Bone Inserts Research Articles

Scatter estimation and correction using time-of-flight and deconvolution in x-ray medical imaging.

Objective Time-of-flight (TOF) scatter rejection requires a total timing jitter,
including the detector timing jitter and the X-ray source's pulses width, of 50 ps or less
to mitigate most of the effects of scattered photons in radiography and CT imaging.
However, since the total contribution of the source and detector to the timing jitter
can be retrieved during an acquisition with nothing between the source and detector,
it can be demonstrated that this contribution may be partially removed to improve
the image quality.
Approach A scatter correction method using iterative deconvolution of the measured
time point-spread function estimates the number of scattered photons detected in each
pixel. To evaluate the quality of the estimation, GATE was used to simulate the
radiography of a water cylinder with bone inserts, and a head and torso in a system
with total timing jitters from 100 ps up to 500 ps full-width-at-half-maximum.
Main results With a total timing jitter of 200 ps, 89% of the contrast degradation
caused by scattered photons was recovered in a head and torso radiography, compared
to 28% with a simple time threshold method. Corrected images using the estimation
have a percent root-mean square error between 2 and 14% in both phantoms with
timing jitters from 100 to 500 ps which is lower than the error achieved with scatter
rejection alone at 100 ps.
Significance TOF X-ray imaging has the potential to mitigate the effects of the
scattering contribution and offers an alternative to anti-scatter grids that avoids loss
of primary photons. Compare to simple TOF scatter rejection using only a threshold,
the deconvolution estimation approach has lower requirements on both the source and
detector. These requirements are now within reach of state-of-the-art systems.

Time-of-flight scatter rejection in x-ray radiography.

Objective.Time-of-flight (TOF) scatter rejection allows for identifying and discarding scattered photons without the use of an anti-scatter grid (ASG). Although TOF scatter rejection was initially presented for cone-beam computed tomography, we propose, herein, to extend this approach to x-ray radiography. This work aims to evaluate with simulations if TOF scatter rejection can outperform ASGs for radiography.Approach.GATE was used to simulate the radiography of a head and a torso and a water cylinder with bone inserts in a system with total timing jitters from 0 ps up to 500 ps full-width-at-half-maximum. The transmission factor of TOF scatter rejection for primary and scattered photons was evaluated as if it were a virtual ASG.Main results.With a total timing jitter of 50 ps, TOF scatter rejection can reach a selectivity of 4.93 with a primary photons transmission of 99%. Reducing the timing jitter close to 0 ps increases the selectivity up to 15.85 for a head and torso radiography, outperforming typical ASGs which usually have a selectivity from 2.5 to 10 with a primary photons transmission from 50% to 70%.Significance.This suggests that TOF scatter rejection may be suitable to replace ASGs in applications requiring lower radiation exposure if sufficiently low timing jitter is achieved.

Comparison of two deep-learning image reconstruction algorithms on cardiac CT images: A phantom study

PurposeThe purpose of this study was to compare the performance of Precise IQ Engine (PIQE) and Advanced intelligent Clear-IQ Engine (AiCE) algorithms on image-quality according to the dose level in a cardiac computed tomography (CT) protocol. Materials and methodsAcquisitions were performed using the CT ACR 464 phantom at three dose levels (volume CT dose indexes: 7.1/5.2/3.1 mGy) using a prospective cardiac CT protocol. Raw data were reconstructed using the three levels of AiCE and PIQE (Mild, Standard and Strong). The noise power spectrum (NPS) and task-based transfer function (TTF) for bone and acrylic inserts were computed. The detectability index (d’) was computed to model the detectability of the coronary lumen (350 Hounsfield units and 4-mm diameter) and non-calcified plaque (40 Hounsfield units and 2-mm diameter). ResultsNoise magnitude values were lower with PIQE than with AiCE (−13.4 ± 6.0 [standard deviation (SD)] % for Mild, -20.4 ± 4.0 [SD] % for Standard and -32.6 ± 2.6 [SD] % for Strong levels). The average NPS spatial frequencies shifted towards higher frequencies with PIQE than with AiCE (21.9 ± 3.5 [SD] % for Mild, 20.1 ± 3.0 [SD] % for Standard and 12.5 ± 3.5 [SD] % for Strong levels). The TTF values at fifty percent (f50) values shifted towards higher frequencies with PIQE than with AiCE for acrylic inserts but, for bone inserts, f50 values were found to be close. Whatever the dose and DLR level, d’ values of both simulated cardiac lesions were higher with PIQE than with AiCE. For the simulated coronary lumen, d’ values were better by 35.1 ± 9.3 (SD) % on average for all dose levels for Mild, 43.2 ± 5.0 (SD) % for Standard, and 62.6 ± 1.2 (SD) % for Strong levels. ConclusionCompared to AiCE, PIQE reduced noise, improved spatial resolution, noise texture and detectability of simulated cardiac lesions. PIQE seems to have a greater potential for dose reduction in cardiac CT acquisition.

