Positron emission tomography/magnetic resonance in musculoskeletal disorders: proper sequences and workflow optimization

Magnetic resonance imaging (MRI) represents a gold standard imaging for detection of oncologic and non-oncologic musculoskeletal disorders (MSK), owing to its high soft tissue contrast. Positron Emission Tomography (PET) was proven to be clinically useful in MSK, owing to its early detection of metabolic disfunction and its high accuracy for monitoring therapy response. With hybrid PET/MRI system, simultaneous availability of both morphologic and metabolic features could potentially enhance the diagnostic accuracy in MSK. Some technical issue should be overcome for best imaging quality: specific MR sequences for accurate visualization of cortical bone and bone marrow involvement, such as zero-time echo (ZTE) or mu time echo (mu TE) sequences, that were shown to provide valuable attenuation coefficients for the bone, which leads to accurate quantitative analysis of bone and extra-bone tissues; implementation of novel attenuation map, owing to the presence of flexible coils in the field of view, additional sequences to reduce artifacts derived from metal implants. Workflow consideration should be addressed to the choice of proper sequences able to answer the clinical demand or the research purpose. Redundant information provided by useless sequences, which could prolong the whole scan time and increase the discomfort of the patient, should be avoided.