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Electronic X-Ray Field Alignment Detection

E mckenzie1*, I Rutel2, (1) University of Alabama at Birmingham, Birmingham, AL, (2) University of Oklahoma Health Science Center, Oklahoma City, OK


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library


Field coincidence in x-ray radiography guarantees a safe and precise radiography procedure where it otherwise would not. There have been many published methods of field alignment testing since AAPM Task Group number 4 using a series of pennies. In light of new developments in the field of electronic design and radiation detection, this experiment capitalizes off of the intrinsic sensitivity of the microcontroller board ‘Arduino Uno’ coupled with consumer level phototransistors.

Methods and Materials:

After a lengthy process of testing a variety of transistor and photodiode as well as phototransistor combinations, this experiment ultimately utilized the Arduino Uno microcontroller board and coupled it with the BPW85 Vishay phototransistor and 2N3904 NPN transistor for amplification. The signal was read by the microcontroller via the use of a voltage divider circuit from a potentiometer. Each transistor, phototransistor and potentiometer made up one of five detectors. Given that the phototransistors are intrinsically sensitive to light, each phototransistor had to be covered with a strip of black electrical tape to reduce background effects. The detector was tested under normal diagnostic energy ranges from 40 to 100 kVp and 10 to 500 mAs on a GE Model 46-155400G46. The instrumentation used for testing included an Amprobe 510 multi-meter, a fluke TNT 12000 Dosemate and the RadCal 9010 ion chamber.


Despite the phototransistor manufacturers recommended peak sensitivity range of 450 to 1000 nm, diagnostic x-rays were able to produce a measureable signal in the range of 100-1000 mV (amplified). This detector can measure the x-ray field to a precision of 3 mm, 0.5 mm larger than its commercially available competition. The spatial resolution is subtended by its price being less than $100 to construct and use.


With sufficient regulatory testing this detector could take the place of current field alignment methods.


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