What is the recommended contrast agent and intravenous fluid (IVF) regimen for a whole abdominal computed tomography (CT) scan?

Contrast Agent and IV Fluid Protocol for Whole Abdominal CT

For a whole abdominal CT scan, use intravenous iodinated contrast agent (such as iohexol 300-350 mg I/mL) injected at 3-4 mL/s via power injector, followed by a 20-50 mL saline flush, with images obtained 50-70 seconds after contrast injection (portal venous phase). 1, 2

Intravenous Contrast Protocol

Contrast Agent Selection

• Iohexol (low-osmolar nonionic contrast) at concentrations of 300-350 mg I/mL is the standard choice for abdominal CT imaging 1, 3
• Typical volume is 100-150 mL for adults, though this can be reduced to 100 mL when using a saline chaser 1, 3, 4
• Iso-osmolar dimeric agents (iodixanol) provide equivalent vascular enhancement to monomeric agents despite 9.3% lower iodine content, making them suitable alternatives for patients with borderline renal function 5

Injection Technique

• Power injector administration at 3-4 mL/s is recommended for optimal enhancement 1
• Follow contrast bolus with 20-50 mL saline flush using a dual-syringe power injector to significantly improve both parenchymal and vascular enhancement 2, 4
• The saline chaser improves liver enhancement by approximately 9 HU, spleen by 8 HU, pancreas by 7 HU, and vascular structures by 8-10 HU without requiring additional contrast volume 2

Timing of Image Acquisition

• Portal venous phase at 60-70 seconds after contrast injection provides optimal visualization of abdominal organs and is the standard for general abdominal CT 1
• For specific indications requiring vascular detail, a late arterial phase at 45-50 seconds may be added 1
• Enteric phase at 50 seconds provides peak bowel wall enhancement when inflammatory conditions are suspected 1

Oral Contrast Considerations

When to Use Oral Contrast

• Neutral oral contrast (water or dilute barium) is preferred when gastric or bowel pathology is the primary concern 1
• For gastric imaging specifically, administer effervescent granules (sodium bicarbonate/citric acid) with minimal water immediately before scanning for optimal gastric distension 1
• Dilute iohexol (6-21 mg I/mL) can be used as oral contrast for CT enterography, administered as 500-1000 mL in adults 20-40 minutes before IV contrast 1, 3

When to Avoid Oral Contrast

• Avoid positive oral contrast for suspected GI bleeding as it obscures contrast extravasation 1
• CT colonography should not use oral contrast as it complicates polyp detection 1
• Emergency situations where rapid scanning is needed may proceed without oral contrast 1

Patient Preparation

Pre-Scan Requirements

• Fasting for at least 6 hours ensures complete gastric emptying 1
• Adequate hydration before imaging prevents urinary activity from causing interpretation problems in pelvic imaging 1
• Consider 0.5-1 mg IV glucagon 3-5 minutes before scanning to minimize peristaltic movements (contraindicated in diabetes, pheochromocytoma, or lactose hypersensitivity) 1

Renal Function Assessment

• Check creatinine and estimated GFR in patients over 60 years, with history of renal disease, diabetes, hypertension, or metformin use 1
• High-risk patients have creatinine >1.5 mg/dL (13 mmol/L) and/or GFR <60 mL/min 1
• Discontinue metformin at time of contrast administration and withhold for 48 hours afterward in high-risk patients 1

Technical Parameters

Acquisition Settings

• Slice thickness of 2-3 mm for optimal detection of pathology 1
• Consider low-dose techniques (tube potential selection, automatic exposure control, iterative reconstruction) adapted to patient size 1
• Ensure complete coverage from dome of liver through pelvis 1

Common Pitfalls to Avoid

• Do not use standard CT with IV contrast alone when CT angiography is indicated for suspected bleeding—this is rated "usually not appropriate" by ACR 6
• Avoid excessive oral contrast volume that causes patient discomfort and delays scanning 3, 7
• Do not skip the saline flush—this simple addition significantly improves enhancement while reducing total contrast volume and cost 2, 4
• Ensure proper timing—scanning too early or too late reduces diagnostic quality, particularly for liver lesions 1, 4