Mm In Slice Thickness Research Articles

Exploring CT pixel and voxel size effect on anatomic modeling in mandibular reconstruction

BackgroundComputer-aided modeling and design (CAM/CAD) of patient anatomy from computed tomography (CT) imaging and 3D printing technology enable the creation of tangible, patient-specific anatomic models that can be used for surgical guidance. These models have been associated with better patient outcomes; however, a lack of CT imaging guidelines risks the capture of unsuitable imaging for patient-specific modeling. This study aims to investigate how CT image pixel size (X-Y) and slice thickness (Z) impact the accuracy of mandibular models.MethodsSix cadaver heads were CT scanned at varying slice thicknesses and pixel sizes and turned into CAD models of the mandible for each scan. The cadaveric mandibles were then dissected and surface scanned, producing a CAD model of the true anatomy to be used as the gold standard for digital comparison. The root mean square (RMS) value of these comparisons, and the percentage of points that deviated from the true cadaveric anatomy by over 2.00 mm were used to evaluate accuracy. Two-way ANOVA and Tukey-Kramer post-hoc tests were used to determine significant differences in accuracy.ResultsTwo-way ANOVA demonstrated significant difference in RMS for slice thickness but not pixel size while post-hoc testing showed a significant difference in pixel size only between pixels of 0.32 mm and 1.32 mm. For slice thickness, post-hoc testing revealed significantly smaller RMS values for scans with slice thicknesses of 0.67 mm, 1.25 mm, and 3.00 mm compared to those with a slice thickness of 5.00 mm. No significant differences were found between 0.67 mm, 1.25 mm, and 3.00 mm slice thicknesses. Results for the percentage of points deviating from cadaveric anatomy greater than 2.00 mm agreed with those for RMS except when comparing pixel sizes of 0.75 mm and 0.818 mm against 1.32 mm in post-hoc testing, which showed a significant difference as well.ConclusionThis study suggests that slice thickness has a more significant impact on 3D model accuracy than pixel size, providing objective validation for guidelines favoring rigorous standards for slice thickness while recommending isotropic voxels. Additionally, our results indicate that CT scans up to 3.00 mm in slice thickness may provide an adequate 3D model for facial bony anatomy, such as the mandible, depending on the clinical indication.

Automated Linac QA Using Scripting and Varian Developer Mode

Purpose: Linac quality assurance (QA) can be time consuming involving set up, execution, analysis and subject to user variability. The purpose of this study is to develop qualitative automation tools for mechanical and imaging QA to improve efficiency, consistency, and accuracy. Methods and Materials: Traditionally QA has been performed with graph paper, film, and multiple phantoms. Analysis consists of ruler and vendor provided software. We have developed a single four-phantom method for QA procedures including light-radiation coincidence, imaging quality, table motion and Isocentricity and separately cone beam computed tomography. XML scripts were developed to execute a series of tasks using Varian’s Truebeam Developer Mode. Non-phantom QA procedures have also been developed including field size, dose rate, MLC position, MLC and gantry speed, star shot, Winston-Lutz and Half Beam Block. All analysis is performed using inhouse MATLAB codes. Results: Overall time savings were 2.2 hours per Linac per month. Consistency improvements (standard deviation, STD) were observed for some tests. For example: field size improved from 0.11 mm to 0.04 mm and table motion improved from 0.17 mm to 0.12 mm. CBCT STD improved from 0.99 mm to 0.61 mm for slice thickness. No STD change was observed for Isocentricity test. We noticed an increase in STD from 0.33 mm to 0.41 mm for light-radiation coincidence test. There was a small drop in field size accuracy. Isocentricity showed an increase in measurement accuracy from 0.47 mm to 0.15 mm. Table motion increased in accuracy from 0.20 mm to 0.16 mm. Conclusion: Automation is a viable, accurate and efficient option for monthly and annual QA.

