Gantry Tilt Research Articles

Decreasing Lens Irradiation on Brain Imaging: A Multi-CT Scanner Quality Improvement Project.

Cataracts, a leading global cause of blindness, are associated with ionising radiation exposure. This audit aimed to enhance lens exclusion during non-contrast head computed tomography (CT) scans at Newham University Hospital (NUH) using two CT scanners. A retrospective audit of non-contrast head CT scans at NUH excluded scans for trauma and imaging of orbital structures. A one-week audit in April 2023 assessed lens exclusion, compared to the Royal College of Radiologists (RCR) standards. A total of 101 consecutive scans were analysed and 63 (62%) scans were included in the final study. Thirty-eight percent of the scans were excluded according to the exclusion criteria of head, neckand facial traumas, orbital infectionsand papilledema. Results were presented, followed by a three-month radiographer re-education period, emphasizing gantry tilt and patient positioning. A reaudit in August 2023 evaluated outcomes. For the reaudit, 183 consecutive scans were analysed, with 131 (72%) scans included in the final studyand 52 (28%) scans excluded according to the same exclusion criteria as the first audit. Lens exclusion in non-contrast head CT scans improved significantly from 0/63 (0%) compliance to 19/131 (14.50%) (p=0005) compliance with the standards. Variability in radiographer practices, 'near misses' and time constraints were identified as challenges. Staff turnover impacted compliance. This audit has shed light on a critical aspect of patient care in the field of radiology. This research underscores the importance of rigorous and standardised protocols in radiological procedures, particularly when it comes to protecting the lens of the eye. By enhancing lens exclusion during non-contrast head CT scans, we have taken a significant step in mitigating the risk associated with ionising radiation exposure. Although substantial improvements were made, achieving the RCR audit standard remained elusive. Ongoing re-education, reauditsand a multidisciplinary approach are necessary to optimise radiographer adherence and reduce ionising radiation exposure to the lens during head CT scans.This quality improvement project proves thatcontinued emphasis on gantry tilt and patient positioning in radiographer education and training can make a significant difference in patient safety.As we move forward, let us remember that even small improvements can make a big difference in safeguarding the health and well-being of patients.

Percutaneous CT-Guided Abdominal and Pelvic Biopsies: Comparison of an Electromagnetic Navigation System and CT Fluoroscopy

PurposeTo compare electromagnetic navigation (EMN) with computed tomography (CT) fluoroscopy for guiding percutaneous biopsies in the abdomen and pelvis. Materials and MethodsA retrospective matched-cohort design was used to compare biopsies in the abdomen and pelvis performed with EMN (consecutive cases, n = 50; CT-Navigation; Imactis, Saint-Martin-d’Hères, France) with those performed with CT fluoroscopy (n = 100). Cases were matched 1:2 (EMN:CT fluoroscopy) for target organ and lesion size (±10 mm). ResultsThe population was well-matched (age, 65 vs 65 years; target size, 2.0 vs 2.1 cm; skin-to-target distance, 11.4 vs 10.7 cm; P > .05, EMN vs CT fluoroscopy, respectively). Technical success (98% vs 100%), diagnostic yield (98% vs 95%), adverse events (2% vs 5%), and procedure time (33 minutes vs 31 minutes) were not statistically different (P > .05). Operator radiation dose was less with EMN than with CT fluoroscopy (0.04 vs 1.2 μGy; P < .001), but patient dose was greater (30.1 vs 9.6 mSv; P < .001) owing to more helical scans during EMN guidance (3.9 vs 2.1; P < .001). CT fluoroscopy was performed with a mean of 29.7 tap scans per case. In 3 (3%) cases, CT fluoroscopy was performed with gantry tilt, and the mean angle out of plane for EMN cases was 13.4°. ConclusionsPercutaneous biopsies guided by EMN and CT fluoroscopy were closely matched for technical success, diagnostic yield, procedure time, and adverse events in a matched cohort of patients. EMN cases were more likely to be performed outside of the gantry plane. Radiation dose to the operator was higher with CT fluoroscopy, and patient radiation dose was higher with EMN. Further study with a wider array of procedures and anatomic locations is warranted.

