Additional contents from webparts: Bolus injections result in a rapid increase in signal intensity until a plateau is reached and there is then a gradual decay in contrast concentration, the rate of which varies in each patient. There is a theoretical point at which there is a ‘steady-state’ concentration of contrast, but this cannot be predicted because peak signal intensity is affected by numerous factors including, for example, cardiac output and the rate of injection of contrast. Bolus injections are acceptable for studies in which the aim is to improve endocardial border delineation (EBD), perform left ventricular opacification (LVO) or enhance Doppler signals. We recommend that it is avoided during perfusion studies, when an infusion is preferable.
Continuous infusion provides a steady state concentration of microbubbles and reduces the likelihood of artefacts. It also allows calculation of myocardial blood flow, as both myocardial blood volume and microbubble velocity can be calculated if there is a steady-state concentration of contrast. Continuous infusions can also be used for EBD or LVO purposes but are mandatory for perfusion imaging.
Table 1: Summary of advantages and disadvantages of bolus vs. infusion of contrast
|Easy to perform||Short duration of contrast effect|
|Rapid enhancement||Changing contrast effects during study|
|Bolus timing can be challenging|
|Increased chance of contrast artefacts|
|2nd operator required for injection(s)|
|Extends enhancement time||More complex; requires infusion pump|
|Consistent contrast effect||Infusion titration takes time / effort|
|Recording can be repeated under comparable conditions||Stability of microbubbles can be an issue if syringe pump not well rotated|
|Reduced likelihood of artefacts such as blooming / shadowing||If no pump available, 2nd person needed to agitate contrast continuously|
|Easy to adjust dose when scanning to suit each patient's needs|
|Allows quantification of myocardial blood flow and thus coronary flow reserve (during stress imaging)|
The figures above demonstrate the concentration curves for a contrast agent after bolus injection or continuous infusion administration. Though the bolus may reach a higher peak concentration, this is often above the dynamic range of the system (see previous Chapter 1.2 Machine settings) resulting is saturation of the image. The concentration also falls much faster, thus dropping below the dynamic range of the system resulting in lack of contrast effect. The curve for infusion clearly demonstrates the longer lasting effect, which occurs because the concentration is maintained within the dynamic range of the machine for a considerably longer time period.
< Previous chapter: An introduction to contrast
> Next page