First things First...Learn and understand iodine contrast BOLUS TRACKING Techniques before learning CT Angiography technique

smart prep protocol on a GE CT scanner

"Can you do angiography?"...That's an irritating question right?.."Of course I can because I am a medical radiographer and that's  what I do". 

But I get the "heat". A lot of us have been made to believe that CT angiography studies are very complex studies and it creates a lot of tension around the procedure especially for younger medical radiographers who are just getting introduced to the practice or older ones who have not been working with a CT scanning equipment.

abdominal angiography 

cerebral angiography showing circle of willis

Angiographic images are beautiful...Ain't they??

Now let's pour some ice on the heat. Let's just chill and get this things straight. I have been thinking. What is it about Angiography studies? What the heck?? The only angiography study that should seem complex is the coronary (cardiac) angiography. So whatever we are going to discus here doesn't really apply to cardiac/coronary angiography which unarguably involves a much more complicated technique including slowing the heart rate down and synchronizing ECG readings with the scan. I have done a coronary angiography only once in my practice and that was as an intern and I was simply observing.

The big deal in Angiography really is the approach we take especially while learning the procedure. So there are lots of things to learn all at once. Patient preparation, positioning, contrast administration, volume reconstructions and so one and so forth. How about we take the most essential of the things to learn and learn and understand it first before even trying to learn CT angiography techniques.

Ever heard of BOLUS TRACKING??? If you haven't then I am wondering how you even bothered to learn CT angiography. Now what is bolus tracking and why the h*ll do I have to learn about it? Let me break this down very well for you so you will understand it. First the real essence of angiography is to inject iodine contrast into the arteries and take scans while the iodine contrast is still within the arteries. How do you monitor the contrast flow to know when the contrast has fully entered the arteries? You use the technique called bolus tracking. The essence of this bolus tracking is that you visualize the contrast as it fills an artery selected as the region of interest (ROI). No vex!!! My technical grammar can be confusing. But what I mean is with bolus tracking, you see the contrast as it fills up the artery and then decide when the contrast has optimally filled the arteries and then you start the scan .

Some of us that have used GE CT machines are very familiar with SMART PREP. The very first thing you should learn even before you learn how to position a patient for angiographic studies is bolus tracking technique that is peculiar to your CT machine. If you are using  a GE CT scanner, it is called Smart prep, CARE bolus for Siemens; SUREStart for Toshiba; Predict scan in Hitachi and Philips refused to name it anything but bolus tracking. So whatever it is called in your machine, the function is same. Bolus tracking technique is used to monitor the flow of iodine contrast into the arteries to be sure that when you take the scan, there will be maximum enhancement of the arteries. By maximum enhancement, I mean that the arteries are very visible.

I am going to try to explain how bolus tracking works in a GE CT machine. It's called smart prep. I already mentioned what Siemens and others call theirs. The user interface might be different for different  CT brands makers but the technicalities are relatively the same. It's your responsibility to learn how it works in your own machine. I am sure that your colleagues who know it better will gladly teach you. It's a technique that you learn on the job.

You will need to have prepared the patient, positioned the patient connected the IV line on the patient to the auto-injector, obtained a scout image and possibly taken plain scans before you activate the smart prep (bolus tracking technique). Please let me repeat again; don't go looking for smart prep in a Siemens CT scanner. It is called  CARE bolus. So moving on, once you activate the smart prep protocol, you are able to bring out the localizer. The localizer is more like a line that shows you where the actual slice/ cut will take place. Depending on the angiographic study you are doing,  you can place the localizer on the region of the arch of aorta for cerebral, carotid, upper limb(peripheral) and pulmonary angiography  and if it's renal, abdominal aortic and lower limb (peripheral) angiography, the localizer is best placed around the region of the descending abdominal aorta. Once you are ok with the localizer placement, you accept and then initiate the scan. A single slice is acquired. You place your Region of Interest (ROI). The ROI is usually the best suited arterial vessel to use in monitoring the flow of contrast. when you eventually start the scan, this is where you will see contrast fill and on maximum enhancement, the scan is taken. Please be very careful with placing your ROI especially when you  are using dynamic transmission or auto-scan ( which means that the system detects the maximum enhancement by itself and initiates the scans by itself). On dynamic transmission or auto-scan, the system recognizes when the set Hounsfield Unit/ HU value ( contrast enhancement)for the ROI has been reached and then sets off the scan automatically. So if you place your ROI on the wrong vessel or outside the arterial vessel, the system will either not initiate the scan or it will delay the initiation and you will make a mess of the procedure. Personally I deactivate dynamic transmission so that I am able to initiate the scan myself ( manually). If I am working with a Toshiba CT scanner, I use manual  scan instead of auto-scan. It's the same thing I am trying to achieve. So once you have placed your ROI corrected and of course checked that the auto-injector and IV line and connectors  are also set with the appropriate contrast volume and flow rate, you start the scan (monitor phase) together with the injection. As the CT contrast injection goes on, the machine scans the ROI (only) and you see the contrast filling. On optimal enhancement, the scan phase is initiated either manually  by you (in manual scan) or automatically by the machine (in auto-scan or dynamic transmission). Scan phase is where the machine scans the entire length of the patient that you have selected in your planning.

Please  it is important to note that before you activate bolus tracking technique, you must have planned your localizer for the contrast phase of the study.

 Bolus tracking is not only used for angiography. It is used in liver studies (tri and dual phase  studies) and any other studies where you need to monitor the flow of iodine contrast real time

if you understand how bolus tracking technique works, you won't have problems with understanding how to perform an angiographic study.

please go back to my earlier post on Angiography and read more about the techniques. if you have any issues, please send me an email on cseiroegbu@yahoo.com or call me on 08034635555