extra-axial point

Lens equation of axis-beyond object point is derived by Fermat s principle, the process of derivation indicates clearly that near axial conditions are necessary and sufficient conditions of ideal image formation.

用费马原理推导透镜对轴外物点的物像公式,推导过程清楚表明近轴条件是理想成像的充分必要条件。

Objective: To study the imaging features of extra-axial tumors and tumor-like lesions involving both middle and posterior cranial fossae and to make a classi?cation.

目的提高对跨中、后颅窝轴外肿瘤及肿瘤样病变的影像学认识。