Accuracy of Electron Density and Planning Dosimetry in a Novel High-Quality CBCT Imaging System

A high-quality Cone-Beam Computed Tomography (CBCT) imaging system has been FDA approved for imaging guidance and dose calculation in radiotherapy. This study aims to evaluate the accuracy of the relative electron density in CBCT images acquired in this CBCT imaging system in a phantom study and its dosimetric impact on treatment planning in a patient study. Astoichiometric CT calibration was performed with a CIRS phantom (SunNuclear, Model 062M) to generate the HU-electron density curve for two tube voltages, 125kVp and 140 kVp, respectively. The phantom has a longitudinal length of 26.5 cm and is equipped with interchangeable inserts of various compositions, supplied by the vendor. Measurements were taken with solid water plates added to both ends of the phantom to allow adequate scattering and repeated for various clinical protocols with different combinations of tube voltages and exposures. The accuracy of the relative electron density of the CBCT imaging system was verified by comparing the calculated electron density from the Hounsfield Units (HU) measurements obtained from a Gammex phantom to the relative electron densities provided in vendor's specifications. To benchmark the relative electron density of the CBCT imaging system against a standard helical CT simulator, ten clinical plans that were created on CT simulation images were copied and recalculated on the CBCT images acquired immediately after the CT simulation, the latter of which was a standard procedure in current radiotherapy care for all patients who had given their consent to participate in the IRB-approved imaging study. The dose grids used in these calculations were 2.5mm x 2.5mm x 3mm. The Gamma passing rate was calculated using a standard 3mm/3% criterion with a 10% threshold. Ourresults showed the difference between the averaged CBCT calibration curves acquired at tube voltages of 125 kVP and 140 kVp was less than 2%. The mean discrepancy of the relative electron densities from vendor's specification was 0.0045 with a range between -0.02 and 0.04. Relative electron densities in all inserts were within 2% from the vendor's specifications except the cortical bone insert. Gamma passing rate was between 96.02% and 98.49% with mean value of 97.4% and a standard deviation of 0.95%. We consider this reflects the fact that the CT simulation and CBCT imaging were performed in separated rooms, which resulted in slight anatomical deformation that could negatively impact the Gamma passing rate. The CBCT imaging system provides sufficient accuracy of electron density for dose calculation, and the dose distribution calculated on the CBCT images is clinically equivalent to those calculated on helical CT images. The enhanced imaging quality of CBCT could further extend the role of imaging guidance to planning for adaptive radiotherapy, potentially reducing the need for re-simulation and interruptions in the radiotherapy course.

Establishing quality control action limits for CT number accuracy in spectral images using an American College of Radiology phantom.

Computed tomography (CT) number accuracy is important for quality assurance in CT imaging. However, in dual-energy CT imaging, there are no widely used action limits for CT number accuracy in spectral images, information that is urgently needed. To establish action limits for spectral CT images using longitudinal spectral data and an American College of Radiology (ACR) phantom. An ACR accreditation phantom was scanned routinely as part of a quality control program in our institution. We selected and analyzed 57 continuous weekly scans. The CT numbers or the density values of conventional and spectral images, including virtual monoenergetic images (40, 50, 70, 120, and 200keV), iodine maps, calcium suppressed, and virtual non-contrast images, were measured in the four inserts (solid water, bone, polyethylene, and acrylic) of the phantom. Longitudinal data were analyzed for correlation using Pearson's correlation coefficient (r) and standard deviation (SD). The SD ratios between spectral images and conventional images were calculated and the action limits for spectral images were established based on the action limits from the ACR. Strong to very strong correlations (r>0.70 or r<-0.70) were found among most spectral image types except the 200keV images using solid water, polyethylene, and acrylic inserts (r=[-0.45, 0.64]). The SD ratio was highest for the 40keV images, ranging from 2.8 to 6.5. The action limits of the bone insert were baseline±5.3mg/mL for the iodine map and ranged from baseline±23.0 HU to baseline±391.9 HU for the other image types. The action limits for solid water ranged from baseline±4.1 HU to baseline±25.3 HU. The results for the polyethylene and the acrylic insert were close to those for solid water. Baselines can be established using the average of the initial 5∼10 measurements. Using longitudinal data, we estimated the action limits for CT number accuracy in the spectral images. This paves the way for establishing a comprehensive quality control program for spectral CT imaging.

