Bone marrow is one of the largest organs in the human body, enclosing adipocytes, hematopoietic stem cells, which are responsible for blood cell production, and mesenchymal stem cells, which are responsible for the production of adipocytes and bone cells. Magnetic resonance imaging (MRI) is the ideal imaging modality to monitor bone marrow changes in healthy and pathological states, thanks to its inherent rich soft‐tissue contrast. Quantitative bone marrow MRI and magnetic resonance spectroscopy (MRS) techniques have been also developed in order to quantify changes in bone marrow water–fat composition, cellularity and perfusion in different pathologies, and to assist in understanding the role of bone marrow in the pathophysiology of systemic diseases (e.g. osteoporosis). The present review summarizes a large selection of studies published until March 2017 in proton‐based quantitative MRI and MRS of bone marrow. Some basic knowledge about bone marrow anatomy and physiology is first reviewed. The most important technical aspects of quantitative MR methods measuring bone marrow water–fat composition, fatty acid composition, perfusion, and diffusion are then described. Finally, previous MR studies are reviewed on the application of quantitative MR techniques in both healthy aging and diseased bone marrow affected by osteoporosis, fractures, metabolic diseases, multiple myeloma, and bone metastases. Level of Evidence: 3 Technical Efficacy: Stage 2J. Magn. Reson. Imaging 2018;47:332–353.

Background: Hemorrhagic transformation (HT) is a major complication of acute ischemic stroke, potentially associated with clinical deterioration. We attempted to identify risk factors and evaluated clinical relevance of minor and major HTs following endovascular thrombectomy (ET) in isolated middle cerebral artery (MCA) occlusions. Methods: This is a retrospective single-center analysis of 409 patients with isolated MCA occlusion treated with ET. Patients' and procedural characteristics, severity of HT according to the European Cooperative Acute Stroke Study criteria, and clinical outcomes were analyzed. Multivariate logistic regression models with standard retention criteria (p < 0.1) were used to determine risk factors and clinical relevance of HT. Results are shown as adjusted OR (aOR) and respective 95% CIs. Good neurologic short-term outcome was defined as National Institutes of Health Stroke Scale (NIHSS) score <5 at the day of discharge. Results: Of 299 patients included, hemorrhagic infarction (HI) was detected in 87 patients, while 13 patients developed parenchymal hematoma (PH). Higher age (aOR 0.970, 95% CI 0.947-0.993, p = 0.012), eligibility for intravenous recombinant tissue plasminogen activator (IV rtPA; aOR 0.512, 95% CI 0.267-0.982, p = 0.044), and complete recanalization (TICI 3, aOR 0.408, 95% CI 0.210-0.789, p = 0.008) were associated with a lower risk of HI. Risk factors for HI included higher admission NIHSS score (aOR 1.080, 95% CI 1.010-1.153, p = 0.024) and higher admission glucose levels (aOR 1.493, 95% CI 1.170-1.904, p = 0.001). Further, female sex tended to be associated with a lower risk of HI (aOR 0.601, 95% CI 0.316-1.143, p = 0.121), while a statistical trend was observable for proximal MCA occlusion (aOR 1.856, 95% CI 0.945-3.646, p = 0.073) and a history of hypertension (aOR 2.176, 95% CI 0.932-5.080, p = 0.072) to increase risk of HI. Longer intervals from symptom onset to first digital subtraction angiography runs (aOR 1.013, 95% CI 1.003-1.022, p = 0.009), lower preinterventional Alberta Stroke Program Early CT score (aOR 0.536, 95% CI 0.307-0.936, p = 0.028) and wake-up stroke (aOR 18.540, 95% CI 1.352-254.276, p = 0.029) were associated with PH. Both, PH and HI were independently associated with lower rates of good neurologic outcome (aOR 0.086, 95% CI 0.008-0.902, p = 0.041 and aOR 0.282, 95% CI 0.131-0.606, p = 0.001). Conclusion: Risk of HI following MCA occlusion and subsequent ET is mainly determined by factors influencing infarct severity. Good recanalization results seem to be protective against subsequent HI. Our results support the notion that occurrence of PH after ET is time dependent and risk increases with more extensive early ischemic damage. Both, HI and PH do not seem to be facilitated by bridging therapy with IV rtPA or the use of oral anticoagulants, but were independently associated with more severe neurologic disability. These results support the notion that HI is not a “benign” imaging sign.

