Digital x-ray tomosynthesis: current state of the art and clinical potential

Improving diagnostic strategies in bronchoscopy for peripheral pulmonary lesions

INTRODUCTION

In the past two decades, bronchoscopy of peripheral pulmonary lesions (PPLs) has improved its diagnostic yield due to the combination of various instruments and devices. Meanwhile, the application is complex and intertwined.

AREAS COVERED

This review article outlines strategies in diagnostic bronchoscopy for PPLs. We summarize the utility and evidence of key instruments and devices based on the results of clinical trials. Future perspectives of bronchoscopy for PPLs are also discussed.

EXPERT OPINION

The accuracy of reaching PPLs by bronchoscopy has improved significantly with the introduction of combined instruments such as navigation, radial endobronchial ultrasound, digital tomosynthesis, and cone-beam computed tomography. It has been accelerated with the advent of approach tools such as newer ultrathin bronchoscopes and robotic-assisted bronchoscopy. In addition, needle aspiration and cryobiopsy provide further diagnostic opportunities beyond forceps biopsy. Rapid on-site evaluation may also play an important role in decision making during the procedures. As a result, the diagnostic yield of bronchoscopy for PPLs has improved to a level comparable to that of transthoracic needle biopsy. The techniques and technologies developed in the diagnosis will be carried over to the next step in the transbronchial treatment of PPLs in the future.

Next-generation digital chest tomosynthesis

The objective of this study was to demonstrate the performance characteristics and potential utility of a novel tomosynthesis device as applied to imaging the chest, specifically relating to lung nodules. The imaging characteristics and quality of a novel digital tomosynthesis prototype system was assessed by scanning, a healthy volunteer, and an andromorphic lung phantom with different configurations of simulated pulmonary nodules. The adequacy of nodule detection on the phantoms was rated by chest radiologists using a standardized scale. Results from using this tomosynthesis device demonstrate in plane resolution of 16lp/cm, with estimated effective radiation doses of 90% less than low dose CT. Nodule detection was adequate across various anatomic locations on a phantom. These proof-of-concept tests showed this novel tomosynthesis device can detect lung nodules with low radiation dose to the patient. This technique has potential as an alternative to low dose chest CT for lung nodule screening and tracking.

Full 3-D modulation transfer function estimation of tomosynthesis system using modified Richardson-Lucy deconvolution

BACKGROUND

Tomosynthesis systems are three-dimensional (3-D) medical imaging devices that operate over limited acquisition angles using low radiation dosages. To measure the spatial resolution performance of a tomosynthesis system, the modulation transfer function (MTF) is widely used as a quantitative evaluation metric.

PURPOSE

We previously introduced a method to estimate the full 3-D MTF of a cone-beam computed tomography system using two-dimensional (2-D) Richardson-Lucy (RL) deconvolution with Tikhonov-Miller regularization. However, this method can not be applied directly to estimate the 3-D MTF of a tomosynthesis system, since the unique artifacts (i.e., shadow artifacts, spreading tails, directional blurring, and high-level noise) of the system produce several errors that lower the estimation performance. Varying positions of the negative pixels due to shadow artifacts and spreading tails cause inconsistent deconvolution performances at each of the directional projections, and the severe noise in the reconstructed images cause noise amplification during estimation. This work proposes several modifications to the previous method to resolve the inconsistent performance and noise amplification errors to increase the full 3-D MTF estimation accuracy.

METHODS

Three modifications were introduced to the 2-D RL deconvolution to prevent estimation errors and improve MTF estimation performance: non-negativity relaxation function, cost function to terminate the iterative process of RL deconvolution, and regularization strength for noise control. To validate the effectiveness of the proposed modifications, we reconstructed sphere phantoms from simulation and experimental tomosynthesis studies in the iso-center and offset-center positions as well as estimated the full 3-D MTFs using the previous and proposed methods. We compared the 3-D render images, central plane images, and center profiles of the estimated 3-D MTFs and calculated the full widths at half and tenth maximum for quantitative evaluation.

RESULTS

The previous method cannot estimate the full 3-D MTF of a tomosynthesis system; its inaccurate negative pixel relaxation produces circular-shaped errors, and the mean squared error based simple cost function for termination causes inconsistent estimation at each directional projection to diminish the clear edges of the low-frequency drop and missing sample regions. Noise amplification from lack of noise regularization is also seen in the previous method results. Compared to the previous method, the proposed method shows superior estimation performance at reducing errors in both the simulation and experimental studies regardless of object position. The proposed method preserves the low-frequency drop, missing sample regions from the limited acquisition angles, and missing cone region from the offset-center position; the estimated MTFs also show FWHM and FWTM values close to those of the ideal MTFs than with the previous method.

CONCLUSIONS

This work presents a method to estimate the full 3-D MTF of a tomosynthesis system. The proposed modifications prevent circular-shaped errors and noise amplification due to the geometry for limited acquisition angles and high noise levels. Compared to our previous method, the proposed scheme show better performance for estimating the 3-D MTF of the tomosynthesis system.

Upright Tomosynthesis of the Lumbar Spine

RATIONALE AND OBJECTIVES

This experimental study investigates the potential of lumbar spine tomosynthesis to offset the traditional limitations of radiographic and computed tomography imaging, that is, superimposition of anatomy and disregard of physiological load-bearing.

MATERIALS AND METHODS

A gantry-free twin robotic scanner was used to obtain lateral radiographs and tomosyntheses of the lumbar spine under weight-bearing conditions in eight body donors. Tomosynthesis protocols varied in terms of sweep angle (20 versus 40°), scan time (2.4 versus 4.8 seconds), and framerate (16 versus 30 fps). Image quality and vertebral endplate assessability were evaluated by five radiologists with 4-8 years of skeletal imaging experience. Aiming to identify potential diagnostic deterioration near the scan volume margins, readers additionally determined the craniocaudal extent of clinically acceptable image quality.

RESULTS

Tomosynthesis scans effectuated a substantial dose reduction compared to standard radiographs (3.8 ± 0.2 to 15.4 ± 0.8 dGy*cm2 versus 77.7 ± 34.8 dGy*cm2; p ≤ 0.021). Diagnostic image quality and endplate assessability were deemed highest for the 30 fps wide-angle tomosynthesis protocol with good to excellent interrater reliability (intraclass correlation coefficients: 0.846 and 0.946). Accordingly, the craniocaudal extent of acceptable image quality was substantially larger compared to radiography (26.9 versus 18.9 cm; p < 0.001), whereas no significant difference was ascertained for the tomosynthesis protocols with 16 fps (15.3-22.1 cm; all p ≥ 0.058).

CONCLUSION

Combining minimal radiation dose with superimposition-free visualization, 30 fps wide-angle tomosynthesis superseded radiography in all evaluated aspects. With superior diagnostic assessability despite significant dose reduction, load-bearing tomosynthesis appears promising as an alternative for first-line lumbar spine imaging in the future.

Tomosynthesis of the Appendicular Skeleton on a Twin Robotic X-ray System: A Cadaveric Fracture Study

RATIONALE AND OBJECTIVES

Aiming to offset image quality limitations in radiographs due to superimposition, this study investigates the diagnostic potential of appendicular skeleton tomosynthesis.

MATERIALS AND METHODS

Eight cadaveric extremities (four hands and feet) were examined employing the prototypical tomosynthesis mode of a twin robotic X-ray scanner. 12 protocols with varying sweep angles (10, 20 vs. 40°), frame rates (13 vs. 26 fps), and tube voltages (60 vs. 80 kV) were compared to radiographs. Four radiologists separately evaluated cortical and trabecular bone visualization and fracture patterns. Interreader reliability was assessed based on the intraclass correlation coefficient (ICC).

RESULTS

Radiation dose in radiography was 0.59 ± 0.20 dGy * cm2 versus 0.11 ± 0.00 to 2.46 ± 0.17 dGy * cm2 for tomosynthesis. Cortical bone display was inferior for radiographs compared to 40° and 20° tomosynthesis. Best results were ascertained for the 80 kV/40°/26 fps protocol. Trabecular bone depiction was also superior in tomosynthesis (p ≤ 0.009) and best with the 80 kV/10°/26 fps setting. Interreader reliability was moderate for cortical bone display (ICC 0.521, 95% confidence interval 0.356-0.641) and good for trabecular bone (0.759, 0.697-0.810). Diagnostic accuracy for articular involvement and multifragment situations was higher in tomosynthesis (93.8-100%/92.2-100%) vs. radiography (85.9%/82.8%.). Diagnostic confidence was also better in tomosynthesis (p ≤ 0.003).

CONCLUSION

Compared to radiography, tomosynthesis allows for superior assessability of cortical and trabecular bone and fracture morphology, especially at high framerates. Operating on a multipurpose X-ray system, tomosynthesis of the appendicular skeleton can be performed without additional scanner hardware.

Imaging in peripheral bronchoscopy

PURPOSE OF REVIEW

Historically the sampling of peripheral lung lesions via bronchoscopy has suffered from inferior diagnostic outcomes relative to transthoracic needle aspiration, and neither a successful bronchoscopic navigation nor a promising radial ultrasonographic image of one's target lesion guarantees a successful biopsy. Fortunately, many of peripheral bronchoscopy's shortcomings - including an inability to detect and compensate for computed tomography (CT)-body divergence, and the absence of tool-in-lesion confirmation - are potentially remediable through the use of improved intraprocedural imaging techniques.

