Digital luminescence radiography of premature and term infants. Possibilities and limitations]

Postmortem images of seven premature and term newborns, acquired with various conventional screen-film combinations and by a digital technique with appropriate radiation exposures, were compared. Images without and with simulated pathology were used in this study. With electronic manipulation of the computed radiographs we obtained well-balanced images with good contrast, and in many cases the artifacts were better visualized than with the conventional screen film. However, in our study no significant dose reduction for this young age group was possible with the digital technique compared with conventional screen film.     

The Electronic Portal Imaging System Siemens Beamview Plus® Versus the Conventional Verification Films CEA-TVS® and DuPont CQL-7®A Critical Appraisal of Visual Image Quality

AIM: The aim of this study was the validation of the visual image quality of electronic portal imaging devices (EPID) and conventional verification films from the point of view of the end-viewers of portal films, the radiotherapists. MATERIAL AND METHODS: The verification image was represented in two different forms, viz. an electronic portal image employing Siemens Beamview Plus (on a computer monitor) and two different portal films using the conventional verification films CEA-TVS and DuPont CQL-7 (on a negatoscope). A total of 270 image sets (simulation film and portal image) were evaluated by each radiotherapist, evaluation extending to 90 sets of each type of verification film. Each set was evaluated by three specialists in radiotherapy examining subjective visual image quality whereby the following aspects served as evaluation criteria: contrast, artifacts, determination of actual radiation field edge position, anatomical structures and main structural feature for the determination of treatment field position. In addition, the anatomical structures employed for visual feature correlation between reference and portal films were classified according to their importance. RESULTS: In general the electronic portal image was rated significantly "visible" or better. Only the evaluation of artifacts showed an appreciable disadvantage for electronic portal imaging caused by physical artifacts due to radiographic technique and data processing aspects peculiar to the Siemens Beamview Plus 1.1. and also caused by different image processing tools reducing physical artifacts and enhancing the visibility of anatomical structures and likewise of anatomical artifacts (e.g. intestinal gas). By calculating the Spearman correlation coefficient to detect a possible relationship between the different criteria of subjective visual image quality, the research demonstrated that artifacts when limited to a tolerable proportion had no significant impact on the other criteria. CONCLUSIONS: As data of EPIDS are digital, images can be postprocessed and enhanced in a wide variety of ways. Using this tool the electronic portal imaging device provides images that, in terms of visual image quality, are at least comparable to the two evaluated types of radiographic films and also have the added advantage that such images are stored and can be transferred electronically being presupposition for digital patient documentation.     

16层螺旋CT中混叠假影的分析

目的认识CT图像中混叠假影(aliasingartifacts)的表现,并探讨成像参数对它的影响。方法使用PHILIPSBrilliance16SCT机器,在不同的扫描和重建参数条件下,扫描浸入水中的成人干颅,对所得原始横断图像在假影方面作出比较评价。结果大部分方案图像可见混叠假影,表现为在纵轴方向上有着径线急剧变化的高密度物体边缘发出的轮辐状假影。探测器组合16×1·5、重建层厚2mm时,螺距为0·3、0·6和0·9mm的图像均见混叠假影,其程度随螺距增大而加重;探测器组合16×0·75、螺距0·6时,重建层厚为0·8和1mm的图像均有混叠假影,且0·8mm图像较1mm图像严重,2mm图像未见混叠假影;螺距0·6、重建层厚2mm时,探测器组合16×0·75的图像未见混叠假影,16×1·5的图像存在该假影;重建间隔和管电流的变化对混叠假影无影响。结论采样不足引起混叠假影,可酌情选择薄的采集层厚、小的螺距和稍宽的重建层厚来抑制或消除这种假影。     

The Dosimetric Effect of Zipper Artifacts on TomoTherapy Adaptive Dose Calculation—A Phantom Study

