In this prospective study, WB-MRI was performed in 26 patients (aged 15-25 years) with severe HA (25 type A and 1 type B) receiving secondary prophylactic treatment. Two patients were excluded because of claustrophobia. In all patients, data on joint disease obtained by clinical examination were recorded and later compared (double-blinded) with the data on joint disease obtained by WB-MRI.

All patients underwent WB-MRI with the use of parallel imaging (iPAT). The following sequences were acquired: high-resolution coronal T1W sequences, GRE-T2 and STIR-sequences at 5 body levels with a 512x512 matrix, and sagittal GRE-T2 sequences targeted at the ankles,6mm thickness. The thorax, abdomen, pelvis and upper and lower extremities were examined. Using a 32-channel whole-body MRI scanner (Magnetom Avanto, Siemens Medical Solutions) with a total field of view of 205 cm and free table movement, all patients could be covered from head to toe within one examination. With this technique, high spatial resolution and acceptable scanning times were obtained.

WB-MRI was performed with the patient in supine decubitus, except in the case of very tall patients, in whom the FOV or study field did not include the elbows. These patients were positioned in supine decubitus with the arms flexed and crossed over the chest . If the elbows still could not be covered in this position, an additional examination was performed targeting the elbows. Total acquisition time was 45-60 minutes.

The examination was supervised and interpreted by two experienced radiologists who read the study on digitized visualization screens.

The following parameters were evaluated:

1) Involvement of the main joints (shoulders, elbows, hips, knees, ankles) to define the extension and degree of hemophilic articular involvement*

2) Bone or muscle-tendinous involvement, including muscle atrophy, hematoma, and pseudotumor (hemophilic extrarticular involvement)

3) Osteoarticular lesions unrelated to HA

* The extension and degree of hemophilic articular involvement were classified according to the European Score.

The European magnetic resonance imaging score is given in the format A(e:s:h)* and has a maximum score of 16(4:4:4)

Subchondral cysts (part of A)

Present in at least one bone

Present in at least two bones

More than three cysts in at least one bone

More than three cysts in at least two bones

Largest size more than 4 mm in at least one bone

Largest size more than 4 mm in at least two bones

Irregularity/erosion of subchondral cortex (part of A)

Present in at least one bone

Present in at least two bones

Involves more than half of joint surface in at least one bone

Involves more than half of joint surface in at least two bones

Cartilage loss (part of A)

Present in at least one bone

Present in at least two bones

Full-thickness defect in at least one bone

Full-thickness defect in at least two bones

Full-thickness defect involves more than one third of joint surface in at least one bone

Full-thickness defect involves more than one third of joint surface in at least two bones

Effusion/hemarthrosis (e) ,Hypertrophic synovial(s) ) ,Hemosiderin (h)

0 Absent ,1 Equivocal ,2 Small ,3 Moderate ,4 Large

*The A component is computed as the sum of true statements in three categories of osteochondral changes (i.e. subchondral cysts, irregularity/erosion of subchondral cortex and cartilage loss). The e- , s- and h components (i.e., effusion/hemarthrosis, synovial hypertrophy and hemosiderin deposition) are evaluated separately according to a five-grade (0-4) system. The maximum score is 16 (4:4:4).