Investigation of image lag and modulation transfer function in fluoroscopy images obtained with a dynamic flat-panel detector

Kawashima, Hiroki; Tanaka, Rie; Ichikawa, Katsuhiro; Matsubara, Kosuke; Iida, Hiroji; Sanada, Shigeru

doi:10.1007/s12194-013-0210-9

Cited by 10 publications

(11 citation statements)

References 12 publications

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“…The difference in lag properties between the direct [,] and indirect-conversion FPDs is caused by the differences in the physical structures used in the FPDs. It was reported previously that the effect of image lag in an indirect-conversion FPD took a longer time to become less than 1.0% than in a direct-conversion FPD [14,17]. Our results were thought to be an accurate reflection of image lag properties in each type of FPD.…”

Section: Discussionsupporting

confidence: 61%

“…The term B is the pixel value measured in the background image, which was obtained without any radiation. The details were described elsewhere [14]. Figure 1 shows one of the image lag properties which was installed in our simulation system as initial data.…”

Section: Measurement Of Lag Propertiesmentioning

confidence: 99%

“…A previous study showed that the amount of image lag could be changed depending on the exposure dose and the type of FPD [14]. If the amount of image blurring on the contours of a moving target could be estimated based on the image lag properties of an FPD system, it would be useful for a margin setting and for parameter selection in radiotherapy planning of real-time target tracking.…”

Section: Introductionmentioning

confidence: 99%

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Simulation system for understanding the lag effect in fluoroscopic images

Tanaka

Kawashima

Ichikawa

et al. 2012

Radiol Phys Technol

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Real-time tumor tracking in external radiotherapy can be achieved by diagnostic (kV) X-ray imaging with a dynamic flat-panel detector (FPD). It is crucial to understand the effects of image lag for real-time tumor tracking. Our purpose in this study was to develop a lag simulation system based on the image lag properties of an FPD system. Image lag properties were measured on flat-field images both in direct-and indirect-conversion dynamic FPDs. A moving target with image lag was simulated based on the lag properties in all combinations of FPD types, imaging rates, exposure doses, and target speeds, and then compared with actual moving targets for investigation of the reproducibility of image lag. Image lag was simulated successfully and agreed well with the actual lag as well as with the predicted effect. In the indirect-conversion FPD, a higher dose caused greater image lag on images. In contrast, there were no significant differences among dose levels in a direct-conversion FPD.There were no relationships between target speed and amount of image blurring in either type of FPD. The maximum contour blurring and the rate of increase in pixel value due to image lag were 1.1 mm and 10.0%, respectively, in all combinations of imaging parameters examined in this study. Blurred boundaries and changes in pixel value due to image lag were estimated under various imaging conditions with use of the simulation system. Our system would be helpful for a better understanding of the effects of image lag in fluoroscopic images.

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Section: Discussionsupporting

confidence: 61%

Section: Measurement Of Lag Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Simulation system for understanding the lag effect in fluoroscopic images

Tanaka

Kawashima

Ichikawa

et al. 2012

Radiol Phys Technol

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“…Image intensifierbased systems were the mainstay for several decades, but suffered from veiling glare, distortions, and degradation of image quality with time. Hence, indirect conversion CsI:Tl scintillator coupled amorphous silicon (a-Si) flat-panel detector, [4][5][6] tiled large-area charge-coupled devices (CCDs) coupled to CsI:Tl scintillator, 7,8 and direct conversion amorphous selenium (a-Se) photoconductor-based flat-panel detector 9 were developed. Current generation of interventional C-arm systems utilize flat-panel detectors with pixel pitch ranging from 143 to 200 µm, depending on the manufacturer and the intended application.…”

Section: Introductionmentioning

confidence: 99%

“…Current generation of interventional C-arm systems utilize flat-panel detectors with pixel pitch ranging from 143 to 200 µm, depending on the manufacturer and the intended application. 5,6,10 The spatial resolution achieved by such systems poses a challenge in visualizing small details such as the struts of the stent or the flow-diverter that is needed to evaluate device apposition during deployment. Additionally, once the site of the abnormality to be treated or intervened is determined, imaging can be directed to a smaller field-ofview (FOV) to reduce radiation dose.…”

