Image quality dependence on in-plane positions and directions for MDCT images

Hara, Takanori; Ichikawa, Katsuhiro; Sanada, Shigeru; Ida, Yoshihiro

doi:10.1016/j.ejrad.2009.03.060

Cited by 17 publications

(11 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%

“…The CT numbers resulted from different materials and scan modes. Used phantoms and expected range by the ACR[17] is given in the last column Images of the Catphan low-contrast objects in the CTP515 module acquired in NR, HR and SHR modes of the UHRCT and on the MDCT (left) at a CTDI vol of 9.1 mGy and (right) for the same low-contrast detectability, the CTDI vol is noted. Note that the window width is not the same for all images; for the SHR and HR modes, it is 60 (left) and 50 (right) and for the NR and MDCT it is 30…”

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confidence: 99%

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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%

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confidence: 99%

Physical evaluation of an ultra-high-resolution CT scanner

et al. 2020

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“…Detailed methodologies for the wire and bead methods have not been investigated for currently available MDCT. In a typical approach for MTF determination, (7–9,13–19) the LSF is first obtained by processing the wire/bead image data. In the present study, to determine the LSF, the square‐shaped ROI was integrated and the obtained data were then offset‐corrected and normalized (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…To evaluate the image sharpness in the scan plane, MTF measurements are performed by using a phantom such as point source, (7–9) line pair, (10) edge, (11) as well as others (12) . Methods that use a point source phantom, such as a thin wire or a microbead, are most widely utilized in current CT systems (13–20) as they are conceptual simplicity and relatively easy to implement. When using such methods, in a typical approach for determination of MTF, (7–9,12–19) the line spread function (LSF) is first obtained by processing the scanned image (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Methods that use a point source phantom, such as a thin wire or a microbead, are most widely utilized in current CT systems (13–20) as they are conceptual simplicity and relatively easy to implement. When using such methods, in a typical approach for determination of MTF, (7–9,12–19) the line spread function (LSF) is first obtained by processing the scanned image (Fig. 1) in which the region of interest (ROI) placed on the point source response is integrated in one of the matrix directions.…”

Section: Introductionmentioning

confidence: 99%

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Accurate determination of CT point‐spread‐function with high precision

Kayugawa

Ohkubo

Wada

2013

J Applied Clin Med Phys

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The measurement of modulation transfer functions (MTFs) in computed tomography (CT) is often performed by scanning a point source phantom such as a thin wire or a microbead. In these methods the region of interest (ROI) is generally placed on the scanned image to crop the point source response. The aim of the present study was to examine the effect of ROI size on MTF measurement, and to optimize the ROI size. Using a 4 multidetector‐row CT, MTFs were measured by the wire and bead methods for three types of reconstruction kernels designated as ‘smooth', ‘standard', and ‘edge‐enhancement’ kernels. The size of a square ROI was changed from 30 to 50 pixels (approximately 2.9 to 4.9 mm). The accuracies of the MTFs were evaluated using the verification method. The MTFs measured by the wire and bead methods were dependent on ROI size, particularly in MTF measurement for the ‘edge‐enhancement’ kernel. MTF accuracy evaluated by the verification method changed with ROI size, and we were able to determine the optimum ROI size for each method (wire/bead) and for each kernel. Using these optimal ROI sizes, the MTF obtained by the wire method was in strong agreement with the MTF obtained by the bead method in each kernel. Our data demonstrate that the difficulties in obtaining accurate MTFs for some kernels such as edge‐enhancement can be overcome by incorporating the verification method into the wire and bead methods, allowing optimization of the ROI size to accurately determine the MTF.PACS numbers: 87.57.‐s, 87.57.cf, 87.57.Q‐

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Aliased noise in X-ray CT images and band-limiting processing as a preventive measure

Sato

Shidahara

Goto

et al. 2015

Radiol Phys Technol

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X-ray CT projection data often include components with frequencies that are markedly higher than the pixel Nyquist frequency f PN, which is determined by the pixel size. Noise components higher than f PN are folded back into a region lower than f PN through the backprojection process, thereby creating aliased noise. With clinical CT scanners, we evaluated the aliased noise using an aliasing prevention measure, band-limiting processing (BLP), which suppresses frequency components higher than f PN in the projection data. Indices we used to evaluate improvement by BLP were the noise power spectrum (NPS), modulation transfer function (MTF), signal-to-noise-ratio (SNR) spectrum, matched filter SNR (MF SNR), and two-alternative forced-choice (2-AFC) test. With BLP, the NPS was decreased not only beyond f PN, but also within f PN. The same level of MTF was maintained as that without BLP within f PN. No remarkable reduction in spatial resolution was observed. The SNR spectrum and the MF SNR of the BLP image nearly agreed with those of an ideal state without aliased noise. A notable improvement in the visuoperceptual image quality by BLP was recognized with a reconstruction field of view (FOV) of more than 45 cm. We then applied BLP to clinical data and confirmed that significant aliased noise of a large FOV image was removed without notable side effects. The results showed that at least some CTs suffering from aliased noise can be improved by proper band-limiting.

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Image quality dependence on in-plane positions and directions for MDCT images

Cited by 17 publications

References 18 publications

Physical evaluation of an ultra-high-resolution CT scanner

Physical evaluation of an ultra-high-resolution CT scanner

Accurate determination of CT point‐spread‐function with high precision

Aliased noise in X-ray CT images and band-limiting processing as a preventive measure

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