A Feasibility Study to Assess the Use of Gadolinium in Computed Tomography

Although safe in most patients, iodine may be associated with lifethreatening adverse events, particularly in high-risk patient. This application is of particular clinical significance in patients with conditions like pulmonary embolism which could be fatal. CT pulmonary angiogram (CTPA) with sensitivity of 83-100% and specificity of 89-97% is currently the gold standard for diagnosis of pulmonary embolism. However, in patients who have allergy to iodinated contrast agent, CTPA cannot be performed. Gadolinium based contrast agent can serve as a viable alternative in such patients and can be used for Gadolinium enhanced MR pulmonary angiography (MRPA) and CTPA. Gadolinium enhanced MRPA however has inherent limitations in evaluating pulmonary embolism as evident from multicentre prospective study (PIOPED III) which reported technically inadequate exams in as many as 25% of patients (range 11% to 52%). The MRPA sensitivity was also low in the range of 78%. Moreover, unlike CT, low spatial and temporal resolution of MR hampers precise evaluation of lung parenchyma. Previously investigators have evaluated gadolinium enhanced CTPA on a single energy CT (SECT) at different tube potential (80 - 120 kV) and reported encouraging results. However, these patients received higher volume of gadolinium contrast (mean 53 ml, range 30-64 ml) and in spite, the scans performed at 120 kV demonstrated overall suboptimal pulmonary artery enhancement. These limitations can be potentially over come with dual-energy CT which simultaneously acquires low and high energy data. From this data, monochromatic images can be reconstructed at any desired energy from 40 keV to 140 keV.

The investigators aim to recruit up to 50 patients who will guide in determining gadolinium contrast volume, injection rate and image delay required to maximize pulmonary arterial enhancement.