ObjectiveThe purpose of this study was to determine whether chemical-shift magnetic
resonance imaging (MRI) could be useful in the diagnosis of osteoid osteoma
when clinical and radiological tumor features are inconclusive.Materials and MethodsThis retrospective study included 17 patients who underwent chemical-shift
MRI for the evaluation of osteoid osteoma. For all patients, two
musculoskeletal radiologists independently recorded signal intensities on
in-phase and out-of-phase images in the nidus of the tumor, in
abnormal-intensity bone marrow surrounding the lesion, and in
normal-appearing bone marrow. For each region, relative signal intensity
ratios were calculated by dividing out-of-phase by in-phase values. Relative
ratios > 1 were considered indicative of neoplastic lesions. Statistical
analysis was carried out to analyze the sample. Inter-observer and
intra-observer agreement for each imaging method were assessed using
intraclass correlation coefficients according to the Fleiss method and a
value > 0.65 was considered to indicate substantial agreement.ResultsThe mean relative signal intensity ratios were 1.2 (range, 0.9-1.4) for the
nidus and 0.35 (range, 0.11-0.66) for the surrounding tissue; these values
differed significantly from the relative signal-intensity ratios for
normal-appearing bone marrow (p < 0.05).ConclusionChemical-shift MRI is useful for the diagnosis and evaluation of osteoid
osteoma.