QUANTITATIVE SINGLE-PHOTON EMISSION TOMOGRAPHY FOR TUMOR BLOOD-FLOW MEASUREMENT IN BRONCHIAL-CARCINOMA

A single-photon emission tomography (SPET) technique for the absolute measurement of tumour perfusion is described. Phantom studies have sho wn that source-background ratios are dependent upon source size and ra dial position within the phantom. A means of correcting source-backgro und count ratios for these variables has been developed and used to co rrect tumour-lung ratios obtained in 28 patients with bronchial carcin omas who underwent technetium-99m hexamethylpropylene amine oxime (Tc- 99m-HMPAO) SPET. On SPET images, the normal lung appears as a relative ly homogeneous background. The relationship between Tc-99m background concentration (kBq/ml) and counts/pixel was determined from phantom st udies and the tumour Tc-99m concentration from the background Tc-99m c oncentration and corrected tumour-lung ratio. The total activity of th e lipophilic Tc-99m-HMPAO species injected was measured. The activity reaching the systemic circulation (A(sys)) was obtained by subtracting the activity trapped in the pulmonary circulation (obtained from back ground Tc-99m concentration and lung volume). Tumour blood flow may th en be calculated from fraction of A(sys) contained in the tumour provi ded cardiac output and extraction fraction are known. Blood flow throu gh the central region of tumours ranged from zero to 59.0 (mean 14.1) ml min-1 100 g-1 and through the whole tumour from 0.6 to 68.0 (mean 2 0.6) ml min-1 100 g-1.