A Heinrich

Measurement of susceptibility artifacts with histogram-based reference value on magnetic resonance images according to standard ASTM F2119.

Abstract Objective: The standard ASTM F2119 describes a test method for measuring the size of a susceptibility artifact based on the example of a passive implant. A pixel in an image is considered to be a part of an image artifact if the intensity is changed by at least 30% in the presence of a test object, compared to a reference image in which the test object is absent (reference value). The aim of this paper is to simplify and accelerate the test method using a histogram-based reference value. Materials and methods: Four test objects were scanned parallel and perpendicular to the main magnetic field, and the largest susceptibility artifacts were measured using two methods of reference value determination (reference image-based and histogram-based reference value). The results between both methods were compared using the Mann-Whitney U-test. Results: The difference between both reference values was 42.35±23.66. The difference of artifact size was 0.64±0.69 mm. The artifact sizes of both methods did not show significant differences; the p-value of the Mann-Whitney U-test was between 0.710 and 0.521. Conclusions: A standard-conform method for a rapid, objective, and reproducible evaluation of susceptibility artifacts could be implemented. The result of the histogram-based method does not significantly differ from the ASTM-conform method.

Software development for the determination of susceptibility artefacts in MRI after ASTM F2119

The standard F2119 developed by the American Society for testing and materials (ASTM) describes a method for the determination of susceptibility artefacts on the example of passive implants. The susceptibility artefact is clearly defined in that standard, but only a vague method for the determination of the artefact expansion is given. This is the reason why there are different methods for the determination of the artefact size, that are based on categorization [2] or estimation of the artefact with a measurement tool [3]. To solve this problem, a platform-independent and open source software for an objective and reproducible measurement of MR-susceptibility artefacts was developed.

Forensic Odontology: Automatic Identification of Persons Comparing Antemortem and Postmortem Panoramic Radiographs Using Computer Vision

PURPOSE  In forensic odontology the comparison between antemortem and postmortem panoramic radiographs (PRs) is a reliable method for person identification. The purpose of this study was to improve and automate identification of unknown people by comparison between antemortem and postmortem PR using computer vision. MATERIALS AND METHODS  The study includes 43 467 PRs from 24 545 patients (46 % females/54 % males). All PRs were filtered and evaluated with Matlab R2014b including the toolboxes image processing and computer vision system. The matching process used the SURF feature to find the corresponding points between two PRs (unknown person and database entry) out of the whole database. RESULTS  From 40 randomly selected persons, 34 persons (85 %) could be reliably identified by corresponding PR matching points between an already existing scan in the database and the most recent PR. The systematic matching yielded a maximum of 259 points for a successful identification between two different PRs of the same person and a maximum of 12 corresponding matching points for other non-identical persons in the database. Hence 12 matching points are the threshold for reliable assignment. CONCLUSION  Operating with an automatic PR system and computer vision could be a successful and reliable tool for identification purposes. The applied method distinguishes itself by virtue of its fast and reliable identification of persons by PR. This Identification method is suitable even if dental characteristics were removed or added in the past. The system seems to be robust for large amounts of data. KEY POINTS   · Computer vision allows an automated antemortem and postmortem comparison of panoramic radiographs (PRs) for person identification.. · The present method is able to find identical matching partners among huge datasets (big data) in a short computing time.. · The identification method is suitable even if dental characteristics were removed or added.. CITATION FORMAT · Heinrich A, Güttler F, Wendt S et al. Forensic Odontology: Automatic Identification of Persons Comparing Antemortem and Postmortem Panoramic Radiographs Using Computer Vision. Fortschr Röntgenstr 2018; 190: 1152 - 1158.

Fully automatic CT-histogram-based fat estimation in dead bodies

Post-mortem body cooling is the foundation of temperature-based death time estimations (TDE) in homicide cases. Forensic science generally provides two types of p.m. body cooling models, the phenomenological and the physical models. Since both of them have to implement important individual parameters like the quantity of abdominal fat explicitly or implicitly, a more exact quantification and localization of abdominal fat is a desideratum in TDE. Particularly for the physical models, a better knowledge of the abdominal fat distribution could lead to relevant improvements in TDEs. Modern imaging methods in medicine like computed tomography (CT) are opening up the possibility to register the quantity and spatial distribution of body fat in individual cases with unprecedented precision. Since a CT-scan of an individual’s abdominal region can comprise 1000 slices as an order of magnitude, it is evident that their evaluation for body fat quantification and localization needs fully automated algorithms. The paper at hand describes the development and validation of such an algorithm called “CT-histogram-based fat estimation and quasi-segmentation” (CFES). The approach can be characterized as a weighted least squares method dealing with the gray value histogram of single CT-slices only. It does not require any anatomical a priori information nor does it perform time-consuming feature detection on the CT-images. The processing result consists in numbers quantifying the amount of abdominal body fat and of muscle-, organ-, and connective tissue. As a by-product, CFES generates a quasi-segmentation of the slices processed differentiating fat from muscle-, organ-, and connective tissue. The tool is validated on synthetic data and on CT-data of a special phantom. It was also applied on a CT-scan of a dead body, where it produced anatomically plausible results.

