Collimator Control for X-ray CT Exposure Reduction

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Solution Overview

Problem

Helical scanning using X-ray cone beams faces challenges in reducing X-ray exposure, which is a critical concern in acquiring cross-sections or 3D views of moving objects like the heart.

Innovation Solution

An X-ray computer tomography apparatus is designed with a collimator control unit that adjusts the position of collimators to minimize X-ray exposure by moving them from an outermost to an innermost position relative to the X-ray central plane, optimizing the cone angle and reconstruction range, thereby reducing unnecessary X-ray irradiation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the collimators are positioned at the outermost position to maximize the cone beam coverage, then the reconstruction range is fully covered, but the X-ray exposure increases unnecessarily

Engineering Contradiction:

Improvereconstruction range coverageVSAvoidX-ray exposure

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The collimators are made dynamically adjustable along the rotation axis through a collimator moving mechanism. The collimator control unit continuously adjusts the collimator positions during helical scanning based on the actual reconstruction range requirements, transitioning from static to dynamic control to minimize X-ray exposure while maintaining adequate coverage.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the positional parameter of the collimators along the rotation axis to optimize the cone beam coverage. By adjusting the collimator positions to match the reconstruction range, the system dynamically modifies the geometric parameters of the X-ray beam to reduce unnecessary exposure.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the collimators are moved to reduce X-ray exposure, then radiation dose is minimized, but the cone beam coverage may be insufficient

Engineering Contradiction:

ImproveX-ray exposureVSAvoidreconstruction range coverage

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The collimator control unit receives feedback information about the reconstruction range settings and continuously adjusts the collimator positions accordingly. This closed-loop control ensures that the collimator positioning accurately matches the required coverage area, preventing both over-exposure and under-coverage.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system pre-calculates and positions the collimators according to the predetermined reconstruction range before actual scanning begins. This preliminary positioning ensures that the collimators are optimally configured to cover exactly the required area from the start of the scan.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If a single collimator is used, then the device complexity is reduced, but the ability to independently optimize different sections of the reconstruction range is limited

Engineering Contradiction:

Improvecollimator structureVSAvoidreconstruction range optimization

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The collimator system is divided into multiple independent collimators (first and second collimators) that can be separately controlled along the rotation axis. This segmentation allows each collimator to independently optimize different sections of the reconstruction range, providing greater adaptability while maintaining relatively simple individual component structures.

Inventive Principle:

Principle #1Segmentation

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 solution effectively minimizes X-ray exposure during helical scanning by dynamically controlling the collimator positions, ensuring that only the necessary amount of X-rays is used for image reconstruction, thus reducing patient radiation while maintaining image quality.

Implementation Method 1

an X-ray tube which generates X-rays; a two-dimensional array type X-ray detector which detects the X-rays

Methodology Applied

Scientific EffectX-ray generation and detection: X-Ray

Implementation Method 2

a pair of collimators which form X-rays from the X-ray tube into a cone beam shape

Methodology Applied

Scientific EffectX-ray absorption: Absorption (EM radiation)

Data Source

PatentUS8094775B2X-ray computer tomography apparatus including a pair of separably movable collimators

Publication Date: 2012.01.10 TOSHIBA MEDICAL SYST CORP

AI summary

An X-ray computer tomography apparatus includes an X-ray tube, a two-dimensional array type X-ray detector, a rotating mechanism, a pair of collimators, a collimator moving mechanism which separately moves the pair of collimators in a direction almost parallel to a rotation axis, a reconstruction processing unit which reconstructs image data in a reconstruction range, and a collimator control unit. The collimator control unit controls the position of each collimator in accordance with the distance between an X-ray central plane corresponding to a cone angle 0° and an end face of the reconstruction range. The collimator moving mechanism moves each of the pair of collimators in the range from the outermost position corresponding to the maximum cone angle to the innermost position offset from a position corresponding to a cone angle of nearly 0° to the opposite side.