RECENT FINDINGS

Recent advances in intraprocedural imaging, including the integration of cone beam CT, digital tomosynthesis, and augmented fluoroscopy into bronchoscopic procedures have yielded promising results. These advanced imaging modalities may improve the outcomes of peripheral bronchoscopy through the detection and correction of navigational errors, CT-body divergence, and malpositioned biopsy instruments.

SUMMARY

The incorporation of advanced imaging is an essential step in the improvement of peripheral bronchoscopic procedures.

Radiographic evaluation of mandibular third molars: an ex vivo comparative study between multilayer and conventional panoramic radiography

OBJECTIVES

To compare the multilayer panoramic radiography (MPAN) and conventional panoramic radiography (CPAN) in the evaluation of mandibular third molars using cone-beam computed tomography (CBCT) as a reference.

METHODS

CPAN, MPAN, and CBCT scans from 33 dry human mandibles were acquired using the OP300 Maxio unit, totalizing 56 mandibular third molars to be evaluated. Three examiners evaluated each third molar according to their position, depth of impaction in the mandibular ramus, proximity between the dental root apexes and the mandibular canal, and the presence of radiographic signs of proximity to the mandibular canal. In addition, when there was a distance between the root apexes and the mandibular canal, it was measured. As a reference, these same parameters were assessed in the CBCT scans by a fourth examiner. For the statistical analysis, the weighted Kappa, Bland Altman, and Wilcoxon tests were performed (α = 0.05).

RESULTS

The agreement between the assessments performed in the panoramic modalities with the CBCT ranged from 66.1% to 100.0% for the categorical variables. Overall, the agreement values of CPAN and MPAN with CBCT were similar. The distances between the dental root apex and the mandibular canal for both CPAN and MPAN were significantly underestimated compared to CBCT (p < 0.05). The intra- and interexaminer agreements of the examiners ranged from poor to almost perfect; in general, the agreements were higher in the evaluation performed in the MPAN than in the CPAN.

CONCLUSIONS

The MPAN performs similarly to CPAN for evaluating mandibular third molars and their proximity relationship to the mandibular canal.

CLINICAL RELEVANCE

Preoperative evaluation of lower mandibular third molars is usually performed using CPAN. Recently, a new tool, MPAN, was developed, which has not yet been tested for the evaluation of mandibular third molars and showed similar performance to CPAN in the present study. Future studies using MPAN are encouraged to evaluate other diagnostic tasks.

AI-based computer-aided diagnostic system of chest digital tomography synthesis: Demonstrating comparative advantage with X-ray-based AI systems

BACKGROUND

Compared with chest X-ray (CXR) imaging, which is a single image projected from the front of the patient, chest digital tomosynthesis (CDTS) imaging can be more advantageous for lung lesion detection because it acquires multiple images projected from multiple angles of the patient. Various clinical comparative analysis and verification studies have been reported to demonstrate this, but there is no artificial intelligence (AI)-based comparative analysis studies. Existing AI-based computer-aided detection (CAD) systems for lung lesion diagnosis have been developed mainly based on CXR images; however, CAD-based on CDTS, which uses multi-angle images of patients in various directions, has not been proposed and verified for its usefulness compared to CXR-based counterparts.

BACKGROUND AND OBJECTIVE

This study develops and tests a CDTS-based AI CAD system to detect lung lesions to demonstrate performance improvements compared to CXR-based AI CAD.

METHODS

We used multiple (e.g., five) projection images as input for the CDTS-based AI model and a single-projection image as input for the CXR-based AI model to compare and evaluate the performance between models. Multiple/single projection input images were obtained by virtual projection on the three-dimensional (3D) stack of computed tomography (CT) slices of each patient's lungs from which the bed area was removed. These multiple images result from shooting from the front and left and right 30/60∘. The projected image captured from the front was used as the input for the CXR-based AI model. The CDTS-based AI model used all five projected images. The proposed CDTS-based AI model consisted of five AI models that received images in each of the five directions, and obtained the final prediction result through an ensemble of five models. Each model used WideResNet-50. To train and evaluate CXR- and CDTS-based AI models, 500 healthy data, 206 tuberculosis data, and 242 pneumonia data were used, and three three-fold cross-validation was applied.

RESULTS

The proposed CDTS-based AI CAD system yielded sensitivities of 0.782 and 0.785 and accuracies of 0.895 and 0.837 for the (binary classification) performance of detecting tuberculosis and pneumonia, respectively, against normal subjects. These results show higher performance than the sensitivity of 0.728 and 0.698 and accuracies of 0.874 and 0.826 for detecting tuberculosis and pneumonia through the CXR-based AI CAD, which only uses a single projection image in the frontal direction. We found that CDTS-based AI CAD improved the sensitivity of tuberculosis and pneumonia by 5.4% and 8.7% respectively, compared to CXR-based AI CAD without loss of accuracy.

CONCLUSIONS

This study comparatively proves that CDTS-based AI CAD technology can improve performance more than CXR. These results suggest that we can enhance the clinical application of CDTS. Our code is available at https://github.com/kskim-phd/CDTS-CAD-P.

Digital Tomosynthesis: Review of Current Literature and Its Impact on Diagnostic Bronchoscopy

Bronchoscopy has garnered increased popularity in the biopsy of peripheral lung lesions. The development of navigational guided bronchoscopy systems along with radial endobronchial ultrasound (REBUS) allows clinicians to access and sample peripheral lesions. The development of robotic bronchoscopy improved localization of targets and diagnostic accuracy. Despite such technological advancements, published diagnostic yield remains lower compared to computer tomography (CT)-guided biopsy. The discordance between the real-time location of peripheral lesions and anticipated location from preplanned navigation software is often cited as the main variable impacting accurate biopsies. The utilization of cone beam CT (CBCT) with navigation-based bronchoscopy has been shown to assist with localizing targets in real-time and improving biopsy success. The resources, costs, and radiation associated with CBCT remains a hindrance in its wider adoption. Recently, digital tomosynthesis (DT) platforms have been developed as an alternative for real-time imaging guidance in peripheral lung lesions. In North America, there are several commercial platforms with distinct features and adaptation of DT. Early studies show the potential improvement in peripheral lesion sampling with DT. Despite the results of early observational studies, the true impact of DT-based imaging devices for peripheral lesion sampling cannot be determined without further prospective randomized trials and meta-analyses.

Stiffness and Strain Properties Derived From Digital Tomosynthesis-Based Digital Volume Correlation Predict Vertebral Strength Independently From Bone Mineral Density

Vertebral fractures are the most common osteoporotic fractures, but their prediction using standard bone mineral density (BMD) measurements from dual energy X-ray absorptiometry (DXA) is limited in accuracy. Stiffness, displacement, and strain distribution properties derived from digital tomosynthesis-based digital volume correlation (DTS-DVC) have been suggested as clinically measurable metrics of vertebral bone quality. However, the extent to which these properties correlate to vertebral strength is unknown. To establish this relationship, two independent experiments, one examining isolated T11 and the other examining L3 vertebrae within the L2-L4 segments from cadaveric donors were utilized. Following DXA and DTS imaging, the specimens were uniaxially compressed to fracture. BMD, bone mineral content (BMC), and bone area were recorded for the anteroposterior and lateromedial views from DXA, stiffness, endplate to endplate displacement and distribution statistics of intravertebral strains were calculated from DTS-DVC and vertebral strength was measured from mechanical tests. Regression models were used to examine the relationships of strength with the other variables. Correlations of BMD with vertebral strength varied between experimental groups (R2adj = 0.19-0.78). DTS-DVC derived properties contributed to vertebral strength independently from BMD measures (increasing R2adj to 0.64-0.95). DTS-DVC derived stiffness was the best single predictor (R2adj = 0.66, p < 0.0001) and added the most to BMD in models of vertebral strength for pooled T11 and L3 specimens (R2adj = 0.95, p < 0.0001). These findings provide biomechanical relevance to DTS-DVC calculated properties of vertebral bone and encourage further efforts in the development of the DTS-DVC approach as a clinical tool.