A systematic task-based image quality assessment of photon-counting and energy integrating CT as a function of reconstruction kernel and phantom size.

Image quality of photon-counting and energy integrating CT scanners changes with object size, dose to the object, and kernel selection. To comprehensively compare task-generic image quality of photon-counting CT (PCCT) and energy integrating CT (EICT) systems as a function of phantom size, dose, and reconstruction kernel. A size-variant phantom (Mercury Phantom 3.0) was used to characterize the image quality of PCCT and EICT systems as a function of object size. The phantom contained five cylinders attached by slanted tapered sections. Each cylinder contained two sections: one uniform for noise, and the other with inserts for spatial resolution and contrast measurements. The phantom was scanned on Siemens' SOMATOM Force and NAEOTOM Alpha at 1.18 and 7.51mGy without tube current modulation. CTDIvol was matched across two systems by setting the required tube currents, else, all other acquisition settings were fixed. CT sinograms were reconstructed using FBP and iterative (ADMIRE2 - Force; QIR2 - Alpha) algorithms with Body regular (Br) kernels. Noise Power Spectrum (NPS), Task Transfer Function (TTF), contrast-to-noise ratio (CNR), and detectability index (d') for a task of identifying 2-mm disk were evaluated based on AAPM TG-233 metrology using imQuest, an open-source software package. Averaged noise frequency (fav ) and 50% cut-off frequency for TTF (f50 ) were used as scalar metrics to quantify noise texture and spatial resolution, respectively. The difference between image quality metrics' measurements was calculated as IQPCCT - IQEICT . From Br40 (soft) to Br64 (sharp), f50 for air insert increased from 0.35mm-1 ±0.04 (standard deviation) to 0.76mm-1 ±0.17, 0.34mm-1 ±0.04 to 0.77mm-1 ±0.17, 0.37mm-1 ±0.02 to 0.95mm-1 ±0.17 for PCCT-T3D-QIR2, PCCT-70keV-QIR2, and EICT-ADMIRE2, respectively, when averaged over all sizes and dose levels. Similarly, from Br40 to Br64, noise magnitude increased from 10.86 HU±7.12 to 38.61 HU±18.84, 10.94 HU±7.08 to 38.82 HU±18.70, 13.74 HU±11.02 to 52.11 HU±26.22 for PCCT-T3D-QIR2, PCCT-70keV-QIR2, and EICT-ADMIRE2, respectively. The difference in fav was consistent across all sizes and dose levels. PCCT-70keV-VMI showed better consistency in contrast measurements for iodine and bone inserts than PCCT-T3D and EICT; however, PCCT-T3D had higher contrast for both inserts. From Br40 to Br64, considering all sizes and dose levels, CNR for iodine insert decreased from 52.30±46.44 to 12.18±10.07, 40.42±33.42 to 9.48±7.16, 39.94±37.60 to 7.84±6.67 for PCCT-T3D-QIR2, PCCT-70keV-QIR2, and EICT-ADMIRE2, respectively. Both PCCT image types, T3D and 70-keV-VMI exhibited similar or better noise, contrast, CNR than EICT when comparing kernels with similar names. For 512×512 matrix, PCCT's sharp kernels had lower resolution than EICT's sharp kernels. For all image quality metrics, except extreme low, every dose condition had a similar set of IQ-matching kernels. It suggests that considering patient size and dose level to determine IQ-matching kernel pairs across PCCT and EICT systems may not be imperative while translating protocols, except when the signal to the detector is extremely low.

