Dabi Atlante EAGLE 3D, Руководство пользователя

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Hounsfield validation
The CT values of water and air in the phantom will be used to evaluate
contrast scale over time.
14.4.3. NOISE AND UNIFORMITY
The Section B of the phantom is an area with acrylic only, the software
select 5 ROIs and measure the pixels values within the ROIs. After that, it
calculates the mean value and SDs for them.
Noise and Uniformity Section
After the calculation of the uniformity, and using same flat-field image
(slice), the software evaluates the noise power spectrum (NPS). The NPS is
defined as:
𝑁𝑃𝑆(𝛼, 𝜑) = 𝑁
𝑥
𝑁
𝑦
∆
𝑥
∆
𝑦
〈|𝐹𝑇{∆𝑃(𝑥, 𝑦)}|
2
〉
where N
x
and N
y
are the number of pixels and Δ
x
and
Δ
y
are the pixel widths in
the X and Y directions, respectively. The term ΔP(x,y) represents the deviation
of the pixel value at the coordinate (x,y) from the mean pixel value in the image,
and FT{ΔP(x,y)} represents the Fourier transform of the pixel value deviation
matrix.
This equation yields a 2-dimensional NPS, which is integrated over all
phase angles φ to give a 1-dimensional representation: