A new method has been developed to perform CT angiography with significantly low contrast volume [13]. At the completion of the diagnostic cath, a 4-French pigtail catheter is positioned at the abdominal aorta, below the level of the renal arteries, and the patient is transferred to the CT suite. For the CT angiogram, iodinated contrast (iopamidol 370 mmol/ml) is mixed with normal saline in a 1:3 to 1:4 dilution in a single chamber of the power injector, and 40 ml of the contrast/saline mixture is injected through the pigtail catheter at 4 ml/s without a saline chaser. The scanning protocol incorporates a scan delay of 6 s followed by a helical CT of the abdomen and pelvis (64 × 0.625-mm collimation, rotation time 0.75 s, pitch 0.64, 120 kV, 154 mAs). With this technique it is possible to image the entire iliofemoral arterial tree with a very small amount of iodinated contrast (10–15 ml) (Fig. 19.4). Numerous technologic hardware innovations—including volume scanners with a greater number of detector rows, faster rotational speeds, iterative reconstruction method, and dual-energy CT imaging—may enable even lower doses of contrast to be required. Virtual endoscopy with CT is at times useful to estimate the distribution of calcium within the lumen along the vessel being considered for access (Fig. 19.5).

Technological advances in computed tomography imaging have improved spatial and temporal resolution without compromising on image quality (Box 19.1). These accomplishments were achieved through increases in the numbers of detectors and improved sampling capabilities in the z-direction. Improvements in image reconstruction, such as the development of iterative reconstruction techniques [14] and multi-segment reconstruction, have been shown to further enhance the signal-to-noise ratios and temporal resolution of cardiac computed tomography. Dual-source CT, which is constructed on the basis of two X-ray tubes and two detectors mounted on the CT gantry, with a mechanical offset of 90°, minimizes the limitations in temporal resolution of standard multidetector CT without the need for a faster gantry rotation. Using dual-source CT, Blanke et al. [15] were able to effectively study the aortic root anatomy and iliofemoral vasculature in a single acquisition using a single shot of 110–130 cc iodinated contrast and combined ECG-assisted scanning of the thorax and non-ECG-assisted scanning of the abdomen. Their experience indicates that adequate images could be achieved in nearly all patients using this method. Wuest et al. [16] further enhanced this protocol by using high-pitch spiral CT, which allows high-resolution imaging of large anatomical volumes in a short acquisition time. This technique also allows for the injection of significantly lower volumes of iodinated contrast (40 cc), which may be advantageous in patients with renal insufficiency or in high-risk AKI patients. Using high-pitch spiral CT, Wuest et al. were able to obtain all the standard aortic root and iliofemoral measurements required for the TAVR procedure.