Automatic Bladder Delineation on MR Images Using a Convolution Neural Network for Online Image-Guided Radiotherapy

Adaptive radiotherapy for bladder cancer is challenging due to its inter- and intra-fractional anatomical variations appeared during the course of treatment. In order to adapt for these changes, anatomical information of patient body needs to be monitored on time. Magnetic resonance imaging (MRI) is able to acquire patient images continuously without any radiation exposure, whereas fast bladder delineation method for MR images is still developing technique. This study aims to develop a method that automatically extracts bladder contours from the MR images using a convolutional neural network (CNN). Total 1,060 pairs of a pelvic T2 weighted axial MR image and its segmented bladder contour, which were delineated by an experienced radiation oncologist, were collected from 100 patients. All MR images had 2.5 mm in slice thickness and were acquired with an MRI scanner. This dataset was divided into 840 image pairs (80 patients) for training, 113 (10) for validation and 107 (10) for test. A U-net-based 2D CNN model was generated. Input and label of the model were set to 2D MR image and its contour, respectively. 100-epoch end-to-end training was applied for the CNN model with 5 mini-batches and data augmentation of random image flip and 90° rotations. Delineation accuracy of the trained CNN model was evaluated with Dice similarity coefficient (DSC). The CNN model is able to calculate bladder contours with high accuracy. A median DSC value over all test data was 94.4%. Despite of this high accuracy, relatively low DSC values were observed for MR images including only bladder margins. We succeeded in developing a bladder delineation model for MR images with high accuracy. Model performance for MR images with bladder margins could be insufficient with 2D CNN, and 3D CNN is expected to improve accuracy. This technique will be utilized in image-guided radiotherapy.

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 a prototype rapid kilovoltage x-ray image guidance system designed for a ring shape radiation therapy unit.

This study aims to characterize the performance of a prototype rapid kilovoltage (kV) x-ray image guidance system onboard the newly released Halcyon 2.0 linear accelerator (Varian Medical Systems, Palo Alto, CA) by use of conventional and innovatively designed testing procedures. Basic imaging system performance tests and radiation dose measurements were performed for all eleven kV-cone beam computed tomography (CBCT) imaging protocols available on a preclinical Halcyon 2.0 LINAC. Both conventional CBCT reconstruction using the Feldkamp-Davis-Kress (FDK) algorithm and a novel, advanced iterative reconstruction (iCBCT) available on this platform were evaluated. Standard image quality metrics, including slice thickness accuracy, high-contrast resolution, low-contrast resolution, regional uniformity and noise, and CT Hounsfield unit (HU) number accuracy and linearity were evaluated using a manufacturer-supplied QUART phantom (GmbH, Zorneding, Germany) and an independent image quality phantom (Catphan 500, The Phantom Laboratory, New York, NY). Due to the simplified design of the QUART phantom, we developed surrogate and clinically feasible strategies for measuring slice thickness and high- and low-contrast resolution. Imaging dose delivered by these eleven protocols was measured using a computed tomography dose index phantom and pencil chamber with commonly accepted methods and procedures. A subset of measurements were repeated on a conventional C-arm LINAC (TrueBeam and Trilogy, Varian Medical System) for comparison. Clinical patient images of pelvic and abdominal regions are also presented for qualitative assessment as part of a feasibility study for clinical implementation. Image acquisition time was 17-42s on the Halcyon system compared with 60s on the C-arm LINAC systems. The kV imager projection offset, imaging and treatment isocenter coincidence and the couch three-dimensional match movement all achieved less than1mm mechanical accuracy. All major image quality metrics were within either the national guideline or vendor-recommended tolerances. The designed surrogate approach with the QUART phantom showed a range of 0.24-0.35cycles/mm for spatial resolution, a contrast-to-noise ratio (CNR) of 2-20 for FDK reconstruction and a tolerance of 0.5mm for slice thickness. Other metrics derived from the Catphan images obtained on the Halcyon and C-arm LINACs showed comparable values for the FDK reconstruction. The iterative reconstruction tended to reduce noise, as evidenced by a higher CNR ratio. The fast scan pelvis protocols for Halcyon resulted in 50% lower dose compared to the standard scans, and the thorax fast protocol similarly delivered 10% lower dose than the standard thoracic scan. Preliminary patient images indicated that rapid kV CBCT with breath-hold is feasible, with improved imaging quality compared to free-breathing scans. Independent and comprehensive characterization of the kV imaging guidance system on the Halcyon 2.0 system demonstrated acceptable image quality for clinical use. The imaging unit onboard the Halcyon meets vendor specifications and satisfies requirements for routine clinical use. The fast kV imaging system enables the potential for volumetric CBCT acquisition during a single breath-hold and the iterative reconstruction tends to reduce the noise therefore has the potential to improve the CNR for normal size patient.

