Low-dose Mode Research Articles

Impact of acquisition volume on cone beam computed tomography imaging of marginal bone: an ex vivo study.

The current study explores whether there is a clinically relevant distinction in the measurement of marginal bone loss when comparing high-dose (HD) versus low-dose (LD) cone beam computed tomography (CBCT) protocols in small and large acquisition volumes. Material and Methods: CBCTs of four human cadaveric preparates were taken in HD and LD mode in two different fields of view 8 × 8 cm2 (LV) and 5 × 5 cm2 (SV). In total, 43 sites of 15 teeth were randomly chosen, and marginal bone loss was measured twice in all protocols at 43 sites of 15 teeth by one calibrated investigator. Bland-Altman plots and Lin's concordance correlation coefficient (CCC) were calculated to assess the extent of agreement of the measurements. Additionally, the rater scored the certainty in each of the measurements. For HD-CBCT CCC of measurements obtained using SV versus LV was 0.991. CCC of measurements obtained using SV versus LV of LD-CBCT was 0.963. Both CCC values indicated excellent agreement between the two volumes in both protocols. CCC also indicated high intramodality correlation between HD-CBCT and LD-CBCT independent of the acquisition volume (0.963 - 0.992). Bland-Altman plots also indicated no substantial differences. Results of certainty scoring showed significant differences (p = 0.004 (LV), p < 0.001(SV)) between the LD and HD-CBCT. Accuracy of measurements of bone loss shows no clinical noticeable effects depending on the CBCT volume in this ex vivo study. There appears to be no relevant advantage of SV over LV, neither in HD-CBCT nor in LD-CBCT and additionally no relevant advantage of HD versus LD in visualizing marginal bone loss.

Do Flat Panel Detector C-Arms Decrease Radiation Exposure Compared to Conventional Image Intensifiers?

To compare the radiation dose and image quality between flat panel detector (FPD) and traditional image intensifier (II) C-arms at their lowest radiation settings. In a ureteroscopy simulation using a cadaver model, the radiation exposure was compared between FPD and II at 4 pulses-per-second (pps) using both low dose and automatic exposure control (AEC) settings. Additionally, the lowest dose settings for each machine were compared (4pps with low dose in the FPD and 1pps with low dose in the II). Five trials of 5minutes were conducted for each setting. Four new optically stimulated luminescent dosimeters were used in each trial to record radiation exposure. Ten blinded urologists completed a survey rating image quality for each setting. When comparing the FPD and II at their lowest possible settings, the FPD produced significantly more radiation (P<.05). Using both machines at 4pps in low dose mode resulted in no significant difference between C-arms (P>.05). Conversely, operating the C-arms at 4pps and AEC resulted in significantly higher radiation exposure from the FPD compared to the II (P<.05). There was no significant difference in image quality at each setting. FPDs produce significantly more radiation at the lowest settings compared to IIs. Surgeons should employ IIs when reducing radiation exposure as low as possible is imperative, such as when operating on pediatric and pregnant patients.

Application of double low-dose mode in left atrial-pulmonary venous computed tomography angiography

This study adopted a 256-slice iCT scanner with the double low-dose mode in left atrial-pulmonary venous computed tomography angiography (CTA) and explored its effect on image quality. 120 patients were included and randomly classified into the Observation group and Control group. Patients in the Control group underwent routine left atrial CTA, while patients in the Observation group performed a double low-dose mode. Other scanning parameters were consistent in the two groups. The Full model-based iterative reconstruction (MBIR) technique was applied to fulfill image reconstruction in observation group. Continuous variables, ordered categorical variables were analyzed by statistical test. The CT values of left atrial in the Observation group were significantly higher than those in the Control group. The exposure doses (ED) and iodine intake were lower in the Observation group, as compared to the Control group. The left atrial-pulmonary venous CTA with the 256-slice iCT scanner in a double low-dose mode can reduce the ED of radiation and iodine contrast while providing high quality images. Comparatively, the ED in the Observation group was reduced by 13% compared with the control, and the iodine intake was reduced by approximately 33%.

Atomic Visualization of the 3D Charge Density Wave Stacking in 1T-TaS2 by Cryogenic Transmission Electron Microscopy.

