Thick Slices from Tomosynthesis Data Sets: Phantom Study for the Evaluation of Different Algorithms

PURPOSE  

Tomosynthesis is a 3-dimensional mammography technique that generates thin slices separated one to the other by typically 1 mm from source data sets. The relatively high image noise in these thin slices raises the value of 1-cm thick slices computed from the set of reconstructed slices for image interpretation. In an initial evaluation, we investigated the potential of different algorithms for generating thick slices from tomosynthesis source data (maximum intensity projection—MIP; average algorithm—AV, and image generation by means of a new algorithm, so-called softMip). The three postprocessing techniques were evaluated using a homogeneous phantom with one textured slab with a total thickness of about 5 cm in which two 0.5-cm-thick slabs contained objects to simulate microcalcifications, spiculated masses, and round masses. The phantom was examined by tomosynthesis (GE Healthcare). Microcalcifications were simulated by inclusion of calcium particles of four different sizes. The slabs containing the inclusions were examined in two different configurations: adjacent to each other and close to the detector and with the two slabs separated by two 1-cm thick breast equivalent material slabs. The reconstructed tomosynthesis slices were postprocessed using MIP, AV, and softMip to generate 1-cm thick slices with a lower noise level. The three postprocessing algorithms were assessed by calculating the resulting contrast versus background for the simulated microcalcifications and contrast-to-noise ratios (CNR) for the other objects. The CNRs of the simulated round and spiculated masses were most favorable for the thick slices generated with the average algorithm, followed by softMip and MIP. Contrast of the simulated microcalcifications was best for MIP, followed by softMip and average projections. Our results suggest that the additional generation of thick slices may improve the visualization of objects in tomosynthesis. This improvement differs from the different algorithms for microcalcifications, speculated objects, and round masses. SoftMip is a new approach combining features of MIP and average showing image properties in between MIP and AV.     

Contrast Detail Phantom Comparison on a Commercially Available Unit. Digital Breast Tomosynthesis (DBT) versus Full-Field Digital Mammography (FFDM)

The performance of a commercial digital mammographic system working in 2D planar versus tomosynthesis mode was evaluated in terms of the image signal difference to noise ratio (SDNR). A contrast detail phantom was obtained embedding 1 cm Plexiglas, including 49 holes of different diameter and depth, between two layers containing a breast-simulating material. The phantom was exposed with the details plane perpendicular to the X-ray beam using the manufacturer’s standard clinical breast acquisition parameters. SDNR in the digital breast tomosynthesis (DBT) images was higher than that of the full-field digital mammography (FFDM) for 38 out of 49 details in complex background conditions. These differences (p < 0.05) are statistically significant for 19 details out of 38. The relative SDNR results for DBT and FFDM images showed a dependence on the diameter of the details considered. This paper proposes an initial framework for a global image quality evaluation for commercial systems that can operate with different image acquisition modality using the same detector.     

Sensitivity of Thoracic Digital Tomosynthesis (DTS) for the Identification of Lung Nodules

Thoracic computed tomography (CT) is considered the gold standard for detection lung pathology, yet its efficacy as a screening tool in regards to cost and radiation dose continues to evolve. Chest radiography (CXR) remains a useful and ubiquitous tool for detection and characterization of pulmonary pathology, but reduced sensitivity and specificity compared to CT. This prospective, blinded study compares the sensitivity of digital tomosynthesis (DTS), to that of CT and CXR for the identification and characterization of lung nodules. Ninety-five outpatients received a posteroanterior (PA) and lateral CXR, DTS, and chest CT at one care episode. The CXR and DTS studies were independently interpreted by three thoracic radiologists. The CT studies were used as the gold standard and read by a fourth thoracic radiologist. Nodules were characterized by presence, location, size, and composition. The agreement between observers and the effective radiation dose for each modality was objectively calculated. One hundred forty-five nodules of greatest diameter larger than 4 mm and 215 nodules less than 4 mm were identified by CT. DTS identified significantly more >4 mm nodules than CXR (DTS 32 % vs. CXR 17 %). CXR and DTS showed no significant difference in the ability to identify the smaller nodules or central nodules within 3 cm of the hilum. DTS outperformed CXR in identifying pleural nodules and those nodules located greater than 3 cm from the hilum. Average radiation dose for CXR, DTS, and CT were 0.10, 0.21, and 6.8 mSv, respectively. Thoracic digital tomosynthesis requires significantly less radiation dose than CT and nearly doubles the sensitivity of that of CXR for the identification of lung nodules greater than 4 mm. However, sensitivity and specificity for detection and characterization of lung nodules remains substantially less than CT. The apparent benefits over CXR, low cost, rapid acquisition, and minimal radiation dose of thoracic DTS suggest that it may be a useful procedure. Work-up of a newly diagnosed nodule will likely require CT, given its superior cross-sectional characterization. Further investigation of DTS as a diagnostic, screening, and surveillance tool is warranted.     

