Parallel-shift tomosynthesis for orthopedic applications

Luckner, Christoph; Sesselmann, Stefan; Mertelmeier, Thomas; Maier, Andreas; Ritschl, Ludwig

doi:10.1117/12.2292384

Cited by 9 publications

(12 citation statements)

References 14 publications

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“…As we investigate a slot‐scanning method and hence have only little angular information, we chose to neglect the reconstruction filter. The reconstruction itself is implemented as a fast voxel‐driven perspective backprojection with high geometric accuracy using projection matrices for each projection and a voxel‐specific weighting function . The underlying idea of the tomosynthesis‐based reconstruction is to acquire overlapping low‐dose projections which are averaged during the reconstruction process.…”

Section: Methodsmentioning

confidence: 99%

“…The reconstruction itself is implemented as a fast voxel-driven perspective backprojection with high geometric accuracy using projection matrices for each projection and a voxelspecific weighting function. 20,33 The underlying idea of the tomosynthesis-based reconstruction is to acquire overlapping low-dose projections which are averaged during the reconstruction process. Note, that in contrast to a conventional isotropic CBCT volume, the effective interslice distance dz eff of a DTS volume for high frequencies is dependent on the cone angle b and can be computed as 22…”

Section: A System Geometry and Image Acquisitionmentioning

confidence: 99%

“…In this work, we aim to create magnification‐free radiography‐like 2D images. Therefore, we use a parallel‐shift trajectory where the source and detector move simultaneously in parallel planes, which is similar to the well‐known slot scan. For image acquisition, we use a modified twin‐robotic cone beam x‐ray system based on the Multitom Rax (Siemens Healthcare GmbH, Erlangen, Germany).…”

Section: Introduction and Purposementioning

confidence: 99%

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High‐speed slot‐scanning radiography using small‐angle tomosynthesis: Investigation of spatial resolution

et al. 2019

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Purpose This paper studies spatial resolution that is achievable with a fast slot‐scanning tomosynthesis approach for orthopedic examinations. Hereby, we use parallel scanning motion implemented in a twin robotic x‐ray system. Methods We have measured and analyzed the modulation transfer function (MTF) for various combinations of scanning speed, x‐ray tube voltage, pulse length, the nominal focal spot size as well as source‐to‐object distances. Moreover, we present a theoretical model which describes the system in terms of the MTF. The system was equipped with newly developed linear trajectory prototypes for slot scanning. The acquired images form the basis for a small‐angle tomosynthesis reconstruction. In total, three different scanning speeds (27, 14, 8 cm/s), pulse lengths (1, 2, 4 ms), tube voltages (80, 100, 120 kV), two nominal focal spot sizes (0.6, 1.0), and three source‐to‐object distances (950, 1050, 1150 mm) were investigated. To determine the resolution capabilities, we measured the MTF for the given parameter space. The results were then used to design a filter that yields a desired resolution in the reconstructed image. In addition, we also measured the noise power spectrum (NPS) to show the influence of the aforementioned filters on the noise distribution. Results We have shown that the presented model is in good agreement with the performed measurements. Scanning speed and pulse width have an impact on the MTF in the scanning direction. Up to a travel distance of 0.3 mm during an x‐ray pulse, an isotropic resolution can be achieved. Longer pulse width or higher scanning speed cause anisotropic resolution. Moreover, it is shown that none of the investigated parameters have an influence on the MTF perpendicular to the scanning direction (slot direction). The 10% MTF value ranges between 9 and 18 lp/cm in the scanning direction and about 18 lp/cm in slot direction. Tube voltage, nominal focal spot size as well as the source‐to‐object distance showed no major impact on the system MTF. In terms of the anisotropic resolution capabilities, we have shown that limiting the resolution in the slot direction to obtain isotropic resolution is possible yet at the cost of an inhomogeneous noise pattern. However, maintaining the resolution in slot direction will provide a better edge response and a more homogeneous noise texture at the cost of an inhomogeneous image resolution. Conclusions We have demonstrated the feasibility of the slot‐scanning technique using a twin‐robotic x‐ray system. Even the fastest scanning mode (27 cm/s) yields image resolution on a level that is sufficient for typical orthopedic examinations in terms of musculoskeletal (MSK) measurements. Moreover, it could be shown that the application of specifically designed target MTFs on two‐dimensional x‐ray images is feasible.