Impact of a novel multilayer imager on metal artifacts in MV-CBCT

Objective. Megavoltage cone-beam computed tomography (MV-CBCT) imaging offers several advantages including reduced metal artifacts and accurate electron density mapping for adaptive or emergent situations. However, MV-CBCT imaging is limited by the poor efficiency of current detectors. Here we examine a new MV imager and compare CBCT reconstructions under clinically relevant scenarios. Approach. A multilayer imager (MLI), consisting of four vertically stacked standard flat-panel imagers, was mounted to a clinical linear accelerator. A custom anthropomorphic pelvis phantom with replaceable femoral heads was imaged using MV-CBCT and kilovoltage CBCT (kV-CBCT). Bone, aluminum, and titanium were used as femoral head inserts. 8 MU 2.5 MV scans were acquired for all four layers and (as reference) the top layer. Prostate and bladder were contoured on a reference CT and transferred to the other scans after rigid registration, from which the structural similarity index measure (SSIM) was calculated. Prostate and bladder were also contoured on CBCT scans without guidance, and Dice coefficients were compared to CT contours. Main results. kV-CBCT demonstrated the highest SSIMs with bone inserts (prostate: 0.86, bladder: 0.94) and lowest with titanium inserts (0.32, 0.37). Four-layer MV-CBCT SSIMs were preserved with bone (0.75, 0.80) as compared to titanium (0.67, 0.74), outperforming kV-CBCT when metal is present. One-layer MV-CBCT consistently underperformed four-layer results across all phantom configurations. Unilateral titanium inserts and bilateral aluminum insert results fell between the bone and bilateral titanium results. Dice coefficients trended similarly, with four-layer MV-CBCT reducing metal artifact impact relative to KV-CBCT to provide better soft-tissue identification. Significance. MV-CBCT with a four-layer MLI showed improvement over single-layer MV scans, approaching kV-CBCT quality for soft-tissue contrast. In the presence of artifact-producing metal implants, four-layer MV-CBCT scans outperformed kV-CBCT by eliminating artifacts and single-layer MV-CBCT by reducing noise. MV-CBCT with a novel multi-layer imager may be a valuable alternative to kV-CBCT, particularly in the presence of metal.

High Spatial-Resolution Skull Base Imaging With Photon-Counting Computed Tomography and Energy-Integrating Computed Tomography: A Comparative Phantom Study.

Photon-counting computed tomography (PCCT) offers better high-resolution and noise performance than energy integrating detector (EID) CT. In this work, we compared both technologies for imaging of the temporal bone and skull base. A clinical PCCT system and 3 clinical EID CT scanners were used to image the American College of Radiology image quality phantom using a clinical imaging protocol with matched CTDI vol (CT dose index-volume) of 25 mGy. Images were used to characterize the image quality of each system across a series of high-resolution reconstruction options. Noise was calculated from the noise power spectrum, whereas resolution was quantified with a bone insert by calculating a task transfer function. Images of an anthropomorphic skull phantom and 2 patient cases were examined for visualization of small anatomical structures. Across measured conditions, PCCT had a comparable or smaller average noise magnitude (120 Hounsfield units [HU]) to the EID systems (144-326 HU). Photon-counting CT also had comparable resolution (task transfer function f25 : 1.60 mm -1 ) to the EID systems (1.34-1.77 mm -1 ). Imaging results supported quantitative findings as PCCT more clearly showed the 12-lp/cm bars from the fourth section of the American College of Radiology phantom and better represented the vestibular aqueduct and oval and round windows when compared with the EID scanners. A clinical PCCT system was able to image the temporal bone and skull base with improved spatial resolution and lower noise than clinical EID CT systems at matched dose.

Monoaxial Mechanical Tests on Porcino Knee Ligaments.

The failure of ligament reconstruction has different risk factors, among which we can highlight the period before its incorporation, which is a mechanically vulnerable period. Loss of resistance over time is a characteristic of living tissues. Dissection with bone insertions of the cruciate ligaments of animal models is not described; however, it is essential for monoaxial assays to extract information from tests such as relaxation. The present work describes the dissection used for the generation of a test body for the performance of nondestructive tests to evaluate the mechanical behavior. We performed dissection of four porcino knee ligaments, proposing a dissection technique for the cruciate ligaments with bone inserts for comparison with collateral ligaments. The ligaments were submitted to relaxation tests and had strain gauges placed during the tests. The results showed viscoelastic behavior, validated by strain gauges and with a loss over time; with some ligaments presenting with losses of up to 20%, a factor to be considered in future studies. The present work dissected the four main ligaments of the knee demonstrating the posterior approach that allows maintaining their bone insertions and described the fixation for the monotonic uniaxial trials, besides being able to extract the viscoelastic behavior of the four ligaments of the knee, within the physiological limits of the knee.

Technical note: Evaluation of artificial 120-kilovolt computed tomography images for radiation therapy applications.