Digital Tomosynthesis as a Problem-Solving Technique to Confirm or Exclude Pulmonary Lesions in Hidden Areas of the Chest

Objectives: To evaluate the capability of digital tomosynthesis (DTS) to characterize suspected pulmonary lesions in the so-called hidden areas at chest X-ray (CXR). Materials and Methods: Among 726 patients with suspected pulmonary lesions at CXR who underwent DTS, 353 patients (201 males, 152 females; age 71.5 ± 10.4 years) revealed suspected pulmonary lesions in the apical, hilar, retrocardiac, or paradiaphragmatic lung zones and were retrospectively included. Two readers analyzed CXR and DTS images and provided a confidence score: 1 or 2 = definitely or probably benign pulmonary or extra-pulmonary lesion, or pulmonary pseudo-lesion deserving no further diagnostic work-up; 3 = indeterminate lesion; 4 or 5 = probably or definitely pulmonary lesion deserving further diagnostic work-up by CT. The nature of DTS findings was proven by CT (n = 108) or CXR during follow-up (n = 245). Results: In 62/353 patients the suspected lung lesions were located in the lung apex, in 92/353 in the hilar region, in 59/353 in the retrocardiac region, and in 140/353 in the paradiaphragmatic region. DTS correctly characterized the CXR findings as benign pulmonary or extrapulmonary lesion (score 1 or 2) in 43/62 patients (69%) in the lung apex region, in 56/92 (61%) in the pulmonary hilar region, in 40/59 (67%) in the retrocardiac region, and in 106/140 (76%) in the paradiaphragmatic region, while correctly recommending CT in the remaining cases due to the presence of true solid pulmonary lesion, with the exception of 22 false negative findings (60 false positive findings). DTS showed a significantly (p < 0.05) increased sensitivity, specificity, and overall diagnostic accuracy and area under ROC curve compared to CXR alone. Conclusions: DTS allowed confirmation or exclusion of the presence of true pulmonary lesions in the hidden areas of the chest.

Xenon-enhanced dual-energy tomosynthesis for functional imaging of respiratory disease-Concept and phantom study

BACKGROUND

Xenon-enhanced dual-energy (DE) computed tomography (CT) and hyperpolarized noble-gas magnetic resonance imaging (MRI) provide maps of lung ventilation that can be used to detect chronic obstructive pulmonary disease (COPD) early in its development and predict respiratory exacerbations. However, xenon-enhanced DE-CT requires high radiation doses and hyper-polarized noble-gas MRI is expensive and only available at a handful of institutions globally.

PURPOSE

To present xenon-enhanced dual-energy tomosynthesis (XeDET) for low-dose, low-cost functional imaging of respiratory disease in an experimental phantom study.

METHODS

We propose using digital tomosynthesis to produce Xe-enhanced low-energy (LE) and high-energy (HE) coronal images. DE subtraction of the LE and HE images is used to suppress soft tissues. We used an imaging phantom to investigate image quality in terms of the area under the reciever operating characteristic curve (AUC) for the Non-PreWhitening model observer with an Eye filter and internal noise (NPWEi). The phantom simulated anatomic clutter due to lung parenchyma and attenuation due to soft tissue and lung tissue. Aluminum slats were used to simulate rib structures. A stepwedge consisting of an acrylic casing with sealed cylindrical air-filled cavities was used to simulate ventilation defects with step thicknesses of 0.5, 1, and 2 cm and cylindrical radii of 0.5, 0.75, and 1 cm. The phantom was ventilated with Xe and projection data were acquired using a flat-panel detector, a tube-voltage combination of 60/140 kV with 1.2  mm of copper filtration on the HE spectrum and an angular range of ± 15 ∘ $\pm 15^{\circ}$ in 1° increments. The AUC of a NPWEi observer that has access only to a single coronal slice was calculated from measurements of the three-dimensional noise power spectrum and signal template. The AUC was calculated as a function of ventilation defect thickness and radius for total patient entrance air kermas ranging from 1.42 to 2.84 mGy with and without rib-simulating Al slats. For the AUC analysis, the observer internal noise level was obtained from an ad hoc calibration to a high-dose data set.

RESULTS

XeDET was able to suppress parenchyma-simulating clutter in coronal images enabling visualization of the simulated ventilation defects, but the limited angle acquisition resulted in residual clutter due to out-of-plane bone-mimmicking structures. The signal power of the defects increased linearly with defect radius and showed a ten-fold to fifteen-fold increase in signal power when the defect thickness increased from 0.5 to 2 cm. These trends agreed with theoretical predictions. Along the depth dimension, the power of the defects decreased exponentially with distance from the center of the defects with full-width half maxima that varied from 1.85 to 2.85 cm depending on the defect thickness and radius. The AUCs of the 1-cm-radius defect that was 2 cm in thickness ranged from good (0.8-0.9) to excellent (0.9-1.0) over the range of air kermas considered.

CONCLUSIONS

Xenon-enhanced DE tomosynthesis has the potential to enable functional imaging of respiratory disease and should be further investigated as a low-cost alternative to MRI-based approaches and a low-dose alternative to CT-based approaches.

Advances in Bone Joint Imaging-Metal Artifact Reduction

Numerous types of metal implants have been introduced in orthopedic surgery and are used in everyday practice. To precisely evaluate the postoperative condition of arthroplasty or trauma surgery, periprosthetic infection, and the loosening of implants, it is important to reduce artifacts induced by metal implants. In this review, we focused on technical advances in metal artifact reduction using digital tomosynthesis, computed tomography, and magnetic resonance imaging. We discussed new developments in diagnostic imaging methods and the continuous introduction of novel technologies to reduce metal artifacts; however, these innovations have not yet completely removed metal artifacts. Different algorithms need to be selected depending on the size, shape, material and implanted body parts of an implant. Future advances in metal artifact reduction algorithms and techniques and the development of new sequences may enable further reductions in metal artifacts even on original images taken previously. Moreover, the combination of different imaging modalities may contribute to further reductions in metal artifacts. Clinicians must constantly update their knowledge and work closely with radiologists to select the best diagnostic imaging method for each metal implant.

"Digital Tomosynthesis" As a Technique for the Evaluation of Endobronchial Stents in Lung Transplant Recipients

Lung transplant patients often suffer from posttransplant airway pathologies that require placement of endobronchial stents. In addition to surveillance bronchoscopy, patients often undergo radiographic stent evaluations. Chest x-rays are extremely limited in their ability to diagnose stent complications, so many patients require chest computed tomography (CT) scans for stent evaluation. Chest CT scans are costly and expose patients to higher cumulative radiation doses. Digital tomosynthesis (DTS) is an imaging modality that provides high-resolution images using limited angle tomography. The costs and radiation doses are comparable to conventional x-ray. We present a series of 4 postlung transplant patients with bronchial stents in whom we performed DTS and chest x-ray simultaneously. The DTS images were far superior to chest x-ray and comparable with CT in evaluating the placement and patency of the stents, especially in the case of silicone stents. Furthermore, the improved resolution provided clinically relevant diagnostic information that resulted in therapeutic bronchoscopy for suctioning of mucus impaction in one of the patients.

Diagnostic Performance and Advanced Imaging Reduction With Digital Tomosynthesis in Scaphoid Fracture Management

BACKGROUND

Management of scaphoid fractures often requires advanced imaging to achieve accurate diagnoses and appropriate treatment. Digital tomosynthesis (DTS) is a cross-sectional imaging modality that may be used to substitute magnetic resonance imaging or computed tomographic scans. The purpose of this study is to: (1) determine the diagnostic accuracy of DTS in occult scaphoid fractures; and (2) report on the reduction of other advanced imaging when using DTS.

METHODS

From May 2014 to October 2017, the charts of all patients who underwent scaphoid tomogram were retrospectively reviewed. The diagnostic accuracy of DTS for occult fracture was compared with 2-week follow-up plain films. To measure the reduction in utilization of advanced imaging, it was determined whether DTS eliminated the need for advanced imaging by providing adequate information regarding the clinical question.

RESULTS

A total of 78 patients underwent scaphoid tomography in this time frame: 39 for occult fracture, 33 for fracture union, 5 for fracture morphology, and 1 for hardware positioning. For the detection of occult fracture, DTS had a sensitivity of 100%, specificity of 83%, positive predictive value of 64%, and negative predictive value of 100%. Advanced imaging was not used in 35 of the remaining 39 patients based on the results obtained by DTS. In patients who did receive advanced imaging, 83% of tomograms provided conclusive diagnostic information.

CONCLUSIONS

Digital tomosynthesis increases the diagnostic sensitivity of occult scaphoid fractures, reducing unnecessary immobilization and advanced imaging. Digital tomosynthesis provides clinical detail beyond plain film, which reduces the need to obtain advanced imaging when assessing union, fracture pattern, and hardware placement.

Online Calibration of a Linear Micro Tomosynthesis Scanner

In a linear tomosynthesis scanner designed for imaging histologic samples of several centimeters size at 10 µm resolution, the mechanical instability of the scanning stage (±10 µm) exceeded the resolution of the image system, making it necessary to determine the trajectory of the stage for each scan to avoid blurring and artifacts in the images that would arise from the errors in the geometric information used in 3D reconstruction. We present a method for online calibration by attaching a layer of randomly dispersed micro glass beads or calcium particles to the bottom of the sample stage. The method was based on a parametric representation of the rigid body motion of the sample stage-marker layer assembly. The marker layer was easy to produce and proven effective in the calibration procedure.

Online Geometric Calibration of a Hybrid CT System for Ultrahigh-Resolution Imaging

A hybrid imaging system consisting of a standard computed tomography (CT) scanner and a low-profile photon-counting detector insert in contact with the patient's body has been used to produce ultrahigh-resolution images in a limited volume in chest scans of patients. The detector insert is placed on the patient bed as needed and not attached. Thus, its position and orientation in the scanner is dependent on the patient's position and scan settings. To allow accurate image reconstruction, we devised a method of determining the relative geometry of the detector insert and the CT scanner for each scan using fiducial markers. This method uses an iterative registration algorithm to align the markers in the reconstructed volume from the detector insert to that of the concurrent CT scan. After obtaining precise geometric information of the detector insert relative to the CT scanner, the two complementary sets of images are summed together to create a detailed image with reduced artifacts.

