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Evaluation of Errors and Limitations in Ultrasound Imaging Systems
KTH, School of Technology and Health (STH), Medical Engineering.ORCID iD: 0000-0001-9419-910X
2011 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , x, 74 p.
Series
Trita-STH : report, ISSN 1653-3836 ; 2011:3
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-34177ISBN: 978-91-7501-026-7OAI: oai:DiVA.org:kth-34177DiVA: diva2:419683
Public defence
2011-06-10, Sal 3-221, Alfred Nobels Allé 10, Flemingsberg, 13:00 (Swedish)
Opponent
Supervisors
Note
QC 20110527Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2011-05-30Bibliographically approved
List of papers
1. Assessment of left ventricular volumes using simplified 3-D echocardiography and computed tomography - a phantom and clinical study
Open this publication in new window or tab >>Assessment of left ventricular volumes using simplified 3-D echocardiography and computed tomography - a phantom and clinical study
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2008 (English)In: Cardiovascular Ultrasound, ISSN 1476-7120, Vol. 6Article in journal (Refereed) Published
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.

Keyword
cardiac magnetic-resonance, 3-dimensional echocardiography, 2-dimensional echocardiography, ejection fraction, size, cineventriculography, quantification, transducer, spect
National Category
Medical Laboratory and Measurements Technologies Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-17613 (URN)10.1186/1476-7120-6-26 (DOI)000256849500001 ()2-s2.0-44949255615 (ScopusID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2014-12-01Bibliographically approved
2. High incidence of defective ultrasound transducers in use in routine clinical practice
Open this publication in new window or tab >>High incidence of defective ultrasound transducers in use in routine clinical practice
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2009 (English)In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 10, no 3, 389-394 p.Article in journal (Refereed) Published
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.

Keyword
Ultrasound, Transducer, Probe, Test, Defect, Error
National Category
Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-32380 (URN)10.1093/ejechocard/jen295 (DOI)000264889300008 ()2-s2.0-64749104230 (ScopusID)
Note

QC 20110413

Available from: 2011-04-13 Created: 2011-04-13 Last updated: 2014-12-01Bibliographically approved
3. Ultrasound transducer function: annual testing is not sufficient
Open this publication in new window or tab >>Ultrasound transducer function: annual testing is not sufficient
2010 (English)In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 11, no 9, 801-805 p.Article in journal (Refereed) Published
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.

Keyword
Transducer, Probe, Ultrasound, Testing, Maintenance, Service
National Category
Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-26307 (URN)10.1093/ejechocard/jeq072 (DOI)000282750900018 ()2-s2.0-77957981090 (ScopusID)
Note

QC 20101121

Available from: 2010-11-21 Created: 2010-11-21 Last updated: 2014-12-01Bibliographically approved
4. Evaluation of tissue Doppler-based velocity and deformation imaging: a phantom study of ultrasound systems.
Open this publication in new window or tab >>Evaluation of tissue Doppler-based velocity and deformation imaging: a phantom study of ultrasound systems.
2011 (English)In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 12, no 6, 467-476 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2011
Keyword
Ultrasound scanner; Tissue Doppler, Velocity imaging, Strain imaging, Phantom, Quality assurance
National Category
Medical Laboratory and Measurements Technologies Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-34176 (URN)10.1093/ejechocard/jer056 (DOI)000293527600012 ()21565867 (PubMedID)2-s2.0-80051995818 (ScopusID)
Note

QC 20110527

Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2014-12-01Bibliographically approved

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