When to choose a study without contrast vs with contrast?

When to Choose a Study Without Contrast vs With Contrast

The decision to use contrast in imaging studies should be based on the clinical question being asked, with contrast-enhanced studies being preferred for evaluating soft tissue pathology, inflammatory processes, infections, neoplasms, and vascular structures.

General Principles for Contrast Use

• CT with intravenous contrast is recommended as the primary imaging modality for evaluating soft tissue pathology, inflammatory processes, infections, and neoplasms due to its ability to significantly improve characterization of masses and map lesion borders 1
• MRI with contrast provides superior characterization of lesion components, enhances diagnostic accuracy, and improves detection of malignancy in soft tissue masses 2
• Non-contrast studies are appropriate for initial evaluation of trauma, fractures, and in patients with contraindications to contrast agents 1
• Performing both contrast and non-contrast CT in the same session is generally not recommended as it doubles radiation exposure with minimal additional diagnostic benefit 1

Specific Clinical Scenarios for Contrast Use

When to Use Contrast:

• Suspected infection or abscess: Contrast-enhanced CT or MRI is preferred for detecting inflammatory processes and abscesses 1
• Tumor/mass evaluation: Contrast is essential for characterizing lesions, determining tumor margins, and identifying viable tumor for biopsy 2
• Diverticulitis: Abdominal and pelvic CT with contrast (rating 8/9) is preferred over CT without contrast (rating 6/9) 3
• Osteomyelitis with draining sinus: MRI with and without contrast is the preferred study (rating 9/9) 3
• Recurrent ovarian cancer: Contrast-enhanced CT is the modality of choice for detecting recurrence 3
• Soft tissue masses: MRI without and with IV contrast is the preferred imaging study 2

When to Avoid Contrast:

• Pregnancy: Non-contrast studies are generally preferred, though iodinated contrast can be used if absolutely necessary 3
• Severe renal insufficiency: Avoid iodinated contrast due to risk of contrast-induced nephropathy 1
• Known contrast allergy: Consider alternative imaging or appropriate premedication 4
• Initial evaluation of suspected soft tissue gas: CT without contrast is appropriate (rating 6/9) 3

Special Considerations

Pregnancy

• Ultrasound without contrast is the preferred imaging modality throughout pregnancy 3
• MRI without gadolinium is preferred over CT imaging when ultrasound is insufficient 3
• Gadolinium is contraindicated in pregnancy 3
• Abdominal CT without contrast is generally safe but should be limited 3

Renal Function

• Baseline serum creatinine values should be obtained in patients at risk for contrast-induced nephropathy, not all patients 4
• Calculated creatinine clearance is a better way to determine risk than serum creatinine alone 4
• Major risk factors for contrast-induced nephropathy include renal dysfunction, long-standing diabetes mellitus, dehydration, and use of other nephrotoxic medications 4

Contrast Allergy

• History of contrast allergy does not absolutely contraindicate future contrast use, but special care must be taken 4
• Pretreatment with steroids is well established for preventing minor reactions but may not prevent major reactions 4
• Allergic reactions to iodinated contrast media are uncommon (less than 1% of procedures) and mostly non-severe 5

Practical Algorithm for Deciding Between Contrast and Non-Contrast Studies

1. Identify the clinical question:

   • For bone/structural evaluation (fractures, calcifications) → Non-contrast study 1
   • For soft tissue pathology (masses, infections, inflammation) → Contrast study 1, 2

2. Assess patient factors:

   • Pregnancy → Prefer ultrasound or non-contrast MRI 3
   • Severe renal insufficiency → Consider non-contrast study or alternative imaging 4
   • History of contrast reaction → Consider premedication or alternative imaging 4

3. Consider the specific anatomical region:

   • Abdomen/pelvis for diverticulitis → CT with contrast preferred 3
   • Jaw pain/swelling → CT with contrast preferred unless evaluating for fracture 1
   • Soft tissue mass → MRI with and without contrast preferred 2

4. Weigh radiation concerns:

   • Avoid ordering both contrast and non-contrast CT in the same session 1
   • Consider MRI as an alternative to CT when appropriate to reduce radiation exposure 3