Objective To find a new method of tangential view of patello femoral joint. Methods 62 cases of lateral knee radiographs were studied. The knee flexion angles, patello femoral angles, patello tibial angles and frontal patello tibial angles were measured and their relationships analyzed. The knee flexion angles and the patello femoral angles had linear relationship with a linear equation = 2 + 0.8x . The angles of posterior patellar line with tibial long axis and frontal tibial line were 3.3? and 12.7?respectively. According to the measurement results, an accessary positoning table was designed. The patients′ patello femoral joints were examined with the knee flexed at an angle of 30?. The patients were in supine position and the central X ray was angled at 73?vertically toward the film. Results 58 patello femoral joints of 40 patients were radiographically studied (10 males, 30 females) .All radiographs were classified into 4 degrees as Grade A, B, C and D. Eighteen cases were Grade A (31%), 30 cases were Grade B(52%), 8 cases were Grade C(18%)and 2 Grade D(3%).The reason for Grade D was due to small or negtive anterior patellotibial angles. Conclusion This new method of tangential view of patello femoral joint is accurate, comfortable and simple and could be used as routine examination for patello femoral joint diseases.

Objective To get the maximum information from computed radiography (CR) output images by changing post-processing parameters. Methods Six experimental photos of polypropylene balls of 2.0 mm in diameter were taken by means of one time X-ray exposing on an imaging plate (IP) with different post-processing parameters including rotation amount (GA), gray gradation type (GT), rotation center (GC), shifting amount (GS), frequency rank (RN), frequency type (RT), and degree of enhancement (RE). 6 photos were viewed by three students and one radiologist on a 6 000 lx illuminance viewbox. Receiver operating characteristic (ROC) curves were made by means of 5-value-differentiation method. Results The largest mean area value (Az) below ROC curves of a low contrast experimental photo with post-processing parameters GA=1.0,GT=A, GC=1.6, GS=0.3, RN=4.0, RT=R and RE=3.0 was 0.96, and the maximum information was obtained. The smallest mean area value (Az) was 0.78 with changed post-processing parameters GA=0.8, GS=-0.2 and RE=0.5 while other parameters were not changed. The minimum information was obtained from this photo. Conclusion In order to get the maximum information from a CR output image, the post-processing parameters should be suitably selected.