ARDMS Ultrasound Physics & Instrumentation Practice Exam

In ultrasound physics, density is typically measured in what units?

1. Grams per cubic meter

2. Pascals per liter

3. Kilograms per centimeter cubed

4. Milliliters per gram

The correct answer is: Kilograms per centimeter cubed

Density in ultrasound physics is an important property that describes the mass of a substance per unit volume, allowing understanding of how sound waves propagate through different media. The standard unit of density is kilograms per cubic meter (kg/m³) in the International System of Units (SI), but it's often expressed in grams per cubic centimeter (g/cm³) in many scientific and medical contexts. The correct answer, which refers to kilograms per centimeter cubed, effectively conveys density in a commonly used metric that directly relates to ultrasound studies. One cubic centimeter (cm³) is equal to one milliliter (mL), and thus this unit of measurement is compatible with biological substances that are often measured in grams or milliliters. This choice aligns with the broader understanding that in medical ultrasound, knowing the density of various tissues can affect how sound waves interact with that medium, influencing both imaging and diagnostic capabilities. Understanding density is critical, as tissues with different densities will have different acoustic impedances, impacting the quality of ultrasound images and the behavior of ultrasound waves. In comparison, other options do not accurately reflect standard density measurements used in this context. Grams per cubic meter is less commonly used in practical applications in physiology or medical imaging, Pascals per liter pertains more