Significance of xenon‐133 clearance rate from canine and human joints

The clearance curve of 133 Xe from canine and human knee joints has two monoexponential components. The rapid half clearance time is designated T 1/2 F and the slower T 1/2 S . 133 Xe concentration in periarticular tissues was measured; the nuclide was predominately in the intraarticular fat during T 1/2 S and was distributed between the synovial fluid, synovial membrane and fat during T 1/2 F . Because of predominant tissue localization of 133 Xe during T 1/2 S and T 1/2 F , T 1/2 S is thought to represent clearance from articular fat and T 1/2 F to represent clearance from synovial fluid and membrane. Use of xenon clearance to calculate the blood flow to synovium or articular fat requires several assumptions that cannot be experimentally verified at this time. Elevation of intraarticular pressure, but not intraarticular volume, decreased 133 Xe clearance from both compartments. Crystal‐induced inflammation was usually associated with faster T 1/2 S , although in one human volunteer T 1/2 S was slower until a part of the inflammatory exudate was removed. On the other hand, T 1/2 F was variable.