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

Luckner, Christoph; Herbst, Magdalena; Weber, Thomas; Beister, Marcel; Ritschl, Ludwig; Kappler, S.; Maier, Andreas

doi:10.1002/mp.13828

Cited by 6 publications

(12 citation statements)

References 44 publications

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“…During the continuous motion, x‐ray projections are acquired with 30 frames per second. In the high‐speed mode, the acquisition of the entire body takes about 7 s. The acquired projections form the basis for the image reconstruction using a dedicated ultra‐small‐angle tomosynthesis technique 43 . This reconstruction technique is required due to the small but inevitable cone angle that has to be considered during reconstruction.…”

Section: Methodsmentioning

confidence: 99%

“…, yields that the ratio between the irradiated and the penumbra area is

r_{C} = 0.11

, which results in a weighting factor of

w_{κ} = 1 ‐ r_{C} = 0.89

. Note that we assume that the shape of the focal spot can be approximated by a rectangular function, but the following considerations are true for any symmetric focal spot shape due to the convolution properties 43 …”

Section: Methodsmentioning

confidence: 99%

“…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%

“…In the highspeed mode, the acquisition of the entire body takes about 7 s. The acquired projections form the basis for the image reconstruction using a dedicated ultra-small-angle tomosynthesis technique. 43 This reconstruction technique is required due to the small but inevitable cone angle that has to be considered during reconstruction. The size s of the irradiated slot on the detector is controlled by the built-in lead collimator of the system.…”

Section: A Radiographic System and Acquisition Geometrymentioning

confidence: 99%

“…Note that we assume that the shape of the focal spot can be approximated by a rectangular function, but the following considerations are true for any symmetric focal spot shape due to the convolution properties. 43 Thus, for a comparison of the proposed slot scan (SS) to a full-field (FF) acquisition the dose efficiency coefficient (κ SS FF ) has to be penalized due to the collimator penumbra…”

Section: C1 Theoretical Considerationsmentioning

confidence: 99%

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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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Section: Methodsmentioning

confidence: 99%

“…, yields that the ratio between the irradiated and the penumbra area is

r_{C} = 0.11

, which results in a weighting factor of

w_{κ} = 1 ‐ r_{C} = 0.89

Section: Methodsmentioning

confidence: 99%

Section: A Radiographic System and Acquisition Geometrymentioning

confidence: 99%

Section: A Radiographic System and Acquisition Geometrymentioning

confidence: 99%

Section: C1 Theoretical Considerationsmentioning

confidence: 99%

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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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Intraoperative cone‐beam and slot‐beam CT: 3D image quality and dose with a slot collimator on the O‐arm imaging system

et al. 2021

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To characterize the 3D imaging performance and radiation dose for a prototype slot-beam configuration on an intraoperative O-arm™ Surgical Imaging System (Medtronic Inc., Littleton, MA) and identify potential improvements in soft-tissue image quality for surgical interventions. Methods: A slot collimator was integrated with the O-arm ™ system for slotbeam axial CT. The collimator can be automatically actuated to provide 1.2 • slotbeam longitudinal collimation. Cone-beam and slot-beam configurations were investigated with and without an antiscatter grid (12:1 grid ratio, 60 lines/cm). Dose, scatter, image noise, and soft-tissue contrast resolution were evaluated in quantitative phantoms for head and body configurations over a range of exposure levels (beam energy and mAs), with reconstruction performed via filteredbackprojection. Qualitative imaging performance across various anatomical sites and imaging tasks was assessed with anthropomorphic head, abdomen, and pelvis phantoms. Results:The dose for a slot-beam scan varied from 0.02-0.06 mGy/mAs for head protocols to 0.01-0.03 mGy/mAs for body protocols, yielding dose reduction by ∼1/5 to 1/3 compared to cone-beam, owing to beam collimation and reduced x-ray scatter. The slot-beam provided an ∼6-7× reduction in scatterto-primary ratio (SPR) compared to the cone-beam, yielding SPR ∼20-80% for head and body without the grid and ∼7-30% with the grid. Compared to conebeam scans at equivalent dose, slot-beam images exhibited an ∼2.5× increase in soft-tissue contrast-to-noise ratio (CNR) for both grid and gridless configurations. For slot-beam scans, a further ∼10-30% improvement in CNR was achieved when the grid was removed. Slot-beam imaging could benefit certain interventional scenarios in which improved visualization of soft tissues is required within a fairly narrow longitudinal region of interest (±7 mm in z)--for example, checking the completeness of tumor resection, preservation of adjacent anatomy, or detection of complications (e.g., hemorrhage). While preserving existing capabilities for fluoroscopy and cone-beam CT, slot-beam scanning could enhance the utility of intraoperative imaging and provide a useful mode for safety and validation checks in image-guided surgery. Conclusions: The 3D imaging performance and dose of a prototype slot-beam CT configuration on the O-arm ™ system was investigated. Substantial improvements in soft-tissue image quality and reduction in radiation dose are evident with the slot-beam configuration due to reduced x-ray scatter.

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

Cited by 6 publications

References 44 publications

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

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

Intraoperative cone‐beam and slot‐beam CT: 3D image quality and dose with a slot collimator on the O‐arm imaging system

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

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