Overview

The SimSET package uses Monte Carlo techniques to model the physical processes and instrumentation used in emission imaging. The software is written in a modular format, and the core module is the Photon History Generator or PHG. A typical simulation proceeds decay-by-decay: the PHG generates a decay and the resulting photon(s) and tracks the photon(s) through the phantom; the Collimator Module receives photons from the PHG and tracks them through the collimator; the Detector Module receives photons either directly from the PHG module or from the Collimator module and tracks them in the detector, determining the detected position; the Binning Module histograms the detected photons or coincident events into a user-formatted output array. A simulation can be broken off between modules and a History File (a list-mode record of the decays and photons) created: the simulation can later be resumed using the history file as input. In PET simulations, the Random Coincidence Generation module can add random coincidences to a history file from the Detector module before the history file is processed by the Binning module.

The phantom to simulate is defined using the Object Editor. The input data for executing SimSET include: the Activity and Attenuation Objects; text Parameter Files defining the phantom, scan and tomograph parameters; and Data Tables defining the physical properties (e.g., attenuation) of the phantom activity and materials and scanner materials.

The SimSET package also comes with a range of utilities for manuipulating datasets and history files.

Below is a clickable block diagram illustrating how the different modules fit together. If you run into trouble with the pop-ups or get JavaScript errors, try reloading the page.

This work supported by PHS Grants #CA42593, "A Simulation System For Emission Tomography," and #CA126593, "University of Washington Emission Tomography Simulation Resource."

 

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Last revised by:	Robert Harrison
Revision date:	9 April 2011

Parameter Files and Data Tables are used to configure the PHG, Detector and Collimator modules. Examples of these files can be found in each of the module chapters and in the tutorial page.

The Object Editor is a utility used to create the attenuation and activity objects for Photon History Generator (PHG) simulations. These "objects" are effectively digital phantoms, providing the PHG with the spatial distribution of activity and attenuation material.

The Photon History Generator (PHG) is the software module which performs Monte-Carlo simulations of photon creation and transport through heterogeneous attenuators for both SPECT and PET - i.e. it generates photons and transports them through the "object" to the face of the collimator or detector.

The Collimator Module receives photons from the PHG and tracks photons through the collimator being modeled.

The Detector module receives photons either directly from the PHG module or from the Collimator module. It tracks photons through the specified detector, recording the interactions within the detector for each photon. The interactions are used to compute a detected location and total energy deposited.

Photon history files contain records for each photon accepted by the module creating the history file. These files may be created for all photons which reach the target cylinder (PHG Module), all photons which leave the collimator (Collimator Module), and all photons which are accepted by the detector (Detector Module).

The Binning Module is used to process photon and detection records. It can be used during the simulation as each record is accepted (on-the-fly), or it can be used after the simulation for processing a standard history file.

Histograms and images, together with the photon history files, make up the final output from a simulation.