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  • 1.
    Frank A, Flachskampf
    et al.
    Uppsala Universitet, Institutionen för Medicinska Vetenskaper, Akademiska sjukhuset.
    Mattias, Mårtensson
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    How should tissue Doppler tracings be measured?2014In: European Heart Journal Cardiovascular Imaging, ISSN 2047-2404, E-ISSN 2047-2412, Vol. 15, no 7, p. 828-829Article in journal (Refereed)
  • 2. Fröberg, Asa
    et al.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Janerot-Sjöberg, Birgitta
    KTH, School of Technology and Health (STH), Medical Engineering.
    D'Hooge, Jan
    Arndt, Anton
    High variability in strain estimation errors when using a commercial ultrasound speckle tracking algorithm on tendon tissue2016In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 57, no 10, p. 1223-1229Article in journal (Refereed)
    Abstract [en]

    Background: Ultrasound speckle tracking offers a non-invasive way of studying strain in the free Achilles tendon where no anatomical landmarks are available for tracking. This provides new possibilities for studying injury mechanisms during sport activity and the effects of shoes, orthotic devices, and rehabilitation protocols on tendon biomechanics. Purpose: To investigate the feasibility of using a commercial ultrasound speckle tracking algorithm for assessing strain in tendon tissue. Material and Methods: A polyvinyl alcohol (PVA) phantom, three porcine tendons, and a human Achilles tendon were mounted in a materials testing machine and loaded to 4% peak strain. Ultrasound long-axis cine-loops of the samples were recorded. Speckle tracking analysis of axial strain was performed using a commercial speckle tracking software. Estimated strain was then compared to reference strain known from the materials testing machine. Two frame rates and two region of interest (ROI) sizes were evaluated. Results: Best agreement between estimated strain and reference strain was found in the PVA phantom (absolute error in peak strain: 0.21 +/- 0.08%). The absolute error in peak strain varied between 0.72 +/- 0.65% and 10.64 +/- 3.40% in the different tendon samples. Strain determined with a frame rate of 39.4Hz had lower errors than 78.6Hz as was the case with a 22mm compared to an 11mm ROI. Conclusion: Errors in peak strain estimation showed high variability between tendon samples and were large in relation to strain levels previously described in the Achilles tendon.

  • 3. Fröberg, Åsa
    et al.
    Cissé, Ann-Sophie
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering.
    Peolsson, Michael
    Movin, Tomas
    Arndt, Anton
    Altered patterns of displacement within the Achilles tendon following surgical repair.2016In: Knee Surgery, Sports Traumatology, Arthroscopy, ISSN 0942-2056, E-ISSN 1433-7347Article in journal (Refereed)
    Abstract [en]

    PURPOSE: Ultrasound speckle tracking was used to compare tendon deformation patterns between uninjured and surgically repaired Achilles tendons at 14-27-month follow-up. The hypothesis was that the non-homogenous displacement pattern previously described in uninjured tendons, where displacement within deep layers of the tendons exceeds that of superficial layers, is altered following tendon rupture and subsequent surgical repair.

    METHODS: In the first part of this study, an in-house-developed block-matching speckle tracking algorithm was evaluated for assessment of displacement on porcine flexor digitorum tendons. Displacement data from speckle tracking were compared to displacement data from manual tracking. In the second part of the study, eleven patients with previous unilateral surgically treated Achilles tendon rupture were investigated using ultrasound speckle tracking. The difference in superficial and deep tendon displacement was assessed. Displacement patterns in the surgically repaired and uninjured tendons were compared during passive motion (Thompson's squeeze test) and during active ankle dorsiflexion.

    RESULTS: The difference in peak displacement between superficial and deep layers was significantly (p < 0.01) larger in the uninjured tendons as compared to the surgically repaired tendons both during Thompson's test (-0.7 ± 0.2 mm compared to -0.1 ± 0.1 mm) and active dorsiflexion (3.3 ± 1.1 mm compared to 0.3 ± 0.2 mm). The evaluation of the speckle tracking algorithm showed correlations of r ≥ 0.89 between displacement data acquired from speckle tracking and the reference displacement acquired from manual tracking. Speckle tracking systematically underestimated the magnitude of displacement with coefficients of variation of less than 11.7%.

    CONCLUSIONS: Uninjured Achilles tendons display a non-uniform displacement pattern thought to reflect gliding between fascicles. This pattern was altered after a mean duration of 19 ± 4 months following surgical repair of the tendon indicating that fascicle sliding is impaired. This may affect modulation of the action between different components of the triceps surae, which in turn may affect force transmission and tendon elasticity resulting in impaired function and risk of re-rupture.

  • 4.
    Lindberg, Frida
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Aesthetic ultrasound devices: Current state of knowledge and suggested measurement set-up for characterization of exposure2013Report (Other academic)
    Abstract [en]

    This report concerns the ultrasound devices used for the aesthetic purposes of body contouring and fat reduction (ablation of adipose tissue). Such devices have recently become more frequent on the Swedish market. These ultrasound devices are currently not medically regulated in Sweden and little is known about their safety and potentially harmful exposure when using them.

