CT Automatic Exposure Control via Helical Pitch Modulation

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Solution Overview

Problem

Current CT imaging systems face limitations in automatic exposure control, particularly in dual energy imaging and scenarios where tube current modulation is insufficient, due to rapid kVp switching and physical constraints.

Innovation Solution

The method involves estimating attenuation properties of a subject and varying the helical pitch during a scan based on these properties, allowing for optimized image quality and reduced radiation dose without modulating the tube current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If tube current modulation is used for automatic exposure control, then image quality is optimized, but it cannot be applied in dual energy imaging due to rapid kVp switching constraints

Engineering Contradiction:

Improveautomatic exposure control functionalityVSAvoidapplicability in dual energy imaging

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Instead of modulating tube current to control exposure, the patent inverts the approach by modulating the helical pitch (table movement speed) while keeping tube current constant. This alternative control mechanism achieves automatic exposure control functionality in scenarios where traditional tube current modulation is unavailable, such as dual energy imaging with rapid kVp switching.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the controlled parameter from tube current to helical pitch. By varying the pitch factor (ratio of table movement to slice thickness) during scanning, the system adjusts the effective radiation dose delivered to different body regions, enabling automatic exposure control without modifying electrical parameters of the x-ray tube.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If tube current modulation is applied, then radiation dose is reduced while maintaining image quality, but physical constraints may render such approach insufficient

Engineering Contradiction:

Improveradiation doseVSAvoidautomatic exposure control performance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent introduces dynamic helical pitch modulation during the scan. The pitch is varied continuously based on the attenuation properties of different body regions, allowing the system to adapt the radiation dose in real-time. This dynamic adjustment complements or replaces tube current modulation, providing more reliable automatic exposure control when physical constraints limit current modulation effectiveness.

Inventive Principle:

Principle #15Dynamics

3Object-affected harmful factors

If helical pitch is varied based on attenuation properties, then radiation dose is reduced while maintaining image quality, but requires real-time attenuation estimation

Engineering Contradiction:

Improveradiation doseVSAvoidattenuation estimation requirement

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent performs attenuation estimation using a preliminary low-dose scout scan or predictive algorithms before the main diagnostic scan. This preliminary attenuation map is then used to pre-calculate the optimal helical pitch profile, eliminating the need for complex real-time attenuation measurement during the actual scan and reducing system complexity.

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 maintains desired image quality while reducing radiation dose, with image noise performance comparable to tube current modulation, and is applicable in various imaging modalities including CT, tomosynthesis, and C-arm angiography.

Implementation Method 1

technologies such as computed tomography (CT) use various physical principles, such as the differential transmission of x-rays through the target volume, to acquire image data

Methodology Applied

Scientific EffectX-ray transmission: X-Ray

Implementation Method 2

estimating attenuation properties of a subject along a direction

Methodology Applied

Scientific EffectX-ray attenuation: Absorption (EM radiation)

Data Source

PatentUS10561391B2Methods and systems for computed tomography

Publication Date: 2020.02.18 GE PRECISION HEALTHCARE LLC

AI summary

Methods and systems are provided for automatic exposure control in a computed tomography imaging system. In one embodiment, a method comprises estimating attenuation properties of a subject along a direction, and varying, based on the attenuation properties, a helical pitch along the direction during a scan of the subject. In this way, a desired image quality can be maintained while reducing radiation dose, without modulating tube current.