There is currently a pandemic-related shortage of iodinated contrast used for CT scans, predicted to last for several months. While the industry is addressing its own lessons on the supply side of production and distribution, those of us in clinical medicine may use this shortage as an educational opportunity to address contrast demand.
There are multiple ways to perform a CT scan of the same body part, depending on the patient’s condition, the clinical questions, and desired information. It is generally up to the ordering provider to state relevant history and select the requested study technique, including its inclusion of contrast. Radiologists and technologists sometimes see CT study requests with intravenous contrast that may be unnecessary, even detrimental to the goals of the study. Other times a CT scan may not be the best imaging modality if imaging is needed.
Intravenous contrast is a great tool to better assess blood vessels and organ perfusion, but not every clinical question requires a contrast injection to answer. Contrast also adds expense and time to a study, plus a small risk of allergic-like reaction or renal insult, so contrast usage is best when likely to add genuine benefit.
The partial list below has been compiled with input from several colleagues in a large practice, where members specialize in various imaging areas. This list cannot serve as an absolute, as every patient is unique, and not everyone has equal access to alternative imaging modalities like MRI, ultrasound, or nuclear medicine. Nevertheless, these categorized guidelines are offered as suggestions to avoid requesting unnecessary CT contrast in this time of particular scarcity.
CT to evaluate for osteomyelitis or bone tumor is preferably without contrast.
CT for the presence of hematoma does not require contrast unless to assess for active bleeding.
For patients with extremity cellulitis, MRI is preferred to CT to assess for abscess.
CT angiogram is a great tool to assess cerebral perfusion with symptoms of an acute stroke. However, when symptoms are less compelling, e.g., headache or dizziness for days to weeks without more ominous stroke symptoms, neuroradiology colleagues recommend a non-contrast head CT to exclude hemorrhage, followed by a brain MRI.
Initial CT of a sizable, suspicious lung mass is best with IV contrast to help delineate blood vessels and lymph nodes for staging. If this is the clinical scenario, add the abdominal CT at the same time as the chest CT, to get all staging information with one contrast dose.
However, follow-up of previously detected small lung nodules to assess for growth does not require contrast. Nodule visibility on lung windows is essentially identical without an injection.
Before ordering a CT angiogram to assess for pulmonary embolism, consider a d-dimer test. No blood test is perfect, but a normal d-dimer usually means no clot.
Measuring the outer diameter of an aortic aneurysm, whether thoracic or abdominal, does not require contrast. Assessing the arterial lumen does.
Retroperitoneal hematoma is generally visible without contrast, although IV contrast is required to assess for active bleeding.
Inflammatory conditions like appendicitis and diverticulitis may be more visible with contrast but can sometimes be detectable without. It depends on a patient’s anatomy, including appendiceal location, body fat content, and the degree of inflammation. While morbid obesity limits detail on almost any imaging study, a little extra adipose may sometimes separate structures and delineate, e.g., an appendix on CT more clearly.
The older the patient, the less the concern from the low-dose radiation of a diagnostic CT. For some patients, you may consider non-contrast abdominal pelvic imaging as an initial step during this contrast shortage and inject afterward only if needed.
Ultrasound can be more successful in detecting the appendix in children than adults—not because the patients are young, but because most are small. If the ultrasound is not diagnostic and where MRI is available, some facilities encourage MRI as an alternative to CT for appendicitis evaluation, at least in children who do not require sedation, as MRI emits no ionizing radiation.
The American College of Radiology provides excellent resources online, including its guidelines on the appropriateness criteria to help providers determine which study may be best to order under normal circumstances.
In this abnormal time of iodinated CT contrast shortage, adjustments must be made, including ordering non-contrast CT vs. ultrasound, MRI, nuclear medicine, or other studies when useful. If contrast CT is by far the ideal study, yet the situation is not urgent, then it may be advised to wait and perform the CT when contrast becomes more available. One excellent recent article in Radiology offers some useful suggestions.
Most importantly, please consult with the radiologists and technologists in your community as needed, as we work together to provide imaging as a component of patient care. Non-contrast studies, or modalities other than CT, may be beneficial or even preferred alternatives when imaging is required.
Cullen Ruff is a radiologist and author of Looking Within: Understanding Ourselves through Human Imaging.
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