The study was approved by the local institutional review board and was conducted over a period of 1 year.
Patients
The study involved 63 patients with known hematological malignancy (leukemia or lymphoma) and bone marrow infiltration. Forty-eight (76.2%) of them had leukemia (42 had ALL and 6 had AML). Fifteen (23.8%) patients had lymphoma. All were diagnosed by bone marrow biopsy. They were 26 (41%) females and 37 (59%) males. Their age ranged from 1.5 years to 16 years, with a mean age of 9 years. All cases were referred to the MRI unit for head, spine, or extremity imaging to delineate the extent of marrow infiltration that was detected on plain X-ray. Sedation was used in uncooperative young patients below 7 years of age.
Exclusion criteria
Control subjects
An age- and sex-matched control group was selected from our PACS station. They were pediatric patients referred for brain MRI. Indications for MRI in these children were convulsion, headache or dizziness. They were a total of 20 controls: 12 males and 8 females, with a mean age of 6.5 years (range: 19 months to 14 years). The exclusion criteria for control subjects were:
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History of preterm delivery or low birth weight.
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Musculoskeletal, metabolic, or systemic diseases.
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Children with a history of any medications which may affect the bone marrow.
MR imaging sequences, processing, and interpretation
The MRI examinations were performed on a superconducting 1.5 T unit (Siemens, MAGNETOM® scanner).
Sequences
All subjects were scanned using standard protocol with a dedicated coil. The pulse sequences included:
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T1-weighted (T1W) images (fast spin-echo sequence): repetition time (TR) = 595 ms, echo time (TE) = 11 ms, number of excitations (NEX) 2, flip angle 90, matrix 150 × 236 with a field of view (FOV) as small as possible, slice thickness 4–5 mm, and gap 0.5 mm.
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T2-weighted (T2W) images (fast spin-echo sequence): TR = 3670 ms, TE = 92 ms, NEX = 3, flip angle 90,matrix 150 × 236 with a FOV as small as possible, slice thickness 4–5 mm, and gap 0.5 mm.
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STIR: TR = 3670 ms, TE = 92 ms, NEX = 3, flip angle 110, matrix 150 × 236 with a FOV as small as possible, slice thickness 4–5 mm, and gap 0.5 mm.
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Post contrast fat-suppressed T1WI in at least two planes.
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DWI: Fat-suppressed single-shot echo-planar DW imaging was acquired in the axial/sagittal plane with three directional diffusion gradients by using b values 0, 400, and 800 s/mm2 in the spine and extremity imaging while using b values of 0 and 1000 s/mm2 in the head imaging. Parameters were as follows: TR = 6090 ms, TE = 83 ms, NEX = 3, matrix 150 × 236, slice thickness 4–5 mm, and gap 0.5 mm.
Image evaluation
-A marrow lesion was considered to be infiltrative lesion if it shows:
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1)
Increase bone girth (Fig. 1)
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2)
Abnormal signal (low T1WI and high T2WI and STIR signal) concerning marrow conversion pattern of the affected bone (Figs. 1 and 2).
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3)
Heterogeneous contrast enhancement (Fig. 1c).
ADC calculation
Patients: The mean ADC value of the detected marrow lesion was calculated by drawing an ROI (region of interest) over the whole lesion. The ROIs might be drawn directly on the ADC map or copied from those drawn on the DW-MR images onto the map (Figs. 1d and 2e).
Controls: ROIs were placed on 6 points as follows: The frontal bone, the right and left parietal bones, the right and left greater wings of sphenoid, and the occipital bone (Fig. 3). Then, the mean ADC value was calculated for the six measurements.
Statistical analysis
Mann-Whitney U test was used to compare ADC values of normal red marrow versus infiltrative marrow lesions. A p value of less than 0.05 was considered statistically significant.
Receiver operating characteristic (ROC) curve analyses were performed to assess the diagnostic performance of the ADC values and to determine suitable ADC cutoff points to separate red marrow from infiltrated marrow. A p value of less than 0.05 was considered statistically significant.
All analyses were performed using IBM SPSS statistical software (V. 24.0, IBM Corp., USA, 2016).