Robotic X-ray System Research Articles

Radiation Exposure and Safety Considerations in Interventional Radiology: Comparison of a Twin Robotic X-ray System to a Conventional Angiography System.

Background/Objectives: To evaluate radiation exposure in standard interventional radiology procedures using a twin robotic X-ray system compared to a state-of-the-art conventional angiography system. Methods: Standard interventional radiology procedures (port implantation, SIRT, and pelvic angiography) were simulated using an anthropomorphic Alderson RANDO phantom (Alderson Research Laboratories Inc. Stamford, CT, USA) on an above-the-table twin robotic X-ray scanner (Multitom Rax, Siemens Healthineers, Forchheim, Germany) and a conventional below-the-table angiography system (Artis Zeego, Siemens Healthineers, Forchheim, Germany). The phantom's radiation exposure (representing the potential patient on the procedure table) was measured with thermoluminescent dosimeters. Height-dependent dose curves were generated for examiners and radiation technologists in representative positions using a RaySafe X2 system (RaySafe, Billdal, Sweden). Results: For all scenarios, the device-specific dose distribution differs depending on the imaging chain, with specific advantages and disadvantages. Radiation exposure for the patient is significantly increased when using the Multitom Rax for pelvic angiography compared to the Artis Zeego, which is evident in the dose progression through the phantom's body as well as in the organ-related radiation exposure. In line with these findings, there is an increased radiation exposure for the performing proceduralist, especially at eye level, which can be significantly minimized by using protective equipment (p < 0.001). Conclusions: In this study, the state-of-the-art conventional below-the-table angiography system is associated with lower radiation dose exposures for both the patient and the interventional radiology physician compared to an above-the-table twin robotic X-ray system for pelvic angiographies. However, in other clinical scenarios (port implantation or SIRT), both devices are suitable options with acceptable radiation exposure.

Feasibility of bone marrow edema detection using dual-energy cone-beam computed tomography.

Dual-energy (DE) detection of bone marrow edema (BME) would be a valuable new diagnostic capability for the emerging orthopedic cone-beam computed tomography (CBCT) systems. However, this imaging task is inherently challenging because of the narrow energy separation between water (edematous fluid) and fat (health yellow marrow), requiring precise artifact correction and dedicated material decomposition approaches. We investigate the feasibility of BME assessment using kV-switching DE CBCT with a comprehensive CBCT artifact correction framework and a two-stage projection- and image-domain three-material decomposition algorithm. DE CBCT projections of quantitative BME phantoms (water containers 100-165mm in size with inserts presenting various degrees of edema) and an animal cadaver model of BME were acquired on a CBCT test bench emulating the standard wrist imaging configuration of a Multitom Rax twin robotic x-ray system. The slow kV-switching scan protocol involved a 60kV low energy (LE) beam and a 120kV high energy (HE) beam switched every 0.5° over a 200° angular span. The DE CBCT data preprocessing and artifact correction framework consisted of (i) projection interpolation onto matched LE and HE projections views, (ii) lag and glare deconvolutions, and (iii) efficient Monte Carlo (MC)-based scatter correction. Virtual non-calcium (VNCa) images for BME detection were then generated by projection-domain decomposition into an Aluminium (Al) and polyethylene basis set (to remove beam hardening) followed by three-material image-domain decomposition into water, Ca, and fat. Feasibility of BME detection was quantified in terms of VNCa image contrast and receiver operating characteristic (ROC) curves. Robustness to object size, position in the field of view (FOV) and beam collimation (varied 20-160mm) was investigated. The MC-based scatter correction delivered>69% reduction of cupping artifacts for moderate to wide collimations (>80mm beam width), which was essential to achieve accurate DE material decomposition. In a forearm-sized object, a 20% increase in water concentration (edema) of a trabecular bone-mimicking mixture presented as ∼15 HU VNCa contrast using 80-160mm beam collimations. The variability with respect to object position in the FOV was modest (<15% coefficient of variation). The areas under the ROC curve were>0.9. A femur-sized object presented a somewhat more challenging task, resulting in increased sensitivity to object positioning at 160mm collimation. In animal cadaver specimens, areas of VNCa enhancement consistent with BME were observed in DE CBCT images in regions of MRI-confirmed edema. Our results indicate that the proposed artifact correction and material decomposition pipeline can overcome the challenges of scatter and limited spectral separation to achieve relatively accurate and sensitive BME detection in DE CBCT. This study provides an important baseline for clinical translation of musculoskeletal DE CBCT to quantitative, point-of-care bone health assessment.

