A Computed Tomography (CT) scan is a diagnostic imaging tool that uses X-rays and computer processing to create detailed, cross-sectional images of the body. This technology allows physicians to view bones, soft tissues, and blood vessels with greater clarity than a standard X-ray, helping to diagnose a wide range of conditions, from internal injuries to tumors.
The Sound Level During a CT Scan
The primary concern for many patients is whether the CT machine produces loud or jarring noises. While not quiet, the noise level is generally mild to moderate and not considered disruptive. The sound is a mechanical whirring, buzzing, or steady humming noise originating from the internal gantry, the large ring housing the X-ray tube and detectors.
The X-ray tube and detectors rotate rapidly around the patient to capture multiple images from different angles. This continuous, high-speed motion generates the operational sounds. The noise is intermittent, occurring primarily when the table is moving or the tube is actively spinning to acquire data. The sound level is often comparable to that of a running washing machine, usually falling around 75 decibels.
What to Expect During the Procedure
Upon entering the scanning room, you will be asked to lie on a narrow, motorized table, often on your back. This table then slides into the large, donut-shaped opening of the CT machine. The technologist will be in an adjacent control room but will maintain constant visual and verbal contact with you through an intercom system.
Remaining completely still is necessary to ensure the captured images are clear and sharp, preventing motion blur. The technologist may ask you to briefly hold your breath for a few seconds while the images are being acquired. The actual scanning time is very fast, often taking only a few minutes, though the entire appointment may last longer due to preparation.
Distinguishing CT Noise from MRI Noise
The acoustic experience of a CT scan is fundamentally different from that of a Magnetic Resonance Imaging (MRI) scan, which is often much louder. CT noise is generated by the mechanical rotation of the X-ray source and detectors, resulting in a steady whirring or humming sound.
In contrast, an MRI machine uses powerful magnetic fields and radiofrequency pulses to create images. The loud, repetitive hammering or thumping sounds heard during an MRI are caused by the rapid turning on and off of electrical currents in the gradient coils. Because of this distinct mechanism, MRI noise is significantly more intense and usually requires the use of earplugs or headphones, which are not typically required for a CT scan.
Radiation Exposure and Safety
CT scans utilize ionizing radiation to create internal images of the body. The amount of radiation exposure from a single diagnostic CT scan is low, generally ranging from 1 to 10 millisieverts (mSv), depending on the area being imaged. For context, the average person is exposed to approximately 3 mSv per year from natural background sources.
Modern CT technology and safety protocols are designed to minimize the radiation dose while still ensuring high-quality images for diagnosis. Radiologists and technologists use dose optimization techniques, such as automatic tube current modulation, to deliver the lowest possible dose necessary. The benefits of obtaining an accurate diagnosis from the scan are considered to outweigh the small risks associated with this low level of radiation exposure.