SU‐E‐J‐30: The Effect of Planning CT Slice Thickness On Evaluation of SRS Target Localization Accuracy

Purpose:To evaluate the effect of planning CT slice thickness on SRS target localization accuracy on Varian Edge SRS treatment platform.Methods:A metal BB of diameter 5 mm was inserted in a Rando head phantom. Planning CTs were scanned with 0.8, 2 and 3 mm slice thickness respectively. The center of BB was setup as isocenter and tattoos were marked on phantom surface. The phantom was initially aligned using laser and tattoos, then a CBCT was acquired and 6‐degree of freedom (DOF) image registration was performed based on bony anatomy. The 6D couch correction was applied. A verification CBCT was taken to evaluate couch corrections. Three orthogonal pairs of images (MV‐MV, KV‐KV and MVKV), were also taken to verify the position of the phantom using a 2D‐3D registration algorithm. Winston‐Lutz tests were taken at 12 combinations of gantry, collimator and couch angles using 1×1cm MLC aperture and 10mm circular cone.Results:The vector lengths of the residual error measured with verification CBCT were 0.3, 0.2 and 0.2 mm for the planning CT of 0.8, 2 and 3 mm slice thicknesses respectively. Residual setup error vector lengths for 0.8, 2, and 3 mm CT measured by orthogonal pair were as following: a) MV‐MV: 0.2, 0.5, 0.5mm; b) KV‐KV: 0.2, 0.3, 0.3mm; c)MV‐KV: 0.1, 0.6, 0.3mm respectively. The vector lengths for the Winston‐Lutz tests were: a) MLC: 0.55, 0.32, and 0.2mm; b) CONE: 0.16, 0.17, and 0.29mm for slice thickness of 0.8, 2, and 3mm respectively.Conclusion:The residual setup error in this study measured by the 2D‐3D algorithm was comparable to that of the 3D‐3D algorithm. The planning CT slice thickness in the range of 0.8 to 2 mm has no significant impact on the evaluation of the residual setup error and the Result of Winston‐Lutz test.

Influence of image slice thickness on rectal dose–response relationships following radiotherapy of prostate cancer*

When pooling retrospective data from different cohorts, slice thicknesses of acquired computed tomography (CT) images used for treatment planning may vary between cohorts. It is, however, not known if varying slice thickness influences derived dose–response relationships. We investigated this for rectal bleeding using dose–volume histograms (DVHs) of the rectum and rectal wall for dose distributions superimposed on images with varying CT slice thicknesses. We used dose and endpoint data from two prostate cancer cohorts treated with three-dimensional conformal radiotherapy to either 74 Gy (N = 159) or 78 Gy (N = 159) at 2 Gy per fraction. The rectum was defined as the whole organ with content, and the morbidity cut-off was Grade ≥2 late rectal bleeding. Rectal walls were defined as 3 mm inner margins added to the rectum. DVHs for simulated slice thicknesses from 3 to 13 mm were compared to DVHs for the originally acquired slice thicknesses at 3 and 5 mm. Volumes, mean, and maximum doses were assessed from the DVHs, and generalized equivalent uniform dose (gEUD) values were calculated. For each organ and each of the simulated slice thicknesses, we performed predictive modeling of late rectal bleeding using the Lyman–Kutcher–Burman (LKB) model. For the most coarse slice thickness, rectal volumes increased (≤18%), whereas maximum and mean doses decreased (≤0.8 and ≤4.2 Gy, respectively). For all a values, the gEUD for the simulated DVHs were ≤1.9 Gy different than the gEUD for the original DVHs. The best-fitting LKB model parameter values with 95% CIs were consistent between all DVHs. In conclusion, we found that the investigated slice thickness variations had minimal impact on rectal dose–response estimations. From the perspective of predictive modeling, our results suggest that variations within 10 mm in slice thickness between cohorts are unlikely to be a limiting factor when pooling multi-institutional rectal dose data that include slice thickness variations within this range.

