10:30
Imaging Ultrasound I
10:30
15 mins
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THERMAL IMAGING: (RE)DISCOVERING THE POTENTIALS FOR DIAGNOSTICS AND TREATMENT IN THE CLINICAL PROCEDURES
Rudolf Verdaasdonk, John Klaessens, Albert van der Veen
Abstract: Although thermo camera's have been around for decades, they were too cumbersome to be accepted for routine clinical applications. Nowadays, thermo camera's have become as small as smart phones and are practical in use without special cooling systems and calibration procedures with a high image and temperature resolution (<0.1 K). Some clinical applications have been re-invented and new applications are being developed. Thermal imaging can be useful to image physiological processes, perfusion, inflammation, friction and breathing. Temperature changes can be induced or provoked to observe dynamic changes to differentiate between healthy and abnormal responses.
In the VU University Medical Center many specialism's have become interested in the potential of thermo imaging and various feasibility studies have started:
Cardiology: prediction of spasm of the artery in the arm before cardiac catheterization.
Urology: cause of impotence after radical prostatectomy
Anesthesiology: effectiveness of anesthetic block and pain treatment,
Neonatology: non contact monitoring of vital functions in neonates
Plastic surgery: perfusion quality of skin flap for breast reconstruction, effectiveness of cryotherapy of hypertrophic scars, burn wound skin transplantation
Dermatology: objective and sensitive imaging of allergic reactions, evaluation of laser treatments and wound healing
The thermo camera could easily be used in the clinic with approval of ethical committee since there is no contact with the patient so risks are minimal. Clinician appreciate the technology and are more 'image minded' . Either the thermo imaging helps to improve an treatment or can become a new diagnostics tool. Still, there is a longer way for acceptance and becoming the new golden standard. Besides the many potentials in the hospital, thermo camera's should become standard equipment in the office of general practitioners.
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10:45
15 mins
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A METHOD FOR DETERMINING PHYSIOLOGICAL CROSS SECTIONAL AREAS OF LOWER LIMB MUSCLES USING DIFFUSION WEIGHTED MRI
Pieter Oomen, Tessa Kierkels, Kenneth Meijer, Maarten Drost
Abstract: Introduction: Muscle architecture is a main determinant of muscle function. Architecture of a muscle can be described as the arrangement of muscle fibers within a muscle relative to the axis of force generation [1]. Literature provides architectural parameters (i.e. physiological cross sectional area (PCSA), pennation angle and fiber length) only post-mortem [2, 3]. Besides, it has been shown that scaling using anthropometry is not sufficient for predicting these parameters [4]. Fortunately, recent advances in imaging techniques give the opportunity to study these parameters in vivo [5]. Diffusion Tensor Imaging (DTI) is a promising non-invasive method to determine muscle fiber trajectories in-vivo. The purpose of this study is to determine in vivo PCSA, fiber lengths and volume from muscles in the lower extremities.
Methods: One healthy adult male (27 years, 78 kg, 1.76 m) participated in this study. A Philips 3.0 T Achieva MR scanner was used to obtain T1 and diffusion weighted images. The right leg was measured from ankle until superior iliac spine. The workflow consisted of the following steps: 1) The program VolumeTool was used for the segmentation of individual muscles volumes; 2) The program vISTe was used for fiber tracking within these volumes; 3) Custom software was developed to calculate muscles’ PCSA; The program consists of 3a) Manually selecting muscle trajectories from the whole volume seeding; 3b) Fitting a surface through the selected trajectories, single order planes were shown to be sufficient for unipennate muscles; 3c) Boundaries for the surface were set based on the segmentation; 3d) the scalar product was calculated: a mesh of triangles was created knowing their main tensor direction and area, consequently the sum of all projected surfaces was calculated.
Results: So far the results were completed for the m. semitendinosus (ST), m. biceps femoris longus (BFL) and brevis (BFB). Study results are summarized in Table 1, showing muscle volumes, PCSA and calculated muscle fiber lengths. For comparison reasons, literature values from cadaveric datasets were included.