Charge density waves (CDWs) in 1T-TaS2 maintain 2D ordering by forming periodic in-plane star-of-David (SOD) patterns, while they also intertwined with orbital order in the c axis. Recent theoretical calculations and surface measurements have explored 3D CDW configurations, but interlayer intertwining of a 2D CDW order remains elusive. Here, we investigate the in- and out-of-plane ordering of the commensurate CDW superstructure in a 1T-TaS2 thin flake in real space, using aberration-corrected cryogenic transmission electronic microscopy (cryo-TEM) in low-dose mode, far below the threshold dose for an electron-induced CDW phase transition. By scrutinizing the phase intensity variation of modulated Ta atoms, we visualize the penetrative 3D CDW stacking structure, revealing an intertwining multidomain structure with three types of vertical CDW stacking configurations. Our results provide microstructural evidence for the coexistence of local Mott insulation and metal phases and offer a paradigm for studying the CDW structure and correlation order in condensed-matter physics using cryo-TEM.

Imaging doses for different CBCT protocols on the Halcyon 3.0 linear accelerator – TLD measurements in an anthropomorphic phantom

IntroductionImage guided radiotherapy allows for particularly conformal tumour irradiation through precise patient positioning. Becoming the standard for radiotherapy, this increases imaging doses to the patient. The Halcyon 3.0 linear accelerator (Varian Medical Systems, Palo Alto, CA) requires daily imaging due to its geometry. For this reason, the accelerator is equipped with on-line kV and MV imaging. However, daily CBCT images required for irradiation apply additional radiation, which increases the dose to normal tissue and therefore can affect the patient's secondary cancer risk. In this study, actual organ doses were measured for the kV system, and a comparison of normal tissue doses for all available kV CBCT protocols was presented to demonstrate differences in imaging doses across entities and protocols. In addition, effective dose and secondary cancer risk from imaging are evaluated. Material and methodsMeasurements were performed with thermoluminescent dosimeters in an anthropomorphic phantom positioned according to each entity (brain, head and neck, breast, lung, pelvis). CBCT images were obtained, using all available pre-set protocols without further adjustment of the parameters. Measured doses for each position and each protocol were then compared and secondary cancer risk of relevant and specifically radiosensitive organs was calculated. ResultsIt was found that imaging doses for protocols such as Pelvis and Head could be reduced by up to half using the corresponding Fast and Low Dose modes, respectively. On the other hand, larger field sizes or the Large mode yielded higher doses than their initial protocols. Image Gently was found to spare normal tissue best, however it is not suitable for certain entities due to low image quality or insufficient projection data. DiscussionBy using appropriate kV-CBCT protocols, it is possible to reduce imaging doses to a significant extent and therefore spare healthy tissue. Combined with studies of image quality, the results of this study could lead to adjustments in workflow regarding the choice of protocols used in daily routine. This could prevent unnecessary radiation exposure and reduce secondary cancer risk.

Radiation safety for pain physicians: principles and recommendations.

C-arm fluoroscopy is a useful tool for interventional pain management. However, with the increasing use of C-arm fluoroscopy, the risk of accumulated radiation exposure is a significant concern for pain physicians. Therefore, efforts are needed to reduce radiation exposure. There are three types of radiation exposure sources: (1) the primary X-ray beam, (2) scattered radiation, and (3) leakage from the X-ray tube. The major radiation exposure risk for most medical staff members is scattered radiation, the amount of which is affected by many factors. Pain physicians can reduce their radiation exposure by use of several effective methods, which utilize the following main principles: reducing the exposure time, increasing the distance from the radiation source, and radiation shielding. Some methods reduce not only the pain physician’s but also the patient’s radiation exposure. Taking images with collimation and minimal use of magnification are ways to reduce the intensity of the primary X-ray beam and the amount of scattered radiation. It is also important to carefully select the C-arm fluoroscopy mode, such as pulsed mode or low-dose mode, for ensuring the physician’s and patient’s radiation safety. Pain physicians should practice these principles and also be aware of the annual permissible radiation dose as well as checking their radiation exposure. This article aimed to review the literature on radiation safety in relation to C-arm fluoroscopy and provide recommendations to pain physicians during C-arm fluoroscopy-guided interventional pain management.

