Contrast



Phases of Intravenous Contrast

CT Protocols

  • Protocols are tailored for specific indications and will often include multiple phases​

  • For example, a renal CT will include noncontrast and multiple post contrast phases to better characterize a renal mass


Noncontrast Phase

Good for:​

  • Calcifications, including stones​

  • Blood products such as hematomas​

  • Intrinsic density measurements such as for fatty liver or lesion evaluation​


Only a few indications (usually when contrast may obscure the pathology of interest)​:

  • Renal stone evaluation​

  • Vascular calcification for renal transplant​

  • Contraindication to contrast (renal failure or allergies)


Arterial Phase

Peak arterial enhancement (~20-40s after injection)​


Good for:​

    • Arterial evaluation​

    • Contrast extravasation​


Indications for CT Angiogram​

  • Acute aortic syndrome​

  • Vascular pathologies such as vasculitis​

  • Active bleeding​


CTA protocols vary based on indication, so history is crucial!


Portal Venous Phase

Peak solid organ enhancement (~70-90s after injection)​

Good for:​

  • Organ parenchymal evaluation (liver, spleen, etc.)​

  • Infectious and inflammatory pathologies such as abscess (Rim enhancing fluid collection)​


Indications for portal venous CT (routine CT with contrast)​

  • Most acute pathology including trauma​

  • Initial screening for metastatic disease/malignancy (exceptions include, but not limited to, HCC and pancreatic cancer evaluation)​

Venous Phase

Peak venous enhancement (~120-150s after injection)​


Good for:​

    • Vein evaluation​


Indications for CT Venogram​

  • Venous anatomy evaluation

  • Deep venous thrombosis and/or IVC filter

Delayed/Excretory Phase

Renal excretion of contrast (~5-10 min after injection)

Good for:​

  • Renal collecting system/ureteral evaluation


Indications for excretory phase CT

  • Urothelial lesion (as part of CT urogram)

  • Urine leak

Oral Contrast

Positive contrast (barium or iodine based) or neutral contrast (water or water-like density)

Pros:

  • Distension of bowel for better evaluation

  • Increased sensitivity for certain nonbowel pathologies (e.g. interloop fluid collection)

Cons:

  • Requires waiting 30-45 minutes for administration and passage

  • Often overused and sometimes contraindicated. Contrast can obscure pathologies such as intraluminal bleeding!