Рентгенология & Радиология, 2010, XLІХ 265-270

Factors influencing image quality in X-ray Mammography

S. Avramova-Cholakova1, N. Dilova2, L. Trifonov3


1
Radiation “Protection at Medical Exposure Section”, NCRRP – Sofia
2DCC “Borola” – Sofia
3MDL “Ahiles – 2000” – Stara Zagora

Abstract.

The purpose of this work is to explore the influence of different parameters, including viewing conditions, on image quality in X-ray mammography. Images of Barts and ACR mammography phantoms, obtained at different tube voltage (kV) and optical density (OD) values were estimated on 3 viewing boxes with different luminance by 2 observers. Subjective and objective quality indices (QI) were determined. Tube voltage increase from 25 to 32 kV leads to 7 % deterioration of subjective and 37 % of objective QI, while incident air kerma (IAK) and mean glandular dose (MGD) decrease by 71 % and 58 % respectively. OD increase of Barts images from 0.79 to 1.52 results in 2 %
decrease of the subjective QI determined by observer I, but observer II finds 7 % increase of this parameter, and IAK and MGD increase by 64 %. This augmentation of OD results in increase of contrast (objective QI) by 32 % but optimal viewing conditions must be assured for better visualization. OD increase of ACR images from 2.01 to 2.66 leads to 15 % deterioration of QI while IAK and MGD increase by 23 %. A “bright light” must be assured for regions of the film with higher OD. Results from subjective perception of image quality depending on viewing boxes luminance are contradictory. Observer I finds the best perception with viewing box 1 (3000 cd.m-2) and observer II – with viewing box 2 (1520 cd. m-2). The lack of masking of the bright area on the viewing box around the film leads to decrease of visualisation up to 59 % for low contrast objects and up to 32 % for microcalcifications.

Key words:

MAMMOGRAPHY. IMAGE QUALITY. VIEWING BOX
LUMINANCE. BRIGHT AREA MASKING