In vitro stent assessment by MRI: visibility of lumen and artifacts for 27 modern stents.

Abstract Purpose: The purpose of this study was to measure artifacts and visibility of lumen for modern and most commonly used stents in vascular interventions according to a standardized test method of the American Society for Testing and Materials (ASTM). Materials and methods: Twenty-four peripheral self-expanding nitinol stents and three stainless steel stents with diameters between 5 and 8 mm and lengths between 30 and 250 mm from seven different manufacturers were compared on a 1.5T and a 3T magnetic resonance (MR) scanner. The visualization of lumen and artifacts was measured according to ASTM F2119 for a turbo spin echo (TSE) [repetition time(TR)/echo time (TE) 500/26 ms] and a gradient echo (GRE) (TR/TE 100/15 ms) sequence. The stents were placed parallel and perpendicular to the radio frequency field (B1). Results: There were large differences in visibility of the lumen for the stent models. The visualization of the lumen varies between 0% and 93% (perpendicular to B1), and 0% and 78% (parallel to B1), respectively. The maximum signal loss beyond the actual diameter was 6 mm (TSE) and 10 mm (GRE) for stents made of stainless steel, and lower than 1 mm (TSE) and 4 mm (GRE) for nitinol stents. Conclusion: Reliable stent lumen visualization is possible for Misago, Supera, Tigris, and Viabahn stents, if their axis is perpendicular to B1, and independent of the orientation with respect to B1 for short Tigris stents at 1.5T.

Initial clinical experience with a quadrupole butterfly coil for spinal injection interventions in an open MRI system at 1.0 tesla

Abstract Purpose: To report our initial clinical experience with a new magnetic resonance imaging (MRI) quadrupole coil that allows interventions in prone position. Materials and methods: Fifteen patients (seven women, eight men; average age, 42.8 years) were treated in the same 1.0-Tesla Panorama High Field Open (HFO) MRI system (Panorama HFO) using a quadrupole butterfly coil (Bfly) and compared with 15 patients matched for sex, age, and MR intervention using the MultiPurposeL coil (MPL), performed in conventional lateral decubitus position (all, Philips Medical Systems, Best, The Netherlands). All interventions were performed with a near-real-time proton density turbo spin echo (PD TSE) sequence (time to repeat/time to echo/flip angle/acquisition time, 600 ms/10 ms/90°/3 s/image). Qualitative and quantitative image analyses were performed, including signal intensity, signal-to-noise and contrast-to-noise ratio (SNR, CNR), contrast, and full width at half maximum (FWHM) measurements. Results: Contrast differed significantly between the needle and muscles (Bfly 0.27/MPL 0.17), as well as the needle and periradicular fat (0.13/0.24) during the intervention (both, p=0.029), as well as the CNR between muscles and the needle (10.61/5.23; p=0.010), although the FWHM values did not (2.4/2.2; p=0.754). The signal intensity of the needle in interventional imaging (1152.9/793.2; p=0.006) and the postinterventional SNR values of subcutaneous fat (15.3/28.6; p=0.007), muscles (6.6/11.8; p=0.011), and the CNR between these tissues (8.7/17.5; p=0.004) yielded significant differences. Conclusion: The new coil is a valid alternative for MR-guided interventions in an open MRI system at 1.0 tesla, especially if patients cannot (or prefer not to) be in a lateral decubitus position or if prone positioning yields better access to the target zone.

Development of a pneumatic x-ray transparent and MR-safe bone drilling system for interventional MRI

The precise drilling of bones is a common requirement in orthopaedic surgery [1-3]. Bone drills are manufactured by metallic components because of their high mechanic load. Image-guided bone bores were usually performed under computed tomography (CT) control. Due to their radiodensity, the metallic components lead to a limited image quality, and thus hinder the control of surgery. Moreover, those devices are not adequate for MRI due to their typically ferromagnetic components. The goal of development was to build a MR-safe prototype, allowing MRIand CT-interventions and eneables to place Kirschner-wires.

Introduction of an open source middleware for automatic FOV adjustment in interactive MRI according to a medical tracking-system

In real-time MRI-guided interventions and surgery [1], the field-of-view (FOV) of interactive sequences needs to be permanently changed according to the instruments movement. Dynamic tracking [2] allows the automatic adaption of the FOV to the instruments location acquired by a medical tracking-system. To accomplish manufacturer independent use of dynamic tracking, a middleware was developed allowing the use of various MRIs and tracking-systems.