| Sign In to gain access to subscriptions and/or personal tools. |
DOI: 10.1016/J.JHSB.2005.08.001
Mri ‘Magic Angle’ Imaging of Finger TendonsDepartment of Human Anatomy and Cell Biology, The University of Liverpool, Ashton Street, Liverpool, Merseyside, UK, North Western Medical Physics, UK and Whiston Hospital, Liverpool, UK Correspondence: Mr G Lambe, RCS(Eng) BSSH Research Fellow, 3 Gawsworth Close, Prenton, Birkenhead, Wirral, CH43 2GS, UK. Tel.: +44 151 670 0548; fax: +44 151 670 0548., E-mail: Gedlambe{at}bigfoot.com
The value of using the technique of magic angle MR imaging to demonstrate finger tendons is explored. Images of fresh frozen cadaveric specimens are presented and the structures that can be visualized in the finger are described. The results suggest that magic angle MR imaging may be a useful non-invasive technique of visualizing the details of the tendons and their surrounds in the hand.
Key Words: magnetic resonance imaging • flexor tendon • pulleys • magic angle
Previous reports have noted the value of Magnetic Resonance Imaging (MRI) in hand surgery for pre-operative localization of tendons in closed injuries (Concannon et al., 1996; Kumar et al., 2000; Scott et al., 1995) or suspected cases of rupture following surgical repair (Matloub et al., 1996). However, all these reports present images that show the tendons only as signal voids. Using conventional MRI, tendons are usually only visualized as signal voids. In some circumstances, tendon pathologies can appear as regions of high signal density (Peterfy et al., 1994; Timins et al., 1995) but the value of routine MRI is limited, since only the tendon outline is visualized. The "Magic Angle Effect" has been reported previously, although it has been considered mostly to be an artefact (Oatridge et al., 2001; Timins et al., 1995). The magic angle effect describes the image appearance of the tendons when they are orientated at 55° to the magnetic field, with the resulting images displaying a greatly increased signal. A signal from water molecules associated with collagen fibres within a tendon is not normally achieved because of dipolar interactions, which result in very short T2 relaxation times, i.e. rapid signal decay. At an angle of about 55° to the main magnetic field, the dipolar interactions become zero, resulting in an increase in signal of the order of one hundred fold. Bydder (2002) first suggested the potential for improvement of visualization of tendons and ligamentous structures using this effect, with particular reference to the back and knee. This report describes the methodology of obtaining magic angle images of the tendons of the hand, illustrated with sample images showing the degree of anatomical detail which can be achieved using this simple technique.
Full ethical approval for the study was obtained. Two fresh frozen human cadaveric hand specimens were imaged. The cadaveric specimens were obtained from patients within 2 hours of death. The patients had no known previous history of significant hand pathology or injury. The specimens were defrosted and maintained at room temperature for 8 hours before the images were acquired. All specimens were mounted on a testing rig to hold them at an angle of 55° to the magnetic field. Imaging was performed on a 1.5T Siemens Maestro Symphony scanner (Siemens, Ehrlangen, Germany). This is normally used for routine clinical imaging in our teaching hospital. The data was acquired using a 4 cm diameter surface coil positioned over the palmar surface of the proximal interphalangeal joint. Conventional T1-weighted images were acquired with TE 24 ms, TR 400 ms, NSA 2, FOV 92 mm with 512 matrix giving an in-plane resolution of 0.18 mm with a 1 mm slice thickness. Scan time was approximately 9 minutes for each sequence.
The figures demonstrate the image quality that can be achieved by exploiting the magic angle effect. Fig 1 is a sample image from the sequence with the digit orientated along the magnetic field. The tendon is shown only as a black outline against the high signal from the surrounding fat.
Fig 2 is an image obtained using the same scanner settings but with the orientation of the specimen changed to gain the magic angle effect. The tendon now displays a much higher signal and the intratendinous architecture can be seen. The distinction between the flexor digitorum superficialis and flexor digitorum profundus tendons is also clearly demonstrated.
Fig 3 demonstrates a cross section of the pulley system in this sagittal image. The pulley system appears black against the high signal of the tendon.
Fig 4 demonstrates a coronal view of the terminal part of the flexor digitorum superficialis tendon.
Fig 5 is a close up view of the palmar, or, volar plate of the proximal interphalangeal joint, which also demonstrates increased signal with the magic angle effect.
Previous work has examined the magic angle effect. Oatridge et al. (2001) applied the technique to imaging the Achilles tendon. Bydder (2002) reported the use of the technique more widely, but mainly to image the spine and the knee. He, also, presented a single image of a finger. This study explores the possibility of exploiting the magic angle effect to image tendons in the finger in greater detail, for the first time. Imaging of cadaveric specimens using the magic angle effect achieved increased signal detection within an otherwise signal deficient tissue type, viz. tendon. The architecture and relationship of the FDS to FDP within the flexor sheath is accurately defined using a non-invasive imaging technique and the pulley system can be clearly imaged in cross-section. The technique is equally applicable to the clinical setting. The only proviso is that, depending on the field strength of the scanner, prolonged scan times may be required and this can result in movement artefacts. However, as scanner technology advances, scan times are decreasing and, therefore, movement artefacts will be less likely (Worthington, 1999). There are a number of clinical areas in which the technique could be exploited. The investigation of closed injuries would, in some cases, negate the need for unnecessary exploration or limit the dissection required. This technique could be of particular use in rheumatoid flexor tendon ruptures, acute closed flexor digitorum profundus tendon pull-offs from the distal phalanx and in confirmation of flexor tendon rupture after primary repair. The images obtained in this study show the pulley system much more clearly than those of Hauger et al. (2000) in a study investigating the ability of CT, MRI and ultrasound to visualize the pulley system in cadaveric specimens. These investigators even employed contrast within the sheath to improve visualization of the pulleys. By exploiting the contrast of the low signal of the pulley system against the bright signal of the tendon, using the magic angle effect, it becomes possible to identify both the annular and cruciate pulleys in cross section clearly. This technique has the potential to allow diagnosis of disruption of the pulley system. Knowledge of the magic angle effect can also prevent the incorrect interpretation of areas of high signal as always being indicative of tendon pathology.
This study was funded by a grant from The Royal College Of Surgeons Of London and The British Society For Surgery Of The Hand. Additional funding was received from Royal Preston Hospital Research Directorate. We would like to thank these organizations for their assistance. We would also like to thank the Royal Preston Hospital Radiology Department, North Western Medical Physics Department and Dr C. Coutinho, Consultant Radiologist, for their help and assistance with imaging. Received for publication March 21, 2005. Accepted for publication August 8, 2005.
  CiteULike  Connotea  Del.icio.us  Digg  Reddit  Technorati What's this?
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|
|
 |
|
Sign In to gain access to subscriptions and/or personal tools.
TOP
Abstract
INTRODUCTION
