Utility of positron emission tomography-magnetic resonance imaging in musculoskeletal imaging

Differentiation between neoplastic and nonneoplastic conditions magnetic resonance imaging(MRI) has established itself as one of the key clinical tools in evaluation of musculoskeletal pathology. However, MRI still has several key limitations which require supplemental information from additional modalities to complete evaluation of various disorders. This has led to the development hybrid positron emission tomography(PET)-MRI which is rapidly evolving to address key clinical questions by using the morphological strengths of MRI and functional information of PET imaging. In this article, we aim to review physical principles and techniques of PET-MRI and discuss clinical utility of functional information obtained from PET imaging and structural information obtained from MRI imaging for the evaluation of musculoskeletal pathology. More specifically, this review highlights the role of PET-MRI in musculoskeletal oncology including initial diagnosis and staging, treatment planning and posttreatment follow-up. Also we will review utility of PET-MRI in evaluating musculoskeletal infections(especially in the immunocompromised and diabetics) and inflammatory condition. Additionally, common pitfalls of PET-MRI will be addressed.

Shoulder adhesive capsulitis in cancer patients undergoing positron emission tomography-computed tomography and the association with shoulder pain

BACKGROUND Adhesive capsulitis is a relatively common condition that can develop in cancer patients during treatment.Positron emission tomography-computed tomography(PET-CT)is routinely performed as a follow-up study in cancer patients after therapy.Being aware of PET-CT findings to suggest shoulder adhesive capsulitis may help to alert clinicians for the diagnosis of unsuspected shoulder capsulitis.AIM To assess the association of shoulder adhesive capsulitis with cancer/therapy type and symptoms in cancer patients undergoing PET-CT.METHODS Our prospective study received Institutional Review Board approval.Written informed consent was obtained from all patients,who answered a questionnaire regarding shoulder pain/stiffness at the time of PET-CT study,between March 2015 and April 2019.Patients with advanced glenohumeral arthrosis,metastatic disease or other mass in the shoulder,or shoulder arthroplasty were excluded.Patterns of shoulder capsule 18F-fluorodeoxyglucose(FDG)uptake were noted.Standard Uptake Value(SUV)max and SUVmean values were measured at rotator interval(RI)and deltoid muscle in bilateral shoulders.Normalized SUV(SUV of RI/SUV of deltoid muscle)was also calculated.We assessed if SUV values are different between symptomatic and asymptomatic patients in both shoulders.Covariates were age,gender,and therapy type(surgery,chemotherapy,radiation).Wilcoxon rank sum tests were used to compare unadjusted marginal differences for age,SUV measurements between symptomatic and asymptomatic patients.Multiple linear regression models were used to examine the relationship between right or left shoulder SUV measurements and symptom status,after adjusting for covariates.Statistical significance level was set at P<0.05.RESULTS Of 252 patients initially enrolled for the study(mean age 66 years,67 symptomatic),shoulder PET-CT data were obtained in 200 patients(52 were excluded due to exclusion criteria above).The most common cancer types were lymphoma(n=61),lung(n=54)and breast(n=53).No significant difference was noted between symptomatic and asymptomatic patients in terms of age,gender,proportion of patients who had surgical therapy and radiation therapy.A proportion of patients who received chemotherapy was higher in patients who were asymptomatic in the right shoulder compared to those symptomatic in the right shoulder(65%vs 48%,P=0.012).No such difference was seen for the left shoulder.In both shoulders,SUVmax and SUVmean were higher in symptomatic shoulders than asymptomatic shoulders(Left SUVmax 2.0 vs 1.6,SUVmean 1.6 vs 1.3,both P<0.002;Right SUVmax 2.2 vs 1.8,SUVmean 1.8 vs 1.5,both P<0.01).For lung cancer patients,bilateral RI SUVmax and SUVmean values were higher in symptomatic shoulders than asymptomatic shoulders.For other cancer patients,symptomatic patients had higher left RI SUVmax/mean than asymptomatic patients after adjustment.CONCLUSION In symptomatic patients metabolic activities in RI were higher than asymptomatic patients.Adhesive capsulitis should be considered in cancer patients with shoulder symptoms and positive FDG uptake in RI.