 2009 Sep;27(7):988-93 Authors: Li J, Wang Y, Jiang Y, Xie H, Li G An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method. PMID: 19369023 [PubMed - indexed for MEDLINE]

Magnetic Resonance in Medicine

The impact of the relaxivity definition on the quantitative measurement of glycosaminoglycans in cartilage by the MRI dGEMRIC method
ShaoKuan Zheng, Yang Xia Fri, 13 Nov 2009 13:55:00 -0000
The relaxivities (R-values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)2-) ions in a series of skim-milk solutions at 0-40% milk concentrations were measured using NMR spectroscopy. The R-value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R-value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium-enhanced MRI of cartilage method without the customary scaling factor of 2. This finding is also supported by the measurements using 23Na NMR spectroscopy, 23Na inductively coupled plasma analysis, and biochemical assay. The choice of the R-value definition in the MRI delayed gadolinium-enhanced MRI of cartilage method is discussed, and the definition of Gd(DTPA)2- ions as "millimole per volume of tissue (or milk solution for substitution)" should be used. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.
Magnetic field homogenization of the human prefrontal cortex with a set of localized electrical coils
Christoph Juchem, Terence W. Nixon, Scott McIntyre, Douglas L. Rothman, Robin A. de Graaf Fri, 13 Nov 2009 13:53:00 -0000
The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air-filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external electrical coils is presented that provides localized and high-amplitude shim fields in the prefrontal cortex, with minimum impact on the rest of the brain when combined with regular zero- to second-order spherical harmonics shimming. The experimental realization of the new shim method strongly minimized or even eliminated signal dropout in gradient-echo images acquired at settings typically used in functional magnetic resonance at 4 T. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.
T2 relaxation time abnormalities in bipolar disorder and schizophrenia
Dost Ă–ngĂĽr, Andrew P. Prescot, J. Eric Jensen, Elizabeth D. Rouse, Bruce M. Cohen, Perry F. Renshaw, David P. Olson Fri, 13 Nov 2009 13:55:00 -0000
There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate + N-acetylaspartylglutamate, creatine + phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T2 quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T2 relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine + phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T2 relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T2 relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T2 relaxation and highlight the importance of measuring and correcting for this variable. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Magnetic Resonance Materials in Physics, Biology and Medicine

