Informativeness of whole-body diffusion-weighted magnetic resonance imaging and positron emission tomography with computed tomography in follicular lymphoma

Aim. This study conducted the possibilities of diffusion-weighted magnetic resonance imaging of the whole body – diffusion WB-MRI (in comparison with positron emission tomography with computed tomography – PET/CT) in assessing the volume and prevalence of the tumor, as well as determining bone marrow (BM) damage (for various cytological types) in the diagnosis and staging of the disease in patients with FL.

Materials and methods. A prospective comparative search study included 15 patients (4 men and 11 women, with a median age of 53 years) with newly diagnosed FL. Patients have not received antitumor chemotherapy previously. After the diagnosis was established, all patients (with the blindness of both the cases themselves and some specialists regarding the results of other specialists) were examined by PET/CT and diffusion WB-MRI, after which a BM examination was performed (histological examination and determination of B-cell clonality in BM puncture by PCR). Using the diffusion WB-MRI method, the prevalence of tumor lesion (nodal and extranodal foci) in each patient was estimated, and the total tumor volume was calculated, BM lesion was detected, and BM lesion volume was calculated. For lesions of different localization, the measured diffusion coefficient (DC) of the diffusion WB-MRI and the standardized rate of accumulation of the radiopharmaceutical in tissues (SUV) of the PET/CT method were determined and compared with each other (for the same areas). Statistical analysis was performed using the estimate of agreement (by Cohen’s kappa coefficient and asymptotic test) of the results of the compared methods.

Results. Estimates of the prevalence of tumor damage (lymph nodes and extranodal foci) using the diffusion WB-MRI and PET/CT methods were the same. High DC and SUV were observed in the peripheral lymph nodes, extranodal foci and bulky, low DC and SUV – in the foci of BM. All 4 methods successfully determined BM damage, however, the diffusion WB-MRI had comparatively less negative results. The highest values of SUV and CD were noted in cases of the 3 grade of FL. Using the diffusion WB-MRI method, the prevalence of tumor lesion was assessed in each patient (nodal and extranodal foci were detected) and the total tumor volume was calculated, BM lesion detection was performed, and the volume of BM lesion was calculated. It is important to note that with the help of diffusion WB-MRI, it was possible to measure separately the total tumor volume (46–2025 cm³) and separately the volume of bulky (25–1358 cm³). The diffusion WB-MRI allowed us to differentiate the volume of tumor tissue (reduced as a result of treatment) and residual (fibrous-adipose) tissue in residual formations (which averaged 21% of the initial volume). The predictors of a poor antitumor response were the maximum SUV values (more than 14.0) and the minimum DC values (0.5¥10^-3 mm²/s) in the BM foci.

Conclusion. The diffusion WB-MRI allows for detailed visualization of BM lesions and surrounding soft tissues both in the debut of the FL and in the process of tracking the effectiveness of chemotherapy, which makes it possible to use it along with PET/CT. Diffusion WB-MRI allows to separately evaluate the volume of true tumor tissue and residual tissue. Cases of the 3 grade of FL (including the transformation of FL into diffuse B-large cell lymphoma) are isolated due to low DC values (and high SUV values) in the tumor tissue. BM foci of FL lesion also have (in comparison with nodal and extranodal foci) lower DC values. The predictors of a poor antitumor response were high (from 14.0 or more) SUV valuesin the tumor (and especially in bulky), and low (about 0.5¥10³ mm²/s) DC values of BM foci. The PET/CT and diffusion WB-MRI have proven to be reliable diagnostic tools for establishing the stage of FL and detecting BM damage. Diffusion WB-MRI for FL is an informative first-line diagnostic method that allows regular monitoring of the disease and early detection of foci of relapse and disease progression.