MRI for Bone Marrow Disorders

What Are Bone Marrow Disorders?

Bone marrow is the spongy tissue inside your bones that produces blood cells — red blood cells (carrying oxygen), white blood cells (fighting infection), and platelets (clotting). Bone marrow disorders encompass a wide range of conditions where this production goes wrong.

The major categories include:

• Haematological malignancies: Multiple myeloma (cancer of plasma cells within the marrow), leukaemia (cancer of white blood cells), and lymphoma (which can infiltrate the marrow).
• Myeloproliferative disorders: Conditions where the marrow overproduces certain blood cell types — polycythaemia vera, essential thrombocythaemia, myelofibrosis.
• Myelodysplastic syndromes: The marrow produces abnormal, immature blood cells that don't function properly.
• Aplastic anaemia: The marrow fails to produce enough blood cells.
• Bone marrow infiltration: Metastatic cancer from other organs (breast, prostate, lung) spreading to the marrow, and storage disorders (Gaucher disease).

Multiple myeloma alone affects around 5,700 people in the UK each year, making it the second most common blood cancer. Leukaemia affects roughly 10,000 people annually. Together, bone marrow disorders represent a significant proportion of cancer diagnoses.

Why MRI Is Used for Bone Marrow Assessment

MRI has become the single most sensitive imaging technique for detecting bone marrow abnormalities. Its advantages over other modalities are substantial:

• Direct marrow visualisation: MRI is the only imaging technique that directly visualises the bone marrow composition. It distinguishes normal fatty marrow (yellow marrow) from haematopoietic marrow (red marrow) from pathological infiltration.
• Superior sensitivity to X-ray and CT: By the time a myeloma deposit is visible on X-ray, it has already destroyed 30-50% of the trabecular bone. MRI detects marrow infiltration long before bone destruction occurs.
• Whole-body coverage: Whole-body MRI (WBMRI) images the entire skeleton in a single session, providing a comprehensive map of disease distribution. This has largely replaced skeletal surveys (multiple X-rays) for myeloma staging.
• Treatment response monitoring: MRI can detect early response to chemotherapy as marrow signal normalises — faster than structural changes visible on CT or X-ray.
• No radiation: For diseases requiring repeated imaging over years (monitoring myeloma, tracking metastatic disease), avoiding cumulative radiation exposure is a significant advantage.
• NICE and international guidelines: The International Myeloma Working Group, NICE, and BSH (British Society for Haematology) all recommend WBMRI as the standard imaging for myeloma staging and response assessment.

MRI Sequences Used

• T1-weighted: The cornerstone sequence for marrow assessment. Normal fatty marrow appears bright on T1 (fat is inherently bright). Pathological infiltration replaces the fatty marrow with tumour cells and water, causing the marrow signal to drop — appearing darker than the adjacent intervertebral disc or skeletal muscle. This "reversal" of normal marrow-disc signal relationship is a key diagnostic sign.
• STIR (Short Tau Inversion Recovery): Fat signal is suppressed, so normal fatty marrow appears dark. Pathological marrow (containing water-rich tumour) lights up bright. STIR is extremely sensitive to marrow abnormalities — arguably the most sensitive MRI sequence for detecting marrow infiltration.
• T2-weighted with fat saturation: Similar principle to STIR — pathological marrow appears bright against suppressed normal fat.
• DWI (Diffusion-Weighted Imaging): Increasingly used in whole-body protocols. Tumour-infiltrated marrow (with tightly packed cells) restricts water diffusion, appearing bright on DWI and dark on ADC maps. DWI is particularly useful for assessing treatment response — residual viable tumour restricts diffusion; treated, necrotic tissue does not.
• Contrast-enhanced (gadolinium): Not routinely used in WBMRI screening but adds value when characterising focal lesions. Active myeloma deposits enhance; treated or necrotic deposits do not.
• Dixon technique: Separates water and fat signals, allowing precise quantification of the fat fraction in marrow. This enables objective measurement of marrow composition rather than subjective visual assessment.

