Purpose To evaluate the sensitivity of quantitative MRI techniques (T1, T1,Gd, T2, continous wave (CW) T1ρ dispersion, adiabatic T1ρ, adiabatic T2ρ, RAFF and inversion-prepared magnetization transfer (MT)) for assessment of human articular cartilage with varying degrees of natural degeneration. Methods Osteochondral samples (n = 14) were obtained from the tibial plateaus of patients undergoing total knee replacement. MRI of the specimens was performed at 9.4 T and the relaxation time maps were evaluated in the cartilage zones. For reference, quantitative histology, OARSI grading and biomechanical measurements were performed and correlated with MRI findings. Results All MRI parameters, except T1,Gd, showed statistically significant differences in tangential and full-thickness ROIs between early and advanced osteoarthritis (OA) groups, as classified by OARSI grading. CW-T1ρ showed significant dispersion in all ROIs and featured classical laminar structure of cartilage with spin-lock powers below 1000 Hz. Adiabatic T1ρ, T2ρ, CW-T1ρ, MT and RAFF correlated strongly with OARSI grade and biomechanical parameters. Conclusion MRI parameters were able to differentiate between early and advanced OA. Furthermore, rotating frame methods, namely adiabatic T1ρ, adiabatic T2ρ, CW-T1ρ and RAFF, as well as MT experiment correlated strongly with biomechanical parameters and OARSI grade, suggesting high sensitivity of the parameters for cartilage degeneration.

Several laboratory and rotating frame quantitative MRI parameters were evaluated and compared for detection of changes in articular cartilage following selective enzymatic digestion. Bovine osteochondral specimens were subjected to 44h incubation in control medium or in collagenase or chondroitinase ABC to induce superficial collagen or proteoglycan (glycosaminoglycan) alterations. The samples were scanned at 9.4T for T1, T1Gd (dGEMRIC), T2, adiabatic T1ρ, adiabatic T2ρ, continuous-wave T1ρ, TRAFF2 and T1sat relaxation times and for magnetization transfer ratio (MTR). For reference, glycosaminoglycan content, collagen fibril orientation and biomechanical properties were determined. Changes primarily in the superficial cartilage were noted after enzymatic degradation. Most of the studied parameters were sensitive to the destruction of collagen network, whereas glycosaminoglycan depletion was detected only by native T1 and T1Gd relaxation time constants throughout the tissue and by MTR superficially. T1, adiabatic T1ρ, adiabatic T2ρ, continuous-wave T1ρ, and T1sat correlated significantly with the biomechanical properties while T1Gd correlated with glycosaminoglycan staining. The findings indicated that most of the studied MRI parameters were sensitive to both glycosaminoglycan content and collagen network integrity, with changes due to enzymatic treatment detected primarily in the superficial tissue. Strong correlation of T1, adiabatic T1ρ, adiabatic T2ρ, continuous-wave T1ρ and T1sat with the altered biomechanical properties, reflects that these parameters were sensitive to critical functional properties of cartilage.

The results revealed that passive diffusion of Gd-DTPA²⁻ was significantly slower than previously assumed, leading to overestimation of the GAG content at equilibrating times of few hours. Moreover, Gd-DTPA²⁻ distribution was found to depend not only on GAG content, but also on collagen content and diffusion direction. Interestingly, the dGEMRIC technique was found to be most sensitive to cartilage degradation in the early stages of diffusion process, suggesting that full equilibrium between gadopentetate and cartilage may not be required in order to detect cartilage degeneration.

Threose treatment induced collagen cross-linking and changes in the properties of articular cartilage, which were detected by T1, T1Gd and T1ρ relaxation time constants. Cross-linking should be considered especially when interpreting the outcome of contrast-enhanced MRI in aging populations.

Adequate reproduction of low contrast image detail is essential for accurate diagnosis in diagnostic radiology. Artinis CDRAD and Leeds Test Object TO20 are commercially available test objects that can be used to test this aspect of imaging performance in digital radiography. Automated analysis software is available for both test objects (CDRAD Analyser and AutoPIA (TO20)). This study evaluated and compared both test objects and software, including their sensitivity to changes in exposure parameters and image processing. Images of the test objects were acquired in scatter and scatter-free environments and analysed using a range of metrics derived from automated analysis, visual assessment and manual contrast-to-noise ratio measurements. The CNR (TO20) and correctly identified holes (%) (CDRAD) were found to be the most sensitive to changes in exposure conditions. The total number of detected discs (TO20) was the least sensitive. None of the image quality metrics was sensitive to a change in image processing. Other methods, such as anthropomorphic phantoms, would therefore be required to evaluate changes in clinical image processing. The results of this investigation help to inform best use of these test objects in routine quality control and image quality benchmarking for optimisation.