Three-dimensional visualization of lithium metal anode via low-dose cryogenic electron microscopy tomography

SummaryThe structure of lithium (Li) metal anode, including the Li metal and the solid electrolyte interphase (SEI), is critical to the investigation of cycle stability or decay mechanisms. The three-dimensional (3D) visualization of Li metal and SEI, however, has not been demonstrated yet, owing to the lack of 3D characterization techniques and the susceptibility of Li metal anode toward oxygen, moisture, as well as electron beam. Herein, we introduce a successful 3D presentation of deposited Li metal and SEI established via low-dose cryogenic electron microscopy tomography. The Li metal anode is imaged in low-dose mode at different tilt angles and then aligned and reconstructed into a 3D image through an expectation-maximization algorithm. The spherical Li deposits and SEI are confirmed in the 3D tomography of Li metal anode. It is also discovered that the Li metal corrodes and SEI turns concave owing to possible self-discharge after long-time rest.

Diagnostic Accuracy of Cystic Lesions Using a Pre-Programmed Low-Dose and Standard-Dose Dental Cone-Beam Computed Tomography Protocol: An Ex Vivo Comparison Study.

Background: This study aimed to analyze the diagnostic reliability of radiographic assessment of cystic lesions using a pre-set, manufacturer-specific, low-dose mode compared to a standard-dose dental cone-beam computed tomography (CBCT) imaging protocol. Methods: Forty pig mandible models were prepared with cystic lesions and underwent both CBCT protocols on an Orthophos SL Unit (Dentsply-Sirona, Bensheim, Germany). Qualitative and quantitative analysis of CBCT data was performed by twelve investigators independently in SIDEXIS 4 (Dentsply-Sirona) using a trial-specific digital examination software tool. Thereby, the effect of the two dose types on overall detectability rate, the visibility on a scale of 1 (very low) to 10 (very high) and the difference between measured radiographic and actual lesion size was assessed. Results: Low-dose CBCT imaging showed no significant differences considering detectability (78.8% vs. 81.6%) and visibility (9.16 vs. 9.19) of cystic lesions compared to the standard protocol. Both imaging protocols performed very similarly in lesion size assessment, with an apparent underestimation of the actual size. Conclusion: Low-dose protocols providing confidential diagnostic evaluation with an improved benefit–risk ratio according to the ALADA principle could become a promising alternative as a primary diagnostic tool as well as for radiological follow-up in the treatment of cystic lesions.

Prospective evaluation of radiation dose with conventional fluoroscopic voiding cystourethrogram in pediatric patients

Skin entrance doses for voiding cystourethrogram (VCUG) have not been well characterized in the literature. Radiation exposure is measured as either dose area product (DAP) or air kerma, which estimates the effective dose, but does not accurately reflect absorbed dose at skin level. The objective of this study was to measure the skin entrance dose during fluoroscopic VCUG study in pediatric patients using single point dosimeters. Pediatric patients undergoing fluoroscopic VCUG were prospectively enrolled in our study. Landauer NanoDot™OSLD dosimeters were affixed to the skin overlying the sacrum to measure skin entrance dose. The fluoroscopic unit was set to the following parameters: low dose setting, skin-to-source distance of 54cm, pulsed fluoroscopy at 3 frames/sec. Forty-four patients with a median age of 13.6 months (IQR 3.7-42.3) were enrolled. Median fluoroscopic time was 54s (IQR 36-72). The median values absorbed dose by dosimeter and air kerma were 0.32mGy (IQR 0.13-0.56, range 0.01-2.9) and 0.24mGy (IQR 0.14-0.37), respectively. There was a positive correlation between the air kerma and absorbed dose (r=0.69, p<0.001) and fluoroscopy time and absorbed dose mGy (r=0.60, p<0.001). Absorbed dose was independent of age, body mass index and body surface area (p=0.19, p=0.57 and p=0.16, respectively). Median whole body effective dose was 0.04mSv (IQR 0.02-0.7). Overall, the absorbed dose received by the dosimeter remained low at a median of 0.32mGy (range 0.01-2.91). These values are remarkably low and well within the accepted radiation exposure norms. Our radiologists follow a strict protocol to reduce the overall radiation emitted during a VCUG. These measures include setting the x-ray source at a low dose mode, collimating to the smallest area possible, and using pulsed fluoroscopy at 3 frames/sec. Limitations to this study include a slight variability in technique of VCUG between different technicians and providers, for which we cannot control. The radiation dose absorbed at the skin entrance and uniform whole body effective dose is low for a single VCUG when utilizing strict parameters. While newer non-ionizing technologies continue to emerge, our data is encouraging and will serve as a valuable tool when educating parents regarding radiation doses associated with a VCUG.

