Theory, method, and test tools for determination of 3D MTF characteristics in cone‐beam CT

Wu, Pu‐Wei; Boone, John M.; Hernandez, Andrew M.; Mahesh, Mahadevappa; Siewerdsen, Jeffrey H.

doi:10.1002/mp.14820

Cited by 15 publications

(17 citation statements)

References 52 publications

(152 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The MTF measured at a 45°tilt angle with respect to the axial plane [i.e., the "oblique" MTF(f r ; φ = 45°)] has been shown to be a useful metric which captures aspects of both the axial-plane and longitudinal MTF in a single MTF curve, 16 and this was further demonstrated in this work when comparing the effects of the different resolution modes (see Fig. 3).…”

Section: Discussionmentioning

confidence: 69%

“…A 1D slice of the 3D MTF along any direction in the 3D image reconstruction of the sphere can be analyzed from the 3D edge-spread function (ESF). 16 Notation introduced and detailed in our related work 16 will be used here. A VOI containing each Teflon sphere was first extracted from the CT volume and the center of each sphere was determined using a 3D Hough transform.…”

Section: C 3d Mtf Characterization Using the Spherical Edge Methodsmentioning

confidence: 99%

“…Oversampling of the spread function allows measurement of the MTF in a manner that reflects blur characteristics (including detector element size) beyond the original Nyquist frequency. The oversampled ESF [esf (k)] was then numerically differentiated using the central difference operation to yield the plane-spread function (PlSF 16 ).…”

Section: C 3d Mtf Characterization Using the Spherical Edge Methodsmentioning

confidence: 99%

“…Spherical objects have more recently become an attractive approach to estimating the directional-dependent MTF. [13][14][15][16] Spheres are advantageous in that they have an extent much greater than the image voxel size and nearly all voxels within a given volume of interest (VOI) can be utilized in the assessment. Spheres are also rotationally symmetric and therefore do not require careful alignment with respect to the source or detector array.…”

Section: Introductionmentioning

confidence: 99%

“…More recently, the MTF along a direction that is 45°with respect to the axial plane [i.e., MTF(φ = 45°); where φ is the tilt angle above or below the central axial plane] has been shown to be a good overall descriptor of the 3D spatial resolution characteristics of modern 3D x-ray imaging systems because it reflects contributions of both the axial-plane and longitudinal MTF. 16 Recently, a high-resolution MDCT system (Aquilion Precision: Canon Medical Systems, Otawara, Japan) was developed and is now clinically available in the US. This CT system has three resolution modes corresponding to different detector element sizes in the channel and row directions: normal resolution "NR" (0.5 mm × 0.5 mm), high resolution "HR" (0.25 mm × 0.5 mm), and super high resolution "SHR" (0.25 mm × 0.25 mm).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

Hernandez

Mahesh

et al. 2021

Medical Physics

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 69%

Section: C 3d Mtf Characterization Using the Spherical Edge Methodsmentioning

confidence: 99%

Section: C 3d Mtf Characterization Using the Spherical Edge Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Hernandez

