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  • 1
    In: Magnetic Resonance in Medicine, Wiley, Vol. 66, No. 3 ( 2011-09), p. 901-910
    Abstract: When volume coils are used for 1 H imaging of the human head at 7T, wavelength effects in tissue cause a variation in intensity, that is typically brighter at the center of the head and darker in the periphery. Much of this image nonuniformity can be attributed to variation in the effective transmit B 1 field, which falls by ∼ 50% to the left and right of center at mid‐elevation in the brain. Because most of this B 1 loss occurs in the periphery of the brain, we have explored use of actively controlled, off‐resonant loop elements to locally enhance the transmit B 1 field in these regions. When tuned to frequencies above the NMR frequency, these elements provide strong local enhancement of the B 1 field of the transmit coil. Because they are tuned off‐resonance, some volume coil detuning results, but resistive loading of the coil mode remains dominated by the sample. By digitally controlling their frequency offsets, the field enhancement of each inner element can be placed under active control. Using an array of eight digitally controlled elements placed around a custom‐built head phantom, we demonstrate the feasibility of improving the B 1 homogeneity of a transmit/receive volume coil without the need for multiple radio frequency transmit channels. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
    Type of Medium: Online Resource
    ISSN: 0740-3194 , 1522-2594
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2011
    detail.hit.zdb_id: 1493786-4
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  • 2
    Online Resource
    Online Resource
    American Society of Clinical Oncology (ASCO) ; 2000
    In:  Journal of Clinical Oncology Vol. 18, No. 5 ( 2000-03-01), p. 1020-1020
    In: Journal of Clinical Oncology, American Society of Clinical Oncology (ASCO), Vol. 18, No. 5 ( 2000-03-01), p. 1020-1020
    Abstract: PURPOSE: Proton magnetic resonance spectroscopic imaging ( 1 H-MRSI) is a noninvasive technique for spatial characterization of biochemical markers in tissues. We measured the relative tumor concentrations of these biochemical markers in children with recurrent brain tumors and evaluated their potential prognostic significance. PATIENTS AND METHODS: 1 H-MRSI was performed on 27 children with recurrent primary brain tumors referred to our institution for investigational drug trials. Diagnoses included high-grade glioma (n = 10), brainstem glioma (n = 7), medulloblastoma/peripheral neuroectodermal tumor (n = 6), ependymoma (n = 3), and pineal germinoma (n = 1). 1 H-MRSI was performed on 1.5-T magnetic resonance imagers before treatment. The concentrations of choline (Cho) and N-acetyl-aspartate (NAA) in the tumor and normal brain were quantified using a multislice multivoxel method, and the maximum Cho:NAA ratio was determined for each patient’s tumor. RESULTS: The maximum Cho:NAA ratio ranged from 1.1 to 13.2 (median, 4.5); the Cho:NAA ratio in areas of normal-appearing brain tissue was less than 1.0. The maximum Cho:NAA ratio for each histologic subtype varied considerably; approximately equal numbers of patients within each tumor type had maximum Cho:NAA ratios above and below the median. Patients with a maximum Cho:NAA ratio greater than 4.5 had a median survival of 22 weeks, and all 13 patients died by 63 weeks. Patients with a Cho:NAA ratio less than or equal to 4.5 had a projected survival of more than 50% at 63 weeks. The difference was statistically significant (P = .0067, log-rank test). CONCLUSION: The maximum tumor Cho:NAA ratio seems to be predictive of outcome in children with recurrent primary brain tumors and should be evaluated as a prognostic indicator in newly diagnosed childhood brain tumors.
    Type of Medium: Online Resource
    ISSN: 0732-183X , 1527-7755
    RVK:
    RVK:
    Language: English
    Publisher: American Society of Clinical Oncology (ASCO)
    Publication Date: 2000
    detail.hit.zdb_id: 2005181-5
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