Finding the optimal tube current and iterative reconstruction strength in liver imaging; two needles in one haystack

Objectives

The aim of the study was to find the lowest possible tube current and the optimal iterative reconstruction (IR) strength in abdominal imaging.

Material and methods

Reconstruction software was used to insert noise, simulating the use of a lower tube current. A semi-anthropomorphic abdominal phantom (Quality Assurance in Radiology and Medicine, QSA-543, Moehrendorf, Germany) was used to validate the performance of the ReconCT software (S1 Appendix). Thirty abdominal CT scans performed with a standard protocol (120 kVref, 150 mAsref) scanned at 90 kV, with dedicated contrast media (CM) injection software were selected. There were no other in- or exclusion criteria. The software was used to insert noise as if the scans were performed with 90, 80, 70 and 60% of the full dose. Consequently, the different scans were reconstructed with filtered back projection (FBP) and IR strength 2, 3 and 4. Both objective (e.g. Hounsfield units [HU], signal to noise ratio [SNR] and contrast to noise ratio [CNR]) and subjective image quality were evaluated. In addition, lesion detection was graded by two radiologists in consensus in another 30 scans (identical scan protocol) with various liver lesions, reconstructed with IR 3, 4 and 5.

Results

A tube current of 60% still led to diagnostic objective image quality (e.g. SNR and CNR) when IR strength 3 or 4 were used. IR strength 4 was preferred for lesion detection. The subjective image quality was rated highest for the scans performed at 90% with IR 4.

Conclusion

A tube current reduction of 10–40% is possible in case IR 4 is used, leading to the highest image quality (10%) or still diagnostic image quality (40%), shown by a pairwise comparison in the same patients.

CoroNet: A deep neural network for detection and diagnosis of COVID-19 from chest x-ray images

BACKGROUND AND OBJECTIVE

The novel Coronavirus also called COVID-19 originated in Wuhan, China in December 2019 and has now spread across the world. It has so far infected around 1.8 million people and claimed approximately 114,698 lives overall. As the number of cases are rapidly increasing, most of the countries are facing shortage of testing kits and resources. The limited quantity of testing kits and increasing number of daily cases encouraged us to come up with a Deep Learning model that can aid radiologists and clinicians in detecting COVID-19 cases using chest X-rays.

METHODS

In this study, we propose CoroNet, a Deep Convolutional Neural Network model to automatically detect COVID-19 infection from chest X-ray images. The proposed model is based on Xception architecture pre-trained on ImageNet dataset and trained end-to-end on a dataset prepared by collecting COVID-19 and other chest pneumonia X-ray images from two different publically available databases.

RESULTS

CoroNet has been trained and tested on the prepared dataset and the experimental results show that our proposed model achieved an overall accuracy of 89.6%, and more importantly the precision and recall rate for COVID-19 cases are 93% and 98.2% for 4-class cases (COVID vs Pneumonia bacterial vs pneumonia viral vs normal). For 3-class classification (COVID vs Pneumonia vs normal), the proposed model produced a classification accuracy of 95%. The preliminary results of this study look promising which can be further improved as more training data becomes available.

CONCLUSION

CoroNet achieved promising results on a small prepared dataset which indicates that given more data, the proposed model can achieve better results with minimum pre-processing of data. Overall, the proposed model substantially advances the current radiology based methodology and during COVID-19 pandemic, it can be very helpful tool for clinical practitioners and radiologists to aid them in diagnosis, quantification and follow-up of COVID-19 cases.

Evaluation of three-dimensional iterative image reconstruction in virtual monochromatic imaging at 40 kilo-electron volts: phantom and clinical studies to assess the image noise and image quality in comparison with other reconstruction techniques

OBJECTIVE

The purpose of this study was to evaluate the image quality in virtual monochromatic imaging (VMI) at 40 kilo-electron volts (keV) with three-dimensional iterative image reconstruction (3D-IIR).

METHODS

A phantom study and clinical study (31 patients) were performed with dual-energy CT (DECT). VMI at 40 keV was obtained and the images were reconstructed using filtered back projection (FBP), 50% adaptive statistical iterative reconstruction (ASiR), and 3D-IIR. We conducted subjective and objective evaluations of the image quality with each reconstruction technique.

RESULTS

The image contrast-to-noise ratio and image noise in both the clinical and phantom studies were significantly better with 3D-IIR than with 50% ASiR, and with 50% ASiR than with FBP (all, p < 0.05). The standard deviation and noise power spectra of the reconstructed images decreased in the order of 3D-IIR to 50% ASiR to FBP, while the modulation transfer function was maintained across the three reconstruction techniques. In most subjective evaluations in the clinical study, the image quality was significantly better with 3D-IIR than with 50% ASiR, and with 50% ASiR than with FBP (all, p < 0.001). Regarding the diagnostic acceptability, all images using 3D-IIR were evaluated as being fully or probably acceptable.

CONCLUSIONS

The quality of VMI at 40 keV is improved by 3D-IIR, which allows the image noise to be reduced and structural details to be maintained.

ADVANCES IN KNOWLEDGE

The improvement of the image quality of VMI at 40 keV by 3D-IIR may increase the subjective acceptance in the clinical setting.

XAP-Lab: A software tool for designing flexible X-ray acquisition protocols

BACKGROUND AND OBJECTIVE

The availability of digital X-ray detectors, together with the development of new robotized hardware and reconstruction algorithms, opens the opportunity to provide 3D capabilities with conventional radiology systems. This would be based on the acquisition of a limited number of projections with non-standard geometrical configurations. The versatility of these techniques is enormous, enabling the introduction of tomography in situations where a CT system is hardly available, such as during surgery or in an ICU, or in which a reduction of radiation dose is key, as in pediatrics. Computer simulations are a valuable tool to explore these possibilities before their actual implementation on real systems. Existing software tools generally simulate only standard acquisition protocols, such as cone-beam with circular trajectory, thus not allowing the users to evaluate more sophisticated projection geometries. The goal of this work is to design a simulation tool that enables the design of acquisition protocols with flexible projection geometries.

METHODS

We present XAP-Lab, a software tool for the design of X-ray acquisition protocols with flexible trajectories. For a given projection geometry, defined through a graphical user interface, it allows the user to simulate projections using GPU-accelerated kernels, the visualization of the scanned field of view and the estimation of the total radiation dose. The complete acquisition protocol can then be exported with the appropriate format for its use on real systems. We tested the software by optimizing a tomosynthesis protocol and validating the results with real acquisitions using a SEDECAL NOVA FA radiography system and phantoms for quantitative and qualitative evaluation.

RESULTS

Quantitative evaluation using a phantom showed a mean error under 4 mm for each position, below the ±5 mm tolerance of the system specified by the manufacturer. Visual evaluation on a thorax acquisition also showed a good geometrical agreement between simulated and real projections.

CONCLUSIONS

Results showed an excellent matching with simulations, supporting the usefulness of XAP-Lab for the design of new acquisition protocols with non-standard geometries.

Performance of the sinogram-based iterative reconstruction in sparse view X-ray computed tomography

Performing X-ray computed tomography (CT) examinations with less radiation has recently received increasing interest: in medical imaging this means less (potentially harmful) radiation for the patient; in non-destructive testing of materials/objects such as testing jet engines, the reduction of the number of projection angles (which for large objects is in general high) leads to a substantial decreasing of the experiment time. In the experiment, less radiation is usually achieved by either (1) reducing the radiation dose used at each projection angle or (2) using sparse view X-ray CT, which means significantly less projection angles are used during the examination. In this work, we study the performance of the recently proposed sinogram-based iterative reconstruction algorithm in sparse view X-ray CT and show that it provides, in some cases, reconstruction accuracy better than that obtained by some of the Total Variation regularization techniques. The provided accuracy is obtained with computation times comparable to other techniques. An important feature of the sinogram-based iterative reconstruction algorithm is that it is simpler and without the many parameters specific to other techniques.

