Papers by Christian Langton
Springer eBooks, 2015
Recent studies have shown that ultrasound transit time spectroscopy (UTTS) is an alternative meth... more Recent studies have shown that ultrasound transit time spectroscopy (UTTS) is an alternative method to describe ultrasound wave propagation through complex samples as an array of parallel sonic rays. This technique has the potential to characterize bone properties including volume fraction and may be implemented in clinical systems to predict osteoporotic fracture risk. In contrast to broadband ultrasound attenuation, which is highly frequency dependent, we hypothesise that UTTS is frequency independent. This study measured 1 MHz and 5 MHz broadband ultrasound signals through a set of acrylic step-wedge samples. Digital deconvolution of the signals through water and each sample was applied to derive a transit time spectrum. The resulting spectra at both 1 MHz and 5 MHz were compared to the predicted transit time values. Linear regression analysis yields agreement (R 2 ) of 99.23% and 99.74% at 1 Mhz and 5 MHz respectively indicating frequency independence of transit time spectra.
Frontiers in Materials, 2017
Journal of Tissue Engineering, 2018
The current ‘active’ solution to overcome the impediment of ultrasound wave degradation associate... more The current ‘active’ solution to overcome the impediment of ultrasound wave degradation associated with transit-time variation in complex tissue structures, such as the skull, is to vary the transmission delay of ultrasound pulses from individual transducer elements. This article considers a novel ‘passive’ solution in which constant transit time is achieved by propagating through an additional material layer positioned between the ultrasound transducer and the test sample. To test the concept, replica models based on four cancellous bone natural tissue samples and their corresponding passive ultrasound phase-interference compensator were 3D-printed. Normalised broadband ultrasound attenuation was used as a quantitative measure of wave degradation, performed in transmission mode at a frequency of 1 MHz and yielding a reduction ranging from 57% to 74% when the ultrasound phase-interference compensator was incorporated. It is suggested that the passive compensator offers a broad utili...
Proceedings Of The Institution Of Mechanical Engineers, Part H: Journal Of Engineering In Medicine, Mar 5, 2014
Bone, Feb 1, 2018
Conventional mechanical testing is the 'gold standard' for assessing the stiffness (N mm -1 ) and... more Conventional mechanical testing is the 'gold standard' for assessing the stiffness (N mm -1 ) and strength (MPa) of bone, although it is not applicable in-vivo since it is inherently invasive and destructive. The mechanical integrity of a bone is determined by its quantity and quality; being related primary to bone density and structure respectively. Several nondestructive, non-invasive, in-vivo techniques have been developed and clinically implemented to estimate bone density, both areal (dual-energy X-ray absorptiometry (DXA)) and volumetric (quantitative computed tomography (QCT)). Quantitative ultrasound (QUS) parameters of velocity and attenuation are dependent upon both bone quantity and bone quality, although it has not been possible to date to transpose one particular QUS parameter into separate estimates of quantity and quality. It has recently been shown that ultrasound transit time spectroscopy (UTTS) may provide an accurate estimate of bone density and hence quantity. We hypothesised that UTTS also has the potential to provide an estimate of bone structure and hence quality. In this in-vitro study, 16 human femoral bone samples were tested utilising three techniques; UTTS, micro computed tomography (µCT), and mechanical testing. UTTS was utilised to estimate bone volume fraction (BV/TV) and two novel structural parameters, inter-quartile range of the derived transit time (UTTS-IQR) and the transit time of maximum proportion of sonic-rays (TTMP). µCT was utilised to derive BV/TV along with several bone structure parameters. A destructive mechanical test was utilised to measure the stiffness and strength (failure load) of the bone samples. BV/TV was calculated from the derived transit time spectrum (TTS); the correlation coefficient (R 2 ) with μCT-BV/TV was 0.885. For predicting mechanical stiffness and strength, BV/TV derived by both μCT and UTTS provided the strongest correlation with mechanical stiffness (R 2 = 0.567 and 0.618 respectively) and mechanical strength (R 2 = 0.747 and 0.736 respectively). When respective structural parameters were incorporated to BV/TV, multiple regression analysis indicated that none of the μCT histomorphometric parameters could improve the prediction of mechanical stiffness and strength, while for UTTS, adding TTMP to BV/TV increased the prediction of mechanical stiffness to R 2 = 0.711 and strength to R 2 = 0.827. It is therefore envisaged that UTTS may have the ability to estimate BV/TV along with providing an improved prediction of osteoporotic fracture risk, within routine clinical practice in the future.
