1.
Lorentsson, Robert, 1969, et al.
(författare)
A 4-afc study comparing ultrasound machines using a greyscale phantom
2015
Ingår i: 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
Konferensbidrag (refereegranskat) 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.
2.
Sandblom, Viktor, 1987, et al.
(författare)
Evaluation of the impact of a system for real-time visualisation of occupational radiation dose rate during fluoroscopically guided procedures
2013
Ingår i: Journal of Radiological Protection. - : IOP Publishing. - 0952-4746 .- 1361-6498. ; 33:3, s. 693-702
Tidskriftsartikel (refereegranskat) abstract
Optimisation of radiological protection for operators working with fluoroscopically guided procedures has to be performed during the procedure, under varying and difficult conditions. The aim of the present study was to evaluate the impact of a system for real-time visualisation of radiation dose rate on optimisation of occupational radiological protection in fluoroscopically guided procedures. Individual radiation dose measurements, using a system for real-time visualisation, were performed in a cardiology laboratory for three cardiologists and ten assisting nurses. Radiation doses collected when the radiation dose rates were not displayed to the staff were compared to radiation doses collected when the radiation dose rates were displayed. When the radiation dose rates were displayed to the staff, one cardiologist and the assisting nurses (as a group) significantly reduced their personal radiation doses. The median radiation dose (Hp(10)) per procedure decreased from 68 to 28 μSv (p = 0.003) for this cardiologist and from 4.3 to 2.5 μSv (p = 0.001) for the assisting nurses. The results of the present study indicate that a system for real-time visualisation of radiation dose rate may have a positive impact on optimisation of occupational radiological protection. In particular, this may affect the behaviour of staff members practising inadequate personal radiological protection.
3.
Sund, Patrik, et al.
(författare)
Detection of low contrast test patterns on an LCD with different luminance and illuminance settings
2008
Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6917
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt) abstract
The DICOM part 14 grayscale standard display function provides one way of harmonizing image appearance under different monitor luminance settings. This function is based on ideal observer conditions where the eye is always adapted to the target luminance and thereby also at peak contrast sensitivity. Clinical workstations are however often exposed to variations in ambient light due to a sub-optimal reading room light environment. Also, clinical images are inhomogeneous and low-contrast patterns must be detected even at luminance levels that differ from the eye adaptation level. All deviations from ideal luminance conditions cause the observer to detect patterns with reduced eye sensitivity but the magnitude of this reduction is unclear. The purpose of this paper was to quantify the effect different luminance settings have on the contrast threshold. A method to display well-defined sinusoidal low-contrast test patterns on an LCD has previously been developed and was used in this study. The observers were exposed to light from three different areas: 1) A small sinusoidal test pattern. 2) The remaining of the display surface. 3) Ambient light from outside the display area covering most of the observer's field of view. By adjusting the luminance from each of these three areas, two major effects could be quantified. The first effect was similar to Barten's f-factor where the target luminance differs from the observer's adaptation level while the second effect concerned the influence of areas outside the display surface. When a luminance range of 1-350 cd/m2 was used, the contrast needed to detect a dark object in a gray surrounding was almost doubled compared to a dark object in a dark surrounding. Ambient light from outside the display area has a moderate effect on the contrast threshold, except for the combination of high ambient light and dark objects where the contrast threshold increased considerably.
4.
5.
Sund, Patrik, et al.
(författare)
The effect of fixed adaptation on the calibration of medical displays
2015
Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
Purpose: Medical displays are normally calibrated according to the DICOM part 14 calibration method, the grayscale standard display function (GSDF). Based on the assumption of variable adaptation, calibration according to the GSDF results in a perceptually linearized display, for which the perceived contrast is equally distributed at all luminance levels. However, the assumption of variable adaptation is questionable and recently a method of calibration of medical displays that instead is based on the assumption of fixed adaptation was presented (Sund et al, Med Phys 2015). The new calibration method results in a fixed-adaptation compensated grayscale standard display function (GSDFFAC), for which the contrast perceived at fixed adaptation is equally distributed. The purpose of the present work was to investigate the effect of the choice of the adaptation level on the GSDFFAC. Material and methods: Based on the formulation of the GSDFFAC, theoretical calibration curves for fictitious medical displays with different luminance ranges were determined. The calibrations were performed at different assumed adaptation levels. For comparison, the original GSDF was determined for each type of display. Results: For fixed adaptation at a luminance level close to the logarithmic average of the minimum and maximum luminance levels, a small but significant difference between the GSDF and the GSDFFAC was obtained. The more the adaptation level deviated from this average, the larger the difference between the two calibrations. For example, for adaptation at a luminance level given by the linear average of the luminance levels corresponding to all digital driving levels (DDLs) – corresponding to fixed adaptation at a histogram-equalized image – the contrast enhancement at low luminance levels was substantially higher with the GSDFFAC than with the GSDF. Conclusions: The present study shows that the GSDFFAC is strongly dependent on the adaptation level. The study indicates that although an improvement in terms of even distribution of contrast compared with the GSDF can be expected with the GSDFFAC, knowledge of the correct adaptation level is crucial.
