Whole-Body Functional MRI and PET/MRI in Multiple Myeloma

Abstract

Bone disease is one of the major features of multiple myeloma (MM), and imaging has a pivotal role in both diagnosis and follow-up. Whole-body magnetic resonance imaging (MRI) is recognized as the gold standard for the detection of bone marrow involvement, owing to its high sensitivity. The use of functional MRI sequences further improved the performances of whole-body MRI in the setting of MM. Whole-body diffusion-weighted (DW) MRI is the most attractive functional technique and its systematic implementation in general clinical practice is now recommended by the International Myeloma Working Group. Whole-body dynamic contrast-enhanced (DCE) MRI might provide further information on lesions vascularity and help evaluate response to treatment. Whole Body PET/MRI is an emerging hybrid imaging technique that offers the opportunity to combine information on morphology, fat content of bone marrow, bone marrow cellularity and vascularization, and metabolic activity. Whole-body PET/MRI allows a one-stop-shop examination, including the most sensitive technique for detecting bone marrow involvement, and the most recognized technique for treatment response evaluation. This review aims at providing an overview on the value of whole-body MRI, including DW and DCE MRI, and combined whole-body ¹⁸F-FDG PET/MRI in diagnosis, staging, and response evaluation in patients with MM.

Keywords: MRI; PET/MRI; functional imaging; multiple myeloma; whole-body imaging.

Figure 1

T1-weighted spin-echo and Dixon T2-weighted water-only images of the whole spine in the sagittal plane. Typical MRI findings associated with the five recognized bone marrow infiltration patterns. From left to right—normal appearance of bone marrow, focal lesion or focal involvement (arrows), homogeneous diffuse infiltration, combined diffuse and focal (arrows) involvement, and variegated or salt-and-pepper appearance.

Figure 2

Transverse diffusion-weighted images acquired with three different b values (from left to right: 50 s/mm², 400 s/mm² and 800 s/mm²) and the corresponding ADC images in a 76-year-old man with bone marrow focal lesions in the pelvis (red arrows) and left axillary extramedullary disease (yellow arrows). Bone marrow diffuse involvement appears as diffuse high signal intensity areas on both low and high b values diffusion-weighted images, with increased ADC values (mean 0.420 × 10⁻³ mm²/s). Both signal intensity on high b value diffusion-weighted images and ADC values (0.620 × 10⁻³ mm²/s in one pelvic lesion and 0.710 × 10⁻³ mm²/s in the axillary lesion) are highest in the focal lesions.

Figure 3

Hybrid PET/MRI provides simultaneous acquisition of morphological, functional, and metabolic information. Focal lesions localized in both the axial skeleton (yellow arrows) and the proximal appendicular skeleton (red arrows) are clearly depicted on the different images. ¹⁸F-FDG PET, DW MR, and DCE MR images provide combined information on the activity of the multifocal disease.

Figure 4

Coronal T1-weighted spin-echo and fat-suppressed T2-weighted images of the pelvis shows bilateral focal lesions in the right and left iliac bones, hypointense on T1- and hyperintense on T2-weighted images. Focal lesion on the right iliac bone (red arrows) appears to be metabolically active on transverse ¹⁸F-FDG PET image, has high signal intensity on both low and high b value DW images, higher ADC value than surrounding, and apparently normal bone marrow. Coronal DCE MR image shows an early and intense contrast-enhancement after contrast media administration, consistent with an active lesion. On the other hand, focal lesion on the left iliac bone (yellow arrows) appears to be metabolically inactive, and with no restriction of diffusion. Weak and thin linear and peripheral enhancement can be seen after contrast media administration, which is consistent with an inactive lesion.