講座

磁気共鳴分光
�Y．磁気共鳴イメージング（MRI）

Magnetic Resonance Spectroscopy
�Y．Magnetic Resonance Imaging

渡邉 英宏
Hidehiro WATANABE

磁気共鳴を用いたイメージング法、いわゆるMRIについて解説する。この方法は、T_l 、T₂などの情報をもとに磁化大きさの差をつけることでコントラストを付与し、勾配磁場パルスを利用して磁化の分布を計測する方法と言うことができる。これにより、特に軟部組織でコントラスト比の優れた画像を取得することが可能となる。この方法の基本概念であるコントラスト付与、分布計測に関して解説する。

Magnetic resonance imaging (MRl) method gives us images of subject with good quality non-invasively. Nowadays，this is an indispensable method especially in clinical field. In a 2 dimensional imaging method, amplitude of magnetization in each pixel on a slice of a subject is controlled using T₁ , T₂ , diffusion constant and etc. This differentiation of magnetization amplitude generates imaging contrast. The controlled magnetization in each pixel was measured using gradient pulses which transform position to frequency. It means that position is treated as frequency in MRI during application of gradients. As a result, images with good contrast to noise ratio can be obtained. These important two techniques which are c imaging using gradients and contrast generation are described. In imaging section，a slice，a frequency encoding and phase encoding techniques are described in detail. In contrast generation section, T_l and T₂ weighted imaging methods are described using pulse sequences.

Keywords: Imaging, in vivo, T₁ , T₂