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Speeding Shimming-Measure Strategy for MRI System

IP.com Disclosure Number: IPCOM000185615D
Original Publication Date: 2009-Aug-14
Included in the Prior Art Database: 2009-Aug-14
Document File: 3 page(s) / 166K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Field homogeneity is a fundamental condition for MRI (Magnetic Resonance Imaging) systems. As a installation/service step, the shimming field takes normally long time and requires much man power, especially for a permanent MRI system, which takes more iterations and normally over one to two working days. One part of shimming work is to measure the field with a specific shimming device as well as plotting the field. Currently, the shimming device is designed as phantom array and each little phantom is surrounded by one local coil to detect corresponding spatial resonance frequency in order to get local field strength. Normally, phantoms are distributed evenly along (half-) circle with certain diameter and after each measurement for all the phantoms the shim device has to be turned for an angle and measured again. After repeating these steps, field distribution on a ball surface will be plotted (see Figure1).

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Speeding Shimming-Measure Strategy for MRI System

Idea: Chaoming He, CN-Shenzhen; Zhicheng Deng, CN-Shenzhen; Junqiang He, CN-Shenzhen;
Bin Kuang, CN-Shenzhen

Field homogeneity is a fundamental condition for MRI (Magnetic Resonance Imaging) systems. As a installation/service step, the shimming field takes normally long time and requires much man power, especially for a permanent MRI system, which takes more iterations and normally over one to two working days. One part of shimming work is to measure the field with a specific shimming device as well as plotting the field.

Currently, the shimming device is designed as phantom array and each little phantom is surrounded by one local coil to detect corresponding spatial resonance frequency in order to get local field strength. Normally, phantoms are distributed evenly along (half-) circle with certain diameter and after each measurement for all the phantoms the shim device has to be turned for an angle and measured again. After repeating these steps, field distribution on a ball surface will be plotted (see Figure1).

This method has two deficiencies. Firstly, the diameter of the circle is fixed so that one can only get a field plot on a ball volume with fixed diameter. That means, the inner field distribution can only be deduced and the application for the specific hardware is limited to a certain MRI system. Secondly, one has to turn the shim device again and again in order to get shim plot on a whole ball surface, which is time-consuming.

To overcome these deficiencies, the following solution raises a systematical strategy to speed up the procedure of field measuring. Thereby, the fixed diameter shim device will be updated to a changeable diameter shim device (see Figure 2). The shim device of 3D distributed phantoms will be used to plot directly the field on the ball surface. If possible, rough gradient will be applied to distinguish signals from different spatial points.

With the changeable diameter,...