IMAGE QUALITY-CONTROL IN BREAST ULTRASOUND

Sonography is well suited for breast studies. Adequate equipment is ne eded to acquire high quality images because several technical factors influence ultrasound images. Thus, the use of high frequency dynamic s canning probes, the ultrasound beam focusing corrected for the near he ld, the adjustment of the gain and image contrast may all interfere wi th ultrasound beam reflection and scattering, determined by the hetero geneity of the gland parenchyma. In the last few years, a line of ultr asound equipment dedicated to this kind of application has been develo ped with 'small parts' transducers and frequencies ranging 10-13 MHz. These units can improve the evaluation of superficial structures and p rovide diagnostic results that conventional equipment cannot achieve. The higher the quality, the more a sonographic image corresponds to re al anatomy. This capability depends on the different kinds of system r esolution. Axial spatial resolution is the capability to resolve discr ete structures along the beam axis. Pulse length is inversely proporti onal to frequency and thus, the higher the transducer frequency, the b etter the axial resolution However, the increase in frequency reduces the depth of penetration of the ultrasound beam. The spectrum of frequ encies emitted by the crystal has been recently modified in order to o btain a good trade-off between the beam resolution and its penetration . Indeed, the development of the multifrequency technology allowed to improve the near field resolution while retaining a good penetration i nto the distant field. Furthermore, the use of compound ceramics with a broad bandwidth helps Doppler analysis because flow studies are opti mized by low frequencies, whereas two-dimensional morphologic imaging is optimized by high frequencies. Lateral spatial resolution is the ca pability to resolve discrete structures perpendicular or lateral to th e beam axis. This parameter strictly depends on the size of the ultras ound beam section and it is optimal only in the focal area. Therefore, it improves with narrow beams. Several transducers are available in b reast sonography, but the most adequate one is currently the annular t ransducer. The equipment should be able to detect even slight differen ces in acoustic impedance between the several breast tissues. This may be obtained by optimizing the dynamic range and the pre- and postproc essing setting. Apart from equipment, two other technical factors shou ld be optimized to obtain high quality images, namely beam intensity a nd gain curve. A new Doppler technique has been recently introduced: p ower Doppler, which allows the demonstration of breast nodule vascular ization with higher sensitivity than color Doppler. Finally, a rigorou s examination technique is required to obtain high quality images. In the last few years, several quality assurance programs have been intro duced. Dedicated phantoms are generally used. Recently, computer syste ms have been also developed. (C) 1998 Elsevier Science Ireland Ltd. Al l rights reserved.