Effect of optical blurring of X-ray source on breast tomosynthesis image quality: Modulation transfer function, anatomical noise power spectrum, and signal detectability perspectives

We investigated the effect of the optical blurring of X-ray source on digital breast tomosynthesis (DBT) image quality using well-designed DBT simulator and table-top experimental systems. To measure the in-plane modulation transfer function (MTF), we used simulated sphere phantom and Teflon sphere phantom and generated their projection data using two acquisition modes (i.e., step-and-shoot mode and continuous mode). After reconstruction, we measured the in-plane MTF using reconstructed sphere phantom images. In addition, we measured the anatomical noise power spectrum (aNPS) and signal detectability. We constructed simulated breast phantoms with a 50% volume glandular fraction (VGF) of breast anatomy using the power law spectrum and inserted spherical objects with 1 mm, 2 mm, and 5 mm diameters as breast masses. Projection data were acquired using two acquisition modes, and in-plane breast images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. For the experimental study, we used BR3D breast phantom with 50% VGF and obtained projection data using a table-top experimental system. To compare the detection performance of the two acquisition modes, we calculated the signal detectability using the channelized Hotelling observer (CHO) with Laguerre-Gauss (LG) channels. Our results show that spatial resolution of in-plane image in continuous mode was degraded due to the optical blurring of X-ray source. This blurring effect was reflected in aNPS, resulting in large β values. From a signal detectability perspective, the signal detectability in step-and-shoot mode is higher than that in continuous mode for small spherical signals but not large spherical signals. Although the step-and-shoot mode has disadvantage in terms of scan time compared to the continuous mode, scanning in step-and-shoot mode is better for detecting small signals, indicating that there is a tradeoff between scan time and image quality.

X-ray zooming optics for analyzer-based multi-contrast computed tomography

An X-ray analyzer-based optics with a zoom function is proposed for observing various samples with apparent-absorption contrast, phase contrast and scattering contrast. The proposed X-ray optics consists of a collimator crystal and an analyzer crystal arranged in a nondispersive (+, -) geometry with a sample placed between them. For the implementation of the zoom function, an asymmetrically cut crystal in the rotated-inclined geometry was used for the analyzer. Proof-of-principle experiments were performed at the vertical wiggler beamline BL-14B of the Photon Factory. First, the magnification was set to 1×, and then it was zoomed into the optimal magnification (10×). At these magnifications, tri-modal contrast cross-sectional images of a sample were obtained by computed tomography. It was confirmed that the image quality at 10× was superior to that at 1×. This achievement opens up new possibilities for observing an entire sample or regions of interest within a sample at optimal magnification, and is expected to be useful for materials science, condensed matter physics, archeology and biomedical science.

Diagnostic Accuracy of Chest Digital Tomosynthesis in Patients Recovering after COVID-19 Pneumonia

Purpose: To assess the diagnostic accuracy of traditional chest X-ray (CXR) and digital tomosynthesis (DTS) compared to computed tomography (CT) in detecting pulmonary interstitial changes in patients having recovered from severe COVID-19. Materials and Methods: This was a retrospective observational study, and received local ethics committee approval. Patients suspected of having COVID-19 pneumonia upon emergency department admission between 1 March and 31 August 2020, and who underwent CXR followed by DTS and CT, were considered. Inclusion criteria were as follows: (1) patients with previous SARS-CoV-2 infection proven by a positive RT-PCR on nasopharyngeal swabs performed upon admission to the hospital, and with complete clinical recovery; (2) a diagnosis of SARS-CoV-2-related ARDS, according to the Berlin criteria, during hospitalization; (3) no recent history of other lung disease; and (4) complete imaging follow-up by CXR, DTS, and CT for at least 6 months and up to one year. Analysis of DTS images was carried out independently by two radiologists with 16 and 10 years of experience in chest imaging, respectively. The following findings were evaluated: (1) ground-glass opacities (GGOs); (2) air-space consolidations with or without air bronchogram; (3) reticulations; and (4) linear consolidation. Indicators of diagnostic performance of RX and digital tomosynthesis were calculated using CT as a reference. All data were analyzed using R statistical software (version 4.0.2, 2020). Results: Out of 44 patients initially included, 25 patients (17 M/8 F), with a mean age of 64 years (standard deviation (SD): 12), met the criteria and were included. The overall average numbers of findings confirmed by CT were GGOs in 11 patients, lung consolidations in 8 patients, 7 lung interstitial reticulations, and linear consolidation in 20 patients. DTS showed a significantly higher diagnostic accuracy compared to CXR in recognizing interstitial lung abnormalities—especially GGOs (p = 0.0412) and linear consolidations (p = 0.0009). The average dose for chest X-ray was 0.10 mSv (0.07–0.32), for DTS was 1.03 mSv (0.74–2.00), and for CT scan was 3 mSv. Conclusions: According to our results, DTS possesses a high diagnostic accuracy, compared with CXR, in revealing lung fibrotic changes in patients who have recovered from COVID-19 pneumonia.

Measuring the thickness of vertebral endplate and shell using digital tomosynthesis

The vertebral endplate and cortical shell play an important structural role and contribute to the overall strength of the vertebral body, are at highest risk of initial failure, and are involved in degenerative disease of the spine. The ability to accurately measure the thickness of these structures is therefore important, even if difficult due to relatively low resolution clinical imaging. We posit that digital tomosynthesis (DTS) may be a suitable imaging modality for measurement of endplate and cortical shell thickness owing to the ability to reconstruct multiplanar images with good spatial resolution at low radiation dose. In this study, for 25 cadaveric L1 vertebrae, average and standard deviation of endplate and cortical shell thickness were measured using images from DTS and microcomputed tomography (μCT). For endplate thickness measurements, significant correlations between DTS and μCT were found for all variables when comparing thicknesses measured in both the overall endplate volume (R² = 0.25-0.54) and when measurements were limited to a central range of coronal or sagittal slices (R² = 0.24-0.62). When compared to reference values from the overall shell volume, DTS thickness measurements were generally nonsignificant. However, when measurement of cortical shell thickness was limited to a range of central slices, DTS outcomes were significantly correlated with reference values for both sagittal and coronal central regions (R² = 0.21-0.49). DTS may therefore offer a means for measurement of endplate thickness and, within a limited sagittal or coronal measurement volume, for measurement of cortical shell thickness.

Evaluation of a Generative Adversarial Network to Improve Image Quality and Reduce Radiation-Dose during Digital Breast Tomosynthesis

In this study, we evaluated the improvement of image quality in digital breast tomosynthesis under low-radiation dose conditions of pre-reconstruction processing using conditional generative adversarial networks [cGAN (pix2pix)]. Pix2pix pre-reconstruction processing with filtered back projection (FBP) was compared with and without multiscale bilateral filtering (MSBF) during pre-reconstruction processing. Noise reduction and preserve contrast rates were compared using full width at half-maximum (FWHM), contrast-to-noise ratio (CNR), peak signal-to-noise ratio (PSNR), and structural similarity (SSIM) in the in-focus plane using a BR3D phantom at various radiation doses [reference-dose (automatic exposure control reference dose: AECrd), 50% and 75% reduction of AECrd] and phantom thicknesses (40 mm, 50 mm, and 60 mm). The overall performance of pix2pix pre-reconstruction processing was effective in terms of FWHM, PSNR, and SSIM. At ~50% radiation-dose reduction, FWHM yielded good results independently of the microcalcification size used in the BR3D phantom, and good noise reduction and preserved contrast. PSNR results showed that pix2pix pre-reconstruction processing represented the minimum in the error with reference FBP images at an approximately 50% reduction in radiation-dose. SSIM analysis indicated that pix2pix pre-reconstruction processing yielded superior similarity when compared with and without MSBF pre-reconstruction processing at ~50% radiation-dose reduction, with features most similar to the reference FBP images. Thus, pix2pix pre-reconstruction processing is promising for reducing noise with preserve contrast and radiation-dose reduction in clinical practice.

Frequency of Change in Assessment from Bony Union to Nonunion after Lumbar Interbody Fusion: A Multicenter Study

Introduction

Assessments of early postoperative bony union after posterior lumbar interbody fusion via computed tomography (CT) have revealed cases in which interbody fixation by bony union resulted in nonfusion due to bone absorption. The apparent bone union state reverted to a nonunion state several months later, exhibiting a so-called “fake union” phenomenon. Additionally, few reports have evaluated the effect of teriparatide on bony union. The present study aimed to evaluate the frequency of change in assessment from fusion to nonfusion in the postoperative follow-up of lumbar interbody fusion, compare the late postoperative bony union rates in groups with or without early postoperative fusion, and examine the effect of postoperative teriparatide in those groups.

Methods

Sixty-nine subjects enrolled from multiple hospitals were prospectively evaluated following single-level lumbar interbody fusion. The patients were randomly allocated into treatment with or without weekly postoperative teriparatide. The subjects were then classified as having bony union or nonfusion at 2 months postoperatively, and fusion rates at 6 months were compared. For the evaluation of bony union, blinded radiological examinations were performed via CT. Additional comparisons were made according to teriparatide use.