The purpose of this work is to evaluate the scaled computed tomography (CT) number accuracy of an artificial 120kV reconstruction technique based on phantom experiments in the context of radiation therapy planning. An abdomen-shaped electron density phantom was scanned on a clinical CT scanner capable of artificial 120kV reconstruction using different tube potentials from 70 to 150kV. A series of tissue-equivalent phantom inserts (lung, adipose, breast, solid water, liver, inner bone, 30%/50% CaCO3 , cortical bone) were placed inside the phantom. Images were reconstructed using a conventional quantitative reconstruction kernel as well as the artificial 120kV reconstruction kernel. Scaled CT numbers of inserts were measured from images acquired at different kVs and compared with those acquired at 120kV, which were deemed as the ground truth. The relative error was quantified as the percentage deviation of scaled CT numbers acquired at different tube potentials from their ground truth values acquired at 120kV. Scaled CT numbers measured from images reconstructed using the conventional reconstruction demonstrated a strong kV-dependence. The relative error in scaled CT numbers ranged from 0.6% (liver insert) to 31.1% (cortical bone insert). The artificial 120kV reconstruction reduced the kV dependence, especially for bone tissues. The relative error in scaled CT number was reduced to 0.4% (liver insert) and 2.6% (30% CaCO3 insert) using this technique. When tube potential selection was limited to the range of 90 to 150kV, the relative error was further restrained to<1.2% for all tissue types. Phantom results demonstrated that using the artificial 120kV technique, it was feasible to acquire raw projection data at the desired tube potential and then reconstruct images with scaled CT numbers comparable to those obtained directly at 120kV. In radiotherapy applications, this technique may allow optimization of tube potential without complicating clinical workflow by eliminating the necessity of maintaining multiple sets of CT calibration curves.

Dose calculations for preclinical radiobiology experiments conducted with single-field cabinet irradiators.

To provide percentage depth dose (PDD) data along the central axis for dosimetry calculations in small-animal radiation biology experiments performed in cabinet irradiators. The PDDs are provided as a function of source-to-surface distance (SSD), field size, and animal size. The X-ray tube designs for four biological cabinet irradiators, the RS2000, RT250, MultiRad350, and XRAD320, were simulated using the BEAMnrc Monte Carlo code to generate 160, 200, 250, and 320kVp photon beams, respectively. The 320kVp beam was simulated with two filtrations: a soft F1 aluminium filter and a hard F2 thoraeus filter made of aluminium, tin, and copper. Beams were collimated into circular fields with diameters of 0.5-10cm at SSDs of 10-60cm. Monte Carlo dose calculations in 1-5-cm diameter homogeneous (soft tissue) small-animal phantoms as well as in heterogeneous phantoms with 3-mm diameter cylindrical lung and bone inserts (rib and cortical bone) were performed using DOSXYZnrc. The calculated depth doses in three test-cases were estimated by applying SSD, field size, and animal size correction factors to a reference case (40-cm SSD, 1-cm field, and 5-cm animal size), and these results were compared with the specifically simulated (i.e., expected) doses to assess the accuracy of this method. Dosimetry for two test-case scenarios of 160 and 250 kVp beams (representative of end-user beam qualities) was also performed, whereby the simulated PDDs at two different depths were compared with the results based on the interpolation from reference data. The depth doses for three test-cases calculated at 200, 320kVp F1, and 320kVp F2 with half value layers (HVLs) ranging from ∼0.6to 3.6mm Cu, agreed well with the expected doses, yielding dose differences of 1.2%, 0.1%, and 1.0%, respectively. The two end-user test-cases for 160 and 250 kVp beams with respective HVLs of ∼0.8 and 1.8mm Cu yielded dose differences of 1.4% and 3.2% between the simulated and the interpolated PDDs. The dose increase at the bone-tissue proximal interface ranged from 1.2 to 2.5 times the dose in soft tissue for rib and 1.3 to 3.7 times for cortical bone. The dose drop-off at 1-cm depth beyond the bone ranged from 1.3% to 6.0% for rib and 3.2% to 11.7% for cortical bone. No drastic dose perturbations occurred in the presence of lung, with lung-tissue interface dose of>99% of soft tissue dose and<3% dose increase at 1-cm depth beyond lung. The developed dose estimation method can be used to translate the measured dose at a point to dose at any depth in small-animal phantoms, making it feasible for preclinical calculation of dose distributions in animals irradiated with cabinet-style irradiators. The dosimetric impact of bone must be accurately quantified as dramatic dose perturbations at and beyond the bone interfaces can occur due to the relative importance of the photoelectric effect at kilovoltage energies. These results will help improve dosimetric accuracy in preclinical experiments.

Virtual monoenergetic images from dual-energy CT: systematic assessment of task-based image quality performance.

