Biphasic split-bolus injection protocol for routine contrast-enhanced chest CT: comparison with conventional early-phase single bolus technique.

Abstract

To present a routine contrast-enhanced chest CT protocol with a split-bolus injection technique achieving combined early- and delayed phase images with a single aquisition, and to compare this technique with a conventional early-phase single-bolus chest CT protocol we formerly used at our institution, in terms of attenuation of great thoracic vessels, pleura, included hepatic and portal venous enhancement, contrast-related artifacts, and image quality. A total of 202 patients, who underwent routine contrast-enhanced chest CT examination aquired with either conventional early-phase single-bolus technique (group A,n = 102) or biphasic split-bolus protocol (group B,n = 100), were retrospectively included. Attenuation measurements were made by two radiologists independently on mediastinal window settings using a circular ROI at the following sites: main pulmonary artery (PA) at its bifurcation level, thoracal aorta (TA) at the level of MPA bifurcation,portal vein (PV) at porta hepatis, left and right hepatic lobe, and if present, thickened pleura (>2 mm) at the level with the most intense enhancement. Respective normalized enhancement values were also calculated. Contrast-related artifacts were graded and qualitative evaluation of mediastinal lymph nodes was performed by both reviewers independently. Background noise was measured and contrast-to-noise ratios (CNRs) of the liver and TA were calculated. While enhancement of thoracic vessels and normalised MPA enhancement did not differ significantly between both groups (p > 0.05), enhancement and normalised enhancement of pleura, liver parenchyma and PV was significantly greater in group B (p < 0.001). Perivenous artifacts limiting evaluation were less frequent in group B than in A and mediastinal lymph nodes were judged to be evaluated worse in group A than in group B with an excellent agreement between both observers. No significant difference was detected in CNRTA (p = 0.633), whereas CNR liver was higher in group B (p < 0.001). Our split-bolus chest CT injection protocol enables simultaneous enhancement for both vascular structures and soft tissues, and thus, might raise diagnostic confidence without the need of multiple acquisitions. We think that this CT protocol might also be a promising alternative in lung cancer staging, where combined contrast-enhanced CT of the chest and abdomen is indicated. We therefore suggest to further evaluate its diagnostic utility in this setting, in particular in comparison with a late delayed chest-upper abdominal CT imaging protocol.