Mixed reality interfaces for achieving desired views with robotic X-ray systems

ABSTRACT Robotic X-ray C-arm imaging systems can precisely achieve any position and orientation relative to the patient. Informing the system, however, what pose exactly corresponds to a desired view is challenging. Currently these systems are operated by the surgeon using joysticks, but this interaction is not necessarily effective because users may be unable to efficiently actuate more than a single axis of the system simultaneously. Moreover, novel robotic imaging systems, such as the Brainlab Loop-X, allow for independent source and detector movements, adding complexity. To address this challenge, we consider complementary interfaces for the surgeon to command robotic X-ray systems effectively. Specifically, we consider three interaction paradigms: (1) the use of a pointer to specify the principal ray of the desired view, (2) the same pointer, but combined with a mixed reality environment to synchronously render digitally reconstructed radiographs from the tool’s pose, and (3) the same mixed reality environment but with a virtual X-ray source instead of the pointer. Human-in-the-loop evaluation with an attending trauma surgeon indicates that mixed reality interfaces for robotic X-ray system control are promising and may contribute to substantially reducing the number of images acquired solely during ‘fluoro hunting’ for the desired view or standard plane.

Dual-Energy Cone-Beam CT with Three-Material Decomposition for Bone Marrow Edema Imaging.

We investigate the feasibility of bone marrow edema (BME) detection using a kV-switching Dual-Energy (DE) Cone-Beam CT (CBCT) protocol. This task is challenging due to unmatched x-ray paths in the low-energy (LE) and high-energy (HE) spectral channels, CBCT non-idealities such as x-ray scatter, and narrow spectral separation between fat (bone marrow) and water (BME). We propose a comprehensive DE decomposition framework consisting of projection interpolation onto matching LE and HE view angles, fast Monte Carlo scatter correction with low number of tracked photons and Gaussian denoising, and two-stage three-material decompositions involving two-material (fat-Aluminium) Projection-Domain Decomposition (PDD) followed by image-domain three-material (fat-water-bone) base-change. Performance in BME detection was evaluated in simulations and experiments emulating a kV-switching CBCT wrist imaging protocol on a robotic x-ray system with 60 kV LE beam, 120 kV HE beam, and 0.5° angular shift between the LE and HE views. Cubic B-spline interpolation was found to be adequate to resample HE and LE projections of a wrist onto common view angles required by PDD. The DE decomposition maintained acceptable BME detection specificity (<0.2 mL erroneously detected BME volume compared to 0.85 mL true BME volume) over +/-10% range of scatter magnitude errors, as long as the scatter shape was estimated without major distortions. Physical test bench experiments demonstrated successful discrimination of ~20% change in fat concentrations in trabecular bone-mimicking solutions of varying water and fat content.

Metal artifact reduction in ultra-high-resolution cone-beam CT imaging with a twin robotic X-ray system

Cone-beam computed tomography (CBCT) has been shown to be a powerful tool for 3D imaging of the appendicular skeleton, allowing for detailed visualization of bone microarchitecture. This study was designed to compare artifacts in the presence of osteosynthetic implants between CBCT and multidetector computed tomography (MDCT) in cadaveric wrist scans. A total of 32 scan protocols with varying tube potential and current were employed: both conventional CBCT and MDCT studies were included with tube voltage ranging from 60 to 140 kVp as well as additional MDCT protocols with dedicated spectral shaping via tin prefiltration. Irrespective of scanner type, all examinations were conducted in ultra-high-resolution (UHR) scan mode. For reconstruction of UHR-CBCT scans an additional iterative metal artifact reduction algorithm was employed, an image correction tool which cannot be used in combination with UHR-MDCT. To compare applied radiation doses between both scanners, the volume computed tomography dose index for a 16 cm phantom (CTDIvol) was evaluated. Images were assessed regarding subjective and objective image quality. Without automatic tube current modulation or tube potential control, radiation doses ranged between 1.3 mGy (with 70 kVp and 50.0 effective mAs) and 75.2 mGy (with 140 kVp and 383.0 effective mAs) in UHR-MDCT. Using the pulsed image acquisition method of the CBCT scanner, CTDIvol ranged between 2.3 mGy (with 60 kVp and 0.6 mean mAs per pulse) and 61.0 mGy (with 133 kVp and 2.5 mean mAs per pulse). In essence, all UHR-CBCT protocols employing a tube potential of 80 kVp or more were found to provide superior overall image quality and artifact reduction compared to UHR-MDCT (all p < .050). Interrater reliability of seven radiologists regarding image quality was substantial for tissue assessment and moderate for artifact assessment with Fleiss kappa of 0.652 (95% confidence interval 0.618–0.686; p < 0.001) and 0.570 (95% confidence interval 0.535–0.606; p < 0.001), respectively. Our results demonstrate that the UHR-CBCT scan mode of a twin robotic X-ray system facilitates excellent visualization of the appendicular skeleton in the presence of metal implants. Achievable image quality and artifact reduction are superior to dose-comparable UHR-MDCT and even MDCT protocols employing spectral shaping with tin prefiltration do not achieve the same level of artifact reduction in adjacent soft tissue.

