Slide 1: For which of these clinical scenarios would you order an imaging study with contrast? Bonus: which should be ordered with and without contrast?

Clinical scenario 1: A 75-year-old with fevers, night sweats and weight loss.

Clinical scenario 2: A 55-year-old female with “the worst headache of my life.”

Clinical scenario 3: A 60-year-old male with renal mass concerning for malignancy.

Clinical scenario 4: A 65-year-old female with lower left quadrant pain and fever.

Clinical scenario 5: An 80-year-old male with BRBPR.

Slide 2: Answer: You would use contrast in the clinical scenario of a 75-year-old female with fevers, night sweats, and weight loss, and in the clinical scenario of a 65-year-old female with lower left quadrant pain and fever.

Contrast can help distinguish soft tissue structures of very similar innate density by increasing the density of structures that have more relative blood flow. Imaging shown with and without contrast.

Look how these enlarged mediastinal lymph nodes stand out against the mediastinal fat because of contrast.

Inflammation brings increased blood flow and can help us see the bowel wall thickening and surrounding fat stranding of this acute diverticulitis.

Compare to the normal, thin-walled neighbor.

Seeing such wall detail is very difficult without contrast.

Slide 3: Answer: You do not use contrast in the clinical scenario of a 55-year-old female with “the worst headache of my life.”

There are times when contrast actually hurts evaluation of a study! Remember that some very dense substances such as blood clot and renal stones already have good contrast with the surrounding soft tissues. Look how well this subarachnoid hemorrhage stands out on the non-contrast image.

It’s not so easy to see after contrast though…Is that blood in the fissure?…Or just contrast in a vessel?…

Slide 4: Answer: With and without contrast applies to the clinical scenario of a 60-year-old male with renal mass concerning for malignancy and the clinical scenario of an 80-year-old male with BRBPR.

Usually, the reason for this seldom-needed protocol is to have a pre-contrast image for reference to confirm that something actually is contrast and not a background calcification.

The non-contrast images help confirm that the density in the rectum is, in-fact, contrast from a bleed…and not an innocent calcification.

Also consider the renal mass protocol, where we can measure the enhancement of a mass as >20HU to differentiate the subtle enhancement of a papillary renal cell carcinoma from a complicated cyst.

Slide 5: This is just a brief overview to help us understand why we need contrast and when it is likely appropriate. Great resources include the ACR Appropriateness Criteria for even more reference material! Another helpful resource: Rawson et al. “When to Order Contrast-Enhanced CT” American Family Physician. 2013 Sep 1;88(5).

Study: Non-contrast. Purpose: Look for inherently bright structures such as clot and calcification. Common indications: Head CT and Renal Stone protocol (looking for inherently dense pathology)

Study: Contrast. Purpose: Better tissue detail, inflammation. Common Indications: Infection/abscess protocol and oncologic work-ups.

Study: With and without contrast. Purpose: Usually only to look for contrast extravasation or to quantify enhancement (use the non-contrast images to rule out overlying calcification). Common indications: GI bleeding, aortic injury, and renal tumor protocol.