[Comparison between pig lumbar zypapophyseal joint cartilage acquired from multiple magnetic resonance image sequences and gross specimens].

OBJECTIVE: To evaluate the capability and limitation of magnetic resonance image(MRI)for Lumbar zygapophyseal joint cartilage through comparing pig lumbar zygapophyseal joint cartilage acquired from multiple MRI sequences of a 1.5 Tesla MR and gross specimens.

METHODS: Six fresh lumbar spines from adult pigs were sagittaly scanned by Siemens 1.5 Tesla MR. The scan sequences included fast spin echo T1-weighted imaging (FSE T1WI), fast spin echo T2-weighted imaging (FSE T2 weighted T2WI), fat saturation proton density-weighted imaging (FS PDWI), 3-dimensional fast low angle shot imaging (3D-FLASH), and water excitation 3-dimensional fast low angle shot imaging (WE 3D-FLASH). Each scan sequence acquired images from the same layer. The signal-noise ratio (SNR) for articular cartilage, contrast-noise ratio (CNR) for cartilage versus bone cortex, cartilage versus bone marrow, and cartilage versus saline were calculated. Right after the scanning, the lumbar spines were snap-frozen, incised sagittally along the midline lumbar zypapophyseal joints, and photographed to compare the gross specimens with corresponding MRIs. The thickness of sagittal midline center of 6 pairs of lumbar(L₃/L₄) zypapophyseal joint cartilage was measured by vernier caliper. The thickness of the back ventral articular cartilage was added and then compared with corresponding MR images.

RESULTS: 3D-FLASH (FA 20°) and WE 3D-FLASH (FA 20°) sequences had significant advantages compared with other sequences in imaging lumbar zypapophyseal joint cartilage, and were mostly close to the real thickness.(1) Comparison of the 4 flip angle (FA 10°, FA 20°, FA 30°, and FA 40°) 3D-FLASH sequences:The highest cartilage SNR and best CNR of cartilage versus bone cortex were both found in the 3D-FLASH(FA 20°) sequence, which was significantly different from the other three 3D-FLASH sequences.The satisfactory CNR of cartilage versus bone marrow, cartilage versus saline were found more in the 3D-FLASH(FA 20°) sequence. (2) Comparison of the 4 flip angle(FA 10°, FA 20°, FA 30°, and FA 40°) WE 3D-FLASH sequences: the highest cartilage SNR,best CNR of cartilage versus bone cortex,and best CNR of cartilage versus bone marrow were found in the WE 3D-FLASH (FA 20°) sequence, which was significantly different from the other three 3D-FLASH sequences. The CNR of cartilage versus saline was found more satisfactory in the WE 3D-FLASH (FA 20°) sequence. (3) The highest cartilage SNR and best CNR of cartilage versus bone cortex were both found in the 3D-FLASH (FA 20°) sequence, which was significantly different from those in the PDWI, FSE T1WI,and FSE T2WI sequences (P<0.05), but with no significance (P>0.05) in the WE 3D-FLASH (FA 20°) sequence. The highest CNR of cartilage versus bone marrow was seen in WE 3D-FLASH (FA 20°) sequence. It was statistically significant compared with that in FS PDWI,FSE T1WI, and T2WI sequences respectively, but the difference was not significant compared with 3D-FLASH (FA 20°) sequence (P>0.05). Both the FS PDWI and T2WI sequences displayed ideal CNR of cartilage versus saline, with no significant difference (P>0.05). The lower SNR of cartilage versus saline was shown in 3D-FLASH (FA 20°) and WE 3D-FLASH (FA 20°) sequence, and the difference was not significant (P>0.05). However, they were significantly different compared with FS PDWI and T2WI sequences (P<0.05). (4) WE 3D-FLASH (FA 20°) and 3D-FLASH (FA 20°) sequences were relatively better than the FS PDWI when comparing the thickness of articular cartilage, which was significantly different from the FS PDWI sequence (P<0.05).

CONCLUSION: The 3D-FLASH sequence and derived WE 3D-FLASH sequence have better definition of cartilage images and are mostly close to the real thickness, which possibly are the optimal scanning sequences for lumbar zypapophyseal joint articular cartilage MR imaging.