Lange Mammography Practice Exam

MRI images rely on hydrogen nuclei responding to a magnetic field. A strong external magnetic field aligns the protons in the breast. A radiofrequency pulse then perturbs this alignment. As the protons return to equilibrium, they emit signals that the scanner detects and converts into images. The magnet provides the steady field that makes the protons align, and the radio waves (the RF pulses and the emitted signals) provide the excitation and readout needed to form the image. This gives detailed soft-tissue contrast without ionizing radiation. Other imaging modalities use different physics—X-rays or gamma rays, ultrasound with sound waves, or light with photons—so they don't rely on magnets and radio waves like MRI.