Abstract P-12:Three-dimensional Structure of the Yeast Transmembrane Mechanosensor Wsc1

Background: Wsc1 is the best studied of the five mechanosensors of the cell wall integrity (CWI) signal transduction pathway in Saccharomyces cerevisiae. In genetic and biophysical studies, Wsc1 functions were assessed either in living yeast cells or in crude cell extracts. So far, no attempts to purify the sensor and determine its structure have been reported. Methods: The Wsc1-green fluorescent protein (GFP) fusion was expressed in S. cerevisiae following standard protocols. For solubilization, a 5% (w/v) solution of styrene-maleic acid (SMA) copolymer was added dropwise to the membrane suspension to get a final cell-to-SMA weight ratio of 1:2.5. The suspension was incubated for 30 min at room temperature (RT) and then for 16 hours at 4 °C, followed by centrifugation for 20 min at 134000 g at 4 °C. The supernatant was subsequently purified on affinity resin. Protein samples (3 µL) were placed onto the glow-discharged grid, stained twice, using 1% aquatic uranyl acetate solution for 30 s at RT, and air-dried. Micrographs were acquired using a transmission electron microscope Jem-2100 (Jeol, Japan) equipped with a 2K x 2K CCD camera Ultrascan 1000XP (Gatan, USA). The microscope operated at 200 kV in a low dose mode, with a magnification x40000 (2.5 Å/pix) and defocus 0.5-1.9 µm. Images were acquired automatically with SerialEM software. Results: We applied the 3:1 SMA copolymer to isolate Wsc1-GFP fusions into SMA/lipid particles (SMALPs) directly from native yeast membranes. We purified Wsc1-GFP-containing SMALPs by affinity chromatography; characterization by dynamic light scattering confirmed the presence of monodisperse nano-sized particles. The intensity-weighted diameter was estimated to be in the 10-nm range. The purified Wsc1-GFP-containing SMALPs were further analyzed by transmission electron microscopy (TEM). 46500 single particles were used to generate the 3D reconstructions of Wsc1-GFP. The resulting model showed the three functional parts of the Wsc1 sensor: the extracellular part, which has a clasp-like appearance, the transmembrane domain, and the short cytosolic part of Wsc1 fused to the GFP beta-barrel. Conclusion: The 3:1 SMA copolymer enabled isolation of Wsc1-GFP fusion complexes into SMALPs directly from native yeast membranes. Image analysis of the TEM data showed the Wsc1 in its contracted conformation. We propose a model of conformational changes in Wsc1 in response to mechanical stress.

Abstract OR-2: The Formation of Dps-DNA Complexes under Different Conditions According to Cryo-EM and SAXS

Background: The effect of Dps-DNA co-crystals formation, which occurs in stressed Escherichia coli cells exposed to extreme conditions, is well described in the literature. However, the exact mechanisms of co-crystals formation are yet to be postulated remaining largely unknown. Here we summarize the results obtained by our group over the last few years using cryo-Electron Microscopy (cryo-EM) and Small Angle X-ray Scattering (SAXS). Methods: Samples for cryo-EM were plunge frozen in liquid ethane with Vitrobot Mark IV and studied with Titan Krios (ThermoFisher Scientific, US) cryo-EM, equipped with Falcon 2 direct electron detector, Image corrector (CEOS, Germany), and Volta phase plate. Single Particle Analysis (SPA) and cryo-Electron Tomography (cryo-ET) studies were conducted with 300 kV accelerating voltage in low dose mode using EPU and Tomography software (ThermoFisher Scientific, US). Cryo-EM data processing was conducted using Warp, CryoSPARC, IMOD, EMAN, and Relion software packages. SAXS measurements were performed at the EMBL on the P12 BioSAXS beam line at the PETRAIII storage ring (DESY, Hamburg). Results: In this work, Dps-DNA complex formation is thoroughly studied using complementary cryo-EM (including SPA, cryo-ET, and subtomogram averaging) and SAXS methods. The formation of individual complexes of Dps with small linear DNA fragments and the Dps-Dps interaction was visualized using cryo-EM. It was found that Dps-DNA complex remains stable under various conditions and while the addition of different ions leads to the disruption of co-crystals, the process is completely or partially reversible. Conclusion: Recent studies conducted by our group showed that Dps-DNA co-crystals adopt triclinic or cubic crystal lattice (FEBS Lett., 2019; Biomolecules, 2020). Here we present the results on the studies of Dps interaction with small linear DNA fragments, demonstrate the effects of MgCl2, FeSO4, and EDTA on the Dps-DNA complex and individual Dps protein structure, discuss the influence of the temperature and time on the co-crystals.