RADIATION DOSE OF THE EYE LENS IN CT EXAMINATIONS OF THE BRAIN IN CLINICAL PRACTICE-THE EFFECT OF RADIOGRAPHER TRAINING TO OPTIMISE GANTRY TILT AND SCAN LENGTH.

Lenses are always exposed to radiation in brain computed tomography (CT) scans. However, the lens dose can be reduced by excluding lens from scanning area by optimising gantry tilt and scan length. The object of this study is to retrospectively analyse if the optimisation by gantry tilt and scan length have been adequate in the CT scan of the brain, and to prospectively analyse the effect of radiographer training to the quality of the CT examinations. This study was conducted in two parts. In all, 329 brain CTs performed in the Tampere University Hospital from 2017 to 2019 were revised retrospectively. The prospective part included 51 brain CT studies conducted in October 2021. Dose to the eye of the lens was modelled using CT-Expo using zero-degree beam angle and scan lengths to expose the lens either to the primary or scattered radiation. Non-zero gantry tilt had been used in a large proportion of the CT examinations in the retrospective setting, 84.8%. However, the lenses were successfully excluded from the scan area in only 1.8% of the examinations. In the prospective part, the gantry tilt was used in 98% of the studies and the proportion of successful examinations rose from 1.8 to 11.8%. The lens dose decreased significantly when the eyes were excluded from the imaging area. The modelled lens dose in the large retrospective part was 25.9mGy (17.8-49.2mGy) when the eyes were included and 1.5mGy (0.4-1.9mGy) when the eyes were excluded. The lens dose was similar in the small prospective part. Despite the gantry tilt is widely used, unnecessary lens irradiation occurs extensively because of suboptimal gantry tilt and scan length. The training of radiographers reduces the radiation exposure to the lens by more optimal gantry tilt and scan length.

Gantry-needle-target alignment technique for CT-guided needle approaches to the skull base and cranio-cervical junction.

CT-guided percutaneous procedures involving the skull base and atlanto-axial cervical spine pose particular challenges due to high density of vital vascular and nervous structures and because the ideal needle trajectory often has a cranio-caudal obliquity different from the axial scan plane. We describe how the variable CT gantry tilt, combined with gantry-needle-target alignment technique, is used to obtain precise and safe needle placement in conventional and non-conventional approaches to the skull base and the atlanto-axial spine. We retrospectively analyzed consecutive CT-guided needle accesses to the skull base and atlanto-axial spine performed for tissue sampling through fine-needle aspirates and core biopsies, cementoplasty of neoplastic lytic lesions of atlanto-axial spine, pain management injections, and dural puncture for cerebro-spinal fluid sampling. All the accesses were performed with the gantry-needle-target alignment technique. Procedural complications were recorded. Thirty-nine CT-guided procedures were analyzed. Paramaxillary approach was used in 15 cases, postero-lateral in 11, subzygomatic in 3. Nine non-conventional approach were performed: submastoid in 3 cases, suprazygomatic in 2, trans-nasal in 2, trans-mastoid in 1, and trans-auricular in 1. Two peri-procedural complications occurred: one asymptomatic and one resolved within 24h. All the procedures were successfully completed with successful needle access to the target. The gantry tilt and gantry-needle-target alignment technique allows to obtain double-oblique needle accesses for CT-guided procedures involving the skull base and atlanto-axial cervical spine, minimizing uncertainty of needle trajectory and obtaining safe needle placement in conventional and non-conventional approaches.

Automatic validation of the gantry tilt in a computed tomography scanner using a head polymethyl methacrylate phantom

Abstract The purpose of this study was to develop an automatic method for validating the computed tomography gantry tilt. A head polymethyl methacrylate phantom with a diameter of 16 cm was used. Gantry tilt angles were measured both manually and automatically. Manual measurements were performed by measuring the length of the anteroposterior and lateral diameters from acquired images using electronic calipers. Automatic measurements consisted of a number of steps: phantom segmentation, determination of the center of the phantom, measurement of the anteroposterior and lateral diameters, and computation of the gantry tilt angle. The method was implemented on the gantry angles from 0° to 15°. The proposed method of measuring gantry angles produced accurate gantry tilt angles. The differences with the angles displayed on the gantry were less than 1°. The results of the automatic method were the same as those of the manual method (R2 &gt; 0.98).

