University of Jyväskylä

Dissertation: 12.12 Ultrasound Measurements in Bone Using an Array Transducer (Kilappa)

Start date: Dec 12, 2014 12:00 AM

End date: Dec 12, 2014 03:00 PM

Location: Ylistönrinne, FYS 1

Vantte Kilappa. Kuvaaja: Birgitta KemppainenM.Sc. Vantte Kilappa defends his doctoral dissertation in Physics. Opponent Professor  Kay Raum (Charité - Universitätsmedizin Berlin) and custos Professor Markku Kataja (University of Jyväskylä). The event is in English.

Abstract

Osteoporosis is a prevalent bone disease, especially common among elderly individuals. It is characterized by increased fragility, caused by age-related resorption of the bone mineral content. In particular, osteoporotic resorption affects increase of porosity, decrease of elastic stiffness and thinning of the cortical wall. Osteoporotic fractures cause human suffering and heavy burdens to the economy, but the present clinical standard of diagnosing, dual energy X-ray absorptiometry (DXA), cannot reliably predict whether an individual will later sustain a fracture. Moreover, these devices are expensive and do not permit screening. There is thus a call for alternative approaches. Quantitative ultrasound (QUS) methods have shown promise in development of new alternative modalities for rapid, reliable and inexpensive screening and diagnosing of osteoporosis. As a part of this progress, this Thesis focuses on the development of a new array ultrasound probe, suitable for QUS assessment of the human radius and tibia.

The new probe was tested in an in vivo study on pre- and postmenopausal females (n=254), whose fracture history was recorded and who were also measured by other techniques. The array probe was used to measure the first arriving signal (FAS). It was shown that ultrasound assessment with this device predicted well bone mineral density and cortical thickness at the bone sites analyzed, especially in the radius. In the subset of postmenopausal subjects, the ability of the method to differentiate fractures was consistent to that of X-ray-based bone densitometry (including DXA), and could thereby be used for screening of osteoporosis.

Another emphasis in the Thesis relates to excitation and detection of a fundamental flexural guided wave (FFGW), a mode which is especially sensitive to cortical thickness. It is hard to detect this mode in vivo because it features weak amplitude and it is disturbed by other US modes which propagate in the layer of soft tissue on top of the bone. In one sub-study, a new signal processing method was introduced to determine the velocity of FFGW from signals measured by the array probe developed. In another sub-study, it was predicted by numerical simulations that this array probe can be configured as a phased array of sources. In particular, it was predicted that phased excitation can sufficiently gain the signal-to-interference ratio of FFGW on top of the soft tissue coating, so as to enable in vivo assessment of this mode.

In conclusion, results suggest that it is possible to develop a multi-mode QUS assessment utilizing both FAS and FFGW. Such a method would significantly improve the inference of different bone properties that determine its fracture toughness. Multi-mode QUS is thus expected to significantly improve the clinical relevance of US methods.

The dissertation is published in the series JYFL Research Report nro. 11/2014, ISSN: 0075-465X, ISBN: 978-951-39-5864-0.

  • Further information:

Vantte Kilappa, warma@iki.fi, tel. +358 44 023 0881

Communications intern Birgitta Kemppainen, tiedotus@jyu.fi, +358 40 805 4483