A Continuous Glucose Monitor (CGM) offers real-time insight into glucose levels, helping people manage diabetes with greater precision. A Computed Tomography (CT) scan is a non-invasive diagnostic procedure that uses specialized X-ray equipment to create detailed cross-sectional images of the body. Can the skin-worn sensor safely remain in place during the imaging process? This concern is driven by the need to protect the device and the patient while ensuring the CT scan produces clear, diagnostic quality images. This article explores the current guidance and the science behind the compatibility of CGMs and CT scans.
Official Guidance on CGM and CT Scans
Whether a CGM can remain on during a CT scan depends heavily on the specific device model and the manufacturer’s guidance. Major manufacturers like Abbott (FreeStyle Libre system) have updated their instructions. Some FreeStyle Libre sensors are cleared to be worn during CT scans, meaning they are safe for the patient and the device during the procedure.
Other manufacturers, such as Dexcom, generally advise against wearing the sensor directly in the scanned area. The primary concern is not device damage or patient safety, but the potential for the sensor to interfere with image quality. If the sensor is outside the area being scanned (e.g., a sensor on the arm during a head CT), it may be permissible to keep it on. Always consult the specific user guide for your exact CGM model and share this information with the medical imaging team before the procedure.
If a sensor must be removed, it is typically due to the risk of image distortion. The small metallic components within the sensor can cause “artifacts” on the CT image. These artifacts appear as streaks or distortions that can obscure the anatomical region the doctor needs to examine. Therefore, removing a sensor often prioritizes the clarity of the diagnostic image over the convenience of continuous glucose monitoring.
The Science Behind Imaging Compatibility
Computed Tomography scans use X-rays, a form of ionizing radiation, to create cross-sectional images. The mechanism involves a rotating X-ray tube and detectors that measure how much radiation is absorbed by different tissues. Since the CGM sensor and its adhesive patch are not biological tissue, the materials within them absorb or scatter the X-ray beam differently than the surrounding skin and muscle.
This differential absorption causes image artifacts. The density of the sensor’s internal components, which may include small wires and circuit elements, is much higher than soft tissue. When the X-ray beam passes through these materials, it causes scattering and streaking on the image, compromising its diagnostic quality. The risk is minimized when the sensor is positioned far outside the path of the X-ray beam.
This mechanism is fundamentally different from a Magnetic Resonance Imaging (MRI) scan. MRI uses powerful magnetic fields and radio waves, not X-rays, to generate images. The metal components in a CGM sensor can interact dangerously with the strong magnetic field of an MRI, potentially causing the sensor to overheat, burn the skin, or be rapidly displaced. This contrast in physics explains why CT scans are often conditionally permitted for CGMs, while MRIs are almost universally contraindicated, requiring complete removal of the device.
Practical Steps for Scan Day
Preparation for a CT scan begins with communication. Before the scan, proactively inform the radiology technologist that you are wearing a Continuous Glucose Monitor and indicate its precise location on your body. This allows the technologist to review your device’s specific guidelines and plan the imaging sequence to minimize potential interference.
If the sensor is confirmed to be outside the region of interest, it may remain in place, and the technologist can make adjustments to the scan parameters or patient positioning to avoid the sensor. While the sensor is on, be aware that its readings may be temporarily inaccurate during the scan due to potential electromagnetic interference. You should rely on traditional fingerstick testing for any treatment decisions immediately before, during, and shortly after the procedure.
If the sensor falls directly within the scanning field and must be removed, plan for this sensor downtime. Relying on a blood glucose meter for accurate readings is necessary until a new sensor can be applied and properly calibrated. If the premature removal of a sensor is medically mandated, patients should contact their CGM manufacturer; many companies offer a process for requesting a replacement sensor due to medical necessity.