Use of A Jig to Control Forearm Rotation and Wrist Position for MR and CT Imaging of Patients with Distal Radioulnar Joint and Wrist Dysfunction

with and ease of use by the radiographers. Results: Twenty-three volunteers found the jig to be comfortable during the scanning procedure. Nine patients who had also undertaken standard MRl scans without the jig unanimously reported improved comfort and satisfaction levels with the jig. Radiographers found the device easy to use obviating the need to repeat scans due to patient movement or incorrect wrist positioning. lmages obtained readily permitted intra- and inter-patient comparison. lmage quality was improved with less subject tremor. Conclusion: scans without using any such device. For image analysis, positions of forearm rotation matched for both intra- (31/31) and inter-(63//63) subject comparisons in 100% of wrists for S30, neutral and P30.


Introduction
The distal radioulnar joint (DRUJ), triangular fibrocartilaginous complex (TFCC) and the forearm are frequently imaged by MR and CT for associated disease processes. The standard 'superman' position is often uncomfortable for patients generating movement artefact. Scans are restricted to the prone position of forearm rotation placing potential limitation on the information that might be gained from viewing the same structures in different positions of forearm rotation. For example, a tear of the volar distal radioulnar ligament is easily identified in supination with dorsal subluxation of the distal radius on the ulnar head. However, the diagnosis can be easy to miss with the forearm pronated, where the subluxation is less evident.
Patient discomfort particularly in MRl scanning is significant even with modern generation scanners. Patients must remain as still as they can whilst maintaining the body prone position with extended shoulder and elbow and forearm pronated. Upper limb support is improvised padding if present.
Gross movement blurs images and fine tremor artefact occurs with the strain of trying to maintain perfectly still. This is particularly pertinent with the current use of high-Tesla scanners.
Whilst such scanners offer higher definition imaging unwanted effects from tremor and movement are more troublesome. ln specific research studies, lack of standardization of forearm positioning creates systematic error with respect to intra-and inter-patient comparisons. Even comparison between serial scans in the same individual can be challenging without ensuring an identical posture is maintained. This study reports the development and trialing of a forearm jig used in a research study on soft tissues of the distal forearm, reported elsewhere [1]. A scanning platform was developed for this purpose, with the aim of allowing both clear visualization of key soft tissue structures about the wrist using a 3-Tesla MRl machine, as well as permitting both intra-and interpatient comparability of scans.

Methods
A scanning-platform jig was designed solely from radio-opaque materials, suitable for use with both CT and MRl scanners (   The results were collated and comments noted.

Results
Thirty-three subjects were recruited for the scans: 9 patients (mean age 41 years; range 27-55) and 24 volunteers (mean age 34 years; range 19-57). One-person experienced claustrophobia and the scan was aborted. With the exception of a patient who had metalwork in one wrist, both wrists were scanned in 5 positions for each individual, giving a total of 10 scan series per patient, and an overall dataset of 315 scan series. Due to a variety of image sequences being used, the time taken to scan each wrist was about 50 minutes. A single series contained 40 images at 1mm intervals through the DRUJ and took approximately 13 minutes to obtain using our 3Tesla machine. All scans were performed in body prone arm extended position. All 32 subjects reported the jig as comfortable. All 9 patients who had undertaken previous wrist MR scans said that they preferred the scans using the jig than without because it felt more comfortable. ln particular, a constant factor was that patients stated that they could better relax because their arm was strapped-in and so they didn't need to worry about it moving or actively try to keep it completely still.
Seven people were so relaxed they fell asleep. Four of the first 10 subjects scanned reported slight discomfort using the jig for so long: this was overcome by adjustment of the padding provided.  [3][4][5]. The optimal imaging and sequencing techniques for investigating structures such as the DRUJ and TFCC are still a matter of debate with various opinions expressed [6][7][8][9]. Developing a means by which to allow intra-and inter-individual comparability between MR scans was not without limitation.
There was no pre-existing system for comparison to build upon therefore a logical method was developed to do this by inferring the position of pronosupination in reference to key constant landmarks, notably the orientation of the ulna styloid and ulna fovea. The jig minimized patient movement artefact but did not completely eliminate fine tremor impacting final image quality. Nonetheless, it is important to improve patient comfort and select forearm position during these scans as the gains from higher resolution machines will not be realized if patient position and movement cannot be controlled.

Conflict of Interest Statement
The device as described in the current paper is registered for further development and distribution through UMlP at the University of Manchester. Any future royalties from successful distribution of this jig would be allocated to research funds.