Division of Nuclear Medicine

SimSET Resources :
The Zubal phantom
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Contents

 

Introduction

The Zubal phantom (Zubal et al  1994) is a digital representation of an adult male obtained from a CT scan (figure 1). The data has been segmented into about 50 different tissue types. The original dataset consists of 243x128x128 voxels, with 8-bit depth. Each tissue type is represented by an arbitrary integer.

The Zubal phantom is not distributed with the SimSET package, but can be obtained directly from Dr George Zubal at zubal@biomed.med.yale.edu.

The Zubal phantom is an extremely useful resource for simulations. This page will explain the basics of using the Zubal phantom with SimSET. A working knowlege of the software will be assumed.


Figure 1. Sagittal slice through the Zubal phantom.

Creating the object specification

The appropriate voxelization needs to be specified in the OBJECT GEOMETRY SPECIFICATION section in the phg parameters file. To obtain the original voxel size, you need to set the slice thickness in the z direction to 0.4 cm and use the following specifications for x and y:

xMin = -25.6
xMax = 25.6
yMin = -25.6
yMax = 25.6
num_X_bins = 128
num_Y_bins = 128

The Zubal phantom contains a lot of slices, and editing the phg parameters file by hand can prove tiresome. The following skeleton PERL script may be of use in this respect.

 

Specifying the attenuation distribution

An attenuation index translation table specially designed for the Zubal phantom is provided with the SimSET package. This translates the arbitrary tissue numbers in the original phantom into appropriate attenuation values for the different tissue types. Using this translation table is simply a matter of editing the relevant pointer in the phg run-time parameters file. For example:

STR attenuation_index_trans = "/simset/phg/phg.data/zubal_att_index_trans"

The Zubal attenuation index translation table we use can be found here - the format is as follows:

Zubal tissue index PHG material index Comment describing mapping from Zubal tissue type to PHG tissue type

 

Specifying the activity distribution

In the phg run-time parameters file, set the activity index translation table to point to your file, e.g.:

STR activity_index_trans = "/your_directory/zubal_act_index_trans"

The format of the file is as follows:

Zubal tissue index Your required activity concentration

An example activity index tranlsation file may be here - in this example, all tissues are set to have a relative activty concentration of 1, except lungs ( Zubal tissue type 10), which are set to zero, and brain (Zubal tissue type 2) which is set to 10.

 

Creating the activity and attenuation index files

The next step is to generate the activity and attenuation object index files. This is a achieved using the object editor - see the object editor page for further instructions. Note that the output files have 32-bit voxel depth, so they will each be 4 times the size of the original Zubal phantom.

When this has been done, the rest of the simulation can be configured in the normal way.

 

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Last revised by: Ramsey Badawi
Revision date: 10 Mar 1999