Mammography cancer detection: comparison of single 8MP and pair of 5MP reporting monitors

OBJECTIVE:

To compare breast cancer detection using a single 8MP display with using a standard pair of 5MP monitors.

METHODS:

An observer study was carried out in which mammograms were read using full field views only, and again with the additional use of magnified quadrant views. Seven observers read 300 cases, one view per breast, using each display type. Cases comprised 100 normal cases and 200 cases with cancers of subtle or very subtle appearance: 100 with malignant calcification clusters and 100 with non-calcified lesions. JAFROC software was used to analyse the results.

RESULTS:

When mammograms were viewed full field only, observers performed better (p = 0.050) in detecting malignant calcification clusters when using the pair of 5MP monitors compared with a single 8MP monitor. This result became non-significant when results were generalised to a population of readers. Performance in detecting calcification clusters was improved by using quadrant view in addition to full field view when using either the pair of 5MP monitors or the 8MP monitor. There was no significant difference in detection of all types of cancer between the pair of 5MP monitors and the 8MP monitor when quadrant zoom was used.

CONCLUSION:

Providing quadrant view is used in addition to full field view, there is no significant difference in cancer detection between the 8MP monitor and the pair of 5MP monitors.

ADVANCES IN KNOWLEDGE:

Effect of magnification on the detectability of subtle malignant calcification clusters in breast screening.

Improving signal strength in serial crystallography with DIALS geometry refinement

The DIALS diffraction-modeling software package has been applied to serial crystallography data. Diffraction modeling is an exercise in determining the experimental parameters, such as incident beam wavelength, crystal unit cell and orientation, and detector geometry, that are most consistent with the observed positions of Bragg spots. These parameters can be refined by nonlinear least-squares fitting. In previous work, it has been challenging to refine both the positions of the sensors (metrology) on multipanel imaging detectors such as the CSPAD and the orientations of all of the crystals studied. Since the optimal models for metrology and crystal orientation are interdependent, alternate cycles of panel refinement and crystal refinement have been required. To simplify the process, a sparse linear algebra technique for solving the normal equations was implemented, allowing the detector panels to be refined simultaneously against the diffraction from thousands of crystals with excellent computational performance. Separately, it is shown how to refine the metrology of a second CSPAD detector, positioned at a distance of 2.5 m from the crystal, used for recording low-angle reflections. With the ability to jointly refine the detector position against the ensemble of all crystals used for structure determination, it is shown that ensemble refinement greatly reduces the apparent nonisomorphism that is often observed in the unit-cell distributions from still-shot serial crystallography. In addition, it is shown that batching the images by timestamp and re-refining the detector position can realistically model small, time-dependent variations in detector position relative to the sample, and thereby improve the integrated structure-factor intensity signal and heavy-atom anomalous peak heights.

Significant dose reduction using synchrotron radiation computed tomography: first clinical case and application to high resolution CT exams

Since the invention of Computed Tomography (CT), many technological advances emerged to improve the image sensitivity and resolution. However, no new source types were developed for clinical use. In this study, for the first time, coherent monochromatic X-rays from a synchrotron radiation source were used to acquire 3D CTs on patients. The aim of this work was to evaluate the clinical potential of the images acquired using Synchrotron Radiation CT (SRCT). SRCTs were acquired using monochromatic X-rays tuned at 80 keV (0.350 × 0.350 × 2 mm3 voxel size). A quantitative image quality comparison study was carried out on phantoms between a state of the art clinical CT and SRCT images. Dedicated iterative algorithms were developed to optimize the image quality and further reduce the delivered dose by a factor of 12 while keeping a better image quality than the one obtained with a clinical CT scanner. We finally show in this paper the very first SRCT results of one patient who received Synchrotron Radiotherapy in an ongoing clinical trial. This demonstrates the potential of the technique in terms of image quality improvement at a reduced radiation dose for inner ear visualization.

An iterative reconstruction algorithm for digital breast tomosynthesis imaging using real data at three radiation doses

BACKGROUND

Iterative image reconstruction in Digital Breast Tomosynthesis (DBT) is a developing modality that produces three-dimensional (3D) reconstructed images of a breast to detect suspicious lesions. Algebraic reconstruction technique (ART), one of the iterative image reconstruction methods, was applied to reconstruct 3D data of breast and is becoming as one alternative method for the conventional image reconstruction techniques such as filtered back projection (FBP) in DBT imaging.

OBJECTIVE

A new majorization-minimization (MM) algorithm was presented for TV denoising of signals. In the field of DBT, however, the algorithm has not yet been applied. In this study, we proposed a new method of "ART+TV3D+MM," which applies (MM) algorithm to the images reconstructed by ART+TV3D for different imaging dose levels to investigate a possible reduction of radiation dose.

METHODS

Projections of a real breast phantom (CD Pasmam 1054) were acquired with a Siemens MAMMOMAT DBT system. The proposed new method was repeated and tested with 3 different radiation dose levels. The quality of the images reconstructed using the proposed new method were compared with those generated by the commonly used FBP method using both qualitative and quantitative assessments.

RESULTS

The new method showed superior results in terms of visual assessment, contrast to noise ratios (CNR), full width at half maximum (FWHM) values and 1D profiles compared with FBP of the Siemens MAMMOMAT. CNR values were evaluated for two different region of interests (ROIs). For instance, CNR values of ROI-2 of FBP and of new method were 1.670 and 1.978 at 100 mAs, respectively. Moreover, while CNR value of ROI-1 of FBP at 100 mAs was 0.955, CNR value of ROI-1 of using new method at 100 mAs was 48.163. FWHM values for FBP and the new method were 2.328 and 1.765 at 56 mAs, 2.032 and 1.661 at 100 mAs, and 2.111 and 1.736 at 199 mAs, respectively.

CONCLUSIONS

The results support that using the new method of "ART+TV3D+MM" could help decrease the radiation dose level, which is one of the most critical limitations of DBT imaging.

Improved Estimation of Coronary Plaque and Luminal Attenuation Using a Vendor-specific Model-based Iterative Reconstruction Algorithm in Contrast-enhanced CT Coronary Angiography

RATIONALE AND OBJECTIVES

To investigate the stabilities of plaque attenuation and coronary lumen for different plaque types, stenotic degrees, lumen densities, and reconstruction methods using coronary vessel phantoms and the visualization of coronary plaques in clinical patients through coronary computed tomography (CT) angiography.

MATERIALS AND METHODS

We performed 320-detector volume scanning of vessel tubes with stenosis and a tube without stenosis using three types of plaque CT numbers. The stenotic degrees were 50% and 75%. Images were reconstructed with filtered back projection (FBP) and two types of iterative reconstructions (AIDR3D and FIRST [forward-projected model-based iterative reconstruction solution]), with stenotic CT number of approximately 40, 80, and 150 HU (Hounsfield unit), respectively. In each case, the tubing of the coronary vessel was filled with diluted contrast material and distilled water to reach the target lumen CT numbers of approximately 350 HU and 450 HU, and 0 HU, respectively. Peak lumen and plaque CT numbers were measured to calculate the lumen-plaque contrast. In addition, we retrospectively evaluated the image quality with regard to coronary arterial lumen and the plaque in 10 clinical patients on a 4-point scale.

RESULTS

At 50% stenosis, the plaque CT number with contrast enhancement increased for FBP and AIDR3D, and the difference in the plaque CT number with and without contrast enhancement was 15-44 HU for FBP and 10-31 HU for AIDR3D. However, the plaque CT number for FIRST had a smaller variation and the difference with and without contrast enhancement was -12 to 8 HU. The visual evaluation score for the vessel lumen was 2.8 ± 0.6, 3.5 ± 0.5, and 3.7 ± 0.5 for FBP, AIDR3D, and FIRST, respectively.

