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Regarding factors influencing the dose: a. At a constant mA, a high kV means a higher skin surface dose and a higher absorbed dose b. When mA is doubled, the dose is doubled and the noise would be halved c. Automated modulation of mA according to the thickness of the patient to keep the noise near constant will reduce the dose compared with the constant mA techniqued. If the voxel dimensions are halved to keep the signal-to-noise ratio (SNR) constant, the dose will increase eightfold e. If the SNR is doubled, the dose would be quadrupled |
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Answer» a. True. b. False. mA is in direct relation to the dose but noise is proportional to √mA, so the dose will be doubled and the noise will be √2. c. True. d. True. If the pixels are halved, then the incident photon will be (1/2)3 ; therefore, for the same signal-to-dose ratio, the dose needs to be eight times higher. e. True. mA and therefore dose is proportional to (SNR)2 ; thus, (SNR x 2)2 = 4 x dose. |
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