Abstract
Introduction: Normal adult periosteum and cortical and produces no signal with typical bone has a short T2 Magnetic Resonance pulse sequence echo times available in clinical practice. We wished to assess the value of using pulse sequences with a very short echo time to detect signal from periosteum and cortical bone.
Materials and Methods: Ultrashort echo time (UTE) pulse sequences (TE = 0.08 msec) were used with and without preceding fat suppression and/or long T2 component suppression pulses. Later echo images and difference images produced by subtracting these from the first echo image were also obtained. Two volunteers and ten patients were examined, four of whom had contrast enhancement with intravenous Gadodiamide. Two sheep tibiae were also examined before and after stripping of the periosteum. The separated periosteum was also examined.
Results: The periosteum was seen on the sheep tibiae before stripping but there was only a faint signal adjacent to cortical bone afterwards and the removed tissue produced a high signal when examined separately. High signal regions were observed adjacent to cortical bone in the femur, tibia, spine, calcaneus, radius, ulna and carpal bones. Fat suppression and long T2 suppression generally increased the conspicuity of these regions. The high signal regions were more obvious with contrast enhancement. Periosteum could generally be distinguished from susceptibility artifacts on difference images by its high signal on the initial image and its failure to increase in extent with images with increased TE’s. Signal in cortical bone was detected with UTE sequences in normal adults and patients. This signal was usually made more obvious by subtracting a later echo image from the first provided that the SNR was sufficiently high. Normal mean adult T1’s ranged from 140 msec to 260 msec, and mean T2’s ranged from 0.42 to 0.50 msec. Increased signal was observed after contrast enhancement in a normal volunteer and in all three patients in whom it was administered. Changes in signal in short T2 components were seen in acute fractures in cortical bone and after fracture malunion. In a case of osteoporosis, bone volume and signal were reduced. Furthermore, in fractures increased signal was seen in the periosteum and this showed marked enhancement. Three weeks after fracture, tissue with properties consistent with periosteum was seen displaced from the bone by callus.
Discussion: The normal adult periosteum and cortex can be visualized with ultrashort TE sequences. Conspicuity is usually improved by fat suppression and the use of difference images. Use of subtraction images was useful for selectively demonstrating periosteal and cortical contrast enhancement and separating this from enhancement of surrounding blood. Obvious periosteal and cortical enhancement was seen after fractures. This novel MRI sequence images for the first time the soft tissue component of cortical bone and enables visualization of different haemodynamic situations.
The abstracts were prepared by Michael A. Mont, M.D. and Lynne C. Jones, Ph.D. Correspondence should be addressed to L. Jones at Good Samaritan Prof. Bldg., Suite 201, 5601 Loch Raven Blvd., Baltimore, MD 21239
