| 1. |
- Bengtsson, Alexander, et al.
(author)
-
Characterization and modeling of acousto-optic signal strengths in highly scattering media
- 2019
-
In: Biomedical Optics Express. - 2156-7085. ; 10:11, s. 5565-5584
-
Journal article (peer-reviewed)abstract
- Ultrasound optical tomography (UOT) is an imaging technique based on the acousto-optic effect that can perform optical imaging with ultrasound resolution inside turbid media, and is thus interesting for biomedical applications, e.g. for assessing tissue blood oxygenation. In this paper, we present near background free measurements of UOT signal strengths using slow light filter signal detection. We carefully analyze each part of our experimental setup and match measured signal strengths with calculations based on diffusion theory. This agreement between experiment and theory allows us to assert the deep tissue imaging potential of similar to 5 cm for UOT of real human tissues predicted by previous theoretical studies [Biomed. Opt. Express 8, 4523 (2017)] with greater confidence, and indicate that future theoretical analysis of optimized UOT systems can be expected to be reliable. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
|
|
| 2. |
- Cinthio, Magnus, et al.
(author)
-
Longitudinal Movement of the Common Carotid Artery Wall : New Information on Cardiovascular Aging
- 2018
-
In: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 44:11, s. 2283-2295
-
Journal article (peer-reviewed)abstract
- Putative changes in the multiphasic pattern of longitudinal movement of the common carotid artery wall in the normal aging process are unknown. The aim of this study was to explore the phases, and resulting patterns, of the longitudinal movement of the intima–media complex of the human common carotid artery with respect to age and gender. One hundred thirty-five healthy non-smoking patients of different ages were investigated using in-house-developed ultrasound methods. The patterns of longitudinal movement seen in middle-aged and older patients were markedly different from those commonly seen in young patients, including the appearance of two additional phases of motion and, thus, new complex patterns. The displacement and maximum velocity of one of the phases, occurring at the time of aortic valve closure, increased quadratically with age in both men and women.
|
|
| 3. |
- Erlöv, Tobias, et al.
(author)
-
Determining carotid plaque vulnerability using ultrasound center frequency shifts.
- 2016
-
In: Atherosclerosis. - : Elsevier BV. - 1879-1484 .- 0021-9150. ; 246, s. 293-300
-
Journal article (peer-reviewed)abstract
- The leading cause of morbidity and mortality worldwide is atherosclerotic cardiovascular disease, most commonly caused by rupture of a high-risk plaque and subsequent thrombosis resulting in stroke, myocardial infarction or sudden death depending on the affected arterial territory. Accurate, non-invasive methods to identify such lesions known as vulnerable or high-risk plaques are currently sub-optimal. Our aim was to validate a new non-invasive ultrasound method to identify high-risk carotid plaques.
|
|
| 4. |
- Erlöv, Tobias, et al.
(author)
-
Improved Tracking Performance in High Frame Rate Imaging Using Iterative Phase Tracking
- 2019
-
In: 2019 IEEE International Ultrasonics Symposium (IUS). - 1948-5719 .- 1948-5727. - 9781728145969 - 9781728145976 ; 2019, s. 2158-2161
-
Conference paper (peer-reviewed)abstract
- High frame rate ultrasound imaging is necessary to enable tracking of rapid dynamic events such as the carotid pulse wave velocity. Several studies have shown that it is feasible to use motion tracking methods that are applied on standard ultrasound frame rates also on very high frame rates. However, few studies have addressed the issue of accumulated tracking errors over vast numbers of frames during Lagrangian tracking. These could stem from e.g. limited signal-to-noise ratio often resulting from the use of plane wave imaging. One recently proposed solution was to combine motion tracking with an iterative tracking scheme. The purpose of this study has been to evaluate if the iterative tracking scheme could be exploited to increase the robustness of a phase-based tracking method in high frame rate plane wave imaging to track the carotid artery wall diameter. The results showed the iterative tracking scheme to give increased robustness with significantly (p<0.0003) less differences in measured lumen diameters between adjacent lines. Thus, this study enforces the suggestion to use the iterative tracking scheme during Lagrangian tracking in high frame rate imaging.
