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- Lorentsson, Robert, 1969, et al.
(author)
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A 4-afc study comparing ultrasound machines using a greyscale phantom
- 2015
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In: IFMBE Proceedings. 16th Nordic-Baltic Conference on Biomedical Engineering. October 14-16, 2014, Gothenburg, Sweden. - Cham : Springer International Publishing. - 1680-0737. ; 48, s. 82-85
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Conference paper (peer-reviewed)abstract
- © Springer International Publishing Switzerland 2015. Two ultrasound machines, one high-end and one ordinary, were compared in terms of their ability to reproduce low-contrast objects using the same probe. Images containing 4 mm objects of four different contrasts were collected from a greyscale phantom at 35-42 mm depth. Six observers participated in a 4-alternative forced choice study based on 120 images. At this certain depth and object size the proportion of correct responses was higher (statistically significant) for the high-end machine at three of four contrast levels, indicating the possibility to discriminate between ultrasound machines using a limited number of images of a greyscale phantom. However, the number of images and number of observers needed are larger than usually used for constancy control.
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| 2. |
- Lorentsson, Robert, 1969, et al.
(author)
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Comparison of the low-contrast detectability of two ultrasound systems using a grayscale phantom
- 2016
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In: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 17:6, s. 366-378
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Journal article (peer-reviewed)abstract
- The purpose of the present study was to use a commercially available grayscale phantom to compare two ultrasound systems regarding their ability to reproduce clinically relevant low-contrast objects at different sizes and depths, taking into account human observer variability and other methodological issues related to observer performance studies. One high-end and one general ultrasound scanner from the same manufacturer using the same probe were included. The study was intended to simulate the clinical situation where small low-contrast objects are embedded in relatively homogeneous organs. Images containing 4 and 6.4 mm objects of four different contrasts were acquired from the grayscale phantom at different depths. Six observers participated in a 4-alternative forced-choice study based on 960 images. Case sample and human observer variabilities were taken into account using bootstrapping. At four of sixteen depth/size/contrast combinations, the visual performance of the high-end scanner was significantly higher. Thus, it was possible to use a grayscale phantom to discriminate between the two evaluated ultrasound systems in terms of their ability to reproduce clinically relevant low-contrast objects. However, the number of images and number of observers were larger than those usually used for constancy control.
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| 3. |
- Lorentsson, Robert, 1969, et al.
(author)
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Evaluation of an automatic method for detection of defects in linear and curvilinear ultrasound transducers
- 2021
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In: Physica Medica-European Journal of Medical Physics. - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 84, s. 33-40
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Journal article (peer-reviewed)abstract
- Purpose: The high incidence of defective ultrasound transducers in clinical practice has been shown in several studies. Recently, a novel method using only stored images for automatic detection of defective transducers was presented. The method makes it possible to remotely monitor many transducers at the same time and send a notification when a defective transducer is found. The purpose of the present study was to evaluate the novel method and assess how well it performs when compared to an established method as reference. Methods: To evaluate the novel method, in-air images were collected from 81 transducers in radiologic departments in nine hospitals. Two observers assessed the in-air images and marked the defects. Receiver operating characteristic (ROC)- and alternative free response receiver operating characteristic (AFROC)-curves and their figures of merit (FOM) were calculated for the novel method, using marked defects in the in-air images as reference truth. Results: The area under the ROC curve was 0.88 (SD 0.06), and the AFROC FOM was 0.71 (SE 0.07). Conclusion: The result shows that the novel method has a good agreement with the in-air method for detecting defects in ultrasound systems. This indicates that the novel method could be a complement to the normal quality control for early, and automatic detection of defects.
