Thread by @Prof_TimStick

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(1/8) Multiphasic CT protocols are an awesome place to start working as a team (rad, tech, technical person). Considerations must be made for contrast deliver, scan timing, and scan speed. Lets go over these things.

(2/8) Contrast delivery. Dosing should be weight based. Medrad P3T does it for you, all other injectors you'll need to have an in-house look up table. We care most about total mg of I and injection duration. I included equations to help you here.

(3/8) All those calculations only need to be done during protocol development. You figure: 1 how much iodine you need in mgI, 2 pick your concentration in mgI/cc to get volume in cc, 3 you can look at what flow rates you will use in cc/s 4 then calculate injection duration in s.

(4/8) Once you know how long injection duration will take, look at scan delay. Even if bolus tracking, you'll have a delay between injection and scan/bolus tracking. In most cases, the inj duration needs to be shorter than the scan delay...unless you like bright SVC artifacts.

(5/8) See the equations I gave, scan delay should also factor in scan duration. Longer scans (e.g., older scanners) need shorter scan delays to match the mid point of the scan with the desired enhancement phase. Don't take CTA delays from a 16 slice to your premium scanner...

(6/8) So scan delay is going to be a function of scan speed and the desired body region/contrast enhancement phase. Time from inj to target phase: routine abd ~70 s, CTA ~tens of seconds, routine head ~4 min, bolus tracking delay in liver parenchyma ~40 sec.

(7/8) Interscan delay. Given some target interscan delay in seconds, we have to allow for scan duration for the two phases and the time for the scanner to move between phases. The scanner will take time to move, so scan a phantom using the same settings to get an estimate.

(8/8) Go read KT Bae's 2010 Radiology contrast review and go sit at the scanner and talk to your techs and review the scanner bolus tracking and scan delay options. Figures shown here from my CT handbook @MedPhysPub

Last tweet, I promise.
Weight based dosing, creatinine guidelines, other contrast stuff is on pages 469-475 of this link from our CT protocols at @UWiscRadiology

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