Magnetic resonance imaging of the temporomandibular joint disc: feasibility of novel quantitative magnetic resonance evaluation using histologic and biomechanical reference standards

Abstract

Aims: To use the ultrashort time-to-echo magnetic resonance imaging (UTE MRI) technique to quantify short T2* properties (obtained through gradient echo) of a disc from the human temporomandibular joint (TMJ) and to corroborate regional T2* values with biomechanical properties and histologic appearance of the discal tissues.

Methods: A cadaveric human TMJ was sliced sagittally and imaged by conventional and UTE MRI techniques. The slices were then subjected to either biomechanical indentation testing or histologic evaluation, and linear regression was used for comparison to T2* maps obtained from UTE MRI data. Feasibility of in vivo UTE MRI was assessed in two human volunteers.

Results: The UTE MRI technique of the specimens provided images of the TMJ disc with greater signal-to-noise ratio (~3 fold) and contrast against surrounding tissues than conventional techniques. Higher T2* values correlated with lower indentation stiffness (softer) and less collagen organization as indicated by polarized light microscopy. T2* values were also obtained from the volunteers.

Conclusion: UTE MRI facilitates quantitative characterization of TMJ discs, which may reflect structural and functional properties related to TMJ dysfunction.

Figure 1

(A) UTE (TR=500 ms, TE=8 μs/6.6 ms), (B) T1-weighted (TR=500 ms, TE=15 ms), and (C) proton density-weighted fat-suppressed (TR=1800 ms, TE=11.7 ms) MR images of the TMJ in a cadaveric specimen show increased signal in the TMJ disc (straight arrows) situated between the articular eminence (star), mandibular fossa (circle) and mandibular condyle (rectangle) on the UTE MR image. The fibrocartilaginous articular surfaces (curved arrows) of the condyle (rectangle) and mandibular fossa (circle) are also characterized by linear bright signal intensity. The UTE MR sequence facilitates identification of these short T2 tissues through acquiring signal from them, not afforded by the standard clinical sequences.

Figure 2

(A) TMJ specimen slice was subjected to quantitative MRI and (B) biomechanical indentation testing and analyzed to yield (C) a T2* map and (D) indentation stiffness map of the sample TMJ disc. A general inverse relation between T2* and stiffness values are apparent.

Figure 3

Indentation stiffness of a TMJ disc was correlated with regional T2* values. Significant inverse relationship was found, where a high T2* value was associated with softer disc, suggesting possible deterioration.

Figure 4

Correspondence between MRI and histologic measures in a TMJ disc. (A) T2* map of TMJ disc was compared with its (B) Sirius red staining, (C) Safranin-O and fast green staining, and (D) a heat map for fiber orientation obtained by using qPLM methods. * represents the central region with low T2* value, less Safranin-O staining, and greater collagen orientation. O represents posterior region with the opposite characteristics.

Figure 5

(A) Left TMJ of a volunteer was imaged quantitatively using a 3D UTE MRI sequence, and analyzed to yield (B) a T2* map. (C) Goodness of the fit during the fitting.