What is the indication for a Computed Tomography (CT) scan of the head and chest with or without contrast?

From the Guidelines

CT scans of the head and chest should be performed with or without contrast depending on the clinical indication, with the most recent evidence from 2023 suggesting that contrast is valuable for evaluating tumors, infections, vascular abnormalities, or inflammatory processes, while non-contrast scans are preferred for initial evaluation of stroke, trauma, or hemorrhage 1. When evaluating the need for contrast in CT scans of the head and chest, several factors must be considered, including the clinical question being addressed, the patient's kidney function, and any history of contrast reactions or iodine allergies.

• For head CT, contrast is typically used when evaluating for tumors, infections, vascular abnormalities, or inflammatory processes, while non-contrast scans are preferred for initial evaluation of stroke, trauma, or hemorrhage.
• For chest CT, contrast helps visualize blood vessels, lymph nodes, and differentiate masses, making it valuable for suspected pulmonary embolism, aortic pathology, or cancer staging.
• Non-contrast chest CT is appropriate for lung nodules, emphysema assessment, or when contrast is contraindicated. The contrast agent used is typically iodine-based, administered intravenously at a dose determined by the patient's weight (usually 1-2 mL/kg) 1.
• Patients should be screened for kidney function before receiving contrast, as those with renal impairment (eGFR <30 mL/min/1.73m²) have increased risk of contrast-induced nephropathy.
• Patients should also be asked about previous contrast reactions and iodine allergies.
• Adequate hydration before and after contrast administration helps protect kidney function. The specific protocol should be determined by the referring physician in consultation with the radiologist based on the clinical question being addressed, with consideration of the most recent evidence from 2023 1.
• A heavy smoking history may also be a separate indication for CT chest imaging at initial staging or surveillance because tobacco use is a risk factor not only for squamous cell carcinoma of the head and neck but also for primary lung cancer.
• The use of IV contrast may improve detection of mediastinal and hilar adenopathy, distinguishing nodes from mediastinal vessels and aiding in delineation of the soft tissue extension of skeletal metastatic disease.

From the FDA Drug Label

2.5 Instructions for Use with an Automated Contrast Injection System or Contrast Management System for CT of the Head and Body

The iodixanol (IV) drug label does not explicitly state whether a CT of the head and chest should be performed with or without contrast. However, it provides instructions for use with an automated contrast injection system for CT of the head and body, implying that contrast may be used in these procedures.

• The label does not provide a direct answer to the question of whether contrast should be used.
• No conclusion can be drawn regarding the use of contrast for a CT of the head and chest based on the provided information 2.

From the Research

CT of Head and Chest with or without Contrast

• The decision to use contrast agents in CT scans of the head and chest depends on various factors, including the type of contrast agent, its risks, contraindications, and the suspected diagnosis 3.
• Possible contraindications for using intravenous contrast agents during CT scans include a history of reactions to contrast agents, pregnancy, radioactive iodine treatment for thyroid disease, metformin use, and chronic or acutely worsening renal disease 3.
• The American College of Radiology Appropriateness Criteria is a useful online resource for determining the most appropriate study at the lowest cost and risk to the patient 3.

Contrast Agents

• Iodixanol is an iso-osmolar contrast agent that has been shown to be less nephrotoxic than iohexol in patients with renal insufficiency 4, 5.
• A study comparing iodixanol and iohexol in patients with normal baseline renal function found that the risk of contrast-induced nephropathy was significantly higher in patients with underlying renal insufficiency receiving iodixanol, but this should not serve as an absolute contraindication for these patients to receive intravenous iodinated contrast for diagnostic CT examinations 4.
• Another study found that iodixanol provides image quality comparable to that of iohexol, with a lower incidence of adverse events 6.

Vascular Imaging

• A study comparing iodixanol and iohexol for vascular imaging on computed tomography found that the vascular attenuation provided by a 9.3% lower iodine concentration of iso-osmolar iodixanol is equal to that given by hyperosmolar iohexol 7.
• The enhancement across the cross section of the vessel is also similar for both contrast agents, suggesting that vascular studies with iodixanol and iohexol are of equal quality even when a lower dose of iodine is given with iodixanol 7.