| Objective Use of MR imaging to detect normal pig knee joint cartilage morphology and measure articular cartilage of pigs'knee of normal and osteoarthritis quantitatively.To investigate the ability of various cartilage MR imaging and to explore the appearance and the value of MR T2 mapping and DWI sequences in detecting articular cartilage degenration of the pigs'knee.Methods For the joint cartilage morphology study, the fresh pigs' posterior limbs were selected. The same angle scans with different sequences were carried out. The scan sequences included SE-T1W1, FSE-T2WI, FS-3D-SPGR, FIESTA and IDEAL. Range of interest (ROI) was mid sagittal slice in the centre of intercondylar concavity of distal femur, femoral metaphyseal bone, meniscus, ligaments and synovial fluid. Signal intensities were detected and SNR and CNR were calculated. With these values, we evaluated the condition of articular cartilage and analysed the sequences for their clinical application in diagnosing the degenerative changes in the cartilage.In the quantitative analysis,12 pigs were selected and randomly divided into four groups A, B, C and D. In the treatment group, the same dose of papain was injected intraarticularly in the right posterior knee joint in different time interval to produce animal model of articular cartilage degeneration. In the control group, the same dose of phosphate buffer solution (PBS) was injected intraarticularly in the left posterior knee joint. Group A received one injection and was examined 24 hours later. Group B received three injections and was examined 24 hours after the last dose. Group C received three injections and was examined one week after the last dose. Group D received three injections and was examined three weeks after the last dose. MRI T2 mapping and DWI were done for both knee joints. T2 values and ADC values were determined for the severity of joint cartilage degeneration. The knee joints were finally dissected and histopathological analyses were done with various stainings, this being the gold standard method to determine the severity of joint cartilage degeneration in various stages. The histopathological results were compared and correlated with MRI values.Results 1. FIESTA,IDEAL and 3D-FS-SPGR sequences of the articular cartilage, regardless of SNR or CNR, were significantly superior to conventional SE-T1W, FSE-T2W sequences(P<0.05). IDEAL(WATER) and FIESTA sequences had a significantly higher SNR for cartilage and higher CNR between cartilage and synovial fluid, meniscus, ligament than that for other MR sequences. (P<0.05), while the CNR value of cartilage/bone marrow in 3D-FS-SPGR sequence was slightly better than the valus in the other sequence(P<0.05).2. Staining showed that the A, B, C and D each treatment group,along with the observation time, the smooth cartilage surface gradually became rough and fibrosed, surface layer of chondrocytes were disordered, chondrocytes underwent sparse necrosis.Cartilage lacuna disappeared leaving vacuoles.Alcian Blue staining showed that in each treatment group acid mucopolysaccharide gradually faded blue dye, indicating gradual degradation of cartilage proteoglycan.3. Cartilage T2 relaxation values and pseudo-color pictures T2mapping results:T2 values of the A, B, C and D control groups were in the range of 46.67-55.54ms, T2 mapping diagram showed a continuous articular cartilage integrity, red color and uniform signal. After injection of papain, T2 mapping graph showed thinning of cartilage; uneven distribution of color gradation from reddish yellow to yellow, yellow-green transition, D group was uneven green. T2 values in treatment group A were:56.55-58.89ms, group B were 66.86-69.71ms, group C were 68.49-76.61ms and group D were 73.59-83.85ms, whereas in the same period, T2 values of the treatment group were more. T test showed statistically significant difference between treatment and control groups (P<0.05). Comparison within groups showed that the control group had no significant difference (P> 0.05) but the treatment groups had statistically significant difference (P<0.01).4. Result of ADC value and ADC mapping of articular cartilage:control groups in A, B, C and D showed uniform thickening of articular cartilage, ADC map showed intermediate signal, ADC pseudo-color mapping showed uniform green, and their ADC values were(8.50±0.25×10-4mm2/s,(8.47±1.07)×10-4mm2/s,(8.42±0.82)×10-4mm2/s and (9.11×0.25)×10-4mm2/s respectively. The difference in ADC values within control groups was not statistically significant. Treatment groups in A, B, C and D showed relatively uniform to non uniform articular cartilage thickening. Color scales were unevenly distributed with color gradation from light yellow, yellow, to dark yellow.Their ADC values were (9.86±0.75)×10-4mm2/s, (10.7±0.51)×10-4mm2/s, (12.3±0.72)×10-4mm2/s and (13.4±0.73)×10-4mm2/s respectively. The differences in ADC values within the treatment groups were statistically significant. In addition, the t test revealed the difference in ADC values between treatment and control groups were tatistically significant (P <0.05).5. The water content in each treatment group was more than that in the control group over the same period by 7.91%,10.68%,20.81%,24.11%. The t test, compared between treatment and control groups, showed statistically significant difference (P<0.01). At the same time comparison within groups showed that the control group had no significant difference (P>0.05),but the treatment groups had statistically significant difference (P<0.01).Conclusions 1. FIESTA,IDEAL and 3D-FS-SPGR sequences of the articular cartilage were significantly superior to conventional SE-T1W, FSE-T2W sequences. FIESTA and IDEAL sequences are the promising new MR imaging sequences for cartilage diagnosis.2.Three-dimensional MRI techniques for data reconstruction in any direction, is not affected by slice thickness and spacing constraints, spatial resolution is not affected, you can display all parts of the articular cartilage, levels of restrictions will not miss subtle lesions.3.The staining results showed that intra-articular injection of certain amount of papain in pigs can rapidly result in osteoarthritis without biomechanical changes in joint, this simple and effective method can be used to get early articular cartilage degeneration.4. The spatial variation of articular cartilage T2 relaxation time and the changes in pseudo-color pictures Levels T2mapping can reflect the occurrence of early biological changes, before morphological changes, during cartilage degeneration. This can be of certain diagnostic value in early diagnosis of articular cartilage degeneration.5. Articular cartilage ADC value and ADC map can reflect the occurrence of early biological changes, before the morphological changes, during cartilage degeneration. This can be of certain diagnostic value in early diagnosis of articular cartilage degeneration.6. During the early and intermediate stages of articular cartilage degeneration, water content gradually increases in the cartilage, the T2 value and ADC value also gradually increases. This trend of water content in the degenerating cartilage has a potential role in clinical evaluation.The study suggests that using magnetic resonance imaging technology, not only can reflect the characteristics of cartilage morphology, and can use magnetic resonance imaging T2mapping to find Changes in the composition of articular cartilage before morphological changes. Using MR diffusion imaging and ADC value measurements can reflect the abnormal water diffusion level which was due to changes of the biochemical structure in cartilage.So that the diagnosis of early articular cartilage injury will be a step forward from a simple form of diagnostic imaging to quantitative analysis. |
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