Standardisation of liver MDCT by tracking liver parenchyma enhancement to trigger imaging

OBJECTIVE:To assess parenchymal bolus-triggering in terms of liver enhancement, lesion-to-liver conspicuity and inter-image variability across serial follow-up MDCTs.METHODS:We reviewed MDCTs of 50 patients with hepatic metastases who had a baseline CT and two follow-up examinations. In 25 consecutive patients CT data acquisition was initiated by liver parenchyma triggering at a 50-HU enhancement threshold. In a matched control group, imaging was performed with an empirical delay of 65 s. CT attenuation values were assessed in vessels, liver parenchyma and metastasis. Target lesions were classified according to five enhancement patterns.RESULTS:Compared with the control group, liver enhancement was significantly higher with parenchyma triggering (59.8 ± 7.6 HU vs. 48.8 ± 11.2 HU, P = 0.0002). The same was true for conspicuity (liver parenchyma - lesion attenuation) of hypo-enhancing lesions (72.2 ± 15.9 HU vs. 52.7 ± 19.4 HU, P = 0.0006). Liver triggering was associated with reduced variability for liver enhancement among different patients (P = 0.035) and across serial follow-up examinations in individual patients (P < 0.0001). The number of patients presenting with uniform lesion enhancement pattern across serial examinations was significantly higher in the triggered group (20 vs. 11; P = 0.018).CONCLUSION:Liver parenchyma triggering provides superior lesion conspicuity and improves standardisation of image quality across follow-up examinations with greater uniformity of enhancement patterns. KEY POINTS : • Liver parenchyma tracking improves liver enhancement and lesion-to-liver conspicuity in abdominal CT • In serial CT studies this technique reduces variability of conspicuity and enhancement patterns • Higher liver-to-lesion conspicuity is a prerequisite for reliable detection of liver lesions • Stabilisation of enhancement permits more accurate follow-up of oncology patients.