Computed tomography (CT) has established itself as a primary diagnostic imaging modality in cardiac anomalies1. With its fast scanning speed and isotropic spatial resolution at 0.3–0.4 mm, CT allows diagnosis safely and accurately than alternative more invasive or less sensitive imaging techniques. With high quality CT imaging being performed more frequently, patients can benefit from a quicker and more accurate diagnosis and precise anatomic information for planning therapeutic procedures. However, in spite of the tremendous contributions of CT to modern healthcare, some attention must also be given to the very small health risk associated with the ionizing radiation received during a CT exam2.
The radiation dose associated with a typical CT scan (1–14 mSv depending on the exam) is comparable to the annual dose received from natural sources of radiation, such as radon and cosmic radiation (1–10 mSv), depending on where a person lives3. Hence, the health risk to an individual from exposure to radiation from a typical CT scan is comparable to background levels of radiation.
The use of CT in pediatric patients has grown dramatically, reaching at least 4 million examinations in the USA in 2006 4. Minimization of radiation dose associated with pediatric CT examinations is of particular importance because the risk to children due to radiation exposure is two- to three-times greater than the risk to adults10. This is because children’s organs are more sensitive to radiation exposure and they have a much longer life expectancy relative to adults, thereby allowing more time for a potential radiation-induced cancer to develop.
When a CT examination is deemed necessary for a pediatric patient, scanning protocols specifically designed for children must be used. Adapting the dose level to different patient size has become a common practice in the CT community, which is further endorsed by the special requirement on pediatric CT technique in ACR accreditation 13.
There is no question that the benefit of an appropriately indicated CT scan far exceeds the associated estimated risk or that CT providers need to prescribe the minimal amount of radiation required to obtain images adequate for evaluating the patient’s condition2.
Although the radiation dose can be reduced by decreasing the tube current–time product settings, this alteration also reduces the contrast-to-noise ratio (CNR) 5.
The concern about the potential carcinogenic effects of diagnostic levels of radiation has recently been heightened by reports suggesting that some patients may incur substantial cumulative radiation doses due to repeated CT scans, radionuclide testing, and/or fluoroscopy over the course of their lifetimes6. Although the rate of occurrence of cancer induction from diagnostic radiation remains controversial, it is generally accepted that even very low radiation doses have some cancer-inducing potential7.
We conducted a clinical audit at our department, the goal of which was to reduce the radiation dose of CT with minimal or no compromise in image quality. Different cardiac CT techniques were modified and planned protocols were made for pediatric patients. Implementing these techniques is a practical challenge for radiologists and technologists trying to achieve optimal diagnostic image quality8.
Two guiding principles must be followed2, which we implemented in our trial too. First, CT examinations must be appropriately justified for each individual patient 9. The requesting clinicians and radiologists share the major responsibility to direct patients to the most appropriate imaging modality for the required diagnostic task. Second, for each CT examination, all technical aspects of the examination must be optimized, such that the required level of image quality can be obtained while keeping the doses as low as possible.
This article will focus on the second guiding principle and summarize the general technological strategies that we used for radiation dose reduction in cardiac anomaly MDCT. Some perspectives on future CT dose-reduction techniques are presented.