QUANTITATIVE AND QUALITATIVE HIGH-RESOLUTION PULMONARY VENTILATION-PERFUSION IMAGING USING SIMULTANEOUS ACQUISITION OF KRYPTON AND Tc-MAA IN HEALTHY AND RAO AFFECTED HORSES D J Marlin, R C Schroter1, H A Jones2, J Weekes, J C Clark3, C Deaton, D Kingston, C Roberts and T Donovan3. Centre for Equine Studies, Animal Health Trust, Newmarket, UK; 1Department of Bioengineering and 2National Heart and Lung Institute, Imperial College, London, UK; 3Wolfson Brain Imaging Centre, University of Cambridge Clinical School, UK. Pulmonary scintigraphy has been used in horses to assess the distribution of ventilation (V) and perfusion (Q) and V:Q matching in healthy horses and horses with airway disease. However, as far as we are aware, V using krypton-81m (81Krm) has previously only been reported in healthy horses and simultaneous acquisition of 81Krm and technetium-99m-MAA (99Tcm-MAA) has not been reported in horses. We determined V using 81Krm and Q using 99Tcm-MAA and whole lung V/Q ratios in 8 healthy horses and ponies and 8 horses and ponies with a history and clinical diagnosis of recurrent airway obstruction (RAO), a condition similar to human asthma, whilst in clinical remission (bronchoalveolar lavage neutrophil count <20/l recovered fluid). Following sedation with romifidine, 81Krm 99Tcm-MAA (1 MBq/Kg) was injected via a catheter in the jugular vein. gas was administered in air via a mask and non-rebreathing valve. Once steady state had been reached with 81Krm (20-30 seconds), radioactive counts were acquired as 60 x 2 sec sequential time frames in a 128 x 128 pixel matrix using a low-energy, general-purpose collimator and a 500mm circular field of view GE gamma camera linked to a dedicated nuclear medicine computer system (Nuclear Diagnostics Ltd). When the lung was too large to be imaged in one field of view, 99Tcm-MAA markers were placed on the thorax to allow caudal and cranial images to be obtained. Dorsal views of left and right lungs were also obtained. Mean (±SD) V/Q ratio for the whole left lateral lung field were similar for the 2 groups; 1.01 ± 0.26 for healthy controls and 0.98 ± 0.25 for RAO affected horses in clinical remission (P>0.05). Left lung dorsal images had a wider spread of V/Q ratios than seen in the left lateral images. This appears to be the first report of the range of V/Q ratios in the lungs of healthy horses and horses with RAO in remission. 20.0 20.0 Left Lateral mean ± sem 18.0 16.0 16.0 14.0 14.0 12.0 12.0 normal RAO 10.0 % % Left Dorsal mean ± sem 18.0 8.0 6.0 6.0 4.0 4.0 2.0 2.0 0.0 normal 10.0 8.0 RAO 0.0 0.0 0.5 1.0 1.5 V/Q Ratio 2.0 2.5 3.0 0.0 0.5 1.0 1.5 V/Q Ratio 2.0 2.5 3.0