Abstract P-16: Cryo-Electron Microscopy Study of Vesicles from Various Species

Background: Plant-derived extracellular vesicles (PEVs) are studied as a natural carrier of functional biomolecules and as a potential system of targeted delivery of therapeutic agents. One of the urgent tasks in this direction is the selection of the carrier with optimal physicochemical parameters and morphology from a variety of plant sources. To date, vesicles from only a few plants were visualized using cryo-electron microscopy (cryo-EM). Here we investigated the morphology and physical parameters of extracellular vesicles from plant sources not previously studied utilizing this method. Methods: PEVs derived by ultracentrifugation from juice and cultural medium of 11 plants and mushrooms were studied using methods of cryo-EM. Samples were plunge frozen in liquid ethane with Vitrobot Mark IV and examined under cryogenic transmission electron microscope Titan Krios 60-300 (ThermoFisher Scientific, USA) in low dose mode using EPU software. Results: Most of the observed particles in each sample were classified as extracellular vesicles due to the presence of the lipid bilayer. Morphology and size characteristics of PEVs were determined and compared with each other. A variety of morphological configurations of PEVs were found: with single and multiple membranes, with different conformations and integrity state. Most of the isolated PEVs were single, round-shaped, and in a size range from 30 to 150 nm. Conclusion: Cryo-EM allowed us to obtain high-quality images of PEVs isolated from 11 plants and mushrooms (blueberry, chanterelle, cowberry, fly agaric, garlic, redcurrant, chlamydomonas, cucumber, shadberry, viburnum, gooseberry) which have been characterized by their size and morphology. From the data obtained, the most promising sources of vesicles were proposed. The approbation of the selected vesicles as effective delivery systems requires further research.

Effect of ion dose ratio on multilevel energy smoothing model of gas cluster

In this study, two kinds of gas cluster ion beam energy modes with different ion dose ratios are proposed to improve the traumatic surface of n-Si (100) single crystal. In mode1, low-dose high-energy clusters and high-dose low-energy clusters are used, while in mode2, high-dose high-energy clusters and low-dose low-energy clusters are used. The results show that the flattening effect of mode 1 is better than that of mode 2, and the root mean square roughness of mode 1 and mode 2 are 0.62 nm and 1.02 nm, respectively. This is because in multi-level energy mode 2, high-dose high-energy clusters are used to bombard the target surface in the early stage, so that more ion damages will be left after high-energy cluster bombardment. In the later stage, low-dose low-energy clusters can only remove part of the ion damages, and the repair strength is not strong enough. In multi-level energy mode1, we first use low-dose high-energy clusters to bombard the surface of the target, so that the high-energy clusters can quickly remove the shape objects with high protrusion on the sample surface, and in the low-dose mode, it will not leave too many ion damages, which is conducive to the later repair. In the first stage of multi-level energy mode, high-dose low-energy clusters are used to bombard the target surface, which can not only reduce the ion loss, but also increase the time for low-energy clusters to repair ion damages, thereby yielding the optimal flattening effect. In order to verify the relationship among the damage removal, ion damage degree and cluster energy, a single energy cluster bombardment experiment with mechanical damage is carried out before the multi-level energy mode modification is studied. The results show that when the cluster ions are accelerated at 15 kV high voltage, the scratch removal efficiency is highest, and the surface scratch is very shallow, but the decease of roughness is not obvious; when the cluster ions are accelerated at 8 kV and 5 kV, the sample surface becomes fine and the remaining ion damages are least. At the same time, a comparison of the target bombarded by the multi-level energy mode 1 clusters with that by the single energy clusters shows that the multi-level energy mode can obtain a smoother target surface than the single 15 keV high-energy cluster treatment; the multi-level energy mode can better remove scratches and other wounds than the single 5 keV low-energy cluster treatment. Multistage energy mode 1 integrates the advantages of high and low energy clusters, thereby achieving the best flattening effect.