One-stop-shop CT arthrography of the wrist without subject repositioning by means of gantry-free cone-beam CT

Modern cone-beam CT systems are capable of ultra-high-resolution 3D imaging in addition to conventional radiography and fluoroscopy. The combination of various imaging functions in a multi-use setup is particularly appealing for musculoskeletal interventions, such as CBCT arthrography (CBCTA). With this study, we aimed to investigate the feasibility of CBCTA of the wrist in a “one-stop-shop” approach with a gantry-free twin robotic scanner that does not require repositioning of subjects. Additionally, the image quality of CBCTA was compared to subsequent arthrograms on a high-end multidetector CT (MDCTA). Fourteen cadaveric wrists received CBCTA with four acquisition protocols. Specimens were then transferred to the CT suite for additional MDCTA. Dose indices ranged between 14.3 mGy (120 kVp/100 effective mAs; full-dose) and 1.0 mGy (70 kVp/41 effective mAs; ultra-low-dose) for MDCTA and between 17.4 mGy (80 kVp/2.5 mAs per pulse; full-dose) and 1.2 mGy (60 kVp/0.5 mAs per pulse; ultra-low-dose) for CBCTA. Subjective image quality assessment for bone, cartilage and ligamentous tissue was performed by seven radiologists. The interrater reliability was assessed by calculation of the intraclass correlation coefficient (ICC) based on a two-way random effects model. Overall image quality of most CBCTA was deemed suitable for diagnostic use in contrast to a considerable amount of non-diagnostic MDCTA examinations (38.8%). The depiction of bone, cartilage and ligaments in MDCTA with any form of dose reduction was inferior to any CBCTA scan with at least 0.6 mAs per pulse (all p < 0.001). Full-dose MDCTA and low-dose CBCTA were of equal quality for bone tissue visualization (p = 0.326), whereas CBCTA allowed for better depiction of ligaments and cartilage (both p < 0.001), despite merely one third of radiation exposure (MDCTA–14.3 mGy vs. CBCTA–4.5 mGy). Moderate to good interrater reliability was ascertained for the assessment all tissues (ICC 0.689–0.756). Overall median examination time for CBCTA was 5.4 min (4.8–7.2 min). This work demonstrates that substantial dose reduction can be achieved in CT arthrography of the wrist while maintaining diagnostic image quality by employing the cone-beam CT mode of a twin robotic X-ray system. The ability of the multi-use X-ray system to switch between fluoroscopy mode and 3D imaging allows for “one-stop-shop” CBCTA in minimal examination time without the need for repositioning.

Combining gantry-free cone-beam computed tomography with iterative metal artefact reduction for surgical follow-up imaging of the appendicular skeleton

