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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 cm 2 . 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/cm 2 for phantoms with average cortical bone fraction w cortical  = 10% to ∼0.01 g/cm 2 for phantoms with w cortical  = 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 w cortical  = 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/cm 2 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 w cortical  = 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 w cortical  = 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/cm 2 across all three simulated ESP vertebrae and all added PMMA attenuator settings., Conclusions: We demonstrated that accurate aBMD measurements can be obtained on a motorized FPD-based x-ray system using DE slot-scans with kernel-based scatter correction, backprojection-based slot view tiling, and DE decomposition with adipose correction., (© 2021 American Association of Physicists in Medicine.)

Purpose: 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 KSNR 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 KSNR 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‐to‐primary 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 state‐of‐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. [ABSTRACT FROM AUTHOR]