Use of high concentration contrast media: principles and rationale—vascular district

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Abstract

Optimal contrast medium delivery remains a crucial issue in CT angiography and it will become even more critical with continuously evolving, faster CT scanner technology. This review article first explains the fundamentals of arterial enhancement using mathematical models of early contrast medium dynamics. The relationship of contrast medium volume, injection flow rates and injection duration are explicitly illustrated. Next, current techniques of contrast medium application are reviewed, with particular attention to methods of accurate timing of the scanning delay (test-bolus and automated bolus triggering), tools for automated saline-flushing of the veins (double-syringe power injectors) and the use of high-concentration contrast medium. From there, rational CT angiographic injection protocols for a wide range of selectable acquisition times for 4-, 8- and 16-channel MDCT are proposed.

Introduction

Optimal vessel opacification remains one of the most crucial but difficult aspects of multiple detector-row CT angiography (MD-CTA). Since its introduction in 1998, MD-CT technology has spread rapidly, with 4-channel systems being widely available today. Recently even faster systems with 8 and 16 channels have been introduced. Controlling the level and time-course of arterial enhancement and correct synchronizing CT acquisition relative to arterial enhancement becomes more difficult and ‘less forgiving’ with MD-CT acquisition times in the range of 5–10 s. A basic understanding of contrast medium dynamics is crucial for the rational design of contrast medium injection technique.

The purpose of this article is (a) to review the basic pharmacokinetic principles of intravenously injected contrast medium for arterial enhancement, (b) to introduce new mathematical tools for modeling and individually tailoring arterial enhancement, and (c) to use the gained insights to derive practical injection strategies using state of the art power injectors and high concentration contrast medium.

Section snippets

Physiologic and pharmacokinetic principles

Intravenously injected contrast medium travels from the arm veins to the right heart, the lungs, and the left heart before it reaches the arterial system for the first time (‘first pass’). After the contrast medium is distributed throughout the organs with their intravascular and interstitial fluid compartments it reenters the right heart (‘recirculation’). It is important to recognize that within the time-frame relevant for CTA one will not only observe the first pass of contrast medium but

Mathematical modeling and controlling arterial enhancement

Accurate prediction and controlling of time dependent arterial enhancement is highly desirable for CTA, particularly with faster scanners. Ideally, one wants to predict and control the time course as well as the degree of arterial enhancement in each individual—independent of an individual's underlying physiology. Two mathematical techniques addressing this issue have been developed.

The first is a compartmental model, which predicts arterial enhancement using a system of more than 100

Intravenous access

For MD-CT the thickest cubital vein is the most favorable site for contrast medium delivery. If high injection flow rates are desired, a fast manual saline injection with the patient's arms in scanning position before contrast delivery is recommended to assure correct cannula position. Recently automatic devices for the local detection of paravenous injection have been developed, in order to avoid the extravasation of significant volumes of contrast medium. With a securely placed I.V. line,

Conclusion

Contrast medium delivery remains an important issue in CT angiography and will become even more critical with faster scanner technology. Understanding the physiologic principles of early contrast medium dynamics facilitates a rational approach to the design of current and future contrast medium injection protocols for vascular applications of MD-CT. High-concentration contrast media allow high Iodine administration rates. Together with accurate timing of the scan delay using a test-bolus or an

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    Citation Excerpt :

    This avoids the potential for pseudofilling defects. Other advantages of the saline chaser include savings in the total of intravenous contrast administered and increased enhancement by pushing the contrast lodged in the arm and central veins.9,27,38,47 Caudocranial scanning has also been advised to reduce streak artifact.29,33,46

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