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Scan2MCNP


Introduction


Scan2MCNP converts CT, MRI, and other scan data to an input file for the Monte Carlo transport programs MCNP and MCNPX. The input file contains only the geometry and materials of the scan region. Any desired geometry external to the scan region and source, tally, and other data items must be added elsewhere. Scan2MCNP can append a file containing data items to the MCNP input file. A 3D model is constructed from a file with multiple image frames or from a collection of files with single images. The scan data are read from DICOM files or several types of files containing an optional header and pixel data; we refer to the latter as raw pixel or IMG files. Several features support segmented IMG files where the pixel values represent an identified object, such as an organ, rather than image intensities.

An image consists of a 2D array of pixel values. A range of pixel values is associated with an MCNP material. Scan2MCNP offers a variety of tools to define the ranges (or partitions) and to assign materials to them. A number of display and enhancement features are provided for viewing and manipulation of the images. It is, however, the user's responsibility to define meaningful ranges and associated materials.

The MCNP geometry is defined in a voxel grid overlaying the scans. The user can choose the voxel size in the directions parallel to the scans. The size perpendicular to the scans is set by the spacing between the 2D planes. Information in the DICOM file determines the physical size, position, and orientation of the voxel grid. If a voxel encompasses multiple pixels with different materials, a new material is defined from a fraction weighted mixture of the original materials. The MCNP geometry can be written as a lattice or as normal cells. A cell combination algorithm used with the latter option combines neighboring cells of the same material.

By default, Scan2MCNP looks for the library Materials.lib in the directory in which the program runs. The Choose Library item in the Material Library submenu of the MCNP menu selects the library to use. In addition to the library, the program requires a DICOM dictionary to process some DICOM files. The default dictionary is Dicom.dic in the execution directory. Another dictionary can be chosen with the Select item in the Dictionary submenu of the File menu.

The next § describes the basic program elements and their operation. We next describe the pertinent features of DICOM files, followed by how to manage the files within the program. The next § covers display of the scan images including color schemes, contrast adjustment, and zooming. The definition, display, and use of the partition boundaries that define the pixel value ranges to which materials are assigned is covered in the following §. This is followed by a description of the material library. The MCNP Conversion § covers the options for setting up a voxel grid and creating the MCNP geometry. The Reference §s explain the menu items and dialogs.



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