What’s most important to consider in vascular enhancement?

Achieving adequate enhancement in the vessels is the foremost technical concern for CT
Angiography (CTA), and Iodine Flow Rate (also referred to as iodine-administration rate or flux)
is a key consideration in contrast protocol design. Typically, high flow rates must be used at
CTA to ensure optimal contrast enhancement -- particularly when imaging with 64 and greater
detector CT scanners. Scan timing plays a critical role in obtaining ideal enhancement of
vascular regions of interest. To optimize diagnostic quality, scan delays should be computed
factoring in patient and study variables (including contrast concentration) as well as the scanner
type. Cardiac output is the most important patient variable to consider in designing protocols for
vascular studies. Because cardiac output is difficult to measure non-invasively, patient weight
and features of timing-bolus injections are appropriate features for estimating the effects of
cardiac output on contrast bolus propagation.

What’s important to consider about IV access with high CTA flow rates?

Especially with current scanners, optimal contrast enhancement at CTA requires intravenous
access with a catheter capable of administering iodinated contrast at a high injection rate using
a power injector. ACR Practice Guidelines for performance and interpretation of CTA suggest
technologists place a 20-guage or larger needle in the vein at or above the elbow level.²

How does achieving optimal parenchymal enhancement differ from vascular
enhancement?

For purely parenchymal studies, body weight (and, arguably, body surface area) is the most
important patient variable. If the scan is initiated without bolus-tracking software, the injection
duration should be considered when computing the fixed scan delay. The most important
contrast protocol variable for ensuring consistent and appropriate parenchymal enhancement is
the iodine dose (volume of contrast times the concentration). Flow rate is less of a concern,
except for studies in which an arterial phase is mandated. Tailoring iodine volume (iodine mass)
according to patient weight (measured in amount of iodine per body weight) directly impacts the
magnitude of parenchymal enhancement.

What additional variables are important in optimizing CT opacification?

Industry focus in two additional areas has increased in recent years. Higher-end scanners have
heightened the technical complexity of contrast enhancement and the need to reconsider
contrast protocol design for each patient and examination. Although the impact is less direct,
the relationship between contrast enhancement and radiation-dose management also continues
to gain attention in this area.

How does radiation dose relate to contrast enhancement?

Improved diagnostic quality and image consistency can help reduce the radiation exposure
associated with unnecessary rescans. Tailoring contrast dose can be a natural extension of
radiation-dose management to each patient and examination – each of which represents one
facet of widespread growth in personalized radiology.

What challenges are important to recognize in implementing personalized contrast
protocol design?

Protocol personalization is a specialized and continually evolving area. Without adequate
support and tools, individualizing protocols can challenge workflow, quality and consistency.
MEDRAD’s P3T® software makes personalizing protocols practical at the point-of-care. It’s
exciting and rewarding to be part of this growth, and to innovate in ways that help make a
difference for our customers and their patients.

References:

1. Presented at Society of Thoracic Radiology (2008) Poster Session; Christopher R. Deible, MD, PhD. Study supported by MEDRAD.

2. American College of Radiology (ACR). ACR Guidelines and Technical Standards. ACR Practice Guidelines for performance and
interpretation of CTA. Revised 2005 (Res. 27)* Amended 2009 (Resolution 11)