OBJECTIVE To investigate compositional cartilage changes measured with 3T MRI-based T2 values over 48 months in overweight and obese individuals with different degrees of weight loss and to study whether weight loss slows knee cartilage degeneration and symptom worsening. DESIGN We studied participants from the Osteoarthritis Initiative with risk factors or radiographic evidence of mild to moderate knee OA with a baseline BMI ≥25kg/m2. We selected subjects who over 48 months lost a, moderate (BMI change, 5-10%, n=180) or large amount of weight (≥10%, n=78) and frequency-matched these to individuals with stable weight relative to their baseline BMI (<3%, n=258). T2 maps of the cartilage compartments of the right knee, grey-level co-occurrence matrix (GLCM) texture and laminar analyses were evaluated and associations with weight loss and clinical symptoms (WOMAC subscales for pain, stiffness and disability) were assessed using multivariable regression models adjusting for age, sex, baseline BMI and KL. RESULTS The amount of weight change was significantly associated with change in cartilage T2 of the medial tibia (β 0.9ms, 95%CI 0.4 to 1.1, P=0.001). An increase of T2 in the medial tibia was significantly associated with an increase in WOMAC pain (β 0.5ms, 95%CI 0.2 to 0.6, P=0.02) and disability (β 0.03ms, 95%CI 0.003 to 0.05, P=0.03. GLCM contrast and variance over all compartments showed significantly less progression in the >10% weight loss group compared to the stable weight group (both comparisons, P=0.04). CONCLUSIONS Weight loss over 48 months is associated with slowed knee cartilage degeneration and improved knee symptoms.

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BACKGROUND AND PURPOSE:Established methods of assessing bone mineral density are associated with additional radiation exposure to the patient. In this study, we aimed to validate a method of assessing bone mineral density in routine multidetector row CT of the lumbar spine.

Objectives To evaluate the performance of 3D T1w spoiled gradient-echo (T1SGRE) and ultra-short echo time (UTE) MRI sequences for the detection and assessment of vertebral fractures and degenerative bone changes compared with conventional CT. Methods Fractures (n = 44) and degenerative changes (n = 60 spinal segments) were evaluated in 30 patients (65 ± 14 years, 18 women) on CT and 3-T MRI, including CT-like images derived from T1SGRE and UTE. Two radiologists evaluated morphological features on both modalities: Genant and AO/Magerl classifications, anterior/posterior vertebral height, fracture age; disc height, neuroforaminal diameter, grades of spondylolisthesis, osteophytes, sclerosis, and facet joint degeneration. Diagnostic accuracy and agreement between MRI and CT and between radiologists were assessed using crosstabs, weighted κ, and intraclass correlation coefficients. Image quality was graded on a Likert scale. Results For fracture detection, sensitivity, specificity, and accuracy were 0.95, 0.98, and 0.97 for T1SGRE and 0.91, 0.96, and 0.95 for UTE. Agreement between T1SGRE and CT was substantial to excellent (e.g., Genant: κ, 0.92 [95% confidence interval, 0.83–1.00]; AO/Magerl: κ, 0.90 [0.76–1.00]; osteophytes: κ, 0.91 [0.82–1.00]; sclerosis: κ, 0.68 [0.48–0.88]; spondylolisthesis: ICCs, 0.99 [0.99–1.00]). Agreement between UTE and CT was lower, ranging from moderate (e.g., sclerosis: κ, 0.43 [0.26–0.60]) to excellent (spondylolisthesis: ICC, 0.99 [0.99–1.00]). Inter-reader agreement was substantial to excellent (0.52–1.00), respectively, for all parameters. Median image quality of T1SGRE was rated significantly higher than that of UTE (p < 0.001). Conclusions Morphologic assessment of bone pathologies of the spine using MRI was feasible and comparable to CT, with T1SGRE being more robust than UTE. Key Points • Vertebral fractures and degenerative bone changes can be assessed on CT-like MR images, with 3D T1w spoiled gradient-echo–based images showing a high diagnostic accuracy and agreement with CT. • This could enable MRI to precisely assess bone morphology, and 3D T1SGRE MRI sequences may substitute additional spinal CT examinations in the future. • Image quality and robustness of T1SGRE sequences are higher than those of UTE MRI for the assessment of bone structures.

BACKGROUND AND PURPOSE:Vessel anatomy is assumed to influence results of endovascular mechanical thrombectomy using stent retrievers. The purpose of this study was to analyze the influence of vessel curvature on recanalization results in patients with acute ischemic stroke caused by large-vessel occlusion.

2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1517-1526.