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Quantifying Sodium in the Human Wrist in Vivo by Using MR Imaging¹

¹ From the Department of Radiology, University of Pennsylvania, B1 Stellar-Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104-6100. Received June 13, 2001; revision requested August 6; revision received December 3; accepted January 22, 2002. This work was performed at an NIH-supported resource center (NIH RR02305) and supported by grants R01-AR45242 and R01-AR45404 from National Institutes of Arthritis, Musculoskeletal and Skin Diseases. Address correspondence to A.B. (e-mail: ari@mail.mmrrcc.upenn.edu).

View larger version (104K): [in a new window]   Figure 1. Sodium RF coil used in our experiments. The location of the viewing window facilitated accurate positioning of the wrist inside the coil. To minimize involuntary patient motion during imaging, we placed an adjustable peg between the thumb and forefinger, and the subject’s wrist was strapped to the coil with a wristband.

View larger version (61K): [in a new window]   Figure 2. Diagram of the joints of the human wrist (15). The ROIs where sodium content was measured were located in the (a) radiocarpal joint, (b) distal radioulnar joint, (c) ulnar collateral ligament, and the (d) scapholunate, (e) lunotriquetral, (f) scaphocapitate, and (g) capitotriquetral joints. The articular surfaces are white.

View larger version (28K): [in a new window]   Figure 3. An example of a calibration curve obtained from the sodium MR signal intensity of the calibration phantoms imaged alongside the wrist. The signal intensities of four agarose gel phantoms containing sodium chloride are plotted against their individual sodium concentrations (100, 150, 200, and 250 mmol/L). The first data point, the background signal intensity, is also included in the straight-line regression, resulting in a high correlation (R2 = 0.98, P < .01). The slope and intercept were used to determine the sodium concentration of every other pixel on the image.

View larger version (88K): [in a new window]   Figure 4. Calculated sodium concentration maps in the wrist joint of a healthy 22-year-old man. The scale at the top right indicates the sodium concentration in the tissue. Three consecutive coronal MR sections from a 3D data set of 16 sections are shown (top row). The proton MR images obtained in the same location with a 3D fat-suppressed spoiled gradient-echo sequence are shown for comparison (bottom row). The sodium content in the wrist joint of this individual ranged from 100 to 220 mmol/L.

View larger version (22K): [in a new window]   Figure 5. Graph shows average sodium concentrations in the locations indicated in Figure 2. Locations containing cartilage are shown in black, whereas noncartilaginous regions (eg, ligaments and synovial fluid) are shown in gray. Maximum sodium concentration was observed in the radiocarpal joint (210 mmol/L), while the region between the scaphoid and lunate bones showed the lowest concentration of sodium (120 mmol/L).