Calculation of Lens Exposure Reduction Using Organ-effective Modulation in Pediatric Head CT

Using a pediatric head phantom constructed in our department, we examined a method to reduce exposure by using organ-effective modulation (OEM; Toshiba Medical Systems Corporation, Tochigi) to tilt the gantry during pediatric head computed tomography (CT) scanning. The radiation reduction and CT image standard deviation (SD) were measured at gantry angles at which the orbit was slightly irradiated, partially irradiated, and completely irradiated. The OEM incident surface dose reduction rate was measured using an automatic exposure control (AEC) phantom with a diameter of 6-18 cm. The lens surface dose reduction rate using OEM was 21.2%. When the gantry was tilted and the orbit was completely out of the scanning range, the rate of reduction was 47.8%. OEM incident surface dose reduction rates were 27.4% for a phantom diameter of 18 cm, 22.0% for that of 16 cm, 17.8% for that of 14 cm, 17.2% for that of 12 cm, 8.4% for that of 10 cm, and 0% for that of 8 cm and 6 cm. OEM effectiveness decreased with decreasing phantom diameter. The use of OEM increased the rate of change of SD by 1.25´ when the gantry inclination was 0°, 1.27´ when the gantry inclination was 10°, and 1.27´ when the gantry inclination was 20°in the 12 o'clock position. The degree of reduction in exposure dose to the lens in pediatric head CT imaging was 47.8% by completely removing the lens from the irradiation range using gantry tilt and 21.2% by using OEM. The effect of OEM changed in proportion to tube current. The exposure reduction effect of the OEM decreases with decreasing head size, indicating its reduced effectiveness in head CT scans of smaller infants.

PERANAN HEART RATE TERHADAP KUALITAS CITRA PENGGUNAAN “COVID-19” WINDOW UNTUK PEMERIKSAAN CT-SCAN THORAX POLOS PADA PASIEN SUSPEK COVID-19

Background: Non-contrast chest CT-Scan is one of the COVID-19 screening methods. At Panti Waluyo hospital of Surakarta, Non-contrast chest CT-Scan did not use the HRCT technique, low-dose technique, Lung Window, and Mediastinum Window, but used a standard-dose technique and “COVID-19” window.&#x0D; Methods: The research was conducted at Panti Waluyo hospital of Surakarta, scanning process using GE Brightspeed 8 Slices CT-Scan. The position of the patient is supine feet first, the midline is at the midsagittal plane and axillary line, the scanning process begins with a vertical and horizontal scout photo, scanning area from Thoracal 1st to lumbar 3rd, using a helical scan, and “COVID-19” window with 120 kV, 100 mA, 0.8 s, 5 mm slice thickness, FoV 34 cm, gantry tilt 0 °, reconstruction 1.25 mm, pitch 1.35: 1, window width 1600, and window level -250.&#x0D; Results: The expertise of Radiologists indicates bilateral pneumonia (typical COVID-19). The "COVID-19" window presents GGO and clarifies the difference between GGO and lung consolidation. It shows the contour of the heart and part of the liver, without adding another window. So, it can increase the effectiveness of time and radiological film.&#x0D; Conclusions: For non-contrast chest CT-scan in patients with suspected COVID-19, it is better to use the “COVID-19” window than the lung or mediastinal window.

Lateral Position With Gantry Tilt Further Improves Computed Tomography Image Quality Reconstructed Using Single-Energy Metal Artifact Reduction Algorithm in the Oral Cavity.

To assess the limitations of single-energy metal artifact reduction algorithm in the oral cavity and evaluate the availability of a solution by setting the patient in a lateral position (LP) with the use of a gantry tilt (GT). We analyzed 88 patients with dental metals retrospectively in study 1, and 74 patients prospectively in study 2. Patients were classified: metal I with dental metals in 1 region, metal II in 2 regions, and metal III in 3 regions. Patients underwent neck computed tomography examinations in a supine position (SP) in study 1, and 2 positions, an LP with a GT and an SP, in study 2. All images were reconstructed with this algorithm. Image quality was scored using a 4-point scale: 1 = severe artifact, 2 = moderate artifact, 3 = slight artifact, 4 = no artifact. The scores were compared between metal I, metal II, and metal III using the Mann-Whitney U test in study 1, and between an LP with a GT and an SP using the Wilcoxon signed ranks test in study 2. The scores outside the dental arch were significantly higher in metal I than in metal II and metal III (3.0 ± 0.6 vs 2.3 ± 0.5 vs 2.2 ± 0.4; P < 0.0001 for metal I vs metal II and for metal I vs metal III) and significantly higher in an LP with a GT than an SP (3.2 ± 0.4 vs 2.3 ± 0.4; P < 0.0001). Single-energy metal artifact reduction algorithm could reduce metal artifacts adequately in patients with dental metals in 1 region, but not in 2 or more regions. However, even for the latter, combination of this algorithm and an LP with a GT could further improve the image quality.

