Using a multifield image intensifier tube, which of the following input phosphor diameters will provide the best spatial resolution? A 35 cm B 25 cm C 17 cm D 12 cm
The Correct Answer is: D Multifield image intensifier tubes are usually either dual-field or tri-field and are designed this way in order to permit magnification imaging. As voltage is applied to the electrostatic focusing lenses, the focal point moves back—closer to the input phosphor—and a smaller portion of the input phosphor is utilized. As a result, the FOV decreases and magnification increases, producing better spatial resolution. At the same time, brightness is decreased requiring an increase in mA (therefore increased patient dose). This increase in mA increases image quality. It can be likened to an increase in signal-to-noise ratio (SNR), with mA being the signal.
The best spatial resolution is obtained when the input phosphor diameter is smallest. Therefore, option D, 12 cm input phosphor diameter, will provide the best spatial resolution using a multifield image intensifier tube.
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