Table 1: Muscle volume, PCSA and muscle fiber length for the m. semitendinosus (ST), m. biceps femoris longus (BFL) and brevis (BFB). Rangeref: displays the range of reference values [2, 3, 6, 7]
Semitendinosus Biceps femoris longus Biceps femoris brevis
Our data Rangeref Our data Rangeref Our data Rangeref
Volume (ml) 211.9 45-212 195.4 60-232 112.0 52-108
PCSA (cm2) 7.5 4.4-23.3 15.8 7.4-27.3 8.2 4.7-11.8
Fiber length (cm) 28.2 8.9-19.3 12.0 6.6-9.8 13.7 9.1-14.6
Discussion: A limitation of this study is the comparison with cadaveric datasets, since these data sets mostly include specimens of elderly which are prone to decreased muscle volumes. Surprisingly, PCSAs of these three muscles were shown to be below average compared to literature and muscle fiber lengths were rather long. This might be explained by stretched, beyond optimal, muscle fibers. Additional points of concern are DTI quality, manually selecting of the trajectories (step 3A), order of the fitted surface and PCSA calculation for complex (bipennate) muscles. Therefore only unipennate muscles with accurate DTI tensors and promising fiber tracking were included.
References:
1. Lieber, R.L., Skeletal muscle structure, function, and plasticity : the physiological basis of rehabilitation. 3rd ed. 2010, Philadelphia, Pa., [etc.]: Wolters Kluwer/Lippincott Williams & Wilkins. VIII, 304, [8] p. pl.
2. Ward, S.R., et al., Are current measurements of lower extremity muscle architecture accurate? Clin Orthop Relat Res, 2009. 467(4): p. 1074-82.
3. Wickiewicz, T.L., et al., Muscle architecture of the human lower limb. Clin Orthop Relat Res, 1983(179): p. 275-83.
4. Oomen, P., et al., Development and validation of a rule-based strength scaling method for musculoskeletal modelling. Int. J. Human Factors Modelling and Simulation,, 2014. (in press).
5. Galban, C.J., et al., Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf. Eur J Appl Physiol, 2004. 93(3): p. 253-62.
6. Friederich, J.A. and R.A. Brand, Muscle fiber architecture in the human lower limb. J Biomech, 1990. 23(1): p. 91-5.
7. Klein Horsman, M.D., et al., Morphological muscle and joint parameters for musculoskeletal modelling of the lower extremity. Clin Biomech (Bristol, Avon), 2007. 22(2): p. 239-47.
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11:00
15 mins
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FUNCTIONAL TESTING OF A NOVEL PULSE WAVE VELOCITY SENSOR
Marit van Velzen, Arjo Loeve, Egbert Mik, Sjoerd Niehof, Robert Jan Stolker
Abstract: INTRODUCTION Pulse wave velocity (PWV), the velocity of a pressure pulse wave (PW) traveling through a vessel, is the gold standard measure of arterial stiffness. Arterial stiffness is a reliable prognostic index for cardiovascular morbidity and mortality in the general adult population. In a healthy population, the PWV, depending of age, is about 6 to 10 m/s. The PWV in cardiovascular risk patients can be as high as 20 m/s. The PWV can be measured invasively and non invasively and is highly reproducible. Invasiveness and the requirement of an experienced operator are disadvantages of many methods. We designed a novel device, the “Multi Photodiode Array” (MPA), for non invasive measuring of the local PWV in a finger. The aim of the current work was to verify the functionality of the MPA.
METHODS The MPA utilizes photoplethysmography, which is a widely used non invasive optical technique for measuring the volumetric expansion and contraction of the vessels. The MPA consists of light sources emitting red and infrared light, and a photodiode array. Sixteen photodiodes are placed in a single row with their successive centers placed 0.8 mm apart. The time differences between detecting the passing of the PW by the successive photodiodes can be used to calculate the local PWV. To validate the MPA, a setup was built in which a red laser light dot traveled over the photodiode array with a known and constant input-velocity (varied to be either 12.5, 25, 35 or 45 m/s). The wavelength of the laser was 632.8 nm, chosen to mimic the spectrum transmission in the finger. The laser dot was aimed at the photodiode array using a rotating mirror, controlled to deliver the desired input velocity of the light dot over the photodiode array. The accuracy of the validation setup was calculated, as well as the measurement accuracy for the MPA. For each input velocity it was verified whether the calculated output velocity matched the supplied input velocity.
