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Effect of radiographic techniques (kVp and mAs) on image quality and patient doses in digital subtraction angiography
Author(s) -
Gkanatsios Nikolaos A.,
Huda Walter,
Peters Keith R.
Publication year - 2002
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1493213
Subject(s) - image intensifier , kerma , imaging phantom , computed radiography , nuclear medicine , image quality , fluoroscopy , digital radiography , digital subtraction angiography , subtraction , materials science , iopromide , radiography , dosimetry , optics , angiography , physics , medicine , radiology , contrast medium , mathematics , computer science , image (mathematics) , arithmetic , artificial intelligence
We investigated how varying the x‐ray tube voltage and image receptor input exposure affected image quality and patient radiation doses in interventional neuroradiologic imaging. Digital subtraction angiography (DSA) images were obtained of a phantom with 1 mm diameter vessels containing iodine at concentrations between 4.5 and 50 mg/cc. The detection threshold concentration of iodine was determined by inspecting DSA images obtained at a range of x‐ray tube voltages and input exposure levels. Surface doses were obtained from measured x‐ray tube output data, and corresponding values of energy imparted were determined using the exposure‐area product incident on the phantom. In one series of experiments, the air kerma at the image intensifier ( X ) was varied between 0.44 μGy per frame and 8.8 μGy per frame at a constant x‐ray tube voltage of 70 kVp. In a second series of experiments, the tube voltage was varied between 50 and 100 kVp, and the mAs adjusted to maintain a constant exposure level at the input of the image intensifier. At a constant x‐ray tube voltage, the surface dose and energy imparted were directly proportional to the input exposure per frame used to acquire the DSA images. On our DSA system operated below 2.2 μGy per frame, the threshold iodine concentration was found to be proportional to X − 0.57, which is in reasonable agreement with the theoretical prediction for a quantum noise limited imaging system. Above 2.2 μGy per frame, however, the threshold iodine concentration was proportional to X − 0.26, indicating that increasing the input exposure above this value will only achieve modest improvements in image quality. At a constant image intensifier input exposure level, increasing the x‐ray tube voltage from 50 kVp to 100 kVp reduced the surface dose by a factor of 6.1, and the energy imparted by a factor of 3.5. The detection threshold iodine concentration was found to be proportional to kVp n , where n was 2.1 at 1.1 μGy per frame, and 1.6 at 3.9 μGy per frame. For clinical situations that can be modeled by a uniform phantom, reducing the x‐ray tube voltage rather than increasing the exposure level would best achieve improvements on our DSA imaging system performance.