Contrast-Detail-Dose Analysis of Six Different Computed Tomographic Scanners

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Low-contrast visibility of various rotate-translate, rotating detector, and stationary detector computed tomography (CT) scanners is measured at contrasts ranging from 0.3 to 3% using a phantom based on the partial volume of water and polystyrene. The results are plotted on log-log curves, as a function of entrance dose, to provide a family of contrast (C)-detail (d)-dose (D) visibility curves. The transition region, ∼ 1 to 10% contrast, depends on modulation transfer function (MTF), contrast, and dose (noise), while the noise region, ≤ 1% contrast, is independent of MTF. The slopes of the curves in the noise region are consistent with a value of −1, as opposed to a theoretically expected value of −3/2 for ideal CT noise. Relative dose efficiency of various scanners is examined by plotting CdD1/2 versus contrast for both peak dose (Dp) and summation dose (DΣ). The rotating detector systems are shown to be, on the average (at 0.5% contrast), 3.4 (Dp) and 4 (DΣ) times more dose efficient than the stationary array system examined, and 2.4 (Dp) and 3.2 (DΣ) times more efficient than the rotate-translate units examined.

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