Compositions and methods for use in medical diagnosis

A method for delineating and visualizing at least 50% of a tumor bed in a subject, wherein the tumor bed is the tissue covering the cavity obtained following tumor resection in the subject, and wherein the method comprises a step a) of depositing on the tumor bed in the subject a biocompatible gel comprising nanoparticles and/or nanoparticle aggregates wherein:

• i) the nanoparticles and/or nanoparticles of the aggregate comprise hafnium (IV) oxide (HfO2) or comprise gold and hafnium (IV) oxide (HfO2), each of said nanoparticles and/or said nanoparticle aggregate being covered with a biocompatible coating;
• ii) the concentration of the nanoparticle and/or nanoparticle aggregates in the biocompatible gel is about or less than 0.5% (w/w);
• iii) the biocompatible gel comprises cellulose, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, or hyaluronic acid;
• and iv) the apparent viscosity at 2 s−1 of the biocompatible gel comprising nanoparticles and/or nanoparticle aggregates is between about 1 Pa·s and about 750 Pa·s when measured between 20° C. and 37° C. and the gel is deposited in a layer having a thickness between 100 μm and 0.5 cm, wherein the nanoparticles and/or the nanoparticle aggregates of said gel delineate the tumor bed, and a step b) of visualizing at least 50% of the delineated tumor bed in the subject using X-ray imaging equipment.