Do different cone beam computed tomography exposure protocols influence subjective image quality prior to and after root canal treatment?

ObjectivesThe current study aimed to evaluate different CBCT exposure protocols and influencing factors affecting the subjective image quality of scans taken for endodontic indications.Materials and methodsTwelve extracted teeth, comprising of two sets of maxillary molars, premolars, canines and incisors, mandibular premolars, and molars, were endodontically treated, and either received a fiber or metal post. The teeth were scanned by CBCT imaging before and after root canal treatment, and after post insertion. Each scan was performed thrice, using an ultra low dose (ULD), standard (SM), and high-resolution mode (HR), respectively. Twelve observers—4 endodontists, 4 periodontists, and 4 radiologists—assessed the subjective image quality using visual analogue scales (VAS). Potential influencing factors were evaluated including acquisition mode, observer specialty, stage of treatment, type of post, and type of tooth, using one-way ANOVA and T test.ResultsTeeth scanned with the ULD had the highest average VAS score (72.5), followed by HR (70.2), and SM (69.0) for values pooled from all teeth and observers. CBCT acquisition mode was not a significant influencing factor on the VAS scores. Observer specialty, stage of treatment, type of post, and type of tooth were significant influencing factors.ConclusionsBased on the present in vitro data, a low-dose CBCT mode seems not to negatively affect the perception of image quality.Clinical relevanceThe findings from this in vitro study demonstrate that a low-dose CBCT mode might have potential for diagnostics prior to or following endodontic treatment.

Detectability of Osseous Lesions with a Pre-Programmed Low-Dose Protocol for Cone-Beam Computed Tomography

The present study aimed to compare the diagnostic reliability of a pre-set, manufacturer-specific, low-dose mode against a standard-dose mode in the detection of four different osseous lesions in the mandible with cone-beam computed tomography (CBCT). Four types of lesions (periapical lesion, extended periodontal gap, recession of the buccal lamella, sequestrum/fracture) were prepared on 40 pig mandibles. CBCT images were obtained from each mandible, with both the low-dose and standard-dose modes using the Orthophos SL CBCT device (Dentsply-Sirona, Bensheim, Germany). Twelve assessors quantitatively (detection of lesions) and qualitatively (assessment of detectability) evaluated the CBCT images in SIDEXIS 4 (Dentsply-Sirona) using a study-specific digital examination tool. A correct diagnosis was achieved in almost 71% (LD: 70.8%; SD: 70.9%) of 1920 lesions, without a statistically significant difference between the low-dose and standard-dose mode. This finding was consistent across all four lesion types. In conclusion, while low-dose mode and standard-dose mode CBCT scans performed similarly in the detection of four prepared lesions of the mandible, the former may be a promising, user-friendly alternative method of obtaining radiation-optimized, three-dimensional images in accordance with the As Low As Diagnostically Acceptable (ALADA) principle.

Long-term Inter-protocol kV CBCT image quality assessment for a ring-gantry linac via automated QA approach

