Quantitative and qualitative evaluation of three MSCT for high resolution bone imaging.

INTRODUCTION: Strategies for achieving high resolution varies between manufacturers. In CT, the helical mode with narrow collimation has long been considered as the gold standard for high-resolution imaging. More recently, incremental modes with small dexels and focal spot, have been developed but have not been compared with helical acquisitions under optimal conditions. The aim of this work is to compare the high-resolution acquisition strategies currently proposed by recent MSCT. METHODS: Three CT systems were compared. A phantom was used to evaluate geometric accuracy, uniformity, scan slice geometry, and spatial resolution. Human dry bones were used to test different protocols on real bone architecture. A blind visual analysis was conducted by trained CT users for classifying the different acquisitions (p-values). RESULTS: All systems give satisfactory results in terms of geometric accuracy and uniformity. The in-plane MTF at 5% were respectively 13.4, 15.9 and 18.1 lp/cm. Dry-bones evaluation confirms that acquisition#3 is considered as the best. CONCLUSIONS: The incremental acquisition coupled with à small focal spot, and a high-sampling detector, overpasses the reference of low-pitch helical acquisitions for high-resolution imaging. Cortical bone, bony vessels, and tumoral matrix analysis are the very next challenges that will have to be managed to improve normal and pathologic bone imaging thanks to the availability UHR-CT systems.

Cement Plug Fragmentation Following Percutaneous Cementoplasty of the Bony Pelvis: Is it a Frequent Finding in Clinical Practice?

PURPOSE: To report the rate of fragmentation of the cement plug following percutaneous cementoplasty with polymethylmethacrylate (PMMA) in the bony pelvis (i.e., pelvic bones or sacrum). MATERIALS AND METHODS: Post-interventional and follow-up CT scans of 56 patients (36 men; mean age of 68.4 ± 15.4) with a total of 98 percutaneous cementoplasty procedures were analyzed. Indications for treatment included painful malignant tumors (42.9%; 42/98) and insufficiency fractures (57,1%; 56/98). Fragmentation of PMMA was recorded for each cement plug. RESULTS: Mean interval between the procedure and the last available CT scan was 29.3 ± 18.8 months. There was no significant difference between the length of follow-up of malignant lesions (27.6 ± 15.1 months) and insufficiency fractures (29 ± 20.5 months) (p = 0.69). Fragmentation was diagnosed following 2/98 (2%) procedures, both in the malignant lesions group. The time intervals between the procedure and the first visualization of cement fragmentation were 6 for the first and 24 months for the second patient. CONCLUSION: Fragmentation of the PMMA plug following percutaneous cementoplasty in the bony pelvis is a rare finding at midterm follow-up. It was only observed in cementoplasty performed in malignant lesions and seems to be more a consequence of local mechanical stresses than as a result of porosity.

Biomechanics of the Osseous Pelvis and Its Implication for Consolidative Treatments in Interventional Oncology.

The osseous pelvis is a frequent site of metastases. Alteration of bone integrity may lead to pain but also to functional disability and pathological fractures. Percutaneous image-guided minimally invasive procedures, such as cementoplasty and screw fixation, have emerged as a viable option to provide bone reinforcement and fracture fixation, as stand-alone or combined techniques. Understanding the biomechanics of the osseous pelvis is paramount to tailor the treatment to the clinical situation. The purpose of the present review is to present the biomechanics of the osseous pelvis and discuss its implication for the choice of the optimal consolidative treatment.

Subjective Analysis of the Filling of an Acetabular Osteolytic Lesion Following Percutaneous Cementoplasty: Is It Reliable?

PURPOSE: To study the interobserver agreement for the analysis of lesion filling following cementoplasty of an acetabular osteolytic lesion, and investigate how subjective analysis compares to volumetric analysis. MATERIALS AND METHODS: A total of 21 acetabular osteolysis were retrospectively analysed on pre- and immediate post-cementoplasty CT-scans by two senior interventional radiologists and one resident using a 4 grade scale to quantify lesion filling (Fsubjective): F ≤ 25%, 25% < F ≤ 50%, 50% < F ≤ 75% or F > 75%. Volumetric analysis (Fvolumetric) was performed with the delineation of the osteolysis and the cement using regions of interest. The interobserver agreement for Fsubjective was evaluated using the Fleiss' Kappa test for the 4 grade scale and for a simplified 2 grades scale (F ≤ 50% and F > 50%). The performance of Fsubjective versus Fvolumetric (considered as the gold standard) was then evaluated for each reader using the calculation of accuracy and error to reference for the 4 grades scale and accuracy, sensitivity, specificity, positive predictive value and negative predictive value for the 2 grade scale. RESULTS: Interobserver agreement was considered as very low (< 0.2) for the 4 grade scale analysis and as low (> 0.2 and < 0.4) for the 2 grade scales analysis with kappa factors of 0.196 and 0.36 respectively. Compared to volumetric analysis, the overall accuracy of the 4- and 2- grade scales were 36.5% and 60% respectively. CONCLUSION: Subjective evaluation of cement filling of an acetabular osteolytic lesion is associated with poor interobserver agreement and overestimation of the percentage compared to volumetric analysis.

Bone cement modeling for percutaneous vertebroplasty.

Vertebroplasty procedures provide a significant benefit for patients suffering from vertebral fractures. In order to address current issues of vertebroplasty procedures, an injection device able to control the bone cement viscosity has been developed. In addition, this device allows to protect the practitioner by removing him/her from the X-rays area. In this context, a study is first proposed to quantify the bone cement viscosity during its polymerization reaction on a rotational rheometer. These experimental measurements have led to the identification of a complete behavior law that takes into account the simultaneous effects of shear rate, time, and temperature. Based on this preliminary study, this article finally aims to prove the ability of estimating the viscosity of the flowing bone cement on the developed injection system. A final set of experiments validates that the injection device dedicated to vertebroplasty procedures can control the flowing bone cement viscosity by acting on the temperature. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1504-1515, 2019.

An automatic differentiation-based gradient method for inversion of the shear wave equation in magnetic resonance elastography: specific application in fibrous soft tissues.

Quantitative and accurate measurement of in vivo mechanical properties using dynamic elastography has been the scope of many research efforts over the past two decades. Most of the shear-wave-based inverse approaches for magnetic resonance elastography (MRE) make the assumption of isotropic viscoelasticity. In this paper, we propose a quantitative gradient method for inversion of the shear wave equation in anisotropic media derived from a full waveform description using analytical viscoelastic Green formalism and automatic differentiation. The abilities and performances of the proposed identification method are first evaluated on numerical phantoms calculated in a transversely isotropic medium, and subsequently on experimental MRE data measured on an isotropic hydrogel phantom, on an anisotropic cryogel phantom and on an ex vivo fibrous muscle. The experiments are carried out by coupling circular shear wave profiles generated by acoustic radiation force and MRE acquisition of the wave front. Shear modulus values obtained by our MRE method are compared to those obtained by rheometry in the isotropic hydrogel phantom, and are found to be in good agreement despite non-overlapping frequency ranges. Both the cryogel and the ex vivo muscle are found to be anisotropic. Stiffness values in the longitudinal direction are found to be 1.8 times and 1.9 times higher than those in the transverse direction for the cryogel and the muscle, respectively. The proposed method shows great perspectives and substantial benefits for the in vivo quantitative investigation of complex mechanical properties in fibrous soft tissues.