Effectiveness of Commercial Software–Enhanced Image Artifact Reduction Software

IntroductionArtifact reduction (AR) software has been incorporated into some cone-beam computed tomographic (CBCT) systems to reduce the severity of beam hardening (BH) artifacts and improve image quality. This study quantifies BH artifact and evaluates the effectiveness of AR in 2 CBCT systems.MethodsPalatal roots of Dent-Alike (Dentsply Sirona, Tulsa, OK) teeth were prepared and root filled with gutta-percha and EndoSequence BC Sealer (Brasseler, Savannah, GA). Six teeth were imaged with and without AR software using the ProMax3D (Planmeca Oy, Helsinki, Finland) and the Pax-i3D (Vatech, Hwaseong-si, South Korea) systems. FSL (FMRIB, Oxford, UK) software was used to quantify the light and dark components of the BH artifact along the tooth root using a specific region of interest approach and an image-wide analysis approach. Statistical analysis was performed using paired t tests and corrected for multiple comparisons with cluster mass correction using a nonparametric statistical analysis to evaluate the differences in the artifact volumes and areas with and without AR.ResultsA significant reduction in the light artifact was observed with the Planmeca system (P < .05), but no significant differences were observed for either the light or dark artifacts with the Vatech system when AR was applied. There were also significant reductions in the volumes of light and dark artifacts along the entire root length when the AR was applied with the Planmeca system (cluster mass P < .05), but no significant differences were observed with the Vatech system.ConclusionsProprietary AR software is not equally effective in reducing the light and/or dark components of CBCT BH artifacts.     

Static Field Influences on Transcranial Magnetic Stimulation: Considerations for TMS in the Scanner Environment

BackgroundTranscranial magnetic stimulation (TMS) can be combined with functional magnetic resonance imaging (fMRI) to simultaneously manipulate and monitor human cortical responses. Although tremendous efforts have been directed at characterizing the impact of TMS on image acquisition, the influence of the scanner's static field on the TMS coil has received limited attention.Objective/hypothesisThe aim of this study was to characterize the influence of the scanner's static field on TMS. We hypothesized that spatial variations in the static field could account for TMS field variations in the scanner environment.MethodsUsing an MRI-compatible TMS coil, we estimated TMS field strengths based on TMS-induced voltage changes measured in a search coil. We compared peak field strengths obtained with the TMS coil positioned at different locations (B₀ field vs fringe field) and orientations in the static field. We also measured the scanner's static field to derive a field map to account for TMS field variations.ResultsTMS field strength scaled depending on coil location and orientation with respect to the static field. Larger TMS field variations were observed in fringe field regions near the gantry as compared to regions inside the bore or further removed from the bore. The scanner's static field also exhibited the greatest spatial variations in fringe field regions near the gantry.ConclusionsThe scanner's static field influences TMS fields and spatial variations in the static field correlate with TMS field variations. Coil orientation changes in the B0 field did not result in substantial TMS field variations. TMS field variations can be minimized by delivering TMS in the bore or outside of the 0–70 cm region from the bore entrance.     

生理盐水注射流率在头颈部CT动脉血管成像检查中消除对比剂伪影影响的观察

目的:探讨在头颈部CT动脉血管成像(CTA)中的生理盐水最佳注射流率。方法:选取2012年11月~2013年9月行双源CT头颈部CTA 84例患者为研究对象,按时间顺序等分为对照组、试验1组和试验2组,3组分别采用生理盐水注射流率为5.0 ml/s,5.5 ml/s,6.0 ml/s进行检查,比较3组患者的对比剂存留和不良反应发生情况。结果:试验2组对比剂存留明显少于对照组和试验1组(P0.05)。3组患者不良反应比较差异无统计学意义(P0.05)。结论:在头颈部CT检查中生理盐水注射流率为6.0 ml/s可明显消除对比剂伪影的影响。     

Open MR imaging in spine surgery: experimental investigations and first clinical experiences