Influence of Various Setup Parameters on Scattered Fraction in Interventional Cardiology

It is important to examine the positions of the medical staff involved in interventional cardiology in order to minimize their accumulated scattered radiation doses. This study used the design of experiment (DOE) method with three parameters (C-arm gantry tilt, position and height), each at three levels (low, medium and high), on both the left and right sides of the patient, to analyse the interactions between the parameters that influence the scattered fraction in interventional cardiology. In this experiment, a RANDO phantom and an Unfors Xi survey detector were used to measure the rate of the scattered dose exposed to staff without protective shielding in a Cath lab. The parameters that significantly influenced the scattered fraction at a confidence level of 95% (P< 0.05) to the right of the patient were the gantry tilt and the height. To the left of the patient, all parameters significantly influenced the scattered fraction.

The optimization of radiation protection to interventional cardiologists

Scattered dose radiation to occupational in interventional cardiology cannot be neglected due to the long time for each procedure. The limit dose for occupational is 20 mSv per year or 0.01 mSv/h. The aim of this study is to calculate the effective dose of occupational and to analyse the optimization of radiation protection in the Cath lab. The simulation has been done using Rando phantom as a patient and Unfors Xi as scattered dose measuring instrument (in mGy/h). The data is collected in 6 different positions from altitudes 25 cm to 75 cm with a range of 15 cm without protective shielding. Field size of primary beam is varied to 20×20 cm and 25×25 cm, while gantry tilt is varied to caudal, cranial, and Left Anterior Oblique (LAO). The obtained data is multiplied by weighting factor base on its height. The result shows that the effective dose of occupational is in the range of 0.18-0.94 mSv/h, which is exceed the limit dose. To accommodate the limit dose for occupational, we propose the limitation of procedure time to 21-110 hours a year or the use of protective shielding as thick as 1-1.6 mm lead.

Radiation dose and risk to the lens of the eye during CT examinations of the brain.

Cataracts are the leading cause of blindness and visual disability worldwide. Of the known contributing factors to this condition, ionising radiation is considered the primary concern in a radiological context given the particular radiosensitivity of the lens of the eye. In light of the substantially increased application of computed tomography in brain imaging, an investigation of the relevent literature is warranted to assess thresholds, lens radiation doses and dose reduction techniques in respect to the cataractogenic risk of such examinations. The value and very existence of a lens dose threshold is debatable given different considerations of radiation dose, latency, opacity classifications and historical sample populations, though ICRP guidelines suggest a threshold of 0.5Gy. Documented CT-specific radiation doses to the eye following scans of the brain are highly variable between studies (2-130mGy), primarily owing to discrepancies in scanning technique. These findings, when coupled with the relative ambiguity of known threshold values, present difficulties in assessing the overall risk of cataracts following serial CT examinations to the head. In the absence of definitive risk evaluations, a cautionary approach is advised. The implementation of gantry tilt along the supraorbital margin is recommended as standard practice on account of its highly effective radiation dose reduction outcomes. Organ-based tube modulation and reductions in tube current may also be considered beneficial. Bismuth eye shielding is only advised where gantry tilting is unachievable, and in such cases, ensure careful adherence to appropriate shield placement and infection control measures.

