Imaging tooth enamel using zero echo time (ZTE) magnetic resonance imaging

Abstract

In an event where many thousands of people may have been exposed to levels of radiation that are sufficient to cause the acute radiation syndrome, we need technology that can estimate the absorbed dose on an individual basis for triage and meaningful medical decision making. Such dose estimates may be achieved using in vivo electron paramagnetic resonance (EPR) tooth biodosimetry, which measures the number of persistent free radicals that are generated in tooth enamel following irradiation. However, the accuracy of dose estimates may be impacted by individual variations in teeth, especially the amount and distribution of enamel in the inhomogeneous sensitive volume of the resonator used to detect the radicals. In order to study the relationship between interpersonal variations in enamel and EPR-based dose estimates, it is desirable to estimate these parameters nondestructively and without adding radiation to the teeth. Magnetic Resonance Imaging (MRI) is capable of acquiring structural and biochemical information without imparting additional radiation, which may be beneficial for many EPR dosimetry studies. However, the extremely short T2 relaxation time in tooth structures precludes tooth imaging using conventional MRI methods. Therefore, we used zero echo time (ZTE) MRI to image teeth ex vivo to assess enamel volumes and spatial distributions. Using these data in combination with the data on the distribution of the transverse radio frequency magnetic field from electromagnetic simulations, we then can identify possible sources of variations in radiation-induced signals detectable by EPR. Unlike conventional MRI, ZTE applies spatial encoding gradients during the RF excitation pulse, thereby facilitating signal acquisition almost immediately after excitation, minimizing signal loss from short T2 relaxation times. ZTE successfully provided volumetric measures of tooth enamel that may be related to variations that impact EPR dosimetry and facilitate the development of analytical procedures for individual dose estimates.

Magnetic Resonance Imaging of Hard Tissues and Hard Tissue Engineered Bio-substitutes

“…However, when compared to the ZTE-MRI, μCT showed better signal from enamel and dental calculus as present on the tooth surface. When UTE-and ZTE-based images were compared, ZTE imaging showed a better contrast of both dentin and enamel as also confirmed by the quantification of the SNR for each imaging modalities [95,99].…”

“…CPC combined with a dedicated dual contrast agent (DCA) consisting of SPIO with a mean size of 200 nm, and gold nanoparticles (AuNPs) with a mean size of 4 nm (respectively, as MRI and CT contrast agent) was imaged in vivo by ZTE-MRI and CT after installation in rat femoral defects. Longitudinal ZTE acquisitions allowed the identification of the implanted CPC until 8 weeks post-implantation, while the CT contrast of the CPC was lost 4 weeks after implantation [99]. However, because of the strong susceptibility properties of the SPIO particles, a strong imaging artifact (named blooming effect) was observed on the ZTE-MR images.…”

Enhancing Precision in L-band Electron Paramagnetic Resonance Tooth Dosimetry: Incorporating Digital Image Processing and Radiation Therapy Plans for Geometric Correction

“…These results indicated that using GC with labial enamel area could improve the accuracy in D est . The effects of tooth dimensions on the A RIS from the tooth have been introduced (Williams et al 2014; Rychert et al 2015; Umakoshi et al 2017). GC using tooth labial enamel area showed improved accuracy in dose estimation (Park et al 2021).…”

“…Radiation-induced signals ( RIS s) can be significantly influenced by the position and geometry of the tooth when using an L-band EPR spectrometer (Demidenko et al 2007; Williams et al 2010; Rychert et al 2015; Desmet et al 2016; Umakoshi et al 2017; Fattibene et al 2023). Even with meticulous care in tooth positioning, the geometry can affect the measured RIS (mRIS) .…”

Factors Affecting the Quality of Tooth Enamel forIn VivoEPR-Based Retrospective Biodosimetry

“…It was demonstrated that a better reproducibility in measurements were obtained after normalization of the results by the tooth size (21) . Also, several works (22,23) evidenced that the geometry of the tooth as well as the geometry of the coil and the positioning of the tooth regarding to the surface coil were particularly important for dose estimation by EPR. In this context, works are also made to image and quantify tooth enamel using a magnetic resonance imaging technique (MRI) (zero echo time MRI) in order to evaluate relationship between enamel variations (in terms of size and defects) and dose estimations based on EPR (23) .…”