CONCLUSIONS

The FIRST method controls the increase in plaque density and the lumen-plaque contrast. Consequently, it improves the visualization of coronary plaques in coronary CT angiography.

Mobile Image Interpretation: Diagnostic Performance of CT Exams Displayed on a Tablet Computer in Detecting Abdominopelvic Hemorrhage

To investigate whether abdominopelvic hemorrhage shown on computed tomography (CT) images can be diagnosed with the same accuracy on a tablet computer as on a dedicated reading display. One hundred patients with a clinical suspicion of abdominopelvic hemorrhage that underwent biphasic CT imaging were retrospectively read by two readers on a dedicated reading display (reference standard) and on a tablet computer (iPad Air). Reading was performed in a dedicated reading room with ambient light conditions. Image evaluation included signs of an active hemorrhage (extravasation of contrast media) and different signs indicating a condition after abdominopelvic hemorrhage (hematoma, intestinal clots, vessel stump, free abdominopelvic fluid with a mean Hounsfield unit value >20, and asymmetric muscle volume indicating intramuscular hemorrhage). Sensitivity, specificity, and positive and negative predictive values (PPV/NPV) were calculated for the tablet-based reading. Active abdominopelvic hemorrhage (n = 72) was diagnosed with the tablet computer with a sensitivity of 0.96, a specificity of 0.93, a PPV of 0.97, and an NPV of 0.90. The results for the detection of the signs indicating a condition after abdominopelvic hemorrhage range from 0.83 to 1.00 in the case of sensitivity, from 0.95 to 1.00 in the case of specificity, from 0.94 to 1.00 in the case of the PPV, and from 0.96 to 1.00 in the case of the NPV. Abdominopelvic hemorrhage shown on CT images can be diagnosed on a tablet computer with a high diagnostic accuracy allowing mobile on-call diagnoses. This may be helpful because an early and reliable diagnosis at any time is crucial for an adequate treatment strategy.

[Image Quality and Clinical Usefulness of Ray-summation Image Reconstructed from CT Data, Compared with Digital Radiography]

Ray-summation (raysum) images reconstructed from computed tomography (CT) volume data resemble digital radiography (DR) images. Therefore, they have a potential to be used instead of DR images.The aim of this study was to compare the physical image quality evaluated by signal-difference-to-noise ratio (SDNR) and clinical usefulness between raysum and DR images. We employed an oval water phantom simulating adult abdomen for image quality measurement. Raysum images were reconstructed from CT volume data using an assumed x-ray quality of 70 keV. DR images were obtained using an indirect-type flat panel detector system. The normalized noise-power spectrum (NNPS) for various same dose indices (DR: entrance surface dose, CT: CT dose index volume) were measured from raysum and DR images. SDNRs were calculated from the results of NNPSs, modulation transfer function (MTF), and cartilage material contrast. Five experienced observers visually compared each pair of a clinical raysum image and a DR image for nine clinical cases (head, finger, pelvis, and foot). MTF of raysum was significantly lower than that of DR. SDNRs of DR were superior to those of raysum for each dose index, by an average factor of 1.24. For head and pelvis images, raysum images were comparable or a little superior compared with the DR images, because the radiation doses of raysum was much higher than those of DR. For finger and foot cases, the raysum images were inferior to DR images due to its lower resolution. Our results indicated a limited clinical usefulness of raysum compared with DR.

Noise Power Characteristics of a Micro-Computed Tomography System

OBJECTIVE

The aim of this study was to investigate the noise power properties of a micro-computed tomography (micro-CT) system under different operating conditions.

METHODS

A commercial micro-CT was used in the study that used a flat panel detector with a 127-μm-pixel pitch and a micro-focus x-ray tube. Conical tubes of various diameters were used under different acquisition conditions. Multidimensional noise power spectrums were used as a metric to investigate the noise properties of the system. Noise power spectrum was calculated from the difference data generated by subtraction of 2 identical scans. The noise properties with respect to various parameters that include the impact of number of projections, x-ray spectra, milliampere-second, slice location, object diameter, voxel size, geometric magnification (M), back-projection filters, and reconstruction magnification (Mrecon) were studied.

RESULTS

At a same isocentric exposure rate of 270 mR/s, the noise power was much lower for the image reconstructed with 3672 views (122 seconds) as compared with the 511 views (17 seconds), whereas at a fixed isocentric exposure of 4600 mR, the noise power levels were almost similar. Image noise with a 50-kV beam was higher as compared with the 90-kV beam at a same isocentric exposure. Image noise from a 16-mm-diameter conical tube was much lower as compared with the 28- and 56-mm tubes under identical isocentric exposures. The choice of back-projection filter influences noise power spectrum curves in terms of width and amplitudes. Reconstruction magnification applied during the reconstruction process increased the noise power at lower spatial frequencies but reduced the noise power at higher spatial frequencies. It can be established that, for small details corresponding to high spatial frequencies, reconstruction magnification can provide an improved signal-to-noise ratio. At all spatial frequencies, the in-plane images had lower noise power levels as compared with the z-plane images.

CONCLUSIONS

The noise power properties investigated in this study provide important image quality references for refined cone beam system development, optimization, and operations.

[Optimization of Couch Modeling in the Change of Dose Calculation Methods and Their Versions]

In external radiotherapy, the X-ray beam passes through the treatment couch, leading to the dose reduction by the attenuation of the couch. As a method to compensate for the reduction, radiation treatment planning systems (RTPS) support virtual couch function, namely "couch modeling method". In the couch modeling method, the computed tomography (CT) numbers assigned to each structure should be optimized by comparing calculations to measurements for accurate dose calculation. Thus, re-optimization of CT numbers will be required when the dose calculation algorithm or their version changes. The purpose of this study is to evaluate the calculation accuracy of the couch modeling method in different calculation algorithms and their versions. The optimal CT numbers were determined by minimizing the difference between measured transmission factors and calculated ones. When CT numbers optimized by Anisotropic Analytical Algorithm (AAA) Ver. 8.6 were used, the maximum and the mean difference of transmission factor were 5.8% and 1.5%, respectively, for Acuros XB (AXB) Ver. 11.0. However, when CT numbers optimized by AXB Ver. 11.0 were used, they were 2.6% and 0.6%, respectively. The CT numbers for couch structures should be optimized when changing dose calculation algorithms and their versions. From the comparison of the measured transmission to calculation, it was found that the CT numbers had high accuracy.

A rig for acquisition of standardized trabecular bone radiographs

To assess osteoarthritic changes in knee joints a radiography rig for acquisition of standardized radiographs of trabecular bone has been developed. The rig contains a steel frame on castors, a turntable, a cassette holder frame, calibration Plexiglas sheets, body supports and points. It is used to lock the patient in a standardized position. A film cassette holder frame was also developed to reduce scattering of X-rays, and consequently the amount of noise in the radiographs. Calibration Plexiglas sheets were mounted on ball bearing slides to obtain radiographs without a calibration pattern (suitable for the analysis of trabecular bone texture) and radiographs containing a calibration pattern (suitable for the measurement of leg alignment).

Development and evaluation of a teleradiology and videoconferencing system

We developed a teleradiology system linking a general hospital on Sado Island to tertiary care hospitals in Niigata City. The island is 40 km from Niigata City on the mainland and has only one diagnostic radiologist (for 72,000 islanders). Fibre optic cables between Sado Island and Niigata City were used for transmission. The introduction of the teleradiology system facilitated diagnostic and therapeutic consultation with specialists in Niigata City. The performance of the system was evaluated (on a scale of 0–6, with higher scores indicating better performance) by five diagnostic radiologists, who rated 32 features of the system twice, once in April 2002 and once in September 2003. The performance ratings improved from 1.38 to 2.86. While many of the initial problems with the software had been resolved, many still remained.

