DETECTION OF NECROSIS IN HUMAN TUMOR XENOGRAFTS BY PROTON MAGNETIC-RESONANCE-IMAGING

Tumours with necrotic regions have an inadequate blood supply and are expected to differ from well-vascularised tumours in response to treat ment. The purpose of the present work was to investigate whether proto n magnetic resonance imaging (MRI) might be used to detect necrotic re gions in tumours. MR images and histological sections from individual tumours of three different amelanotic human melanoma xenograft lines ( BEX-t, HUX-t, SAX-t) were analysed in pairs. MRI was performed at 1.5T using two spin-echo pulse sequences, one with a repetition time (TR) of 600 ms and echo times (TEs) of 20, 40, 60 and 80 ms and the other w ith a TR of 2000 ms and TEs of 20, 40, 60 and 80 ms. Spin-lattice rela xation time (T-1), spin-spin relaxation time (T-2) and proton density (N-0) were calculated for each volume element corresponding to a pixel . Synthetic MR images, pure T-1, T-2 and N-0 images and spin-echo imag es with chosen values for TR and TE were generated from these data. T- 1, T-2 and N-0 distributions of tumour subregions, corresponding to ne crotic regions and regions of viable tissue as defined by histological criteria, were also generated. T-1 and T-2 were significantly shorter in the necrotic regions than in the regions of viable tissue in all t umours. These differences were sufficiently large to allow the generat ion of synthetic spin-echo images showing clear contrast between necro sis and viable tissue. Maximum contrast was achieved with TRs within t he range 2800-4000 ms and TEs within the range 160-200 ms. Necrotic ti ssue could also be distinguished from viable tissue in pure T-1 and T- 2 images. Consequently, the possibility exists that MRI might be used for detection of necrotic regions in tumours and hence for prediction of tumour treatment response.