A very short examination may require a higher power to produce an adequate image.By using a higher mA the maximum kV is reduced and vice versa.Other factors to take into consideration are: Decreasing disk diameter (heat spread over smaller circumference and area).This means the heat is spread over a smaller area and the rate of heat dissipation is reduced) Larger target angles for a given effective focal spot size (for a given effective focal spot size the actual focal spot track is smaller with larger anode angles.Decreasing effective focal spot size (heat is spread over a smaller area).The maximum allowable power decreases with: These display the maximum power (kV and mA) that can be used for a given exposure time before the system overloads.
The capacity for each focal spot on a machine is given in tube rating graphs provided by the manufacturer. Temperature rise = energy applied / heat capacityĮach machine has a different capacity for dissipating heat before damage is caused. The molybdenum stem conducts very little heat to prevent damage to the metal bearings.Ī higher heat capacity means the temperature of the material rises only a small amount with a large increase in heat input. Heat is normally removed from the anode by radiation through the vacuum and into the conducting oil outside the glass envelope. The more uniform the waveform the lower the heat production W = waveform of the voltage through the x-ray tube.
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