ITERATIVE SCATTER CORRECTION FOR GRID-LESS BEDSIDE CHEST RADIOGRAPHY: PERFORMANCE FOR A CHEST PHANTOM

The aim of this work was to experimentally compare the contrast improvement factors (CIFs) of a newly developed software-based scatter correction to the CIFs achieved by an antiscatter grid. To this end, three aluminium discs were placed in the lung, the retrocardial and the abdominal areas of a thorax phantom, and digital radiographs of the phantom were acquired both with and without a stationary grid. The contrast generated by the discs was measured in both images, and the CIFs achieved by grid usage were determined for each disc. Additionally, the non-grid images were processed with a scatter correction software. The contrasts generated by the discs were determined in the scatter-corrected images, and the corresponding CIFs were calculated. The CIFs obtained with the grid and with the software were in good agreement. In conclusion, the experiment demonstrates quantitatively that software-based scatter correction allows restoring the image contrast of a non-grid image in a manner comparable with an antiscatter grid.

ASSESSING THE USEFULNESS OF THE QUASI-IDEAL OBSERVER FOR QUALITY CONTROL IN FLUOROSCOPY

The aim of this work was to evaluate the reliability of the square of the signal-to-noise ratio rate, [Formula: see text], as a precise measurement for quality control test in a digital fluoroscopy system. The quasi-ideal model observer was used to measure [Formula: see text] The dose rate, pulse rate and field of view were varied, and their effect on dose efficiency, defined as [Formula: see text], was evaluated (where [Formula: see text] is the air kerma-area product rate). Measurements were repeated to assess reproducibility. The relative standard deviation in [Formula: see text] over seven consecutive measurements was 5 %. No significant variation in [Formula: see text] was observed across different pulse rates (10-30 pulses s(-1)). The low-dose-rate setting had a superior dose efficiency compared with the medium- and high-dose-rate settings. A smaller field of view resulted in higher dose efficiency.The results show that [Formula: see text] measurements offer the high precision required in quality control constancy tests.

CHARACTERISING THE EOS SLOT-SCANNING SYSTEM WITH THE EFFECTIVE DETECTIVE QUANTUM EFFICIENCY

As opposed to the standard detective quantum efficiency (DQE), effective DQE (eDQE) is a figure of merit that allows comparing the performances of imaging systems in the presence of scatter rejection devices. The geometry of the EOS™ slot-scanning system is such that the detector is self-collimated and rejects scattered radiation. In this study, the EOS system was characterised using the eDQE in imaging conditions similar to those used in clinical practice: with phantoms of different widths placed in the X-ray beam, for various incident air kerma and tube voltages corresponding to the phantom thickness. Scatter fractions in EOS images were extremely low, around 2 % for all configurations. Maximum eDQE values spanned 9-14.8 % for a large range of air kerma at the detector plane from 0.01 to 1.34 µGy. These figures were obtained with non-optimised EOS setting but still over-performed most of the maximum eDQEs recently assessed for various computed radiology and digital radiology systems with antiscatter grids.

Spectral X-Ray CT Image Reconstruction with a Combination of Energy-Integrating and Photon-Counting Detectors

The purpose of this paper is to develop an algorithm for hybrid spectral computed tomography (CT) which combines energy-integrating and photon-counting detectors. While the energy-integrating scan is global, the photon-counting scan can have a local field of view (FOV). The algorithm synthesizes both spectral data and energy-integrating data. Low rank and sparsity prior is used for spectral CT reconstruction. An initial estimation is obtained from the projection data based on physical principles of x-ray interaction with the matter, which provides a more accurate Taylor expansion than previous work and can guarantee the convergence of the algorithm. Numerical simulation with clinical CT images are performed. The proposed algorithm produces very good spectral features outside the FOV when no K-edge material exists. Exterior reconstruction of K-edge material can be partially achieved.

Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner

In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.

Accurate determination of segmented X-ray detector geometry

Recent advances in X-ray detector technology have resulted in the introduction of segmented detectors composed of many small detector modules tiled together to cover a large detection area. Due to mechanical tolerances and the desire to be able to change the module layout to suit the needs of different experiments, the pixels on each module might not align perfectly on a regular grid. Several detectors are designed to permit detector sub-regions (or modules) to be moved relative to each other for different experiments. Accurate determination of the location of detector elements relative to the beam-sample interaction point is critical for many types of experiment, including X-ray crystallography, coherent diffractive imaging (CDI), small angle X-ray scattering (SAXS) and spectroscopy. For detectors with moveable modules, the relative positions of pixels are no longer fixed, necessitating the development of a simple procedure to calibrate detector geometry after reconfiguration. We describe a simple and robust method for determining the geometry of segmented X-ray detectors using measurements obtained by serial crystallography. By comparing the location of observed Bragg peaks to the spot locations predicted from the crystal indexing procedure, the position, rotation and distance of each module relative to the interaction region can be refined. We show that the refined detector geometry greatly improves the results of experiments.

Radiographers' Ability to Detect Low-Contrast Detail in Digital Radiography Systems

PURPOSE

To evaluate radiographers' ability to detect low-contrast detail using various digital planar radiographic systems.

METHODS

A low-contrast detail phantom was placed between two 5-cm thick Perspex sheets (Lucite International). Images were obtained using different kilovoltage peak and milliamperage second (mAs) settings with computed radiography (CR), indirect conversion digital radiography (IDR), and direct conversion digital radiography (DR) systems. Six groups of 6 radiographers were asked to score 39 images; each group scored 2 images from each system for a total of 6 images. The seventh group scored only one image from each system for a total of 3 images. The radiographers' results were compared with the results of analyzer software. The inverse image quality factor was used to measure low-contrast detail detectability performance.

RESULTS

Radiographers performed significantly worse than the computerized software in determining low-contrast detail in planar radiographic images (P < .01). However, a positive correlation (R = 0.558) existed between the 2 sets of scores in terms of low-contrast detail detectability performance.

DISCUSSION

On average, radiographers were able to detect increased image quality resulting from increased mAs. Radiographers reached results similar to the software regarding whether IDR and DR have better detectability performances than CR. Differences found among individual radiographers were not as significant with DR.

CONCLUSION

When radiographers' performance in detecting low-contrast detail was evaluated and compared with that of the software, radiographers exhibited poorer performances. Because radiographers are responsible for image quality optimization, additional training might improve their ability to detect low-contrast detail in DR systems.

Spectral CT using multiple balanced K-edge filters

Our goal is to validate a spectral computed tomography (CT) system design that uses a conventional X-ray source with multiple balanced K-edge filters. By performing a simultaneously synthetic reconstruction in multiple energy bins, we obtained a good agreement between measurements and model expectations for a reasonably complex phantom. We performed simulation and data acquisition on a phantom containing multiple rods of different materials using a NeuroLogica CT scanner. Five balanced K-edge filters including Molybdenum, Cerium, Dysprosium, Erbium, and Tungsten were used separately proximal to the X-ray tube. For each sinogram bin, measured filtered vector can be defined as a product of a transmission matrix, which is determined by the filters and is independent of the imaging object, and energy-binned intensity vector. The energy-binned sinograms were then obtained by inverting the transmission matrix followed by a multiplication of the filter measurement vector. For each energy bin defined by two consecutive K-edges, a synthesized energy-binned attenuation image was obtained using filtered back-projection reconstruction. The reconstructed attenuation coefficients for each rod obtained from the experiment was in good agreement with the corresponding simulated results. Furthermore, the reconstructed attenuation coefficients for a given energy bin, agreed with National Institute of Standards and Technology reference values when beam hardening within the energy bin is small. The proposed cost-effective system design using multiple balanced K-edge filters can be used to perform spectral CT imaging at clinically relevant flux rates using conventional detectors and integrating electronics.

