Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Rubert, Nicholas; Szczykutowicz, Timothy P.; Ranallo, Frank N.

doi:10.1120/jacmp.v17i3.6039

Cited by 12 publications

(5 citation statements)

References 18 publications

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“…This drop in resolution as a function of distance from the centre is likely caused by the finite number of views and focal spot size. In UHRCT, the relative drop in resolution is comparable to that of other systems [17][18][19].…”

Section: Discussionmentioning

confidence: 83%

Physical evaluation of an ultra-high-resolution CT scanner

et al. 2020

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Objectives To evaluate the technical performance of an ultra-high-resolution CT (UHRCT) system. Methods The physico-technical capabilities of a novel commercial UHRCT system were assessed and compared with those of a current-generation multi-detector (MDCT) system. The super-high-resolution (SHR) mode of the system uses 0.25 mm (at isocentre) detector elements (dels) in the in-plane and longitudinal directions, while the high-resolution (HR) mode bins two dels in the longitudinal direction. The normal-resolution (NR) mode bins dels 2 × 2, resulting in a del-size equivalent to that of the MDCT system. In general, standard procedures and phantoms were used to perform these assessments.Results The UHRCT MTF (10% MTF 4.1 lp/mm) is twice as high as that of the MDCT (10% MTF 1.9 lp/mm), which is comparable to the MTF in the NR mode (10% MTF 1.7 lp/mm). The width of the slice sensitivity profile in the SHR mode (FWHM 0.45 mm) is about 60% of that of the MDCT (FWHM 0.77 mm). Uniformity and CT numbers are within the expected range. Noise in the high-resolution modes has a higher magnitude and higher frequency components compared with MDCT. Low-contrast visibility is lower for the NR, HR and SHR modes compared with MDCT, but about a 14%, for NR, and 23%, for HR and SHR, dose increase gives the same results. Conclusions HR and SHR mode scanning results in double the spatial resolution, with about a 23% increase in dose required to achieve the same low-contrast detectability. Key Points • Resolution on UHRCT is up to twice as high as for the tested MDCT.• With abdominal settings, UHRCT needs higher dose for the same low-contrast detectability as MDCT, but dose is still below achievable levels as defined by current diagnostic reference levels. • The UHRCT system used in normal-resolution mode yields comparable resolution and noise characteristics as the MDCT system.

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Section: Discussionmentioning

confidence: 83%

Physical evaluation of an ultra-high-resolution CT scanner

et al. 2020

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“…In some clinical datasets, adaptive filtration is used in the reconstruction process and different edges in the image can be treated differently (i.e., the spine/soft tissue edge yielding different spatial resolution than the air/skin edge). 25,26 In these cases, the air/skin interface would not provide a complete characterization of the image resolution.…”

Section: Discussionmentioning

confidence: 99%

Patient‐specific quantification of image quality: An automated method for measuring spatial resolution in clinical CT images

2016

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“…CT spatial resolution is impacted by the physical hardware (detector element size, detector frame rate, gantry rotation time, focal spot dimension, and focal spot deflection techniques), geometrical magnification, and reconstruction parameters (algorithm and kernel). The extent to which these various contributing factors affect the spatial resolution on a given scanner depends on the location and direction of interest within the scanner field of view (FOV) 8–10 . Variations in the axial‐plane and longitudinal resolution are dependent on the detector element size, the 2D focal spot size (plus potential focal spot deflection), geometrical magnification, and the apodization kernel applied during reconstruction.…”

Section: Introductionmentioning

confidence: 99%

“…The extent to which these various contributing factors affect the spatial resolution on a given scanner depends on the location and direction of interest within the scanner field of view (FOV). [8][9][10] Variations in the axial-plane and longitudinal resolution are dependent on the detector element size, the 2D focal spot size (plus potential focal spot deflection), geometrical magnification, and the apodization kernel applied during reconstruction. Even with the anode-cathode axis of the x-ray tube along the z direction of the image (the orientation for MDCT scanners), as the MTF measurement location moves radially outward from isocenter, the radial component of the axial-plane resolution is increasingly impacted by the apparent elongation of the 2D focal spot projected onto the detector.…”

