La Radiologia medica
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La Radiologia medica · May 2003
Contrast medium injection optimisation in spiral CT for the diagnosis of pulmonary embolism.
Spiral CT, normally a highly accurate diagnostic method to diagnose pulmonary embolism, has its weak point in the synchronisation of contrast medium (CM) injection and the start of the acquisition, essential to obtain optimal vascular enhancement. The aim of this paper is to introduce a method to control the CM injection based on the enhancement of blood vessels in the diagnosis of pulmonary embolism. ⋯ In order to be diagnostically useful, spiral CT requires good vascular enhancement and synchronisation of the start of acquisitions with the highest concentration of CM, as an incorrect scan delay will lead to artefacts and interpretation errors. The proposed method allows correct timing of the CM injection. The diagnostic bolus is preceded by a slow-flow timing bolus that is intercepted by the electronic trigger, which starts the scan when the CM passes into the right heart and pulmonary arteries. The slow-flow bolus volume was 30 ml injected at 1.5 ml/s, whereas the volume of the real bolus was 100 ml, injected at 4.5 ml/s. Monitor scans were performed with the trigger ROI centred on the right heart (trigger value set at 30/35 HU). The time needed for the complete spiral CT exam did not exceed 30 min. The first low-flow bolus injection takes approximately 10 min, but this time becomes shorter as the operator's experience grows. The correct positioning of the ROI on the right heart is the most time-consuming step in the procedure. The procedure was well accepted by all patients with no complaints due to the CM or to the duration of the procedure. There is a high level of concordance between arterial enhancement and image quality. In conclusion, the proposed method is simple, easy to reproduce, and does not give rise to interpretation problems. It is well accepted by patients and suffers few limitations, mainly represented by patients with severe cardiac arrhythmia.