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- Mangat, Jasvinder, et al.
(författare)
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A study of the image quality of CT brain adaptive statistical iterative reconstructed (ASIR) images using subjective and objective methods
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The aim of this study was to investigate the image quality of ASIR reconstructed brain images using subjective, observer-based assessment and objective metrics to elucidate trends and possible alternatives to the current standard protocol featuring 40%ASIR and a noise index of 11.20, possibly facilitating a dose decrease. Method: An audit of image quality of patient brain scans (n=55) was performed using Visual Grading Assessment (VGA) by two radiologist-observers, using CEC image criteria of retrospectively reconstructed images at 0% -70% & 100% ASIR-levels originally scanned using the standard protocol. Analysis was conducted using Visual Grading Characteristics (VGC). Empirical phantom-based assessments of high-contrast spatial resolution (HCSR) and Noise Power Spectrum (NPS) with 0-100%ASIR increments and decrementing tube currents (565-235mA), were also conducted. Results: VGC analysis showed that the mid-range increments (50%-70%ASIR) were not significantly different to 40%ASIR (p>0.05). Low-contrast spatial resolution (LCSR) showed slight, non-significant improvement with 70% and 60%ASIR increments compared with 40%ASIR (p>0.05). Subjective image noise remained constant across this range, but was slightly worse than 40%ASIR (p>0.05). However, 70%ASIR reconstructions were found to be overly susceptible to artefact appearance. Hence pairwise-analysis was performed using 60% & 50%ASIR, which showed 60%ASIR was the preferred increment. Phantom-based HCSR investigations showed MTF50 and MTF10 increases of up-to 4.1% and 3.0%, respectively (p<0.05) for ASIR reconstructed images as compared to those produced using FBP. MTF50 and MTF10 showed a linearly improving relationship with increasing %ASIR. With tube current, MTF behaviour was more complex with a rapid increase up to 305mA, a plateau between 305 and 420mA and then a rapid fall off. The NPS study revealed peak-frequency decreased linearly with increasing %ASIR and remained constant with tube current. Peak-variance decreased non-linearly with %ASIR and tube current. Empirical ranges for MTF50, MTF10, peak frequency NPS & peak variance NPS of (0.370- 0.375mm-1), (0.617- 0.622mm-1), (0.199- 0.176mm-1) & (99.28- 84.92mm-1) respectively, were obtained for the standard protocol for the mid-range ASIR increments. Conclusion: This study demonstrated the trends for objective and subjective image quality metrics with ASIR increment and tube-current. 60%ASIR with a tube current of 305mA (NI=12.20) was proposed as an alternative to the current standard, as it was the best fit with these empirical ranges, producing a possible dose saving of 16.1%.
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- Urquiza-González, M., et al.
(författare)
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Benchmark evaluation for a single frequency continuous wave OPO seeded pulsed dye amplifier for high-resolution laser spectroscopy
- 2023
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510659032
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Konferensbidrag (refereegranskat)abstract
- The study of the atomic spectrum via resonant laser excitation provides access to underlying effects caused by the nuclear structure, which is of special interest in short-lived radioisotopes produced at Isotope Separator On-Line (ISOL) facilities. Current implementations of resonant laser ionization techniques often limit the extraction of the nuclear observables due to the low spectral resolution of the pulsed laser systems deployed. Several high-resolution spectroscopy techniques demand spectral widths in the order of hundreds of MHz and below. A proven solution to reduce this linewidth is the pulsed amplification of a narrow-band continuous wave (cw) laser. This work presents the demonstration of a pulsed dye amplifier seeded by a commercially available cw Optical Parametric Oscillator (OPO). The performance of this system was compared with competing setups using a cw dye laser seed source as well as a frequency mixing technique using a combination of an injection-locked titanium:sapphire (Ti:Sa) and a Nd:YVO4 laser. Spectral bandwidths of the systems were measured using a high finesse Fabry-Perot Interferometer, resulting in comparable optical linewidths between 140 to 156 MHz at a wavelength of 328 nm for the different laser setups. Suitability for on-line experiments was validated by performing high-resolution spectroscopy of radioactive silver isotopes in the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the Isotope Separator On-Line Device (ISOLDE), at the European Organization for Nuclear Research (CERN). The quality of the hyperfine spectra was similar for the dye and the OPO seed and the deduced hyperfine splitting was in good agreement with literature, while the frequency mixing technique exhibited less precise results attributed to the frequency instabilities and mode-hops of the single-mode Nd:YVO4 laser.
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