2012 7th IEEE Conference on Industrial Electronics and Applications (ICIEA)
Power electronic converters for high power ultrasound transducers. In Xiang, W (Ed.) Proceedings ... more Power electronic converters for high power ultrasound transducers. In Xiang, W (Ed.) Proceedings of the 7th IEEE Conference on Industrial Electronics and Applications. Institute of Electrical and Electronic Engineers (IEEE), United States of America, pp. 647-652.
Next-generation devices to diagnose residuum health of individuals suffering from limb loss: A narrative review of trends, opportunities, and challenges
Journal of Science and Medicine in Sport
A 3D printed phantom to assess MRI geometric distortion
Biomedical Physics & Engineering Express, 2021
Geometric distortions in magnetic resonance can introduce significant uncertainties into applicat... more Geometric distortions in magnetic resonance can introduce significant uncertainties into applications such as radiotherapy treatment planning and need to be assessed as part of a comprehensive quality assurance program. We report the design, fabrication, and imaging of a custom 3D printed unibody MR distortion phantom along with quantitative image analysis. Methods: The internal cavity of the phantom is an orthogonal three-dimensional planar lattice, composed of 3 mm diameter rods spaced equidistantly at a 20 mm centre-centre offset repeating along the X, Y, and Z axes. The phantom featured an overall length of 308.5 mm, a width of 246 mm, and a height of 264 mm with lines on the external surface for phantom positioning matched to external lasers. The MR phantom was 3D printed in Nylon-12 using an advancement on traditional selective laser sintering (SLS) (HP Jet Fusion 3D—4200 machine). The phantom was scanned on a Toshiba Aquilion CT scanner to check the integrity of the 3D print ...
Transducer impulse response correction for a deconvolution derived ultrasound transit time spectrum
Physics in Medicine & Biology, 2018
Propagation of ultrasound through a complex composite sample may exhibit phase interference betwe... more Propagation of ultrasound through a complex composite sample may exhibit phase interference between two or more sonic-rays if differences in transit time are less than the pulse length. The transit time spectrum of a test sample, equivalent to its impulse response, was derived through active-set deconvolution of ultrasound signals with, and without, the test sample. The aim of this study was to test the hypothesis that in cases where only the transmit ultrasound transducer's digitally-coded excitation signal is available, hence not the input ultrasound signal without the test sample, incorporation of the transducer impulse response may increase both accuracy and precision of ultrasound transit time spectroscopy. A digital 1 MHz sinusoid signal was used to create an ultrasound pulse that was propagated through a 5 step-wedge acrylic sample immersed in water. Transit time spectra were obtained through deconvolution utilising an ultrasound input signal, along with a digital input signal, with and without incorporation of the transducer impulse response. Incorporation of the transducer impulse response reduced a quantitative measure of noise-to-signal ratio by a factor of 12. The paper has demonstrated the potential for increased accuracy and precision of transit time spectroscopy when the transducer impulse response is incorporated within active-set deconvolution analysis.
