Calibration standard of body tissue with magnetic nanocomposites for MRI and X-ray imaging

• We developed a joint long-term stable calibration phantom of MNC enriched biological tissue which is suitable for MRI and XCT.
• The phantoms were tested with SQUID, NMR, ICP-MS, MRI and XµCT.
• We determined out a shared sensitivity range for MRI and XµCT.
• PG-MNC phantoms are suitable as long-term stable phantoms of biological tissues enriched with MNC for MRI and XµCT.

We present a first study of a long-term phantom for Magnetic Resonance Imaging (MRI) and X-ray imaging of biological tissues with magnetic nanocomposites (MNC) suitable for 3-dimensional and quantitative imaging of tissues after, e.g. magnetically assisted cancer treatments.We performed a cross-calibration of X-ray microcomputed tomography (XµCT) and MRI with a joint calibration standard for both imaging techniques. For this, we have designed a phantom for MRI and X-ray computed tomography which represents biological tissue enriched with MNC.The developed phantoms consist of an elastomer with different concentrations of multi-core MNC. The matrix material is a synthetic thermoplastic gel, PermaGel (PG).The developed phantoms have been analyzed with Nuclear Magnetic Resonance (NMR) Relaxometry (Bruker minispec mq 60) at 1.4 T to obtain R2 transverse relaxation rates, with SQUID (Superconducting QUantum Interference Device) magnetometry and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to verify the magnetite concentration, and with XµCT and 9.4 T MRI to visualize the phantoms 3-dimensionally and also to obtain T2 relaxation times. A specification of a sensitivity range is determined for standard imaging techniques X-ray computed tomography (XCT) and MRI as well as with NMR.These novel phantoms show a long-term stability over several months up to years. It was possible to suspend a particular MNC within the PG reaching a concentration range from 0 mg/ml to 6.914 mg/ml.The R2 relaxation rates from 1.4 T NMR-relaxometry show a clear connection (R2=0.994) with MNC concentrations between 0 mg/ml and 4.5 mg/ml. The MRI experiments have shown a linear correlation of R2 relaxation and MNC concentrations as well but in a range between MNC concentrations of 0 mg/ml and 1.435 mg/ml.It could be shown that XµCT displays best moderate and high MNC concentrations. The sensitivity range for this particular XµCT apparatus yields from 0.569 mg/ml to 6.914 mg/ml.The cross-calibration has defined a shared sensitivity range of XµCT, 1.4 T NMR relaxometer minispec, and 9.4 T MRI. The shared sensitivity range for the measuring method (NMR relaxometry) and the imaging modalities (XµCT and MRI) is from 0.569 mg/ml, limited by XµCT, and 1.435 mg/ml, limited by MRI.The presented phantoms have been found to be suitable to act as a body tissue substitute for XCT imaging as well as an acceptable T2 phantom of biological tissue enriched with magnetic nanoparticles for MRI.