OPTIMISATION OF CONTRAST AGENT ADMINISTRATION FOR CT AND MRI

During the PhD course my research projects focused mainly on the effectiveness, safety and optimisation of contrast agents in computed tomography (CT) and magnetic resonance imaging (MRI), subdivided into different studies. This doctoral thesis aims at explore the possible optimisation of contrast medium administration protocols in different clinical contexts. In the first section of my thesis, we proposed two studies focused on the optimisation of the practice of iodinated contrast medium (ICM) injection in CT. First, we tried to verify the conditions for a change in the dose calculation to be administered in patients undergoing an abdominal CT. Since decades, it is an established practice to inject a dose of ICM calculated on the patient total body weight (TBW). However, this approach does not consider the different volume of biodistribution among patients with different body mass index (BMI). Indeed, it was demonstrated that the ICM poorly distributes in adipose tissue and obese patients may receive a higher dose than that really needed. We have hypothesized that dosing ICM as based on the lean body weight (LBW) would be a more appropriate approach. We firstly retrospectively calculated an ICM dose based on LBW that was equivalent to the dose based on TBW in terms of liver contrast enhancement (LCE). We found that the injected ICM dose was highly variable, with underweight patients receiving a higher dose than obese patients, as a radiologist-driven compensation effect. Starting from the results obtained from the retrospective study, we conducted a randomized controlled trial based on the dose equivalent between the ICM based on patient TBW and the dose calculated using LBW. The Ethics Committee approved the single-center, double-blinded randomized controlled trial (trial registration NCT03384979). Patients were randomized to LBW-based ICM dose (0.61 gI/kg of lean body weight), or TBW-based ICM dose (0.44 gI/kg of TBW) and these equivalent doses derived from the retrospective study. In conclusion, LBW- and TBW-based ICM doses lead to a similar LCE with no significantly different variation for the LBW group, negating the study hypothesis and highlighting the knowledge gap about factors affecting LCE. The last part of the section I aimed to systematically review contrast-enhanced spectral mammography (CESM) studies, focusing on adopted CESM technique, ICM issues and adverse reactions ICM related. Of 120 retrieved articles, 84 were included, totalling 14,012 patients. Contrast type and concentration was reported in 79/84 studies (94%), with Iohexol 350 mgI/mL mostly used (25/79, 32%), dose and flow rate in 72/84 (86%), with 1.5 mL/kg dose at 3 mL/s in 62/72 studies (86%). Thirty adverse reactions were reported by 14/84 (17%) studies (26 mild, 3 moderate, 1 severe non-fatal) with a pooled rate of 0.82%. Factory-set kVp, contrast 1.5-mL/kg at 3 mL/s, and 120-s acquisition delay were mostly used and only 1 severe adverse reaction was reported. In the second PhD thesis section, I focused on gadolinium-based contrast agent (GBCA) protocol issues. A systematic review was conducted in collaboration with the University College Dublin (Dublin, Ireland) during the six months fellowship and it was regarding GBCA administration protocols used for cardiothoracic applications of time-resolved (TR) magnetic resonance angiography (MRA) sequences. A search of the literature was performed to identify articles utilising TR-MRA sequences, focusing on type of sequence, adopted technical parameters, GBCA issues and acquisition workflow. Of 117 retrieved articles, 16 matched the inclusion criteria and study population ranged from 5 to 185 patients, for a total of 506 patients who underwent cardiothoracic TR-MRA. The administered GBCA was gadobutrol (Gadovist) in 6/16 (38%) articles, gadopentetate dimeglumine (Magnevist) in 5/16 (31%), gadobenate dimeglumine (Multihance) in 2/16 (13%), gadodiamide (Omniscan) in 2/16 (13%), gadofosveset trisodium (AblavarTM) in 1/16 (6%). GBCA showed highly variable doses among studies: fixed amount or based on patient body weight (0.02–0.2 mmol/kg). In conclusions, a consensus on technique for cardiothoracic applications of TR-MRA is still far from reached, mostly due to differences regarding contrast agent type and dose. Further studies are warranted to provide a common standardised acquisition protocol.