Quantitative magnetic resonance imaging of rat brain tumors: In vivo NMR relaxometry for the discrimination of normal and pathological tissues

Abstract

The in vivo relaxation times T₁ and T₂ were quantitatively determined in rat brain. Animals with implanted experimental brain tumors were investigated for discrimination of pathological regions from normal brain structures based on relaxation time differences. The different cerebral tumors (glioma, schwannoma, neuroblastoma) showed no difference in relaxation times, but all tumors had T₁(1301 ± 167 ms) and T₂(91 ± 9 ms) times distinctly longer than normal brain (T₁: 1057 ± 77 ms; T₂: 77 ± 6 ms). T₁ can be used for distinction of tumor and edema from normal brain, while T₂ is the better parameter for discrimination between tumor and edema.

Furthermore, the effect of MRI contrast agents (GdDTPA, MnTPPS, GdTPPS) on the relaxation times of these experimental brain tumors was measured. The enhancement of tumors produced by GdDTPA disappeared within ten minutes after i.p. application. At later times, central cysts and peritumoral edema became the most enhanced structures. The enhancement of tumor following MnTPPS application remained unchanged in T₁-weighted images during the whole observation period of four days. A significant reduction of enhancement was not observed during this time. The effect of MnTPPS on T₂ was weak. Replacement of manganese with gadolinium as the central ion of the porphyrin TPPS led to a contrast agent with enhancement effects on both, T₁- and T₂-weighted images.