Prosthesis, 2019
Vertical loading rate could be associated with residuum and whole body injuries affecting individ... more Vertical loading rate could be associated with residuum and whole body injuries affecting individuals fitted with transtibial prostheses. The objective of this study was to outline one out of five automated methods of extraction of vertical loading rate that stacked up the best against manual detection, which is considered the gold standard during pseudo-prosthetic gait. The load applied on the long axis of the leg of three males was recorded using a transducer fitted between a prosthetic foot and physiotherapy boot while walking on a treadmill for circa 30 min. The automated method of extraction of vertical loading rate, combining the lowest absolute average and range of 95% CI difference compared to the manual method, was deemed the most accurate and precise. The average slope of the loading rate detected manually over 150 strides was 5.56 ± 1.33 kN/s, while the other slopes ranged from 4.43 ± 0.98 kN/s to 6.52 ± 1.64 kN/s depending on the automated detection method. An original m...
Journal of Colloid and Interface Science, 2019
Metal shell microcapsules have been shown to completely retain their core until its release is tr... more Metal shell microcapsules have been shown to completely retain their core until its release is triggered, making them a promising candidate for use as a controllable drug delivery vehicle due to their superior retention properties as compared to polymer shell microcapsules. Focused ultrasound (FUS) has been successfully utilised to trigger release of lipophilic drugs from polymer microcapsules, and in this work the response of gold shell microcapsules with and without an inner polymeric shell, to FUS and standard ultrasound is explored. The results show that gold shell microcapsules with an inner polymer shell rupture when exposed to standard ultrasound and that there is a linear correlation between the gold shell thickness and the extent of shell rupture. When FUS is applied to these microcapsules, powers as low as 0.16 W delivered in bursts of 10 ms/s over a period of 120 s are sufficient to cause rupture of 53 nm gold shell microcapsules. Additional findings suggest that gold shell microcapsules without the polymer layer dispersed in a hydrogel matrix, as opposed to aqueous media, rupture more efficiently when exposed to FUS, and that thicker gold shells are more responsive to ultrasound-triggered rupture regardless of the external environment. Release of dye from all successfully ruptured capsules was sustained over a period of between 7-35 days. These findings suggest that emulsiontemplated gold shell microcapsules embedded in a hydrogel matrix would be suitable for use as an implantable drug delivery vehicle with FUS used to externally trigger release.
Applied Acoustics, 2019
The ability of pulse-echo ultrasound transit time spectroscopy (PE-UTTS) to improve the axial and... more The ability of pulse-echo ultrasound transit time spectroscopy (PE-UTTS) to improve the axial and lateral spatial resolution of an ultrasound B-scan image was investigated in this study. An acrylic step-wedge sample was used, consisting of 6 axial steps of both 0.2 and 0.1 mm height, at lateral separations ranging from 0.75 mm to 24 mm. The sample was immersed in water and conventional B-scan images obtained using an industrial Olympus Omniscan system with 2.25, 5 and 10 MHz transducers along with a clinical GE Voluson scanner with a 12 MHz transducer. PE-UTTS B-scan images were also created utilising the Omniscan RF data. From a qualitative perspective, the PE-UTTS B-scan images, at all three frequencies, demonstrated significantly greater axial and lateral spatial resolution than the corresponding conventional B-scan images. Quantitative analysis was performed by comparing the actual depth and length of the acrylic step surfaces with those measured from the conventional and PE-UTTS B-scan images. Of particular note, the depth accuracy for PE-UTTS at 10 MHz was greater than the conventional clinical B-scan at 12 MHz, being 99.90-99.94% compared to 95.95-97.77%. Lateral accuracy was also higher for PE-UTTS at 10 MHz, ranging from 86.67% to 96.67%, compared to 40.00% to 84.58% for the conventional scanner at a frequency of 12 MHz. This scientific study suggests that PE-UTTS has potential to improve clinical ultrasound B-scan image fidelity.