PurposePost-surgical evaluation of osteosynthesis material and adjacent tissue can be challenging in both radiography and cross-sectional imaging. This study investigates the performance of a multi-purpose X-ray scanner with cone-beam CT (CBCT) function and iterative metal artefact reduction capabilities in patients after osteoplasty of the appendicular skeleton. MethodEighty individuals who underwent both conventional X-ray imaging and CBCT after osteoplasty of the hand/wrist (48), elbow (14), or ankle/foot (18) with the gantry-free twin robotic system were retrospectively enrolled. Radiological reports from clinical routine for both imaging modalities were retrospectively analyzed and compared with consensus expert reading by two musculoskeletal specialists serving as the standard of reference. Findings of screw dislocation or implant loosening, fragment displacement, and delayed healing were compared between X-ray and CBCT reports using the McNemar test. ResultsThe median dose-area-product of CBCT and X-ray scans amounted to 27.98 and 0.2 dGy*cm2, respectively. Diagnostic accuracy for screw dislocation was superior in CBCT compared to standard radiograms (98.8 % vs 83.8 %; p = 0.002). Implant loosening (98.8 % vs 86.3 %; p = 0.006), fragment displacement (98.8 % vs 85.0 %; p < 0.001), and delayed healing (97.5 % vs 88.8 %; p = 0.016) were also more reliably detected in CBCT. Employing CBCT, postoperative complications were detected with a sensitivity and specificity of at least 95.8 % and 98.1 %, compared to 33.3 % and 92.86 % in radiography. ConclusionsWith superior accuracy for various osteoplasty-related complications, the CBCT scan mode of a gantry-free twin robotic X-ray system with iterative metal artefact reduction aids post-surgical assessment in the appendicular skeleton.

The effect of tin prefiltration on extremity cone-beam CT imaging with a twin robotic X-ray system

IntroductionWhile tin prefiltration is established in various CT applications, its value in extremity cone-beam CT relative to optimized spectra has not been thoroughly assessed thus far. This study aims to investigate the effect of tin filters in extremity cone-beam CT with a twin-robotic X-ray system. MethodsWrist, elbow and ankle joints of two cadaveric specimens were examined in a laboratory setup with different combinations of prefiltration (copper, tin), tube voltage and current–time product. Image quality was assessed subjectively by five radiologists with Fleiss’ kappa being computed to measure interrater agreement. To provide a semiquantitative criterion for image quality, contrast-to-noise ratios (CNR) were compared for standardized regions of interest. Volume CT dose indices were calculated for a 16 cm polymethylmethacrylate phantom. ResultsRadiation dose ranged from 17.4 mGy in the clinical standard protocol without tin filter to as low as 0.7 mGy with tin prefiltration. Image quality ratings and CNR for tin-filtered scans with 100 kV were lower than for 80 kV studies with copper prefiltration despite higher dose (11.2 and 5.6 vs. 4.5 mGy; p < 0.001). No difference was ascertained between 100 kV scans with tin filtration and 60 kV copper-filtered scans with 75% dose reduction (subjective: p = 0.101; CNR: p = 0.706). Fleiss’ kappa of 0.597 (95% confidence interval 0.567–0.626; p < 0.001) indicated moderate interrater agreement. ConclusionConsiderable dose reduction is feasible with tin prefiltration, however, the twin-robotic X-ray system's low-dose potential for extremity 3D imaging is maximized with a dedicated low-kilovolt scan protocol in situations without extensive beam-hardening artifacts. Implications for practiceLow-kilovolt imaging with copper prefiltration provides a superior trade-off between dose reduction and image quality compared to tin-filtered cone-beam CT scan protocols with higher tube voltage.

Slot-scan dual-energy bone densitometry using motorized X-ray systems.

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. 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=70-106cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1cm 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 6cm thick. For the L-spine, the mean aBMD error across all WC settings ranged from 0.08g/cm2 for phantoms with average cortical bone fraction wcortical =10% to ∼0.01g/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=106cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07g/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=106cm 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 ∼0.1g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings. 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.

Dose reduction potential in cone-beam CT imaging of upper extremity joints with a twin robotic x-ray system

Cone-beam computed tomography is a powerful tool for 3D imaging of the appendicular skeleton, facilitating detailed visualization of bone microarchitecture. This study evaluated various combinations of acquisition and reconstruction parameters for the cone-beam CT mode of a twin robotic x-ray system in cadaveric wrist and elbow scans, aiming to define the best possible trade-off between image quality and radiation dose. Images were acquired with different combinations of tube voltage and tube current–time product, resulting in five scan protocols with varying volume CT dose indices: full-dose (FD; 17.4 mGy), low-dose (LD; 4.5 mGy), ultra-low-dose (ULD; 1.15 mGy), modulated low-dose (mLD; 0.6 mGy) and modulated ultra-low-dose (mULD; 0.29 mGy). Each set of projection data was reconstructed with three convolution kernels (very sharp [Ur77], sharp [Br69], intermediate [Br62]). Five radiologists subjectively assessed the image quality of cortical bone, cancellous bone and soft tissue using seven-point scales. Irrespective of the reconstruction kernel, overall image quality of every FD, LD and ULD scan was deemed suitable for diagnostic use in contrast to mLD (very sharp/sharp/intermediate: 60/55/70%) and mULD (0/3/5%). Superior depiction of cortical and cancellous bone was achieved in FDUr77 and LDUr77 examinations (p < 0.001) with LDUr77 scans also providing favorable bone visualization compared to FDBr69 and FDBr62 (p < 0.001). Fleiss’ kappa was 0.618 (0.594–0.641; p < 0.001), indicating substantial interrater reliability. In this study, we demonstrate that considerable dose reduction can be realized while maintaining diagnostic image quality in upper extremity joint scans with the cone-beam CT mode of a twin robotic x-ray system. Application of sharper convolution kernels for image reconstruction facilitates superior display of bone microarchitecture.