To compare task-based image quality (TB-IQ) among virtual monoenergetic images (VMI) and linear-blended images (LBI) from dual-energy CT as a function of contrast task, radiation dose, size, and lesion diameter. A TB-IQ phantom (Mercury Phantom 4.0, Sun Nuclear Corporation) was imaged on a third-generation dual-source dual-energy CT with 100/Sn150 kVp at three volume CT dose levels (5, 10, 15 mGy). Three size sections (diameters 16, 26, 36 cm) with subsections for image noise and spatial resolution analysis were used. High-contrast tasks (e.g., calcium-containing stone and vascular lesion) were emulated using bone and iodine inserts. A low-contrast task (e.g., low-contrast lesion or hematoma) was emulated using a polystyrene insert. VMI at 40-190 keV and LBI were reconstructed. Noise power spectrum (NPS) determined the noise magnitude and texture. Spatial resolution was assessed using the task-transfer function (TTF) of the three inserts. The detectability index (d') served as TB-IQ metric. Noise magnitude increased with increasing phantom size, decreasing dose, and decreasing VMI-energy. Overall, noise magnitude was higher for VMI at 40-60 keV compared to LBI (range of noise increase, 3-124%). Blotchier noise texture was found for low and high VMIs (40-60 keV, 130-190 keV) compared to LBI. No difference in spatial resolution was observed for high contrast tasks. d' increased with increasing dose level or lesion diameter and decreasing size. For high-contrast tasks, d' was higher at 40-80 keV and lower at high VMIs. For the low-contrast task, d' was higher for VMI at 70-90 keV and lower at 40-60 keV. Task-based image quality differed among VMI-energy and LBI dependent on the contrast task, dose level, phantom size, and lesion diameter. Image quality could be optimized by tailoring VMI-energy to the contrast task. Considering the clinical relevance of iodine, VMIs at 50-60 keV could be proposed as an alternative to LBI.

Effect of a new deep learning image reconstruction algorithm for abdominal computed tomography imaging on image quality and dose reduction compared with two iterative reconstruction algorithms: a phantom study.

New reconstruction algorithms based on deep learning have been developed to correct the image texture changes related to the use of iterative reconstruction algorithms. The purpose of this study was to evaluate the impact of a new deep learning image reconstruction [Advanced intelligent Clear-IQ Engine (AiCE)] algorithm on image-quality and dose reduction compared to a hybrid iterative reconstruction (AIDR 3D) algorithm and a model-based iterative reconstruction (FIRST) algorithm. Acquisitions were carried out using the ACR 464 phantom (and its body ring) at six dose levels (volume computed tomography dose index 15/10/7.5/5/2.5/1 mGy). Raw data were reconstructed using three levels (Mild/Standard/Strong) of AIDR 3D, of FIRST and AiCE. Noise-power-spectrum (NPS) and task-based transfer function (TTF) were computed. Detectability index was computed to model the detection of a small calcification (1.5-mm diameter and 500 HU) and a large mass in the liver (25-mm diameter and 120 HU). NPS peaks were lower with AiCE than with AIDR 3D (-41%±6% for all levels) or FIRST (-15%±6% for Strong level and -41%±11% for both other levels). The average NPS spatial frequency was lower with AICE than AIDR 3D (-9%±2% using Mild and -3%±2% using Strong) but higher than FIRST for Standard (6%±3%) and Strong (25%±3%) levels. For acrylic insert, values of TTF at 50 percent were higher with AICE than AIDR 3D and FIRST, except for Mild level (-6%±6% and -13%±3%, respectively). For bone insert, values of TTF at 50 percent were higher with AICE than AIDR 3D but lower than FIRST (-19%±14%). For both simulated lesions, detectability index values were higher with AICE than AIDR 3D and FIRST (except for Strong level and for the small feature; -21%±14%). Using the Standard level, dose could be reduced by -79% for the small calcification and -57% for the large mass using AICE compared to AIDR 3D. The new deep learning image reconstruction algorithm AiCE generates an image-quality with less noise and/or less smudged/smooth images and a higher detectability than the AIDR 3D or FIRST algorithms. The outcomes of our phantom study suggest a good potential of dose reduction using AiCE but it should be confirmed clinically in patients.

A Validation Method for EPID In Vivo Dosimetry Algorithms

The aim of this study was to develop and apply an evaluation method for assessing the accuracy of a novel 3D EPID back-projection algorithm for in vivo dosimetry. The novel algorithm of Dosimetry Check (DC) 5.8 was evaluated. A slab phantom homogeneously filled, or with air and bone inserts, was used for fluence reconstruction of different squared fields. VMAT plans in different anatomical sites were delivered on an anthropomorphic phantom. Dose distributions were measured with radiochromic films. The 2D Gamma Agreement Index (GAI) between the DC and the film dose distributions (3%, 3 mm) was computed for assessing the accuracy of the algorithm. GAIs between films and TPS and between DC and TPS were also computed. The fluence reconstruction accuracy was within 2% for all squared fields in the three slabs’ configurations. The GAI between the DC and the film was 92.7% in the prostate, 92.9% in the lung, 96.6% in the head and the neck, and 94.6% in the brain. An evaluation method for assessing the accuracy of a novel EPID algorithm was developed. The DC algorithm was shown to be able to accurately reconstruct doses in all anatomic sites, including the lung. The methodology described in the present study can be applied to any EPID back-projection in vivo algorithm.