Tomotherapy adaptive dose calculation offers the ability to verify and adjust the therapeutic plan during the treatment. Using tomotherapy adaptive dose calculation, the planned fluence pattern can be used to recalculate the dose distribution on pretreatment megavoltage computed tomography (MVCT) images. Zipper artifacts, which appear as increased density in the central region of MVCT images, may affect the accuracy of adaptive dose recalculation. The purpose of this study was to evaluate the dosimetric effects of zipper artifacts on tomotherapy adaptive dose calculation. MVCT images of a cylindrical water phantom of 22-cm diameter were acquired on a tomotherapy system. The zipper artifacts were enclosed by a cylindrical planning target volume (PTV) contoured on these images. For comparison, artifact-free images were created by replacing the computed tomography (CT) numbers of zipper artifacts with the mean CT number of water. Treatment plans were generated by giving a uniform dose of 2 Gy to the PTV based on these modified images; it was then applied to the images that have the zipper artifacts. The impacts of different pitch ratios on the artifacts were assessed. The dose distribution differences between the 2 sets of images were compared. The absorbed dose that covered 95% volume of PTV and maximum dose, minimum dose, and mean dose of the PTV were also calculated and compared. The water phantom was scanned on the tomotherapy system twice per week for 12 consecutive weeks. The mean CT number of zipper artifacts (101 HU) was three times higher than that of water (34 HU). The CT number value and location of zipper artifacts were not affected by the pitch ratio. Gamma analysis was performed between the original and recalculated dose distributions. The discrepancies between the isodose distributions calculated by two sets of images were within 1%/1-mm tolerance. The dosimetric impact from zipper artifacts was found insignificant such that the recalculated dose was underestimated by less than 0.5%.     

Quantitative digital subtraction arteriography with a calibration catheter

Quantitative intraarterial digital subtraction arteriography (DSA) was performed using a calibration catheter with three distal metallic ring markers. The two outer markers were 50 mm apart, and the third marker was in the middle. Measurements of 54 vessel diameters of the abdominal aorta, renal, lumbar, and iliac arteries were performed in a comparison study with direct film arteriograms in 10 aortofemoral runoff studies. Diameter measurements were made by both the observer on hard copy DSA images and by a computer using modified semiquantitative software. Against measurements on film, which were used as the standard, deviations in measurement on digital images varied from 8 to 13% for arterial diameters <5 mm and from 2 to 6% for diameters ≥5 mm. Projectional artifacts caused 3% or less error. Knowing these variations in measurement is important in order to determine error tolerances for clinical applications. The calibration catheter serves as a convenient internal marker for DSA.     

Does reducing CT artifacts from dental implants influence the PET interpretation in PET/CT studies of oral cancer and head and neck cancer?

In patients with oral head and neck cancer, the presence of metallic dental implants produces streak artifacts in the CT images. These artifacts negate the utility of CT for the spatial localization of PET findings and may propagate through the CT-based attenuation correction into the PET images. In this study, we evaluated the efficacy of an algorithm that reduces metallic artifacts in CT images and the impact of this approach on the quantification of PET images. METHODS: Fifty-one patients with and 9 without dental implants underwent a PET/CT study. CT images through the patient's dental implants were reconstructed using both standard CT reconstruction and an algorithm that reduces metallic artifacts. Attenuation correction factors were calculated from both sets of CT images and applied to the PET data. The CT images were evaluated for any reduction of the artifacts. The PET images were assessed for any quantitative change introduced by metallic artifact reduction. RESULTS: For each reconstruction, 2 regions of interest were defined in areas where the standard CT reconstruction overestimated the Hounsfield units (HU), 2 were defined in underestimated areas, and 1 was defined in a region unaffected by the artifacts. The 5 regions of interest were transferred to the other 3 reconstructions. Mean HU or mean Bq/cm(3) were obtained for all regions. In the CT reconstructions, metallic artifact reduction decreased the overestimated HUs by approximately 60% and increased the underestimated HUs by approximately 90%. There was no change in quantification in the PET images between the 2 algorithms (Spearman coefficient of rank correlation, 0.99). Although the distribution of attenuation (HU) changed considerably in the CT images, the distribution of activity did not change in the PET images. CONCLUSION: Our study demonstrated that the algorithm can enhance the structural and spatial content of CT images in the presence of metallic artifacts. The CT artifacts do not propagate through the CT-based attenuation correction into the PET images, confirming the robustness of CT-based attenuation correction in the presence of metallic artifacts. The study also demonstrated that considerable changes in CT images do not change the PET images.     