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| 4. |
- Lorentsson, Robert, 1969
(author)
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How does the technical status of medical ultrasound equipment affect image quality? Studies based on human observer experiments and a novel method for automatic detection of defective transducers
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Ultrasound as an imaging modality has a fundamental role in modern healthcare. The equipment, especially transducers, is fragile and handled daily, and transducers are known to sometimes become defective. The overall aim of this thesis was to evaluate how the technical status of the equipment affects clinical image quality. In study 1 a novel automatic method to detect defects in linear transducers by analysing the images that are saved for documentation was developed which makes it possible to monitor many transducers without interference with clinical activity. The method was evaluated in study 2 by comparing the result obtained with the automatic method to the well-established in-air method, which is used for quality control, for 81 linear and curvilinear transducers. The methods showed good agreement, the area under curve for the receiver operating characteristics evaluation being 0.88 (SD 0.06). There is a variety of different scanners, from regular to high-end. In study 3 a comparison of a regular and a high-end scanner was made, the images from the clinically relevant objects in a greyscale phantom being assessed by six observers in a detection study. Visibility was substantially better for the advanced scanner in four out of 16 combinations of depth, contrast and size. The method from study 1 was also used in study 4 to find images from defective transducers that had been used clinically. 160 images from four defective transducers, with defects that had different grades of severity, were collected, and were compared to 160 images from non-defective transducers in an observer study with four experienced radiologists. There were four mandatory questions concerning whether the defects were detectable, whether the possible defects might affect the diagnosis, the visibility of structural details and total image quality. For three of the transducers the defects were detectable, the visibility of structural details being assessed as worse for all the four defective transducers. The total image quality was assessed as worse for three of the defective transducers. Out of the assessments of the images produced by the defective transducers, 19 % were “confident that the artifacts could affect the diagnosis”. This thesis shows that differences in image quality between different kind of ultrasound scanners can be detected using human observers. The thesis also shows that clinical image quality can be affected by defective transducers and that there is a risk of misdiagnosis if transducers with severe defects are used. The developed method for automatic detection of non-uniformities in clinical images could be used as a complement to normal quality control for earlier detection of defective transducers.
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| 5. |
- Lorentsson, Robert, 1969, et al.
(author)
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Investigation of the Impact of Defective Ultrasound Transducers on Clinical Image Quality in Grayscale 2-D Still Images.
- 2023
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In: Ultrasound in medicine & biology. - 0301-5629 .- 1879-291X. ; 49:9, s. 2126-2133
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Journal article (peer-reviewed)abstract
- There are several studies that show high defect rates of transducers in clinical use. The purpose of the present study was to investigate whether image quality and the risk for misdiagnosis is affected by using defective transducers.Four defective transducers with varying degrees of defect severity, still in clinical use, were selected. Forty artifact-affected clinical images from each transducer were compared with images acquired from fully functional transducers, of the same model, in an observer study where four experienced radiologists rated each of the 320 images. The rating tasks included if the artifacts were detectable, if the possible artifacts might affect the diagnosis, how well structural details were reproduced and, finally, an assessment of overall image quality.The artifacts in the images were detectable for three of the four transducers (p < 0.05), and in 121 of 640 assessments of the images from the defective transducers the observers were confident that the artifacts could affect the diagnosis. All four faulty transducers were assessed to have decreased ability to resolve structural details (p < 0.05), and three of the four transducers were assessed to have worse overall image quality (p < 0.05).The present study shows that image quality and the risk of misdiagnosis can be affected by using defective transducers. This highlights the importance of frequent quality control of the transducers to avoid decreased image quality and even misdiagnosis.
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| 6. |
- Lorentsson, Robert, 1969, et al.
(author)
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Method for automatic detection of defective ultrasound linear array transducers based on uniformity assessment of clinical images - A case study
- 2018
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In: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 19:2, s. 265-274
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Journal article (peer-reviewed)abstract
- The purpose of the present study was to test an idea of and describe a concept of a novel method of detecting defects related to horizontal nonuniformities in ultrasound equipment. The method is based on the analysis of ultrasound images collected directly from the clinical workflow. In total over 31000 images from three ultrasound scanners from two vendors were collected retrospectively from a database. An algorithm was developed and applied to the images, 150 at a time, for detection of systematic dark regions in the superficial part of the images. The result was compared with electrical measurements (FirstCall) of the transducers, performed at times when the transducers were known to be defective. The algorithm made similar detection of horizontal nonuniformities for images acquired at different time points over long periods of time. The results showed good subjective visual agreement with the available electrical measurements of the defective transducers, indicating a potential use of clinical images for early and automatic detection of defective transducers, as a complement to quality control.
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