Anatomy of the proximal femur as seen with three-dimensional magnetic resonance imaging.

Magnetic resonance imaging (MRI) is being applied successfully to the study of the musculoskeletal system with notable recent advances, including the use of three-dimensional imaging techniques. The authors introduce three-dimensional MRI as a technique for examining proximal femoral anatomy and suggest its use as an improvement on current methods for prosthetic hip design. The proximal femurs of 14 cadavers were scanned using a three-dimensional FISP technique and the images were subsequently manipulated on a three-dimensional MRI image-processing workstation to produce rotated surface reconstructions and multiplanar reformatted images. The surface rotations showed that the marrow cavity contours closely follow the contours of the external cortex. Axially reformatted images allowed relative area measurements of the marrow cavity, quantifying the variability between subjects.

Physiology of the retrocalcaneal bursa.

To clarify the function of the retrocalcaneal bursa the hindfoot was studied by magnetic resonance imaging at various positions of the ankle joint. In normal individuals a tongue-like extension of the retromalleolar fat pad entered the bursa during plantar flexion as the angle between Achilles tendon and calcaneus widened. The reverse occurred in dorsiflexion. In contrast, in a patient with spondyloarthritis and retrocalcaneal bursitis excessive cavitary fluid prevented the intrusion of the fat pad. The sliding motion of the fat pad in and out of the bursa during ankle motion allows a more caudal, advantageous insertion of the Achilles tendon into the calcaneus.

FLASH: clinical three-dimensional magnetic resonance imaging.

Using 3-D FLASH, high resolution, very thin section T1 weighted images of the CNS, spine, and extremities can be obtained. From these single data sets, reformatted images whose resolution is equal to that of the original data set can be constructed in any desired plane. This approach may lead to the replacement of conventional T1 weighted spin echo imaging by 3-D FLASH techniques.

The straight and narrow path to good head and spine MRI.

The path to good head and spine images is narrow and treacherous. We have attempted to give the traveller a small but important set of basic rules, enabling him to cross with success. 1. Averaging can be used to achieve sufficient SNR for thin sections, but the cost in terms of scan time is high. Zooming the image (reducing the field of view) should generally be avoided, as the price in terms of SNR is very high. 2. Rectangular pixels and half-Fourier imaging are two methods for decreasing scan time. HFI, which produces high spatial resolution images, can be used when the SNR is not a limiting factor. Rectangular pixels improve the SNR, but decrease resolution. 3. To achieve good T1 contrast with spin echo imaging, set TE less than or equal to 20 msec. and TR less than or equal to 600 msec. For T2 weighted images, a TR between 2.0 and 3.0 sec. is preferred, typically with two echoes: for example, TEs of 25 and 90 msec. 4. Better slice profiles or gaps between slices can be used to combat slice-to-slice interference. This results in improved SNR on T1 weighted images and improved contrast on T2 weighted images. 5. Low bandwidth techniques may be used to improve the SNR on both T1 and T2 weighted images. Chemical shift artifact puts a finite limit on the extent to which this can be applied. 6. Motion compensating gradients are a tremendous boon to MRI and should be utilized in all possible head and spine applications. These reduce image degradation from CSF and vessel pulsation, as well as from involuntary motion. 7. Fast imaging techniques can be used in 2-D multislice mode to decrease scan time. Unfortunately the T2 contrast with this approach is far inferior to that of spin echo technique. 3-D FLASH, with 1 mm. sections, T1 contrast superior to spin echo technique, and the potential for high resolution reformatted images, may replace conventional 2-D, T1 weighted, spin echo imaging. Pulse techniques that combine all the advantages mentioned lie in the future. For example, one possible approach is a T2 weighted head screen that incorporates low bandwidth technique and HFI. This would produce high resolution images with reasonable SNR in approximately half the present scan time. Despite any further new developments, the trade-off between image quality and scan time will likely always remain.(ABSTRACT TRUNCATED AT 400 WORDS)