K W Leszczynski et al 1990 Phys. Med. Biol. 35 429 doi:10.1088/0031-9155/35/3/011
K W Leszczynski, S Shalev and N Scott Cosby
Show affiliationsTwo complementary approaches to the noise suppression problem in on-line portal imaging have been analysed. Temporal filtering by image summation can substantially reduce the amount of noise in an image. In many cases, however, movements of the patient or the radiation source limit the time period over which the averaging can be done. Any remaining noise has to be dealt with by applying spatial filtering. The adaptive Lee filter is particularly suitable for portal imaging applications. The authors have proposed a modification to the basic Lee technique which permits the calculation of the noise variance locally by utilising the information contained in intermediate images acquired during frame averaging. Unlike the original Lee formulation, no a priori knowledge of the noise variance is required, and in contrast to Mastin's approach (Mastin 1985), the variance may vary with position in the image. The tests of performance of the modified Lee filter, carried out using on-line images, have shown its superiority in comparison with the original Lee technique as well as with conventional averaging and median filters.
Issue 3 (March 1990)
K W Leszczynski et al 1990 Phys. Med. Biol. 35 429
A N Kolmogorov 1983 Russ. Math. Surv. 38 29
M Fitzsimons et al 1999 Physiol. Meas. 20 385
Chen Bao-Qiu et al 2005 Chinese Phys. Lett. 22 302
J S Lee et al 2000 Semicond. Sci. Technol. 15 267
P J Dunmore-Buyze et al 2002 Physiol. Meas. 23 555
F. Großmann and P. Hänggi 1992 Europhys. Lett. 18 1
M Houe and P D Townsend 1995 J. Phys. D: Appl. Phys. 28 1747
A Hooper and D W Lamb 2005 J. Phys.: Conf. Ser. 15 219
K W Allen et al 1956 Proc. Phys. Soc. A 69 705