From the Guidelines
The radiation dose from a contrast CT scan typically ranges from 5 to 20 mGy (milligray), though this can vary based on several factors. The specific dose depends on the body part being scanned, with chest CTs generally delivering 5-7 mGy, abdominal CTs around 10-15 mGy, and head CTs approximately 50-60 mGy 1. The addition of contrast material itself doesn't increase radiation exposure, as the contrast only helps improve image quality by enhancing visibility of certain structures. Factors affecting the dose include:
- The patient's size (larger patients require more radiation for adequate image quality) 1
- The scanner technology (newer machines often use dose reduction techniques) 1
- The specific protocol used by the radiologist, including variables such as scan length, x-ray beam intensity, tube potential, tube current, rotation time, and x-ray beam filtration 1 Medical facilities aim to use the ALARA principle (As Low As Reasonably Achievable) to minimize radiation exposure while still obtaining diagnostically useful images. For context, natural background radiation exposure is about 3 mGy per year, making CT scans a significant but generally justified radiation source when medically necessary. It's worth noting that while older studies like 1 discussed the concerns and knowledge gaps regarding radiation exposure from CT scans, more recent studies like 1 provide updated guidance on optimizing radiation dose and safety in cardiovascular imaging.
From the Research
Radiation Dose in Contrast Computed Tomography (CT) Scan
- The mean radiation doses for a contrast CT scan were found to be 5.2 ± 1.7 mGy for the standard protocol, 7.1 ± 2.0 mGy for the CM dose-saving protocol, and 3.8 ± 0.4 mGy for the radiation dose-saving protocol 2.
- A study on pediatric abdomens using a low-concentration iodinated contrast agent and low tube voltage combined with 70% ASIR algorithm reported a CT dose index (CTDIvol) of 1.44 mGy for Group A and 2.08 mGy for Group B 3.
- Another study on patient radiation doses from adult and pediatric CT reported organ absorbed doses in head CT scans increasing from approximately 30 mGy in newborns to approximately 40 mGy in adults, and body organ absorbed doses of approximately 7 mGy for patients weighing less than 20 kg 4.
- A feasibility study on iterative reconstruction technique for reducing body radiation dose at CT reported CT dose index reductions of 32-65% compared to routine imaging 5.
- A study on assessment of patient exposure to X-radiation from SPECT/CT scanners reported radiation exposure doses of each organ under various CT conditions, with brain radiation exposure doses ranging from 1.39 mGy to 65.07 mGy 6.