| CPC A61N 5/1048 (2013.01) [A61N 5/1042 (2013.01)] | 16 Claims |

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1. A method of characterizing physical properties of an attenuating element in a radiotherapy device including a radiotherapy radiation source located on a first side of the attenuating element and a radiotherapy radiation detector located on a second side of the attenuating element, wherein the attenuating element comprises a cylindrical component, and wherein the cylindrical component comprises one of a cryostat, a gradient coil, or a quadrature body coil, the method comprising:
obtaining an average detected radiotherapy radiation intensity at two or more locations around the attenuating element;
comparing a detected intensity at one location with the average radiotherapy radiation intensity; and
characterizing a corresponding physical property based on the comparison, wherein the characterized physical property is at least one perturbation coefficient given by the equation:
![]() and wherein
![]() is derived from comparing the detected intensity at one location with the average intensity.
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