Twin robotic x-ray system in small bone and joint trauma: impact of cone-beam computed tomography on treatment decisions

ObjectivesTrauma evaluation of extremities can be challenging in conventional radiography. A multi-use x-ray system with cone-beam CT (CBCT) option facilitates ancillary 3-D imaging without repositioning. We assessed the clinical value of CBCT scans by analyzing the influence of additional findings on therapy.MethodsNinety-two patients underwent radiography and subsequent CBCT imaging with the twin robotic scanner (76 wrist/hand/finger and 16 ankle/foot/toe trauma scans). Reports by on-call radiologists before and after CBCT were compared regarding fracture detection, joint affliction, comminuted injuries, and diagnostic confidence. An orthopedic surgeon recommended therapy based on reported findings. Surgical reports (N = 52) and clinical follow-up (N = 85) were used as reference standard.ResultsCBCT detected more fractures (83/64 of 85), joint involvements (69/53 of 71), and multi-fragment situations (68/50 of 70) than radiography (all p < 0.001). Six fractures suspected in radiographs were ruled out by CBCT. Treatment changes based on additional information from CBCT were recommended in 29 patients (31.5%). While agreement between advised therapy before CBCT and actual treatment was moderate (κ = 0.41 [95% confidence interval 0.35–0.47]; p < 0.001), agreement after CBCT was almost perfect (κ = 0.88 [0.83–0.93]; p < 0.001). Diagnostic confidence increased considerably for CBCT studies (p < 0.001). Median effective dose for CBCT was 4.3 μSv [3.3–5.3 μSv] compared to 0.2 μSv [0.1–0.2 μSv] for radiography.ConclusionsCBCT provides advantages for the evaluation of acute small bone and joint trauma by detecting and excluding extremity fractures and fracture-related findings more reliably than radiographs. Additional findings induced therapy change in one third of patients, suggesting substantial clinical impact.Key Points• With cone-beam CT, extremity fractures and fracture-related findings can be detected and ruled out more reliably than with conventional radiography.• Additional diagnostic information provided by cone-beam CT scans has substantial impact on therapy in small bone and joint trauma.• For distal extremity injury assessment, one-stop-shop imaging without repositioning is feasible with the twin robotic x-ray system.

In vivo 3D tomography of the lumbar spine using a twin robotic X-ray system: quantitative and qualitative evaluation of the lumbar neural foramina in supine and upright position

ObjectivesSupine lumbar spine examinations underestimate body weight effects on neuroforaminal size. Therefore, our purpose was to evaluate size changes of the lumbar neuroforamina using supine and upright 3D tomography and to initially assess image quality compared with computed tomography (CT).MethodsThe lumbar spines were prospectively scanned in 48 patients in upright (3D tomographic twin robotic X-ray) and supine (30 with 3D tomography, 18 with CT) position. Cross-sectional area (CSA), cranio-caudal (CC), and ventro-dorsal (VD) diameters of foramina were measured by two readers and additionally graded in relation to the intervertebral disc height. Visibility of bone/soft tissue structures and image quality were assessed independently on a 5-point Likert scale for the 18 patients scanned with both modalities. Descriptive statistics, Wilcoxon’s signed-rank test (p < 0.05), and interreader reliability were calculated.ResultsNeuroforaminal size significantly decreased at all levels for both readers from the supine (normal intervertebral disc height; CSA 1.25 ± 0.32 cm2; CC 1.84 ± 0.24 cm2; VD 0.88 ± 0.16 cm2) to upright position (CSA 1.12 ± 0.34 cm2; CC 1.78 ± 0.24 cm2; VD 0.83 ± 0.16 cm2; each p < 0.001). Decrease in intervertebral disc height correlated with decrease in foraminal size (supine: CSA 0.88 ± 0.34 cm2; CC 1.39 ± 0.33 cm2; VD 0.87 ± 0.26 cm2; upright: CSA 0.83 ± 0.37 cm2, p = 0.010; CC 1.32 ± 0.33 cm2, p = 0.015; VD 0.80 ± 0.21 cm2, p = 0.021). Interreader reliability for area was fair to excellent (0.51–0.89) with a wide range for cranio-caudal (0.32–0.74) and ventro-dorsal (0.03–0.70) distances. Image quality was superior for CT compared with that for 3D tomography (p < 0.001; κ, CT = 0.66–0.92/3D tomography = 0.51–1.00).ConclusionsThe size of the lumbar foramina is smaller in the upright weight-bearing position compared with that in the supine position. Image quality, especially nerve root delineation, is inferior using 3D tomography compared to CT.Key Points• Weight-bearing examination demonstrates a decrease of the neuroforaminal size.• Patients with higher decrease in intervertebral disc showed a narrower foraminal size.• Image quality is superior with CT compared to 3D tomographic twin robotic X-ray at the lumbar spine.

