CT Angiography in the Emergency Department: Maximizing Contrast Enhancement and Image Quality While Minimizing Radiation Dose and Contrast Material Volume: Vascular/Interventional Radiology

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Computed tomographic (CT) angiographic image quality is highly dependent on contrast material injection and image acquisition technique. To provide patient-centric care, one should tailor the technique to the clinical question and the characteristics of each patient. This online presentation helps simplify the topics of intravenous contrast material dynamics and technique optimization and describes how dual-energy and fast CT angiography can allow further image quality improvement while reducing contrast material volume and radiation dose.

Knowledge of intravenous contrast material dynamics underlies all protocol optimization principles. Contrast material is injected into a peripheral vein and is followed by a saline chaser, after which it travels to the right side of the heart, pulmonary circulation, left side of the heart, systemic arteries, and parenchymal organs in succession. Timing for each phase can be empirical, with a timing bolus, or dictated by bolus tracking. For parenchymal organs, empirical timing works acceptably in many cases, but for CT angiography it does not, as multiple factors such as iodine concentration, contrast material injection rate and volume, CT tube potential, image acquisition time, patient cardiac output and blood volume, and intravenous line location and caliber all affect the timing, magnitude, and character of contrast enhancement. Figure 1 shows the influence of the contrast material injection rate on aortic and parenchymal organ enhancement and shows that higher contrast material injection rates increase peak enhancement, shorten time to peak enhancement, and result in decreased time of sustained near-peak enhancement when contrast material volume and other factors are held constant.

Figure 1.

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Patient blood volume and cardiac output have a large influence on the timing and degree of contrast enhancement. One pertinent clinical example of the variation in blood volume is a pregnant woman, who may have a cardiac output more than 50% greater than baseline. Thus, if a given level of enhancement is necessary for a diagnostic study, one must increase the iodine flux by at least 50%, whether through an increase in the contrast material injection volume or the injection rate. Because of concerns of iodine-related acute kidney injury, radiologists should generally be decreasing rather than increasing the contrast material volume. One can decrease the contrast material volume while maintaining high vascular enhancement through precise image acquisition timing, use of modern multidetector scanners that allow fast image acquisition, and use of low kilovoltage peak or dual-energy techniques that capitalize on the k edge of iodine and the resultant increased photoelectric effect. Figure 2 depicts a patient who underwent follow-up CT angiography with a low kilovoltage peak and low contrast material volume protocol (80 kVp, 20 mL of contrast material), where image quality can be seen to be reduced from that of the standard technique but the study is still diagnostic.

Figure 2.

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In the online presentation, figures depict the timing of contrast material administration and the techniques used to optimize it, the effect of contrast material rate and volume variance, the effect of contrast material recirculation and hemodynamic perturbation created by the contrast material injection itself, and the effect of varying kilovoltage peak on iodine attenuation. This material shows how readers can provide patient-centric care by optimizing the contrast material injection and image acquisition technique for each of their patients.

Disclosures of Conflicts of Interest.—M.L.G.: Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: research support from Philips Healthcare. Other activities: spouse is a contractor to Athena Health and Elsevier.