**Question:** LASER that can be used in the treatment of ureteric calculi

**Core Concept:** Lasers are devices that emit monochromatic, collimated, and directional light beams with specific wavelengths, which can be utilized for various medical applications, including lithotripsy (breaking up kidney stones) due to their ability to produce high-intensity focused energy, causing localized thermal damage to the stone, reducing its size and facilitating its passage or removal.

**Why the Correct Answer is Right:** The correct answer is **Nd:YAG laser (Neodymium-doped Yttrium Aluminum Garnet laser)** (Option D). Nd:YAG laser is chosen for ureteric calculi treatment due to several reasons:

1. **Wavelength:** Nd:YAG laser has a wavelength of 1064 nm, which is well-absorbed by water and can penetrate tissues effectively, providing deep penetration and high energy delivery, essential for breaking up kidney stones.
2. **Flexible ureteroscope usage:** Nd:YAG laser can be used with flexible ureteroscopes, which can navigate through the ureter and reach the kidney stone, making the treatment more precise and minimally invasive.
3. **Lithotripsy efficiency:** The high energy output of Nd:YAG laser (up to 100 W) allows for effective stone fragmentation into smaller pieces that can be easily passed or retrieved.

**Why Each Wrong Option is Incorrect:**

A. CO2 laser (Carbon Dioxide laser): Although CO2 lasers are commonly used in lithotripsy, they have a wavelength of 10,600 nm, which is less effective in penetrating tissues and is not as suitable for ureteric calculi treatment.
B. Holmium laser (Ho:YAG laser): While Holmium laser is a popular choice for stone treatment, the wavelength of 2,100 nm is less effective in penetrating tissues, particularly for ureteric calculi, which are often located deeper in the urinary tract.
C. Ruby laser: Ruby laser (694 nm) has a shorter wavelength, making it less effective in penetrating tissues and less suitable for treating ureteric calculi.
D. Nd:YAG laser: As explained above, Nd:YAG laser is the correct choice due to its superior wavelength, energy output, and flexibility in using flexible ureteroscopes.

**Clinical Pearl:**

The choice of laser for ureteric calculi treatment depends on the stone size, location, and the patient's anatomy. In general, lasers with longer wavelengths (e.g., Nd:YAG and Holmium:YAG) are preferred for ureteric calculi treatment due to their better tissue penetration and ability to use flexible ureteroscopes.