Falx cerebri Calcifications and Ossifications in CT Scans – A Data Collection on Frequency, Position and Size

Background: The aim of this study is the acquisition of data regarding the frequency, position, size, sex- and age distribution of falx cerebri calcifications (FCC, including ossifications) using CT scans. Methods: An explorative-retrospective data collection using skull CT scans of all CT devices (in use for patient examinations) at the University Hospital Graz. From August 20 to August 31, 2015, 365 cases of undisturbed and non-contrast brain images were determined. FCC with a density threshold value of &gt; = 100 HU was recorded, analysed according to certain target parameters and evaluated using descriptive statistics. Additionally, lateral views of three-dimensional image reconstructions of certain FCC were produced and measured. Also, superior sagittal sinus calcifications were examined. Results: The occurrence of FCC accounted for 34% in general and was slightly more frequent in older men. Among all FCC 95% were located in anterior and medial falx area. The Spearman’s rank correlation between age and occurrence of FCC was r = .96, p &lt; .001. Considering a sagittal dimension (max. length x max. height x sin (90°-Gantry Tilt) computed in axial layers) of &gt; = 2cm² , FCC incidences still amounted to 9, 8%. Conclusions: The FCC frequency of 10% with a size of &gt; = 2 cm² (sagittal dimension computed in axial layers) corresponded to values of previous x-ray studies. However, the dimension or diameter was never mentioned. FCC of the size mentioned above is relevant to an osteopath’s work since they might influence the craniosacral palpation and treatment of the falx cerebri. Therefore, there is further need for investigation concerning the possible effects of FCC on craniosacral palpation of the falx cerebri, precise measurements of size, as well as a histological comparison alongside CT-imaging. Keywords: Falx cerebri, calcification, ossification, computed tomography

Examination about the Direction for Uses of the Radiation Exposure Reduction Mechanism (Organ Effective Modulation) in Consideration of Organ Sensitivity

Automatic exposure control technology can reduce the radiation dose during CT. The purpose of this study is to reveal the important points regarding the usage of organ effective modulation (OEM), by evaluating the characteristics of OEM, an automatic exposure control technology. An analysis of the dosage profiles revealed that OEM may not work with the first rotation of the X-ray tube in the helical method and wide volume method. This phenomenon can be avoided by using the orbital synchronism helical method. This was also demonstrated upon measurement of the integrated absorption dose at the imaging start position. An analysis of standard deviation measurement revealed that with the combined use of OEM and x-y modulation, the reduction in dose may significantly vary depending on the presence or absence of the gantry tilt. Based on the above results, when using OEM to reduce the dose at the imaging start position, the combined use of x-y modulation should be avoided and the orbital synchronism helical method should be used.

Implementation of iterative metal artifact reduction in the pre-planning-procedure of three-dimensional physical modeling

BackgroundTo assess the impact of metal artifact reduction techniques in 3D printing by evaluating image quality and segmentation time in both phantom and patient studies with dental restorations and/or other metal implants. An acrylic denture apparatus (Kilgore Typodent, Kilgore International, Coldwater, MI) was set in a 20 cm water phantom and scanned on a single-source CT scanner with gantry tilting capacity (SOMATOM Edge, Siemens Healthcare, Forchheim, Germany) under 5 scenerios: (1) Baseline acquisition at 120 kV with no gantry tilt, no jaw spacer, (2) acquisition at 140 kV, (3) acquisition with a gantry tilt at 15°, (4) acquisition with a non-radiopaque jaw spacer and (5) acquisition with a jaw spacer and a gantry tilt at 15°. All acquisitions were reconstructed both with and without a dedicated iterative metal artifact reduction algorithm (MAR). Patients referred for a head-and-neck exam were included into the study. Acquisitions were performed on the same scanner with 120 kV and the images were reconstructed with and without iterative MAR. Segmentation was performed on a dedicated workstation (Materialise Interactive Medical Image Control Systems; Materialise NV, Leuven, Belgium) to quantify volume of metal artifact and segmentation time.ResultsIn the phantom study, the use of gantry tilt, jaw spacer and increased tube voltage showed no benefit in time or artifact volume reduction. However the jaw spacer allowed easier separation of the upper and lower jaw and a better display of the teeth. The use of dedicated iterative MAR significantly reduced the metal artifact volume and processing time. Same observations were made for the four patients included into the study.ConclusionThe use of dedicated iterative MAR and jaw spacer substantially reduced metal artifacts in the head-and-neck CT acquisitions, hence allowing a faster 3D segmentation workflow.

Inefficiencies in Computed Tomography Sinus Imaging for Management of Sinonasal Disease.

