4Oliveira A M, Nascimento A G. Grading in soft tissue tumors: principles and problems[ J]. Skeletal Radiol , 2001, 30(10): 543 -559.
5Koenig M, Kraus M, Theek C, et al. Quantitative assessment of the ischemic brain by means of perfusion-related parameters derived from perfusion CT[J]. Stroke, 2001, 32(2): 431 -437.