    This report aims to provide relevant information about present guidelines and scientific results in the area, a survey of the Swedish market and also recommendations on how to characterize the ultrasound emitted by these devices. This information provides an important basis for possible future regulatory actions.

    All aesthetic ultrasound devices found on the Swedish market use low-frequency non-thermal ultrasound. These types of devices (with one exception) have not yet been studied in peer-reviewed publications and the technical specifications from the suppliers are often incomplete. Consequently, there is a need to evaluate the devices in order to gain adequate knowledge about possible risks associated with their use.

    Ultrasound exposure should be characterized by its frequency and acoustic pressure. It has not been fully investigated whether the mathematical equation for the mechanical index is valid for the low frequencies used by aesthetic ultrasound equipment on the Swedish market. In this report, two different hydrophone measurement set-ups for characterization of ultrasound exposure are proposed. The most common reason behind adverse events or exposure of non-target tissue regions is most likely handling errors by the operator. Hence, only characterization of the ultrasound field does not necessarily imply the safe use of aesthetic ultrasound devices.

    It is recommended that the Swedish Radiation Safety Authority and the Swedish Medical Products Agency discuss their respective future responsibility and how aesthetic ultrasound devices should be regulated.

  • 5.
    Lindberg, Frida
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Grönlund, Christer
    Medicinsk Teknik - FoU, Umeå Univeristet.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of ultrasound Tissue Velocity Imaging: a phantom study of velocity estimation in skeletal muscle low-level contractions2013In: BMC Medical Imaging, ISSN 1471-2342, E-ISSN 1471-2342, Vol. 13, no 1, p. 16-Article in journal (Refereed)
    Abstract [en]

    Background: Tissue Velocity Imaging (TVI) is an ultrasound based technique used for quantitative analysis of the cardiac function and has earlier been evaluated according to myocardial velocities. Recent years several studies have reported applying TVI in the analysis of skeletal muscles. Skeletal tissue velocities can be very low. In particular, when performing isometric contractions or contractions of low force level the velocities may be much lower compared to the myocardial tissue velocities. Methods: In this study TVI was evaluated for estimation of tissue velocities below the typical myocardial velocities. An in-house phantom was used to see how different PRF-settings affected the accuracy of the velocity estimations. Results: With phantom peak velocity at 0.03 cm/s the error ranged from 31% up to 313% with the different PRF-settings in this study. For the peak velocities at 0.17 cm/s and 0.26 cm/s there was no difference in error with tested PFR settings, it is kept approximately around 20%. Conclusions: The results from the present study showed that the PRF setting did not seem to affect the accuracy of the velocity estimation at tissue velocities above 0.17 cm/s. However at lower velocities (0.03 cm/s) the setting was crucial for the accuracy. The PRF should therefore preferable be reduced when the method is applied in low-level muscle contraction.

  • 6. Mattsson, C. M.
    et al.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Enqvist, J. K.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Ekblom, B.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    No evidence of cardiac fatigue in tissue velocity curves at rest after 6 days of ultra-endurance exercise2010In: European Heart Journal, ISSN 0195-668X, E-ISSN 1522-9645, Vol. 31, p. 304-305Article in journal (Refereed)
  • 7.
    Mårtensson, Mattias
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of Errors and Limitations in Ultrasound Imaging Systems2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There are binding regulations requiring safety and efficacy aspects of medical devices. The requirements ask for documentation that the devices are safe and effective for their intended use, i.e. if a device has a measuring function it must be correct. In addition to this there are demands for quality systems describing development, manufacturing, labelling, and manufacturing of a device. The requirements are established to guarantee that non-defective medical devices are used in the routine clinical practice. The fast rates in which the imaging modalities have evolved during the last decades have resulted in numerous new diagnostic tools, such as velocity and deformation imaging in ultrasound imaging. However, it seems as if the development of evaluation methods and test routines has not been able to keep up the same pace. Two of the studies in this thesis, Study I and IV, showed that computed tomography-based and ultrasound based volume measurements can yield very disparate measurements, and that tissue Doppler imaging-based ultrasound measurements can be unreliable.

    Furthermore, the new ultrasound modalities impose higher demands on the ultrasound transducers. Transducers are known to be fragile, but defective transducers were less of a problem earlier when the ultrasound systems to a lesser extent were used for measurements. The two other studies, Study II and III, showed that serious transducer errors are very common, and that annual testing of the transducers is not sufficient to guarantee an error free function.

    The studies in the thesis indicate that the system with Notified Bodies, in accordance with the EU’s Medical Device Directive, checking the function and manufacturing of medical devices does not work entirely satisfactory. They also show that the evaluation of new methods have led to the undesirable situation, where new measuring tools, such as volume rendering from imaging systems, and tissue Doppler-based velocity and deformation imaging in echocardiography are available for clinicians without proven knowledge about their accuracy.

