Removal of bone in CT angiography of the cervical arteries by piecewise matched mask bone elimination
The piecewise MMBE method illustrated with coronal images of the neck region of a patient. The method uses two CT scans: (a) a nonenhanced and (b) a contrast-enhanced scan. First, the bones in the nonenhanced data set are registered with those in the contrast-enhanced data set, resulting in (c) a registered nonenhanced data set. Next, the bone in the registered nonenhanced data set is converted to (d) a mask. Finally, the corresponding voxels in the contrast-enhanced data set are given (e) an arbitrary low value and (f) a MIP image can be made.
Separation of bones by the watershed algorithm. (a) Sagittal image of a detail of the skull base and the upper vertebra. (b) Separated bones. Each gray value represents a region . (c) CT values along the vertical line depicted in (a). The voxels that represent soft tissue have a relatively high CT value at locations between the bones (arrow). The bottom profile depicts the input for the watershed algorithm. The dashed vertical lines give the locations of the transition from one region to the other.
Images of the region of interest of , which is investigated in the phantom study. Window center: . Window width: . (a) Image of the contrast-enhanced scan (, pitch 0.875). (b) As (a), with the true bone voxels indicated with dark gray. The remaining white voxels represent synthetic material, but have a high CT value due to the spatial blurring of the CT imaging process. (c) As (a), with a mask with and voxels using for the nonenhanced scan. The mask voxels included by thresholding are light gray; the mask voxels included by dilation are black.
MIP images after masking for different combinations of threshold and amount of dilation . Top: ground truth MIP image. The numbers on the right represent , , , and . Images are ordered according to the value of . Window center: . Window width: .
Relation between and for different combinations of threshold , amount of dilation , and pitch. The symbols represent different amounts of dilation. Pitch 0.375: ▶ . Pitch 0.875: ▷ ; + ; ◻ ; 엯 ; ◁ ; × . For each amount of dilation data are given for (see numbers in graph). The nonenhanced scans were made with .
Value of and for different mAs values of the nonenhanced scan: ▷ ; + ; ◻ ; 엯 . Threshold value . Amount of dilation . Pitch 0.875. The dashed lines depict the combination of and at .
Histogram of the CT values of soft tissue in the head and neck region of a patient and of the CT values of the synthetic material in phantom data. The dashed line represents the scaled histogram for the phantom shifted to the left by . The patient and phantom were scanned with 65 and , respectively.
Influence of artifacts induced by metal fillings on the separation of bones. (a) Axial image of the nonenhanced CT scan. The vertebra in the same axial plane as the metal is not connected to the mandible and/or the skull via the hyperdense streak artifacts. (b) Coronal image of the nonenhanced CT scan. The hyperdense metal fillings connect the mandible to the maxilla.
MMBE results for different registration methods. (a) Cross-sectional MMBE image with the original method. (b) Cross-sectional MMBE image with the piecewise method. (c) Coronal MIP image with the original method. (d) Coronal MIP image with the piecewise method. With piecewise rigid registration the mandible and vertebrae are all registered correctly.
MMBE results for different registration methods. (a) Coronal MIP image with the original method. (b) Coronal MIP image with the piecewise method. (c) Sagittal contrast-enhanced image after application of piecewise MMBE, showing slight mismatch because not all vertebrae were separated by the watershed algorithm.
List of the scan and reconstruction parameters used for the phantom study and patient study.
List of the parameters that were used to quantify the quality of the mask.
List of the values of the piecewise MMBE parameters that were used in the patient study. The values for and were chosen with the aid of a phantom study (see Sec. IV A).
Success rates of the separation of bones for 35 data sets.
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