3D cone-beam CT with a twin robotic x-ray system in elbow imaging: comparison of image quality to high-resolution multidetector CT

BackgroundElbow imaging is challenging with conventional multidetector computed tomography (MDCT), while cone-beam CT (CBCT) provides superior options. We compared intra-individually CBCT versus MDCT image quality in cadaveric elbows.MethodsA twin robotic x-ray system with new CBCT mode and a high-resolution clinical MDCT were compared in 16 cadaveric elbows. Both systems were operated with a dedicated low-dose (LD) protocol (equivalent volume CT dose index [CTDIvol(16 cm)] = 3.3 mGy) and a regular clinical scan dose (RD) protocol (CTDIvol(16 cm) = 13.8 mGy). Image quality was evaluated by two radiologists (R1 and R2) on a seven-point Likert scale, and estimation of signal intensity in cancellous bone was conducted. Wilcoxon signed-rank tests and intraclass correlation coefficient (ICC) statistics were used.ResultsThe CBCT prototype provided superior subjective image quality compared to MDCT scans (for RD, p ≤ 0.004; for LD, p ≤ 0.001). Image quality was rated very good or excellent in 100% of the cases by both readers for RD CBCT, 100% (R1) and 93.8% (R2) for LD CBCT, 62.6% and 43.8% for RD MDCT, and 0.0% and 0.0% for LD MDCT. Single-measure ICC was 0.95 (95% confidence interval 0.91–0.97; p < 0.001). Software-based assessment supported subjective findings with less “undecided” pixels in CBCT than dose-equivalent MDCT (p < 0.001). No significant difference was found between LD CBCT and RD MDCT.ConclusionsIn cadaveric elbow studies, the tested cone-beam CT prototype delivered superior image quality compared to high-end multidetector CT and showed a potential for considerable dose reduction.

Evaluation of Ultra-High-Resolution Cone-Beam CT Prototype of Twin Robotic Radiography System for Cadaveric Wrist Imaging

Cone-beam CT (CBCT) applications possess potential for dose reduction in musculoskeletal imaging. This study evaluates the ultra-high-resolution CBCT prototype of a twin robotic X-ray system in wrist examinations compared to high-resolution multidetector CT (MDCT). Sixteen wrists of body donors were examined with the CBCT scan mode and a 384 slice MDCT system. Radiation-equivalent low-dose (CTDIvol(16cm) = 3.3 mGy) and full-dose protocols (CTDIvol(16cm) = 13.8 mGy) were used for both systems. Two observers assessed image quality on a seven-point Likert scale. In addition, software-assisted quantification of signal intensity fractions in cancellous bone was performed. Fewer pixels with intermediate signal intensity were considered to indicate superior depiction of bone microarchitecture. Subjective image quality in CBCT was superior to dose equivalent MDCT with p ≤ 0.03 for full-dose and p < 0.001 for low-dose scans, respectively. Median Likert values were 7/7 (reader 1 / reader 2) in full-dose CBCT, 6/6 in full-dose MDCT, 5/6 in low-dose CBCT and 3/3 in low-dose MDCT. Intraclass correlation coefficient was 0.936 (95% confidence interval, 0.897-0.961; p < 0.001), indicating excellent reliability. Objective analysis displayed smaller fractions of "indecisive" pixels with intermediate signal intensity for full-dose CBCT (0.57 [interquartile range 0.13]) compared to full-dose MDCT (0.68 [0.21]), low-dose CBCT (0.72 [0.19]), and low-dose MDCT (0.80 [0.15]) studies. No significant difference was observed between low-dose CBCT and full-dose MDCT. The new CBCT prototype provides superior image quality for trabecula and bone marrow in cadaveric wrist studies and enables dose reduction up to 75% compared to high-resolution MDCT.

