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Medical devices pose unique challenges for economic evaluation and associated decision-making processes that differ from pharmaceuticals. We highlight and discuss these challenges in the context of cardiac device therapy, based on a systematic review of relevant economic evaluations. Key challenges include practical difficulties in conducting randomized clinical trials, allowing for a 'learning curve' and user characteristics, accounting for the wider organizational impacts of introducing new devices, and allowing for variations in product characteristics and prices over time.

Objectiur: To analyze menisco-tibia1 and femoro-tibia1 translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity.Methods: The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MR system at 30" and 90" of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing.Results: Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90") in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+I .3 * 3.8 mm) was significantly larger than in healthy knee (-0.9 k 2.9 mm; p < 0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 f 2.3 mm vs. 0.6 2 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30" knee flexion, but not at 90". This applied to ACL-deficient and healthy knees.Conclusions: This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibia1 translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.

This paper describes the construction of three adult female voxel models, two whole-body and one from head to thighs, from computed tomographic data of 3 women of different stature. Voxel models (also called phantoms) are human models based on computed tomographic or magnetic resonance images obtained from high resolution continuous scans of a single individual. The gray-scale data or information content of the medical images are interpreted into tissues (i.e., organs), a process known as segmentation. The phantoms, consisting of millions of volume elements, called voxels, provide a three-dimensional representation of the human body and the spatial form of its constituent organs and structures. They were initially developed for radiation protection purposes to estimate the organ and effective doses and hence the risk to a person or population due to an irradiation. This paper also presents conversion coefficients for idealized geometries of external photon exposures of energies 10 keV-1 MeV for the three female models, calculated with a Monte Carlo code. Until now there were not any published data on conversion coefficients for explicit female voxel models. Such sets of conversion coefficients exist for voxel adult males or for MIRD-type male, female, and hermaphrodite models. Numerical differences of the calculated conversion coefficients for the voxel female models and MIRD-type models can amount up to 60% or more for external exposures and are due to the improved anatomical realism of the voxel models. The size of the model also has an effect on the conversion coefficients, particularly for deeper lying organs and energies below 200 keV. The three separate sets of conversion coefficients allow one to choose the most suitable model according to the size of the individual as well as to study the dosimetric variations due to the size of the model.

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