CT Scanner Heel Effect Correction via 3D Lookup Table

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Solution Overview

Problem

CT scanners with polychromatic x-ray sources face beam-hardening artifacts, such as cupping, due to the increasing mean energy of the x-ray beam as it passes through objects, leading to image distortions like the heel effect, which existing methods struggle to effectively correct.

Innovation Solution

A method that assigns monochromatic attenuation values to polychromatic attenuation values using a three-dimensional look-up table, generated from calibration data with both polychromatic and monochromatic x-ray beams, to correct for beam-hardening and heel effects, improving image quality by accounting for varying x-ray spectra across the detector array.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If polychromatic x-ray beams are used in CT scanners, then the imaging capability is improved, but beam-hardening artifacts and heel effect distortions occur

Engineering Contradiction:

Improveimaging capabilityVSAvoidbeam-hardening artifacts

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent transforms polychromatic attenuation values into monochromatic attenuation values by changing the energy parameter representation. A lookup table maps polychromatic attenuation values to equivalent monochromatic values at a reference energy level, effectively converting the problematic polychromatic data into corrected monochromatic data that eliminates beam-hardening artifacts while preserving the imaging capability provided by the polychromatic source.

Inventive Principle:

Principle #35Parameter changes

2Area of stationary object

If the detector array has more rows to improve coverage, then the field of view is increased, but the heel effect causes varying intensity distribution across detector rows

Engineering Contradiction:

Improvefield of viewVSAvoidintensity distribution uniformity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent applies row-specific correction factors to account for the local intensity variations caused by the heel effect. Each detector row receives customized attenuation values that are adjusted according to its specific position and the corresponding heel effect characteristics, thereby maintaining uniform image quality across the entire expanded field of view covered by the multi-row detector array.

Inventive Principle:

Principle #3Local quality

3Reliability

If monochromatic attenuation values are assigned to polychromatic values using a lookup table, then beam-hardening correction is achieved, but the processing complexity increases

Engineering Contradiction:

Improvebeam-hardening correctionVSAvoidprocessing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent pre-calculates and stores the transformation relationships between polychromatic and monochromatic attenuation values in a lookup table before actual imaging processing. This preliminary preparation eliminates the need for complex real-time calculations during image acquisition, reducing processing complexity while maintaining reliable beam-hardening correction through simple table lookup operations.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively corrects beam-hardening artifacts and the heel effect, enhancing image quality and allowing for larger detector arrays with more rows, by using a 3D look-up table that assigns monochromatic values to polychromatic values based on cone angle, resulting in improved soft-tissue correction and reduced image distortions.

Implementation Method 1

When passing through an object of interest, the beam gradually becomes harder, i.e. its mean energy increases. This may cause beam-hardening artifacts

Methodology Applied

Scientific EffectBeam hardening: Absorption (EM radiation)

Implementation Method 2

The polychromatic x-ray spectrum depends on the cone angle, such that there is a varying intensity distribution for each detector row

Methodology Applied

Scientific EffectHeel effect: Absorption (EM radiation)

Data Source

PatentUS7724935B2Correction of artifacts caused by the heel effect

Publication Date: 2010.05.25 KONINKLIJKE PHILIPS NV

AI summary

A method for processing polychromatic attenuation values, wherein the polychromatic attenuation values are acquired by means of a polychromatic source of radiation generating a cone beam and radiation detector array with a plurality of detector rows, wherein the plurality of detector rows are arranged adjacent to each other in a first direction perpendicular to a second direction, wherein the second direction is parallel to the plurality of detector rows, the method comprising the step of: assigning the monochromatic attenuation values to polychromatic attenuation values, wherein the polychromatic attenuation values depend on the first direction and a three-dimensional look-up table is used for assigning the monochromatic attenuation values to the polychromatic attenuation values.