Hs. An et al., GADOLINIUM-ENHANCEMENT CHARACTERISTICS OF MAGNETIC-RESONANCE-IMAGING IN DISTINGUISHING HERNIATED INTERVERTEBRAL DISC VERSUS SCAR IN DOGS, Spine (Philadelphia, Pa. 1976), 19(18), 1994, pp. 2089-2095
Study Design. This study is an experimental investigation on the gadol
inium contrast magnetic resonance imaging (MRI) in distinguishing sequ
estered disc fragment versus scar in dogs. The conspicousness of the d
isc fragment and signal intensities of the disc fragment and laminecto
my scar were evaluated using gadolinium-enhanced MRI and histology. Ob
jectives. This study investigated the effects of timing of gadolinium
injections, gadolinium doses, and aging of scar or disc on the enhance
ment characteristics and conspicousness of disc fragment in MRI. Summa
ry of Background Data. Contrast-enhanced MRI has been frequently used
as a procedure to evaluate patients with suspected recurrent herniated
discs. In contrast-enhanced MRI, the postoperative scar tissue enhanc
es to a greater extent than disc fragments. Previous reports suggest d
ifferent contrast enhancement characteristics of scar depending on dos
es, timing of gadolinium, or maturity of scar. There are different com
pounds of gadolinium agents and different doses are becoming available
. There is no previous report on the evaluation of gadolinium enhancem
ent characteristics in dogs with concurrent herniated disc and scar. M
ethods. Six conditioned Beagle dogs underwent hemilaminectomies and di
scectomies at the L3-L4 level. An autogenous disc fragment was obtaine
d from the intervertebral disc of the tail. This disc fragment was pla
ced anterolateral to the thecal sac, simulating a sequestered disc her
niation. Three control animals underwent hemilaminectomies and discect
omies alone. Each dog underwent MRI on a 1.5 Tesla scanner (3.0 mm sli
ce in sagittal and axial projections with TR 500, TE 30 msec and high
dose 0.3 mmol/kg of gadoteridol). Images were obtained at 15 days, 30
days, 60 days, and 90 days after surgery. At each imaging session, con
trast enhancement was measured at 2 minutes, 25 minutes, and 45 minute
s after gadolinium injection for kinematic analysis. Two animals at a
time were killed on 30 days, 60 days, and 90 days postoperatively. Mag
netic resonance imaging was done with conventional low dose 0.1 mmol/k
g of gadopenetetate at 15 days and before death. Results. Results reve
aled that the difference of enhancement between disc and the scar and
therefore conspicuousness of disc fragment was greater on 2-23-minute
images as compared with 45- minute images, and the distinction decreas
ed with aging of the scar. The high dose contrast-enhanced MRI increas
ed signal intensities for both disc and scar. Conspicuousness of disc
fragment seemed to be better with the high-dose gadolinium compound. C
onclusions. In conclusion, contrast enhancement characteristics in MRI
may depend on the timing of MRI after gadolinium injection, doses of
gadolinium, and aging of scar or disc.