Objective A subset of patients with sinonasal disease who obtain a diagnostic computed tomography (CT) sinus scan may require repeat preoperative CT due to the inadequacy of diagnostic CT for image-guided sinus surgery (IGSS). This leads to increased CT utilization, health care costs, and patient exposure to ionizing radiation. The objective of this study is to determine the frequencies of diagnostic CT sinus studies that were inadequate for IGSS and repeat CT studies for purposes of IGSS. Study Design A retrospective chart study was performed between May 2012 and August 2013. Setting Tertiary care rhinology practice. Subjects and Methods New patients with any sinonasal diagnosis who presented with CT sinus scans acquired from outside institutions were included. CT scans were considered inadequate for IGSS for any of the following reasons: >1.5-mm slice thickness, oblique axial planes due to gantry tilt, and incompletely defined or missing IGSS anatomic landmarks. Results Of 183 patients, 85 (46%) presented with diagnostic CT sinus scans that were inadequate for IGSS. Seventy-one patients met indications for IGSS, of which 37 (52%) required repeat CT due to an IGSS-inadequate diagnostic scan. Conclusion The frequency of repeat preoperative CT sinus imaging may be high at tertiary care centers where IGSS is performed. A standardized IGSS-adequate CT sinus protocol may avoid the need for repeat preoperative scans. Potential advantages include improved efficiency, decreased health care costs, and reduced ionizing radiation exposure to the patient.

Signal-to-noise ratio and dose to the lens of the eye for computed tomography examination of the brain using an automatic tube current modulation system.

The study aimed to evaluate the image quality in terms of signal-to-noise ratio (SNR) and dose to the lens of the eye and the other nearby organs from the CT brain scan using an automatic tube current modulation (ATCM) system with or without CT gantry tilt is needed. An anthropomorphic phantom was scanned with different settings including use of different ATCM, fixed tube current time product (mAs) settings and degree angles of gantry tilt. Gafchromic film XR-QA2 was used to measure absorbed dose of the organs. Relative doses and SNR for the various scan settings were compared with the reference setting of the fixed 330 mAs. Average absorbed dose for the lens of the eyes varied from 8.7 to 21.7mGy. The use of the ATCM system with the gantry tilt resulted in up to 60% decrease in the dose to the lens of the eye. SNR significantly decreased while tilting the gantry using the fixed mAs techniques, compared to that of the reference setting. However, there were no statistical significant differences for SNRs between the reference setting and all ATCM settings. Compared to the reference setting of the fixed effective mAs, using the ATCM system and appropriate tilting, the gantry resulted in a substantial decrease in the dose to the lens of the eye while preserving signal-to-noise ratio. CT brain examination should be carefully controlled to optimize dose for lens of the eye and image quality of the examination.

Head computed tomography: Dose output and relationship with anthropotechnical parameters

Background: The number of computed tomography (CT) centers and examinations in Nigeria has shown a steady increase. This will increase the collective dose and may potentially result in an increased incidence of cancer, hereditary diseases, and the possibility of mild deterministic effects. Objective: To determine radiation dose output and its relationship with anthropotechnical parameters. Methodology: A retrospective analyses of digital CT files. Effective dose was derived from the dose-length product and factor for examination of head CT (0.0023 mSv/mGy-cm). SPSS version 20.0 (SPSS Inc., Chicago, IL, USA) was used to analyze the data. Results: Files of 43 male and 42 female (n = 85) adult patients were analyzed. The mean (and 75 th percentile) of the CT dose index (CTDI), dose-length product (DLP), and effective dose in noncontrast examinations were 48 (59) mGy, 874 (1301) mGy-cm, and 1.8 (2.7) mSv, respectively. Contrast examinations yielded 54 (61) mGy, 1476 (2044) mGy-cm, and 3.1 (4.3) mSv, respectively. DLP showed a weak relationship with BPD (r = −0.220), age (r = 0.211), cephalic index (r = −0.186), height (r = 0.158), and gantry tilt (r = 0.154). There was no relationship with weight (r = 0.076), range (r = −0.073), occipitofrontal diameter (r = 0.037), and body mass index (r = −0.018). The correlations were neither statistically nor clinically significant. Conclusion: The CTDI is comparable with local values while the DLP is lower by a range of 5-31% but higher than foreign values by a range of 19-35%. Further optimization of CT radiation dose should be explored to eliminate the gulf between local and foreign dose outputs.

