(a) Illustration of the MRSI data overlaid on one slice of a FLAIR MRI image of a patient with glioma. Inside each square is the corresponding spectrum for that MRSI voxel. This is a screen-dump image generated by GE’s FUNCTOOL software. (b) Illustration of a typical MR spectrum for abnormal brain tumor area. Each peak in the spectrum corresponds to a chemical compound. Labeled for tumor delineation are three major peaks: choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA). For an abnormal brain tumor, the Cho intensity is much higher than that of the Cr or NAA intensity.
Illustration of the converted screen-dumped MRSI image of Fig. 1(a). Although the image screen dumped by the FUNCTOOL is in DICOM format, it cannot be fused with other images because it is a color image and lacks the slice location and pixel size information in the DICOM header. The color image is converted to gray scale, and the pixel size is added to the DICOM header of the converted image. The bold white box is the user-defined MRS acquisition volume of interest. The “MRSI box” consists of the voxels of the MRSI matrix that were covered by the bold white box; “” and “” are the size (mm) of the displayed MRSI box in the x and y directions, while “” and “” are the number of pixels in the corresponding directions.
An example of converting (a) the Cho/Cr ratios in an exported text file by GE’s FUNCTOOL software to (b) a Cho/Cr image. The intensity of each voxel in (b) is mapped from the grades of Cho/Cr ratio according to Table I; numbers in (b) indicate the corresponding Cho/Cr grades of the image intensity.
Demonstration of overlaying a converted MRSI image on a FLAIR MRI image. The pixel values of the MR FLAIR image (left) in the MRSI box are replaced by the converted MRSI image (middle) to produce a merged image (right).
Fusion protocol summary.
An example of verifying the position of the MRSI box. The modified screen-dumped MRSI images are fused with the merged MRSI, and the locations of the MRSI box of both images are compared using the spy windows of the BRAINSCAN 5.1 (BrainLAB AG, Heimstetten, Germany) treatment planning system. The position of the MRSI box is iteratively adjusted until the positional difference is less than 0.5 mm.
Fraction of MRSI voxels for each Cho/Cr grade for low-grade glioma (LGG) and high-grade glioma (HGG). The error bars are one standard deviation.
(a) The dose distribution on one CT slice of an IMRT test plan using the MRSI defined targets. Three dose levels of corresponding to were planned to cover the three PTVs contoured in blue, green, and yellow, respectively. (b) The DVH of this test plan.
The system used to grade the Cho/Cr for each MRS voxel. The first column lists the Cho/Cr ratio, which is mapped to a grade in the second column. Columns 3, 4, and 5 show the corresponding image intensity, clinical target volume, and dose level for each Cho/Cr grade.
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