Digitally Reconstructed Radiograph

Digitally reconstructed radiographs ( Abbr: DRR) are made in the context of modern radiotherapy. They resemble normal radiographs, but derived from image data of a computer tomography. In the computer, a virtual point of view is calculated in the three-dimensional data, for example, the chest, wherein the voxel obtain a density-dependent transparency. The result is a summation of all the image located in the viewing direction structures. The most common purpose is the representation of a radiation field from the perspective of the radiation source, which may be compared for example with the simulator image.

Generation

An image with the same geometrical perspective of the radiation field generated by the irradiation device from the CT data set. The image is created by a Voxelsummation along the propagating to the image plane from the focus divergent beam. It is carried out an averaging of eight adjacent voxels at each node ( trilinear interpolation).

Advantage

• Radiographs non- coplanar fields are possible.

Disadvantage

• Lower spatial resolution ( 1 line pair per mm ) compared to the film (2 line pairs per mm)
• Generation of motion artifacts

Various display options

• Generating contrast between soft tissue and bone
• Generating contrast between soft tissue and lung
• MIP ( maximum intensity projection)
• Equal weighting of all density values