Sleep and Breathing, 2017
Purpose The variations in reported prevalence of rapid eye movement-related obstructive sleep apn... more Purpose The variations in reported prevalence of rapid eye movement-related obstructive sleep apnoea (REM-OSA) have been attributed to different definitions, although the effect of hypopnoea criteria has not been previously investigated. Methods Within this retrospective study, 134 of 382 consecutive patients undertaking polysomnography (PSG) for the suspicion of OSA met the inclusion criteria. PSGs were scored using both the 2007 AASM recommended hypopnoea criteria (AASM 2007Rec ) and the 2012 AASM recommended hypopnoea criteria (AASM 2012Rec ). For each hypopnoea criteria, REM-OSA patients were grouped as REM-related [either as REMpredominant OSA (rpOSA) or REM-isolated OSA (riOSA)] or non-stage-specific OSA (nssOSA). Outcome measures were also compared between groups. Results Incorporation of the AASM 2012Rec criteria compared to the AASM 2007Rec criteria increased the apnoea-hypopnoea index (AHI) for NREM and REM sleep but decreased the AHI REM / AHI NREM ratio from 1.9 to 1.3 (p < 0.001). It also decreased the prevalence of riOSA [15.7 vs 2.2% (p < 0.001) for AASM 2007Rec and AASM 2012Rec , respectively]. The prevalence of rpOSA remained the same for each hypopnoea criteria although the prevalence of nssOSA increased with the AASM 2012Rec hypopnoea criteria [53.0 vs 66.4% (p < 0.006) for AASM 2007Rec and AASM 2012Rec , respectively]. There were no differences in clinical symptoms between the groups, irrespective of hypopnoea criteria used. Conclusions This study demonstrates that in comparison with AASM 2007Rec , the AASM 2012Rec hypopnoea criteria reduce the prevalence of riOSA but not rpOSA by reducing the ratio of REM respiratory events and NREM respiratory events.
Sleep and Breathing, 2016
This study examined the effect of hypopnoea criteria on the prevalence of positional obstructive ... more This study examined the effect of hypopnoea criteria on the prevalence of positional obstructive sleep apnea (pOSA) identified under the Amsterdam Positional OSA Classification (APOC) system. Methods: 303 consecutive patients undertaking polysomnography (PSG) for the suspicion of OSA were included in this retrospective investigation. PSGs were scored using both the 2007 American Academy of Sleep Medicine (AASM) recommended hypopnea criteria (AASM 2007Rec ) and the 2012 AASM recommended hypopnea criteria (AASM 2012Rec ). For each hypopnea criteria OSA patients were grouped according to the APOC categories (I, II or II) or else deemed non-APOC if they did not meet the APOC criteria. Outcome measures, such as Functional Outcomes of Sleep Questionnaire (FOSQ), MOS 36-item short-form health survey (SF-36) and psychomotor vigilance task (PVT), were also compared between the groups. The AASM 2012Rec increased the prevalence of OSA compared to AASM 2007Rec . The AASM 2012Rec trebled the number of APOC I patients compared to AASM 2007Rec (297% increase) as well as increased the proportion of females in the APOC I group. AASM 2012Rec did not change the number of APOC II and APOC III patients. In fact the same patients were present in these categories irrespective of hypopnea criteria. The proportion of non-APOC patients proportionally decreased with the AASM 2012Rec criteria. There were no differences in outcome measures between the AASM 2012Rec and AASM 2007Rec groups. This study demonstrates that, compared to AASM 2007Rec , AASM 2012Rec increases the prevalence of who could be successfully treated with positional therapy. The proportion of females with pOSA also increases as a consequence of AASM 2012Rec .
Sleep Medicine, 2016
The authors did not receive any financial support to carry out this study.
Ultrasonics, Feb 1, 2017
Several factors can affect performance of an ultrasound system such as quality of excitation sign... more Several factors can affect performance of an ultrasound system such as quality of excitation signal and ultrasound transducer behaviour. Nonlinearity of piezoelectric ultrasound transducers is a key determinant in designing a proper driving power supply. Although, the nonlinearity of piezoelectric transducer impedance has been discussed in different literatures, the trend of the nonlinearity at different frequencies with respect to excitation voltage variations has not been clearly investigated in practice. In this paper, to demonstrate how the nonlinearity behaves, a sandwich piezoceramic transducer was excited at different frequencies. Different excitation signals were generated using a linear power amplifier and a multilevel converter within a range of 30-200V. Empirical relation was developed to express the resistance of the piezoelectric transducer as a nonlinear function of both excitation voltage and resonance frequency. The impedance measurements revealed that at higher volt...
