What are the steps to request a computed tomography (CT) scan?

How to Request a CT Scan

To request a CT scan, provide the radiology department with a written or electronic order that includes the patient's diagnosis, specific clinical question to be answered, relevant medical history, and justification for why CT is the appropriate imaging modality. 1

Essential Components of the Request

Your CT scan request must contain sufficient medical information to enable justification of the examination 1:

• Patient diagnosis or clinical presentation (e.g., "neck mass present for 3 weeks," "first-time seizure," "suspected stroke") 1
• Specific clinical question to be answered (e.g., "rule out malignancy," "identify acute intracranial process," "evaluate for stroke") 1
• Relevant medical history including current symptoms, duration of symptoms, and risk factors 1
• Indication for CT over other modalities when applicable 1

Pre-Scan Patient Information to Document

Before requesting the CT, gather and document 1:

• Height and body weight (measured accurately for standardized uptake value calculations if relevant) 1
• Serum glucose level (particularly important for PET/CT) 1
• Renal function (serum creatinine and estimated glomerular filtration rate if IV contrast is planned) 1
• Allergy history, especially to contrast agents 1
• Current medications, particularly antidiabetic drugs, corticosteroids, and any nephrotoxic agents 1
• Pregnancy status in women of childbearing age 1
• Presence of metal implants or devices (relevant if MRI is being considered as alternative) 1

Clinical Scenarios Requiring Specific CT Protocols

For Neck Mass Evaluation

Order neck CT with IV contrast for patients at increased risk for malignancy (mass present ≥2 weeks, smoking/alcohol history, constitutional symptoms, firm/fixed mass >1.5 cm) 2. Specify "neck CT with contrast" rather than non-contrast study, as contrast enhancement is essential for evaluating soft tissue masses and their relationship to vascular structures 2.

For First-Time Seizure

Order emergent non-contrast head CT when acute intracranial process is suspected, particularly in patients with focal neurological deficits, immunocompromised status, or persistent altered mental status 1. The CT should be completed within 25 minutes for patients eligible for thrombolytic therapy 1.

For Stroke Evaluation

Order immediate unenhanced (non-contrast) head CT as the most commonly obtained initial study 1. Pre-notify the CT department that a suspected acute stroke patient is in transport to allow technicians to reserve the scanner for immediate imaging upon arrival 1.

Contrast Considerations

When requesting CT with contrast 1:

• Verify no contrast allergy history - document any previous reactions 1
• Check renal function - particularly important in patients with myeloma-related kidney disease or other renal impairment 1
• Ensure IV access - patient will need needle insertion into vein for contrast administration 1
• Consider volume status - volume depletion may predispose to acute kidney injury in certain patients 1

In most cases, whole-body low-dose CT without contrast can be considered sufficient for anatomical evaluation, but IV contrast should be used when accurate anatomical delineation is needed (e.g., extramedullary disease and relationship to important structures) 1.

Common Pitfalls to Avoid

• Do not delay appropriate imaging by prescribing antibiotics without clear evidence of infection when malignancy is suspected 2
• Do not assume CT is always necessary - consider if required information can be obtained with lower radiation modalities like ultrasound or MRI 3
• Do not order CT for mild head trauma without meeting standardized guideline criteria - this leads to unnecessary radiation exposure 4
• Do not request CT without specifying contrast needs - this often requires repeat scanning and doubles radiation exposure 1

Radiation Exposure Counseling

When ordering CT, be aware that 1, 5:

• A single head/neck CT delivers radiation equivalent to approximately 150 chest X-rays 1
• CT of head and trunk (e.g., polytrauma patient) corresponds to approximately 20 millisievert effective dose, representing an additional lifetime cancer mortality risk of approximately 0.1% 5
• Scan duration is brief (3-5 minutes), causing minimal anxiety even in claustrophobic patients 1

Alternative Imaging Considerations

Before requesting CT, consider whether 1:

• MRI would be more appropriate - superior soft tissue detail, no radiation, but longer scan time (45-60 minutes) and contraindicated with certain metal implants 1
• Ultrasound could answer the clinical question - no radiation, readily available for many soft tissue evaluations 3
• Plain radiography is sufficient - particularly for initial evaluation before proceeding to CT 6