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Section: Methodsmentioning

confidence: 99%

Section: A System Geometry and Image Acquisitionmentioning

confidence: 99%

Section: Introduction and Purposementioning

confidence: 99%

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High‐speed slot‐scanning radiography using small‐angle tomosynthesis: Investigation of spatial resolution

et al. 2019

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“…This setup enables the system to acquire conventional 2D radiographs as well as projection images along predefined trajectories. In our previous papers, 39,43 an acquisition and reconstruction technique for slot scanning with conventional 2D FPDs has been presented. As indicated in Fig.…”

Section: A Radiographic System and Acquisition Geometrymentioning

confidence: 99%

“…37,38 To overcome the mentioned limitation of the slot scan in terms of a limited field-of-view, we utilize a method based on an ultra-small angle parallel-shift tomosynthesis where the source and detector move simultaneously in parallel planes, similar to the well-known slot scan. 39,40 For image acquisition, we use a modified twin-robotic cone-beam x-ray system based on a Multitom Rax (Siemens Healthcare GmbH, Erlangen, Germany). 41 In this work, we aim to compare a slot-scanning method using an ultra-small-angle tomosynthesis approach to conventional 2D radiographs in terms of its scatter rejection ability and the associated image noise.…”

Section: Introduction and Purposementioning

confidence: 99%

A phantom study on dose efficiency for orthopedic applications: Comparing slot‐scanning radiography using ultra‐small‐angle tomosynthesis to conventional radiography

et al. 2021

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This paper studies the abilities of a twin-robotic x-ray slot-scanning system for orthopedic imaging to reduce dose by scatter rejection compared to conventional digital radiography. Methods: We investigate the dose saving capabilities, especially in terms of the signal-and the contrast-to-noise ratio, as well as the scatter-to-primary ratio of the proposed slot-scanning method in comparison to the state-of-the-art method for length-extended imaging. As a baseline, we use x-ray parameters of two clinically established acquisition protocols that provide the same detector entrance dose but are profoundly different in patient dose. To obtain an estimate of the photon-related noise directly from an x-ray image, we implement a Poisson-Gaussian noise model. This model is used to compare the dose efficiency of two settings and combined with the well-known K SNR to determine the transmission parameters. We present a method with an associated measurement protocol, utilizing the robotic capabilities of the used system to automatically obtain quasi-scatter-free ground-truth data with exact geometric correspondence to full-field and slot acquisitions. In total, we investigate two body regions (thoracic spine and lumbar spine) in anterior-posterior view with two patient sizes (BMI = 22 and 30) in two acquisition modes (conventional and slot scan with a flat-panel detector) with and without anti-scatter grid using an anthropomorphic upper-body phantom. Results: We have shown that it is feasible to combine the proposed approach with the K SNR for the determination of scatter rejection parameters. The use of an anti-scatter grid is indicated for full-field acquisitions allowing for dose savings up to 46% compared to their gridless counterparts. When changing the acquisition mode to the investigated slot scan, the use of an anti-scatter grid has no major impact on the image quality in terms of dose efficiency, in particular for patients with a BMI of 22. However, an increased contrast improvement factor was found. For normal-sized patients, up to 53% of dose can be saved additionally in comparison to full-field acquisitions with grid. Moreover, we could demonstrate that a slot size of 5 cm and air gap of 10 cm is sufficient to achieve scatter-toprimary ratios, which are equal or better compared to those of the full-field acquisitions with a grid. Conclusions: We have shown, that the slot-scanning approach is always superior to the conventional full-field acquisition in terms of signal-to-noise and scatter-to-primary ratios. Compared to the stateof-the-art acquisition protocols with a grid, dose savings up to 53% are possible due to the scatter rejection without compromising the SNR. Hence, the use of the slot-scanning method is indicated, especially when it comes to regularly carried-out follow-up acquisitions, for example, in the case of scoliosis monitoring.