Results

The rate of nonunion at 6 months postoperatively in patients with fusion at 2 months postoperatively was 27.8%. Among subjects with bony union at 2 months postoperatively, the fusion rate at 6 months in those who received teriparatide was 93.3% (p=0.027) versus 57.1% in those who did not.

Conclusions

The rate of nonunion at 6 months postoperatively in patients exhibiting union at 2 months after surgery was 27.8%. Postoperative weekly teriparatide treatment significantly reduced the rate of fake union.

A novel few-views arrangement of the fixed X-ray tubes for tomosynthesis

PURPOSE

Tomosynthesis is a technique that reconstructs a volume image from limited-angle projection data. In conventional tomosynthesis, the examination time is long, so it can be difficult for patients to hold their breath during certain examinations, such as chest imaging. Few-views tomosynthesis, which uses a linear arrangement of fixed X-ray tubes and enables an image to be obtained within 1 s, was found to be useful in the clinical setting in our previous study. In the present study, we attempted to develop a novel few-views tomosynthesis system that can obtain images with an improved image quality.

METHODS

A novel few-views arrangement of X-ray tubes was proposed and the image reconstruction method with regularization term was applied. The linear arrangement was used for the X-ray tube arrangement in our previous few-views tomosynthesis, in contrast, a circular arrangement was proposed in this study. The validation of this system was conducted with a numerical simulation and a real data experiment.

RESULTS

The wider the scan angle, the more the object shadow spreads from "in-plane", allowing for artifact suppression. In the circular arrangement, the constant scan angle of θ is used, but in the linear arrangement the scan angle is set from 0 to θ. The artifacts in "out-of-plane" were more strongly suppressed in the circular arrangement than in the linear arrangement.

CONCLUSIONS

Artifacts spreading in the z-direction were more strongly suppressed using the circular arrangement than the linear arrangement. Therefore, the circular arrangement was deemed appropriate for few-views tomosynthesis.

The development of breast radiology: the Acta Radiologica perspective

The encouraging results of modern breast cancer care builds on tremendous improvements in diagnostics and therapy during the 20th century. Scandinavian countries have made important footprints in the development of breast diagnostics regarding technical development of imaging, cell and tissue sampling methods and, not least, population screening with mammography. The multimodality approach in combination with multidisciplinary clinical work in breast cancer serve as a role model for the management of many cancer types worldwide. The development of breast radiology is well represented in the research published in this journal and this historical review will describe the most important steps.

Use of Digital Tomosynthesis in Assessing Accurate Medial Epicondyle Fracture Displacement as Compared With Conventional Radiography and Computed Tomography

INTRODUCTION

Medial epicondyle fracture displacement is notoriously difficult to determine on conventional radiography, and follow-up computed tomography (CT) is often obtained to measure precise displacement. Another option for fracture characterization is digital tomosynthesis (DT), a technology providing high in-plane resolution of bony anatomy by acquiring multiple low-dose images in a linear arc. Advantages of DT include lower radiation exposure and lower cost than CT, rapid image acquisition, and a similar patient experience to conventional radiography. The digital application of tomosynthesis is relatively new and is integrated as an add-on feature with modern radiography equipment. This study compares DT, CT and conventional radiography for measurement accuracy in medial epicondyle fractures with the goal of determining relative accuracy in measuring medial epicondyle fracture displacement.

METHODS

Medial epicondyle fractures were created in 5 cadaveric elbow specimens. Each specimen was imaged with conventional radiography, DT, and CT. True displacement measured by digital calipers was compared with "measured" displacement for each image acquisition. CT images included axial, sagittal, and coronal reformats. DT images of the elbow included anteroposterior (AP) longitudinal and transverse, lateral longitudinal and transverse, and axial longitudinal and transverse. Conventional radiographs included AP, lateral, and axial distal humerus images. Four physicians reviewed all images 3 months later. Each reviewer independently measured maximum apparent fracture displacement to the nearest 0.1 mm. Measurement accuracy was calculated as percent difference [(measured displacement-actual displacement)/actual displacement] for each acquisition. Mean, median, and SD for measurement accuracy were calculated. Two-tailed paired t tests were performed on each acquisition to compare the measurement accuracy.

RESULTS

Compared with conventional radiographs, accuracy of DT was superior in AP longitudinal (P=0.03), AP transverse (P=0.01), axial longitudinal (P=0.0001), and axial transverse projections (P=0.001). Accuracy of CT was superior to conventional radiography in the AP projection (P=0.03), but was equivalent in the axial projection (P=0.9). Accuracy of CT was similar to DT in AP longitudinal (P=0.6), AP transverse (P=0.5), and axial longitudinal projections (P=0.07). Accuracy of DT in the axial transverse projection was superior to CT (P=0.03).

CONCLUSION

DT is more accurate than conventional radiography (both AP and axial views) and as accurate as CT in assessing millimeters of displacement of medial epicondyle fracture fragments.

LEVEL OF EVIDENCE

Level IV-diagnostic study.

Improved detection of solitary pulmonary nodules on radiographs compared with deep bone suppression imaging

Background

The present study aimed to investigate whether deep bone suppression imaging (BSI) could increase the diagnostic performance for solitary pulmonary nodule detection compared with digital tomosynthesis (DTS), dual-energy subtraction (DES) radiography, and conventional chest radiography (CCR).

Methods

A total of 256 patients (123 with a solitary pulmonary nodule, 133 with normal findings) were included in the study. The confidence score of 6 observers determined the presence or absence of pulmonary nodules in each patient. These were first analyzed using a CCR image, then with CCR plus deep BSI, then with CCR plus DES radiography, and finally with DTS images. Receiver-operating characteristic curves were used to evaluate the performance of the 6 observers in the detection of pulmonary nodules.

Results

For the 6 observers, the average area under the curve improved significantly from 0.717 with CCR to 0.848 with CCR plus deep BSI (P<0.01), 0.834 with CCR plus DES radiography (P<0.01), and 0.939 with DTS (P<0.01). Comparisons between CCR and CCR plus deep BSI found that the sensitivities of the assessments by the 3 residents increased from 53.2% to 69.5% (P=0.014) for nodules located in the upper lung field, from 30.6% to 44.6% (P=0.015) for nodules that were partially/completely obscured by the bone, and from 33.2% to 45.8% (P=0.006) for nodules <10 mm.

Conclusions

The deep BSI technique can significantly increase the sensitivity of radiology residents for solitary pulmonary nodules compared with CCR. Increased detection was seen mainly for smaller nodules, nodules with partial/complete obscuration, and nodules located in the upper lung field.

The Effect of Dose Reduction on Overall Image Quality in Clinical Chest Tomosynthesis

RATIONALE AND OBJECTIVES

To evaluate the effect of reduction in effective dose on the reproduction of anatomical structures in chest tomosynthesis (CTS).

MATERIALS AND METHODS

Twenty-four CTS examinations acquired at exposure settings resulting in an effective dose of 0.12 mSv for an average sized patient were included in the study. The examinations underwent simulated dose reduction to dose levels corresponding to 32%, 50%, and 70% of the original dose using a previously described and validated method. The image quality was evaluated by five thoracic radiologists who rated the fulfillment of specified image quality criteria in a visual grading study. The ratings for each image quality criterion in the dose-reduced images were compared to the corresponding ratings for the full-dose examinations using visual grading characteristics (VGC) analysis. The area under the resulting VGC curve (AUC_VGC) provides a measure of the difference between the ratings, where an AUC_VGC of 0.5 indicates no difference.

RESULTS

The dose reductions resulted in inferior reproduction of structures compared to the original dose level (AUC_VGC <0.5). Structures in the central region of the lung obtained the lowest AUC_VGC for each dose level whereas the reproduction of structures in the parenchyma was least affected by the dose reduction.

CONCLUSION

Although previous studies have shown that dose reduction in CTS is possible without affecting the performance of certain clinical tasks, the reproduction of normal anatomical structures is significantly degraded even at small reductions. It is therefore important to consider the clinical purpose of the CTS examinations before deciding on a permanent dose reduction.

Digital Tomosynthesis versus Conventional Radiography for Evaluating Osteonecrosis of the Femoral Head

Objective

The aim of this study was to compare the diagnostic performances of digital tomosynthesis (DTS) and conventional radiography in detecting osteonecrosis of the femoral head (ONFH) using computed tomography (CT), as the reference standard and evaluate the diagnostic reproducibility of DTS.

Materials and Methods

Forty-five patients (24 male and 21 female; age range, 25–77 years) with clinically suspected ONFH underwent anteroposterior radiography, DTS, and CT. Two musculoskeletal radiologists independently evaluated the presence and type of ONFH. The diagnostic performance of radiography and DTS in detecting the presence of ONFH and determining the types of ONFH were evaluated. The interobserver and intraobserver reliabilities of each imaging modality were analyzed using Cohen's kappa.

