Optimising diffusion weighted MRI for imaging metastatic and myeloma bone disease and assessing reproducibility

Objectives To establish normal bone marrow values of apparent diffusion coefficient (ADC) over an age range, compare them with metastatic and myelomatous involvement, to establish reproducibility and to optimise b values. Methods The ADCs of bone marrow in 7 volunteers (mean age 29.7 years), 34 volunteers (mean age 63.3 years) and 43 patients with metastatic and myelomatous involvement (mean age 65.5 years) were measured. In 9 volunteers diffusion weighted MRI was repeated within 7 days. b values were derived to optimise contrast between normal and pathological marrow. Results The mean ADC of bone marrow in younger volunteers was significantly higher than that of older volunteers. The coefficient of reproducibility was 14.8%. The ADC mean of metastatic and myeloma bone disease was 1054 +/- 456 x 10(-6) mm(2)s(-1). An ADC threshold of 655x10(-6) mm(2)s(-1) separated normal and abnormal marrow with a sensitivity and specificity of 90% and 93% respectively. Contrast between normal and abnormal marrow was optimal at b=1389 smm(-2). Conclusion The reproducibility of ADC measurements in bone is equivalent to published data for soft tissue with a high sensitivity and specificity for separating abnormal from age matched normal bone marrow. A b value of around 1,400 smm(-2) is optimal for imaging bone marrow.