Quantitative Analysis of the Effect of Iterative Reconstruction Using a Phantom: Determining the Appropriate Blending Percentage

Purpose

To investigate the optimal blending percentage of adaptive statistical iterative reconstruction (ASIR) in a reduced radiation dose while preserving a degree of image quality and texture that is similar to that of standard-dose computed tomography (CT).

Materials and Methods

The CT performance phantom was scanned with standard and dose reduction protocols including reduced mAs or kVp. Image quality parameters including noise, spatial, and low-contrast resolution, as well as image texture, were quantitatively evaluated after applying various blending percentages of ASIR. The optimal blending percentage of ASIR that preserved image quality and texture compared to standard dose CT was investigated in each radiation dose reduction protocol.

Results

As the percentage of ASIR increased, noise and spatial-resolution decreased, whereas low-contrast resolution increased. In the texture analysis, an increasing percentage of ASIR resulted in an increase of angular second moment, inverse difference moment, and correlation and in a decrease of contrast and entropy. The 20% and 40% dose reduction protocols with 20% and 40% ASIR blending, respectively, resulted in an optimal quality of images with preservation of the image texture.

Conclusion

Blending the 40% ASIR to the 40% reduced tube-current product can maximize radiation dose reduction and preserve adequate image quality and texture.     

Motion Alterations After Anterior Cruciate Ligament Reconstruction: Comparison of the Injured and Uninjured Lower Limbs During a Single-Legged Jump

Context:

Asymmetries subsist after anterior cruciate ligament reconstruction (ACL-R), and it is unclear how lower limb motion is altered in the context of a dynamic movement.

Objective:

To highlight the alterations observed in the injured limb (IL) during the performance of a dynamic movement after ACL-R.

Design:

Cross-sectional study.

Setting:

Research laboratory.

Patients or Other Participants:

A total of 11 men (age = 23.3 ± 3.8 years, mass = 81.2 ± 17.0 kg) who underwent ACL-R took part in this study 7.3 ± 1.1 months (range = 6–9 months) after surgery.

Intervention(s):

Kinematic and kinetic analyses of a single-legged squat jump were performed. The uninjured leg (UL) was used as the control variable.

Main Outcome Measure(s):

Kinematic and kinetic variables.

Results:

Jump height was 24% less for the IL than the UL (F_1,9 = 23.3, P = .001), whereas the push-off phase duration was similar for both lower limbs (P = .96). Knee-joint extension (F_1,9 = 11.4, P = .009), and ankle plantar flexion (F_1,9 = 22.6, P = .001) were less at takeoff for the IL than the UL. The hip angle at takeoff was not different between lower limbs (P = .09). We found that total moment was 14% less (F_1,9 = 11.1, P = .01) and total power was 35% less (F_1,9 = 24.2, P = .001) for the IL than the UL. Maximal hip (P = .09) and knee (P = .21) power was not different between legs. The IL had 34% less maximal ankle power (F_1,9 = 11.3, P = .009) and 31% less angular velocity of ankle plantar flexion (F_1,9 = 17.8, P = .004) than the UL.

Conclusions:

At 7.3 months after ACL-R, motion alterations were present in the IL, leading to a decrease in dynamic movement performance. Enhancing the tools for assessing articular and muscular variables during a multijoint movement would help to individualize rehabilitation protocols after ACL-R.Key Words: knee, dynamic movement, hop test, rehabilitation

Key Points:

• Kinematic and kinetic alterations were demonstrated in the injured leg at 7.3 months after anterior cruciate ligament reconstruction.
• These alterations led to decreased jump height during a single-legged squat jump in the injured leg.
• Enhancing tools for assessing articular and muscular variables during a multijoint movement would help to individualize rehabilitation protocols after anterior cruciate ligament reconstruction.

