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In addition to JSW measurement, objective evaluation of osteophyte formation and subchondral bone density is possible on standard radiographs. The measured differences between OA and healthy individuals suggest that KIDA allows detection of changes in time, although sensitivity to change has to be demonstrated in long-term follow-up studies.

PurposeTo demonstrate the feasibility of a novel, ellipse fitting approach, named PLANET, for simultaneous estimation of relaxation times T1 and T2 from a single 3D phase‐cycled balanced steady‐state free precession (bSSFP) sequence.MethodsA method is presented in which the elliptical signal model is used to describe the phase‐cycled bSSFP steady‐state signal. The fitting of the model to the acquired data is reformulated into a linear convex problem, which is solved directly by a linear least squares method, specific to ellipses. Subsequently, the relaxation times T1 and T2, the banding free magnitude, and the off‐resonance are calculated from the fitting results.ResultsMaps of T1 and T2, as well as an off‐resonance and a banding free magnitude can be simultaneously, quickly, and robustly estimated from a single 3D phase‐cycled bSSFP sequence. The feasibility of the method was demonstrated in a phantom and in the brain of healthy volunteers on a clinical MR scanner. The results were in good agreement for the phantom, but a systematic underestimation of T1 was observed in the brain.ConclusionThe presented method allows for accurate mapping of relaxation times and off‐resonance, and for the reconstruction of banding free magnitude images at realistic signal‐to‐noise ratios. Magn Reson Med 79:711–722, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

Proton resonance frequency shift-based MR thermometry (MRT) is hampered by temporal magnetic field changes. Temporal changes in the magnetic susceptibility distribution lead to nonlocal field changes and are, therefore, a possible source of errors. The magnetic volume susceptibility of tissue is temperature dependent. For water-like tissues, this dependency is in the order of 0.002 ppm/°C. For fat, it is in the same order of magnitude as the temperature dependence of the proton electron screening constant of water (0.01 ppm/°C). For this reason, proton resonance frequency shift-based MR thermometry in fatty tissues, like the human breast, is expected to be prone to errors. We aimed to quantify the influence of the temperature dependence of the susceptibility on proton resonance frequency shift-based MR thermometry. Heating experiments were performed in a controlled phantom set-up to show the impact of temperature-induced susceptibility changes on actual proton resonance frequency shift-based temperature maps. To study the implications for a clinical case, simulations were performed in a 3D breast model. Temperature errors were quantified by computation of magnetic field changes in the glandular tissue, resulting from susceptibility changes in a thermally heated region. The results of the experiments and simulations showed that the temperature-induced susceptibility changes of water and fat lead to significant errors in proton resonance frequency shift-based MR thermometry. Magn Reson Med 64:1360-1372, 2010. V C 2010 Wiley-Liss, Inc. Key words: susceptibility; temperature; PRFS-based MR thermometry; HIFU; fat; glandular tissue Next to excellent soft-tissue contrast, MRI also offers methods to acquire temperature maps, which allow for monitoring and guiding of thermal interventions. Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is the most commonly used temperature monitoring technique. It is based on the temperature dependence of the proton resonance frequency (PRF) of protons in water molecules and is thus applicable in water-containing tissues. The technique does not work for protons in fat molecules and for this reason adequate fat suppression is essential for accurate thermometry in tissues containing both water and fat.PRFS-based MRT is hampered by temporal field changes. In the application of this technique, the contribution of field changes, which originate from temperature-induced magnetic volume susceptibility changes, is commonly ignored. This disregards the fact that the magnetic volume susceptibility x (which will hereinafter be referred to as ''susceptibility'') of water and water-containing tissue is temperature dependent (1,2). Several studies have suggested that this may lead to PRFS-based temperature errors in water and water-containing tissues (1-4). This has been shown for water (3) and brain tissue (2), which both have a temperature dependent susceptibility in the order of dx/dT ¼ 0.002 ppm/ C.In tissues containing both water and fat, more considerable susceptibility-relat...

ObjectiveThe purpose of this prospective multicenter study was to assess the safety and technical feasibility of volumetric Magnetic Resonance-guided High Intensity Focused Ultrasound (MR-HIFU) ablation for treatment of patients with symptomatic uterine fibroids.MethodsThirty-three patients with 36 fibroids were treated with volumetric MR-HIFU ablation. Treatment capability and technical feasibility were assessed by comparison of the Non-Perfused Volumes (NPVs) with MR thermal dose predicted treatment volumes. Safety was determined by evaluation of complications or adverse events and unintended lesions. Secondary endpoints were pain and discomfort scores, recovery time and length of hospital stay.ResultsThe mean NPV calculated as a percentage of the total fibroid volume was 21.7%. Correlation between the predicted treatment volumes and NPVs was found to be very strong, with a correlation coefficient r of 0.87. All patients tolerated the treatment well and were treated on an outpatient basis. No serious adverse events were reported and recovery time to normal activities was 2.3 ± 1.8 days.ConclusionThis prospective multicenter study proved that volumetric MR-HIFU is safe and technically feasible for the treatment of symptomatic uterine fibroids.Key Points• Magnetic-resonance-guided high intensity focused ultrasound allows non-invasive treatment of uterine fibroids.• Volumetric feedback ablation is a novel technology that allows larger treatment volumes• MR-guided ultrasound ablation of uterine fibroids appears safe using volumetric feedback