MRI Phantoms – Are There Alternatives to Agar?

Abstract

The suitability of different gelling agents as MRI phantoms was evaluated in terms of homogeneity, gel stability and reproducibility. Time and effort for preparation were also taken into account. The relaxation times of various gel compositions were estimated. Carbomer-980 and Carbopol-974P were determined to be promising novel phantom materials. These gelling agents are readily available, inexpensive and easy to handle given that thermal treatment is not required. Furthermore, the viscoelasticity of their polymer network is pH-dependent. With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing. This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications. Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging).

Phantoms for diffusion-weighted imaging and diffusion tensor imaging quality control: a review and new perspectives

“…It is observed that synthetic polymer-based gels can be a good alternative to agar, because of their long-term stability and easy synthesis (Hellerbach et al, 2013). The main advantage of gel applications in DWI and DTI phantoms (which have fiber bundles and/or other structures where diffusion is anisotropic) is the reduction of flow and convective effects that cause image artifacts (Hellerbach et al, 2013).…”

“…Some authors say that is impossible to build a multi-purpose MRI phantom (Hellerbach et al, 2013). They are based on the fact that each technique requires specific structures and materials with T1 and T2 compatible to the studied parameter (e.g.…”

“…There are phantoms of isotropic diffusion for DWI (typically spheres or cylinders filled by liquid) (Laubach et al, 1998;Lavdas et al, 2013;Pierpaoli et al, 2009); fiber phantoms to simulate axonal tracts or cardiac muscle (Fieremans et al, 2008;Lorenz et al, 2008;Teh et al, 2016); phantoms made of capillary or microcapillary arrays permeated by liquid with diffusion properties and/or relaxation times similar to biological tissues (Ebrahimi et al, 2010) test tubes with different solutions (Pierpaoli et al, 2009;Tofts et al, 2000); biological phantoms, such as green asparagus inside a water container (Latt et al, 2007); or animal tissues (axons of pigs or mice) (Chen et al, 2014;Komlosh et al, 2008). There are gels, for isotropic or anisotropic diffusion studies, whose magnetic properties are similar to healthy or pathological tissue (Hellerbach et al, 2013;Kato et al, 2005). Some authors propose applying the ACR MRI head phantom to evaluate scanner parameters related to degradation of DWI and DTI images, such as SNR, low contrast detectability and uniformity (Wang et al, 2011).…”

“…Those equations can be useful for the development of gels for DWI and DTI QC (Kato et al, 2005). Gels of sodium alginate, xanthan gum, FAVOR-PAC-300, PNC-, Carbomer-980 and Carbopol-974P have also been tested as an alternative to agar or agarose (Hellerbach et al, 2013). It was observed that images of gels had less distortion than images of liquids due to reduction of the macroscopic flow effect.…”

“…In other words, changes in the MRI scanner tend to degrade DWI and DTI images before they compromise T1, T2 and PD-weighted scans. Recent studies have suggested phantoms for QC of diffusion acquisitions, based on different kinds of materials and a variety of geometries (Fieremans et al, 2008;Hellerbach et al, 2013;Hubbard et al, 2015;Teh et al, 2016). This work provides an overview of current literature related to this issue, highlighting the progress made and the main challenges to overcome, as well as prospects to standardization of diffusion images' QC.…”