Analysis of Age-Related Changes in Asian Facial Skeletons Using 3D Vector Mathematics on Picture Archiving and Communication System Computed Tomography.

PurposeThere are marked differences in facial skeletal characteristics between Asian and Caucasian. However, ethnic differences in age-related facial skeletal changes have not yet been fully established. The aims of this study were to evaluate age-related changes in Asian midfacial skeletons and to explore ethnic differences in facial skeletal structures with aging between Caucasian and Asian.Materials and MethodsThe study included 108 men (aged 20-79 years) and 115 women (aged 20-81 years). Axial CT images with a gantry tilt angle of 0 were analyzed. We measured three-dimensional (3D) coordinates at each point with a pixel lens cursor in a picture archiving and communication system (PACS), and angles and widths between the points were calculated using 3D vector mathematics. We analyzed angular changes in 4 bony regions, including the glabellar, orbital, maxillary, and pyriform aperture regions, and changes in the orbital aperture width (distance from the posterior lacrimal crest to the frontozygomatic suture) and the pyriform width (between both upper margins of the pyriform aperture).ResultsAll 4 midfacial angles in females and glabellar and maxillary angles in males showed statistically significant decreases with aging. On the other hand, the orbital and pyriform widths did not show statistically significant changes with aging.ConclusionThe results of this study suggest that Asian midfacial skeletons may change continuously throughout life, and that there may be significant differences in the midfacial skeleton between both sexes and between ethnic groups.

Tilting the gantry for CT-guided spine procedures

Percutaneous spine procedures can be performed with computed tomography (CT) guidance. The use of CT guidance is cumbersome for procedures where an oblique needle trajectory is imposed by the spatial orientation of the spine, often requiring complex needle triangulation relative to the true axial scan plane. We describe a procedural modification to overcome this limitation. A combination of variable CT gantry tilt, and strategic bolster placement under the patient can be used to obtain optimal imaging planes for guidance along the desired needle trajectory. The needle is aligned with the CT gantry laser beam to guide the needle access to the target, maintained within a single CT slice. We describe our clinical experience using the modified procedure relative to the conventional technique, and provide representative examples.

The effects of gantry tilt on breast dose and image noise in cardiac CT

This study investigated the effects of tilted-gantry acquisition on image noise and glandular breast dose in females during cardiac computed tomography (CT) scans. Reducing the dose to glandular breast tissue is important due to its high radiosensitivity and limited diagnostic significance in cardiac CT scans. Tilted-gantry acquisition was investigated through computer simulations and experimental measurements. Upon IRB approval, eight voxelized phantoms were constructed from previously acquired cardiac CT datasets. Monte Carlo simulations quantified the dose deposited in glandular breast tissue over a range of tilt angles. The effects of tilted-gantry acquisition on breast dose were measured on a clinical CT scanner (CT750HD, GE Healthcare) using an anthropomorphic phantom with MOSFET dosimeters in the breast regions. In both simulations and experiments, scans were performed at gantry tilt angles of 0°-30°, in 5° increments. The percent change in breast dose was calculated relative to the nontilted scan for all tilt angles. The percent change in noise standard deviation due to gantry tilt was calculated in all reconstructed simulated and experimental images. Tilting the gantry reduced the breast dose in all simulated and experimental phantoms, with generally greater dose reduction at increased gantry tilts. For example, at 30° gantry tilt, the dosimeters located in the superior, middle, and inferior breast regions measured dose reductions of 74%, 61%, and 9%, respectively. The simulations estimated 0%-30% total breast dose reduction across the eight phantoms and range of tilt angles. However, tilted-gantry acquisition also increased the noise standard deviation in the simulated phantoms by 2%-50% due to increased pathlength through the iodine-filled heart. The experimental phantom, which did not contain iodine in the blood, demonstrated decreased breast dose and decreased noise at all gantry tilt angles. Tilting the gantry reduced the dose to the breast, while also increasing noise standard deviation. Overall, the noise increase outweighed the dose reduction for the eight voxelized phantoms, suggesting that tilted gantry acquisition may not be beneficial for reducing breast dose while maintaining image quality.