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

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. 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 C-spine 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 1386mm, orbital tilt angles ranging 10° to 40°, and 400 views at 1mAs/view and 0.5° increment; the C-spine scans involved -25° to -45° tilt angles, SDD of 1090mm, and 202 views at 1.3mAs 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-by-frame mean scatter correction. 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 -35° 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. Tilted scan trajectories, enabled by the emerging robotic x-ray system technology, were optimized for CBCT imaging of foot and cervical spine using an advanced simulation framework. The results demonstrated the potential advantages of tilted axis orbits in mitigation of scatter artifacts and improving contrast-to-noise ratio in CBCT reconstructions.

Twin Robotic X-Ray System for 3D Cone-Beam CT of the Wrist: An Evaluation of Image Quality and Radiation Dose.

OBJECTIVE. The purpose of this study was to assess image quality and radiation dose of a novel twin robotic x-ray system's 3D cone-beam CT (CBCT) function for the depiction of cadaveric wrists. MATERIALS AND METHODS. Sixteen cadaveric wrists were scanned using dedicated low-dose and standard-dose CBCT protocols as well as clinical MDCT for comparison. Three readers assessed overall image quality, noise, and artifacts in bone and soft tissue on 5-point Likert scales. For radiation dose analysis, volume CT dose indexes (CTDIvol) were compared. RESULTS. Overall image quality of most studies was very good or excellent in MDCT (for readers 1, 2, and 3: 100%, 100%, and 88%, respectively), standard-dose CBCT (100%, 100%, and 94%), and low dose CBCT (100%, 94%, and 88%) with two readers favoring standard-dose CBCT over MDCT image quality (readers 1 and 2; p ≤ 0.046). In soft tissue, standard-dose (readers 1, 2, and 3; p ≤ 0.021) and low-dose (all p ≤ 0.001) CBCT images had more noise than MDCT in all cases. Standard-dose (all p ≤ 0.003) and low-dose (all p < 0.001) CBCT images also displayed more artifacts. In osseous tissue, one reader observed more noise (p < 0.001) and artifacts (p = 0.020) for low-dose CBCT than for MDCT, whereas no difference was found between standard-dose CBCT and MDCT. Mean CTDIvol was significantly lower for standard-dose (5.2 ± 0.6 mGy; p < 0.001) and low-dose CBCT (1.8 ± 0.2 mGy; p < 0.001) than for clinical MDCT without automatic dose modulation (15.0 ± 0.0 mGy). CONCLUSION. The tested CBCT function delivers suitable image quality for clinical wrist imaging at significantly lower radiation levels than conventional MDCT. In combination with comfortable positioning options and the ability to perform additional radiographic and fluoroscopic examinations, the twin robotic x-ray system may hold the potential to be a one-stop shop device for trauma-associated wrist imaging.

3D cone-beam CT of the ankle using a novel twin robotic X-ray system: Assessment of image quality and radiation dose

PurposeTo evaluate image quality (IQ) and radiation dose in cone-beam computed tomography (CBCT) of the ankle using a novel twin robotic X-ray system. MethodWe examined 16 cadaveric ankles with standard-dose (FD) and low-dose (LD) protocols using the new system’s CBCT mode. For comparison, we performed multi-slice CT imaging (MSCT) with a clinical protocol. Three radiologists assessed IQ, noise and artifacts in bone and soft tissue on a five-point Likert scale (1= poor IQ; strong noise or artifacts; 5= excellent IQ; minimal noise or artifacts). Volume CT dose indices (CTDIvol) were calculated for radiation dose comparison between CBCT and MSCT. ResultsOverall IQ was described as very good or excellent by reader 1/2/3 in 62.5/87.5/56.3% of LD, 87.5/87.5/81.3% of FD and 100/87.5/87.5% of MSCT studies. Readers agreed that IQ was better in MSCT than LD (R1/R2/R3; p ≤ 0.008), two also found advantages of MSCT over FD (R1/R3; p ≤ 0.034). Soft tissue noise and artifacts were stronger in FD (all p ≤ 0.002) and LD (all p ≤ 0.001). In bone, artifacts and noise were also more severe in LD (all p < 0.001) and FD (all p ≤ 0.003). CTDIvol for clinical MSCT scans without dose modulation (15.0 ± 0.0 mGy) were higher than for FD (5.3 ± 1.0 mGy) and LD studies (2.9 ± 0.6 mGy; both p < 0.001). ConclusionsDespite MSCT providing better overall IQ than the twin robotic X-ray system’s CBCT mode, both cone-beam protocols offer very good IQ in most studies and are suitable for clinical ankle imaging. Standard-dose and especially low-dose CBCT studies deliver up to five times less radiation dose than MSCT imaging.

