Patient population
This prospective IRB approved study enrolled 40 consecutive patients.
A diagram shows the patients included in the study (fig 1).
DECT protocol and post-processing
The DECT examinations were performed with a third generation 384-slice dual source CT scanner (Somatom® Definition Force,
Siemens Healthcare).
The scanning parameters were as follows: tube A 80 kV and tube B 150 kV with a tin filter (tube A,
220 quality reference mAs; tube B,
138 quality reference mAs).
Soft-tissue kernel (Qr32) 80-kVp and 150-kVp set images were reconstructed on an offline workstation (SyngoVia® VB20) by using a three-material decomposition resulting in VNCa images.
MRI protocol
MR imaging was performed with a commercially available 1.5-T unit (Magnetom Avanto
Fit; Siemens Healthcare).
Standard T1-weighted spin-echo,
T2-weighted turbo spin-echo,
and turbo inversion-recovery magnitude (TIRM) sequences were performed in the axial and sagittal orientation.
The TIRM sequence was also performed in the coronal plane.
Image analysis
Each ankle was evaluated for the presence of bone marrow edema using a binary classification system (1= presence of BME and 0 = absence of BME).
All MR images were evaluated in random order,
by an experienced radiologist (20 years of experience) blinded to clinical and CT findings.
At MRI,
the diagnosis of BME was a based on signal intensity increase at TIRM imaging.
DECT images (3D and 2D color-coded maps) were analyzed by two independent radiologists (35 and 15 years of experience in radiology,
respectively) in a random order,
blinded to clinical and MRI findings on a dedicated SyngoVia® workstation.
Possible causes of BME,
including OCLs,
meshed fractures and stress fractures were recorded.
For any disagreement on presence of BME,
a consensus reading was appended,
and the consensual results were used for further analysis.
Quantitative analysis of DECT numbers was performed by the same two readers on DECT maps or standard CT images according to radiologist choice by achieving two circular regions of interest (ROI) for each involved area (fig 2),
and using mean value for further analysis.
Statistical analysis
The sensitivity,
specificity,
positive-predictive value (PPV),
negative-predictive value (NPV) and accuracy of DECT for the diagnosis of BME were calculated on a per-patient basis both as regards qualitative and quantitative assessment.
Inter-observer and intra-observer agreement were calculated with weighted k statistics.