DRRLUT

MLModule

genre	Projection
author	MeVis Medical Solutions AG
package	MeVisLab/Standard
dll	MLDRR
definition	MLDRR.def
see also	DRR
keywords	digitally, reconstructed, radiographs, mip, lookup, table

Purpose

The module DRR generates 2-dimensional projections of 3-dimensional CT datasets.

The LUT based processing mode simulates a beam that starts with the intensity 1 and is attenuated by every voxel it passes. The attenuation coefficient of each voxel is defined in an external look-up table (LUT) that must be connected to the LUT input of the DRR module.

This module provides the needed look-up table. The attenuation coefficients (and therefore the values of this LUT) must be in a range from 1 (no attenuation) to 0 (total extinction).

Windows

DRR

Output Fields

outLUT

name: outLUT, type: DRRLUTFunction(MLBase)

LUT output. Needed by some (but not all!) algorithms of ML module DRR.

Parameter Fields

Field Index

(Max): Integer	useHounsfieldUnits: Bool
(Min)    to: Integer	X-Ray energy in keV: Integer
Auto Calc: Bool
Drop Window Bit Depth Reference: Integer
Drop Window Center: Integer
Drop Window Width: Integer
LUT model: Enum
Max Drop Window Height: Double

Visible Fields

LUT model

name: LUTModel, type: Enum, default: Linear

Defines the general shape of the LUT curve.

Values:

Title	Name	Description
Linear	Linear	Generates an arithmetically decreasing curve based on the following formula:
Logarithmic	Logarithmic	Generates a logarithmically decreasing curve based on the following formula:
Logarithmic with sigmoid drop	Logarithmic with sigmoid drop	Generates almost the same curve like the Logarithmic LUT model with an additional sigmoid drop based on the following formula: with WS as the drop window start, WE as the drop window end and WH as the drop window height. The sigmoid drop is generated by subtraction of a cosine function within a so called drop window. The drop window dimensions depend on the parameters Drop Window Center, Drop Window Width, Max Drop Window Height, Auto Calc and Drop Window Bit Depth Reference.

Drop Window Bit Depth Reference

name: bitDepth, type: Integer, default: 12, minimum: 8, maximum: 16

Sets the bit depth the drop window parameters are valid for.

Changing the bit depth will automatically scale the drop window parameters in the GUI.

All drop window parameters can only be valid for a defined bit depth (for example a window center of 1300 is only possible for a bit depth >= 11, because with a bit depth of 10 the last LUT index would be 1023).

Note: this parameter is only for setting up the drop window in the GUI. For calculation of the internal LUT values, the drop window parameters are always scaled to the internal LUT index range.

(Min) to

name: minimumX_RayEnergy_in_kev, type: Integer, default: 60

Sets the minimum X-ray energy for calculating the drop window.

(Max)

name: maximumX_RayEnergy_in_kev, type: Integer, default: 160

Sets the maximum X-ray energy for calculating the drop window.

X-Ray energy in keV

name: x_RayEnergy_in_kev, type: Integer, default: 90, minimum: :field:`minimumX_RayEnergy_in_kev`, maximum: :field:`maximumX_RayEnergy_in_kev`

Sets the simulated X-ray energy in keV.

The attenuation characteristics of ionising radiation in biological tissue strongly depend on the energy of the rays. A low energy results in a strong attenuation and a high energy results in low attenuation.

The closer the X-ray energy in keV value is to the (Min)    to, the steeper the descent of the drop will be. The closer it is to the (Max), the more gently the descent will be (until it disappears completely when energy = max energy):

Graph color	Energy
Yellow	60 keV
Red	90 keV
Blue	160 keV

(Min energy = 60 keV, max energy = 160 keV, drop window center = 1300, drop window max height = 0.2)

Drop Window Center

name: dropWindowCenter, type: Integer, default: 1300

Sets the center in x-direction of the drop window.

The value should be near to the first voxel values for bone tissue. It is scaled automatically when the Drop Window Bit Depth Reference parameter is changed.

Drop Window Width

name: dropWindowWidth, type: Integer, default: 102

Sets the center in x-direction of the drop window.

Narrow drop windows result in a more contrasted DRR than wider windows.

Auto Calc

name: automaticDropWindowWidth, type: Bool, default: TRUE

If checked, the drop window is being calculated automatically.

Max Drop Window Height

name: maxDropWindowHeight, type: Double, default: 0.2, minimum: 0, maximum: 1

Sets the limit of the drop window’s height to a maximum value.

The actual drop window height is calculated based on the energy settings ((Min)    to and (Max)).

Hidden Fields

useHounsfieldUnits

name: useHounsfieldUnits, type: Bool, default: FALSE