Initial Assessment of a Prototype 3D Cone-Beam Computed Tomography System for Imaging of the Lumbar Spine, Evaluating Human Cadaveric Specimens in the Upright Position.

The aims of this study were to assess feasibility, image quality, and radiation dose and to estimate the optimal dose protocol for the lumbar spine of cadaveric specimens with different body mass indices (BMIs) in the upright position using a prototype 3-dimensional cone-beam computed tomography (CT) software implemented on a robotic x-ray system and compare with CT. The lumbar spine of 5 formalin-fixed human cadaveric specimens (BMI, 22-35 kg/m) was prospectively assessed in the upright position using prototype software for 3-dimensional tomography implemented on a robotic x-ray system. Specimens were scanned with varying kilovolt values (70, 81, 90, 100, 109, 121 kV) and thereafter with 80 kV (BMI ≤30 kg/m) and 121 kV (BMI >30 kg/m) and varying dose levels (DLs; 0.278, 0.435, 0.548, 0.696, 0.87, 1.09). Computed tomography data were acquired with a standard clinical protocol. Two independent readers rated visibility of the cortex, endplates, facet joints, trabeculae, neuroforamina, posterior alignment, and spinal canal as well as nerve roots. Radiation dose was measured with a cylindrical CTDI phantom. Descriptive statistics and analysis of variance were used (P < 0.05). Average intraclass correlation was excellent (0.94). The lowest technically possible kilovolt and the highest technically possible DL yielded the best image quality. In specimens with a BMI of 30 kg/m or less, depiction of all structures was good and comparable to CT, except for nerve roots. For specimens with a BMI greater than 30 kg/m, image quality was limited. Three-dimensional cone-beam CT of the lumbar spine in cadaveric specimens in the upright position is feasible. An optimal dose protocol was estimated. Depiction of osseous structures is comparable to CT in specimens with BMI of 30 kg/m or less. Image quality is limited for soft tissue structures and specimens with BMI greater than 30 kg/m.

Initial evaluation of image performance of a 3-D x-ray system: phantom-based comparison of 3-D tomography with conventional computed tomography.

Phantom-based initial performance assessment of a prototype three-dimensional (3-D) x-ray system and comparison of 3-D tomography with computed tomography (CT) were proposed. A 3-D image quality phantom was scanned with a prototype version of 3-D cone-beam CT imaging implemented on a twin robotic x-ray system using three trajectories (163deg = table, 188deg = upright, and 200deg = side), six tube voltages (60, 70, 81, 90, 100, and 121kV), and four detector doses (0.348, 0.696, 1.740, and [Formula: see text]). CT was obtained with a clinical protocol. Spatial resolution (line pairs/cm) and soft-tissue-contrast resolution were assessed by two independent readers. Radiation dose was assessed. Descriptive and analysis of variance (ANOVA) ([Formula: see text]) were performed. With 3-D tomography, a maximum of 16 lp/cm was visible and best soft-tissue-contrast resolution was 2mm at 30 Hounsfield units (HU) for 160 projections. With CT, 10 lp/cm was visible and soft-tissue-contrast resolution was 4mm at 20 HU. The upright trajectory yielded significantly better spatial resolution and soft tissue contrast, and the side trajectory yielded significantly higher soft tissue contrast than the table trajectory ([Formula: see text]). Radiation dose was higher in 3-D tomography (45 to 704 mGycm) than CT (44 mGycm). Three-dimensional tomography renders overall equal or higher spatial resolution and comparable soft tissue contrast to CT for medium- and high-dose protocols in the side and upright trajectories, but with higher radiation doses.