MRI Frequency Shift Measurement Using Bipolar Gradient Phase

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Solution Overview

Problem

Magnetic resonance imaging (MRI) apparatuses face image quality degradation due to frequency shifts caused by fluctuations in static magnetic field strength, leading to reduced signal-to-noise ratio (SNR) and sensitivity irregularities, which existing methods fail to quantify and correct effectively.

Innovation Solution

The MRI apparatus includes a phase image generating unit, an image value acquisition unit, and a frequency shift calculation unit that apply bipolar gradient pulses and determine frequency shifts per unit gradient magnetic field, using multiple sequences to measure and correct frequency shifts, thereby reducing their impact on image quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If gradient magnetic field is applied to perform MRI imaging, then image acquisition is enabled, but frequency shift occurs causing image quality degradation

Engineering Contradiction:

Improveimage acquisition capabilityVSAvoidimage quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by measuring the frequency shift amount before performing the actual MRI imaging. The system measures the frequency shift using a measurement sequence that applies gradient magnetic fields, then uses this pre-measured frequency shift information to correct the imaging sequence, thereby preventing image quality degradation before it occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by measuring the actual frequency shift that occurs when gradient magnetic fields are applied, then using this measured information to adjust and correct the imaging parameters. The system creates a feedback loop where frequency shift measurement results directly influence the correction applied during subsequent imaging operations.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If frequency shift measurement is performed using conventional methods, then some frequency information is obtained, but quantitative measurement and effective correction are not achieved

Engineering Contradiction:

Improvefrequency measurement capabilityVSAvoidcorrection effectiveness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces conventional frequency measurement approaches with a phase-based measurement method. Instead of directly measuring frequency shifts, the system measures phase differences in the MR signal that result from frequency shifts, then calculates the frequency shift amount from these phase measurements. This substitution enables more accurate quantitative measurement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from direct frequency measurement to phase difference measurement. By measuring the phase difference of the MR signal at different time points and converting this phase information into frequency shift amounts, the system achieves more reliable quantitative measurement and correction capability.

Inventive Principle:

Principle #35Parameter changes

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 allows for quantitative measurement and correction of frequency shifts, improving image quality by reducing the effects of eddy currents and environmental noise, resulting in more accurate and stable MR images.

Implementation Method 1

A magnetic resonance imaging (MRI) apparatus magnetically excites nuclear spins of an object placed in a static magnetic field with an RF signal at Larmor frequency

Methodology Applied

Scientific EffectLarmor precession:

Implementation Method 2

it is important to reduce various impacts such as eddy currents which reduce image quality of images

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS9869742B2Magnetic resonance imaging apparatus and frequency shift measuring method

Publication Date: 2018.01.16 TOSHIBA MEDICAL SYST CORP

AI summary

According to one embodiment, a magnetic resonance imaging apparatus includes a phase image generating unit, an image value acquisition unit and a frequency shift calculation unit. The phase image generating unit executes a sequence including an application of a bipolar gradient pulse and thereby generates a first phase image. The image value acquisition unit acquires an image value of the first phase image. The frequency shift calculation unit determines an amount of frequency shift per unit amount of gradient magnetic field based on magnetic field strength of the bipolar gradient pulse and on the image value of the first phase image.