CT能谱成像在消除金属移植物伪影中的应用价值

目的 探讨CT能谱成像(GSI)中单能量图像消除金属移植物硬化伪影的作用.方法 对体内有金属移植物的患者行GSI.其中义齿3例、颈椎钢板植入2例、锁骨钢板植入1例、腰椎金属棒植入1例、人工股骨头3例、髂骨骨折移植物1例、胫骨钢板植入1例.对上述部位行GSI螺旋扫描,管电压采用80 kVp和140 kVp,在0.5 ms内行快速切换扫描.然后重建1.25 mm层厚能谱图像,含40～140 keV共101个单能图像,不同keV单能图像均采用同样的窗宽(1500 HU)、窗位(500HU).测量不同keV单能量图像的伪影指数(AI),分析不同单能量图像伪影消除程度,将AI最小的单能keV图像保存,应用于三维重组.结果 单能图像中AI随keV变化而不同,12例中最大AI为145～225,均在40keV时出现;最小AI为15～190,出现在95～140 keV之间.重组图像时,12例常规的混合能量图像均有明显的金属伪影,用最小AI的单能量图像重建时,可明显肖除或降低金属移植物的硬化伪影.结论 采用CT能谱成像技术,在高keV单能量图像上可以明显降低或消除金属移植物伪影,改善图像质量.     

不同场强下部分DSA介入性器械伪影的探讨

目的 :探讨 0 .3T、1.5T场强下各种DSA介入性器械伪影的大小及其影响因素 ,评价各种介入性器械行MR检查的安全性以及进行MR介入操作的可行性。方法 :将胆管内支架、聚酯动脉化疗药盒、镍钛合金静脉化疗药盒、球囊、微导管等介入性器械置于模具中 ,在 0 .3T、1.5T场强下均行MR扫描 8次 ,观察比较各种介入性器械在两种不同场强下伪影的大小及其影响因素。结果 :胆管内支架在 0 .3T场强下显示比 1.5T更为清晰 ,两种场强下不同序列不同参数对其伪影无明显影响。聚酯动脉化疗药盒在两种场强下不同序列均无伪影。镍钛合金静脉化疗药盒在 0 .3T场强下伪影较小 ,在1.5T场强下伪影较大 ,但两者差异无显著性意义 (P >0 .0 5 )。各种导管在不同场强下无伪影。各种导丝在两种场强下伪影较明显。结论 :行胆管内支架、聚酯动脉化疗药盒、镍钛合金静脉化疗药盒等治疗后行低场强 (0 .3T)MR检查伪影极小 ,是安全可行的。聚酯动脉化疗药盒在 1.5T场强下无伪影 ,胆管内支架、镍钛合金静脉化疗药盒在 1.5T场强下伪影较小 ,但仍适合MR检查。各种导管在不同场强下均无伪影 ,在不同场强下行MR介入操作是安全可行的。     

influence and improvement of metal artifacts in dental structures by CT for radiation treatment planning: reconstruction of transverse images using oblique images by gantry tilt scanning

Intensity-modulated radiation therapy (IMRT) radiation treatment planning (RTP) requires accuracy. Metal artifacts are one of the factors that influence RTP. The metal artifacts from dental structures are problems at the level of the oropharynx, since these artifacts impair visualization of tumors or lymph nodes and change CT (computed tomography) values. We simulated RTP at the level of the oropharynx using CT images with and without artifacts from dental structures. Gantry tilt scanning was performed to avoid artifacts from dental structures and transverse images reconstructed from oblique images by gantry tilt scanning using a technique of multiplanar reconstruction (MPR) . The reconstructed transverse images were used for the RTP. The reconstructed transverse images were useful to obtain accurate target volumes and the RTP of two opposed equally weighted beams by correct CT values. As dose distribution was changed slightly by the metal artifacts, the use of CT images without artifact is recommended in RTP.     