Mahesh

et al. 2021

Medical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

et al. 2022

View full text Add to dashboard Cite

Background Indirect detection flat‐panel detectors (FPDs) consisting of hydrogenated amorphous silicon (a‐Si:H) thin‐film transistors (TFTs) are a prevalent technology for digital x‐ray imaging. However, their performance is challenged in applications requiring low exposure levels, high spatial resolution, and high frame rate. Emerging FPD designs using metal oxide TFTs may offer potential performance improvements compared to FPDs based on a‐Si:H TFTs. Purpose This work investigates the imaging performance of a new indium gallium zinc oxide (IGZO) TFT‐based detector in 2D fluoroscopy and 3D cone‐beam CT (CBCT). Methods The new FPD consists of a sensor array combining IGZO TFTs with a‐Si:H photodiodes and a 0.7‐mm thick CsI:Tl scintillator. The FPD was implemented on an x‐ray imaging bench with system geometry emulating intraoperative CBCT. A conventional FPD with a‐Si:H TFTs and a 0.6‐mm thick CsI:Tl scintillator was similarly implemented as a basis of comparison. 2D imaging performance was characterized in terms of electronic noise, sensitivity, linearity, lag, spatial resolution (modulation transfer function, MTF), image noise (noise‐power spectrum, NPS), and detective quantum efficiency (DQE) with entrance air kerma (EAK) ranging from 0.3 to 1.2 μGy. 3D imaging performance was evaluated in terms of the 3D MTF and noise‐equivalent quanta (NEQ), soft‐tissue contrast‐to‐noise ratio (CNR), and image quality evident in anthropomorphic phantoms for a range of anatomical sites and dose, with weighted air kerma, Kw${K_w}$, ranging from 0.8 to 4.9 mGy. Results The 2D imaging performance of the IGZO‐based FPD exhibited up to ∼1.7× lower electronic noise than the a‐Si:H FPD at matched pixel pitch. Furthermore, the IGZO FPD exhibited ∼27% increase in mid‐frequency DQE (1 mm−1) at matched pixel size and dose (EAK ≈ 1.0 μGy) and ∼11% increase after adjusting for differences in scintillator thickness. 2D spatial resolution was limited by the scintillator for each FPD. The IGZO‐based FPD demonstrated improved 3D NEQ at all spatial frequencies in both head (≥25% increase for all dose levels) and body (≥10% increase for Kw${K_w}$ ≤2 mGy) imaging scenarios. These characteristics translated to improved low‐contrast visualization in anthropomorphic phantoms, demonstrating ≥10% improvement in CNR and extension of the low‐dose range for which the detector is input‐quantum limited. Conclusion The IGZO‐based FPD demonstrated improvements in electronic noise, image lag, and NEQ that translated to measurable improvements in 2D and 3D imaging performance compared to a conventional FPD based on a‐Si:H TFTs. The improvements are most beneficial for 2D or 3D imaging scenarios involving low‐dose and/or high‐frame rate.

show abstract

Objective image quality assurance in cone‐beam CT: Test methods, analysis, and workflow in longitudinal studies

Johnston,

Mahesh,

Uneri

et al. 2024

Medical Physics

Self Cite

View full text Add to dashboard Cite

BackgroundStandards for image quality evaluation in multi‐detector CT (MDCT) and cone‐beam CT (CBCT) are evolving to keep pace with technological advances. A clear need is emerging for methods that facilitate rigorous quality assurance (QA) with up‐to‐date metrology and streamlined workflow suitable to a range of MDCT and CBCT systems.PurposeTo evaluate the feasibility and workflow associated with image quality (IQ) assessment in longitudinal studies for MDCT and CBCT with a single test phantom and semiautomated analysis of objective, quantitative IQ metrology.MethodsA test phantom (CorgiTM Phantom, The Phantom Lab, Greenwich, New York, USA) was used in monthly IQ testing over the course of 1 year for three MDCT scanners (one of which presented helical and volumetric scan modes) and four CBCT scanners. Semiautomated software analyzed image uniformity, linearity, contrast, noise, contrast‐to‐noise ratio (CNR), 3D noise‐power spectrum (NPS), modulation transfer function (MTF) in axial and oblique directions, and cone‐beam artifact magnitude. The workflow was evaluated using methods adapted from systems/industrial engineering, including value stream process modeling (VSPM), standard work layout (SWL), and standard work control charts (SWCT) to quantify and optimize test methodology in routine practice. The completeness and consistency of DICOM data from each system was also evaluated.ResultsQuantitative IQ metrology provided valuable insight in longitudinal quality assurance (QA), with metrics such as NPS and MTF providing insight on root cause for various forms of system failure—for example, detector calibration and geometric calibration. Monthly constancy testing showed variations in IQ test metrics owing to system performance as well as phantom setup and provided initial estimates of upper and lower control limits appropriate to QA action levels. Rigorous evaluation of QA workflow identified methods to reduce total cycle time to ∼10 min for each system—viz., use of a single phantom configuration appropriate to all scanners and Head or Body scan protocols. Numerous gaps in the completeness and consistency of DICOM data were observed for CBCT systems.ConclusionAn IQ phantom and test methodology was found to be suitable to QA of MDCT and CBCT systems with streamlined workflow appropriate to busy clinical settings.

show abstract

Theory, method, and test tools for determination of 3D MTF characteristics in cone‐beam CT

Cited by 15 publications

References 52 publications

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

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

Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

Objective image quality assurance in cone‐beam CT: Test methods, analysis, and workflow in longitudinal studies

Contact Info

Product

Resources

About