ADC measurement in whole-body MRI for multiple myeloma: a three b-values vs. two b-values DWI comparison

To compare apparent diffusion coefficient (ADC) values in whole-body MRI (WB-MRI) reconstructed from diffusion-weighted imaging (DWI) with three b-values (50-500-1000 s/mm²) compared with two b-values (50-1000 s/mm²).

Patients with multiple myeloma who underwent 1.5 T WB-MRI were retrospectively included. Exclusion criteria were severe motion artifacts. Examinations included axial DWI with three b-values (50-500-1000 s/mm²); ADC maps were reconstructed with both three values of b(ADC3b) and two values of b(ADC2b) excluding b500 s/mm². According to MY-RADS guideline, bone lesion with ADC values 700-1400 µm²/sec was considered malignant and regions of interests (ROIs) were placed in bone lesions and healthy bone marrow. Both malignant lesions and healthy bone ADC3b were compared with ADC2b, considering as significant p < 0.05. In case of discordant ROIs on the two ADC maps for malignity/benignity, expert radiologists examined all the WB-MRI sequences to assign a malignant/benign qualitative assessment.

Fifty-five patients (25 females, 29-83 yo) were retrospectively included; 305 bone lesions and 303 healthy bone segments were assessed. Objective analysis showed different ADC values between bone lesions' in ADC3b and ADC2b (965.3 ± 216.7 µm²/sec vs 937.2 ± 218.8 µm²/sec, p < 0.0001) and in healthy bone marrow ROIs (588 ± 271.7 vs 573.1 ± 573.1 ± 271.2, p < 0.0001). Despite significant differences, almost all the analyzed ROIs lay in the same range of ADC for bone lesions. 10/305 bone lesions fell into the range of malignity for ADC3b while showing lower values < 700 µm²/sec for ADC2b (ADC3b 715.82 ± 190.9 µm²/sec vs. ADC2b 687.72 ± 185.2 µm²/sec); focal bone lesion with discordant values was then confirmed as lesions, in accordance with ADC3b, by a panel of experts that blind-reviewed the whole sequences of the examinations.

ADC2b is comparable with ADC3b except for borderline values (650-750 µm²/sec).