Anterior cruciate ligament (ACL) reconstruction involving bone-patellar tendon-bone (BPTB) or hamstrings tendon grafts has been commonly used after ACL rupture.¹ Ligament reconstruction often requires a long period of recovery, with a return to sport typically around 6.2 months after surgery.² However, the return to high-performance pivoting sports is not ensured. Sixty-seven percent were unable to return to their preinjury sport participation levels by 12 months after surgery.³Postoperative follow up, therefore, is crucial to evaluate the functional states of patients and individualize rehabilitation programs to achieve optimal recovery. Currently, several variables can help to monitor postoperative follow up⁴: (1) clinical measures, such as edema, pain, mobility, and stability of the knee joint; (2) subjective measures, such as the subjective knee form of the International Knee Documentation Committee⁵; and (3) objective measures, such as the measurement of anterior translation of the tibia on radiographs and the assessment of muscular recovery. To evaluate muscular recovery, 2 main types of tests are performed: an isokinetic test⁶ and functional tests.^6,7 The uninjured limb (UL) is used as a reference, and the goal of rehabilitation is to increase side-to-side symmetry.^6,8–10The isokinetic test helps to quantify muscular recovery by measuring peak muscle torque of the extensor and flexor muscles of the knee joint. Some authors^1,11 have shown deficits in the quadriceps and hamstrings muscles after ACL reconstruction. However, this test solely focuses on the knee joint and does not take into account the multijoint dimension of movements performed in sport activities.¹²Functional tests use single-legged functional movements involving the hip, knee, and ankle joints to identify performance deficits between the lower extremities. During vertical jumps, jump height was 14% to 24% less in the injured leg (IL) than in the UL¹³ 6 months after ACL reconstruction. Mohtadi et al¹ concluded that the results of functional tests did not differ with graft location. Functional tests use movements performed in sport activities, but they do not allow the identification of the deficit variables⁷ in terms of specific limitations responsible for the decrease in performance. In addition, these tests do not allow deficits to be corrected during rehabilitation.Some authors^14,15 have suggested the development of joint adaptations during multijoint movements after ACL reconstruction, consisting of modified joint positions and range of motion of the lower limb joints. Decker et al¹⁴ reported greater hip-extension and ankle plantar-flexion angles at initial ground contact during landing in the injured group than in the control group, and Pfeifer and Banzer¹⁵ observed that the range of motion of the knee joint during cycle single-legged jumps was less in the IL than in the UL. For kinetic analysis, Ernst et al¹⁶ measured a lower maximal knee moment in the IL than the UL and equivalent maximal hip and ankle moments in both limbs. Castanharo et al¹⁷ studied maximal power during a bilateral vertical jump and also noted a decrease in maximal knee power and equivalent maximal hip power in the ACL group compared with the control group. In these studies, joint and muscular variables were analyzed independently.Therefore, the purpose of our study was to highlight the alterations observed in the IL during the performance of a dynamic movement after ACL reconstruction. Our aim was to bring additional information to the current knowledge in the field of movement analysis to help multidisciplinary teams improve rehabilitation after ACL reconstruction. We hypothesized that (1) jump height would be less in the IL than in the UL, (2) we would find kinematic alterations with a modification in the joint positions of the lower limb joints of the IL at takeoff, and (3) we would find kinetic alterations with decreases in maximal knee moment and power in the IL compensated for by an increase in hip and ankle maximal moments and powers.     

A Comparison of Lung Nodule Segmentation Algorithms: Methods and Results from a Multi-institutional Study

Tumor volume estimation, as well as accurate and reproducible borders segmentation in medical images, are important in the diagnosis, staging, and assessment of response to cancer therapy. The goal of this study was to demonstrate the feasibility of a multi-institutional effort to assess the repeatability and reproducibility of nodule borders and volume estimate bias of computerized segmentation algorithms in CT images of lung cancer, and to provide results from such a study. The dataset used for this evaluation consisted of 52 tumors in 41 CT volumes (40 patient datasets and 1 dataset containing scans of 12 phantom nodules of known volume) from five collections available in The Cancer Imaging Archive. Three academic institutions developing lung nodule segmentation algorithms submitted results for three repeat runs for each of the nodules. We compared the performance of lung nodule segmentation algorithms by assessing several measurements of spatial overlap and volume measurement. Nodule sizes varied from 29 μl to 66 ml and demonstrated a diversity of shapes. Agreement in spatial overlap of segmentations was significantly higher for multiple runs of the same algorithm than between segmentations generated by different algorithms (p?<?0.05) and was significantly higher on the phantom dataset compared to the other datasets (p?<?0.05). Algorithms differed significantly in the bias of the measured volumes of the phantom nodules (p?<?0.05) underscoring the need for assessing performance on clinical data in addition to phantoms. Algorithms that most accurately estimated nodule volumes were not the most repeatable, emphasizing the need to evaluate both their accuracy and precision. There were considerable differences between algorithms, especially in a subset of heterogeneous nodules, underscoring the recommendation that the same software be used at all time points in longitudinal studies.     