  • 8.
    Mårtensson, Mattias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of tissue Doppler-based velocity and deformation imaging: a phantom study of ultrasound systems.2011In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 12, no 6, p. 467-476Article in journal (Refereed)
    Abstract [en]

    AIMS: The objective of this study was to test the accuracy and diagnostic interchangeability of tissue Doppler-based displacement, velocity, strain, and strain rate measurements in commercially used ultrasound (US) systems. METHODS AND RESULTS: Using an in-house made phantom, four different US scanner models were evaluated. Two different scanners of the same model were tested, and one scanner acquisition was tested twice with two generations of the same workstation giving six test results in total. The scanners were in active clinical use and are subject to regular maintenance checks. There were three displacement and four velocity results that stood out from the rest and could be regarded as accurate and interchangeable. Among the deformation measurements, three acceptable strain results were found while there were no acceptable strain rate results. Furthermore, the study showed that measurements from scanners of the same model, same acquisition post-processed on different workstations and repeated measurements from the same scanner, can yield disparate results. CONCLUSION: Measurements that are accurate and of interchangeable use can be found for displacement and velocity measurements, but are less likely to be found for strain and strain rate measurements. It is strongly recommended that the ability of each individual US scanner to measure displacement, velocity, strain, and strain rate is evaluated before it is introduced into clinical practice, and it must always be evaluated together with the workstation the scanner is intended to be used in conjunction with.

  • 9.
    Mårtensson, Mattias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Olsson, Mats
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Ultrasound transducer function: annual testing is not sufficient2010In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 11, no 9, p. 801-805Article in journal (Refereed)
    Abstract [en]

    The objective was to follow-up the study 'High incidence of defective ultrasound transducers in use in routine clinical practice' and evaluate if annual testing is good enough to reduce the incidence of defective ultrasound transducers in routine clinical practice to an acceptable level. A total of 299 transducers were tested in 13 clinics at five hospitals in the Stockholm area. Approximately 7000-15 000 ultrasound examinations are carried out at these clinics every year. The transducers tested in the study had been tested and classified as fully operational 1 year before and since then been in normal use in the routine clinical practice. The transducers were tested with the Sonora FirstCall Test System. There were 81 (27.1%) defective transducers found; giving a 95% confidence interval ranging from 22.1 to 32.1%. The most common transducer errors were 'delamination' of the ultrasound lens and 'break in the cable' which together constituted 82.7% of all transducer errors found. The highest error rate was found at the radiological clinics with a mean error rate of 36.0%. There was a significant difference in error rate between two observed ways the clinics handled the transducers. There was no significant difference in the error rates of the transducer brands or the transducers models. Annual testing is not sufficient to reduce the incidence of defective ultrasound transducers in routine clinical practice to an acceptable level and it is strongly advisable to create a user routine that minimizes the handling of the transducers.

  • 10.
    Mårtensson, Mattias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Olsson, Mats
    Segall, Björn
    Fraser, Alan G.
    Winter, Reidar
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    High incidence of defective ultrasound transducers in use in routine clinical practice2009In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 10, no 3, p. 389-394Article in journal (Refereed)
    Abstract [en]

    The objective was to evaluate the function of ultrasound transducers in use in routine clinical practice and thereby estimating the incidence of defective transducers. The study comprised a one-time test of 676 transducers from 7 manufacturers which were in daily use in clinical departments at 32 hospitals. They were tested with the Sonora FirstCall Test System; 39.8% exhibited a transducer error. Delamination was detected in 26.5% and break in the cable was detected in 8.4% of the tested transducers. Errors originating from the piezoelectrical elements were unusual. Delamination and short circuit occurred without significant differences between transducers from all tested manufacturers, but the errors break in the cable, weak and dead element showed a statistically significant higher frequency in transducers from certain manufacturers. The high error frequency and the risk for incorrect medical decisions when using a defective transducer indicate an urgent need for increased testing of the transducers in clinical departments.

  • 11.
    Mårtensson, Mattias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Winter, Reidar
    Cederlund, Kerstin
    Ripsweden, Jonaz
    Mir-Akbari, Habib
    Nowak, Jacek
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Assessment of left ventricular volumes using simplified 3-D echocardiography and computed tomography - a phantom and clinical study2008In: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 6Article in journal (Refereed)
    Abstract [en]

    Objectives: To compare the accuracy of simplified 3-dimensional (3-D) echocardiography vs. multi-slice computed tomography (MSCT) software for the quantification of left ventricular (LV) volumes. Design: Three-D echocardiography (3-planes approach) and MSCT-CardIQ software were calibrated by measuring known volumes of 10 phantoms designed to closely mimic blood-endocardium interface. Subsequently, LV volumes were measured with both the methods in 9 patients referred routinely for coronary angiography and the agreement between the measurements was evaluated. Results: Simplified 3D-echocardiography provided higher degree of agreement between the measured and true phantom volumes (mean difference 0 +/- 1 ml, variation range + 4 to -4 ml) than MSCT software (mean difference 6 +/- 5 ml; variation range + 22 to -10 ml). The agreement between LV measurements in the patients was considerably poorer, with significantly larger volumes produced by MSCT (mean difference - 23 +/- 40 ml, variation between + 93 and -138 ml). Conclusion: Simplified 3-D echocardiography provides more accurate assessment of phantom volumes than MSCT-CardIQ software. The discrepancy between the results of LV measurements with the two methods is even greater and does not warrant their interchangeable diagnostic use.

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