Prediction of ICG blood clearance from 99mTc-mebrofenine scintigraphy in normal volunteers and in patients

Saelens, C Walrand, Stephan [UCL] Pauwels, Stanislas [UCL] Lhommel, Renaud [UCL]

Aim: ICG blood clearance is increasingly used to assess the liver function in vue of therapeutic hepatic lobectomy. Our aim is to evaluate whether ICG blood clearance can be predicted using the less invasive 99mTc-mebrofenine scintigraphy technique that can visualize other additional informations. Method: ten normal volunteers (38±11y, 6 females) and ten patients (62±11y, 4 females,4 cholangiocarcinoma, 1 hepatocarcinoma, 5 CRC metastasizes) were injected with 85 MBq of 99mTC-mebrofenine. A dynamic acquisition of 1 hour (successively sixty 10 sec and fifty 1 min frames) in anterior-posterior direction was performed with blood samples took 150, 250, 350, 600 and 900 sec post-injection. Three ROIs were drawn: on the heart, on the bowels+macroscopic intra liver biliary ducts and on the remainder of the liver. The 99mTC-mebrofenine blood clearance was assessed assuming a two way blood-liver compartmental model by fitting the parameters of the corresponding equations to the ROIs counts on all the frames acquired after 3 min post-injection. The blood clearance was also assessed by fitting the 99mTC-mebrofenine in the blood samples by a mono-exponential function and by using the Ekman’s method on the scintigraphy. ICG clearance was assessed using the 3 time-points standard method from blood samples took one hour before the scintigraphy for the volunteers, and within 3 days before, up to 5 days after the scintigraphy for the patients. Results: Both, mono-exponential blood fit and the Ekman method provided a low correlation versus the ICG blood clearance: (y=-0.02+1.05xICG [min-1] R2=0.57) and (y=0.08+0.44xICG [min-1] R2=0.44), respectively. Correlation between clearances estimated from mono-exponential fit of the blood samples between 2-4 and 4-6 min gave a fit slope of 0.35, showing that 99mTC-mebrofenine was not cleared following a mono-exponential. The compartmental model provided a good correlation with the ICG blood clearance for the volunteers (y=-0.02+0.85xICG [min-1] R2=0.87). The correlation was lower for the patients (y=0.03+0.77xICG [min-1] R2=0.64). Conclusion: ICG blood clearance can be predicted from 99mTC-mebrofenine scintigraphy using an appropriate compartmental model that doesn’t made the assumption that the compartments follow mono or multi-exponential functions. The slope of the linear regression was close to 1 with a small offset origin. The lower correlation obtained for the patients could be due to the delay between the ICG assessment and the scintigraphy.