RESULTS The input velocity accuracy was about ±2.5% for all measurements. Because PWV between the diodes in the array was calculated by dividing the measured PW travel time between two diodes by the distance between the same diodes, the measurement accuracy of the MPA depends of the tolerance on the distance between the successive photodiodes (0.25 mm over 12 mm) and the accuracy of the detection of the peak of the PWs. This measurement deviation of the MPA was no more than 2.3%. The difference between the input velocity and output velocity, containing all sources of variance was below 1.9% for all measurements.
CONCLUSION. The MPA made in this project can reliably measure the PWV with a high accuracy of 98.1%. Reproducibility and variance data of the local PWV in humans will be available after measuring healthy volunteers and cardiovascular risk patients.
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11:15
15 mins
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3D ULTRASOUND IMAGING OF SOFT TISSUE DEFORMATION IN THE LOWER EXTREMITY: METHODS AND INITIAL RESULTS
Kaj Gijsbertse, André Sprengers, Nico Verdonschot, Chris de Korte
Abstract: The aetiology of many musculoskeletal (MS) diseases is related to biomechanical factors. However, the tools used by clinicians and researchers to assess the biomechanical condition of structures in the lower extremity are often crude and subjective, leading to non-optimal patient analyses and care. We aim to develop advanced diagnostic, pre-planning and outcome tools which yield detailed biomechanical information about abnormal tissue deformations. Quantification of deformations within the tissues can assist clinicians in judging pathologies and can be used to validate and improve biomechanical models. This will open possibilities for more sensitive and objective ways to diagnose and follow-up patients and to perform research on the MS system of humans.
Ultrasound is a clinically attractive imaging modality and can assess local tissue displacement by correlating segments of ultrasound data acquired sequentially. This technique has been successfully used during dynamic loading of tissue, and was also applied in actively deforming tissue, such as the heart [1]. Only few studies report on ultrasound strain imaging in skeletal muscles; Lopata et al. applied a bi-planar acquisition to assess deformation of the biceps during contraction in three orthogonal directions [2]. However, to account for out-of-plane motion and for a comprehensive mapping of the 3D muscle contraction, a full 3D technique is needed. In this study we want to assess the improvement of 3D displacement estimation using 3D phantom data compared to conventional 2D techniques, and to apply the technique to quantify the deformation of the m. gastrocnemius in vivo.
The results illustrate a better agreement between the estimated displacement and ground truth using 3D segments compared to 2D segments. Root mean squared errors (RMSE) for a plane with out-of-plane motion, were 0.62 mm and 0.13 mm for the 2D and 3D techniques respectively. For a plane without out-of-plane motion, the RMSE values were 0.17 mm and 0.07 mm respectively. Application of the technique in vivo is feasible and results in high quality displacement images. Optimization of the cross-correlation window settings might improve the displacement estimation even further.
REFERENCES
[1] J. D'Hooge, A. Heimdal, F. Jamal, T. Kukulski, B. Bijnens, F. Rademakers, L. Hatle, P. Suetens, and G. R. Sutherland, "Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations," Eur J Echocardiogr, vol. 1, pp. 154-70, 2000.
[2] R. G. Lopata, J. P. van Dijk, S. Pillen, M. M. Nillesen, H. Maas, J. M. Thijssen, D. F. Stegeman, and C. L. de Korte, "Dynamic imaging of skeletal muscle contraction in three orthogonal directions," J Appl Physiol (1985), vol. 109, pp. 906-15, Sep 2010.
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11:30
15 mins
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REAL-TIME 3D ULTRASOUND REGISTRATION OF LIVER
Jyotirmoy Banerjee, Camiel Klink, Edward Peters, Wiro Niessen, Adriaan Moelker, Theo van Walsum
Abstract: PURPOSE - With the advent of 4D ultrasound, volumes of human anatomy can be visualized in real-time. Interoperative imaging using 4D ultrasound has huge potential in minimally invasive surgery of the liver. Image registration is a basic requirement in these applications and they aid in image stabilization for better visualization. In this abstract we present 3D rigid registration approach for 4D ultrasound datasets, where images are registered in real-time.
CHALLENGES - Our ultrasound registration approach is motivated by ultrasound speckle tracking literature. In an ideal scenario, tracking information from multiple speckle patterns can be used to estimate the deformation. However in practice not all of the speckle patterns will be tracked well resulting in inaccurate estimate of the transformation.