胸腰椎骨折前路手术小切口显露方式与传统显露方式的临床结果比较

目的通过对小切口手术显露与传统手术显露完成的胸腰椎前路手术的临床结果作比较,总结小切口胸腰椎前路手术的特点,以改进手术质量。方法采用SynFrame和EndoRing前路手术拉钩系统,经胸膜外腹膜后或腹膜外入路完成胸腰椎前路减压、固定、融合手术（ALIF）19例,其结果和传统前路手术完成的25例作比较。统计分析采用卡方检验和t检验。结果所有手术均顺利完成。失血量小切口组398．42±52．52ml,少于传统组739．60±153．88ml（（P〈0．001）;切口长度小切口组11．05±1.31cm,小于传统组19．40±1．55cm（（P〈0．001）;术后24小时胃肠道功能恢复小切口组15人／19人,优于传统组2人／25人（（P〈0．001）：VAS评分改善值小切口组3．57±0．76,而传统组2．64±0．99（（P〈0．001）;其余指标比较均无统计学意义（P〉0．05）。随访时间6～24个月,平均为（14．50±2．40）个月。患者疼痛消失,植骨全部融合。结论SynFrame／Endoring拉钩完成的胸腰椎小切口微创手术创伤较小,暴露好,出血少,并发症减少,易于掌握,其手术减压和植骨融合达到传统手术的治疗效果。值得选用。     

Application of Deep Learning-Based Denoising Technique for Radiation Dose Reduction in Dynamic Abdominal CT: Comparison with Standard-Dose CT Using Hybrid Iterative Reconstruction Method

Journal of Digital Imaging - The purpose is to evaluate whether deep learning-based denoising (DLD) algorithm provides sufficient image quality for abdominal computed tomography (CT) with a 30%...     

体内金属植入物对放疗剂量分布的影响及物理分析

本文总结了目前体内金属植入物对光子线放疗剂量分布影响的研究结果,讨论产生相应影响的物理基础,并概述两大类金属植入物(金属内植入物和各种金属支架)对光子线放疗剂量分布影响的特点及临床处理原则.     

An Experimental Study on the Effect of the Anisotropic Regions in a Realistically Shaped Torso Phantom

Determination of electrically active regions in the human body by observing generated bioelectric and/or biomagnetic signals is known as source reconstruction. In the reconstruction process, it is assumed that the volume conductor consists of isotropic compartments and homogeneous tissue bioelectric parameters but this assumption introduces errors when the tissue of interest is anisotropic. The aim of this study was to investigate changes in the measured signal strengths and the estimated positions and orientations of current dipoles in a realistically shaped torso phantom having a heart region built from single guar gum skeins. Electric data were recorded with 60 electrodes on the front of the chest and 195 sensors measured the magnetic field 2 cm above the chest. The artificial rotating dipoles were located underneath the anisotropic skeins distant from the sensors. It was found that the signal strengths and estimated dipole orientations were influenced by the anisotropy while the estimated dipole positions were not significantly influenced. The signal strength was reduced between 17% and 43% for the different dipole positions when comparing the parallel alignment of dipole orientation and anisotropy direction with the orthogonal alignment. The largest error in the estimation of dipole orientation was 42 degrees. The observed changes in the magnetic fields and electric potentials can be explained by the fact that the anisotropic skeins force the current along its direction. We conclude that taking into account anisotropic structures in the volume conductor might improve signal analysis as well as source strength and orientation estimations for bioelectric and biomagnetic investigations.     

A Technique for Simulating the Effect of Dose Reduction on Image Quality in Digital Chest Radiography

Purpose: The purpose of this study is to provide a pragmatic tool for studying the relationship between dose and image quality in clinical chest images. To achieve this, we developed a technique for simulating the effect of dose reduction on image quality of digital chest images. Materials and Methods: The technique was developed for a digital charge-coupled-device (CCD) chest unit with slot-scan acquisition. Raw pixel values were scaled to a lower dose level, and a random number representing noise to each specific pixel value was added. After adding noise, raw images were post processed in the standard way. Validation was performed by comparing pixel standard deviation, as a measure of noise, in simulated images with images acquired at actual lower doses. To achieve this, a uniform test object and an anthropomorphic phantom were used. Additionally, noise power spectra of simulated and actual images were compared. Also, detectability of simulated lesions was investigated using a model observer. Results: The mean difference in noise values between simulated and real lower-dose phantom images was smaller than 5% for relevant clinical settings. Noise power spectra appeared to be comparable on average but simulated images showed slightly higher noise levels for higher spatial frequencies and slightly lower noise levels for lower spatial frequencies. Comparable detection performance was shown in simulated and actual images with slightly worse detectability for simulated lower dose images. Conclusion: We have developed and validated a method for simulating dose reduction. Our method seems an acceptable pragmatic tool for studying the relationship between dose and image quality.     

