Can contrast-enhanced CT and contrast-enhanced MR be done on the same day?

Nowadays, imaging examination technology, as an indispensable clinical examination method, is more and more accepted by everyone. In order to facilitate the accurate diagnosis of the disease, clinicians often recommend patients to undergo enhanced CT or enhanced MR (magnetic resonance) examinations according to the condition, and some patients even need to do both at the same time. At this time, everyone often has a question: Can enhanced CT and enhanced MR be done on the same day? Will injecting contrast agent harm the body? Today, let the doctor come to answer your questions.

Abnormal renal function avoid two examinations on the same day

Enhanced CT and enhanced MR have different advantages in different disease areas, so there may be cases where patients need to complete the above two examinations at the same time. According to the tenth edition of the European Society of Urogenital Radiology (ESUR) Contrast Media Guidelines (hereinafter referred to as the “Guidelines”), the guidelines for two injections of iodine and gadolinium contrast media are given:

Patients with severely reduced renal function or on dialysis: The interval between two gadolinium contrast injections should be 7 days. In the presence of residual renal function, the interval between two iodinated contrast injections should be at least 48 hours.

It can be seen that for patients with abnormal renal function, CT and MR enhancement should be avoided on the same day. If for a special emergency patient, accompanied by a clinician, hemodialysis is performed immediately after the examination, then such special circumstances can also be handled as appropriate.

Normal kidney function tests at least four hours apart

According to the guidelines, the excretion rates of both iodinated contrast agents and extracellular gadolinium contrast agents can reach 75% after 4 hours of administration in patients with normal or moderately reduced renal function. The interval between two contrast injections should be 4 hours.

Briefly, contrast agents administered into the blood vessels are mainly excreted through urine, while contrast agents administered orally are excreted through feces. Conventional contrast-enhancing agents are absorbed by tissues into the veins and excreted mainly in the urine. The excretion rate into the urine after administration to blood vessels is about 75% in 4 hours, so most of the contrast agent has been excreted in about 4 hours.

Therefore, for patients with normal renal function, contrast-enhanced CT and contrast-enhanced MR can be arranged on the same day, but it is recommended that the two examinations be separated by at least 4 hours.

Sequential contrast-enhanced CT should be done first

How to arrange contrast-enhanced CT and contrast-enhanced MR on the same day? This also needs to be considered from the principles and mechanisms of enhanced CT and enhanced MR.

Let’s talk about the principle of enhanced CT first. It is to enhance the contrast between the blood-rich tissue and the surrounding tissue by introducing iodine contrast agent. The gadolinium contrast agent commonly used in enhanced MR also has a relatively large relative atomic weight, which is higher than the relative atomic mass of iodine, so it can also show high density in CT images. Therefore, if enhanced MR is performed first, then enhanced CT may affect the results of enhanced CT.

Let’s look at the principle of enhanced MR, which is by introducing a paramagnetic metal ion gadolinium contrast agent, while iodine is a halogen element, a non-metal, and has no paramagnetic properties. Therefore, after the iodine contrast agent is applied, it does not affect the image quality of enhanced MR.

Having said that, according to the characteristics of the contrast agents used in the two examinations, we know that the enhanced CT examination first does not affect the MR (unenhanced and enhanced) examination, and the enhanced MR first may affect the CT (unenhanced and enhanced) examination.

Text/Zhang Ning (Beijing Shijitan Hospital)