In this study, all 13 patients underwent both CT and WB-DWI, which allowed for a direct comparison. In most of them, malignant lesions were detected in various localizations, including bones, visceral organs, lymph nodes, and soft tissues.

Bone metastases.

 In each case where CT scan indicated a high suspicion of bone involvement, WB-DWI confirmed the metastatic nature of the lesion by demonstrating restricted diffusion. In 2 of these 13 patients with breast cancer and synonasal carcinoma, WB-DWI revealed additional lesions in the bone marrow that were invisible or indistinct on CT. This result is in line with previous studies (Heindel et al., 2014), which emphasized the higher sensitivity of MRI to early bone marrow involvement.

Visceral lesions.

 In each case where CT scan indicated metastases to visceral organs, WB-DWI confirmed the metastatic nature of the lesion by demonstrating diffusion restriction.

Lymph Node Involvement.

Evaluation of lymph nodes proved more challenging with WB-DWI, as all lymph nodes—whether benign or malignant—can exhibit some degree of restricted diffusion. To address this complexity, findings on DWI were carefully correlated with morphological features on T1_DIXON  and T2W sequences. This anatomical correlation was crucial for differentiating benign from pathologically enlarged lymph nodes, aligning with the approach in previous research (e.g., Schraml et al. [2013]), which underscores the importance of integrating both functional and anatomical data for accurate nodal assessment. By correlating changes in diffusion signal with nodal size, shape, and signal intensity on conventional MRI sequences, it was possible to refine the distinction between reactive lymphadenopathy and metastatic involvement, thereby increasing diagnostic confidence.

2. Limited comparison with PET-CT

Only two patients had PET-CT results available for comparison, reflecting the difficult logistics of accessing PET-CT in Ukraine. Nevertheless, these limited comparisons yielded successful results:

Bone metastases.

 WB-DWI and PET-CT revealed the same number of bone lesions in both patients. Similar to Schraml et al. (2013), who found that WB-MRI was superior to PET-CT in staging neuroendocrine tumors, our observations support the efficacy of MRI techniques in detecting skeletal lesions in various tumor types.

Visceral lesions.

 In one of these patients, WB-DWI demonstrated better visualization of liver metastases compared to PET-CT, where they could not be visualized in the background of the main pool of [18F]FDG PET-CT. Although the sample size is too small to draw definitive conclusions, this scenario emphasizes that MRI may sometimes be superior to PET-CT in certain areas or tumor subtypes due to better soft tissue contrast.

3. The role of WB-DWI in resource-limited settings

Given the current economic crisis in Ukraine and war-related disruptions, PET-CT scanners are not readily available in many centers. In contrast, MRI machines are more readily available, making WB-DWI a more practical imaging modality for detecting metastases. While CT remains the cornerstone for initial screening - especially for pulmonary lesions - WB-DWI can fill the gap in detecting early or subtle metastases in bone and soft tissue. This approach also spares patients the cumulative ionizing radiation exposure associated with repeated CT scans, making WB-DWI safer for long-term follow-up.

4. Advantages and limitations

Strengths.

Realistic application in settings where PET-CT is not available.

Possibility of integration into existing MRI equipment.

High sensitivity of MRI to bone and soft tissue lesions.

Absence of ionizing radiation. 

Limitations.

A small cohort of 13 patients limits the statistical power of the results

Only two patients had access to PET-CT, which reduces the generalizability of WB-DWI results compared to PET-CT for all cancer types.

Future large-scale, multicenter studies may more accurately establish the comparative efficacy, specificity, and sensitivity of WB-DWI compared to PET-CT. Nevertheless, the results of this study suggest that WB-DWI has considerable promise as an additional or alternative method for detecting metastatic lesions when PET-CT resources are limited.