Pulsation artifact in short TR MR imaging and angiography: Exacerbation with signal averaging

Averaging the signals from more than one excitation per phase-encoding view increases the signal-to-noise ratio and, in conventional spin-echo magnetic resonance imaging, reduces most motion artifacts. To determine the effects of signal averaging on two-dimensional gradient-echo images, acquisitions with different TRs and with no averaging versus multiple-signal averaging were compared in a pulsatile flow phantom and the human abdominal aorta. Intraview (each view repeated before changing the phase-encoding value) and interview (obtaining all views sequentially and then repeating the entire set) averaging methods were used. Pulsation artifacts were present on all images of the flow phantom and the aorta. Intraview signal averaging, the method most commonly used, exacerbated rather than ameliorated pulsation artifacts with short TR sequences. Pulsation artifacts on two-dimensional images obtained with a short TR can be minimized by completing the acquisition as rapidly as possible, avoiding signal averaging. If signal averaging is used for short TR images, it should be interview averaging.     

磁共振Propeller技术消除头部伪影的临床应用

目的探讨Propeller技术在头部伪影消除的应用价值。方法对21例磁共振头颅日常检查中出现躁动或不能自控患者，用Propeller技术进行T2WI扫描，与常规T2FRFSE序列进行对比；5例DWI序列磁敏感伪影明显者进行Propeller DWI扫描，与常规DWI进行对比。结果21例应用Propeller技术进行T2VI扫描明显减少或消除了运动伪影，5例Propeller DWI明显消除磁敏感效应引起的伪影，均生成较满意图像。结论应用PropellerT2WI及DWI成像技术可以明显减少或消除患者因运动及磁敏感效应造成的伪影，显著提高图像质量，获得具有临床诊断价值的理想图像。     

A hybrid approach to reducing computed tomography metal artifacts in intracavitary brachytherapy

PURPOSE: To develop a hybrid approach to reduce computed tomography (CT) metal artifacts caused by the Fletcher-Suit applicator. METHODS AND MATERIALS: Using the acquired raw projection data, the hybrid algorithm determines the separate contributions from the metal and non-metal objects. Next, reconstructions of metal and non-metal images are separately obtained from their estimated projections. A final image is formed by appropriately combining the individual images. Phantom and patient data are used to evaluate the performance of this method. RESULTS: CT images reconstructed by use of the standard filtered-backprojection (FBP) algorithm contain significant artifacts even for small metal objects. However, images reconstructed using the hybrid algorithm contain virtually no artifacts. For metal objects with complex structures, the hybrid algorithm can also yield images containing fewer severe streak artifacts than those reconstructed using the FBP algorithm alone. CONCLUSIONS: These studies demonstrate that the hybrid approach can effectively reduce CT metal artifacts caused by the Fletcher-Suit applicator.     

Artifact simulating subarachnoid and intraventricular hemorrhage on single-shot, fast spin-echo fluid-attenuated inversion recovery images caused by head movement: A trap for the unwary