What Radiologists Look For

• Pattern of marrow involvement: Focal (discrete round/oval lesions), diffuse (widespread signal change throughout the marrow), combined (focal lesions on a diffusely abnormal background), or variegated ("salt and pepper" pattern). The pattern helps narrow the differential diagnosis.
• Signal characteristics: Lesions that are dark on T1 and bright on STIR/T2 fat-sat are the classic "red flag" for marrow infiltration. The T1 signal relative to muscle and disc is particularly useful — marrow darker than disc on T1 is abnormal in adults.
• Distribution: Myeloma favours the axial skeleton (spine, pelvis, ribs, skull) and proximal long bones. Metastatic deposits have similar distribution but may also involve the distal appendicular skeleton depending on the primary cancer.
• Fracture assessment: Distinguishing pathological fractures (from tumour-weakened bone) from osteoporotic fractures is a common MRI task. Pathological fractures typically show a mass extending beyond the vertebral margins, posterior element involvement, convex posterior cortex bulge, and abnormal enhancement — features not seen in simple osteoporotic fractures.
• Extraosseous disease: Soft tissue masses arising from bone lesions (plasmacytomas in myeloma), lymphadenopathy, and organ involvement.
• Spinal cord compression: A critical finding — epidural tumour compressing the spinal cord requires urgent treatment (radiotherapy or surgery).
• Response to treatment: Normalisation of marrow signal (return of fatty marrow on T1), reduction in DWI restriction, and shrinkage of focal lesions indicate treatment response.

How to Prepare for the Scan

• No fasting required for a standard WBMRI
• Wear comfortable clothing without metal — hospital gowns are often provided for whole-body scans
• Remove all jewellery, piercings, and removable dental work
• If you have bone pain, take your usual pain medication before the scan — lying still for an extended period on a hard table can be uncomfortable
• Drink normally but avoid caffeine for 4 hours before if DWI is included (some centres request this)
• Bring a list of current medications and relevant blood test results

What Happens During the Scan

Whole-body MRI is one of the longer scans — typically 45-60 minutes. You lie on your back with your arms by your sides. The scanner acquires images from the top of your skull to your mid-thighs (or further if indicated), moving the table through the scanner in stages.

Multiple coils may be placed over different body parts, or the scanner may use a continuous table-moving technique. You'll need to keep very still throughout.

If your haematologist has requested a more focused scan (e.g. spine and pelvis only), the scan will be shorter — around 30-40 minutes.

The scan is painless but can be tiring due to the length. Earplugs and headphones are provided. You can communicate with the radiographer at any time via the intercom.

What MRI Can't Show

• Bone marrow biopsy detail: MRI shows the macroscopic marrow appearance but can't determine cell type, chromosome abnormalities, or molecular markers. Bone marrow biopsy remains necessary for definitive diagnosis, classification, and risk stratification of haematological malignancies.
• Cortical bone detail: MRI is excellent for marrow but relatively poor for cortical bone (the hard outer shell). CT is superior for detecting subtle cortical destruction and assessing fracture risk in weight-bearing bones.
• Lytic lesion size for some criteria: Some myeloma staging systems use the size of lytic bone lesions (seen on CT) as criteria. MRI shows marrow infiltration, which may or may not have caused visible lytic destruction yet.
• Whole-body PET-CT comparison: PET-CT provides metabolic information (showing how active a lesion is) alongside anatomical detail. MRI and PET-CT are complementary rather than interchangeable for some haematological malignancies.

Treatment Pathways After Diagnosis

• Multiple myeloma: Treatment typically involves a combination of chemotherapy agents (bortezomib, lenalidomide, dexamethasone), followed by autologous stem cell transplant for eligible patients. Newer agents including daratumumab and carfilzomib have significantly improved outcomes. WBMRI is used for staging (detecting the number and distribution of lesions) and monitoring treatment response.
• Bone metastases: Treatment of the primary cancer, plus bone-directed therapy (bisphosphonates or denosumab to strengthen bone), radiotherapy for painful deposits, and surgery for impending or actual pathological fractures.
• Spinal cord compression: Emergency management with high-dose dexamethasone, urgent radiotherapy, and/or surgical decompression. MRI findings directly guide this urgent treatment.
• Supportive care: Pain management, fracture prevention (bisphosphonates, vertebroplasty/kyphoplasty for vertebral fractures), and treatment of anaemia (EPO, transfusions) and recurrent infections (immunoglobulins, antibiotics).
• Monitoring and surveillance: Regular WBMRI scans to track treatment response, detect relapse, and guide therapy adjustments. The frequency depends on the disease, treatment phase, and response.

Related Articles

• MRI for Ankylosing Spondylitis