When should I use non‑contrast computed tomography (NCCT) versus spiral (helical) CT?

NCCT vs Spiral CT: When to Use Each Modality

Non-contrast CT (NCCT) and spiral (helical) CT are not mutually exclusive—spiral CT is simply the modern acquisition technique, and NCCT refers to scanning without intravenous contrast; therefore, the current standard of care is to use spiral/helical NCCT for most acute diagnostic imaging. 1

Understanding the Terminology

The question reflects outdated terminology that requires clarification:

• Spiral (helical) CT is a scanning technique that involves continuous patient translation during x-ray tube rotation, allowing volumetric data acquisition in a single breath-hold 2, 3
• Non-contrast CT (NCCT) refers to CT performed without intravenous contrast administration 1
• Modern practice uses spiral/helical NCCT as the standard acquisition method for most emergency and stone imaging 1

Clinical Applications Where Spiral NCCT is Standard of Care

Suspected Kidney Stones (Urolithiasis)

Helical (spiral) non-contrast CT of the abdomen and pelvis is the reference standard imaging modality for acute flank pain with suspected stone disease. 1, 4

• Achieves ≥95% sensitivity and specificity for stone detection 1, 4
• Provides precise stone size and location measurements essential for determining conservative vs. interventional management 1, 4
• Reliably visualizes secondary obstruction signs (ureteral dilatation, perinephric stranding) that guide clinical decisions 1, 4
• ACR appropriateness rating of 8 (usually appropriate) for initial evaluation 1

Critical modification: Use low-dose protocols (<3 mSv) instead of conventional dosing to minimize radiation exposure while maintaining diagnostic accuracy 1, 4

Acute Traumatic Brain Injury

Non-contrast CT (acquired using spiral technique) is the initial triaging diagnostic test of choice for acute moderate-to-severe TBI (Class I recommendation). 1

• Highly sensitive and specific for intracranial hemorrhage, extra-axial collections, skull fractures, cerebral edema, and herniation 1
• Rapid acquisition time (critical in trauma settings) 1
• Widely available with minimal contraindications beyond radiation exposure 1
• Does not require screening for ferromagnetic materials unlike MRI 1

Technical Advantages of Spiral/Helical Acquisition

Spiral CT provides several advantages over older conventional (step-and-shoot) CT:

• Dramatically shortened examination times—entire chest or abdomen in single breath-hold 5, 2
• Volumetric data acquisition allowing retrospective image reconstruction at any desired level 5, 2
• Space-invariant resolution—lesion detection does not depend on random positioning relative to scan slices 6
• Improved lesion contrast by up to 1.8-fold compared to conventional CT through retrospective slice centering 6
• Better vascular enhancement and capability for 3D vascular studies 5

When Contrast-Enhanced CT May Be Appropriate

Avoid Contrast for Stone Imaging

Contrast-enhanced CT should NOT be used as first-line for suspected kidney stones. 4

• Intravenous contrast opacifies renal parenchyma, obscuring stones within the collecting system 4
• Lower sensitivity for detecting small renal calculi compared to NCCT 4
• Increases cost, radiation dose, and contrast-related adverse event risk without diagnostic benefit 4

Consider Contrast for Vascular or Soft-Tissue Evaluation

• CT angiography (CTA) is recommended for suspected traumatic vascular injury in TBI patients with specific risk factors (cervical spine fracture, unexplained focal deficit, basilar skull fracture) 7
• Contrast-enhanced CT may be appropriate when alternative diagnoses beyond stones need evaluation (ACR rating 6) 1

Special Population Considerations

Pregnant Patients

Ultrasound is the imaging modality of choice (ACR rating 8), NOT CT. 1, 4

• Avoids ionizing radiation 4
• Direct stone detection sensitivity only 24-57%, but highly sensitive (95-100%) for hydronephrosis 4
• Low-dose NCCT only as last resort if ultrasound nondiagnostic 1, 4

Recurrent Stone Disease

Use ultra-low-dose CT protocols or limited-area scans to minimize cumulative radiation exposure in patients requiring multiple studies 1, 8, 4

Pediatric Patients

Start with ultrasound to minimize radiation; proceed to low-dose spiral NCCT only if suspicion persists. 4

Common Pitfalls to Avoid

• Do not order "conventional CT" thinking it differs from spiral CT—virtually all modern CT scanners use spiral/helical acquisition 2, 3
• Do not add contrast for stone imaging—it obscures stones and provides no diagnostic advantage 4
• Do not use standard-dose protocols when low-dose is appropriate—radiation reduction is critical for stone imaging 1, 4
• Do not assume ultrasound alone is adequate for stone diagnosis—sensitivity is only 24-57% for direct stone detection 4
• Recognize spiral CT artifacts related to accentuation of vascular/parenchymal enhancement that can occur with this technique 5