tokens: The perfusion defect produced in 16 open chest dogs was compared with the anatomic area at risk measured by the postmortem dual - perfusion technique and with thallium - 201 single - photon emission tomography ( SPECT ). During a transient ( 20 - s ) coronary occlusion , a perfusion defect was observed with contrast echocardiography in 14 of the 15 dogs in which the occlusion was produced .