Arteriovenous shunting of microspheres in patients with colorectal liver metastases: errors in assessment due to free pertechnetate, and the effect of angiotensin II.

In patients receiving locoregional therapy for liver metastases degradable microspheres are being increasingly used in an attempt to improve cytotoxic delivery to the tumour. However, counterproductive arteriovenous shunting through the liver following intrahepatic arterial injection can occur, leading to deposition in the lung. Measurement of the degree of shunting is important in the monitoring of this kind of therapy. In this study we describe the use of technetium-labelled microspheres of serum albumin (99Tcm MSA) to measure baseline shunting during hepatic arterial perfusion scintigraphy in five patients with liver metastases of colorectal origin, and assess the significance of the values obtained for relative lung uptake (RLU) which we define as: RLU = Activity in lung field/Activity in liver + lung fields X 100%. We found that shunting was less than 5% in all cases, zero shunting occurring in 14 of the 16 patients studied. The sources of error in this technique have been assessed, the most important being the presence of free pertechnetate in the injectate. The use of Boots 10 ml vials and glass syringes respectively to dispense and administer this radiopharmaceutical reduces this error to a small predictable level. In our small group of patients, we found no evidence to suggest that use of the vasoactive agent angiotensin II significantly increases baseline shunting in patients with colorectal liver tumour.