Section: Introductionmentioning

confidence: 99%

Location and direction dependence in the 3D MTF for a high‐resolution CT system

Hernandez

Mahesh

et al. 2021

Medical Physics

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Purpose The purpose of this study was to quantify location and direction‐dependent variations in the 3D modulation transfer function (MTF) of a high‐resolution CT scanner with selectable focal spot sizes and resolution modes. Methods The Aquilion Precision CT scanner (Canon Medical Systems) has selectable 0.25 mm or 0.5 mm detectors (by binning) in both the axial (x‐y) and detector array width (z) directions. For the x‐y and z orientations, detectors are configured (x–y) = 0.5 mm/(z) = 0.5 mm for normal resolution (NR), 0.25/0.5 mm for high resolution (HR), and 0.25/0.25 mm for super high resolution (SHR). Six focal spots (FS1‐FS6) range in size from 0.4 (x‐y) × 0.5 mm (z) for FS1 to 1.6 × 1.4 mm for FS6. Phantoms fabricated from spherical objects were positioned at radial distances of 0, 4.0, 7.5, 11.0, 14.5, and 18.5 cm. Axial and helical acquisitions were utilized and reconstructed using filtered back projection with the FC18 “Body,” FC30 “Bone,” and FC81 “Bone Sharp” kernels. The reconstructions were used to measure a 1D slice of the 3D MTF by oversampling the 3D ESF in the axial plane [MTF(fr); φ = 0°)], 45° out of the axial plane [MTF(fr); φ = 45°)], in the longitudinal direction [MTF(fr); φ = 80°)], and along the radial and azimuthal directions within the axial plane. Results The MTF(fr); φ = 45°) drops to 10% (f10) at 1.20, 1.45, and 2.06 mm−1 for NR, HR, and SHR, respectively, for a helical acquisition with FS1, FC30, and r = 4 cm from the isocenter. The MTF(fr); φ = 45°) includes contributions of both the axial‐plane MTF (f10 = 1.10, 2.04, and 2.01 mm−1) and the longitudinal MTF (f10 = 1.17, 1.18, and 1.82 mm−1) for the NR, HR, and SHR modes, respectively. For SHR, the axial scan mode showed a 15–25% improvement over helical mode in the longitudinal resolution. Helical pitch, ranging from 0.569 to 1.381, did not appreciably affect the 3D resolution (<2%). The radial MTFs across the axial field of view (FOV) showed dependencies on the focal spot length in z; for example, for SHR with FS2 (0.6 × 0.6 mm), f10 at r = 11 cm was within 17% of the value at r = 4 cm, but for SHR with FS3 (0.6 × 1.3), the reduction in f10 was 46% from 4 to 11 cm from the isocenter. The azimuthal MTF also decreased as r increased but less so for longer gantry rotation times and smaller focal spot dimensions in the axial plane. The longitudinal MTF was minimally affected (<11%) by position in the FOV and was principally affected by the focal spot length in the z‐dimension. Conclusions The 3D MTF was measured throughout the FOV of a high‐resolution CT scanner, quantifying the advantages of different resolution modes and focal spot sizes on the axial‐plane and longitudinal MTF. Reconstruction kernels were shown to impact axial‐plane resolution, imparting non‐isotropic 3D resolution characteristics. Focal spot size (both in x‐y and in z) and gantry rotation time play important roles in preserving the high‐resolution characteristics throughout the field of view for this new high‐resolution CT scanner technology.

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Improvement in CT image resolution due to the use of focal spot deflection and increased sampling

Cited by 12 publications

References 18 publications

Physical evaluation of an ultra-high-resolution CT scanner

Physical evaluation of an ultra-high-resolution CT scanner

Patient‐specific quantification of image quality: An automated method for measuring spatial resolution in clinical CT images

Location and direction dependence in the 3D MTF for a high‐resolution CT system

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