We develop a fully automated QA process to compare the image quality of all kV CBCT protocols on a Halcyon linac with ring gantry design, and evaluate image quality stability over a 10-month period. A total of 19 imaging scan and reconstruction protocols were characterized with measurement on a newly released QUART phantom. A set of image analysis algorithms were developed and integrated into an automated analysis suite to derive key image quality metrics, including HU value accuracy on density inserts, HU uniformity using the background plate, high contrast resolution with the modulation transfer function (MTF) from the edge profiles, low contrast resolution using the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), slice thickness with the air gap modules, and geometric accuracy with the diameter of the phantom. Image quality data over 10 months was tracked and analyzed to evaluate the stability of the Halcyon kV imaging system. The HU accuracy over all 19 protocols is within tolerance (±50HU). The maximum uniformity deviation is 12.2 HU. The SNR and CNR, depending on the protocol selected, range from 18.5–911.9 and 1.9–102.8, respectively. A much-improved SNR and CNR were observed for iterative reconstruction (iCBCT) modes and protocols designed for large subjects over low dose and fast scanning modes. The Head and Image Gently protocols have the greatest high contrast resolution with MTF10% over 1 lp/mm and MTF50% over 0.6 lp/mm. The iCBCT mode slightly improved the MTF10% and MTF50% compared to the Feldkamp-Davis-Kress approach. The slice thickness (maximum error of 0.31 mm) and geometry metrics (maximum error of 0.7 mm) are all within tolerance (±0.5 mm for slice thickness and ±1 mm for geometry metrics). The long-term study over 10-month showed no significant drift for all key image quality metrics, which indicated the kV CBCT image quality is stable over time.

Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on HalcyonTM for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses.

Purpose: The Varian Halcyon includes an ultrafast 6 MV flattening filter free (FFF) cone-beam computed tomography (MV-CBCT). Although a kV-CBCT add-on is available, in the basic configuration MV is used for image guided radiotherapy (IGRT). We characterized the MV-CBCT imager in terms of reproducibility, linearity, field of view (FOV) dependence, detectability of soft-tissue, and the effect of metal implants. The performance of the MV-CBCT in the clinic, including resulting dose to organs, is also discussed herein.Methods: A Gammex phantom was scanned using a Halcyon MV-CBCT and a 120 kVp Siemens Definition Edge CT. Mean and standard deviation of Hounsfield Units (HUs) for different electron density relative to water () inserts were extracted. Doses to clinical patients due to MV-CBCT are calculated within Eclipse during treatment planning.Results: A stable and near-linear HU-to- curve was obtained using the MV-CBCT. As the scan length increased from 10 to 28cm, the linearity of curve improved while the mean HUs decreased by 30%. All soft tissue inserts in the Gammex phantom were distinguishable. A crescent artifact affected HU measurements by up to 40 HUs. Soft-tissue contrast was sufficient for clinical online image-guidance in the low dose (5 MU) mode. Mean doses per fraction to organs-at-risk (OARs) were as high as 6 cGy for head and neck, 5 cGy for breast, and 4 cGy for pelvis patients. Metal rods did not affect HU values or introduce noticeable artifacts.Conclusions: Halcyon's MV-CBCT has sufficient soft tissue contrast for IGRT and lacks metal-induced artifacts. Even though the absolute HU values vary with phantom size and scanning length, the HU-to- conversions are linear and stable day-to-day. In clinical cases, highest tissue doses from MV-CBCT ranged from 2-7cGy per fraction for various treatment sites, which could be significant for some organs at risk. Dose to out-of-treatment-field organs can be limited by reducing the scan length definition during planning and using the low dose mode. The high quality imaging mode did not provide material advantages over the low dose mode. Adequate IGRT was successfully delivered to multiple tumor sites using MV-CBCT.

Evaluation of mandibular calcification on 3D volume images

ObjectivesBone and soft-tissue calcifications are often coincidentally diagnosed on digital panoramic radiographs (DPRs). As the use of three-dimensional (3D) images has increased in the past decade for diagnostics in the mandibular region, we evaluated 3D volume images derived from 2D panoramic images to determine if this method is suitable for early detection of calcifications in this region. MethodsIn this study, three investigators retrospectively and independently evaluated 822 DPRs. If one or more calcifications were present, the 3D volume image from that patient was retrospectively evaluated to confirm the incidental findings. A radiographic system with a low-dose mode and a high-resolution 3D-image function was used. The investigators focussed on the most common calcifications, including tonsilloliths (TL), idiopathic osteosclerosis (IO) of the mandible, carotid artery calcifications (CAC), calcified submandibular lymph nodes (hereafter, CSL), and sialoliths of the submandibular salivary gland (SSG). ResultsOne or more calcifications were identified in 415 (50.5%) DPRs. In total, 718 calcifications were detected, 30.2% of which were TL, 16.3% IO, 11.3% CAC, 8.8% CSL, and 1.7% SSG. Only 287 (39.97 %) of the calcifications were confirmed on 3D volume images; of these, 29.2% were TL, 58.5% IO, 0.2% CAC, and 1.4% SSG. No CSLs were detected. ConclusionsNot all areas shown on the DPRs were visible in the retrospectively obtained 3D volume images. Whereas DPRs are used to diagnose calcifications such as IO, TL, SSG, CAC, and CSL, the 3D volume images were only useful for confirming the existence of IO, TL, and SSG calcifications.

