tokens: Thallium - 201 SPECT demonstrated a perfusion defect in all 14 dogs analyzed during dipyridamole - induced hyperemia ; the size of the perfusion defect correlated with the anatomic area at risk ( r = 0 . 58 ; p less than 0 . 03 ) and with the perfusion defect by contrast echocardiography ( r = 0 . 58 ; p less than 0 . 03 ) .