A reproducible semi-automatic method to quantify the muscle-lipid distribution in clinical 3D CT images of the thigh

Abstract

Many studies use threshold-based techniques to assess in vivo the muscle, bone and adipose tissue distribution of the legs using computed tomography (CT) imaging. More advanced techniques divide the legs into subcutaneous adipose tissue (SAT), anatomical muscle (muscle tissue and adipocytes within the muscle border) and intra- and perimuscular adipose tissue. In addition, a so-called muscle density directly derived from the CT-values is often measured. We introduce a new integrated approach to quantify the muscle-lipid system (MLS) using quantitative CT in patients with sarcopenia or osteoporosis. The analysis targets the thigh as many CT studies of the hip do not include entire legs The framework consists of an anatomic coordinate system, allowing delineation of reproducible volumes of interest, a robust semi-automatic 3D segmentation of the fascia and a comprehensive method to quantify of the muscle and lipid distribution within the fascia. CT density-dependent features are calibrated using subject-specific internal CT values of the SAT and external CT values of an in scan calibration phantom. Robustness of the framework with respect to operator interaction, image noise and calibration was evaluated. Specifically, the impact of inter- and intra-operator reanalysis precision and addition of Gaussian noise to simulate lower radiation exposure on muscle and AT volumes, muscle density and 3D texture features quantifying MLS within the fascia, were analyzed. Existing data of 25 subjects (age: 75.6 ± 8.7) with porous and low-contrast muscle structures were included in the analysis. Intra- and inter-operator reanalysis precision errors were below 1% and mostly comparable to 1% of cohort variation of the corresponding features. Doubling the noise changed most 3D texture features by up to 15% of the cohort variation but did not affect density and volume measurements. The application of the novel technique is easy with acceptable processing time. It can thus be employed for a comprehensive quantification of the muscle-lipid system enabling radiomics approaches to musculoskeletal disorders.

Quantitative analysis of skeletal muscle by computed tomography imaging—State of the art

“…Although CT studies on muscle assessment appeared not long after the introduction of the first CT scanner in the mid-1970s, little has been published on acquisition protocols for muscle measurements. For the thigh and upper femur, the following settings have been reported: tube voltage of 100–120 kV, exposure: 40–200 mAs, slice thickness 1–10 mm and a soft to medium reconstruction kernel [22] , [23] , [24] , [25] . Thicker slices reduce noise and are adequate when the muscle volume or density is of primary interest.…”

“…In the thigh and proximal femur, scans usually cover 10–20 cm, but in some studies, the complete upper or lower limb was scanned [26] , [27] , while in others, a single 10-mm-thick slice was acquired at mid-thigh [22] , [28] . Several studies applied a retrospective analysis of existing CT scans, often initially collected in epidemiological or cross-sectional studies, to measure the bone mineral density (BMD) and assess fracture risk [25] , [28] , [29] , [30] .…”

Interactions between Muscle and Bone—Where Physics Meets Biology

“…More positive results have been reported from CT studies analyzing muscle attenuation and size [200,201]. In a more recent retrospective analysis of the European Femur Fracture Study (EFFECT), a cross-sectional study of 40 female patients with acute hip fractures and 55 controls, we performed a sophisticated texture analysis of the distribution of EMCL and muscle tissue [202] using a CT density-based histogram analysis was performed [203]. After adjustment for BMD and cortical thickness, the hip fracture group was characterized by the lower relative adipose tissue volume of the upper thigh and some of the texture parameters discriminated the osteoporotic hip fracture [204].…”

Muskelbildgebung bei Sarkopenie

“…7). Nachdem man in der durch die Faszie definierten Region zunächst den Femurknochen segmentiert und dann EML-Aggregationen mithilfe eines einfachen Schwellwertes ebenfalls ausschließt, da sie ähnliche CT-Werte wie SAT haben, kann für alle anderen Voxel des Muskels über ihren CT-Wert der relative Anteil von Muskelgewebe und IML bestimmt werden (29,30).…”

“…CT-Scanner sind nicht immer exakt auf 0 HU für Wasser kalibriert und die HU-Differenz zwischen adipösem und Muskelgewebe ist für unterschiedliche Scanner und individuell verschieden. Durch geeignete Phantommessungen können die Auswirkungen aber minimiert werden (30). Ein zweites Pro-…”