Patient population:
Between October 2008 and December 2009, 19 cases (14 males, and 8 females) with a median age of 66.5 (26-81 y) diagnosed to have recurrent lymphoma (9 HD, and 13 NHL) were referred to our department to undergo whole body MR imaging to evaluate the tumor load and for staging. PET/CT study was done for all patients within the same week of the MR examinations that was used as the reference whole-body modality to which whole-body diffusion and STIR studies were compared.
PET/CT study:
All studies were aquired using a Gemini (Philips Medical Systems, Cleveland, OH, USA). Patients were informed of the procedure and were provided with a written informed consent. They were also instructed to fast for at least 6h before the study and presented a blood glucose level <200 mg/dl before injection of the tracer. Sixty minutes after intravenous injection of FDG (dose range 210-350 MBq), whole-body emission scans, 8-9 bed positions were acquired. A CT bidimensional projection scout view of the patient, from the base of skull to the proximal femur, was first done to define the body axial extension necessary to acquire the CT and PET data. The CT scan had a voltage 120kV, and tube current 80mA and lasted for approximately 1 min. It achieved anatomical localization, and attenuation correction of PET data. Then, the bed position was translated into the PET field of view (FOV) at which whole-body distribution of the tracer was acquired in 3D mode. PET data acquisition was done in 25 min. Data sets in the coronal, axial, and transverse planes were reconstructed using dedicated software named Syntegra.
Magnetic resonance imaging:
Whole-body MR imaging was performed on 1.5T body system (Signa Horizon LX Echospeed GE Medical Systems, Milwaukee, W1) using the body coil. Patients acquired the supine position with their arms to their sides. At first, a localizing sequence was obtained followed by entire body coverage with 3-6 stations. FSE STIR sequences were taken with the following parameters: TR, 3,500-5,700 ms; Te, 20-33 ms; inversion time, 150-165 ms; echo train length, 4-16; NEX, 1; FOV, 320-480 mm; matrix,256x128-512x256; slice thickness, 5-10 mm; interslice gap, 0-2 mm. We obtained 15-32 slices per station depending upon the anatomical location and the chosen slice thickness. Also, coronal FSE STIR sequences were taken. Next, DWIBS sequences were acquired without respiratory triggering while the patient was breathing freely using a single-shot echo-planar imaging sequence with diffusion-module and fat-suppression pulse. Water diffusion was measured with a 3-scan-trace technique and b-value of 0, 400, and 1000s/mm2 at selscted suspicious areas of interest ( measurements were based upon 3D maximun intensity projections), and automated generated ADC-maps (taking into account all 3-b values for ADC calculation) were generated. Whole-body MR studies were completed in 30-35 min.
Detected lesions at regions of interest were documented and compared at all whole-body imaging modalities.
Statistical methods
PET-CT was considered the gold standard. Concordance between DWIBS or STIR and PET-CT as regards the number of lesions detected was expressed as a percentage (number of lesions detected with DWIBS or STIR/ number of lesions detected by PET-CT %). Concordance percentage was expressed as mean (SD) and differences between groups was compared parametrically using the independent samples t-test.
Concordance between DWIBS or STIR and PET-CT as regards the lymphoma stage was expressed as number [%] of patients in whom the two techniques yielded concordant or non-concordant results, and differences between groups were compared using the Pearson’s χ2-test with application of Fisher’s exact test when appropriate.
Correlations among variables were tested non-parametrically using Spearman’s correlation analysis. A correlation coefficient of 0.7-1.0 was taken as denoting strong correlation, 0.4-0.7 as denoting moderates correlation, 0.2-0.4 as denoting mild correlation, and <0.2 as denoting no correlation. P < 0.05 was considered statistically significant.