Get on the train!

83 year old female with BMI of 21.6, presents with abdominal pain. Mesenteric angiogram requested with "minimum contrast dose possible", as the patient had history of renal failure after contrast. 

CT angiogram of the abdomen and pelvis was done with 16 mL of omnipaque 350. The image looks like something more commonly found inside the colon, but occasionally in small bowel with decreased motility.

Spectral to the rescue! Change the keV to 50, and a perfectly adequate CTA emerges. So, here is how I do it:

Plan the bolus train well. I typically add scan time plus delay in seconds, and a couple of extra seconds for good measure. In mesenteric angiogram, I like a delay of at least 8 seconds. Scan time was 3 seconds, and I added 2.3 seconds to make a bolus length of 13.3 seconds. 

Injection rate should generally be about 4 mL/sec, but in a smaller patient (BMI here was 21.6), I went for a 3 mL/sec injection rate. In a bigger patient, you might need 5 mL/sec.

Injection volume is bolus length x injection rate, so in this case is about 40 mL. In a smaller patient, I use 40% contrast (rest is saline) as my injection. So this scan was done with 16 mL contrast. In a bigger patient, you might need to use 50% or even 60% contrast.

Very important: Bolus tracking is critical, but trigger scan as soon as you see contrast arrive in the ROI. DO NOT WAIT for the scan to automatically trigger. Remember, the contrast is dilute!

Load up the spectral, and viola! You have a perfect low dose CTA. 

Volume rendered CTA conventional image: pretty limited

Same image 50 keV reconstruction: looks good!

Selected sagittal MIP image, 50 keV: diagnostic quality