Chemical shift and the double-line sign in MRI of early femoral avascular necrosis.
The double-line sign (DLS) on T2-weighted images in femoral avascular necrosis (AVN) is formed by a high-intensity rim at the reactive interface inside a low-intensity margin. A hypothesis has been advanced that the sign may be seen in early AVN whether or not there is bony sclerosis. On change of direction of the frequency-encoding axis, the high-intensity area rimmed with low-intensity margin was generated on the side where chemical shift misregistration artifact was seen. Transposition of frequency-encoding and phase-encoding axes yielded the same results. The thickness of the low-density rim was almost equal to the amount of expected offset distance due to chemical shift misregistration. Therefore, chemical shift misregistration artifact is the most reasonable explanation for the DLS observed in early femoral AVN.
Sugimoto
H
H
Department of Radiology, Jichi Medical School, Tochigi-Ken, Japan.
Okubo
R S
RS
Ohsawa
T
T
D016477:Artifacts; D005260:Female; D005271:Femur Head Necrosis / Q000175:diagnosis*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D013997:Time Factors