Effect of different approaches to thoracolumbar interfascial plane block on analgesic efficacy after lumbar spinal fusion

Objective To evaluate the effect of different approaches to thoracolumbar interfascial plane (TLIP) block on the analgesic efficacy after lumbar spinal fusion. Methods Seventy-five patients of both sexes, of American Society of Anesthesiologists physical status Ⅰ or Ⅱ, aged 40-70 yr, with body mass index ≤40 kg/m2, undergoing posterior median approach to lumbar spinal fusion, were divided into 3 groups (n=25 each) using a random number table method: patient-controlled intravenous analgesia (PCIA) group (group P), medial approach to TLIP combined with PCIA group (group MP) and lateral approach to TLIP combined with PCIA group (group LP). TLIP block was performed by advancing the block needle in a lateral to medial direction and injecting 0.5% ropivacaine 20 ml locally between the bilateral multifidus and longissimus muscles in group MP.TLIP block was performed by advancing the block needle in a medial to lateral direction and injecting 0.5% ropivacaine 20 ml locally between the bilateral longissimus and iliocostalis muscles in group LP.The identification rate and distinction score between multifidus and iliocostalis muscles obtained from ultrasonic images were recorded before block in MP and LP groups.All the patients received PCIA until 48 h after surgery.PCIA solution contained sufentanil 100 μg and tropisetron 10 mg diluted to 100 ml with 0.9% normal saline.The PCA pump was set up with a 2 ml bolus dose, a 15-min lockout interval and background infusion at a rate of 1 ml/h.When visual analogue scale score at rest >4 after surgery, parecoxib 40 mg was intravenously injected for rescue analgesia.The development of adverse reactions such as nausea and vomiting was recorded within 48 h after surgery. Results The identification rate and distinction score of the iliocostalis was significantly higher than that of the multifidus (P 0.05). There was no significant difference in the parameters mentioned above between group MP and group LP(P>0.05). Conclusion Ultrasound-guided medial and lateral approaches to TLIP block is helpful in achieving low-dose opioid anesthesia mode and more helpful in enhancing the efficacy of PCIA when used for lumbar spinal fusion. Key words: Nerve block; Fascia; Analgesia, patient-controlled

Radiation Reduction in Low Dose Pulsed Fluoroscopy versus Standard Dose Continuous Fluoroscopy during Fluoroscopically-Guided Lumbar Punctures: A Prospective Controlled Study.

Purpose:The purpose of this study was to evaluate radiation dose reduction in fluoroscopically guided lumbar punctures (FGLP) using “pulsed fluoroscopy in a low dose mode” compared with the commonly used “continuous fluoroscopy in a standard dose mode” while maintaining the technical success.Materials and Methods:Thirty-five consecutive patients who underwent FGLP divided randomly to seventeen patients in the control group with standard dose continuous FGLP and eighteen patients in the study group with low-dose low-frame-rate of 3 frames per second (fps) FGLP. Entrance surface dose measurements from a dosimeter device were recorded as well as the dose area product (DAP).Results:A total of 35 patients with average age of 52 years (range: 15–87 [±17 standard deviation [SD]]) were evaluated. Average entrance surface dose of the study group was significantly lower (3.81 mGy [range: 0.21–11.14, [±2.8 SD]]) compared with the control group (22.45 mGy [range: 1.23–73.44, [±19.41 [SD]]). The average DAP of the study group (10 mGy·cm2 [range: 1–41, [±9.8 SD]]) was also significantly lower than the control group (65 mGy·cm2 [range: 5–199, [±53 SD]]). Success rate was similar between the study and control groups.Conclusion:Low dose pulsed fluoroscopy of 3 fps significantly reduces radiation exposure by about 600% compared with standard dose continuous fluoroscopy in FGLP. Utilizing this radiation saving strategy will allow to dramatically reduce radiation exposure, without impacting the technical success rate.