National Physical Therapy Examination (NPTE) Practice Exam

Ultrasound applied at 1 MHz is most effective at heating which type of tissue?

1. Muscle

2. Tendon

3. Blood

4. Fat

The correct answer is: Fat

Ultrasound at a frequency of 1 MHz penetrates tissue to a depth of approximately 5 cm, making it particularly effective for heating deeper tissues. Fat is a less vascularized tissue, meaning it has a relatively lower blood supply, which leads to its increased thermal effects when exposed to ultrasound. This is due to the fact that fat has lower thermal conductivity compared to other tissues, so it can allow for a significant increase in temperature when heated. Moreover, fat can absorb ultrasound energy effectively, leading to localized temperature increases. This heating can be beneficial for therapeutic purposes, including pain reduction and improving tissue extensibility in the case of physical therapy treatments. While other tissues such as muscle or tendon also absorb ultrasound energy, they tend to dissipate heat more efficiently due to their vascular nature, making fat a more efficient target for heating with 1 MHz ultrasound. In summary, the effectiveness of 1 MHz ultrasound in heating fat is largely due to its ability to absorb energy more efficiently in a thermally conductive environment compared to more vascularized tissues, which manage heat dissipation more rapidly.