This article summarizes the dosimetric results of an International Atomic Energy Agency coordinated research program to investigate the feasibility of adopting guidance levels for invasive coronary artery procedures. The main study collected clinical data from hospitals located in five countries. A total of 2265 coronary angiograms (CA) and 1844 percutaneous coronary interventions (PCI) were analyzed. Substudies evaluated the dosimetric performance of 14 fluoroscopes, skin dose maps obtained using film, the quality of CA procedures, and the complexity of PCI procedures. Kerma-area product (PKA) guidance levels of 50 and 125 Gy cm2 are suggested for CA and PCI procedures. These levels should be adjusted for the complexity of the procedures performed in a given institution.
Medical devices equipped with position sensors enable applications like image guided surgical interventions, reconstruction of three-dimensional 3D ultrasound (US) images, and virtual or augmented reality systems. The acquisition of three-dimensional position data in real time is one of the key technologies in this field. The systematic distortions induced by various metals, surgical tools, and US scan probes in different commercial electromagnetic tracking systems were assessed in the presented work. A precise nonmetallic six degree-of-freedom measurement rack was built that allowed a quantitative comparison of different electromagnetic trackers. Also, their performance in the presence of large metallic structures was quantified in a phantom study on an acrylic skull model in an operating room (OR). The trackers used were alternating current (ac) and direct current (dc) based systems. The ac trackers were, on average, distorted by 0.7 mm and 0.5 degree by metallic objects positioned at a distance greater than 120 mm between the geometrical center of the sample and the sensor. In the OR environment, the ac system exhibits mean errors of 3.2 +/- 2.4 mm and 2.9 degrees +/- 1.9 degrees. The dc trackers are more sensitive to distortions caused by ferromagnetic materials (averaged value: 1.6 mm and 0.5 degree beyond a distance of 120 mm). The dc tracker shows no distortions from other conductive materials but was less accurate in the OR environment (typical error: 6.4 +/- 2.5 mm and 4.9 degrees +/- 2.0 degrees). At distances smaller than approximately 100 mm between sample and sensor error increases quickly. It is also apparent from our measurements that the influence of US scan probes is governed by their shielding material. The results show that surgical instruments not containing conductive material are to be preferred when using an ac tracker. Nonferromagnetic instruments should be used with dc trackers. Static distortions caused by the OR environment have to be compensated by precise calibration methods.
A code written in BASIC is described which calculates x-ray spectra for tube voltages from 20 to 150 kVDC. Data for the spectral distribution, the mean photon energy, kerma in air, mean energy of the kerma distribution together with 1. and 2. half-value layers for aluminum are obtained. Numerical values for the differential energy intensity function and the Thomson-Whiddington constant were taken from Birch et al. (6). For target angles up to 30 degrees agreement between calculated and experimental data is good. For larger angles some discrepancies appear which could be either due to increased filtration by tungsten (surface roughness) or limited applicability of the data used. The program is tailored to be run on a personal computer.
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