Results

DTS had higher sensitivity (89.4%–100% vs. 74.5%–76.6%) and specificity (97.3%–100% vs. 78.4%–83.8%) for ONFH detection than radiography. DTS showed higher performance than radiography in identifying the subtypes of ONFH with statistical significance in one reader (type 1, 100% vs. 30.8%, p = 0.004; type II, 97.1% vs. 73.5%, p = 0.008). The interobserver agreement was excellent for DTS and moderate for radiography (kappa of 0.86 vs. 0.57, respectively). The intraobserver agreement for DTS was higher than that of radiography (kappa of 0.96 vs. 0.69, respectively).

Conclusion

DTS showed higher diagnostic performance and reproducibility than radiography in detecting ONFH. DTS may be used as a first-line diagnostic modality instead of radiography for patients suspected of having ONFH.

Usefulness of a Metal Artifact Reduction Algorithm in Digital Tomosynthesis Using a Combination of Hybrid Generative Adversarial Networks

In this study, a novel combination of hybrid generative adversarial networks (GANs) comprising cycle-consistent GAN, pix2pix, and (mask pyramid network) MPN (CGpM-metal artifact reduction [MAR]), was developed using projection data to reduce metal artifacts and the radiation dose during digital tomosynthesis. The CGpM-MAR algorithm was compared with the conventional filtered back projection (FBP) without MAR, FBP with MAR, and convolutional neural network MAR. The MAR rates were compared using the artifact index (AI) and Gumbel distribution of the largest variation analysis using a prosthesis phantom at various radiation doses. The novel CGpM-MAR yielded an adequately effective overall performance in terms of AI. The resulting images yielded good results independently of the type of metal used in the prosthesis phantom (p < 0.05) and good artifact removal at 55% radiation-dose reduction. Furthermore, the CGpM-MAR represented the minimum in the model with the largest variation at 55% radiation-dose reduction. Regarding the AI and Gumbel distribution analysis, the novel CGpM-MAR yielded superior MAR when compared with the conventional reconstruction algorithms with and without MAR at 55% radiation-dose reduction and presented features most similar to the reference FBP. CGpM-MAR presents a promising method for metal artifact and radiation-dose reduction in clinical practice.

Multi-objective optimization for structured illumination in dynamic x-ray tomosynthesis

Dynamic coded x-ray tomosynthesis (CXT) uses a set of encoded x-ray sources to interrogate objects lying on a moving conveyor mechanism. The object is reconstructed from the encoded measurements received by the uniform linear array detectors. We propose a multi-objective optimization (MO) method for structured illuminations to balance the reconstruction quality and radiation dose in a dynamic CXT system. The MO framework is established based on a dynamic sensing geometry with binary coding masks. The Strength Pareto Evolutionary Algorithm 2 is used to solve the MO problem by jointly optimizing the coding masks, locations of x-ray sources, and exposure moments. Computational experiments are implemented to assess the proposed MO method. They show that the proposed strategy can obtain a set of Pareto optimal solutions with different levels of radiation dose and better reconstruction quality than the initial setting.

Compressive X-ray tomosynthesis using model-driven deep learning

Compressive X-ray tomosynthesis uses a few two-dimensional projection measurements modulated by coding masks to reconstruct the three-dimensional object that can be sparsely represented on a predefined basis. However, the coding mask optimization and object reconstruction require significant computing resources. In addition, existing methods fall short to exploits the synergy between the encoding and reconstruction stages to approach the global optimum. This paper proposes a model-driven deep learning (MDL) approach to significantly improve the computational efficiency and accuracy of tomosynthesis reconstruction. A unified framework is developed to jointly optimize the coding masks and the neural network parameters, which effectively increase the degrees of optimization freedom. It shows that the computational efficiency of coding mask optimization and image reconstruction can be improved by more than one order of magnitude. Furthermore, the performance of reconstruction results is significantly improved.

Diagnostic performance of tomosynthesis for evaluation of bone tumors and tumor-like lesions: a comparison with radiography

BACKGROUND

Even though radiologic diagnosis of bone tumors and tumor-like lesions is usually based on radiographs, radiographically faint imaging features sometimes remain challenging due to overlapping anatomical structures.

PURPOSE

To compare tomosynthesis with radiography for the evaluation of bone tumors and tumor-like lesions.

MATERIAL AND METHODS

Forty-seven bone tumors and tumor-like lesions were assessed with radiographs and tomosynthesis images. Two radiologists independently analyzed imaging features of lesions, including margin, periosteal reaction, cortical thinning, matrix mineralization, cortical destruction (such as pathologic fracture), and extraosseous soft-tissue extension. Computed tomography (CT) imaging was used as a reference method. Diagnostic performances of radiography and tomosynthesis were analyzed and compared based on sensitivity, specificity, accuracy, positive predictive value, and negative predictive value. Effective radiation dose was compared among the three imaging modalities by phantom studies.

RESULTS

Inter-observer variability (kappa value) for imaging features was slight to moderate on radiography (0.167-0.588), whereas it was nearly perfect on tomosynthesis (0.898-1.000) except for extraosseous soft-tissue extension (0.647 vs. 0.647). Tomosynthesis showed significantly higher sensitivity than radiography in evaluating the margin for bone tumors or tumor-like lesions (1.00 vs. 0.85; P = 0.016), and significantly higher accuracy than radiography in evaluating the margin and matrix mineralization for those (1.00 vs. 0.85; P = 0.016 and 0.91 vs.0.77; P = 0.023, respectively). In phantom studies, mean effective radiation doses were highest in order of CT, tomography, and radiography.

CONCLUSION

Tomosynthesis increases sensitivity and accuracy of the margin as well as accuracy of the matrix mineralization of bone tumors and tumor-like lesions compared to radiography.

Effect of x-ray energy on the radiological image quality in propagation-based phase-contrast computed tomography of the breast

Purpose: Breast cancer is the most common cancer in women in developing and developed countries and is responsible for 15% of women's cancer deaths worldwide. Conventional absorption-based breast imaging techniques lack sufficient contrast for comprehensive diagnosis. Propagation-based phase-contrast computed tomography (PB-CT) is a developing technique that exploits a more contrast-sensitive property of x-rays: x-ray refraction. X-ray absorption, refraction, and contrast-to-noise in the corresponding images depend on the x-ray energy used, for the same/fixed radiation dose. The aim of this paper is to explore the relationship between x-ray energy and radiological image quality in PB-CT imaging. Approach: Thirty-nine mastectomy samples were scanned at the imaging and medical beamline at the Australian Synchrotron. Samples were scanned at various x-ray energies of 26, 28, 30, 32, 34, and 60 keV using a Hamamatsu Flat Panel detector at the same object-to-detector distance of 6 m and mean glandular dose of 4 mGy. A total of 132 image sets were produced for analysis. Seven observers rated PB-CT images against absorption-based CT (AB-CT) images of the same samples on a five-point scale. A visual grading characteristics (VGC) study was used to determine the difference in image quality. Results: PB-CT images produced at 28, 30, 32, and 34 keV x-ray energies demonstrated statistically significant higher image quality than reference AB-CT images. The optimum x-ray energy, 30 keV, displayed the largest area under the curve ( AUC VGC ) of 0.754 ( p = 0.009 ). This was followed by 32 keV ( AUC VGC = 0.731 , p ≤ 0.001 ), 34 keV ( AUC VGC = 0.723 , p ≤ 0.001 ), and 28 keV ( AUC VGC = 0.654 , p = 0.015 ). Conclusions: An optimum energy range (around 30 keV) in the PB-CT technique allows for higher image quality at a dose comparable to conventional mammographic techniques. This results in improved radiological image quality compared with conventional techniques, which may ultimately lead to higher diagnostic efficacy and a reduction in breast cancer mortalities.

[Extraction of respiratory signals from chest tomosynthesis]

OBJECTIVE

To analyze the respiratory motion of the scanned object during acquisition of digital chest tomosynthesis (CTS) using a linear model.

OBJECTIVE

Respiratory signals were generated by extracting the motion of the diaphragm from the projection radiographs. The diaphragm trajectory obtained by dynamic programming (DP) was modeled and fitted, and according to the fitting of the data, the base motion curve and respiratory signal curve of the diaphragm were separated. Multipurpose chest phantom data, simulated digital Xcat phantom data and the datasets of 3 clinical patients were used to validate the performance of the proposed method.

OBJECTIVE

The motion trajectory of the diaphragm extracted from multipurpose chest phantom simulation data was linear. The respiratory signals could be effectively extracted from the 3 datasets of clinical patients in different respiratory states. The correlation coefficient between the respiratory signal extracted in Xcat simulation experiment and the original design was 0.9797.

OBJECTIVE

The linear model can effectively obtain the respiratory motion information of patients in real time, thus enabling the physicians to make clinical decisions on a rescan.

Directional-TV algorithm for image reconstruction from limited-angular-range data

Investigation of image reconstruction from data collected over a limited-angular range in X-ray CT remains a topic of active research because it may yield insight into the development of imaging workflow of practical significance. This reconstruction problem is well-known to be challenging, however, because it is highly ill-conditioned. In the work, we investigate optimization-based image reconstruction from data acquired over a limited-angular range that is considerably smaller than the angular range in short-scan CT. We first formulate the reconstruction problem as a convex optimization program with directional total-variation (TV) constraints applied to the image, and then develop an iterative algorithm, referred to as the directional-TV (DTV) algorithm for image reconstruction through solving the optimization program. We use the DTV algorithm to reconstruct images from data collected over a variety of limited-angular ranges for breast and bar phantoms of clinical- and industrial-application relevance. The study demonstrates that the DTV algorithm accurately recovers the phantoms from data generated over a significantly reduced angular range, and that it considerably diminishes artifacts observed otherwise in reconstructions of existing algorithms. We have also obtained empirical conditions on minimal-angular ranges sufficient for numerically accurate image reconstruction with the DTV algorithm.