Light beam diaphragm collimation errors and their effects on radiation dose for pelvic radiography

PURPOSE

To investigate the range of collimation errors in x-ray rooms and to calculate their possible effects on the radiation dose for anteroposterior pelvic examinations.

METHODS

A collimator test tool was suspended at 3 heights (14, 21, and 28 cm) above the table Bucky in 9 x-ray rooms. Heights corresponded to the typical patient thickness (mean, ± 2 SD) of 67 patients undergoing anteroposterior pelvic radiography. The x-ray beam was visually collimated to the inner boundary of the test tool and exposed to radiation. Differences between the visualized field size and the resultant x-ray field size (corrected for magnification) indicated a collimation error. Next, using a pelvic phantom, minimum textbook collimation was set and then changed and verified to simulate a range of possible collimation errors. Phantom examinations used a standard anteroposterior technique with exposure termination using outer automatic exposure control chambers. Dose area product (DAP) was recorded.

RESULTS

All but 1 of the 9 x-ray machines had a smaller irradiated area than was visually set. Errors ranged from a 16% reduction in irradiated field size to a slight overirradiation by 0.4%. Assuming that these errors could be larger in other institutions, additional errors with a range of -27% to 18% were simulated. Increases in field size by 1 cm (superiorly/inferiorly) increased the DAP by 5%. Laterally, a 1-cm increase caused a 4% rise in DAP. Increases of 1 cm in both planes raised DAP by 4%.

DISCUSSION

Within a single clinical department, minimal collimation errors were demonstrated. Further evidence from multiple centers would be beneficial; however, such low incidences might reflect strict legislative requirements governing the use of ionizing radiation. Understanding the magnitude of any error is important, but it is also important to ascertain an error's influence on the effective radiation dose for any given examination.

CONCLUSION

Overall, collimation errors were minimal and favored underirradiation. Small collimation errors can affect DAP and are more dose significant in the superior/inferior plane.

Investigation of the influence of image reconstruction filter and scan parameters on operation of automatic tube current modulation systems for different CT scanners

Variation in the user selected CT scanning parameters under automatic tube current modulation (ATCM) between hospitals has a substantial influence on the radiation doses and image quality for patients. The aim of this study was to investigate the effect of changing image reconstruction filter and scan parameter settings on tube current, dose and image quality for various CT scanners operating under ATCM. The scan parameters varied were pitch factor, rotation time, collimator configuration, kVp, image thickness and image filter convolution (FC) used for reconstruction. The Toshiba scanner varies the tube current to achieve a set target noise. Changes in the FC setting and image thickness for the first reconstruction were the major factors affecting patient dose. A two-step change in FC from smoother to sharper filters doubles the dose, but is counterbalanced by an improvement in spatial resolution. In contrast, Philips and Siemens scanners maintained tube current values similar to those for a reference image and patient, and the tube current only varied slightly for changes in individual CT scan parameters. The selection of a sharp filter increased the image noise, while use of iDose iterative reconstruction reduced the noise. Since the principles used by CT manufacturers for ATCM vary, it is important that parameters which affect patient dose and image quality for each scanner are made clear to operator to aid in optimisation.

Virtual colon flattening method based on colonic outer surface

Virtual colon flattening (VF) is a minimally invasive viewing mode used to detect colorectal polyps on the colonic inner surface in virtual colonoscopy. Compared with conventional colonoscopy, inspecting a flattened colonic inner surface is faster and results in fewer uninspected regions. Unfortunately, the deformation distortions of flattened colonic inner surface impede the performance of VF. Conventionally, the deformation distortions can be corrected by using the colonic inner surface. However, colonic curvatures and haustral folds make correcting deformation distortions using only the colonic inner surface difficult. Therefore, we propose a VF method that is based on the colonic outer surface. The proposed method includes two novel algorithms, namely, the colonic outer surface extraction algorithm and the colonic outer surface-based distortion correction algorithm. Sixty scans involving 77 annotated polyps were used for the validation. The flattened colons were independently inspected by three operators and then compared with three existing VF methods. The correct detection rates of the proposed method and the three existing methods were 79.6%, 67.1%, 71.9%, and 72.7%, respectively, and the false positives per scan were 0.16, 0.32, 0.21, and 0.26, respectively. The experimental results demonstrate that our proposed method has better performance than existing methods that are based on the colonic inner surface.

Assessment of prosthesis alignment after revision total knee arthroplasty using EOS 2D and 3D imaging: a reliability study

Introduction

A new low-dose X-ray device, called EOS, has been introduced for determining lower-limb alignment in 2D and 3D. Reliability has not yet been assessed when using EOS on lower limbs containing a knee prosthesis. Therefore purpose of this study was to determine intraobserver and interobserver reliability of EOS 2D and 3D knee prosthesis alignment measurements after revision total knee arthroplasty (rTKA).

Methods

Forty anteroposterior and lateral images of 37 rTKA patients were included. Two observers independently performed measurements on these images twice. Varus/valgus angles were measured in 2D (VV2D) and 3D (VV3D). Intraclass correlation coefficients and the Bland and Altman method were used to determine reliability. T-tests were used to test potential differences.

Results

Intraobserver and interobserver reliability were excellent for VV2D and VV3D. No significant difference or bias between the first and second measurements or the two observers was found. A significant mean and absolute difference of respectively 1.00° and 1.61° existed between 2D and 3D measurements.

Conclusions

EOS provides reliable varus/valgus measurements in 2D and 3D for the alignment of the knee joint with a knee prosthesis. However, significant differences exist between varus/valgus measurements in 2D and 3D.

Role of virtopsy in the post-mortem diagnosis of drowning

PURPOSE

Due to admitted limits of autopsy-based studies in the diagnosis of drowning, virtopsy is considered the new imaging horizon in these post-mortem studies. The aim of our study was to evaluate the role of virtopsy performed through computed tomography (CT) in the forensic diagnosis of drowning.

MATERIALS AND METHODS

We retrospectively examined the CT data of four cadavers recovered from sea water and suspected to have died by drowning. Each patient underwent a full-body post-mortem CT scan, and then a traditional autopsy.

RESULTS

All the cadavers showed fluid in the airways and patchy ground-glass opacities in the lung. Only one patient had no fluid in the digestive tract; this patient had a left parietal bone fracture with a large gap and other multiple bone fractures (nose, clavicle, first rib and patella). One of the three patients who had fluid in the digestive tract had no fluid in the paranasal sinuses. This latter patient showed cerebral oedema with subarachnoid and intraventricular haemorrhage, multiple bone fractures (orbital floor, ribs, sacrum and acetabular edge) and air in the heart, in the aorta and in bowel loops.

CONCLUSION

To date, there are no autopsy findings pathognomonic of drowning. This study proves that virtopsy is a useful tool in the diagnosis of drowning in that it allows us to understand if the victim was alive or dead when he entered the water and if the cause of death was drowning.

Statistical model based iterative reconstruction (MBIR) in clinical CT systems. Part II. Experimental assessment of spatial resolution performance

PURPOSE

Statistical model based iterative reconstruction (MBIR) methods have been introduced to clinical CT systems and are being used in some clinical diagnostic applications. The purpose of this paper is to experimentally assess the unique spatial resolution characteristics of this nonlinear reconstruction method and identify its potential impact on the detectabilities and the associated radiation dose levels for specific imaging tasks.

METHODS

The thoracic section of a pediatric phantom was repeatedly scanned 50 or 100 times using a 64-slice clinical CT scanner at four different dose levels [CTDIvol =4, 8, 12, 16 (mGy)]. Both filtered backprojection (FBP) and MBIR (Veo(®), GE Healthcare, Waukesha, WI) were used for image reconstruction and results were compared with one another. Eight test objects in the phantom with contrast levels ranging from 13 to 1710 HU were used to assess spatial resolution. The axial spatial resolution was quantified with the point spread function (PSF), while the z resolution was quantified with the slice sensitivity profile. Both were measured locally on the test objects and in the image domain. The dependence of spatial resolution on contrast and dose levels was studied. The study also features a systematic investigation of the potential trade-off between spatial resolution and locally defined noise and their joint impact on the overall image quality, which was quantified by the image domain-based channelized Hotelling observer (CHO) detectability index d'.

