Comparison between subtalar joint quantitative kinematic 4-D CT parameters in healthy volunteers and patients with joint stiffness or chronic ankle instability: A preliminary study.

OBJECTIVE: to compare quantitative kinematic 4-D CT parameters between healthy volunteers and pathologic patients (joint stiffness or chronic ankle instability). METHODS: Thirteen healthy volunteers without previous ankle trauma, 18 patients with clinical subtalar joint stiffness and 10 patients with chronic ankle instability diagnosed based on clinical and imaging findings were prospectively evaluated with 4-D CT. This study was approved by the local ethics committee and all patients signed an informed consent. The subtalar joint was evaluated during a prono-supination cycle. Two angles and two distances between the talus and the calcaneus were measured semi-automatically and independently by two readers. Measurement variations were compared in these three different groups. RESULTS: There were statistically significant differences between axial and coronal talocalcaneal angles of healthy volunteers and patients with joint stiffness (p < 0.0001). The best sensitivities and specificities for the identification of subtalar joint stiffness were 92-100% and 74-94%. Mean and maximal posterior calcaneal facet uncovering were significantly lower in patients with chronic ankle instability patients compared to healthy volunteers (p < 0.006) with sensitivities and specificities of 92-95% and 80-92% respectively. CONCLUSION: Quantitative analysis in 4D CT can provide an objective criteria for the differentiation between healthy volunteers and patients with subtalar joint stiffness and chronic ankle instability.

Automatic rib cage unfolding with CT cylindrical projection reformat in polytraumatized patients for rib fracture detection and characterization: Feasibility and clinical application.

OBJECTIVES: To assess the use of CT with unfolded cylindrical projection (UCP) for rib fracture detection and characterization. METHODS: The images from 60 polytraumatized patients who underwent whole body CT were evaluated for the presence and characterization of rib fractures (displaced or not, single or multiple). Two readers independently evaluated conventional CT images and UCP images in two readout sessions at least one month apart. All readouts were timed. A gold standard was established by two radiologists with 12 and 22 years of clinical experience based on the combined analysis of conventional and UCP reformats. RESULTS: Using UCP, the mean evaluation time was 27%-54% shorter (P = 0.01 and <0.0001) while maintaining a comparable diagnostic performance (sensitivity and specificity of 68.4-79.1% and 99.5-99.6% for conventional reformats and 70.6-91.0% and 96.8-97.7% for UCP) and a good reproducibility (Kappa of 0.71). The multiple fracture detection ratio of UCP was similar to that of conventional reformats (>80%). There were more false positives and false negatives using UCP and displaced fractures were harder to characterize. CONCLUSION: UCP yielded a diagnostic performance similar to that of conventional reformats for the detection of rib fractures with a good reproducibility and a noticeable reduction in evaluation time.

Quantitative Analysis of Subtalar Joint Motion With 4D CT: Proof of Concept With Cadaveric and Healthy Subject Evaluation.

OBJECTIVE: The purpose of this study was to show the application of quantitative 4D CT for subtalar joint evaluation in healthy volunteers and cadavers. MATERIALS AND METHODS: Fifteen healthy volunteers with no history of subtalar joint trauma and three cadavers were prospectively evaluated with dynamic CT. The subtalar joint was evaluated during a pronosupination cycle. All acquisitions (cadavers and healthy volunteers) were performed using intermittent sequential mode with a 320-MDCT scanner. Angles and distances between the talus and the calcaneus were measured semiautomatically. Measurement variation was described in healthy volunteers and in cadavers, the latter before and after resection of the cervical and interosseous ligaments. The mean effective dose was below 0.1 mSv. RESULTS: In cadavers, mean increases in joint amplitude over 19% and of 22% were seen after partial ligament sectioning and after full ligament sectioning, respectively. The interobserver variability of the measurement ratios was considered to be excellent for three of the measurements made (ICC > 0.87) and moderate for the fourth (ICC = 0.57). The normal range of joint motion in healthy volunteers is described, with joint amplitudes varying from 6.4% to 22.8%. CONCLUSION: Quantitative dynamic CT of the subtalar joint can provide a detailed analysis of joint motion, supporting its potential role in the evaluation of subtalar instability.

Evidence-based recommendations for musculoskeletal kinematic 4D-CT studies using wide area-detector scanners: a phantom study with cadaveric correlation.

PROPOSE: To establish evidence-based recommendations for musculoskeletal kinematic 4D-CT on wide area-detector CT. MATERIALS AND METHODS: In order to assess factors influencing image quality in kinematic CT studies, a phantom consisting of a polymethylmethacrylate rotating disk with round wells of different sizes was imaged with various acquisition protocols. Cadaveric acquisitions were performed on the ankle joint during motion in two different axes and at different speeds to allow validation of phantom data. Images were acquired with a 320 detector-row CT scanner and were evaluated by two readers. RESULTS: Motion artefacts were significantly correlated with various parameters (movement axis, distance to centre, rotation speed and volume acquisition speed) (p < 0.0001). The relation between motion artefacts and distance to motion fulcrum was exponential (R2 0.99). Half reconstruction led to a 23 % increase in image noise and a 40 % decrease in motion artefacts. Cadaveric acquisitions confirmed phantom data. Based on these findings, high tube rotation speed and half reconstruction are recommended for kinematic CT. The axis of motion significantly influences image artefacts and should be considered in patient training and evaluation of acquisition protocol suitability. CONCLUSION: This study provides evidence-based recommendations for musculoskeletal kinematic 4D-CT. KEY POINTS: • Motion artefacts can hamper the quality and interpretation of dynamic joint studies • The recommendations presented here help increase image quality • Patient training and preparation can be improved • The artefact-free distance concept helps protocol adaptation and comparison.

Musculoskeletal Wide-Detector CT Kinematic Evaluation: From Motion to Image.

Kinematic computed tomography (CT) allows identification of fine positional anomalies of bones during motion and under stress and has a potential role in the evaluation of dynamic joint diseases. The increasing width of CT detector systems has made kinematic CT clinically available. Information on acquisition protocol, patient preparation, and the influence of motion on image quality is scarce in the literature despite the obvious importance for the clinical application of this technique. In this article we review the current knowledge on the relation between motion and artifacts, recommendations for the acquisition protocol, as well as current indications for kinematic CT.