Computer-Generated Index for Evaluation of Idiopathic Scoliosis in Digital Chest Images: A Comparison with Digital Measurement

An intelligence system was used to generate index for scoliosis. Tests were designed to evaluate the consistency of the automatic computer-generated index and to quantify the correlation between Cobb angle and computer generated scoliosis classification index (SCI). A fully automatic computer-generated index can be used to assess the extent of spinal curvature rather than manual measurement on radiographs. This study aims to evaluate the relation of an automatic computer-generated index in assessing the spinal curvature of scoliosis quantitatively on digital chest images. Sixty chest radiographs were obtained in this study. Cobb angle measurement and the index generated were compared by parametric statistical tests. The SCI method was demonstrated to be reproducible. There was also statically significant positive correlation between Cobb angle and SCI (Pearson’s correlation: r = 0.9229). The Computer-generated index method is valid and reliable in quantifying measurement of spinal curvature of scoliosis as the correlation between Cobb’s angle and SCI in nearly perfect positive for Cobb angle more than 10 degree. It is noted that with widely use of this computer method, this quantitative method proposed is a promising method in improving the reliability of scoliosis assessment and reducing the workload of clinical staff.     

Digital radiography: Comparison of different methods for imaging of the thorax and the gastrointestinal tracts

In evaluating the image quality of the chest, four different analog and digital methods were compared. For peripheral lung field, the advanced multiple beam equalization radiography (AMBER) system was given the best score, followed in order by the storagephosphor, conventional, and asymmetric film/screen systems. For the mediastinal field, the highest image quality was given to the AMBER system, followed by storage phosphor and asymmetric film/screen system. The best overall image quality, especially with regard to demonstration of pathologic alteration, was given to the AMBER system, followed by the storagephosphor, conventional, and asymmetric film/screen radiography systems. In conclusion, AMBER demonstrated the highest image quality. The storage-phosphor system provided better results in the peripheral and mediastinal fields in comparison with conventional film/screen systems. Other digital systems including selenium chest radiography system and image intensifier digital radiography were also discussed.     

Dose optimization for the MRI-accelerator: IMRT in the presence of a magnetic field

A combined system of a 6 MV linear accelerator and a 1.5 T MRI scanner is currently being developed. In this system, the patient will be irradiated in the presence of a 1.5 T magnetic field. This causes a strong dose increase at tissue-air interfaces. Around air cavities in the patient, these effects may become problematic. Homogeneous dose distributions can be obtained around regularly shaped symmetrical cavities using opposing beams. However, for more irregularly shaped cavities this approach may not be sufficient. This study will investigate whether IMRT can be used to cope with magnetic field dose effects, in particular for target volumes adjacent to irregularly shaped air cavities. Therefore, an inverse treatment planning approach has been designed based on pre-calculated beamlet dose distribution kernels. Using this approach, optimized dose distributions were calculated for B = 1.5 T and for B = 0 T. Investigated target sites include a prostate cancer, a laryngeal cancer and an oropharyngeal cancer. Differences in the dose distribution between B = 0 and 1.5 T were minimal; only the skin dose increased for B = 1.5 T. Homogeneous dose distributions were obtained for target structures adjacent to air cavities without the use of opposing beams. These results show that a 1.5 T magnetic field does not compromise the ability to achieve desired dose distributions with IMRT.     

Serologic Testing for Celiac Disease in the United States: Results of a Multilaboratory Comparison Study

The aim of this study was to compare the efficiencies of six reference laboratories for serologic testing for celiac disease. Serum from 20 patients with untreated celiac disease and from 20 controls was thawed, divided, and distributed to each participating laboratory, which performed endomysial antibody tests. Five laboratories also performed antigliadin antibody tests. Sensitivity for endomysial antibody immunoglobulin A (IgA) varied from 57 to 90%. In all laboratories, the specificity for celiac disease was 100%. The sensitivity and specificity for both IgA and IgG antigliadin antibody varied significantly. When results from all three tests were combined in each laboratory, sensitivity was 90 to 100%. The specificity for endomysial antibody was 100% in the laboratories. Sensitivity was less than reported previously. Standardization of these tests is needed in the United States.