COMPUTED TOMOGRAPHY (CT) IMAGE IN REPAIRING TENDON INJURY IN ATHLETES

ABSTRACT Introduction: endon injury can usually be divided into the following types: fracture, dislocation, compression, bone insert, tendon injury, among which dislocation and compression are more common. Objective: To evaluate the application value of Computed Tomography (CT) image in tendon display. Methods: CT scan of the hands and feet was performed in our hospital for suspected tendon lesions. The CT and MRI data of 61 patients with tendon injury were retrospectively analyzed, and the diagnostic efficiency of CT and MRI were compared and analyzed. Results: The diagnostic accuracy of 61 patients was 89.71% (61/68). Except for chronic tendon injury (12/19), the diagnostic accuracy of other lesions was 100%. The sensitivity of CT and MRI in the diagnosis of hand tendon injury was 94.7% and 90.7%, the specificity was 99.3% and 98.6%, and the coincidence rate was 97.7% and 96.3%. Conclusions: CT images are accurate in localization and characterization of tendon injury, with high sensitivity and specificity, and can provide accurate anatomical basis for surgery. Level of evidence II; Therapeutic studies - investigation of treatment results.

Scattering proton CT

Proton computed tomography (CT) is an imaging modality investigated mainly in the context of proton therapy as a complement to x-ray CT. It uses protons with high enough energy to fully traverse the imaged object. Common prototype systems measure each proton’s position and direction upstream and downstream of the object as well as the energy loss which can be converted into the water equivalent thickness. A reconstruction algorithm then produces a map of the relative stopping power in the object. As an alternative to energy-loss proton CT, it has been proposed to reconstruct a map of the object’s scattering power based on the protons’ angular dispersion which can be estimated from the measured directions. As in energy-loss proton CT, reconstruction should best be performed considering the non-linear shape of proton trajectories due to multiple Coulomb scattering (MCS), but no algorithm to achieve this is so far available in the literature.In this work, we propose a filtered backprojection algorithm with distance-driven binning to account for the protons’ most likely path. Furthermore, we present a systematic study of scattering proton CT in terms of inherent noise and spatial resolution and study the artefacts which arise from the physics of MCS. Our analysis is partly based on analytical models and partly on Monte Carlo simulations.Our results show that the proposed algorithm performs well in reconstructing relative scattering power maps, i.e. scattering power relative to that of water. Spatial resolution is improved by almost a factor of three compared to straight line projection and is comparable to energy-loss proton CT. Image noise, on the other hand, is inherently much higher. For example, in a water cylinder of 20 cm diameter, representative of a human head, noise in the central image pixel is about 40 times higher in scattering proton CT than in energy-loss proton CT. Relative scattering power in dense regions such as bone inserts is systematically underestimated by a few percent, depending on beam energy and phantom geometry.

Impact of Patient Alignment on Image Quality in C-Arm Computed Tomography - Evaluation Using an ACR Phantom.

To evaluate the influence of patient alignment and thereby heel effect on the image quality (IQ) of C-arm flat-panel detector computed tomography (CACT). An ACR phantom placed in opposite directions along the z-axis (setup A and B) on the patient support was imaged using CACT. Image acquisition was performed with three different image acquisition protocols. The images were reconstructed with four convolution kernels. IQ was assessed in terms of high contrast using the modulation transfer function (MTF) and low contrast by assessing the image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratios (CNR) as well as the reliability of density measurements. Furthermore, the dose intensity profiles were measured free-in-air. The MTF in setup B is higher than the MTF measured in setup A (p < 0.01). The image noises measured in setup A for the air and bone inserts were higher compared to those measured in setup B (p > 0.05). Opposite behavior has been observed for the polyethylene, water-equivalent and acrylic inserts. The SNR for all inserts is inversely related to the image noise. A systematically increasing or decreasing trend of CNR could not be observed (p > 0.05). The intensity profile measured by the detector system free-in-air showed that the anode heel effect is perpendicular to the z-axis. The patient alignment has a minor influence on the IQ of CACT. This effect is not based on the X-ray anode heel effect but is caused mainly by the non-symmetrical rotation of CACT. · The impact of patient alignment and thereby the heel effect on the image quality of CACT was analyzed.. · The patient alignment has a minor influence on the physical parameters related to image quality, such as noise, SNR, and MTF.. · This effect is based mainly on the non-symmetrical rotation of CACT.. · Alikhani B, Renne J, Maschke S et al. Impact of Patient Alignment on Image Quality in C-Arm Computed Tomography - Evaluation Using an ACR Phantom. FortschrRöntgenstr 2021; 193: 417 - 426.

