Sirius the First Positive-Signal MRI Marker

T1W MR Image of Sirius MRI Markers


T2W MR Image of Sirius MRI Markers


The Sirius MRI Marker has been demonstrated to be visible with T1W and T2W signals, and can positively identify the location of implanted radioactive seeds.

The superior image quality of MRI could improve the accuracy of prostate contouring.

If seeds could be readily localized with MRI, it could reveal the true relationship of radiation dose to the prostate and critical dose-limiting structures.

No impact on treatment planning and delivery
— Sirius simply replaces seed spacers

MRI Marker in Brachytherapy Strand

C4 Imaging has developed a novel positive-signal MRI Marker for seed localization, which could allow physicians to effectively incorporate MRI into post-treatment assessment.

T1W MR Image of Sirius MRI Markers

The Sirius MRI Marker consists of a sealed biocompatible, polymer capsule containing C4, a unique MRI agent. The length of each capsule is 5.5 mm and the diameter is 0.8 mm. The Sirius MRI Marker is intended to be implanted as a brachytherapy seed spacer that will facilitate the anatomical post-implant localization of seeds.

Anisotropy measurements taken when attached to Iodine 125 seeds were equivalent to the standard TG43U parameters. 6 A Monte Carlo study was performed to assess the impact on a simulated prostate implant. The Sirius MRI Markers does not alter radiation treatment delivery when compared with a standard seed spacer. 7


  1. Frank SJ, et al. Anisotropy characterization of I-125 seed with attached encapsulated cobalt chloride complex contrast agent markers for MRI-based prostate brachytherapy. Med Dosim. 2011 36(2): 200-205.
  2. Melhus C, et al. Dosimetric Influence of Brachytherapy Seed Spacers. Brachytherapy. 2011 10(1, Suppl): S94 - S95 (#PD71)