To determine whether orientation in the static field may be responsible for the frequent occurrence of increased signal intensity within normal tendons at magnetic resonance (MR) imaging, seven healthy volunteers were imaged by means of a 1.5-T unit and standard clinical pulse sequences. The wrist, ankle, and shoulder regions were evaluated with local coils. Imaging was performed with tendon orientations ranging from 0 degree to 90 degrees in relation to the constant magnetic induction field (B0). Markedly increased intratendinous signal intensity was observed at the "magic angle" of 55 degrees, intermediate signal intensity was observed at 45 degrees and 65 degrees, and no signal intensity was observed at 0 degree and 90 degrees. Signal intensity was evident only when a short echo time was used. The authors believe that tendon orientation greatly affects tendon signal intensity in vivo. Increased signal intensity due to the magic angle effect may be misdiagnosed as tendinous degeneration, tendinitis, or frank tear.

No abstract

An anatomic study was performed on living subjects using magnetic resonance imaging (MRI) to distinguish the relative contribution of skin, subcutaneous tissue, and muscle to dynamic changes in the nasolabial fold during facial animation and aging. MRI scans with the face in repose and then holding a full smile were performed in both young and old adult subjects. Anatomic landmarks were identified, and measurements characterizing their position were made on the MRI console. MRI resulted in excellent image resolution of facial tissue planes. Comparison between young and old subjects with the face in repose demonstrated that progressive thickening of the dependent portion of the check fat pad and overlying skin, with no appreciable change in the muscle plane comprising the levators of the upper lip, resulted in a deeper and more acute nasolabial fold in older subjects. In both age groups there was significant shortening of the mimetic muscles with smiling, with the lateral mimetic muscles drawn closer to the underlying facial bones. This was accompanied by redistribution of the cheek fat pad, thereby maintaining projection of surface landmarks within the cheek mass in young subjects with smiling. These findings indicate that in order to diminish the nasolabial fold, surgery for facial rejuvenation should be directed to the skin and subcutaneous tissue planes superficial to the mimetic muscles to the upper lip. In order to recreate a natural nasolabial fold during surgery for facial reanimation, contraction of the levator muscles to the upper lip should result in redistribution of the cheek fat pad without change in surface projection of the cheek mass or upper lip; this can only be accomplished if the reconstructed levator muscle is positioned deep to the cheek fat pad, with its insertion toward the deep (mucosal) surface of the upper lip.

Fifteen patients (17 feet) with symptoms suggestive of plantar interdigital neuroma underwent magnetic resonance (MR) imaging at 1.5 T with a solenoid forefoot coil with an 8-cm field of view. Surgery was subsequently performed on six feet. Fifteen interdigital masses were identified with MR imaging. Five of these, in feet that underwent surgery, were pathologically confirmed neuromas. In the remaining foot that underwent surgery, flexor tendon injury with probable inflammatory reaction was demonstrated with MR imaging but was interpreted as indeterminate for neuroma. No neuronal was identified at surgery, which otherwise confirmed the MR imaging findings. Neuromas were most conspicuous on T1-weighted images as foci of decreased signal intensity well demarcated from adjacent fat tissue. The lesions were poorly seen on T2-weighted images, where they appeared isointense or slightly hypointense to fat tissue in all cases. Prominent regions of increased signal intensity, presumably representing fluid in intermetatarsal bursae, were seen proximal to 10 of the 15 masses found with MR imaging.

We propose the following rules to govern the choice of local coils by the practicing radiologist: 1. Smaller coils permit smaller FOVs and better resolution. The coil should be as small as possible. 2. Match the ROS of the coil to the FOV, which will be determined by the anatomic region of interest. 3. For the case of a choice between surface coils or between a surface and a whole- or partial-volume coil, the anatomic region should lie on the high side of the crossover point. For the case of a choice among whole-volume coils, the smallest coil that surrounds the region of interest should be chosen. 4. Considerations in regard to the anatomic shape or the need to vary the position of the structure may alter the choice of coil from that obtained by S/N considerations alone.