Why do mri machines make noise

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 8, 2026

Quick Answer: MRI machines make loud knocking and buzzing noises primarily due to the rapid switching of gradient coils during imaging. These coils create magnetic field gradients that help spatially encode the body's tissues, and when electrical currents pulse through them at frequencies up to 1-3 kHz, they vibrate against their mountings. The noise levels can reach 65-95 decibels, comparable to a lawnmower or heavy traffic, which is why patients wear ear protection. This acoustic phenomenon is an inherent byproduct of the physics behind MRI's ability to produce detailed anatomical images without ionizing radiation.

Key Facts

MRI noise levels typically range from 65-95 decibels during scanning
Gradient coils switch electrical currents at frequencies of 1-3 kHz during imaging
The first clinical MRI scan on a human patient was performed on July 3, 1977
Modern MRI machines can generate magnetic fields up to 3.0 Tesla for clinical use
Approximately 40 million MRI scans are performed annually worldwide

Overview

Magnetic Resonance Imaging (MRI) machines produce distinctive loud noises during operation, a characteristic that has been present since the technology's development in the 1970s. The first full-body MRI scanner was built by Raymond Damadian's team in 1977, with the first human scan performed on July 3, 1977. These machines work by using powerful magnets, typically 1.5-3.0 Tesla for clinical systems (about 30,000-60,000 times stronger than Earth's magnetic field), to align hydrogen protons in the body. When radiofrequency pulses are applied, these protons emit signals that are detected and converted into detailed anatomical images. The noise generation is not a malfunction but rather an inherent physical consequence of how MRI technology functions, particularly related to the gradient subsystem that provides spatial information for image reconstruction.

How It Works

The primary source of MRI noise comes from the gradient coils, which are sets of wire loops positioned inside the main magnet bore. During imaging sequences, these coils carry rapidly switching electrical currents (typically pulsing at 1-3 kHz) to create temporary magnetic field gradients that vary linearly across the imaging volume. This gradient switching allows spatial encoding of the MRI signal by altering the resonance frequency of protons based on their position. When the currents change direction, the coils experience Lorentz forces that cause them to vibrate against their mountings and housing. Additionally, the changing magnetic fields induce eddy currents in nearby conductive structures, creating further mechanical vibrations. The specific noise patterns (knocking, buzzing, or chirping sounds) correspond to different pulse sequences like spin echo or gradient echo, with faster sequences producing higher frequency noise.

Why It Matters

Understanding MRI noise is important for both patient comfort and diagnostic quality. The loud sounds (65-95 dB) can cause anxiety, discomfort, and temporary hearing threshold shifts if ear protection isn't used. Manufacturers have developed quieter technologies like 'Silent Scan' systems that reduce noise by 90% through optimized gradient designs and acoustic damping materials. Beyond patient experience, noise management affects image quality since vibrations can cause artifacts. MRI's ability to produce detailed soft tissue images without ionizing radiation makes it invaluable for diagnosing conditions from brain tumors to ligament tears, with approximately 40 million scans performed globally each year. The characteristic noise serves as an audible reminder of the complex physics enabling this non-invasive diagnostic tool.