What type of computed tomography (CT) scan should be done?

CT Imaging Recommendations

For most clinical scenarios requiring CT evaluation, contrast-enhanced multiphase CT is the appropriate study, as non-contrast CT has limited diagnostic utility and exposes patients to unnecessary radiation without providing adequate diagnostic information. 1, 2, 3

General Principles for CT Selection

Contrast-Enhanced CT is Standard

• Multiphase contrast-enhanced CT should be performed as the primary study for most abdominal, pelvic, and thoracic imaging indications 1
• Non-contrast CT followed by contrast-enhanced CT doubles radiation exposure and should be avoided unless specifically indicated 2, 3
• In children especially, performing non-contrast CT before contrast-enhanced CT for suspected mass lesions is inappropriate and exposes them to unnecessary radiation 3

Specific Contrast Protocols by Clinical Scenario

For liver lesion characterization:

• Triple-phase contrast-enhanced CT (arterial, portal venous, and delayed phases) is recommended for indeterminate liver lesions >1 cm 1
• In patients with chronic liver disease, multiphase CT following LI-RADS technical recommendations is appropriate 1
• For patients with known extrahepatic malignancy and indeterminate liver lesions, multiphase contrast-enhanced CT is usually appropriate 1

For oncologic staging:

• Contrast-enhanced CT of chest and upper abdomen is required for lung cancer staging 1
• PET-CT should use high-resolution diagnostic CT technique, not low-dose CT, for initial staging 1
• For lymphoma, contrast-enhanced diagnostic CT (CECT) is standard, though IV contrast-enhanced PET/CT is an adequate alternative 1

For acute abdominal pain:

• Enhanced CT with intravenous contrast is superior to non-contrast CT for diagnosing acute appendicitis across all age groups and genders 2
• Non-contrast CT has only 64% negative predictive value for nonspecific upper abdominal pain, frequently missing pancreaticobiliary inflammation and gastritis 4

When Non-Contrast CT is Appropriate

Non-contrast CT should be limited to specific clinical scenarios:

• Suspected urolithiasis (kidney stones) - this is the primary indication where non-contrast CT is preferred 1
• Evaluation of calcifications when contrast would obscure them
• When IV contrast is contraindicated due to severe renal impairment or contrast allergy 1, 2
• CT for radiation therapy planning in some oncologic protocols

Radiation Dose Optimization

Technical Considerations

• Use low-dose protocols appropriate for the clinical indication, particularly in children 1, 5, 6
• Adjust dose based on patient body size - smaller patients and children require lower doses 5, 6
• High-contrast lesions can be scanned with reduced dose, but avoid excessive dose reduction for low-contrast lesions 5

Pediatric-Specific Strategies

• Dual-energy CT can consolidate multiphase protocols into single-phase imaging with virtual non-enhanced images, reducing radiation dose 6
• Low tube voltage (kV) techniques reduce radiation while increasing conspicuity of contrast-enhanced structures 6
• Rapid scanning with ultrahigh pitch or wide-area detectors can eliminate sedation needs in many children 6

Common Pitfalls to Avoid

Do not routinely perform non-contrast followed by contrast-enhanced CT - this doubles radiation exposure without improving diagnostic accuracy in most scenarios 2, 3

Do not use non-contrast CT for suspected abdominal masses in children - only post-contrast enhanced CT is needed, and adding a non-contrast phase is inappropriate 3

Do not assume all CT protocols require the same radiation dose - protocols must be tailored to patient size, with children receiving substantially lower doses than adults 5, 6

Do not skip contrast when clinically indicated to reduce radiation - a single properly performed contrast-enhanced study provides better diagnostic information than multiple non-contrast studies 2, 3

Alternative Imaging Considerations

When CT is being considered, evaluate whether alternative modalities are more appropriate:

• MRI may be preferable for liver lesion characterization, particularly for indeterminate lesions in patients with chronic liver disease 1
• Ultrasound with contrast (CEUS) can characterize 95% of subcentimeter liver lesions and detect 6.5 times more subcentimeter metastases than baseline dual-phase CT 1
• MRI achieves 99% accuracy for acute abdominal pathology and may identify conditions missed on CT, particularly for persistent pain after negative CT 4