Microstructure, mechanical properties and in vitro biocompatibilities of a novel bionic hydroxyapatite bone scaffold prepared by the addition of boron nitride

Hydroxyapatite (HA) is an ideal bone insert material due to its biocompatibility and osteoconductivity, but the poor mechanical properties limit its wide application in clinical practice. The aim of this work is to fabricate a novel composite that with similar porous structure to cortical bone and high mechanical properties by the addition of boron nitride (BN) and sintered in air at 1250 °C for 40 min. In mechanical properties, the maximum flexural strength, elastic modulus and fracture toughness are 94.04 MPa, 69.46 GPa and 1.16 MPa m1/2, respectively, which are improved by 20.56%, 12.87% and 8.41%, respectively. In the microscopy of surface and fracture surface, the porous structure similar to cortical bone is observed. There are microscale and nanoscale pores, and the pores present an interconnected structure. In vitro biocompatibility assessment, the addition of BN and its reaction product have no adverse effect on osteoblast viability, which even promotes osteogenic differentiation and mineralization.

An inhomogeneous most likely path formalism for proton computed tomography

PurposeMultiple Coulomb scattering (MCS) poses a challenge in proton CT (pCT) image reconstruction. The assumption of straight paths is replaced with Bayesian models of the most likely path (MLP). Current MLP-based pCT reconstruction approaches assume a water scattering environment. We propose an MLP formalism based on accurate determination of scattering moments in inhomogeneous media. MethodsScattering power relative to water (RScP) was calculated for a range of human tissues and investigated against relative stopping power (RStP). Monte Carlo simulation was used to compare the new inhomogeneous MLP formalism to the water approach in a slab geometry and a human head phantom. An MLP-Spline-Hybrid method was investigated for improved computational efficiency. ResultsA piecewise-linear correlation between RStP and RScP was shown, which may assist in iterative pCT reconstruction. The inhomogeneous formalism predicted Monte Carlo proton paths through a water cube with thick bone inserts to within 1.0 mm for beams ranging from 210 to 230 MeV incident energy. Improvement in accuracy over the conventional MLP ranged from 5% for a 230 MeV beam to 17% for 210 MeV. There was no noticeable gain in accuracy when predicting 200 MeV proton paths through a clinically relevant human head phantom. The MLP-Spline-Hybrid method reduced computation time by half while suffering negligible loss of accuracy. ConclusionsWe have presented an MLP formalism that accounts for material composition. In most clinical cases a water scattering environment can be assumed, however in certain cases of significant heterogeneity the proposed algorithm may improve proton path estimation.

Effect of tin filter-based spectral shaping CT on image quality and radiation dose for routine use on ultralow-dose CT protocols: A phantom study

PurposeThe purpose of this study was to assess the impact of tin filter (TF) on X-ray beam quality, image quality and radiation dose and its suitability for routine use for chest and lumbar-spine/pelvis-hip ultralow-dose (ULD) CT examination protocols. Materials and methodsThe X-ray beam quality was determined by measuring the half-value layer (HVL) and calculating the mean weighted energy for 100, 120, 150kVp (using standard filtration) and for 100 and 150kVp using TF (Sn100kVp and Sn150kVp, respectively). Acquisitions were performed on a phantom at four dose levels for each previously definedkVp. The mean attenuation (NCT), noise-power-spectrum (NPS) and task-based transfer function (TTF) were computed. The detectability index (d’) was computed to model the detection of two lesions in spine and pelvic/hip examination and two for chest exploration. Image quality and detectability using a TF were assessed for two routinely used ULD protocols. ResultsThe HVL and mean weighted energy increased using a TF for the same tube voltage. Using a TF for the same tube voltage changed NCT for bone and acrylic inserts, decreased the NPS peak without changing the NPS spatial frequency and increased the TTF values. The d’ values were improved using a TF and with the dose increase. d’ values of all modeled lesions were improved using Sn100kVp and Sn150kVp for the lumbar-spine/pelvis-hip and chest ULD protocols except for sclerotic bone lesion using Sn150kVp. ConclusionThe use of TF increases the X-ray beam quality and improves the image quality characteristics in phantom images, thus appearing as a promising tool for reducing dose and/or improving the image quality of ULD protocols.