Movement artefact suppression in blood perfusion measurements using a multifrequency technique.
The standard way of suppressing movement artefacts in Doppler measurements is by means of a high-pass filter. This is because artefacts usually are of high amplitude, but have low frequencies. The immediate drawback is, then, that low-velocity blood flow is also filtered out. In this paper, a method to reduce movement artefacts in blood perfusion measurements is proposed, using simultaneous transmission and reception of multiple frequencies in a continuous-wave Doppler system. It is shown that Doppler signals originating from blood may be considered uncorrelated for a large enough frequency separation between channels, and tissue movements are more correlated. By subtracting perfusion estimates obtained by time-domain processing, correlated signals can be suppressed. The subtraction algorithm is shown to produce a linear perfusion estimate, but with twice the standard deviation compared to an estimate obtained by simply averaging channels. Movement artefacts in both in vitro and in vivo models are shown to be reduced by the algorithm. Imbalance between channels does, however, cause the artefacts to be only partly reduced. The problem can be alleviated by filtering the signals prior to subtraction, but this results in a nonlinear estimate, especially for large time constants in the filter. Some amount of filtering can still be desirable to suppress partly correlated artefacts, even if identical time-domain processing units are implemented, as could be done digitally.
Jansson
Tomas
T
Department of Electrical Measurements, Lund University, Lund, Sweden. tomas.jansson@elmat.lth.se
Persson
Hans W
HW
Lindström
Kjell
K
D000328:Adult; D016477:Artifacts; D001783:Blood Flow Velocity / Q000502:physiology*; D002196:Capillaries / Q000000981:diagnostic imaging*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008962:Models, Theoretical; D009068:Movement / Q000502:physiology*; D013933:Thumb / Q000000981:diagnostic imaging; D018608:Ultrasonography, Doppler / Q000379:methods*