Section: Introductionmentioning

confidence: 99%

Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

et al. 2016

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Purpose: High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector. Methods: A 650 µm thick CdTe Schottky photon-counting detector capable of concurrently acquiring up to two energy-windowed images was operated in a single energy-window mode to include photons of 10 keV or higher. The detector had hexagonal pixels with apothem of 30 µm resulting in pixel pitch of 60 and 51.96 µm along the two orthogonal directions. The detector was characterized at IEC-RQA5 spectral conditions. Linear response of the detector was determined over the air kerma rate relevant to image-guided interventional procedures ranging from 1.3 nGy/frame to 91.4 µGy/frame. Presampled modulation transfer was determined using a tungsten edge test device. The edge-spread function and the finely sampled line spread function accounted for hexagonal sampling, from which the presampled modulation transfer function (MTF) was determined. Since detectors with hexagonal pixels require resampling to square pixels for distortion-free display, the optimal square pixel size was determined by minimizing the root-mean-squared-error of the aperture functions for the square and hexagonal pixels up to the Nyquist limit. Results: At Nyquist frequencies of 8.33 and 9.62 cycles/mm along the apothem and orthogonal to the apothem directions, the modulation factors were 0.397 and 0.228, respectively. For the corresponding axis, the limiting resolution defined as 10% MTF occurred at 13.3 and 12 cycles/mm, respectively. Evaluation of the aperture functions yielded an optimal square pixel size of 54 µm. After resampling to 54 µm square pixels using trilinear interpolation, the presampled MTF at Nyquist frequency of 9.26 cycles/mm was 0.29 and 0.24 along the orthogonal directions and the limiting resolution (10% MTF) occurred at approximately 12 cycles/mm. Visual analysis of a bar pattern image showed the ability to resolve close to 12 line-pairs/mm and qualitative evaluation of a neurovascular nitinol-stent showed the ability to visualize its struts at clinically relevant conditions. Conclusions: Hexagonal pixel array photon-counting CdTe detector provides high spatial resolution in single-photon counting mode. After resampling to optimal square pixel size for distortion-free display, the spatial resolution is preserved. The dual-energy capabilities of the detector could allow for artifact-free subtraction angiography and basis material decomposition. The proposed high-resolution photon-counting detector with energy-resolving capability can be of importance for several imageguided interventional procedures as well as for pediatric applications. C 2016 Amer...

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Slot‐scan dual‐energy bone densitometry using motorized X‐ray systems

et al. 2021

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Purpose We investigate the feasibility of slot‐scan dual‐energy (DE) bone densitometry on motorized radiographic equipment. This approach will enable fast quantitative measurements of areal bone mineral density (aBMD) for opportunistic evaluation of osteoporosis. Methods We investigated DE slot‐scan protocols to obtain aBMD measurements at the lumbar spine (L‐spine) and hip using a motorized x‐ray platform capable of synchronized translation of the x‐ray source and flat‐panel detector (FPD). The slot dimension was 5 × 20 cm2. The DE slot views were processed as follows: (1) convolution kernel‐based scatter correction, (2) unfiltered backprojection to tile the slots into long‐length radiographs, and (3) projection‐domain DE decomposition, consisting of an initial adipose–water decomposition in a bone‐free region followed by water–CaHA decomposition with adjustment for adipose content. The accuracy and reproducibility of slot‐scan aBMD measurements were investigated using a high‐fidelity simulator of a robotic x‐ray system (Siemens Multitom Rax) in a total of 48 body phantom realizations: four average bone density settings (cortical bone mass fraction: 10–40%), four body sizes (waist circumference, WC = 70–106 cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1 cm off‐center). Experimental validations included: (1) x‐ray test‐bench feasibility study of adipose–water decomposition and (2) initial demonstration of slot‐scan DE bone densitometry on the robotic x‐ray system using the European Spine Phantom (ESP) with added attenuation (polymethyl methacrylate [PMMA] slabs) ranging 2 to 6 cm thick. Results For the L‐spine, the mean aBMD error across all WC settings ranged from 0.08 g/cm2 for phantoms with average cortical bone fraction wcortical = 10% to ∼0.01 g/cm2 for phantoms with wcortical = 40%. The L‐spine aBMD measurements were fairly robust to changes in body size and positioning, e.g., coefficient of variation (CV) for L1 with wcortical = 30% was ∼0.034 for various WC and ∼0.02 for an obese patient (WC = 106 cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07 g/cm2 for a centered patient. The reproducibility of hip aBMD was slightly worse than in the L‐spine (e.g., in the femoral neck, the CV with respect to changing WC was ∼0.13 for phantom realizations with wcortical = 30%) due to more challenging scatter estimation in the presence of an air–tissue interface within the slot FOV. The aBMD of the hip was therefore sensitive to lateral positioning of the patient, especially for obese patients: e.g., the CV with respect to patient lateral shift for femoral neck with WC = 106 cm and wcortical = 30% was 0.14. Empirical evaluations confirmed substantial reduction in aBMD errors with the proposed adipose estimation procedure and demonstrated robust aBMD measurements on the robotic x‐ray system, with aBMD errors of ∼0.1 g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings. Conc...

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Investigation of image lag and modulation transfer function in fluoroscopy images obtained with a dynamic flat-panel detector

Cited by 10 publications

References 12 publications

Simulation system for understanding the lag effect in fluoroscopic images

Simulation system for understanding the lag effect in fluoroscopic images

Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

Slot‐scan dual‐energy bone densitometry using motorized X‐ray systems

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