Translating principles of quality control to cardiovascular magnetic resonance: assessing quantitative parameters of the left ventricle in a large cohort.

Cardiac magnetic resonance (CMR) examinations require standardization to achieve reproducible results. Therefore, quality control as known as in other industries such as in-vitro diagnostics, could be of essential value. One such method is the statistical detection of long-time drifts of clinically relevant measurements. Starting in 2010, reports from all CMR examinations of a high-volume center were stored in a hospital information system. Quantitative parameters of the left ventricle were analyzed over time with moving averages of different window sizes. Influencing factors on the acquisition and on the downstream analysis were captured. 26,902 patient examinations were exported from the clinical information system. The moving median was compared to predefined tolerance ranges, which revealed an overall of 50 potential quality relevant changes ("alerts") in SV, EDV and LVM. Potential causes such as change of staff, scanner relocation and software changes were found not to be causal of the alerts. No other influencing factors were identified retrospectively. Statistical quality assurance systems based on moving average control charts may provide an important step towards reliability of quantitative CMR. A prospective evaluation is needed for the effective root cause analysis of quality relevant alerts.

Introduction of Lazy Luna an automatic software-driven multilevel comparison of ventricular function quantification in cardiovascular magnetic resonance imaging.

Cardiovascular magnetic resonance imaging is the gold standard for cardiac function assessment. Quantification of clinical results (CR) requires precise segmentation. Clinicians statistically compare CRs to ensure reproducibility. Convolutional Neural Network developers compare their results via metrics. Aim: Introducing software capable of automatic multilevel comparison. A multilevel analysis covering segmentations and CRs builds on a generic software backend. Metrics and CRs are calculated with geometric accuracy. Segmentations and CRs are connected to track errors and their effects. An interactive GUI makes the software accessible to different users. The software's multilevel comparison was tested on a use case based on cardiac function assessment. The software shows good reader agreement in CRs and segmentation metrics (Dice > 90%). Decomposing differences by cardiac position revealed excellent agreement in midventricular slices: > 90% but poorer segmentations in apical (> 71%) and basal slices (> 74%). Further decomposition by contour type locates the largest millilitre differences in the basal right cavity (> 3 ml). Visual inspection shows these differences being caused by different basal slice choices. The software illuminated reader differences on several levels. Producing spreadsheets and figures concerning metric values and CR differences was automated. A multilevel reader comparison is feasible and extendable to other cardiac structures in the future.

Frameless image guidance improves accuracy in three-dimensional interstitial brachytherapy needle placement.

PURPOSE: The aim of this work was to adapt a computer-assisted real-time three-dimensional (3D) navigation system for interstitial brachytherapy procedures. METHODS AND MATERIALS: The 3-D navigation system Surgical Planning and Orientation Computer System (SPOCS; Aesculap, Tuttlingen, Germany) was adapted for use in interstitial brachytherapy. A special needle holder with mounted infrared-emitting diodes (IRED) for 3D navigation-based needle implantation was developed. Measurements were made on a series of different phantoms to study the feasibility and the overall accuracy and precision of the navigation system with regard to single-needle application and volume implants (multiple-needle implantations). In all, 250 single implants and 20 volume implants were performed. Accuracy was measured as the target registration error (TRE) between the preoperatively defined and the achieved target position. RESULTS: Analyses of the 250 different targets showed a mean TRE for single-needle applications of 1.1 mm (SD +/- 0.4 mm), 0.9 mm (SD +/- 0.3 mm), and 0.7 mm (SD +/- 0.3 mm) in the x, y, and z direction, respectively. The maximal deviation was 2.3 mm. The corresponding TRE in the x, y, and z direction for volume implants was 1.6 mm (SD +/- 0.4 mm), 1.9 mm (SD +/- 0.6 mm), and 1.0 mm (SD +/- 0.4 mm), respectively. The maximum deviation was 2.9 mm. CONCLUSIONS: The adaptation of a commercially available surgical planning and navigation system to interstitial brachytherapy is feasible. It enables virtual planning and improved accuracy in 3D interstitial needle implantation.

Creating a statistical atlas of the cranium.

Normative data is very important for simulation procedures in craniofacial surgery. While treating e.g. a malformed skull the surgeon seeks to reconstruct its natural and harmonic shape. Atlas or normative data of the skull could support the surgeon in this effort, as it would provide a standard model of the skull which gives an idea of the natural shape. We create a standard skull by averaging regularly formed skulls in a shape space spanned by spherical harmonics. While state-of-the-art methods use landmarks to define the shape and mean shapes, this method is deterministic, i.e. it manages averaging without landmarks and it provides a complete description of the shape. In addition the shape space can be used to classify shapes to identify different types of an anatomy.

Intraoperative guidance of pre-planned bone deformations with a surface scanning system.

Computer- and robot-based systems to support interventions become more and more important in modem surgery. In general these systems provide methods to plan an intervention pre-operatively and to execute it with support from a autonomous robot-system. Due to the principle restriction of a robot to comparatively simple work steps, there are some complex work steps which the surgeon may plan but which he/she has to execute manually. In craniofacial surgery osteotomised bone segments are deformed by hand to a shape given by the planning system. We support the execution of pre-planned deformation by comparison of the actual shape of an object with the target shape. The actual shape is obtained intra-operatively with a surface scanning device, the deviation from the target shape are visualised by projecting colour-coded error values directly on the object to be deformed. The surgeon uses these projections to adjust further deformation steps. The system is therefore able to validate the correct execution of planned deformations, especially of bony structures.

A new, accurate and easy to implement camera and video projector model.

In 2000, the Institute for Process Control and Robotics/Universität Karlsruhe (TH) has developed a prototype system for projector based augmented reality consisting of a state-of-the-art PC, two CCD cameras and a video projector which is used for registration and projection of surgical planning data. Tracking, registration as well as projection require an accurate calibration process for cameras and video projectors. We have developed a new, flexible, plain and easy to implement model, which can both be used for calibration of cameras and video projectors.