|
|
| 5. |
- Erlöv, Tobias
(author)
-
On the Use of Ultrasound Phase Data for Arterial Characterization
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- Atherosclerosis is one of the major causes of death in the world. It is an inflammatory disease in the arteries which causes a gradual increase in arterial wall thickness and stiffness. Eventually a plaque could be formed, protruding into the artery and partially occluding the blood flow. Rupture of such a plaque could cause cardiac infarction or stroke. This dissertation revolves around finding better methods to detect and diagnose different stages of atherosclerosis and also to better understand the physiology of arteries. The methods developed and presented in this dissertation are all based on non-invasive ultrasound images. Ultrasound is the most common tool to image, particularly, the carotid artery in clinics today. The first method utilizes the time domain phase of the ultrasound radio frequency data for plaque/tissue characterization. The center frequency of the backscattered signal is estimated using phase differences measured in the time domain. We have shown that there is a clear correlation between the center frequency shift (CFS) and scatter size using a series of agar phantoms with well-defined sizes of glass beads. We have also shown that the CFS can be used in vivo to determine carotid plaque vulnerability. The method could potentially become a useful tool to identify patients at risk for development of acute cardiovascular events as well as to monitor response to interventions. The second and third methods are based on motion tracking (one is again based on time domain phase data) and could be used to measure e.g. the longitudinal movement of the arterial wall. The longitudinal movement is a relatively recent discovered physiological phenomena and could potentially be used as an image-derived biomarker for vascular dysfunction. Measurements of the longitudinal movement are also interesting from a physiological point of view since the mechanism behind it is unclear. The fourth and fifth methods measure the thickness and diameter of the arterial wall during the cardiac cycle. Arterial wall thickness measurements are a standard procedure in cardiovascular research and may be used for early diagnosis of atherosclerosis. Although there is a large number of automatic methods developed for this purpose, most of these measurements are still made manually. One of our methods is the first to automatically measure the thickness and diameter of arteries in a small animal model.
|
|
| 6. |
- Erlöv, Tobias, et al.
(author)
-
Scatterer size estimation using the center frequency assessed from ultrasound time domain data
- 2016
-
In: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966. ; 140:4, s. 2352-2357
-
Journal article (peer-reviewed)abstract
- Scatterer size estimation is useful when characterizing tissue using ultrasound. In all previous studies on scatterer size, the estimations are performed in the frequency domain and are thus subjected to a trade off in time-frequency resolution. This study focused on the feasibility of estimating scatterer size in the time domain using only the ultrasound center frequency, assuming a Gaussian-shaped pulse. A model for frequency normalization was derived and the frequency-dependent attenuation was compensated. Five phantoms with well-defined sizes of spherical glass beads were made and scanned with two different linear array transducers with variable center frequencies. A strong correlation (r = 0.99, p < 10-19) between the backscattered center frequency and the product between the wave number and scatterer radius was demonstrated. On average the scatterer diameter was underestimated by 6% ± 24%. These results suggest that estimation of scatterer size is possible using only the center frequency assessed in the time domain.
|
|
| 7. |
- Rydén Ahlgren, Åsa, et al.
(author)
-
Profound Increase in Longitudinal Displacements of the Porcine Carotid Artery Wall Can Take Place Independently of Wall Shear Stress: A Continuation Report.
- 2015
-
In: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 41:5, s. 1342-1353
-
Journal article (peer-reviewed)abstract
- The mechanisms underlying longitudinal displacements of the arterial wall, that is, displacements of the wall layers along the artery, and the resulting intramural shear strain remain largely unknown. We have already found that these displacements undergo profound changes in response to catecholamines. Wall shear stress, closely related to wall shear rate, represents the viscous drag exerted on the vessel wall by flowing blood. The aim of the work described here was to study possible relations between the wall shear rate and the longitudinal displacements. We investigated the carotid arteries of five anesthetized pigs in different hemodynamic situations using in-house developed non-invasive ultrasound techniques. The study protocol included administration of epinephrine, norepinephrine and β-blockade (metoprolol). No significant correlation between longitudinal displacement of the intima-media complex and wall shear rate was found. This result suggests that one or multiple pulsatile forces other than wall shear stress are also working along arteries, strongly influencing arterial wall behavior.
|
|
