Thus, with adenosine-induced hyperemic flow, both 201Tl and sestamibi significantly underestimated the magnitude of the flow disparity between stenotic and normal perfusion beds. The degree of underestimation was greater for sestamibi. The clinical implication of these experimental findings for vasodilator perfusion imaging remains to be determined, since factors such as greater redistribution and scatter with 201Tl could offset its advantages.

Risk of injury in cold environments is related to a combination of athlete preparedness, preexisting medical conditions, and the body's physiologic response to environmental factors, including ambient temperature, windchill, and wetness. The goal of this section is to decrease the risk of hypothermia, frostbite, and nonfreezing cold injuries as well as to prevent worsening of preexisting conditions in cold environments using a preparticipation screening history, examination, and counseling. Cold weather exercise can be done safely with education, proper preparation, and appropriate response to changing weather conditions.

Although 99mTc-sestamibi and 201Tl defect magnitudes and regional activities were comparable in dogs with sustained low coronary flows and superimposed subendocardial infarctions and in dogs with large infarctions, approximately 5% more 201Tl than 99mTc-sestamibi uptake was observed in dogs with chronic low flow and severe systolic dysfunction. Substantial 99mTc-sestamibi uptake in asynergic zones was observed in this low-flow model, with some slight resting 99mTc-sestamibi redistribution observed on serial images. Systolic thickening was negligibly enhanced during dobutamine infusion in dogs with sustained low flow, whereas 201Tl uptake was only mildly reduced.

These experimental data suggest that Sestamibi uptake and retention are dependent on myocardial viability as well as regional flow. If Sestamibi is administered early after reperfusion and imaging is performed soon afterward, the degree of myocardial salvage could be significantly overestimated.

Risk of injury in cold environments is related to a combination of athlete preparedness, preexisting medical conditions, and the body's physiologic response to environmental factors, including ambient temperature, windchill, and wetness. The goal of this section is to decrease the risk of hypothermia, frostbite, and nonfreezing cold injuries as well as to prevent worsening of preexisting conditions in cold environments using a preparticipation screening history, examination, and counseling. Cold weather exercise can be done safely with education, proper preparation, and appropriate response to changing weather conditions.