In the treatment of oncological blood diseases (such as leukemia, lymphoma, and multiple myeloma), imaging plays a crucial role in diagnosis, staging, treatment planning, and monitoring response. The choice between MRI and PET-CT depends on the clinical question being addressed.
When is MRI needed?
MRI is primarily used for evaluating bone marrow involvement, soft tissue infiltration, and central nervous system (CNS) involvement. It is most commonly indicated in the following cases:
- Multiple Myeloma
- Detects bone marrow infiltration when standard X-rays are negative.
- Identifies focal lesions that may not be visible on PET-CT.
- Helps assess compression fractures or spinal cord compression caused by myeloma involvement.
- Leukemia (Especially Acute Leukemia with Suspected CNS Involvement)
- Evaluates leukemic infiltration in the brain, meninges, or spinal cord (CNS leukemia).
- Used when cerebrospinal fluid (CSF) analysis is inconclusive.
- Lymphomas with CNS Involvement
- Used to detect primary CNS lymphoma or secondary spread of systemic lymphoma to the brain/spinal cord.
- Bone Marrow Diseases (Myelodysplastic Syndromes, Aplastic Anemia, and Bone Marrow Failure Syndromes)
- Assesses bone marrow composition and infiltration.
- Assessing Bone Damage
- Used when there is concern for avascular necrosis (a side effect of chemotherapy or corticosteroid treatment).
When is PET-CT needed?
PET-CT is the preferred imaging method when looking for metabolically active disease, staging, and monitoring treatment response. It is most useful in:
- Lymphoma (Hodgkin’s and Aggressive Non-Hodgkin’s Lymphomas)
- Gold standard for staging, restaging, and assessing treatment response.
- Differentiates active disease from post-treatment fibrosis.
- Detects residual disease or relapse.
- Multiple Myeloma
- Identifies active bone lesions.
- Detects extramedullary myeloma (spread outside the bone marrow).
- Monitors treatment response.
- Leukemia (Certain Types with Extramedullary Involvement)
- PET-CT is not commonly used for leukemia but may be helpful in specific cases with extramedullary disease, such as chloromas (leukemic tumors).
- Detecting Relapse or Residual Disease
- PET-CT is preferred to check for minimal residual disease (MRD) in lymphoma and multiple myeloma.
Summary
- MRI is best for bone marrow assessment, spinal cord and CNS involvement, and detecting bone changes (e.g., in myeloma).
- PET-CT is best for detecting active disease, staging, monitoring response, and assessing relapse, particularly in lymphoma and multiple myeloma.