RESULTS

(1) The axial spatial resolution of MBIR depends on both radiation dose level and image contrast level, whereas it is supposedly independent of these two factors in FBP. The axial spatial resolution of MBIR always improved with an increasing radiation dose level and/or contrast level. (2) The axial spatial resolution of MBIR became equivalent to that of FBP at some transitional contrast level, above which MBIR demonstrated superior spatial resolution than FBP (and vice versa); the value of this transitional contrast highly depended on the dose level. (3) The PSFs of MBIR could be approximated as Gaussian functions with reasonably good accuracy. (4) Thez resolution of MBIR showed similar contrast and dose dependence. (5) Noise standard deviation assessed on the edges of objects demonstrated a trade-off with spatial resolution in MBIR. (5) When both spatial resolution and image noise were considered using the CHO analysis, MBIR led to significant improvement in the overall CT image quality for both high and low contrast detection tasks at both standard and low dose levels.

CONCLUSIONS

Due to the intrinsic nonlinearity of the MBIR method, many well-known CT spatial resolution and noise properties have been modified. In particular, dose dependence and contrast dependence have been introduced to the spatial resolution of CT images by MBIR. The method has also introduced some novel noise-resolution trade-off not seen in traditional CT images. While the benefits of MBIR regarding the overall image quality, as demonstrated in this work, are significant, the optimal use of this method in clinical practice demands a thorough understanding of its unique physical characteristics.

Effects of radiographic techniques on the low-contrast detail detectability performance of digital radiography systems

PURPOSE

To evaluate the effects of the radiation exposure factors kilovolt peak and tube current time (milliampere seconds) on the low-contrast detail detectability performance of 3 types of planar digital radiography systems. Detectability performance of an imaging system refers to its ability to detect and present the low-contrast details of organs in the acquired image. The authors also compare detectability performance between computed radiography, indirect digital radiography, and direct digital radiography by evaluating low-contrast details of the obtained images.

METHODS

A low-contrast detail phantom was inserted within 10-cm thicknesses of Perspex plastic sheets. The images were obtained with various kilovolt peak and milliampere second settings for each of the 3 digital radiography systems. Artinis CDRAD Analyser software was used to score the images and calculate the inverse image quality figure (IQFinv).

RESULTS

The higher milliampere second levels in each kilovolt peak selection resulted in higher IQFinv in computed radiography and indirect and direct digital radiography. IQFinv values significantly increased in indirect digital radiography with increasing kilovolt peak in only 1 and 2 mAs. There were insignificant differences in IQFinv values when altering kilovolt peak in each milliampere second level in direct digital radiography. The indirect digital radiography system generally demonstrated better detectability performance than computed radiography and direct digital radiography. However, direct digital radiography demonstrated better detectability performance than indirect digital radiography at lower kilovolt peak and milliampere second settings, as did computed radiography at lower kilovolt peak settings.

DISCUSSION

Higher milliampere second settings increase photon count, which results in a higher signal-to-noise ratio and thus increased detectability. Lower milliampere second settings increase noise level on images, which increases the risk of diagnostic detail loss. Changing the kilovolt peak at the different milliampere second settings essentially did not affect the IQFinv of the different digital radiography systems.

CONCLUSION

Increasing milliampere seconds in all digital imaging systems generally improves detectability performance. However, altering the kilovolt peak setting does not significantly change the IQFinv and detectability of objects in a digital radiograph. Imaging system selection should be based on typical radiographic examinations. Indirect digital radiography systems are better for studies that require higher kilovolt peak, such as large organs, and direct digital radiography is better for studies that require low kilovolt peak, such as small organs and mammography, which is used to examine fine tissue details.

Effects of kilovoltage, milliampere seconds, and focal spot size on image quality

PURPOSE

To determine how kilovoltage (kV), milliampere seconds (mAs), and focal spot size affect perceptual image quality using a hand phantom.

METHODS

Using computed radiography, 70 images of a posteroanterior (PA) oblique hand phantom were acquired with different kilovoltage and milliampere second values using large and small focal spot sizes. Images were displayed on quality-controlled monitors with dimmed ambient lighting. The look-up table for hand radiography was used for image display. Five diagnostic radiographers scored each image for perceptual image quality against a reference image using a 5-point Likert scale.

RESULTS

No significant difference in image quality was found between small and large focal spot sizes at different kilovoltage (P = .46) and milliampere second (P = .56) values. As milliampere seconds increase, perceptual image quality increases gradually from 0.4 mAs to 4 mAs, after which perceptual image quality begins to deteriorate. When kilovoltage increases to within the range of 40 kV to 55 kV, perceptual image quality increases; image quality remains stable after 55 kV.

DISCUSSION

This study shows that both large and small focal spot sizes produce images of similar quality, and a wide range of kilovoltage and milliampere seconds can be used to produce images of acceptable quality. The implications of these findings include the potential for extending the life of radiography equipment and the potential for reducing the dose patients receive during appendicular examinations.

CONCLUSION

Large focal spot size can be used for PA oblique hand imaging without affecting perceptual image quality. Perceptual image quality remains acceptable and stable for a wide range of kilovoltage and milliampere second values. Optimization of these technical factors to achieve image quality is critical to avoiding higher radiation doses than necessary.

Optimization of configuration parameters in a newly developed digital breast tomosynthesis system

The purpose of the present work was to investigate the effects of variable projection-view (PV) and angular dose (AD) distributions on the reconstructed image quality for improving microcalcification detection. The PV densities at central and peripheral sites were varied through the distribution of 21 PVs acquired over ± 25° angular range. To vary the AD distribution, 7 PVs in the central region were targeted with two, four and six times the peripheral dose, and the number of central PVs receiving four times the peripheral dose was increased from 3 to 11. The contrast-to-noise ratio (CNR) for in-focus plane quality and the full width at half maximum (FWHM) of artifact spread function (ASF) for resolution in the z-direction were used. Although the ASF improved with increasing PV densities at two peripheral sites, the CNRs were inferior to those obtained with other subsets. With increasing PV density in the central area, the vertical resolution decreased but the CNR increased. Although increasing the central PV or AD concentrations improved image quality, excessive central densities reduced image quality by increasing noise in peripheral views.

Dose reduction in standard head CT: first results from a new scanner using iterative reconstruction and a new detector type in comparison with two previous generations of multi-slice CT

Purpose

Computed tomography (CT) accounts for more than half of the total radiation exposure from medical procedures, which makes dose reduction in CT an effective means of reducing radiation exposure. We analysed the dose reduction that can be achieved with a new CT scanner [Somatom Edge (E)] that incorporates new developments in hardware (detector) and software (iterative reconstruction).

Methods

We compared weighted volume CT dose index (CTDI_vol) and dose length product (DLP) values of 25 consecutive patients studied with non-enhanced standard brain CT with the new scanner and with two previous models each, a 64-slice 64-row multi-detector CT (MDCT) scanner with 64 rows (S64) and a 16-slice 16-row MDCT scanner with 16 rows (S16). We analysed signal-to-noise and contrast-to-noise ratios in images from the three scanners and performed a quality rating by three neuroradiologists to analyse whether dose reduction techniques still yield sufficient diagnostic quality.

Results

CTDI_Vol of scanner E was 41.5 and 36.4 % less than the values of scanners S16 and S64, respectively; the DLP values were 40 and 38.3 % less. All differences were statistically significant (p < 0.0001).

