| Objective To investigate features of uric acid salt’s deposition in joint of knee in gout using gemstone spectral computed tomography (CT), and measure series spectrum parameters of uric acid salt to assess its clinical value.Methods Gemstone spectral CT scans of knee were performed on 46 patients w ith gout.The features of uric acid salt’s deposition were investigated, series spe ctrum parameters of uric acid salt and cortical bone, muscle, cancellous bone ar ound,which include effective atomic number(Eff-Z),spectrum curve slope,content of uric acid(calcium)-[UA(ca)],content of calcium (uric acid) [CA(ua)],specific v alue of UA(ca)/CA(ua) were analyzed.The statistical methods between four grou ps comparison use Kruskal Wallis H test (P< 0.05), pairwise comparisone use the Mann-Whitney U test. The CNR of deposition urate were calculated and st atistics analyzed to get the optimal single energy keV, The chi-square test was used to test the difference significance(P<0.05).Results 1.The deposition of uric acid salt was found in all patients,which distributes in 271 areas.The most common affected sites were collateral ligaments(98/271, 36.09%),cruciate ligament(37/271,13.70%),quadriceps tendon(23/271,8.49%) successively. The possibility of deposite in other site of knee articular is lower.2. The effective atomic number (Eff-Z)of uric acid salt is 8.12±0.29, The Eff-Z of cortical bone is 13.27±0.48, The Eff-Z of muscle is 7.71±0.15, The Eff-Z of cancellous bone is 9.16±0.62, which were significantly different with cortical bone, muscle, cancellous bone around.3. The spectrum curve slope of uric acid salt is 1.08±0.66, The spectrum curve slope of cortical bone is 25.42±2.95, The spectrum curve slope of muscle is 0.24±0.22, The spectrum curve slope of cancellous bone is 3.09±1.44, which were significantly different with cortical bone, muscle, cancellous bone around.4.UA(ca) is (1261.5±49.31) mg/cm3,CA(ua) is (19.25±7.89) mg/cm3,UA(ca)/CA(ua) is 70.93±69.1, UA(ca) of cortical bone (1440.6±55.02)mg/cm3> UA(ca) of uric acid salt (1261.5±49.31)mg/cm3> UA(ca) of muscle (1138.8±6.92)mg/cm3> UA(ca) of cancellous bone (1068.3±17.89)mg/cm3. UA(ca) of uric acid salt which were significantly different with cortical bone, muscle, cancellous bone around. CA(ua) of cortical bone (388.12±58.31)mg/cm3> CA(ua) cancellous bone (49.23±18.82)mg/cm3> CA(ua) of uric acid salt (19.25±7.89)mg/cm3> CA(ua) of muscle (9.82±2.92)mg/cm3. CA(ua) of uric acid salt which were significantly different with cortical bone, muscle, cancellous bone around. UA(ca)/CA(ua) of muscle 137.13±114.3> UA(ca)/CA(ua) of uric acid salt 70.93±69.1> UA(ca)/CA(ua) of cancellous bone 31.31±5.83> UA(ca)/CA(ua) of cortical bone 3.81±0.62. UA(ca)/CA(ua) of uric acid salt which were significantly different with cortical bone, muscle, cancellous bone around. S.The number of optimal CNR appear in single energy of 65keV gets to 138 of all 217 deposited uric acid salt. By chi-square test,the difference of probability appear in 65keV with others single energy was statistically significant.6. In one follow-up Patient,we found the deposited uric acid salt in leading edge of tibial plateau was disappeared,UA(ca) of uric acid salt decrese mostly.Conclusion 1.The uric acid salt deposited more in ligaments and tendons of knee where stresses more, so we guess that the deposition of uric acid salt may be in proportion to stress.2.The GSI parameter analysis [Eff-Z,spectrum curve slope, the optimal single energy,UA(ca) and CA(ua) and UA(ca)/CA(ua)] can help qualitatively diagnosis of uric acid salt, UA(ca)/CA(ua) may be more sensitive to detect the change of uric acid. |
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