Detection of polyunsaturated omega-6 fatty acid in human malignant prostate tissue by 1D and 2D high-resolution magic angle spinning NMR spectroscopy
Tue, 17 Nov 2009 23:49:29 -0000
Abstract Object  Polyunsaturated omega-6 fatty acids (PUFAs) have been shown to promote prostate cancer. Here, we describe the use of HRMAS NMR spectroscopy to detect omega-6 PUFA species in prostate tissues. Materials and methods  Samples originating from non-malignant (n = 54) and malignant (n = 27) prostate tissues (from 27 prostatectomized men) were studied by 1D 1H, 2D 1H–1H and 1H–13C HRMAS NMR spectroscopy followed by histopathological characterization. Results  HRMAS NMR proved to be a powerful, non-destructive method to identify and characterize PUFAs. The omega-6 PUFA was found in 15% of examined human prostate tumors. Conclusion  It is possible to detect PUFAs in prostate tissues using our NMR-based spectroscopic approach. Content Type Journal ArticleCategory Short CommunicationDOI 10.1007/s10334-009-0187-xAuthors Katarina Stenman, UmeĂĄ University and University Hospital of Northern Sweden Department of Radiation Sciences, Diagnostic Radiology UmeĂĄ 901 87 SwedenJĂłn B. Hauksson, UmeĂĄ University and University Hospital of Northern Sweden Radiation Physics UmeĂĄ SwedenGerhard Gröbner, UmeĂĄ University Department of Chemistry UmeĂĄ SwedenPär Stattin, UmeĂĄ University and University Hospital of Northern Sweden Department of Surgery and Perioperative Sciences, Urology and Andrology UmeĂĄ SwedenAnders Bergh, UmeĂĄ University and University Hospital of Northern Sweden Department of Medical Biosciences Pathology UmeĂĄ SwedenKatrine Riklund, UmeĂĄ University and University Hospital of Northern Sweden Department of Radiation Sciences, Diagnostic Radiology UmeĂĄ 901 87 Sweden Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Structural–acoustic modal analysis of cylindrical shells: application to MRI scanner systems
Mon, 26 Oct 2009 18:00:23 -0000
Abstract Object  The acoustic noise in a magnetic resonance imaging (MRI) scanner bore is mainly introduced by the vibration of gradient coils. The interaction between acoustic modes in the scanner bore and structure modes in the coil structure leads to structural–acoustic coupling. In order to implement quiet MRI design, the structural–acoustic coupling mechanism in MRI machines needs to be fully investigated. Materials and method  Structural analysis was first implemented using Love’s classical shell theory. The concept of a “virtually closed cavity” was used in the acoustic modal analysis of the gradient coil duct. The dispersion curves and the number of modes per frequency band were used to reveal modal distribution properties for both structural modes and acoustic modes. Structural–acoustic coupling modes were identified by superposition of the dispersion diagrams of the structural waves and acoustic waves. Experimental validation was implemented separately for the structural analysis and acoustic analysis. Results  Independent structural modes and acoustic modes and their distribution patterns were calculated up to 3000Hz with various boundary conditions. Coupling modes were clearly revealed using the analysis procedures presented in this paper and were found to be in agreement with the ones identified from experimental measurements. Conclusion  These methods are effective for coupled and uncoupled modal analysis of MRI scanner systems and can be used for quiet MRI design or sound absorber design for existing MRI systems. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0185-zAuthors Gemin Li, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 CanadaChris K. Mechefske, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Quantitative metabolic profiles of 2nd and 3rd trimester human amniotic fluid using 1H HR-MAS spectroscopy
Thu, 24 Sep 2009 16:42:27 -0000
Abstract Object  To establish and compare normative metabolite concentrations in 2nd and 3rd trimester human amniotic fluid samples in an effort to reveal metabolic biomarkers of fetal health and development. Materials and methods  Twenty-one metabolite concentrations were compared between 2nd (15–27 weeks gestation, N = 23) and 3rd (29–39 weeks gestation, N = 27) trimester amniotic fluid samples using 1H high resolution magic angle spinning (HR-MAS) spectroscopy. Data were acquired using the electronic reference to access in vivo concentrations method and quantified using a modified semi-parametric quantum estimation algorithm modified for high-resolution ex vivo data. Results  Sixteen of 21 metabolite concentrations differed significantly between 2nd and 3rd trimester groups. Betaine (0.00846±0.00206 mmol/kg vs. 0.0133±0.0058 mmol/kg, P < 0.002) and creatinine (0.0124±0.0058 mmol/kg vs. 0.247±0.011 mmol/kg, P < 0.001) concentrations increased significantly, while glucose (5.96±1.66 mmol/kg vs. 2.41±1.69 mmol/kg, P < 0.001), citrate (0.740±0.217 mmol/kg vs. 0.399±0.137 mmol/kg, P < 0.001), pyruvate (0.0659±0.0103 mmol/kg vs. 0.0299±0.286 mmol/kg, P < 0.001), and numerous amino acid (e.g. alanine, glutamate, isoleucine, leucine, lysine, and valine) concentrations decreased significantly with advancing gestation. A stepwise multiple linear regression model applied to 50 samples showed that gestational age can be accurately predicted using combinations of alanine, glucose and creatinine concentrations. Conclusion  These results provide key normative data for 2nd and 3rd trimester amniotic fluid metabolite concentrations and provide the foundation for future development of magnetic resonance spectroscopy (MRS) biomarkers to evaluate fetal health and development. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0184-0Authors Brad R. Cohn, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USABonnie N. Joe, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAShoujun Zhao, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kornak, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAVickie Y. Zhang, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USARahwa Iman, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kurhanewicz, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAKiarash Vahidi, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJingwei Yu, University of California Department of Laboratory Medicine San Francisco CA USAAaron B. Caughey, University of California Department of Obstetrics & Gynecology San Francisco CA USAMark G. Swanson, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

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