When talking about ultrasound what is the difference between 50% and 100% duty cycle? I know 20% is used with more acute injuries because it doesn’t have a thermal effect but between 50 and 100 is there really a difference when given the choice? Is one just more thermal?

The higher the percentage of the US (Ultrasound) duty cycle, the more continuous the delivery of US waves and the more thermal the effects of the treatment. Lower duty cycle percentages often indicate pulsed treatments or ‘on-off’ deliveries. Therefore, you are right, 100% duty cycle is more ‘thermal’ than 50% duty cycle and may be preferred in the treatment of chronic conditions. The use of 100% duty cycle in acute conditions is discouraged as it may worsen the early inflammatory reactions of most acute injuries due to its unwelcome thermal effects.