BACKGROUND AND PURPOSE:The accurate delineation of tumor recurrence presents a significant problem in neuro-oncology. Our aim was to improve the identification of brain tumor recurrence from chemoradiation injury by using CE-SWI, a technique that provides improved visualization of the heterogeneous patterns of brain tumor pathology, to guide the analysis of ADC measures within the peritumoral territory.
SUMMARY: MR spectroscopy is used to provide in vivo biochemical information about cerebral metabolites. Magnetic field homogeneity secondary to anatomic interfaces, hemorrhage, or necrosis may lead to suboptimal MR spectroscopy. Susceptibility-weighted imaging (SWI) can identify field inhomogeneity and could be used to guide MR spectroscopy voxel placement, leading to higher-quality MR spectroscopy examinations. Proton MR spectroscopy is used in clinical and research MR imaging studies to help differentiate between regions of normal and abnormal brain tissue and to monitor disease progression. Usually, key cerebral metabolites such as N-acetylaspartate (NAA), choline-containing compounds (Cho), and creatine/phosphocreatine (Cr) are identified, and quantitative data or metabolite ratios are measured.1 A homogeneous magnetic field and good signal-to-noise ratio are required for high-quality spectra. Spectral quality may be compromised at both 1.5 and 3T by signal-to-noise ratio issues and by magnetic field inhomogeneity, leading to poor water suppression, increased spectral line widths, and excessive baseline roll. 2,3 Interfaces between bone, air, and soft tissue cause localized perturbations in the magnetic field, and this is typically noted at the skull base adjacent to the sphenoid, frontal, and petrous air cells.If regions of magnetic field heterogeneity are unwittingly included within the sampling voxel by the operator, MR spectroscopy may be suboptimal. Susceptibility-weighted imaging (SWI) is a relatively new imaging sequence that is increasingly routinely used. 4 This sequence can detect subtle signal intensity phase differences within tissues, visualized as a signal intensity image or a phase map. 4 Anatomic regions with increased susceptibility differences can contribute to magnetic field inhomogeneity. Therefore, SWI or phase maps could be used to guide placement of the MR spectroscopy sampling voxel or aid interpretation of poor spectral results. TechniqueMR imaging studies were performed at 1.5T with use of a 12-channel receiver coil (Siemens, Erlangen, Germany). Data from a healthy subject and from a patient with recurrent glioblastoma multiforme were analyzed. We acquired SWI data by using a velocity-compensated radio-frequency-spoiled high-resolution 3D gradient-echo sequence (TR, 49 ms; TE, 40 ms; 72 sections; matrix, 256.177; voxel size, 1.1 ϫ 0.9 ϫ 2 mm). Phase and SWI maps were generated with use of VB15 software (Siemens). We acquired MR spectroscopy data by using a multivoxel point-resolved spectroscopy sequence (TR, 1700 ms; TE, 135 ms; MR spectroscopy voxel size, 10 mm ϫ 10 mm ϫ 15 mm). Fully automated shimming and water suppression were used and peripheral saturation bands placed. A gadolinium-enhanced T1-weighted acquisition (same section prescription as SWI) was used for placement of the multivoxel MR spectroscopy grid.We investigated the relationship between spectral quality and the degree of susceptibility-induced phase distortion (ie, field inhomogeneity) by processing the phase maps...
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