When is contrast indicated in medical imaging?

From the Guidelines

Contrast is indicated in medical imaging when enhanced visualization of specific anatomical structures, tissues, or pathological processes is needed for accurate diagnosis, as seen in the use of IV contrast in imaging of malignant pleural mesothelioma to obtain the most accurate imaging of tumor extent 1. When considering the use of contrast in medical imaging, it is essential to weigh the diagnostic benefits against potential risks, particularly in patients with renal impairment, previous contrast reactions, or certain medical conditions like severe asthma or multiple myeloma. Some key points to consider when deciding to use contrast include:

• The type of imaging modality being used, such as CT scans, MRI, or gastrointestinal studies
• The specific anatomical structures or pathological processes being evaluated, such as tumor detection and characterization, vascular imaging, or assessment of organ perfusion
• The potential benefits of contrast use, including improved diagnostic accuracy and enhanced visualization of specific tissues or structures
• The potential risks of contrast use, including allergic reactions, renal impairment, and other adverse effects. In general, contrast is particularly valuable when examining the brain, heart, liver, kidneys, and blood vessels, as seen in the guidelines for imaging of acute abdominal pain in adults 1 and the evaluation of left lower-quadrant pain in older patients with suspected diverticulitis 1. However, the decision to use contrast should be made on a case-by-case basis, taking into account the individual patient's medical history, current condition, and the specific clinical question being addressed, as noted in the guidelines for the surgical management of stones 1 and the evaluation of back pain in children 1. Ultimately, the goal of using contrast in medical imaging is to obtain the most clinically useful information to guide patient management, while minimizing the risks associated with contrast use, as seen in the guidelines for postmenopausal subacute or chronic pelvic pain 1.

From the FDA Drug Label

Because unenhanced scanning may provide adequate diagnostic information in the individual patient, the decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological, and unenhanced CT findings.

The decision to ask for contrast in imaging is based on a careful evaluation of clinical, other radiological, and unenhanced CT findings. Contrast enhancement may be indicated when:

• Unenhanced scanning does not provide adequate diagnostic information
• Clinical and radiological findings suggest the need for contrast to improve diagnostic assessment
• The potential benefits of contrast enhancement outweigh the associated risks and increased radiation exposure 2.

Key considerations for contrast enhancement include:

• Tumor and lesion detection and characterization
• Vascularized vs. non-vascularized lesions
• Dynamic computed tomographic imaging to improve enhancement and diagnostic assessment
• Patient factors, such as renal impairment, that may affect contrast excretion and increase the risk of adverse effects 2.

From the Research

Indications for Contrast in Medical Imaging

• Contrast agents are essential for providing diagnostic information in various medical imaging modalities, including multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) 3.
• They are particularly useful in vascular, inflammatory, or oncologic diseases, where they can help provide essential diagnostic information that would otherwise be unavailable 3.
• Contrast agents are also used in diagnostic angiography and vascular interventions, where they can help visualize blood vessels and guide procedures 4.

Patient Selection and Risk-Benefit Analysis

• The use of contrast agents requires a careful risk-benefit analysis, particularly in patients with reduced renal function, pregnancy, lactation, or pediatric population 3, 5, 6.
• Patients with renal disease or contrast allergy may require alternative contrast media, such as carbon dioxide, gadolinium, or dilute iodinated contrast media 4, 7.
• A careful evaluation of the patient's medical history, renal function, and potential allergies is necessary to determine the safest and most effective contrast agent to use 3, 5.

Safety Considerations and Alternative Contrast Media

• Iodinated and gadolinium-based contrast media can cause adverse reactions, including allergic reactions, nephrogenic systemic fibrosis, and contrast-induced nephropathy 3, 5, 6.
• Alternative contrast media, such as gadolinium, may be used in patients with iodine allergy or renal insufficiency 7.
• The use of low kV and DE-scan protocols with MDCT can help reduce the amount of iodinated contrast agents used, while macrocyclic contrast agents are recommended for enhanced MRI exams 3.