DETERMINANTS OF SIGNAL INTENSITY IN MRI OF HUMAN ASTROCYTOMAS

MRI studies at 1.5 T of 38 patients with histologically confirmed astr ocytomas were reviewed to search for a relationship of signal intensit y with grade of malignancy, radiotherapy used for recurrent tumours an d calcium deposits in surgical specimens. Signal intensity of tumours compared with normal brain was rated on a scale of 1 to 5 on T1- and T 2-weighted images. Surgical specimens of each tumour were graded histo pathologically on a scale of I to III and examined for calcium deposit s. CT scans were searched for evidence of calcification. The majority of astrocytomas appeared hypointense on T1-weighted and hyperintense o n T2-weighted images. Of 18 tumours with increased signal on T1-weight ed images, grade III were prevalent, followed by calcified astrocytoma s. Among 14 tumours with decreased signal on T2-weighted images the or der was similar, but the ratio of high-grade to low-grade tumours did not differ in relation to signal intensity, while on T1-weighted image s the ratio was higher in the group with increased signal intensity. A high grade of malignancy and microcalcifications were associated with an increased signal intensity of astrocytomas on T1-weighted sequence s without contrast agent. The above factors did not influence signific antly the signal intensity on T2-weighted images.