The main objective of phase 3 trials is to verify the therapeutic action of a new substance in a large number of patients, essentially to determine the risk/benefit ratio. Before phase 3, the substance is not regarded as a drug, but after a positive phase 3 trial it becomes a drug.
As an x-ray tube ages, the inside can become coated with tungsten, which can cause arcing in the tube.
When there is a short circuit inside the tube, usually from the cathode to the tube envelope, tube arcing happens. A brief loss of x-ray output and a localised artefact are the consequences. On transaxial computed tomography (CT) scans, it appears as a near-parallel, equidistant streak pattern, and on coronal and sagittal CT images, as a "horizontal" hypodense band.
The most frequent cause of x-ray tube failure is an inability to effectively disperse the heat produced during routine operation. It is common knowledge that at the anode target, heat accounts for 99% or more of the kinetic energy given to the electron beam.
Therefore, an x-ray tube ages, the inside can become coated with tungsten, which can cause arcing in the tube.
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