SU‐E‐J‐26: Analysis of Image Quality in CBCT QA Using a Treatment Planning System

Purpose:The objective of this study is to propose an alternative QA technique that analyzes imaging quality(IQ) in CBCT‐QA processing.Methods:A catphan phantom was used to take CT imaging data set that were imported into a treatment planning system – Eclipse. The image quality was analyzed in terms of in‐slice geometry resolution, Hounsfield numbers(HU) accuracy, mean‐slice thickness, edge‐to‐center uniformity, low contrast resolution, and high contrast spatial resolution in Eclipse workstation. The CBCT‐QA was also analyzed by OBI‐workstation and a commercial software. Comparison was made to evaluation feasibility in a TPS environment.Results:The analysis of IQ was conducted in Eclipse v10.0 TPS. In‐slice geometric resolution was measured between 2‐rods in section CTP404 and repeated for all 4 rods with the difference between expected and measured values less than +/−0.1 cm. For HU, the difference between expected and measured values in HU was found much less than +/−40. Mean slice thickness measured by a distance on the wire proportional to scanner increment multiplying by a factor of 0.42. After repeating measurements to 4 wires, the average difference between expected and measured values was less +/−0.124 mm in slice thickness. HU uniformity was measured in section CTP486 with the tolerance less than +/−40 HU. Low contrast resolution in section CTP515 and high contrast resolution in section CTP528 were found to be 7 disks in diameter of 4 mm and 6 lp/cm, respectively. Eclipse TPS results indicated a good agreement to those obtained in OBI workstation and ImagePro software for major parameters.Conclusion:An analysis of IQ was proposed as an alternative CBCT QA processing. Based upon measured data assessment, proposed method was accurate and consistent to IQ evaluation and TG142 guideline. The approach was to utilize TPS resource, which can be valuable to re‐planning, verification, and delivery in adaptive therapy.

Qualitative near-infrared vascular imaging system with tuned aperture computed tomography

We developed a novel system for imaging and qualitatively analyzing the surface vessels using near-infrared (NIR) radiation using tuned aperture computed tomography (TACT(®)). The system consisted of a NIR-sensitive CCD camera surrounded by sixty light emitting diodes (with wavelengths alternating between 700 or 810 nm). This system produced thin NIR tomograms, under 0.5 mm in slice thickness. The venous oxygenation index reflecting oxygen saturation levels calculated from NIR tomograms was more sensitive than that from the NIR images. This novel system makes it possible to noninvasively obtain NIR tomograms and accurately analyze changes in oxygen saturation.

Visualization of coronary artery stents by MSCT at 0.5-mm slice thickness

Coronary artery visualization by multi-slice CT and the evaluation of coronary stenosis were examined. Multi-slice CT could not be used for evaluation after the coronary artery stent custody method. We examined various coronary artery stent custody phantoms and stent visualization of clinical examples by using multi-slice CT with a slice thickness of 0.5 mm. ECG-gated scanning was done by inputting ECG using 4DAS (Data Acquisition System) multi-slice CT with a slice thickness of 0.5 mm. We carried out image reconstruction, measured the CT number, and examined the inside stent. The CT number of the inside stent rose in accordance with stent diameter. The inside stent was visualized clearly at 0.5 mm in comparison with 1.0 mm in slice thickness. Visualization of the lumen was influenced in the Stent Custody Phantom by the quality of the stent material, Strut form, and the size of the diameter. The inside stent could be evaluated with the S670 4 mmphi stent. Form evaluation of the inside stent was possible, although the cavity in the stent was influenced by the difference in distance between peaks.

聴神経腫よう画像診断の進歩

The history of radiodiagnosis of acoustic tumors (AT) is reviewed in this paper. Plain Xray films and tomograms of the internal auditory canal provided information suggesting the presence of AT, but the direct visualization of AT became possible after the introduction of posterior fossa myelography. Using this method, W. House and his group did splendid work in the early diagnosis of AT in the 1960s and 1970s. Pneumoencephalographic roulette tomography introduced in 1968 was also a useful method of visualizing these tumors. These methods, however, required a spinal tap and the injection of contrast material (Pantopaque or air), and these disadvantages prevented them from becoming routine clinical examinations. CT Scan-ning introduced by Hounsfield and Ambrose in 1973, was less invasive and provided a clear image of AT. However, an AT less than 1.5 cm in diameter could not be visualized. CT Scanning apparatus was further improved and diagnosis of intracanalicular tumors became possible with the third generation apparatus which can image thin section (1 to 2 mm in slice thickness). Although air CT cisternography, intro-duced by Sortland (1979), provided a clearer view of small tumors, the necessary injection of air into the subarachnoid space was a disadvantage, and a less invasive method was sought. Magnetic resonance imaging (MRI) is non-invasive, but a small tumor could not be detected with the earlier MRI with its normoconductive magnet. However, MRI with a superconductive magnet provides by far the clearest image of AT regardless of the size of the tumor. This new MRI apparatus is now widely distributed throughout the country and will greatly contribute to the early diagnosis of AT.