Algebraic model for negative focused ultrasound beam width

Jakobsen, Christian Elmholt

4. term

Biomedical Engineering and Informatics, Master

2016

2016-05-31

74

Ultralydsbilleder dannes ved at sende stråler af lyd ind i vævet og måle ekkoerne. I dag bruges typisk enten ufokuserede stråler (brede, simple) eller fokuserede stråler (smalle, skarpe), men man er ved at nå en grænse for, hvor hurtigt data kan indsamles. En lovende mulighed er negativ fokus, som bevidst skaber en mere spredende, bred stråle og dermed kan øge den parallelle fokusering. Der mangler dog viden om negativ fokus sammenlignet med de to andre tilgange. Denne afhandling præsenterer en enkel algebraisk model, der forbinder tre forhold: størrelsen af aperturen (den aktive del af sonden), den negative fokuseringsafstand og dybden (range) for at forudsige strålebredde. Modellen viser, at strålebredde kan forstås som en geometrisk projektion af aperturen. Den er udviklet på baggrund af en ny teknik til at simulere ultralydsstråler og er valideret med målinger af strålebredde fra to forskellige ultralydsprober (transducere). Resultaterne stemmer godt overens med målingerne, og modellen har potentiale til at samle de adskilte teorier for ufokuserede, fokuserede og negativt fokuserede stråler i én ramme.

Ultrasound images are formed by sending beams of sound into tissue and listening for echoes. Most systems use either unfocused beams (wide, simple) or focused beams (narrow, sharper detail), but current approaches are reaching limits in acquisition speed. A promising alternative is negative focus, which deliberately produces a wider, more diverging beam and can improve parallel focusing. However, it is less well understood than the unfocused and focused cases. This thesis presents a simple algebraic model that links three factors: aperture size (the active area of the probe), negative focal distance, and range (depth) to predict beam width. The model shows that beam width can be understood as a geometric projection of the aperture. It is built on a newly developed technique for simulating ultrasound beams and is validated by measuring beam width with two different transducers. The results agree well with measurements, and the model could help unify the separate theories for unfocused, focused, and negative-focus beams into a single framework.

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Jakobsen, Christian Elmholt:

• Algebraic model for negative focused ultrasound beam width (2016)