Each prefix scales a base unit by a power of 10. Click any row to see its origin and story.
Think of the prefixes as steps. Each step up multiplies by 10. Each step down divides by 10.
A shorthand for very large or small numbers. Write a number between 1 and 10, then multiply by a power of 10.
The decimal moved 3 places left, so the exponent is positive 3.
The decimal moved 2 places right, so the exponent is negative 2.
Positive exponent = big number (decimal moved left).
Negative exponent = small number (decimal moved right).
Four prefixes you will use constantly in sonography physics. These appear in every chapter going forward.
Ultrasound lives in the Megahertz range. A 12 MHz transducer reveals exquisite surface detail. A 2 MHz transducer reaches deep into the body. The tradeoff between resolution and penetration is the central tension of your craft.
Axial resolution is measured in fractions of a millimeter. It determines whether your image shows two structures or smears them into one. At the milli scale, the difference between seeing and missing is everything.
The kilohertz range is the rhythm of motion. Doppler shift and Pulse Repetition Frequency live here. When you track a thousand pulses per second to watch blood move through a vessel, you are counting at the kilo scale.
The microsecond is the period: the duration of one wave cycle. A 1 MHz wave lasts 1 microsecond. A 5 MHz wave lasts 0.2 microseconds. This reciprocal relationship between Mega and Micro is the single most important formula on the SPI exam.
Ultrasound physics involves numbers ranging from billionths to millions. Without metric prefixes and scientific notation, these would be impossible to work with. You will see these prefixes in every chapter going forward.
Test your understanding of metric prefixes.