MAGNETIC RESONANCE IMAGING APPARATUS AND CORRECTION VALUE CALCULATION METHOD

摘要

In order to obtain a high-quality image even in multi-slice imaging in a UTE sequence that uses a half RF pulse, a refocusing pulse of the slice gradient magnetic field is adjusted and applied so that the excitation profiles of positive polarity data and negative polarity data have phase distributions that are 180 [deg] inverted with respect to each other in side lobe portions. In addition, the irradiation frequency of the half RF pulse is adjusted so as to eliminate a position shift between the intensity distributions of the positive polarity data and the negative polarity data.

主权项

1. A magnetic resonance imaging apparatus, comprising:
a static magnetic field generation system; a measurement system including a gradient magnetic field generation system, a high frequency magnetic field generation system, and a high frequency magnetic field detection system; and an arithmetic system that controls an operation of the measurement system according to a pulse sequence to measure a nuclear magnetic resonance signal and performs calculation using data obtained from the nuclear magnetic resonance signal, wherein the pulse sequence is an ultra-short echo time sequence to obtain each echo signal by performing two slice selection excitations by inverting a polarity of a slice gradient magnetic field, which is applied together with a half RF pulse, between a positive polarity and a negative polarity, the arithmetic system includes a pre-processing unit that calculates a correction value used in the measurement and the calculation and a main measurement unit that sets the correction value calculated by the pre-processing unit in the pulse sequence, performs main measurement by controlling the measurement system according to the pulse sequence after the setting, and reconstructs an image, the pre-processing unit includes a refocusing pulse application amount calculation section that calculates an application amount of a refocusing pulse of each slice gradient magnetic field as the correction value, the main measurement unit includes an image reconstruction section that adds positive polarity data, which is an echo signal obtained when the slice gradient magnetic field having a positive polarity is applied, and negative polarity data, which is an echo signal obtained when the slice gradient magnetic field having a negative polarity is applied, in the main measurement and reconstructs the image using polarity-added data after the addition, and the refocusing pulse application amount calculation section calculates the application amount of each refocusing pulse so as to reduce a side lobe signal of an excitation profile obtained by adding the positive polarity data and the negative polarity data.