Nature reviews. Neurology, 2016
Like cardiovascular disease and cancer, neurological disorders present an increasing challenge fo... more Like cardiovascular disease and cancer, neurological disorders present an increasing challenge for an ageing population. Whereas nonpharmacological procedures are routine for eliminating cancer tissue or opening a blocked artery, the focus in neurological disease remains on pharmacological interventions. Setbacks in clinical trials and the obstacle of access to the brain for drug delivery and surgery have highlighted the potential for therapeutic use of ultrasound in neurological diseases, and the technology has proved useful for inducing focused lesions, clearing protein aggregates, facilitating drug uptake, and modulating neuronal function. In this Review, we discuss milestones in the development of therapeutic ultrasound, from the first steps in the 1950s to recent improvements in technology. We provide an overview of the principles of diagnostic and therapeutic ultrasound, for surgery and transient opening of the blood-brain barrier, and its application in clinical trials of str...
Physics in medicine and biology, Jan 21, 2015
The quality of ultrasound computed tomography imaging is primarily determined by the accuracy of ... more The quality of ultrasound computed tomography imaging is primarily determined by the accuracy of ultrasound transit time measurement. A major problem in analysis is the overlap of signals making it difficult to detect the correct transit time. The current standard is to apply a matched-filtering approach to the input and output signals. This study compares the matched-filtering technique with active set deconvolution to derive a transit time spectrum from a coded excitation chirp signal and the measured output signal. The ultrasound wave travels in a direct and a reflected path to the receiver, resulting in an overlap in the recorded output signal. The matched-filtering and deconvolution techniques were applied to determine the transit times associated with the two signal paths. Both techniques were able to detect the two different transit times; while matched-filtering has a better accuracy (0.13 μs versus 0.18 μs standard deviations), deconvolution has a 3.5 times improved side-lo...
A high frequency current source converter with adjustable magnitude to drive high power piezoelectric transducers
2012 15th International Power Electronics and Motion Control Conference (EPE/PEMC), 2012
ABSTRACT A general electrical model of a piezoelectric transducer for ultrasound applications con... more ABSTRACT A general electrical model of a piezoelectric transducer for ultrasound applications consists of a capacitor in parallel with RLC legs. A high power voltage source converter can however generate significant voltage stress across the transducer that creates high leakage currents. One solution is to reduce the voltage stress across the piezoelectric transducer by using an LC filter, however a main drawback is changing the piezoelectric resonant frequency and its characteristics. Thereby it reduces the efficiency of energy conversion through the transducer. This paper proposes that a high frequency current source converter is a suitable topology to drive high power piezoelectric transducers efficiently.
Biomedical Engineering / 765: Telehealth / 766: Assistive Technologies, 2012
This paper presents the ultrasonic velocity measurement method which investigates the possible ef... more This paper presents the ultrasonic velocity measurement method which investigates the possible effects of high voltage high frequency pulsed power on cortical bone material elasticity. Before applying a pulsed power signal on a live bone, it is essential to determine the safe parameters of pulsed power applied on bone nondestructively. Therefore, the possible changes in cortical bone material elasticity due to a specified pulsed power excitation have been investigated. A controllable positive buck-boost converter with adjustable output voltage and frequency has been used to generate high voltage pulses (500V magnitude at 10 KHz frequency). To determine bone elasticity, an ultrasonic velocity measurement has been conducted on two groups of control (unexposed to pulse power but in the same environmental condition) and cortical bone samples exposed to pulsed power. Young's modulus of cortical bone samples have been determined and compared before and after applying the pulsed power signal. After applying the high voltage pulses, no significant variation in elastic property of cortical bone specimens was found compared to the control. The result shows that pulsed power with nominated parameters can be applied on cortical bone tissue without any considerable negative effect on elasticity of bone material.
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Papers by Christian Langton