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Cone‐beam imaging with tilted rotation axis: Method and performance evaluation

et al. 2020

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The recently introduced robotic x-ray systems provide the flexibility to acquire cone-beam computed tomography (CBCT) data using customized, application-specific source-detector trajectories. We exploit this capability to mitigate the effects of x-ray scatter and noise in CBCT imaging of weight-bearing foot and cervical spine (C-spine) using scan orbits with a tilted rotation axis. Methods: We used an advanced CBCT simulator implementing accurate models of x-ray scatter, primary attenuation, and noise to investigate the effects of the orbital tilt angle in upright foot and Cspine imaging. The system model was parameterized using a laboratory version of a three-dimensional (3D) robotic x-ray system (Multitom RAX, Siemens Healthineers). We considered a generalized tilted axis scan configuration, where the detector remained parallel to patient's long body axis during the acquisition, but the elevation of source and detector was changing. A modified Feldkamp-Davis-Kress (FDK) algorithm was developed for reconstruction in this configuration, which departs from the FDK assumption of a detector that is perpendicular to the scan plane. The simulated foot scans involved source-detector distance (SDD) of 1386 mm, orbital tilt angles ranging 10°to 40°, and 400 views at 1 mAs/view and 0.5°increment; the C-spine scans involved À25°to À45°tilt angles, SDD of 1090 mm, and 202 views at 1.3 mAs and 1°increment The imaging performance was assessed by projection-domain measurements of the scatter-to-primary ratio (SPR) and by reconstruction-domain measurements of contrast, noise and generalized contrast-to-noise ratio (gCNR, accounting for both image noise and background nonuniformity) of the metatarsals (foot imaging) and cervical vertebrae (spine imaging). The effects of scatter correction were also compared for horizontal and tilted scans using an ideal Monte Carlo (MC)-based scatter correction and a frame-byframe mean scatter correction. Results: The proposed modified FDK, involving projection resampling, mitigated streak artifacts caused by the misalignment between the filtering direction and the detector rows. For foot imaging (no grids), an optimized 20°tilted orbit reduced the maximum SPR from~1.5 in a horizontal scan to <0.5. The gCNR of the second metatarsal was enhanced twofold compared to a horizontal orbit. For the C-spine (with vertical grids), imaging with a tilted orbit avoided highly attenuating x-ray paths through the lower cervical vertebrae and shoulders. A À35°tilted orbit yielded improved image quality and visualization of the lower cervical spine: the SPR of lower cervical vertebrae was reduced from~10 (horizontal orbit) to <6 (tilted orbit), and the gCNR for C5-C7 increased by a factor of 2. Furthermore, tilted orbits showed potential benefits over horizontal orbits by enabling scatter correction with a simple frame-by-frame mean correction without substantial increase in noise-induced artifacts after the correction. Conclusions: Tilted scan trajectories, enabled by the emerging robotic x-ray system technolo...

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Parallel-shift tomosynthesis for orthopedic applications

Cited by 9 publications

References 14 publications

High‐speed slot‐scanning radiography using small‐angle tomosynthesis: Investigation of spatial resolution

High‐speed slot‐scanning radiography using small‐angle tomosynthesis: Investigation of spatial resolution

A phantom study on dose efficiency for orthopedic applications: Comparing slot‐scanning radiography using ultra‐small‐angle tomosynthesis to conventional radiography

Cone‐beam imaging with tilted rotation axis: Method and performance evaluation

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