plastimatch

drr

Synopsis

drr [options] [infile]

Description

A digitally reconstructed radiograph (DRR) is a synthetic radiograph which can be generated from a computed tomography (CT) scan. It is used as a reference image for verifying the correct setup position of a patient prior to radiation treatment.

DRR usage

The drr program that comes with plastimatch takes a CT image as input, and generates one or more output images. The input image is in MHA format, and the output images can be either pgm, pfm, or raw format. The command line usage is:

Usage: drr [options] [infile]
Options:
 -A hardware       Either "cpu" or "cuda" (default=cpu)
 -a num            Generate num equally spaced angles
 -N angle          Difference between neighboring angles (in degrees)
 -nrm "x y z"      Set the normal vector for the panel
 -vup "x y z"      Set the vup vector (toward top row) for the panel
 -g "sad sid"      Set the sad, sid (in mm)
 -r "r c"          Set output resolution (in pixels)
 -s scale          Scale the intensity of the output file
 -e                Do exponential mapping of output values
 -c "r c"          Set the image center (in pixels)
 -z "s1 s2"        Set the physical size of imager (in mm)
 -w "r1 r2 c1 c2"  Only produce image for pixes in window (in pix)
 -t outformat      Select output format: pgm, pfm or raw
 -i algorithm      Choose algorithm {exact,uniform}
 -o "o1 o2 o3"     Set isocenter position
 -I infile         Set the input file in mha format
 -O outprefix      Generate output files using the specified prefix

The drr program can be used in either single image mode or rotational mode. In single image mode, you specify the complete geometry of the x-ray source and imaging panel for a single image. In rotational mode, the imaging geometry is assumed to be

The command line options are described in more details as follows.

-A hardware

Choose the threading mode, which is either “cpu” or “cuda”. The default value is “cpu”.

When using CPU hardware, DRR generation uses OpenMP for multicore acceleration if your compiler supports this. Gcc and Microsoft Visual Studio Professional compilers support OpenMP, but Microsoft Visual Studio Express does not.

At the current time, cuda acceleration is not working.

-a num

Generate num equally spaced angles

-r """r1 r2"""

Set the resolution of the imaging panel (in pixels). Here, r1 refers to the number of rows, and r2 refers to the number of columns.

Single image mode

The following example illustrates the use of single image mode:

drr -nrm "1 0 0" \
    -vup "0 0 1" \
    -g "1000 1500" \
    -r "1024 768" \
    -z "400 300" \
    -c "383.5 511.5" \
    -o "0 -20 -50" \
    input_file.mha

In the above example, the isocenter is chosen to be (0, -20, -50), the location marked on the CT image. The orientation of the projection image is controlled by the nrm and vup options. Using the default values of (1, 0, 0) and (0, 0, 1) yields the DRR shown on the right:

_images/drr_input.png _images/drr_output_1.png

By changing the normal direction (nrm), we can choose different beam direction within an isocentric orbit. For example, an anterior-posterior (AP) DRR is generated with a normal of (0, -1, 0) as shown below:

_images/drr_output_2.png

The rotation of the imaging panel is selected using the vup option. The default value of vup is (0, 0, 1), which means that the top of the panel is oriented toward the positive z direction in world coordinates. If we wanted to rotate the panel by 45 degrees counter-clockwise on our AP view, we would set vup to the (1, 0, 1) direction, as shown in the image below. Note that vup doesn’t have to be normalized.

_images/drr_output_3.png

Rotational mode

In rotional mode, multiple images are created. The source and imaging panel are assumed to rotate in a circular orbit around the isocenter. The circular orbit is performed around the Z axis, and the images are generated every -N ang degrees of the orbit. This is illustrated using the following example:

drr -N 20 \
    -a 18 \
    -g "1000 1500" \
    -r "1024 768" \
    -z "400 300" \
    -o "0 -20 -50" \
    input_file.mha

In the above example, 18 images are generated at a 20 degree interval, as follows:

_images/drr_output_4.png