Signal-to-noise and contrast-to-noise ratios were best in S64; these differences also reached statistical significance. Image analysis, however, showed “non-inferiority” of scanner E regarding image quality.

Conclusions

The first experience with the new scanner shows that new dose reduction techniques allow for up to 40 % dose reduction while still maintaining image quality at a diagnostically usable level.

Evaluation of imaging performance of megavoltage cone-beam CT over an extended period

A linear accelerator vendor and the AAPM TG-142 report propose that quality assurance testing for image-guided devices such megavoltage cone-beam CT (MV-CBCT) be conducted on a monthly basis. In clinical settings, however, unpredictable errors such as image artifacts can occur even when quality assurance results performed at this frequency are within tolerance limits. Here, we evaluated the imaging performance of MV-CBCT on a weekly basis for ∼ 1 year using a Siemens ONCOR machine with a 6-MV X-ray and an image-quality phantom. Image acquisition was undertaken using 15 monitor units. Geometric distortion was evaluated with beads evenly distributed in the phantom, and the results were compared with the expected position in three dimensions. Image-quality characteristics of the system were measured and assessed qualitatively and quantitatively, including image noise and uniformity, low-contrast resolution, high-contrast resolution and spatial resolution. All evaluations were performed 100 times each. For geometric distortion, deviation between the measured and expected values was within the tolerance limit of 2 mm. However, a subtle systematic error was found which meant that the phantom was rotated slightly in a clockwise manner, possibly due to geometry calibration of the MV-CBCT system. Regarding image noise and uniformity, two incidents over tolerance occurred in 100 measurements. This phenomenon disappeared after dose calibration of beam output for MV-CBCT. In contrast, all results for low-contrast resolution, high-contrast resolution and spatial resolution were within their respective tolerances.

Automatable sample fabrication process for pump-probe X-ray holographic imaging

Soft X-ray holography is a recently developed imaging technique with sub-50 nm spatial resolution. Key advantages of this technique are magnetic and elemental sensitivity, compatibility with imaging at free electron laser facilities, and immunity to in-situ sample excitations and sample drift, which enables the reliable detection of relative changes between two images with a precision of a few nanometers. In X-ray holography, the main part of the experimental setup is integrated in the sample, which consequently requires a large number of fabrication steps. Here we present a generic design and an automatable fabrication process for samples suitable, and optimized for, efficient high resolution X-ray holographic dynamic imaging. The high efficiency of the design facilitates the acquisition of magnetic images in a few minutes and makes fully automatic image reconstruction possible.

[Effect of preoperative digital planning in acetabular reconstruction in development dysplasia of the hip]

OBJECTIVE

To evaluate the effect of preoperative digital planning in acetabular reconstruction of total hip arthroplasty (THA) for development dysplasia of the hip (DDH).

METHODS

A prospective study was performed on 42 patients with DDH undergoing primary THA between January 2009 and December 2011. The patients were divided into 2 groups according to whether preoperative digital planning was made or not; before operation, conventional imaging method was used in 23 cases (group A), and TraumaCad software was used for preoperative digital planning in 19 cases (group B). There was no significant difference in gender, age, body mass index, DDH classification, and preoperative Harris score between 2 groups (P > 0.05). The operation time, amount of bleeding, and postoperative complication were observed. After 7 days of operation, X-ray films were done to measure the vertical location, horizontal location, radiographic anteversion angle, radiographic inclination angle, and prosthesis size by TraumaCad software. The qualified rate of cup placement was compared between 2 groups. Coincidence rate of cup size between preoperative predicted by the digital planning and actually implanted in group B also was calculated.

RESULTS

The operation time and the amount of bleeding were (119.25 +/- 47.16) minutes and (410.00 +/- 200.39) mL in group A and were (155.31 +/- 84.03) minutes and (387.50 +/- 251.99) mL in group B respectively, showing no significant difference between 2 groups (P > 0.05). Incision infection and prosthetic anterior dislocation occurred in 1 case of group A respectively, prosthetic posterior dislocation in 1 case of group B. The patients were followed up 1 year and 1 month to 4 years and 1 month (mean, 2 years and 8 months ) in group A, and 1 year and 3 months to 4 years (mean, 2 years and 7 months) in group B. At last follow-up, the Harris scores were 91.09 +/- 5.35 in group A and 91.72 +/- 3.48 in group B, which were significantly increased when compared with preoperative scores (P < 0.05), but no significant difference was found between 2 groups (t=0.41, P=0.69). The qualified rate of cup placement of group B (78.95%, 15/19) was significantly higher than that of group A (43.48%, 10/23) (chi2=5.43, P=0.02); the coincidence rate of the cup size between preoperative predicted by the digital planning and actually implanted was 68.42% (13/19).

CONCLUSION

Preoperative digital planning can further optimize the acetabular reconstruction in THA for DDH.

Comparison of different phantom designs for CT scanner automatic tube current modulation system tests

Modern CT scanners modulate tube current during scans according to patient size, shape and attenuation. However, the ATCM (automatic tube current modulation) systems for different CT manufacturers work on different principles. Although the systems are used for the majority of patients and examinations, there is no standard phantom for routine quality control of CT scanner ATCM operation. The ideal phantom for testing these systems should be capable of evaluating how tube current and image quality as well as dose vary according to changes in patient size and shape. For this study, a conical phantom designed by ImPACT has been compared with two phantoms made from elliptical sections with varying dimensions. The concept of the designs is to reflect the ATCM performance for the varying shapes and dimensions along the length of the human body. The first phantom comprises five elliptical sections with a wide range of different dimensions and the second has three sections that are more similar in size. The phantoms have been used to test ATCM systems for Philips, Siemens, GE and Toshiba scanners. Although the results of the tube current modulation patterns were similar for all CT scanners, the abrupt changes in attenuation for the first sectional phantom provoked an abnormal ATCM response for the GE and Toshiba scanners. The second sectional phantom was developed from the results of the first, and was more effective for ATCM system testing and could be used for dose and image quality assessment in standard positions. However, the ImPACT conical phantom provided the best overall assessment of performance in terms of tube current modulations and noise pattern.

Grating-based x-ray phase-contrast imaging with a multi energy-channel photon-counting pixel detector

We have carried out grating-based x-ray differential phase-contrast measurements with a hybrid pixel detector in 16 energy channels simultaneously. A method for combining the energy resolved phase-contrast images based on energy weighting is presented. An improvement in contrast-to-noise ratio by 58.2% with respect to an emulated integrating detector could be observed in the final image. The same image quality could thus be achieved with this detector and with energy weighting at 60.0% reduced dose compared to an integrating detector. The benefit of the method depends on the object, spectrum, interferometer design and the detector efficiency.

An analysis of radiation dose reduction in paediatric interventional cardiology by altering frame rate and use of the anti-scatter grid

The purpose of this work is to investigate removal of the anti-scatter grid and alteration of the frame rate in paediatric interventional cardiology (IC) and assess the impact on radiation dose and image quality. Phantom based experimental studies were performed in a dedicated cardiac catheterisation suite to investigate variations in radiation dose and image quality, with various changes in imaging parameters. Phantom based experimental studies employing these variations in technique identified that radiation dose reductions of 28%-49% can be made to the patient with minimal loss of image quality in smaller sized patients. At present, there is no standard technique for carrying out paediatric IC in the UK or Ireland, resulting in the potential for a wide variation in radiation dose. Dose reductions to patients can be achieved with slight alterations to the imaging equipment with minimal compromise to the image quality. These simple modifications can be easily implemented in clinical practice in IC centres.

