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1H magnetic resonance of human tumours. Analysis of the transverse relaxation of the methylene protons using continuous distributions of relaxation times

In tumours, the decay of 1H transverse magnetization (relaxation profile) of the methylene resonances is usually not a single exponential. The conventional sum‐of‐exponentials approximation often leads to several solutions which fit the experimental data; choosing one solution over another is highly subjective. We have therefore analyzed transverse relaxation data for the methylene resonance of lipids in human tumours, assuming a continuous distribution of relaxation times. We have studied 89 colon tumours (27 with metastasis), 12 ‘normal’ colon tissues, 40 breast tumours (24 with metastasis) and 13 malignant lymph nodes. All were primary tumours and the patients had received no previous treatment. Two continuous distribution approximations were tested. The two‐parameter lognormal distribution provides a simple representation of the relaxation profile. The constrained regularization method (Contin) complements and extends the lognormal approach. The average T2 values, 〈T2〉, whether derived from the lognormal or the Contin approximations, are consistent and comparable. Tumour and ‘normal’ colon tissue taken from the same patient show important differences in relaxation behaviour. A considerable broadening of the lognormal distribution, with 〈T2〉 shifted to shorter values, is observed for the colon tumours. This is verified by the constrained regularization method. The ‘normal’ colon tissues are usually characterized by a single, relatively narrow distribution, while tumours show one or more broad peaks. A substantial broadening of the distribution of relaxation times is observed in colon tumours, whether metastasized or not. A similar broadening is noted for breast tumours and malignant lymph nodes, although the range is slightly less than for colon tumours. The distribution of the transverse relaxation times reflects the biological (and chemical) heterogeneities of cancer cells and disorder in the tumour tissue. This approach to a more precise representation of the relaxation profile should allow better design of experimental conditions for the optimal visualization of tumours by 1H MRI.