Introduction: The latest open MRI technology allows to perform open and closed surgical procedures under real-time imaging. Before performing spinal trauma surgery preclinical examinations had to be done to evaluate the artifacts caused by the implants. Methods: The MRT presented is a prototype developed by GE. Two vertically positioned magnetic coils are installed in an operation theater. By that means two surgeons are able to access the patient between the two coils. Numerous tests regarding the material of instruments and implants were necessary in advance. The specific size of the artifact depending on the pulse sequence and the positioning within the magnetic field had to be examined. Results: The magnifying factors of the artifact in the spin echo sequence regarding titanium are between 1.7 and 3.2, depending on the direction of the magnetic vector. Regading stainless steel they are between 8.4 and 8.5. In the gradient echo sequence the factors are between 7.5 and 7.7 for titanium and between 16.9 and 18.0 for stainless steel. The tip of an implant is imaged with an accuracy of 0 to 2 mm. Since September 1997 16 patients with unstable fractures of the thoracic and lumbar spine have been treated by dorsal instrumentation in the open MRI. Percutaneous insertion of the internal fixator has proven a successful minimally invasive procedure. The positioning of the screws in the pedicle is secure, the degree of indirect reduction of the posterior wall of the vertebral body can be imaged immediately. The diameter of the spinal canal can be determined in any plane. Discussion and conclusion: The open MRI has proven useful in orthopedic and trauma surgery. The size and configuration of the artifacts caused by instruments and implants is predictable. Therefore exact positioning of the implants is achieved more easily. Dorsal instrumentation of unstable thoracolumbar fractures with a percutaneous technique has turned out safe and less traumatic under MR-imaging. Real-time imaging of soft tissue and bone in any plane improves security for the patient and allows the surgeon to work less invasively and more precisely. Received: 30 July 1999 Accepted: 7 August 1999     

MR成像中脉冲序列特征与图像质量控制

目的 :为了提高扫描速度与图像质量 ,解决不合作病人及儿童扫描问题。方法 :在 5年工作中 ,利用西门子提供的 30 0多个序列对 30 0 0 0余病人扫描 ,梯度场包括 10 m T/ m,15 m T/ m二种。结果 :通过不断的工作与分析 ,我们提高了扫描速度 ,改善了图像质量 ,解决了不合作病人与儿童的扫描问题。结论 :一般来说梯度回波比自旋回波速度快 ,信噪比低 ,而快速序列多了一个回波链长 ,时间为常规序列的 1/ ETL,平面回波最快     

Assessment of Cone-beam Computed Tomographic Artifacts from Different Intracanal Materials on Birooted Teeth

Introduction

This study quantitatively evaluated the type and amount of image artifacts generated by different intracanal materials in birooted teeth scanned at different exposure parameters.

Review of artifacts associated with transrectal ultrasound: Understanding,recognition, and prevention of misinterpretation

Artifacts are inadequate representations of the structures being imaged. Transrectal ultrasound (TRUS) used for evaluating rectal tumors has its own, unique spectrum of artifacts such as (1) pseudomasses (beam thickness: imaging of rectal folds; mirror image: reflection at an intraluminal fluid level); (2) inadequate size of the lesion (mirror image or grating lobes); (3) simulation of malignant infiltration (beam thickness, attenuation or refraction); (4) incomplete field of view (shadowing; reverberation or mirror-image); (5) confusing echo patterns (side lobe artifacts or mirror image: reflection at the balloon surface). The understanding of the physical properties of ultrasound is the basis for the recognition of these artifacts and prevention of misinterpretation. We present a review of these artifacts and their causes. © 1995 John Wiley & Sons, Inc.     

基于条状挡板的kV级锥形束CT散射校正

目的 校正锥形束CT投影中的散射信号,以提高图像质量。 方法 使用条状挡板测量Varian机载kV级锥形束CT投影图像中的散射信号,并将其从再次扫描的投影中扣除,以获得原始射线的投影图像。使用空域自适应的BayesShrink小波对投影图像进行去噪处理,并导入Varian On Board Imager工作站进行重建;比较处理前后的图像质量。 结果 校正后图像的低对比度分辨力提高,噪声降低,CT值的准确性和均匀性得到改善。 结论 条状挡板能准确获取投影图像中的散射信号;扣除散射信号后使用小波阈值法去噪,可有效提高图像质量。