Preclinical magnetic resonance imaging in the presence of Alpha-DaRT seeds: mitigation of metal artifacts

<i>Objective</i>. Diffusing alpha-emitters radiation therapy (Alpha-DaRT) involves implanting stainless-steel seeds containing 70-200 kBq of²²⁴Ra into solid tumors. The decay of²²⁴Ra generates alpha particles and short-lived alpha-emitting atoms, which diffuse and deposit absorbed dose up to millimeters from the seed. As magnetic res- onance imaging (MRI)-guided brachytherapy is commonly used in colorectal cancer, it has also been adopted in pre-clinical orthotopic intra-rectal studies to investigate the therapeutic potential of Alpha-DaRT. However, the metallic seeds cause metal artifacts in MRI, distorting signals and degrading images. Overcoming these artifacts is essential for accurate tumor assessment and treatment planning. This study aimed to reduce metal artifacts in images acquired with 7 T pre-clinical MRI in the presence of Alpha-DaRT seeds using an orthotopic colorectal adenocarcinoma animal model.<i>Approach</i>. Inert seeds were imaged in gelatin phantoms and the dorsal cavity of a mouse carcass. For the<i>in-vivo</i>animal model, NOD scid gamma mice with HT-29 colorectal adenocarcinoma tumors (∼5-7 mm) were injected with inert seeds. MRI sequence parameters such as echo and repetition times, slice thickness, and readout bandwidth were tested using the phantom and refined with carcass imaging, leading to<i>in-vivo</i>imaging.<i>Main results</i>. Multiple sequence protocols were tested on gelatin phantoms and compared to the original T₂-weighted turbo spin echo (TSE) sequence protocol. An improved T₂-weighted TSE sequence protocol reduced metal artifact volumes in the gelatin phantom from 147.8 ± 31.0 mm³to 87.0 ± 22.4 mm³in the axial slices, resulting in a 41% reduction. Validation in the mouse carcass confirmed high-quality soft-tissue imaging.<i>In-vivo</i>images with live mice showed a statistically significant reduction (p<i><</i>0.001) in metal artifact volume with the improved sequence.<i>Significance</i>. A T₂-weighted turbo spin echo protocol effectively mitigated metal artifacts from Alpha-DaRT seeds in a colorectal adenocarcinoma animal model, allowing for clearer visualization of seed placement within the tumor and improving the accuracy of pre-clinical studies.