BACKGROUND AND PURPOSE: Single-shot, fast spin-echo, fluid attenuated inversion recovery (SS-FSE-FLAIR) images are frequently used to detect disease in the brain and subarachnoid space in confused or uncooperative patients who may move during the examination. In some of these patients, high signal intensity areas are seen on good-quality images in the subarachnoid space and ventricular system in locations not associated with high CSF flow. These artifacts may simulate hemorrhage or leptomeningeal disease. The purpose of this article was to determine the cause of these artifacts, describe ways to recognize them, and find methods to reduce or eliminate them. METHODS: Healthy volunteers were studied on 6 occasions with conventional multisection FSE-FLAIR images and SS-FSE-FLAIR images while at rest and while nodding and rotating their heads at different speeds. In addition, SS-FSE-FLAIR images with different section widths of the initial inverting pulse and a non-section-selective initial inversion pulse were performed with the subjects moving their heads in the same way. The scans of 30 successive patients with acute neurologic syndromes who had been studied with SS-FSE-FLAIR sequences were reviewed for evidence of high signal intensity in the CSF in regions not associated with high CSF flow. RESULTS: Each of the volunteers showed areas of increased signal intensity in CSF at sites apart from those associated with rapid pulsatile CSF flow on SS-FSE-FLAIR images acquired during head motion. The images were otherwise virtually free of motion artifact. The use of a wider initial inversion pulse section and a non-section-selected initial inversion pulse reduced the extent of these artifacts. Nineteen of the 30 patients showed areas of high signal intensity in the CSF in regions not associated with highly pulsatile CSF flow. Six of these patients had negative lumbar punctures for blood and xanthochromia and normal CSF protein levels. CONCLUSION: High signal intensity artifacts may be seen in CSF as a result of head movement on otherwise artifact-free images when imaging uncooperative patients with SS-FSE-FLAIR sequences. These artifacts have a different mechanism and distribution from those caused by CSF pulsation and may simulate subarachnoid and intraventricular hemorrhage. Artifact recognition is aided by signs of patient motion during the examination. The artifacts can be reduced by use of increased section width and non-section-selective initial inversion pulses. Recognition of these artifacts is important, because the circumstances in which the SS-FSE-FLAIR sequence is used and the particular properties of the sequence may conspire to produce a trap for the unwary.     

Coronary arterial stents: safety and artifacts during MR imaging

PURPOSE: To investigate the safety and imaging artifacts with different coronary arterial stents and magnetic resonance (MR) imaging sequences. MATERIALS AND METHODS: The heating, artifacts, and ferromagnetism with different stents were studied with a 1.5-T MR tomograph with ultrafast gradients by using turbo spin-echo, turbo gradient-echo, and echo-planar imaging sequences. Nineteen stents, which were 8-25 mm in length and 3.0-4.5 mm in diameter, were evaluated. Stent deviation induced by the magnetic field and during MR imaging, migration, and heating caused by the radio-frequency pulses were examined. The size of imaging artifacts was measured with all the stents under standardized conditions and with six stents after their implantation into the coronary arteries of freshly explanted pig hearts. RESULTS: All except two types of stents showed minimal ferromagnetism. No device migration or heating was induced. Turbo spin-echo images had minimal artifacts; larger artifacts were seen on the turbo gradient-echo and echo-planar images. With ultrafast gradients, the artifacts on the echo-planar images were substantially reduced. CONCLUSION: The studied coronary stents were not influenced by heating or motion during 1.5-T MR imaging. Artifact size differed according to the type and size of the stent and the MR imaging sequence used. Thus, patients with these stents can be safely examined.     

Improving image quality around subtle lung nodules by reducing artifacts in similar subtraction imaging

Similar subtraction imaging is useful for the detection of lung nodules; however, some artifacts on similar subtraction images reduce their utility. The authors attempted to improve the image quality of similar subtraction images by reducing artifacts caused by differences in image contrast and sharpness between two images used for similar subtraction imaging. Image contrast was adjusted using the histogram specification technique. The differences in image sharpness were compensated for using a pixel matching technique. The improvement in image quality was evaluated objectively based on the degree of artifacts and the contrast-to-noise ratio (CNR) of the lung nodules. The artifacts in similar subtraction images were reduced in 94% (17/18) of cases, and CNR was improved in 83% (15/18) of cases. The results indicate that the combination of histogram specification and pixel matching techniques is potentially useful in improving image quality in similar subtraction imaging.     

