**Core Concept:** Ultrasound (USG) is an imaging modality that uses high-frequency sound waves to produce images of internal organs and tissues in the human body. The frequency of the sound waves determines the depth penetration and resolution of the image.

**Why the Correct Answer is Right:** The correct answer is **D**. Ultrasound machines operate at specific frequencies, and the choice D represents the correct frequency range used in most ultrasound machines: between 1 and 15 MHz. These high frequencies allow for excellent image resolution (detail) and depth penetration.

**Why Each Wrong Option is Incorrect:**

A. **1 MHz:** This low frequency is insufficient for producing detailed images, as it lacks the necessary depth penetration.
B. **100-200 kHz:** These frequencies are too low for accurate imaging and provide limited penetration.
C. **1000 kHz:** Although higher than option B, this frequency is still too low for accurate imaging.

**Clinical Pearl / High-Yield Fact:** High-frequency ultrasound (>10 MHz) is typically used for superficial structures (e.g., skin, soft tissues), while lower frequencies (1-10 MHz) are used for imaging deeper structures (e.g., organs, bones). This helps optimize image quality and penetration, ensuring accurate diagnosis and treatment planning.

---

**Question:** Frequency of sound waves used in Ultrasound (USG)

A. Low frequency (1 MHz)
B. High frequency (1000 kHz)
C. Medium frequency (10 MHz)
D. High frequency (1-15 MHz)

**Correct Answer:** D. High frequency (1-15 MHz)

---

**Core Concept:** Ultrasound (USG) is a diagnostic imaging technique that uses high-frequency sound waves to create images of internal structures and organs. The frequency of the sound waves used in USG determines the image resolution and penetration depth.

**Why the Correct Answer is Right:** High-frequency sound waves (1-15 MHz) are used in USG because they provide better image resolution and penetration depth. These frequencies allow for accurate visualization of deep structures and organs, which is essential for precise diagnosis and treatment planning.

**Why Each Wrong Option is Incorrect:**

A. Low frequency (1 MHz) is too low to provide adequate image resolution and penetration depth for deep structures and organs.
B. High frequency (1000 kHz) is still too low for reliable imaging of deep structures and organs.
C. Medium frequency (10 MHz) is acceptable for superficial structures but is inadequate for imaging deeper structures due to limited penetration depth.

**Clinical Pearl / High-Yield Fact:** High-frequency ultrasound machines are used for imaging deeper structures, while low-frequency ultrasound machines are used for superficial structures and dermatology applications. When choosing the appropriate ultrasound machine and probe frequency, consider the depth of the structures you wish to image and the desired image resolution.