Bone health assessment via digital wrist tomosynthesis in the mammography setting

Bone fractures attributable to osteoporosis are a significant problem. Though preventative treatment options are available for individuals who are at risk of a fracture, a substantial number of these individuals are not identified due to lack of adherence to bone screening recommendations. The issue is further complicated as standard diagnosis of osteoporosis is based on bone mineral density (BMD) derived from dual energy x-ray absorptiometry (DXA), which, while helpful in identifying many at risk, is limited in fully predicting risk of fracture. It is reasonable to expect that bone screening would become more prevalent and efficacious if offered in coordination with digital breast tomosynthesis (DBT) exams, provided that osteoporosis can be assessed using a DBT modality. Therefore, the objective of the current study was to explore the feasibility of using digital tomosynthesis imaging in a mammography setting. To this end, we measured density, cortical thickness and microstructural properties of the wrist bone, correlated these to reference measurements from microcomputed tomography and DXA, demonstrated the application in vivo in a small group of participants, and determined the repeatability of the measurements. We found that measurements from digital wrist tomosynthesis (DWT) imaging with a DBT scanner were highly repeatable ex vivo (error = 0.05%-9.62%) and in vivo (error = 0.06%-10.2%). In ex vivo trials, DWT derived BMDs were strongly correlated with reference measurements (R = 0.841-0.980), as were cortical thickness measured at lateral and medial cortices (R = 0.991 and R = 0.959, respectively) and the majority of microstructural measures (R = 0.736-0.991). The measurements were quick and tolerated by human patients with no discomfort, and appeared to be different between young and old participants in a preliminary comparison. In conclusion, DWT is feasible in a mammography setting, and informative on bone mass, cortical thickness, and microstructural qualities that are known to deteriorate in osteoporosis. To our knowledge, this study represents the first application of DBT for imaging bone. Future clinical studies are needed to further establish the efficacy for diagnosing osteoporosis and predicting risk of fragility fracture using DWT.

X-ray Dark-Field Imaging (XDFI)-a Promising Tool for 3D Virtual Histopathology

X-ray dark-field imaging (XDFI) utilizing a thin silicon crystal under Laue case enables visualizing three-dimensional (3D) morphological alterations of human tissue. XDFI uses refraction-contrast derived from phase shift rather than absorption as the main X-ray image contrast source to render 2D and 3D images of tissue specimens in unprecedented detail. The unique features of XDFI are its extremely high sensitivity (approximately 1000:1 compared to absorption for soft tissues under X-ray energy of around 20 keV, theoretically) and excellent resolution (8.5 μm) without requiring contrast medium or staining. Thus, XDFI-computed tomography can generate 3D virtual histological images equivalent to those of stained histological sections pathologists observe under low-power light microscopy as far as organs and tissues selected as samples in preliminary studies. This paper reviews the fundamental principles and the potential of XDFI, describes two optical setups for XDFI with examples, illustrates features of XDFI that are salient for histopathology, and presents XDFI examples of refraction-contrast images of atherosclerotic plaques, musculoskeletal tissue, neuronal tissue, and breast cancer specimens. Availability of this X-ray imaging in routine histopathological evaluations of tissue specimens would help guide clinical decision making by highlighting suspicious areas in unstained, thick sections for further sampling and analysis using conventional histopathological techniques. XDFI is a promising tool for 3D virtual histopathology.

X-ray microtomosynthesis of unstained pathology tissue samples

In pathology protocols, a tissue block, such as one containing a mouse brain or a biopsy sample from a patient, can produce several hundred thin sections. Substantial time may be required to analyse all sections. In cases of uncertainty regarding which sections to focus on, noninvasive scout imaging of intact blocks can help in guiding the pathology procedure. The scouting step is ideally done in a time window of minutes without special sample preparation that may interfere with the pathology procedures. The challenge is to obtain some visibility of unstained tissue structures at sub‐10 µm resolution.

We explored a novel x‐ray tomosynthesis method as a way to maximise contrast‐to‐noise ratio, a determinant of tissue visibility. It provided a z‐stack of thousands of images at 7.3 μm resolution (10% contrast, half‐period of 68.5 line pairs/mm), in scans of 5‐15 minutes. When compared with micro‐CT scans, the straight‐line tomosynthesis scan did not need to rotate the sample, which allowed flat samples, such as paraffin blocks, to be kept as close as possible to the x‐ray source. Thus, given the same hardware, scan time and resolution, this mode maximised the photon flux density through the sample, which helped in maximising the contrast‐to‐noise ratio. The tradeoff of tomosynthesis is incomplete 3D information.

The microtomosynthesis scanner has scanned 110 unstained human and animal tissue samples as part of their respective pathology protocols. In all cases, the z‐stack of images showed tissue structures that guided sectioning or provided correlative structural information. We describe six examples that presented different levels of visibility of soft tissue structures. Additionally, in a set of coronary artery samples from an HIV patient donor, microtomosynthesis made a new discovery of isolated focal calcification in the internal elastic lamina of coronary wall, which was the onset of medial calcific sclerosis in the arteries.

FleXCT: a flexible X-ray CT scanner with 10 degrees of freedom

Laboratory based X-ray micro-CT is a non-destructive testing method that enables three dimensional visualization and analysis of the internal and external morphology of samples. Although a wide variety of commercial scanners exist, most of them are limited in the number of degrees of freedom to position the source and detector with respect to the object to be scanned. Hence, they are less suited for industrial X-ray imaging settings that require advanced scanning modes, such as laminography, conveyor belt scanning, or time-resolved imaging (4DCT). We introduce a new X-ray scanner FleXCT that consists of a total of ten motorized axes, which allow a wide range of non-standard XCT scans such as tiled and off-centre scans, laminography, helical tomography, conveyor belt, dynamic zooming, and X-ray phase contrast imaging. Additionally, a new software tool 'FlexRayTools' was created that enables reconstruction of non-standard XCT projection data of the FleXCT instrument using the ASTRA Toolbox, a highly efficient and open source set of tools for tomographic projection and reconstruction.

Enhancing digital tomosynthesis (DTS) for lung radiotherapy guidance using patient-specific deep learning model

Digital tomosynthesis (DTS) has been proposed as a fast low-dose imaging technique for image-guided radiation therapy (IGRT). However, due to the limited scanning angle, DTS reconstructed by the conventional FDK method suffers from significant distortions and poor plane-to-plane resolutions without full volumetric information, which severely limits its capability for image guidance. Although existing deep learning-based methods showed feasibilities in restoring volumetric information in DTS, they ignored the inter-patient variabilities by training the model using group patients. Consequently, the restored images still suffered from blurred and inaccurate edges. In this study, we presented a DTS enhancement method based on a patient-specific deep learning model to recover the volumetric information in DTS images. The main idea is to use the patient-specific prior knowledge to train the model to learn the patient-specific correlation between DTS and the ground truth volumetric images. To validate the performance of the proposed method, we enrolled both simulated and real on-board projections from lung cancer patient data. Results demonstrated the benefits of the proposed method: (1) qualitatively, DTS enhanced by the proposed method shows CT-like high image quality with accurate and clear edges; (2) quantitatively, the enhanced DTS has low-intensity errors and high structural similarity with respect to the ground truth CT images; (3) in the tumor localization study, compared to the ground truth CT-CBCT registration, the enhanced DTS shows 3D localization errors of ≤0.7 mm and ≤1.6 mm for studies using simulated and real projections, respectively; and (4), the DTS enhancement is nearly real-time. Overall, the proposed method is effective and efficient in enhancing DTS to make it a valuable tool for IGRT applications.

Endorectal digital prostate tomosynthesis (endoDPT): a proof-of-concept study

In this study we present endorectal digital prostate tomosynthesis (endoDPT), a proposed method of high resolution prostate imaging using an endorectal x-ray sensor and an external x-ray source. endoDPT may be useful for visualizing the fine detail of small structures such as low dose rate brachytherapy (LDRBT) seeds that are difficult to visualize with current methods. The resolution of endoDPT was characterized through measurement of the modulation transfer function (MTF) and artifact spread function (ASF) in computational and physical phantoms. The qualitative resolution of endoDPT was assessed relative to computed tomography (CT) through imaging of LDRBT seeds implanted inex vivocanine prostates. The x-ray sensor MTF reached 10% at 11.50 mm^-1, the reconstruction algorithm MTF reached a maximum at 7.08 mm^-1, and the ASF was 2.5 mm (full-width at half-maximum). Fine structures in LDRBT seeds like the 0.05 mm thick shell were visible with endoDPT but not CT. All endoDPT images exhibited an overshoot artifact. The measured MTFs were consistent with other studies using similar x-ray sensors and demonstrated improved resolution compared to digital breast tomosynthesis; this result was due to the smaller endoDPT x-ray sensor detection element size and quantitatively demonstrates the high resolution of endoDPT. The ASF demonstrated worse depth resolution compared to in-plane resolution, due to partial angular sampling; partial angular sampling also caused the observed overshoot artifact in the endoDPT images. However, endoDPT still was able to visualize fine structures such as the LDRBT seed shell to a much higher degree than CT. This high-resolution visualization may be useful for improvements in patient specific LDRBT dosimetry. Overall, these results indicate endoDPT is capable of high in-plane spatial resolution and is thus well poised for optimization and studies assessing clinical utility.