METHOD – Our registration method consists of three basic steps a) Point Selection, b) Block-matching, and c) Outliers Rejection followed by a rigid transformation using the inliers. The block-matching step uses a similarity metric to establish correspondences between the selected points in the fixed image and the moving image. The outlier rejection step removes the erroneous matchings’ from the block-matching, based on geometric consistency.
EXPERIMENTS - Thirteen 4D US volume sequences were acquired from six healthy volunteers at 6 Hz from iU22 Philips machine. From the 4D US sequences, pairs of frames were selected in a systematic way such that they are representative of the whole breathing cycle. We use Elastix registration toolbox [1] to generate the reference standard. Different grids were used in the method and the evaluation. The block-matching and outlier rejection was additionally implemented in OpenCL. The implementation was run on a NVIDIA GTX 780 Ti graphics processing unit (GPU).
RESULTS - For 85 pairs of 3D ultrasound volumes acquired from 4D ultrasound sequences, a mean registration error of 1.3 mm is achieved. A GPU implementation runs the 3D US registration at 8 Hz.
CONCLUSION - To conclude, we proposed and evaluated a US to US registration approach to obtain a robust registration of liver volumes. Additionally we demonstrate that, a GPU implementation of our registration approach can be used in real-time.
REFERENCES
[1] S. Klein, M. Staring, K. Murphy, M.A. Viergever and J.P.W. Pluim, “elastix: A toolbox for intensity-based medical image registration”, IEEE Trans. Med. Imaging., Vol. 29(1), pp. 96–205, (2010).
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11:45
15 mins
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MECHANICAL CHARACTERIZATION OF ASCENDING THORACIC AORTIC ANEURYSMS USING 4-D ULTRASOUND
Emiel van Disseldorp, Jan Nijs, Erwin Tan, Marc van Sambeek, Frans van de Vosse, Richard Lopata
Abstract: Aortic aneurysms are a hazardous, asymptomatic condition and the 13th cause of death in Western society . The major complication of aneurysms is rupture, which leads to death in 75 to 90% of all cases. Surgery is recommended for aneurysms with a diameter exceeding 5.5 cm and for small aneurysms if the aneurysm has grown over 1 cm in the last year. However, this method has proven to be inadequate as a criterion for intervention planning. Hence, a new approach for rupture risk assessment is needed. The aneurysm will rupture if the mechanical stress exceeds the local strength of the vessel wall. Therefore, the state of the aortic wall, i.e., the mechanical properties, will be a better predictor for rupture risk. This study, focused on aneurysms in the ascending thoracic aorta (ATAAs), aims to characterize the mechanical properties of the aortic wall using 4D ultrasound in vivo, and verify these results by biaxial tensile testing in vitro.
Twenty ATAA-patients, who underwent graft replacement surgery, were included and 4D (3D+time) ultrasound (US) datasets were captured perioperatively as well as intraluminal pressure. The 4D US data were segmented manually at end-diastolic and end-systolic pressure. The resulting contours and pressures were used as the input for a finite element (FE) model for which the contours were converted into a quadratic tetrahedral element mesh. An incompressible Neo-Hookean material model was explicitly calculated using a hybrid element formulation. A backward incremental method was executed, to determine the initial stress at diastolic pressure. Finally, the in vivo incremental shear modulus, Ginc, was found by optimizing the model until the model output resembled the in vivo data. Secondly, in a more direct, elastography approach, the geometrical data and pressure were used to estimate Ginc directly, using LaPlace's law.
Verification of the in vivo characterization was performed in vitro using biaxial tensile tests. An axial pre-stretch of 1.25 was applied to samples of aortic tissue, and was subsequently stretched to 1.45 to capture the total stress-strain behavior.
The results of this study showed a good agreement between the two in vivo US-based methods, and characterized a mean incremental shear modulus of Ginc=227±98 kPa and Ginc=231±98 kPa for the finite element analysis and the elastrography approach, respectively. This in vitro determined shear modulus (Ginc=148±48 kPa) was lower than the overall in vivo shear modulus. However, for five out of the nine patients which were suitable for finite element analysis, a good agreement was found between the two US-based in vivo measurements and the in vitro analysis. In future work, an accurate 3D speckle tracking algorithm and an automated segmentation approach will improve characterization of the aortic wall, although the differences between the in vivo and in vitro findings requires further research.
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