Module: Linear DECT ()

Description:

This module allows the user to analyze density and chemical composition in a sample. It uses Dual Energy Computed Tomography method to find these parameters. The algorithm is based on H.Alves, Methodology for atteinment of density and effective atomic number through dual energy technique using microtomographic imaged - Applied Radiation and Isotopes 89(2014) 6-12.
Thanks to monophasic or pure material phantoms for which the density and the chemical composition are known, we can calibrate a linear DECT system. It is possible to find a linear equation of the generic form:

For high and low energies by doing a least mean square method on the data (mass attenuation coefficients by ), the coefficients found are used to find density and Z effective with these equations:

With:
, the density.
, the effective atomic number.
, angular constants for low and high energies.
, linear constants for low and high energies.
, linear attenuation coefficients for low and high energies: they are computed from the low and high energy computed tomography input datasets.

The module generates four outputs:

• the density map,
• the Z effective map,
• the corrected Z effective map (computed by a postprocessing Median Filter from the Z effective map),
• the map of predicted materials (based on the database).

Connections:

Low Energy Data [required]
Input for low energy computed tomography dataset.

High Energy Data [required]
Input for high energy computed tomography dataset.

Database [required]
Input for the reference database in csv. The format of the database is Material;Density;Atomic Number. The predicted material map depends on this database.

Coefficients [optional]
Input for the coefficient of the affine functions in csv. The format is :
Low energy angular coefficient; Low energy linear coefficient
High energy angular coefficient; High energy linear coefficient
If set, the Low Energy Coefficients and High Energy Coefficients ports are automatically deduced and set from them given values.

Ports:

Low Energy Coefficients

This port allows modifying the value of the Low Energy Coefficients. If the coefficients are pre-loaded, the values are displayed and it's possible to change them.

High Energy Coefficients

This port allows modifying the value of High Energy Coefficients. If coefficients are pre-loaded, the values are displayed and it's possible to change them.

Iterations

This port defines the number of iterations for the recursive Median Filter.
The median filter is applied as a postprocessing step to generate the corrected Z effective map.
Iterations of 3 is recommended for fast computation (default value).

Mu Water for Energy Range

This port describes the value of lineic attenuation coefficients for Water. The first value is for Low energy and the second value corresponds to High energy.

Option

If you use Imasim simulated volume as input data, you have to check the box to properly read the voxel values.