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- Johansson, Anders, et al.
(författare)
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A spectroscopic approach to imaging and quantification of cartilage lesions in human knee joints
- 2011
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Ingår i: Physics in Medicine and Biology. - : IOP. - 0031-9155 .- 1361-6560. ; 56:6, s. 1865-1878
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Tidskriftsartikel (refereegranskat)abstract
- We have previously described a technology based on diffuse reflectance of broadband light for measuring joint articular cartilage thickness, utilizing that optical absorption is different in cartilage and subchondral bone. This study is the first evaluation of the technology in human material. We also investigated the prospects of cartilage lesion imaging, with the specific aim of arthroscopic integration. Cartilage thickness was studied ex vivo in a number of sites (n = 87) on human knee joint condyles, removed from nine patients during total knee replacement surgery. A reflectance spectrum was taken at each site and the cartilage thickness was estimated using the blue, green, red and near-infrared regions of the spectrum, respectively. Estimated values were compared with reference cartilage thickness values (taken after sample slicing) using an exponential model. Two-dimensional Monte Carlo simulations were performed in a theoretical analysis of the experimental results. The reference cartilage thickness of the investigated sites was 1.60 ± 1.30 mm (mean ± SD) in the range 0–4.2 mm. Highest correlation coefficients were seen for the calculations based on the near-infrared region after normalization to the red region (r = 0.86) and for the green region (r = 0.80).
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| 4. |
- Johansson, Anders, 1972-, et al.
(författare)
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Estimation of respiratory volumes from the photoplethysmographic signal. Part 1 : experimental results
- 1999
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:1, s. 42-47
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the possibility of respiratory-volume measurement using photoplethysmography (PPG), PPG signals from 16 normal volunteers are collected, and the respiratory-induced intensity variations (RIIV) are digitally extracted. The RIIV signals are studied while reepiratory volume is varied. Furthermore, respiratory rate, body posture and type of respiration are varied. A Fleisch pneumotachograph is used as the inspired volume reference. The RIIV and pneumotachography signals are compared, and a statisical analysis is performed (linear regression and t-tests). The key idea is that the amplitude of the RIIV signal is related to the respiratory volume. The conclusion from the measurements is that there exists a relationship between the amplitude of the RIIV signal and the respiratory volume (R=0.842, s=0.428, p<0.005). Absolute measurements of the respiratory volume are not possible from the RIIV signal with the present set-up. The RIIV signal also seems to be affected by respiratory rate and type. More knowledge about respiratory parameters and improved sensor and filter design are required to make absolute measurements of volumes possible.
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| 5. |
- Johansson, Anders, 1972-, et al.
(författare)
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Estimation of respiratory volumes from the photoplethysmographic signal. Part 2 : a model study
- 1999
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:1, s. 48-53
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Tidskriftsartikel (refereegranskat)abstract
- A Windkessel model has been constructed with the aim of investigating the respiratory-volume dependence of the photoplethysmographic (PPG) signal. Experimental studies show a correlation between respiratory volume and the peak-to-peak value of the respiratory-induced intensity variations (RIIV) in the PPG signal. The model compartments are organised in two closed chambers, representing the thorax and the abdomen, and in a peripheral part not directly influenced by respiration. Cardiac pulse and respiration are created by continuous adjustment of the pressures in the affected compartments. Together with the criteria for heart and venous valves, the model is based on a set of 17 differential equations. These equations are solved for varying thoracic and abdominal pressures corresponding to different respiratory volumes. Furthermore, a sensitivity analysis is performed to evaluate the properties of the model. The PPG signals are created as a combination of peripheral blood flow and pressure. From these signals, the respiratory synchronous parts are extracted and analysed. To study some important limitations of the model, respiratory type and rate are varied. From the simulations, it is possible to verify our earlier experimental results concerning the relationship between respiratory volume and the peak-to-peak value of the RIIV signal. An expected decrease in the amplitude of the respiratory signal with increased respiratory rate is also found, which is due to the lowpass characteristics of the vessel system. Variations in the relationship between thoracic and abdominal respiration also affect the RIIV signal. The simulations explain and verify what has been found previously in experimental studies.
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| 8. |
- Johansson, Anders, 1972-, et al.
(författare)
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Monitoring of heart and respiratory rates in newborn infants using a new photoplethysmographic technique
- 1999
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Ingår i: Journal of clinical monitoring and computing. - 1387-1307 .- 1573-2614. ; 15:7-8, s. 461-467
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Tidskriftsartikel (refereegranskat)abstract
- Objective.A new photoplethysmographic (PPG) device for respiratoryand heart rate monitoring has been evaluated in the neonatal care units at theUniversity Children's Hospital of Uppsala, Sweden. The purpose of thisstudy was to compare this new device with more established techniques, i.e.,transthoracic impedance plethysmography (TTI) for monitoring of respiratoryrate and ECG for heart rate monitoring.Methods.Data were acquiredcontinuously for 8-hours in each of 6 neonates. The signals were analysed forperiods of 30 seconds, in which the heart and respiratory signals from the PPGdevice were compared with the ECG and the impedance plethysmogram.Results.The ECG recordings were of high quality in 77% of the analysed periods.In these periods, excluding periods (6%) disturbed by offset-adjustement ofthe PPG signal, the PPG heart signal included 1.1% (±0.7% SD) falsenegative beats and 0.9% (±0.6%) false positive beats. In periods withan impedance signal of high quality (29% of total time), the part of the PPGsignal synchronous with respiration included 2.7% (±1.1%) falsenegative breaths and 1.5% (±0.4%) false positive breaths. Here, 2% ofthe periods were discarded because of offset-adjustment. From the periods oflow signal quality, two other conclusions were drawn: 1) The impedance signalcontains more power in the respiratory range than the corresponding PPGrespiratory signal. 2) The breaths are easier to identify in the PPGrespiratory signal than in the impedance signal (subjective measure).Conclusions.Electrode and motion artefacts seem to disturb the ECGsignals and, particularly, the impedance signals. During periods of highquality ECG and impedance signals, the new optical device produces signals ofequal quality to these traditional methods, and is in some cases even better.The new device is non-invasive and has a small optical probe. These factors indicate further advantages of the photoplethysmographic method.
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