[68Ga]Ga-NODAGA-TriGalactan, a low molecular weight tracer for the non-invasive imaging of the functional liver reserve

BACKGROUND

Determination of the functional liver mass is important in a variety of clinical settings including liver surgery and transplantation. [99mTc]Tc-diethylenetriamine-pentaacetic acid galactosyl human serum albumin (99mTc-GSA) is a radiotracer targeting the asialoglycoprotein receptor (ASGR) and is routinely used in Japan for this purpose. Here we describe the development and evaluation of [68Ga]Ga-NODAGA-TriGalactan a low molecular weight PET-tracer targeting this structure.

RESULTS

For synthesis TRIS as branching unit and NODAGA as chelator for labelling with [68Ga]Ga are included. Three galactose moieties are conjugated via a click chemistry approach resulting in the desired labelling precursor.68Ga-labelling could be accomplished in high radiochemical yield and purity. [68Ga]Ga-NODAGA-TriGalactan is very hydrophilic and revealed high plasma stability and low plasma protein binding. Fluorescence imaging showed binding on ASGR-positive organoids and the IC50-value was in the nanomolar range. Most importantly, both biodistribution as well as animal imaging studies using normal mice demonstrated high liver uptake with rapid elimination from all other organs leading to even higher liver-to-background ratios as found for 99mTc-GSA.

CONCLUSION

[68Ga]Ga-NODAGA-TriGalactan shows high in vitro stability and selectively binds to the ASGR allowing imaging of the functional liver mass with high contrast. Thus, our first generation compound resulted already in an alternative to 99mTc-GSA for imaging the functional liver reserve and might allow the broader use of this imaging technique.

Comparison of the efficacy of the gadoxetic acid MRI-derived relative enhancement index (REI) and functional liver imaging score (FLIS) in predicting liver function: validation with Albumin-Bilirubin (ALBI) grade

PURPOSE

This study compared the predictive performance of the relative enhancement index (REI) derived from gadoxetic acid (GA)-enhanced MRI with that of the functional liver imaging score (FLIS) in estimating liver function among patients with chronic liver disease (CLD) or liver cirrhosis (LC) by validating them with the albumin-bilirubin (ALBI) grade.

MATERIALS AND METHODS

We retrospectively examined 166 patients (79 women, 87 men; 57.4 years) who were diagnosed with LC or CLD and underwent GA-enhanced MRI between August 2020 and September 2023. The enhancement ratio (ER) is calculated using the formula: ER = [hepatobiliary phase liver signal (SI HBP20)-precontrast liver signal (SI pre)]/SI pre. The REI is calculated using the formula: REI = Liver Volume (LV) × ER. FLIS was assigned from the sum of three HBP image features, each scored between 0 and 2: liver parenchymal enhancement, biliary contrast excretion, and portal vein sign. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cutoff values of ER, REI, and FLIS in differentiating between ALBI grades. The area under the curve (AUC), accuracy, sensitivity, and specificity were calculated for REI and FLIS to distinguish the ALBI grades. Spearman's rank correlation was used to evaluate the ER, REI, and FLIS correlations between the ALBI grades. To evaluate inter-reader reliability for LV, ER, REI, and FLIS, intraclass correlation coefficient (ICC) was used.

RESULTS

ROC curve analysis showed that the optimal cutoff value of REI for predicting ALBI Grade 1 was 899-905 for readers 1 and 2 and 461-477 for ALBI Grade 3, respectively. REI performed best in predicting ALBI Grade 1, achieving an accuracy range of 94%-92.2%, sensitivity of 94.9%-94.1%, and specificity of 91.7%-87.5% for readers 1 and 2, respectively. All parameters showed high accuracy in distinguishing ALBI Grade 3 from other grades. However, REI outperformed the others, showing an accuracy range of 98.8%-97.6%, sensitivity of 94.4%-94.4%, and specificity of 99.3%-98% for readers 1 and 2, respectively. REI showed the best and very strong correlation with ALBI for both readers.

CONCLUSION

REI showed a very strong correlation with the ALBI grades for assessing liver function. It outperformed FLIS in predicting the ALBI grades, indicating its potential as a radiologic tool comparable to or better than FLIS in predicting liver function, especially given its dependence on liver volume.