Improved digital chest tomosynthesis image quality by use of a projection-based dual-energy virtual monochromatic convolutional neural network with super resolution

We developed a novel dual-energy (DE) virtual monochromatic (VM) very-deep super-resolution (VDSR) method with an unsharp masking reconstruction algorithm (DE–VM–VDSR) that uses projection data to improve the nodule contrast and reduce ripple artifacts during chest digital tomosynthesis (DT). For estimating the residual errors from high-resolution and multiscale VM images from the projection space, the DE–VM–VDSR algorithm employs a training network (mini-batch stochastic gradient-descent algorithm with momentum) and a hybrid super-resolution (SR) image [simultaneous algebraic reconstruction technique (SART) total-variation (TV) first-iterative shrinkage–thresholding algorithm (FISTA); SART–TV–FISTA] that involves subjective reconstruction with bilateral filtering (BF) [DE–VM–VDSR with BF]. DE-DT imaging was accomplished by pulsed X-ray exposures rapidly switched between low (60 kV, 37 projection) and high (120 kV, 37 projection) tube-potential kVp by employing a 40° swing angle. This was followed by comparison of images obtained employing the conventional polychromatic filtered backprojection (FBP), SART, SART–TV–FISTA, and DE–VM–SART–TV–FISTA algorithms. The improvements in contrast, ripple artifacts, and resolution were compared using the signal-difference-to-noise ratio (SDNR), Gumbel distribution of the largest variations, radial modulation transfer function (radial MTF) for a chest phantom with simulated ground-glass opacity (GGO) nodules, and noise power spectrum (NPS) for uniform water phantom. The novel DE–VM–VDSR with BF improved the overall performance in terms of SDNR (DE–VM–VDSR with BF: 0.1603, without BF: 0.1517; FBP: 0.0521; SART: 0.0645; SART–TV–FISTA: 0.0984; and DE–VM–SART–TV–FISTA: 0.1004), obtained a Gumbel distribution that yielded good images showing the type of simulated GGO nodules used in the chest phantom, and reduced the ripple artifacts. The NPS of DE–VM–VDSR with BF showed the lowest noise characteristics in the high-frequency region (~0.8 cycles/mm). The DE–VM–VDSR without BF yielded an improved resolution relative to that of the conventional reconstruction algorithms for radial MTF analysis (0.2–0.3 cycles/mm). Finally, based on the overall image quality, DE–VM–VDSR with BF improved the contrast and reduced the high-frequency ripple artifacts and noise.

X-ray dark-field phase-contrast imaging: Origins of the concept to practical implementation and applications

The basic idea of X-ray dark-field imaging (XDFI), first presented in 2000, was based on the concepts used in an X-ray interferometer. In this article, we review 20 years of developments in our theoretical understanding, scientific instrumentation, and experimental demonstration of XDFI and its applications to medical imaging. We first describe the concepts underlying XDFI that are responsible for imparting phase contrast information in projection X-ray images. We then review the algorithms that can convert these projection phase images into three-dimensional tomographic slices. Various implementations of computed tomography reconstructions algorithms for XDFI data are discussed. The next four sections describe and illustrate potential applications of XDFI in pathology, musculoskeletal imaging, oncologic imaging, and neuroimaging. The sample applications that are presented illustrate potential use scenarios for XDFI in histopathology and other clinical applications. Finally, the last section presents future perspectives and potential technical developments that can make XDFI an even more powerful tool.

Digital tomosynthesis and ground glass nodules: Optimization of acquisition protocol. A phantom study

INTRODUCTION

Ground-glass nodules may be the expression of benign conditions, pre-invasive lesions or malignancies. The aim of our study was to evaluate the capability of chest digital tomosynthesis (DTS) in detecting pulmonary ground-glass opacities (GGOs).

METHODS

An anthropomorphic chest phantom and synthetic nodules were used to simulate pulmonary ground-glass nodules. The nodules were positioned in 3 different regions (apex, hilum and basal); then the phantom was scanned by multi-detector CT (MDCT) and DTS. For each set (nodule-free phantom, nodule in apical zone, nodule in hilar zone, nodule in basal zone) seven different scans (n = 28) were performed varying the following technical parameters: Cu-filter (0.1-0.3 mm), dose rateo (10-25) and X-ray tube voltage (105-125 kVp). Two radiologists in consensus evaluated the DTS images and provided in agreement a visual score: 1 for unidentifiable nodules, 2 for poorly identifiable nodules, 3 for nodules identifiable with fair certainty, 4 for nodules identifiable with absolute certainty.

RESULTS

Increasing the dose rateo from 10 to 15, GGOs located in the apex and in the basal zone were better identified (from a score = 2 to a score = 3). GGOs located in the hilar zone were not visible even with a higher dose rate. Intermediate density GGOs had a good visibility score (score = 3) and it did not improve by varying technical parameters. A progressive increase of voltage (from 105 kVp to 125 kVp) did not provide a better nodule visibility.

CONCLUSION

DTS with optimized technical parameters can identify GGOs, in particular those with a diameter greater than 10 mm.

IMPLICATIONS FOR PRACTICE

DTS could have a role in the follow-up of patients with known GGOs identified in lung apex or base region.

Emulation of X-ray Light-Field Cameras

X-ray plenoptic cameras acquire multi-view X-ray transmission images in a single exposure (light-field). Their development is challenging: designs have appeared only recently, and they are still affected by important limitations. Concurrently, the lack of available real X-ray light-field data hinders dedicated algorithmic development. Here, we present a physical emulation setup for rapidly exploring the parameter space of both existing and conceptual camera designs. This will assist and accelerate the design of X-ray plenoptic imaging solutions, and provide a tool for generating unlimited real X-ray plenoptic data. We also demonstrate that X-ray light-fields allow for reconstructing sharp spatial structures in three-dimensions (3D) from single-shot data.

Diagnosis of and Early Revision Surgery for Biological Fixation Failure Due to Proximal-Distal Mismatch of Proximally Coated Tapered Cementless Stem

The diagnosis of and decision-making for early revision surgery to treat failure of biological fixation with a proximally coated cementless stem are challenging. A 73-year-old woman was referred to our hospital with thigh pain 2 years after the initial total hip arthroplasty. Although a plain radiograph showed no signs indicating biological fixation failure, digital tomosynthesis showed a highly radiodense line along the proximal part, and bone scintigraphy showed uptake at the distal part. With the diagnosis of biological fixation failure due to the proximal-distal mismatch, the cementless stem was revised to a cemented stem, and the thigh pain was improved after the revision surgery. Digital tomosynthesis and bone scintigraphy can be helpful for the diagnosis of biological fixation failure due to proximal-distal mismatch.

A synthesizing method for signal-enhanced and artifact-reduced mammogram from digital breast tomosynthesis

In this paper, we propose a method for compositing a synthetic mammogram (SM) from digital breast tomosynthesis (DBT) slice images. The method consists of four parts. The first part is image reconstruction of DBT from the acquired projection data by use of backprojection-filtration (BPF) algorithm with a low-frequency boosting scheme and a high-density object reduction technique embedded. Also, a few expectation-maximization (EM) iterations have been additively implemented on top of the BPF algorithm to prepare a separate volume image. The second is generating three kinds of intermediate SMs. A forward projection image and a linear structure weighted forward projection image were computed. A maximum intensity projection of the BPF reconstructed volume image was also generated. The third part is integrating three intermediate SMs. The last is the post-processing of the SM. We scanned two physical phantoms in a prototype DBT scanner, and we have evaluated the performance of the proposed method. We also performed a clinical data study by use of 30 patient data who went through both DBT and digital mammography (DM) scans. Three experienced radiologists have read the SMs generated by several component techniques and also read the DM of each patient, and evaluated the generated SMs. The experimental phantom study and the clinical reader study consistently demonstrated the usefulness of the proposed method.

Single-snapshot X-ray imaging for nonlinear compressive tomosynthesis

Traditional compressive X-ray tomosynthesis uses sequential illumination to interrogate the object, leading to long scanning time and image distortion due to the object variation. This paper proposes a single-snapshot compressive tomosynthesis imaging approach, where the object is simultaneously illuminated by multiple X-ray emitters equipped with coded apertures. Based on rank, intensity and sparsity prior models, a nonlinear image reconstruction framework is established. The coded aperture patterns are optimized based on uniform sensing criteria. Then, a modified split Bregman algorithm is developed to reconstruct the object from the set of nonlinear compressive measurements. It is shown that the proposed method can be used to reduce the inspection time and achieve robust reconstruction with respect to shape variation or motion of objects.