Cats can scan now?

Weight-based intravenous contrast injection parameters for Enhanced CT Scanning.


This page is showing a method of giving weight based doses of contrast agent for CT scanning. No-one would argue that fixed-dose is superior to weight-based dose. The only question, “is it too much trouble”?

by Steven B. Halls, MD, FRCPC.

I created this page in 1999. In 2014 I redid the styling and added a few paragraphs. Way back in 1999, a “single slice” “Spiral CT scanning” was the new technology. In 2014, that is OLD technology, and the progress in CT scanners is expected to continue.

The table below shows DOSES, RATES, and TIMING.

The Dose information is perfectly fine, even in 2014.

The Rate information is reasonably fine, even in 2014. Fashion may change rates over time.

The Timing (delay) information will need adjustments in 2014 and beyond, because CT scanners can cover the body a lot faster than in 1999.

So keep all this in mind as you review this table. I will comment further, below, about 2014 and future adjustments. You can click on the red headings in the table, which are links to further information.

click the headings
for more info
Abdomen Chest Chest &
Weight Dose Rate Delay Delay Delay
118 + kg 160ml 3.3 72 55 42
98 – 117 kg 140ml 3.1 70 53 40
78 – 97 kg 120ml 2.8 68 51 38
64 – 77 kg 100ml 2.6 66 49 36
48 – 63 kg 80ml 2.4 63 46 34
38 – 47 kg 70ml 2.2 62 46 34
*31– 37 kg 60ml 2.0 61 46 34


* for pediatrics use formulas:  Dose= kg*2.0,  Rate= kg*0.04 + 0.4

The "Cross Method". I called it the Cross method in 1999, because I developed all this while I was working at the Cross Cancer Institute, in Edmonton, Alberta, Canada. But I moved onto a different job in 2005, so it’s been a while, and I don’t know if they still use it there. But I STILL USE IT, in my daily CT practice, at St. Mary’s hospital in Camrose, Alberta.


What is this page all about? It’s for radiologists to use for CT scanning ( "cat scans" or "computed tomography"). It’s like a recipe for prescribing medicine according to the patient’s body weight.

It might seem a little strange that this website has a variety of health/medical topics, including body mass index, body surface area, ideal weight, breast cancer, and CT scanning protocols (here), but there is a slight common thread… that big people and small people aren’t the same, but you can treat everyone equally by making logical adjustments.

Comments added in 2014. I’ve used these protocols for 14 years, and I am still very proud of what they have accomplished. Having enhancement of liver and kidneys look EXACTLY THE SAME, in very heavy and very light people, is a wonderful benefit, that I have come to trust deeply. It is SO RELIABLE, that when I do see delay in enhancement of liver and kidneys, then I know with certainty that the patient has low cardiac output. Let me restate the corollary, If you see delayed enhancement of liver after a fixed dose and fixed rate and fixed delay, you say “that’s the sort of variation I have to put up with”, and you don’t even mention low cardiac output in your report. Another comment: Because I have such trust in these protocols, I rarely do dual-phase scanning (arterial and portal) and never do triple-phase. I rarely will do portal + 10-minute delay, for situations where I’m looking for stones or tumors or leak in renal pelvis or ureters or bladder. What I’m saying, is that because the portal venous phase images are so uniform and trusted, I just don’t need to give extra radiation very often.

During the past 14 years, I’ve changed CT scanners several times, and changed to different contrast vendors several times. Hospital administration buyers make deals on contrast purchases, and some years they might favor buying “300” osmolality bottles, in other years “320” and occasionally “”350″. My tables were created initially for “300”. During those times when “320” is in use, I changed the Doses by multiplying by 300/320. Rates stayed the same.

Delays, refer to how many seconds after the start of injection, until scanning begins in the Abdomen. Most times, for average size patients, the delay is 66 or 68 seconds. My opinion of Chest delays is that it doesn’t matter very much. Of course it matters for Pulmonary Emboli detection, which didn’t exist in 1999. For PE scanning in 2014, the delay is triggered by monitoring for the arrival of enhancement in the pulmonary outflow tract. For aortic arch dissection and thoracic aortogram CTAs, the delay is triggered by the arrival of contrast in the arch.

Notice that pediatrics formula. It is fantastic, and fairly standard, AND it specifies Dose and Rate. But what delay for pediatrics. For abdomens, just use use 61 second delay, or mabye 60 for really small children. A great feature of the pediatric formula, and my weight-based numbers for adults, is that when plotted on a graph, they make a nice smooth curved line. In other words, pediatric cases get the same image quality as adults, and visa versa. And because the radiologst is SO familiar with the standard “look”, diagnostic confidence extends to pediatric reporting.

Did you click on any faces or find other surprises?


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