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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 | 384x 384x 384x 728x 728x | import VOILUTFunctionType from '../enums/VOILUTFunctionType';
import { logit } from './logit';
/**
* Given a low and high window level, return the window width and window center
* Formulas from note 4 in
* https://dicom.nema.org/medical/dicom/current/output/html/part03.html#sect_C.11.2.1.2.1
* extended to allow for low/high swapping
* @param low - The low window level.
* @param high - The high window level.
* @returns a JavaScript object with two properties: windowWidth and windowCenter.
*/
function toWindowLevel(
low: number,
high: number
): {
windowWidth: number;
windowCenter: number;
} {
// Allow for swapping high/low
const windowWidth = Math.abs(high - low) + 1;
const windowCenter = (low + high + 1) / 2;
return { windowWidth, windowCenter };
}
/**
* Given a window width and center, return the lower and upper bounds of the window.
* The calculation depends on the VOI LUT Function:
*
* LINEAR (default):
* - Uses the DICOM standard formula from C.11.2.1.2.1:
* if x {'<='} c - 0.5 - (w-1)/2 {'=>'} lower bound
* if x {'>'} c - 0.5 + (w-1)/2 {'=>'} upper bound
*
* LINEAR_EXACT (C.11.2.1.3.2):
* - Uses:
* lower = c - w/2
* upper = c + w/2
*
* SIGMOID (C.11.2.1.3.1):
* - The sigmoid does not define linear "bounds" in the same way. It's asymptotic.
* - We define approximate bounds by choosing output thresholds (e.g., 1% and 99%)
* and solving for input x:
* y = 1/(1 + exp(-4*(x - c)/w))
* For y=0.01 and y=0.99, solve for x.
*
* @param windowWidth - The width of the window
* @param windowCenter - The center of the window
* @param voiLUTFunction - 'LINEAR' | 'LINEAR_EXACT' | 'SIGMOID'
* @returns An object containing the lower and upper bounds of the window
*/
function toLowHighRange(
windowWidth: number,
windowCenter: number,
voiLUTFunction: VOILUTFunctionType = VOILUTFunctionType.LINEAR
): {
lower: number;
upper: number;
} {
if (voiLUTFunction === VOILUTFunctionType.LINEAR) {
// From C.11.2.1.2.1 (linear function)
return {
lower: windowCenter - 0.5 - (windowWidth - 1) / 2,
upper: windowCenter - 0.5 + (windowWidth - 1) / 2,
};
} else Eif (voiLUTFunction === VOILUTFunctionType.LINEAR_EXACT) {
// From C.11.2.1.3.2 (linear exact function)
return {
lower: windowCenter - windowWidth / 2,
upper: windowCenter + windowWidth / 2,
};
} else if (voiLUTFunction === VOILUTFunctionType.SAMPLED_SIGMOID) {
// From C.11.2.1.3.1 (sigmoid function)
// Sigmoid: y = 1 / (1 + exp(-4*(x - c)/w))
const xLower = logit(0.01, windowCenter, windowWidth);
const xUpper = logit(0.99, windowCenter, windowWidth);
return {
lower: xLower,
upper: xUpper,
};
} else {
throw new Error('Invalid VOI LUT function');
}
}
export { toWindowLevel, toLowHighRange };
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