IEC TS 62558:2011 pdf – Ultrasonics – Real-time pulse-echo scanners -Phantom with cylindrical,artificial cysts in tissue-mimicking material and method for evaluation and periodic testing of 3D-distributions of void-detectability ratio (VDR).
The VDR1 values are stored in a matrix similar to the matrix containing the 3D. ROl grey-scale Information-set to allow direct viewing and further processing.
The VDR1 values are evaluated for each C-plane. There are different approaches to this evaluation. Either statistical data can be derived directly for a complete C-plane or the VDRdata can be first calculated for each void and then the information of the individual voids can be subsumed in one information-set for the plane. Statistical evaluation can use calculation of either mean values of VDR or maximum values of VDR.
NOTE I Maximum values are a reasonable approach, as the grey-scale cstnbut,on within each void shows a sharp drop towards the centre ol the void Isee Annex A) and experience shows that visibility Of the void 5 strongly corelaIed to thiS maximum value.
Mean values are more diffecult to obtain, as the border for each void must be defined, either by defining an amplitude limit or by using additional information on the location of the Individual void.
NOTE 2 This deten’nination ot the void edges is the main source of error for the mean evaluation
The mean or the maximum VDR-values of all the C-planes are plotted In a graph giving VDR over depth. Statistics may be performed on these data by offering a fitted curve.
A void of a given diameter and location shall be called detectable if its value of VDR exceeds 2,5. The range where the VDR-plot exceeds this value is the useful working range for the void diameters contained in this ROl [41.
The stored ROl grey-scale and the VDR, 3D-data sets are used to visually check the automated evaluation of the lransducer VDRI visualisatlon of non-void regions Is also important, as it reveals where the interference-pattern will give the impression of voids where there are none.
NOTE 3 The VDR1vaiu.s on their own do not represent relevant information, but in the context of all the other VDB -values within an image of a voId, a C-plane or a ROt, they are fundamental values for obtaiwng a 3D-image of the VOR-levela. mean values of VDR inside an image of a single void or a group of voids and maximum values of VDR in an image of a single void or a group of voids.
A.1 .1.2.1
attenuation slice
layer of TMM having an attenuation coefficient greater than the average attenuation coefficient of an assembled phantom
A.1 .1.2.2
void slice
layer of TMM containing voids and having an attenuation coefficient less than the average attenuation coefficient of an assembled phantom
Tcc2:3D artificial anechoic cyst phantom
phantom containing defined, alternating, attenuation- and void slices of backscattering material, oriented mainly perpendicular to the direction of sound propagation, and filled with an anechoic liquid material, such that the speed of sound and the mean attenuation and backscatler coefficients of the phantom closely approximate those of human soft tissue
A.2 Phantom
A.2.1 General
The example phantom is housed In a tight plastic box with external dimensions: height 22 cm x length 15cm x 8cm.
The body of the phantom consists of alternating layers of polyurethane foam (attenuation slices and void slices), each with a thickness of 5 mm, Every second layer (the void slices) contains artificial cylindrical voids. which are cut into the foam (see Figures A.2, A.3 and A.4). Foam and voids are soaked with de9assed 7 % (by weight) saline water. The concentration of the saline is adjusted so that the speed of sound of the soaked foam is I 540 ± 1Dm r at 20 °C. It was found that the backscattering level for both foams immersed in saline was the same.