Abstract
Magnetic resonance imaging (MRI) is a non-invasive diagnostic imaging tool based on the detection of protons into the tissues. This imaging technique is remarkable because of high spatial resolution, strong soft tissue contrast and specificity, and good depth penetration. However, MR imaging of hard tissues, such as bone and teeth, remains challenging due to low proton content in such tissues as well as to very short transverse relaxation times (T2). To overcome these issues, new MRI techniques, such as sweep imaging with Fourier transformation (SWIFT), ultrashort echo time (UTE) imaging, and zero echo time (ZTE) imaging, have been developed for hard tissues imaging with promising results reported. Within this article, MRI techniques developed for the detection of hard tissues, such as bone and dental tissues, have been reviewed. The main goal was thus to give a comprehensive overview on the corresponding (pre-) clinical applications and on the potential future directions with such techniques applied. In addition, a section dedicated to MR imaging of novel biomaterials developed for hard tissue applications was given as well.
Highlights
Magnetic resonance imaging (MRI) is a non-invasive imaging technology that performs three-dimensional (3D) imaging for body organs with high spatial resolution (G 1 mm)
The state-of-art MRI techniques include 1) MR spectroscopy (MRS) and chemical shift imaging (CSI), which permit the identification and classification of tumors through the assessment of the chemical metabolism in a specific area of the body; 2) functional MRI, which is able to image the neuronal activity through the detection of the blood oxygenation level-dependent (BOLD) changes occurring in the brain; and 3) MR elastography (MRE), which can be used for the characterization of the biomechanical properties of soft tissues by the visualization of propagating shear waves [5,6,7]
MRI sequences for the imaging of hard tissues and biomaterials used for restoration of such tissues are becoming more and more advanced
Summary
Magnetic resonance imaging (MRI) is a non-invasive imaging technology that performs three-dimensional (3D) imaging for body organs with high spatial resolution (G 1 mm). Detection of P-31 content into bone tissue can be performed with UTE-CSI method [86] This approach is based on the minimization of the RF excitation as well as of the time delay between the end of the RF pulse and the start of the data acquisition. The exact materials composition was not described, the authors were able to estimate their relaxation properties, i.e., T1 = 223.1 ms and T2* = 0.295 ms [109] Dental restoration materials, such as amalgam and ceramic inlays, inserted in human molars have been imaged with high-resolution ZTE sequence and compared with μCT acquisitions. The relaxation properties of the CPC to follow its degradation in vivo [115]
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