Multiple slice FLASH imaging: An improved pulse sequence for contrast enhanced MR brain studies

Summary A multisclice gradient echo sequence (FLASH) was compared with a conventional spin-echo (SE) technique with regard to its value for contrast enhanced brain studies. In 50 patients with contrast enhancing intracranial lesions, MR studies (0.5 Tesla MR tomograph) were performed with SE images (SE 400/30; four images/3.4 min) and FLASH scans (FLASH 315/14, 90°; 15 images/1.4 min) before and after Gd-DTPA. Based on visual and quantitative assessment diagnostic results of postcontrast SE- and FLASH images were equivalent with respect to contrast enhancement, lesion/brain-contrast, lesion/edema-contrast, and lesion delineation. Although image quality generally was excellent on postcontrast FLASH images, susceptibility artifacts were more severe on FLASH scans than on SE images. However, with the exception of postoperative patients with artifacts due to metal remains, diagnostic information was not decreased by artifacts on postcontrast FLASH images. In conclusion, because of the clearly higher efficiency of the multisclice FLASH technique, this pulse sequence offers the opportunity to speed up contrast enhanced brain imaging.     

US artifacts: effects on out-of-plane us images reconstructed from three-dimensional data sets

Three-dimensional volumetric data sets of stacked ultrasonographic (US) scans were obtained in vitro and in vivo to investigate the effect of common US artifacts on cross-sectional images reconstructed out-of-plane to the plane of acquisition of these data sets. The appearance of the artifacts on the reconstructed images was different from that on the source images. Such artifacts have the potential to simulate pathologic abnormalities.     

Frequency of common bile duct motion artifacts caused by inferior vena cava pulsation on magnetic resonance cholangiopancreatography.

PURPOSE: We assessed the frequency of common bile duct (CBD) motion artifacts caused by inferior vena cava (IVC) pulsation on magnetic resonance cholangiopancreatography (MRCP). METHODS: We retrospectively evaluated CBD motion artifacts in 4 MRCP sequences from each of 115 consecutive patients. RESULTS: We observed 37 (32.2%) ghost artifacts at the ventral and dorsal aspects of the CBD on transaxial, half-Fourier acquisition single-shot turbo spin-echo (HASTE-ax) images; no such artifacts were observed on transaxial T(2)-weighted turbo spin-echo images. In 10 patients, we observed 9 (7.8%) pseudo-defects of the CBD on 3-dimensional T(2)-weighted turbo spin-echo with navigator-triggered prospective acquisition correction technique MRCP and 6 (5.2%) pseudo-defects on single-shot rapid acquisition with relaxation enhancement MRCP. Pseudo-defects were significantly more frequent in patients with ghost artifacts than without (9 of 37 [24.3%] versus one of 78 [1.3%]; P<0.01, McNemar test). CONCLUSION: Although uncommon, pseudo-defects of the CBD caused by IVC pulsation are observed on MRCP. MRCP interpretation that includes comparison with HASTE-ax images can diminish the potential misinterpretation of such CBD motion artifact as bile duct tumor or biliary stone.     

Thoracic aortic dissection: pitfalls and artifacts in MR imaging

Results of 53 thoracic magnetic resonance (MR) imaging examinations were reviewed to determine the prevalence and severity of artifacts and pitfalls that may occur in the evaluation of acute aortic dissection. Grade 1 artifacts and pitfalls were mimics of aortic dissection on individual images but could be demonstrated not to represent a dissection when other images from the same sequence were evaluated. Grade 2 artifacts and pitfalls required the use of images from other planes or sequences to distinguish them from a dissection. Grade 3 artifacts and pitfalls could not be distinguished from a dissection without the use of other imaging modalities. Of the 53 cases examined, 34 (64%) had artifacts or pitfalls of grade 1 or higher, 10 (19%) had artifacts or pitfalls of grade 2 or higher, and one case (2%) had grade 3 artifacts or pitfalls. Sixteen cases had more than one artifact or pitfall. Pitfalls and artifacts that mimic aortic dissection occur in a significant percentage of thoracic MR imaging examinations. An awareness of their existence, knowledge of normal anatomy, the use of axial images in all cases with the addition of images in other planes as needed, rotation of phase and frequency gradients as needed, and clinical correlation may avert misinterpretation in nearly all cases.     

Diffusion imaging with prospective motion correction and reacquisition

A major source of artifacts in diffusion‐weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion‐weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion‐weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion‐weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.