Rigid fixation for facial osteotomies in fibrous dysplasia: a histological study

Palpation is routinely used for the evaluation of mechanical properties of tissue in regions that are accessible to touch. This means of detecting pathology using the “stiffness” of the tissue is more that 2000 years old. Even today it is common for surgeons to find lesions during surgery that have been missed by advanced imaging methods. Palpation is subjective and limited to individual experience and to the accessibility of the tissue region to touch. It appears that a means of noninvasively imaging elastic modulus (the ratio of applied stress to strain) may be useful to distinguish tissues and pathologic processes based on mechanical properties such as elastic modulus [1]. To this end many approaches have been developed over the years [2–9]. The approaches have been to use conventional imaging methods to measure the mechanical response of tissue to mechanical stress. Static, quasi-static or cyclic stresses have been applied. The resulting strains have been measured using ultrasound [1–9] or MRI [10–15] and the related elastic modulus has been computed from visco-elastic models of tissue mechanics. Recently a new MRI phase contrast technique has been reported in which transverse strain waves propagating in tissue are imaged [13, 14, 16]. Because the wavelengths of propagating waves are related to density and the shear modulus and because the wavelengths of transverse waves for low frequency is on the order of millimeters this method promises to have good resolution and to be sensitive to the shear modulus. This paper reviews the theory of the method, presents some applications and discusses the implications of the method

Absolute temperature imaging using intermolecular multiple quantum MRI

PURPOSE: A review of MRI temperature imaging methods based on intermolecular multiple quantum coherences (iMQCs) is presented. Temperature imaging based on iMQCs can provide absolute temperature maps that circumvent the artefacts that other proton frequency shift techniques suffer from such as distortions to the detected temperature due to susceptibility changes and magnetic field inhomogeneities. Thermometry based on iMQCs is promising in high-fat tissues such as the breast, since it relies on the fat signal as an internal reference. This review covers the theoretical background of iMQCs, and the necessary adaptations for temperature imaging using iMQCs. MATERIALS AND METHODS: Data is presented from several papers on iMQC temperature imaging. These studies were done at 7T in both phantoms and in vivo. Results from phantoms of cream (homogeneous mixture of water and fat) are presented as well as in vivo temperature maps in obese mice. RESULTS: Thermometry based on iMQCs offers the potential to provide temperature maps which are free of artefacts due to susceptibility and magnetic field inhomogeneities, and detect temperature on an absolute scale. CONCLUSIONS: The data presented in the papers reviewed highlights the promise of iMQC-based temperature imaging in fatty tissues such as the breast. The change in susceptibility of fat with temperature makes standard proton frequency shift methods (even with fat suppression) challenging and iMQC-based imaging offers an alternative approach