[Effects of 3-megapixel and 5-megapixel monitors on detecting micro-calcification in high- and low-resolution breast images]

To evaluate the influence of 3- and 5-megapixel medical professional monitors in detecting the micro-calcifications on high- and low-resolution breast images, we performed a retrospective study in low- (n = 100) and high-resolution (n = 100) data, including 40 micro-calcification patients in a group and 60 normal ones in control group respectively. Two doctors, one junior, and the other senior, reviewed all the images without knowing the clinical data and histology, and their observations of each image with different monitors were calculated. The areas under the ROC curves (Az) were compared. Finally, the interpretation consistency of the two doctors was assessed using Kappa analysis. In the low resolution data group, the two doctors' detection performance of breast micro-calcifications were very similar in the 3M and 5M medical professional monitors (P = 0.451 and 0.559). In the high resolution group, however, the senior doctor's recognition rate on the 5M monitor was significantly higher than that on the 3M (P = 0.022), while the junior's recognition rate had no significant difference (P = 0.141) between the two readings. The two doctors' interpretation consistency on 5M monitor was better than that on 3M monitor. For the high-resolution images on the 5M monitor, the interpretation of the two doctors had extremely great consistency (K = 0.862). Therefore, different breast images of different resolutions should match corresponding resolution monitor. Interpretation of high-resolution images with 5M monitor has more advantages in the micro-calcification detection for senior doctors.

First demonstration of multiplexed X-ray fluorescence computed tomography (XFCT) imaging

Simultaneous imaging of multiple probes or biomarkers represents a critical step toward high specificity molecular imaging. In this work, we propose to utilize the element-specific nature of the X-ray fluorescence (XRF) signal for imaging multiple elements simultaneously (multiplexing) using XRF computed tomography (XFCT). A 5-mm-diameter pencil beam produced by a polychromatic X-ray source (150 kV, 20 mA) was used to stimulate emission of XRF photons from 2% (weight/volume) gold (Au), gadolinium (Gd), and barium (Ba) embedded within a water phantom. The phantom was translated and rotated relative to the stationary pencil beam in a first-generation CT geometry. The X-ray energy spectrum was collected for 18 s at each position using a cadmium telluride detector. The spectra were then used to isolate the K shell XRF peak and to generate sinograms for the three elements of interest. The distribution and concentration of the three elements were reconstructed with the iterative maximum likelihood expectation maximization algorithm. The linearity between the XFCT intensity and the concentrations of elements of interest was investigated. We found that measured XRF spectra showed sharp peaks characteristic of Au, Gd, and Ba. The narrow full-width at half-maximum (FWHM) of the peaks strongly supports the potential of XFCT for multiplexed imaging of Au, Gd, and Ba ( FWHM(Au,Kα1) = 0.619 keV, FWHM(Au,Kα2)=1.371 keV , FWHM(Gd,Kα)=1.297 keV, FWHM(Gd,Kβ)=0.974 keV , FWHM(Ba,Kα)=0.852 keV, and FWHM(Ba,Kβ)=0.594 keV ). The distribution of Au, Gd, and Ba in the water phantom was clearly identifiable in the reconstructed XRF images. Our results showed linear relationships between the XRF intensity of each tested element and their concentrations ( R(2)(Au)=0.944 , R(Gd)(2)=0.986, and R(Ba)(2)=0.999), suggesting that XFCT is capable of quantitative imaging. Finally, a transmission CT image was obtained to show the potential of the approach for providing attenuation correction and morphological information. In conclusion, XFCT is a promising modality for multiplexed imaging of high atomic number probes.

Transport of intensity phase reconstruction to solve the twin image problem in holographic x-ray imaging

We have implemented a deterministic method for solving the phase problem in hard x-ray in-line holography which overcomes the twin image problem. The phase distribution in the detector plane is retrieved by using two images with slightly different Fresnel numbers. We then use measured intensities and reconstructed phases in the detection plane to compute the exit wave in the sample plane. No further a priori information like a limited support or the assumption of pure phase objects is necessary so that it can be used for a wide range of complex samples. Using a nano-focused hard x-ray beam half period resolutions better than 30 nm are achieved.

Analytical and experimental determination of signal-to-noise ratio and figure of merit in three phase-contrast imaging techniques

We present a theoretical and experimental comparison of three X-ray phase-contrast techniques: propagation-based imaging, analyzer-based imaging and grating interferometry. The signal-to-noise ratio and the figure of merit are quantitatively compared for the three techniques on the same phantoms and using the same X-ray source and detector. Principal dependencies of the signal upon the numerous acquisition parameters, the spatial resolution and X-ray energy are discussed in detail. The sensitivity of each technique, in terms of the smallest detectable phase shift, is also evaluated.

Volume-of-interest imaging of the inner ear in a human temporal bone specimen using a robot- driven C-arm flat panel detector CT system

VOI imaging can provide higher image quality at a reduced dose for a subregion. In this study with a robot-driven C-arm FDCT system, the goals were proof of feasibility for inner ear imaging, higher flexibility during data acquisition, and easier processing during reconstruction. First a low-dose OV scan was acquired allowing an orientation and enabling the selection of the VOI. The C-arm was then moved by the robotic system without a need for patient movement and the VOI was scanned with adapted parameters. Uncompromised artifact-free image quality was achieved by the 2-scan approach and the dose was reduced by 80%-90% in comparison with conventional MSCT and FPCT scans.

Augmented reality patient-specific reconstruction plate design for pelvic and acetabular fracture surgery

PURPOSE

The objective of this work is to develop a preoperative reconstruction plate design system for unilateral pelvic and acetabular fracture reduction and internal fixation surgery, using computer graphics and augmented reality (AR) techniques, in order to respect the patient-specific morphology and to reduce surgical invasiveness, as well as to simplify the surgical procedure.

MATERIALS AND METHODS

Our AR-aided implant design and contouring system is composed of two subsystems: a semi-automatic 3D virtual fracture reduction system to establish the patient-specific anatomical model and a preoperative templating system to create the virtual and real surgical implants. Preoperative 3D CT data are taken as input. The virtual fracture reduction system exploits the symmetric nature of the skeletal system to build a "repaired" pelvis model, on which reconstruction plates are planned interactively. A lightweight AR environment is set up to allow surgeons to match the actual implants to the digital ones intuitively. The effectiveness of this system is qualitatively demonstrated with 6 clinical cases. Its reliability was assessed based on the inter-observer reproducibility of the resulting virtual implants.

RESULTS

The implants designed with the proposed system were successfully applied to all cases through minimally invasive surgeries. After the treatments, no further complications were reported. The inter-observer variability of the virtual implant geometry is 0.63 mm on average with a standard deviation of 0.49 mm. The time required for implant creation with our system is 10 min on average.

CONCLUSION

It is feasible to apply the proposed AR-aided design system for noninvasive implant contouring for unilateral fracture reduction and internal fixation surgery. It also enables a patient-specific surgical planning procedure with potentially improved efficiency.

Fast lung nodule detection in chest CT images using cylindrical nodule-enhancement filter

PURPOSE

Existing computer-aided detection schemes for lung nodule detection require a large number of calculations and tens of minutes per case; there is a large gap between image acquisition time and nodule detection time. In this study, we propose a fast detection scheme of lung nodule in chest CT images using cylindrical nodule-enhancement filter with the aim of improving the workflow for diagnosis in CT examinations.

METHODS

Proposed detection scheme involves segmentation of the lung region, preprocessing, nodule enhancement, further segmentation, and false-positive (FP) reduction. As a nodule enhancement, our method employs a cylindrical shape filter to reduce the number of calculations. False positives (FPs) in nodule candidates are reduced using support vector machine and seven types of characteristic parameters.

RESULTS

The detection performance and speed were evaluated experimentally using Lung Image Database Consortium publicly available image database. A 5-fold cross-validation result demonstrates that our method correctly detects 80 % of nodules with 4.2 FPs per case, and detection speed of proposed method is also 4-36 times faster than existing methods.

CONCLUSION

Detection performance and speed indicate that our method may be useful for fast detection of lung nodules in CT images.